DEVELOPMENT OF ACTIVE PACKAGING TRAYS WITH ETHYLENE REMOVING CAPACITY By Gauri Sudhir Awalgaonkar A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Packaging - Master of Science 2018 ABSTRACT DEVELOPMENT OF ACTIVE PACKAGING TRAYS W ITH ETHYLENE REMOVING CAPACITY By Gauri Sudhir Awalgaonkar Active p ackaging is an innovative packaging solution to recent consumer demands for fresher and safe produce for longer periods . Ethylene - removing packaging can take away ethylene from the produce surrounding leading to an increase in shelf life. The focus of the present work was to develop a tray with ethylene removing capacity. Ethylene scavengers (potassium permanganate, two activated carbons, two zeolites, metal - organic frameworks) were characterized by studying their ethylene removing capabil ity under temperature (23 o C and 4 o C) and humidity (< 5%, 55%, and 100% RH) conditions, while p etroleum - based and bio - based plastics were compared by measuring their barrier properties . Thermoformed trays were developed with selected scavenger and plastic characterized for their ethylene scavenging capacity , thermal, mechanical, and barrier properties and evaluated for packaging application in produce. Trays were developed with activated carbon as the scavenger as it had good ethylen e removing capacity at ow density polyethylene was selected as the polymer of choice because of its barrier properties. Thermoformed trays able to adsorb ethylene were developed with 10% activated carbon and no differences in terms of thermal, mechanical and barrier properties were obtained compared to trays without activated carbon. Further studies on the ethylene removing capacity of the developed trays need to be carried out. Copyright by GAURI SUDHIR AWALGAONKAR 2018 iv Dedicated to my husband Chinmay Naphade v ACKNOWLEDGEMENTS When I wanted to write this section, I was at loss of words of how to communicate the gratitude I felt and like for most other things, I went to Google! I found my answer on Google t have been possible without my research advisor, committee, research team, family and friends. Firstly, I am extremely thankful to my advisor Dr. Eva Almenar (School of Packaging, Michigan State University) for her never - ending support, guidance and motiv ation to keep this research going . She had been an excellent mentor and teacher particularly in putting the domains of both food and packaging together. Sh e also constantly helped me improve myself in scientific writing , communication and analytical skill s. Moreover, I am extremely thankful to my committee members, Dr. Susan Selke (School of Packaging, Michigan State University) and Dr. Randy Beaudry (Department of Horticulture, Michigan State University) for their time commitment, expertise and suggestion s. I would also like to acknowledge Mr. Aaron Walworth (School of Packaging, Michigan s research team specially Chris, Anna, Jack, Dylan, Argus, Kikung, Karen for helping me understand the domain of food packaging better and making lab a fun place to work. This research would not have been possible without the help of my friends Sonal, Yuzhu, Wan, Vijay, Pooja for constantly cheering me up and being there for me in thick and thin. Finally, I must express my very profound gra titude towards my husband Chinmay, my parents and in - laws for providing me with unfailing support and continuous encouragement . They have always been there for me whenever I needed them. vi TABLE OF CONTENTS LIST OF TABLES ................................ ................................ ................................ ....................... viii LIST OF FIGURES ................................ ................................ ................................ ....................... ix Chapter 1 ................................ ................................ ................................ ................................ ......... 1 INTRODUCTION ................................ ................................ ................................ .......................... 1 1.1 Introduction ................................ ................................ ................................ ........................... 1 1.2 Objectives ................................ ................................ ................................ ............................. 4 REFERENCES ................................ ................................ ................................ ............................... 5 Chapter 2 ................................ ................................ ................................ ................................ ......... 8 LITERATURE REVIEW ................................ ................................ ................................ ............... 8 2.1 Ethylen e in produce ................................ ................................ ................................ .............. 8 2.2 Ethylene - removing packaging ................................ ................................ ............................ 10 2.2.1 Overview ................................ ................................ ................................ ...................... 10 2.2.2 Classification of ethylene - removing packaging ................................ ........................... 11 2.2.3. Types ................................ ................................ ................................ ............................... 13 2.2.3.1 Ethylene - removing packaging based on ethylene oxidation ................................ .... 13 2.2.3.2 Ethylene - removing packaging based on ethylene adsorption/absorption ................. 19 R EFERENCES ................................ ................................ ................................ ............................. 27 CHAPTER 3 ................................ ................................ ................................ ................................ . 32 Identification of ethylene scavenger and packaging material for development of a tray with ethylene removing capacity ................................ ................................ ................................ ...... 32 3.1 Materials ................................ ................................ ................................ ............................. 32 3.1.1. Scavengers ................................ ................................ ................................ .................. 32 3.1.2. Fi lms ................................ ................................ ................................ ........................... 32 3.2. Methods ................................ ................................ ................................ .............................. 34 3.2.1 Activation of scavengers ................................ ................................ .............................. 34 3.2.2 Assay systems ................................ ................................ ................................ .............. 34 3.2.3 Storage conditions ................................ ................................ ................................ ........ 34 3.2.4 Adsorption measurements ................................ ................................ ............................ 35 3.2.5 Barrier properties ................................ ................................ ................................ ......... 36 3.2.6 Statistical analysis ................................ ................................ ................................ ........ 37 3.3 Results and discussion ................................ ................................ ................................ ........ 38 3.3.1 Effects of temperature and relative humidity on the sorption capacity of ethylene scavengers ................................ ................................ ................................ ............................. 38 3.3.2 Effect of competitive adsorption (CO 2 , O 2 and water) on ethylene adsorption ........... 42 3.3.3 Barrier properties ................................ ................................ ................................ ......... 44 REFERENCES ................................ ................................ ................................ ............................. 46 vii CHAPTER 4 ................................ ................................ ................................ ................................ . 50 Development and characterization of an ethylene removing tray and its validaton for produce packaging applications ................................ ................................ ................................ .............. 50 4.1 Materials ................................ ................................ ................................ ............................. 50 4.2 Methods ................................ ................................ ................................ ............................... 50 4.2.1 Tray development ................................ ................................ ................................ ........ 50 4.2.2 Tray selection ................................ ................................ ................................ ............... 52 4.2.3 Tray characterization ................................ ................................ ................................ ... 53 4.2.4 Shelf - life study ................................ ................................ ................................ ............. 54 4.2.5 Statistical analysis ................................ ................................ ................................ ........ 56 4.3 Results and discussion ................................ ................................ ................................ ........ 57 4.3.1 Tray selection ................................ ................................ ................................ ............... 57 4.3.2 Tray characterization ................................ ................................ ................................ ... 59 4.3.3. Shelf - life study ................................ ................................ ................................ ............ 64 REFERENCES ................................ ................................ ................................ ............................. 68 CONCLUSIONS ................................ ................................ ................................ ........................... 72 5.1 Conclusions ................................ ................................ ................................ .................... 72 5.2 Future work ................................ ................................ ................................ .................... 72 viii LIST OF TABLES Table 2.1 Ethylene - removing packages based on KMnO 4 created during the last decade and their effects on produce shelf - life extension. ................................ ................................ ........................ 16 Table 2.2 Commercial ethylene scavengers in their available formats (adapted from Awalgaonkar and Almenar (2018)) ................................ ................................ .............................. 17 Table 2.3 Advantages and disadvantages of ethylene oxid izers and scavengers in active packaging (adapted from Awalgaonkar and Almenar (2018)) ................................ ..................... 18 Table 2.4 Ethylene - removing packages based on ethylene adsorption/absorption created during the last decade and their effects on produce shelf - life extension ................................ .................. 22 Table 3.1 Properties of scavengers used in the study. ................................ ................................ .. 33 Table 3.2 Competitive adsorption of CO 2 and ethylene of MOF and PAC at 23 o C and 100% RH ................................ ................................ ................................ ................................ ....................... 44 Table 3.3 Water and ethylene permeability of various petroleum - based and bio - based films. .... 45 Table 4.1 Thickness profile of the sheets and the developed tray ................................ ................ 62 Table 4.2 Thermal, mechanical, and barrier properties of the LDPE tray and LDPE/10% AC tray. ................................ ................................ ................................ ................................ ....................... 62 Table 4. 3 Changes in total soluble solids content of cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH for 9 days. ................................ ............... 66 ix LIST OF FIGURES Figure 2. 1 Different types in which active packaging can be used (adapted from Awalgaonkar and Al menar (2018)) ................................ ................................ ................................ ..................... 11 Figure 2.2 Classification of ethylene - removing packaging (adapted from Awalgaonkar and Almenar (2018)) ................................ ................................ ................................ ............................ 12 Figure 3.1 Images of scavengers used for the study. ................................ ................................ .... 33 Figure 3.2 Schematic representation of the system used to measure ethylene permeation . ......... 37 Figure 3.3 Impact of temperature an d relative humidity on the ethylene removing capacity of six scavengers. ................................ ................................ ................................ ................................ .... 40 Figure 4.1 Schematic representation of the preparation of the thermoformed trays .................... 51 Figure 4.2 Control tray (left) and a tray containing AC (right). ................................ ................... 52 Figure 4.3 Packaging systems with and without trays containing AC. ................................ ........ 55 Figure 4.4 Trays developed with LDPE and 0%, 5%, 10%, and 20% activated carbon. ............. 58 Figure 4.5 Ethylene adsorption after 5 days by developed trays containing 0%, 5%, 10% and 20% of AC. ................................ ................................ ................................ ................................ ... 59 Figure 4.6 Shelf - life study parameters of cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH for 9 days. ................................ ................................ ......... 63 Figure 4.7 Microbiological evaluation of the cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH after 6 day ................................ ................................ .. 67 1 Chapter 1 INTRODUCTION 1.1 I ntroduction In recent years, c onsumer expectations and demands have changed owing to an increase in technological, scientific, and social innovations . In terms of food, t oday consumer expects fresh ness , safe ty , healthi ness , and minimal process ing (Singh et al . , 2011). The se new requirements are putting huge demands on the food packaging industry and are major driving forces to provide new packaging solutions ( Ghaani et al., 2016). Active packaging (AP) is one of the innovative solutions to mounting consumer requirements . AP is a packaging technology where certain additives are intentionally incorporated into the packaging material or placed within the packaging container to interact directly with the peris hable product to extend its shelf life. AP differs depending on the type of additive: oxygen scavenger, ethylene a d sorber, drip absorber, flavor absorber , etc ( A lmenar et al., 2006). E thylene - removing packaging is a type of AP that intentionally and dynam ically modifies the ethylene levels within the package through use of scavenging compounds ( A lmenar et al., 2006). This lowering or removing of ethylene is essential in the case that ethylene acts as a ripening hormone (climacteric fruits) and/or leads to detrimental effects such as excessive softening of fruits, abscission of leaves and flowers, toughening of vegetables, and increased pathogen susceptibility (Zagory 1995). Compounds such as potassium permanganate (KMnO 4 ), activated carbon, zeolites , and me tal - organic frameworks (MOFs) have been reported to be effective in removing ethylene (Keller et al. , 2013 ; Martínez - Romero et al. , 2007 ; Zhang et al ., 2016). KMnO 4 is highly effective in removing ethylene and consequently, it has been widely studied and commercialized as an ethylene remover (Keller et al. , 2013 ). Activated carbon varies in ethylene 2 removing capacity depending on its format. P owdered activated carbon (PAC) and granulated activated carbon (GAC) adsorb more ethylene than carbon fibers (Bailen et al., 2007). The former two are also easily available and regenerated ( Martínez - Romero et al. , 2007 ). Like activated carbon, different form s of zeolites are avai lable. They differ in structure and origin (natural vs synthetic), which leads to differences in ethylene removing capacity. Among these, the synthetic zeolite 4A and the natural zeolite clinoptilolite (CL ) have shown promising ethylene removing capacities ( 2015; et al. , 2008 ). In contrast, Peiser & Suslow ( 1998 ) reported that CL did not adsorb ethylene. MOFs are a new class of synthetic porous compounds that can selectively adsorb and desorb many volatile molecules including ethylene (Kuppler et al. , 2009; Li et al . , 2011 ). In agreement, Chopra et al . (2017) reported that Basolite C300 and Basolite 520 can sorb, store , and release ethylene, with Basolite C300 being more effective . Zhang et al . ( 2016 ) reported that copper terephthalate (CuTPA) MOF can adsorb and release up to 654 ppm of ethylene. The main mechanisms of action for the aforementioned scavenging compounds are ethylene adsorption (activated carbon, zeolites, and MOFs) and ethylene oxidation (KMnO 4 ) ( Pereira de Abreu et al., 2012 ; Lopez Rubio et al., 2004 ; Zagory 1995; Chopra et al. , 2017 ). The former mechanism is highly affected by temperature, humidity, adsorbate concentration, magnitude and distribution of pore volume (pore structure) , surface chemistry , a nd molecules compet ing for the adsorption sites with ethylene like oxygen (O 2 ) and carbon dioxide (CO 2 ) (Martínez - Romero et al . , 2007 ; Keller et al. , 2013 ; Chopra et al. , 2017 ). Although all these factors are important, getting to know about the effects of combinations of temperature and h umidity including those occurring during the post harvest period on the scavenging capacit ies of these compounds can help selecting the best scavenger , thereby contributing to the advancement of ethylene - removing packaging. Currently, t here is a lack of comparative data for the scavenging 3 capacity among these compounds at the aforementioned conditions (Keller et al. , 2013 ; Zagory 1995). Besides the type of scavenger, another factor key for creating adequate ethylene - removing packaging is the type of packaging material since its barrier properties define the contents of ethylene, O 2 , CO 2 , and water vapor in the package headspace, all molecules that affect ethylene scavenging capacity. The current methods for developing an eth ylene removing AP are either through placing the active compound inside the package along with the product (e . g ., sachets) or by making the active compound a part of the packaging material itself ( Almenar, 2018 ). Wilson et al. (2018) found that consumers p refer to use packages without sachets rather than the ones with sachets. However, the addition of an active compound to the packaging material c an alter its properties and hence it is important to characterize the thermal, mechanical , and barrier propertie s of any developed material. Cherry tomatoes are climacteric fruits (require the action of ethylene for ripening) and are generally harvested when deep red and destined directly to fresh market. They are usually held at typical retail outlet display tempe ratures, which are around 20 o C and are generally packaged in rigid clamshell containers. Ethylene - removing packaging ha s been shown to extend the shelf life of tomatoes. Tas et al. ( 2017 ) reported that composite films made of h alloystic nanotubes and polyethylene retained tomato firmness for 10 days. Maneerat, & Hayata ( 2008 ) observed that titanium dioxide coated films reduced the ethylene content by 88 % . Salamanca et al. ( 2014 ) found that the combination of KMnO 4 and zeolite when placed as a sachet in a thermoformed polyethylene terephthalate container can reduce weight loss and retained firmness and soluble solids content. Most of the aforementioned studies on tomatoes have been carried out with active compounds ( h alloystic nanotubes , zeolites, KMnO 4 , titanium dioxide) in sachets, films , or 4 corrugated boar ds. However, no studies have been carried out on rigid containers such as trays that are more commonly used for packaging delicate fruits such as cherry tomatoes and other climacteric fruits . Hence the present study was carried out with following objectiv es. 1.2 Objectives The ultimate objective of this study is to develop a tray with ethylene removing capacity for produce packaging . To achieve this objective, the following specific objectives were proposed: Identify an ethylene scavenger and a packaging material for development of a tray with ethylene removing capacity . Selection of scavenger: Different ethylene scavengers (KMnO 4, MOF, GAC, PAC, CL and 4A) were test ed for their ethylene removing capability at different combinations of temperatu re (23 o C and 4 o C) and relative humidity (<5 %, 55 % and ~100 % RH) . Shortlisted scavengers were studied for ethylene removing capability in the presence of competing molecules (O 2 and CO 2 ). Selection of packaging material : T he permeability of petroleum - based (LLDPE, LDPE, PP, nylon) and bio - based (PLA, carbohydrate - and protein - based ) plastics to ethylene and water was tested. Develop an ethylene - removing tray using the thermoforming process and characterize the properties of the developed tray (ethylene scavenging capacity, mechanical, barrier, thermal, thickness profile) . Study the possible use of the developed ethylene - removing tray to package produce using cherry tomatoes. 5 REFERENCES 6 REFERENCES 1. Singh, P., Abas Wani, A., & Saengerlaub, S. (2011). Active packaging of food products: recent trends. Nutrition & Food Science , 41 (4), 249 - 260. 2. Ghaani, M., Cozzolino, C. A., Castelli, G., & Farris, S. (2016). An overview of the intelligent packaging technologies in t he food sector. Trends in Food Science & Technology , 51 , 1 - 11. 3. Almenar, E., Hernández - Muñoz, P., Lagarón, J.M., Catalá, R., Gavara, R., (2006). Advances in packaging technologies for fresh fruit and vegetables. In: Noureddine, B., Norio, S.(Eds.), Advances in Postharvest Technologies of Horticultural Crops. Research Signpost, Kerala, India, 87 112. 4. Zagory, D. (1995). Ethylene - removing packaging. In Active food packaging (pp. 38 - 54). Springer US. 5. Keller, N., Ducamp, M. N., Robert, D., & Keller, V. (2013). Et hylene removal and fresh product storage: a challenge at the frontiers of chemistry. Toward an approach by photocatalytic oxidation. Chemical R eviews , 113 (7), 5029 - 5070. 6. Martínez - Romero, D., Bailén, G., Serrano, M., Guillén, F., Valverde, J.M., Zapata, P., Castillo, S. & Valero, D., (2007). Tools to maintain postharvest fruit and vegetable quality through the inhibition of ethylene action: a review. Critical R eviews in F ood S cience and N utrition , 47 (6), 543 - 560. 7. Zhang, B., Luo, Y., Kanyuck, K., Bauchan, G., Mowery, J., & Zavalij, P. (2016). Development of metal organic framework for gaseous plant hormone encapsulation to manage ripening of climacteric produce. Journal of A gricultural and F ood C hemistry , 64 (25), 5164 - 5170. 8. Bailén, G., Guillén, F., Castillo, S., Zapata, P.J., Serrano, M., Valero, D., & Martínez Romero, D., (2007). Use of a palladium catalyst to improve the capacity of activated carbon to absorb ethylene, and its effect on tomato ripening. Spanish Journal of Agricultural Research 5, 579 586. 9. Sz scavenge carbon dioxide and ethylene by incorporation of zeolites. PhD Thesis. Michigan State University, East Lansing, USA. 10. E. (2008). Characterization and ethylene adsorption of natural and modified clinoptilolites. Applied Surface Science , 254 (8), 2450 - 2457. 11. Peiser, G., & Suslow, T. V. (1998). Factors affecting ethylene adsorption by zeolite: the last word (from us). Perishab le Handling Quarterly Issue , (95), 17 - 19. 12. Kuppler, R.J., Timmons, D.J., Fang, Q. - R., Li, J. - R., Makal, T.A., Young, M.D. & Zhou, H. - C., (2009). Potential applications of metal - organic frameworks. Coordination Chemistry Reviews, 253 (23 24), 3042 3066. 7 13. Li, J. - R., Kuppler, R.J. & Zhou, H. - C., (2011 ). Selective gas adsorption and separation in metal organic frameworks. Chemical Society Reviews 38 (5), 1477 1504. 14. Chopra, S., Dhumal, S., Abeli, P., Beaudry, R., & Almenar, E. (2017). Metal - organic frameworks h ave utility in adsorption and release of ethylene and 1 - methylcyclopropene in fresh produce packaging. Postharvest Biology and Technology , 130, 48 - 55. 15. López - Rubio, A., Almenar, E., Hernandez - Muñoz, P., Lagarón, J. M., Catalá, R., & Gavara, R. (2004). Overv iew of active polymer - based packaging technologies for food applications. Food Reviews International , 20 (4), 357 387 . 16. Pereira de Abreu, D. A., Cruz, J. M., & Paseiro Losada, P. (2012). Active and intelligent packaging for the food industry. Food Reviews International, 28 (2), 146 - 187. 17. Almenar, E. (2018). Innovations in packaging technologies. In: Beaudry, RM, Gil, MI, editors. Controlled and Modified Atmosphere Use for Fresh and Fresh - cut Produce. 18. Wilson, C. T., Harte, J., & Almenar, E. (2018). Effects of sachet presence on consumer product perception and active packaging acceptability - A study of fresh - cut cantaloupe. LWT Food Science and Technology , 92, 531 - 539 19. Maneerat, C., & Hayata, Y. (2008). Gas - phase photocatalytic oxidation of ethylene w ith TiO2 - coated packaging film for horticultural products. Transactions of the ASABE , 51 (1), 163 168. 20. Salamanca, F. A., Balaguera - López, H. E., & Herrera, A. O. (2014, January). Efecto del Permanganato de Potasio sobre Algunas Características Poscosecha de Frutos de Tomate In II International Conference on Postharvest and Quality Management of Horticultural Products of Interest for Tropical Regions , 1016, 171 - 176 . 21. Tas, C. E., Hendessi, S., Baysal, M., Unal, S., Ceb eci, F. C., Menceloglu, Y. Z., & Unal, H. (2017). Halloysite nanotubes/polyethylene nanocomposites for active food packaging materials with ethylene scavenging and gas barrier properties. Food and Bioprocess Technology , 10 (4), 789 798. 8 Chapter 2 LITERATURE REVIEW 2.1 Ethylene in produce Ethylene is a gas molecule with two carbon atoms linked by a double bond . Ethylene is common in the environment due to its artificial and natural production. Ethylene is naturally generated by produce and several species of bacteria and fungi (Zagory, 1995) . In produce, ethylene is formed during ripening, mechanical injury, and diseased conditions (Zagory, 1995) through a complex metabolic pathway of enzymatic action on the amin o acid methionine. Methionine is converted to S - adenosyl - methionine (SAM) by the addition of adenine and consumption of adenosine triphosphate. SAM is transformed to 1 - aminocyclopropane - 1 - carboylic acid (ACC) by the enzyme ACC synthase (ACS) and generates 5 - methylthioadenosine (MTA) as a by - product. ACC is oxidized to ethylene by ACC oxidase and MTA is recycled to produce methionine (Martinez et al., 2007 ) . Climacteric fruits (e.g., tomato, apple, peach, and banana) are characterized by rapid ripening, high respiration and high ethylene production. Whereas non - climacteric fruits (e.g. citrus, grape, and strawberry), ripening does not occur after harvest little or no ethylene is produced (Zagory, 1995). In both, climacteric and non - climacteric fruits, ethylen e can have negative effects during postharvest storage. Furthermore, beneficial or detrimental changes caused in produce by ethylene depend on the type and ripening stage. Beneficial effects of ethylene include stimulation of ripening in climacteric fruits , color development through pigment (anthocyanin and lycopene) synthesis, chlorophyll degradation (degreening), and enhancement of flavor. Detrimental effects of ethylene can be excessive softening of fruits, production of bitter compounds, abscission of l eaves and flowers, hastened toughening of vegetables, increased pathogen susceptibility, promotion of discoloration, sprouting stimulation, changes in shape, formation of bitter 9 compounds and russet spotting (Saltveit, 1999 ). These undesired changes often occur due to exposure to the ethylene produced by adjacent produce and/or to the ethylene generated as a pollutant in greenhouse locations, storage, and transportation. Thus, it is crucial t o reduce surrounding ethylene in addition to inhibiting ethylene biosynthesis in order to minimize its impact on produce (Zagory, 1995). Different approaches have been used to inhibit ethylene biosynthesis including the use of (1) compounds that compete with ethylene for either ethylene receptor binding sites or ethylene precursors, (2) compounds and specific types of irradiation that inhibit the activity of ethylene - forming enzymes, and (3) specific types of storage like controlled atmosphere and hypobaric storage. With regard to control led atmosphere, e xposu re to a low O 2 concentration inhibits ethylene production (Gorny & Kader, 1997) while concentrations of O 2 greater than 21% (air) have been reported to alter ethylene production in a way that enhances ethylene - induced physiological disorders in a variety o f crops including pears, potato tubers, tomatoes, and lettuce ( C reech, et al. , 1973). O 2 participates in the oxidation of ACC to ethylene and the details of the mechanism can be found in Dilley et al. ( 2013 ) . In contrast, CO 2 has been shown to be a competi tive inhibitor of ethylene action by displacing ethylene from its receptor site (Burg & Burg, 1967). Burg & Burg (1967) reported that 1.55% CO 2 reduces ethylene action by 50%. In agreement, Colelli , et al., (1991) also reported less ethylene production whe n produce is exposed to CO 2 - enriched atmospheres. The mechanism of CO 2 on inhibiting ethylene action is not yet fully understood (Beaudry, 2010). 10 2 . 2 Ethylene - removing packaging 2. 2. 1 Overview Technologies like controlled atmosphere have been used for several decades and therefore, they could be considered today as conventional or mature technologies used to control ethylene. Recently, considerable research has been carried out to develop technologies to reduce the ethylene produced o r its biosynthesis. Packaging technologies like modified atmosphere packaging (MAP) can expose the produce to depleted O 2 and/or enriched CO 2 amounts like controlled atmosphere does and thus, MAP can reduce ethylene synthesis and action (Beaudry, 1999 ; Zagory & Kader, 1988 ). However, the required gaseous composition will most likely not be maintained at an optimal level like in controlled atmosphere due to the changes over time caused by the interplay between produce respiration and packaging material pe rmeability. Additionally, the resulting gaseous composition may not be the most beneficial for the produce in terms of physiological responses other than ethylene. Active packaging (AP) is a relatively new packaging technology compared to MAP. AP can be d efined as a packaging technology where certain additives are incorporated into the packaging material or placed within the packaging container in order to interact directly with the perishable product and/or its environment to extend its quality and/or safety ( Almenar, 2018 ). The current mechanisms to make packages active are: (1) placing the active compound inside the package along with the product to be packed (e.g., sachets and labels), and (2) making the active compound par t of the materials that form the package itself (e.g., blended in the bulk polymer matrix, applied to the package as a coating, integrated in the ink used for printing) as shown in Figure 2. 1. In the last decade, there has been a shift towards direct incorporation of the active compound into the packaging material since this allows manufacturers 11 to continue using the packing equipment commonly used for non - active packaging and consumers to appreciate not having foreign objects with in the package that could be ingested by mistake (Almenar, 2018). Supporting the latter, Wilson et al. (2018) found through a consumer sensory evaluation that consumers like packages with sachets less than packages without sachets. Figure 2 . 1 Different types in which active packaging can be used (adapted from Awalgaonkar and Almenar (2018 ) ) Active packaging with ethylene removing capacity , a.k.a. ethylene - removing packaging, can be defined as a type of active packaging that can c ounteract the action of ethylene due to the presence of compounds that can adsorb, absorb, or chemically alter ethylene ( Almenar, 2018 ). 2. 2. 2 Classification of ethylene - removing packaging Ethylene - removing packaging can be classified into two types depending on the basic mechanism of action of the compound used to remove ethylene: oxidation or adsorption/absorption. Each type can subsequently be divided into sub types based on the used compound, which generally represent a whole family instead of a si ngle compound . For example, zeolites used to develop e thylene - removing packaging can have a natural origin ( Coloma et al . , 12 2014 ) or be synthetic ( 2015). These subtypes can be further split depending on the nature of the compound as discussed ab ove. Figure 2 .2 provides an overview of this classification. The mechanism of action, integration into the package, advantages and disadvantages, combination with other compounds, combination with other shelf - life extending technologies, applications, and commercial and academia progress made for each of these types of e thylene - removing packaging are covered below. Figure 2 .2 Classification of ethylene - removing packaging (adapted from Awalgaonkar and Almenar (2018 ) ) Ethylene - removing packaging based on ethylene oxidation potassium permanganate sodium permanganate titanium dioxide based on ethylene adsorption/absorption activated carbon zeolites clays metal organic frameworks 13 2. 2. 3. Types 2. 2 . 3.1 Ethylene - removing packaging based on ethylene oxidation Ethylene oxidizes to carbon dioxide and water irreversibly. Potassium permanganate can oxidize ethylene and thus, e thylene - removing packaging using potassium permanganate (KMnO 4 ) has been developed and its effect on produce shelf life has been studied extensively. KMnO 4 attacks the double bond in the ethylene molecule to oxidize it. Ethylene when oxidized by KMnO 4 initially forms acetaldehyde, followed by acetic acid, and finall y produces carbon dioxide and water. The redox reaction caused by KMnO 4 results in its change in color from purple (MnO 4 - ions) to brown (MnO 2 ). The evolution of the integration of KMnO 4 into the package has been from being placed on trays or dishes to i n sachets, and finally blended into the polymer bulk to make it part of the packaging film. Regardless, KMnO 4 is always incorporated onto inert carriers prior to its integration into the package . These carriers serve to increase the surface area of KMnO 4 i n contact with the ethylene and make an easily handled solid scrubber. However, the quantity of KMnO 4 that can be incorporated is about 4 - 6% of the inert carrier , and the resulting mixture does not have the same effectiveness as the oxidizer alone. This re sult s in the need for large amounts of impregnated material to achieve the desired scrubbing results (Ahvenainen, 20 0 3). According to Álvarez - Hernández et al. ( 2018 ), the selection of the inert carrier depends on characteristics such as surface area , size, material type, shape , and ethylene adsorption ability. Examples of KMnO 4 carriers include aluminum oxide, silica gel, vermiculite, celite, and perlite (Saltveit, 1980). A discussible of t he p hysical properties of these and other materials used as ca rriers for KMnO 4 including pore volume, pore size distribution, surface area, and effectiveness in extending produce shelf life can be found in Álvarez - Hernández et al . ( 2018 ). 14 The work done with trays and dishes can be considered as a way to prove the ef fectiveness of packages containing KMnO 4 in reducing ethylene in the headspace and extending fruit shelf life ( Shorter, et al., 1992 ; Szczerbanik, et al. , 2005) but not the development of packaging feasible for supply chain conditions. The effectiveness of KMnO 4 when integrated into the package in the form of sachets and films has been evaluated during the last decade . A ctive packages that use KMnO 4 as an active compound to scavenge ethylene are compiled and described in Table 2. 1 . Generally speaking , the f ruits in the active packages had lower ethylene and CO 2 production, less weight loss, higher firmness retention, lower soluble solids content (SSC) increase, higher titratable acidity (TA) , and less sugar accumulation and decay incidence compared to identi cal packages without the oxidizer. KMnO 4 is used due to its high effectiveness in scavenging ethylene generated by climacteric fruits . It can be found in the form of sachets and films for placement inside packages, storage facilities, and transportation vehicles and in the form of sprays and filters for other applications. The integration of KMnO 4 into the package in the form of sachets or as a part of multilayer films has solved the toxicity issue associated with KMnO 4 . This is the reason KMnO 4 is commercially used although it is caustic in nature. Commercial scavengers based on KMnO 4 that are currently used by industry are tabulated in Table 2. 2 . Some of them have been evaluated and validated by academia. For example, Shorter et al. (1992) reported that Granny Smith apples held in PE bags containing Purafil had less bitter pit and superficial scald, which the authors attributed to the et hylene removal by Purafil. Advantages and disadvantages of us ing KMnO 4 as ethylene oxidizer i n active packaging are compiled in Table 2. 3. Active packaging containing KMnO 4 combined with other shelf - life extending compounds has also been developed. The effect of the mix has been shown to be beneficial or not on a case - 15 by - case basis. KMnO 4 and 1 - MCP inside LD PE bags resulted in higher ethylene content that increased physiological disorders such as yellowing, flesh br owning, and core browning in Japanese pears compared to LD PE bags with only KMnO 4 ( Szczerbanik et al., 2005) . Active packages containing KMnO 4 sachets and sorbitol sachets were evaluated on the removal of volatiles associated with off - odors in packaged bro ccoli (DeEll , et al., 2006). The authors concluded that sorbitol and KMnO 4 combined in specific amounts could be used to remove off - odors like acetaldehyde and ethanol and to maintain appearance and texture, thus, extending bro ccoli quality and marketabili ty 16 Table 2. 1 Ethylene - removing packages based on KMnO 4 created during the last decade and their effect s on produce shelf - life extension. Integration technique Active compound amount Inert carrier Packaging format Packaging material Produce Storage conditions Effect Reference Sachet Not specified Not specifie d Box Corrugated fiber board Sapota 27 - 32 o C & 65 - 75% RH. Lower ethylene and CO 2 production, less weight loss, higher firmness retention, lower SSC increase, higher TA, less sugar accumulation and decay incidence in mature and half - ripe fruits but not in ripe fruits. Extended marketable life up to 13 days for mature - state sapota. Bhut ia, et al., 2011 Sachet 5ml Vermicu lite (5g) Bags LDPE (0.15mm) Banana 19 - 25 o C Treated samples prevented change in peel color and obtained a shelf life extension of 62 days compared with 55 days of untreated bananas Hassan, et al., 2005 17 Table 2. 2 Commercial ethylene scavengers in their available formats (adapted from Awalgaonkar and Almenar (2018) ) Active ingredient Carrier Format Commercial name Manufacturer KMnO 4 Alumina pellets Sachet Purafil Purafil, Inc., USA https://www.purafil.com/products/chemical - filtration/filtration/sachet/ accessed on 9 June 2018 Silica Sachet Greenpack Rengo, Co., Japan http://www.rengo.co.jp/english/products/cardboard. html accessed on 9 June 2018 Zeolite Sachet EC - 3+ Ethylene Control, Inc., USA https://www.ethylenecontrol.com/products/sachets/ accessed on 9 June 2018 Activated alumina beads Film, carton liner, pallet cover PrimePro® DeltaTrak ® , Inc., USA https://www.deltatrak.com/products/ethylene - absorbers accessed on 9 June 2018 Zeolite None Films , Peak Fresh® Dry Pak Industries, Inc., USA http://www.drypak.com/ethyleneAbsorbers.html accessed on 9 June 2018 None Fi lter, pad, label It's Fresh! It USA h ttp://www.itsfresh.com/default.asp?contentID=70 1 accessed on 9 June 2018 A ctivated carbon None Sachet Ethylene adsorber Vamsha Nature Care, India http://vamshacare.com/ethylene - absorber accessed on 9 June 2018 18 Table 2. 3 Advantages and disadvantages of ethylene oxidizers and scavengers in active packaging (adapted from Awalgaonkar and Almenar (2018) ) a= Keller et al. , 2013; b=Martínez et al., 2007; c= Zagory, 1995; d= Álvarez - Hernández et al., 2018; e = DeEll et al., 2006; f=Bailen et al., 2007 . Ethylene oxidizer/scavenger Advantages Disadvantages Potassium permanganate Highly effective in scavenging ethylene compared to other scavengers such as activated carbon, zeolites, metal organic frameworks, clay a, d, c Commercially available compared to sodium permanganate and titanium dioxide a Irreversible interaction with ethylene b Continuous reaction until saturation b Rapidly consumed, needs frequent replacement Needs an inert carrier a,b,c Purple color of KMnO4 may not be aesthetically pleasing c Caustic nature c , careful handling required during transporta tion and storage b Efficiency of ethylene oxidation is dependent on relative humidity conditions d Activated carbon Regeneration possible a environmentally friendly nature b Surface area (BET 1,120 m 2 /g) available for adsorption c Relatively cheap production and low cost b Good porosity a and non - toxic a Ease of availability b Efficiency of ethylene adsorption is dependent on temperature and relative humidity conditions f Can adsorb other compounds such as oxygen, carbon dioxide, and organic compounds b,f Zeolite Non - toxic c Environmentally friendly c Surface area (BET 320m 2 /g) available for adsorption a Low cost d Regeneration possible d Can adsorb/absorb other compounds such as oxygen, carbon - dioxide, and organic compounds b, Efficiency of ethylene adsorption is d ependent on relative humidity conditions d Low ethylene adsorption capacity (1.3 - 19.6 mmol/kg) a Lack significant ethylene adsorbing capacity when embedded in films a Metal - organic frameworks Exceptionally high surface area available for adsorption (BET 1,500 - 2,100m2/g) e Regeneration possible e Efficiency of ethylene adsorption is dependent on relative humidity conditions 19 2. 2. 3.2 Ethylene - removing packaging based on ethylene adsorption/absorption Adsorption is a surface phenomenon in which a particle is held on the surface of a solid material (Martínez et al., 2007). In contrast, absorption is a bulk phenomenon where the particle is held inside the solid material ( Keller & Staudt, 2005). Activated carbon/charcoal, zeolites and metal - organic frameworks can adsorb/absorb ethylene and thus, they have been used to develop ethylene - removing packaging as discussed below. 2. 2. 3.2.1 Activated carbon Any carbonaceous material can be used to make activated carbon (AC). The choice of material is depend ent on parameters such as low inorganic matter, ease of activation, ready availability, lower cost , and lower degradation (Martínez et al ., 2007). The m ost common materials used for activated carbon production are wood, fruit shells, fruit stones, apple pulp, wheat, cotton stalks, viscose rayon, and coal (Puziy et al ., 2002). AC is widely used in many f ields as an efficient and versatile adsorbent including as a purification agent, gas adsorber, decolorizing agent, and taste - odor removing agent (Martínez et al ., 2007). The use of AC as an ethylene scavenger can be dated back to the 19 40s when Southwick & Smock (1943) used brominated charcoal to remove ethylene from the storage atmosphere, which resulted in the reduction of scald and a considerable lengthening of the shelf life of McIntosh apples in controlled atmosphere storage (2 - 3 months). AC differing in particle size has been used for ethylene scavenging . G ranular, powdered , and fiber AC are the most common forms . Recently, carbon based nano - particles h ave been investigated for ethylene adsorption capacities. The particle size of AC affects its ethyle ne removal capacity due to differences in surface area, porosity, and activation efficiency. Bailen et al . ( 2007 ) reported that granular AC ( 20 - 60 mesh ) can adsorb 70% of available ethylene while powdered AC 20 ( 100 - 400 mesh ) can only adsorb 40%. Liu et al . ( 2006 ) found that carbon nano - particles could scavenge between 64 - 100 ppm of ethylene . Other factors affecting the capacity of AC to remove ethylene include impregnation with catalyst (e.g, palladium ; increases adsorption), ethylene concentration (the highe r the concentration the more the adsorption ), heat treatment (increases adsorption), activation with H 2 (increases adsorption), etc. ( Liu et al., 2006 ) . Ethylene adsorption of granular AC follows a Langmuir isotherm ( Bailen et al., 2007 ), which means that ethylene accumulates as a monolayer on the surface of the adsorbent. The area available for adsorption depends on the particle size of AC and the use of an activation treatment. Keller et al. ( 2013 ) reported that the AC surface area available for adsorption ranges between 827 and 1120m 2 /g. AC scavenges ethylene through adsorption. The pore size of AC plays an important role i n the adsorption process. A pore diameter greater than 3.9Å (kinetic diameter of ethylene) is ess ential for ethylene adsorption ( , 2015). The ability and efficacy of AC depends on factors like surface chemistry, surface area, pore volume, temperature, and relative humidity , etc . (Martínez et al ., 2007). Major advantages of AC as ethylene sc avenger include its environmental ly friendly nature, low toxicity, availability , and low cost. However, its non - specific nature of adsorption is a major limitation for its widespread use. Table 2 3 provides a detail ed list o f the advantages and drawbacks of AC as ethylene scavenger . AC has commonly been integrated into the package through sachets. However, two recent studies report the integration of AC into the packaging medium. Sothornvit ( 2012 ) incorporat ed rice straw and activated carbon to the pulp mixture during the paper making process to create paper sheets with an ethylene scavenger . When the sheets were tested for ethylene adsorption, almost 70% of ethylene was adsorbed in the first hour, and the maximum ethylene adsorption was 77%. Th e researchers claim that an application of AC - rice straw papers would be as a separate bag or 21 wrapper or as a laminate inside a carton to extend the shelf life of fruits. It is worth noting that the authors chose paper instead of plastic as a polymer subst rate since plastics have commonly been selected as material for active packaging creation. Table 2 4 provides examples of shelf life studies that evaluate AC as an ethylene scavenger. The combination of a ctive packag es containing AC with other shelf - life extending technologies has also been reported in the literature as shown in Table 2. 4 . Sachets containing adsorbers based on AC are commercialized as shown in Table 2 .2 . They can be placed inside packages to create active packages. 2. 2. 3.2.2 Ze olites Zeolites are microporous three - dimensional framework structures of crystalline aluminosilicates. Zeolites have negative charge s on their framework that are balanced with alkali or alkali earth ion s (Patdhanagul et al., 2012). The pore size of zeolites ranges from 3 to 12 Å , providing them with the ability to adsorb many chemicals including ethylene. 22 Table 2. 4 Ethylene - removing packages based on ethylene adsorption/absorption created during the last decade and their effects on produce shelf - life extension Active Compound Active compound amount Integration technique Packaging format Packaging material Produce Storage conditions Effect Reference AC granulated 5g Sachet Bags Oriented polypropyl ene Tomato 8°C and 90% RH with 8 kPa for O 2 and 7kPa CO 2 MAP and granulated AC treated with Pd, led to lower ethylene concentration, treated tomatoes exhibited a reduction in color, softening and weight loss Bailen et al ., 2006 AC and PdCl 2 CuSO 4 10,20, 30g/kg of broccoli Sachet Pouch Polyethyle ne (0.05 mm) Broccoli 20°C and 90% RH Delay yellowing and quality loss, reduced ethylene production and ethylene producing enzymes Cao et al., 2015 AC powdered, granulated 1.25g/lit Sachet Porous paper Glass Jars Tomato 20°C Significant reduction in softening and color changes in tomatoes Bailen et al. , 2007 23 AC , palm shell charcoal 40% w/w Liner and edium of box Corrugated board Kraft paper Tomato 27°±1°C Delayed rate of ripening, color change, shrivelin g and water loss observed in tomatoes treated with activated charcoal Taechutra kul 2009 A C 10g Paper packet Metal tray with glass cover Kiwi slices, Spinach, Banana slices 20°C Retained fruits firm for longer time, , degradation of chlorophyll minimized Abe & Watada 1991 Zeolite (Tazetut 50% of aluminosilicate minerals) 8% w/w Film Film Polyethyle ne Broccoli 4°C and 75% RH for 20 days Delayed weight loss, chlorophyll degradation, stem hardening. Shelf life increased by 15 days Esturk et al., 2014 Zeolite 2% Film Film Zeolite melt blended with LDPE Banana Not specified Improved quality attributes and better preservation in bananas Li et al., 2012 24 Du e to cation exchange capacity, molecular sieving , and adsorption, zeolites can be used to remove ethylene ( Limtrakul et al ., 2001 ; Suslow, 1997 ) . Zeolites have been reported to have a l ow ethylene adsorption capacity (1.3 - 19.6 mmol/kg) (Keller et al., 2013) ; however, this can be modified by cationic agents. Sue - aok et al. ( 2010 ) studied the modification of NaY zeolite caused by several ions including potassium (K - NaY), rubidium (Rb - NaY), and cesium (Cs - NaY). T he modified zeolite s adsorbed more ethylene and followed the pattern K - NaY > Rb - NaY > Cs - NaY >NaY . Z eolites are environmentally fr iendly and non - toxic . However, they have a low ethylene sorption capacity. Table 2 . 3 lists advantages and drawbacks associated with using zeolites as ethylene scavenger s . Ethylene can be absorbed within the zeolite framework and adsorbed on the surface of the zeolite framework ( Coloma et al., 2014) . For natural zeolites, a large pore diameter ( 12Å) favors ethylene (kinetic diameter 3.9 Å) to pass through zeolite pore openings and be absorbed within the zeolite framework ( 2015) . There two theories to explain this phenomenon . The f irst one assumes that a cation - interaction occurs between the - electrons of the double bond of ethylene and metal cations. It involves s - donation and p* back - donation between the metal cations and the orbital of ethylene. The s econd theory involves a CH - O interaction, resulting from hydrogen bonding between hydrogen atoms of ethylene and oxygen atoms at the zeolite surface ( Coloma et al ., 2014) . Only the blending of zeolites with polymer matrixes has b een studied as integration technique. Dirim et al . ( 2001 ) studied various methods to manufacture a PE film containing zeolite . The se methods were addition of zeolite to molten PE , coating PE beads with zeolite, extrusion of PE with zeolite, and hot pressing of co - extruded zeolite - PE film. Among all these methods, the latter was found to be most effective for produce shelf - life extension . Coloma et al. ( 2014 ) obtained 25 a 37% reduction in ethylene concentration when the authors ev aluated a LDPE film containing 10% zeolite (Zn - Ch ) . Ethylene permeability for a double layer composite film, prepared by laminating LDPE and poly[styrene - b - (ethylene - co - butylene) - b - styrene] (SEBS) modified with zeolite , was improved due to enhanced adsorp tion of ethylene by the incorporated zeolite and the dispersion of the zeolite s ( Monprasit et al ., 2011). The combination of a ctive packag es containing zeolites with other shelf - life extending technologies has also been reported in the literature . Thermofo rmed PET containers containing zeolites combined with KMnO4 in amounts of 0, 0.5, showed that several of the combinations of scavenger and oxidizer were able to delay tomato ripening. Ho wever, each combination enhanced a different quality attribute (Salamanca et al., 2014). S achets and films containing zeolites for creation of packages able to scavenge ethylene are commercially available. Table 2 lists some manufacturers of the aforementioned formats . 2.2.3.2.3 Metal - Organic Framework (MOFs) MOFs are a new class of synthetic porous materials, consisting of metal ions or ion clusters bound to organic molecules to form a porous structure. The combination of different organic and inorganic building blocks gives flexibility in terms of pore size, shape , and structure (Kuppler et al ., 200 9). Li et al . ( 2009 ) reported that MOFs have an exceptionally high surface area (1 , 000 3 , 000 m 2 /g or more ). In addition, they have a g reater adsorptive surface per gram (BET) than zeolites (320 m 2 /g) and activated carbon (827 - 1,120 m 2 /g) (Table 2 . 4) . MOFs can selectively adsorb volatile compounds such as ethylene (Kuppler et al., 2009 ; Chopra et al., 2017). Chopra et al . ( 2017 ) reported that MOFs did not adsorb ethylene very efficiently if water is present in the surrounding environment . The authors also reported that MOFs can be successfully use d for ethylene releasing applications. Zhang et al . ( 2016 ) and Zhang & Luo ( 2017 ) in vestigated the 26 effectiveness of MOF for on - demand ripening. They found that 50 mg of copper - based MOF can adsorb and release up to 654 µ l/l of ethylene in a 4 L container . It is worth to note that i f the hydrophilicity of MOF s is controlled, then they have potential to be used in ethylene scavenging applications where high relative humidity is present . MOFs scavenge ethylene due to adsorption (Chopra et al., 2017) . While the mechanism is not yet proven, modelling by Li et al . ( 2009) suggests that electrostatic interactions take place between the partial positive charges of coordinately - electrons of the double bond in ethylene molecules. A dvantages and drawbacks of using MOFs as ethylene scavenge rs are compiled in Table 2. 3 . 27 REFERENCES 28 REFERENCES 1. Abe, K. & Watada W. A. (1991). Ethylene absorbent to maintain quality of lightly processed fruits and vegetables. Journal of Food Science , 56 (6), 1589 1592. 2. Almenar, E. (2018). Innovations in packaging technologies . In: Beaudry, RM, Gil, MI, editors. Controlled and Modified Atmosphere Use for Fresh and Fresh - cut Produce. 3. Álvarez - Hernández, M. H., Artés - Hernández, F., Ávalos - Belmontes, F., Castillo - Campohermoso, M. A., Contreras - E squivel, J. C., Ventura - Sobrevilla, J. M., & Martínez - Hernández, G. B. (2018). Current scenario of adsorbent materials used in ethylene scavenging systems to extend fruit and vegetable postharvest life . Food and Bioprocess Technology , 11(3): 511 - 525 . 4. Bail én, G., Guillén, F., Castillo, S., Serrano, M., Valero, D., & Martínez - Romero, D. (2006). Use of activated carbon inside modified atmosphere packages to maintain tomato fruit quality during cold storage. Journal of Agricultural and Food Chemistry , 54 (6), 2 229 2235. 5. Bailén, G., Guillén, F., Castillo, S., Zapata, P.J., Serrano, M., Valero, D., & Martínez Romero , D. (2007). Use of a palladium catalyst to improve the capacity of activated carbon to absorb ethylene, and its effect on tomato ripening. Spanish Jo urnal of Agricultural Research , 5, 579 586 6. Beaudry, R. M. (2009). Future trends and innovations in controlled atmosphere storage and modified atmosphere packaging technologies. In X International Controlled and Modified Atmosphere Research Conference , 876 : 21 - 28. 7. Beaudry, R. M. (1999). Effect of O 2 and CO 2 partial pressure on selected phenomena affecting fruit and vegetable quality. Postharvest Biology and Technology , 15 (3), 293 302. 8. Bhutia, W., Pal, R. K., Sen, S., & Jha, S. K. (2011). Response of different maturity stages of sapota (Manilkara achras Mill.) cv. Kallipatti to in - package ethylene absorbent. Journal of Food Science and Technology , 48 (6), 763 768 9. Burg, S. P., & Burg, E. ( 1967). Molecular requirements for the biological activity of ethylene. Plant Physiology , 42 (1), 144 152. 10. Cao, J., Li, X., Wu, K., Jiang, W., & Qu, G. (2015). Preparation of a novel PdCl2 CuSO4 based ethylene scavenger supported by acidified activated carb on powder and its effects on quality and ethylene metabolism of broccoli during shelf - life. Postharvest Biology and Technology , 99 , 50 - 57. 11. Chopra, S., Dhumal, S., Abeli, P., Beaudry, R., & Almenar, E. (2017). Metal - organic frameworks have utility in adsorption and release of ethylene and 1 - methylcyclopropene in fresh produce packaging. Postharvest Biology and Technology , 130 , 48 55. 29 12. Chaves, M. A., Bonomo, R. C. F., Silva, A. A. L., Santos, L. S., Carvalho, B. M. A., Souza, T. S., & Soares, R. D. (2007). Use of potassium permanganate in the sugar apple post - harvest preservation. Journal of Food , 5(5), 346 - 351. 13. Figs by CO2 - enriched Atmospheres. HortScience , 26 (9), 1193 1195. 14. Coloma, A., Rodríguez, F. J., Bruna, J. E., Guarda, A., & Galotto, M. J. (2014). Development of an active film with natural zeolite as ethylene scavenger. Journal of the Chilean Chemical Society , 5 9 (2), 2409 2414 15. Creech, D.L., Workman, M. & Harrison, M. D. (1973). The influence of storage factors on endogenous ethylene production by potato tubers. American Journal of Potato Research , 50 (5), 145 150. 16. DeEll, J. R., Toivonen, P. M. A., Cornut, F., Roge r, C., & Vigneault, C. (2006). Addition of sorbitol with KMnO4 improves broccoli quality retention in modified atmosphere packages. Journal of Food Quality , 29 (1), 65 75. 17. Dirim, S. N., Esin, A., & Bayindirli, A. (2003). A new protective polyethylene based film containing zeolites for the packaging of fruits and vegetables: Film preparation. Turkish Journal of Engineering and Environmental Sciences , 27 (1), 1 9. 18. Esturk, O., Ayhan, Z., & Gokkurt, T. (2014). Production and application of active packaging film with ethylene adsorber to increase the shelf life of Broccoli ( Brassica oleracea L. var. Italica). Packaging Technology and Science , 27 (3), 179 191. 19. Gorny, J. R., & Kader, A. A. (1997). Low oxygen and elevated carbon dioxide atmospheres inhibit ethylene b iosynthesis in preclimacteric and climacteric apple fruit. Journal of the American Society for Horticultural Science , 122 (4), 542 546. 20. Hassan, M. K., Shipton, W. A., Coventry, R. J., & Gardiner, C. P. (2005). Maintenance of fruit quality in organically - gro wn bananas under modified atmosphere conditions. Asian Journal of Plant Sciences , 4(4) , 409 412. 21. Keller, N., Ducamp, M. N., Robert, D., & Keller, V. (2013). Ethylene removal and fresh product storage: A challenge at the frontiers of chemistry. Toward an a pproach by photocatalytic oxidation. Chemical Reviews , 113 (7), 5029 5070. 22. Keller, J. U., & Staudt, R. (2005). Gas adsorption equilibria: experimental methods and adsorptive isotherms . Springer Science & Business Medi a . 23. Kuppler, R. J., Timmons, D. J., Fang, Q. - R., Li, J. - R., Makal, T. A., Young, M. D., Yuan, D., Zhao, D., Zhuang, W., & Zhou, H. - C. (2009). Potential applications of metal - organic frameworks. Coordination Chemistry Reviews , 253 (23 24), 3042 3066. 30 24. Li, D. L., Shi, Q. P., & Xu, W. C. (2012). Effects of zeolite modified LDPE film on Banana fresh keeping. Biotechnology, Chemical and Materials Engineering, Pts 1 - 3 , 393 395 , 724 728. 25. Li, J. R., Kuppler, R. J., & Zhou, H. C. (2009). Selective gas adsorption and sep aration in metal organic frameworks. Chemical Society Reviews , 38 (5), 1477 - 1504. 26. Limtrakul, J., Nanok, T., Jungsuttiwong, S., Khongpracha, P., & Truong, T. N. (2001). Adsorption of unsaturated hydrocarbons on zeolites: The effects of the zeolite framework on adsorption properties of ethylene. Chemical Physics Letters , 349 (1 2), 161 166. 27. Liu, Z. - X., Park, J. - N., Abdi, S. H. R., Park, S. - K., Park, Y. - K., & Lee, C. W. (2006). Nano - sized carbon hollow spheres for abatement of ethylene. Topics in Catalysis , 39 (3 4), 221 226. 28. Martínez - Romero, D., Bailén, G., Serrano, M., Guillén, F., Valverde, J.M., Zapata, P., Castillo, S. & Valero, D., (2007). Tools to maintain postharvest fruit and vegetable quality through the inhibition of ethylene action: a review. Critic al R eviews in F ood S cience and N utrition , 47 (6), 543 - 560. 29. Monprasit, P., Ritvirulh, C., Sooknoi, T., Rukchonlatee, S., Fuongfuchat, A., & Sirikittikul, D. (2011). Selective ethylene - permeable zeolite composite double - layered film for novel modified atmosphere packaging. Polymer Engineering and Science , 51 (7), 126 4 1272. 30. Patdhanagul, N., Rangsriwatananon, K., Siriwong, K., & Hengrasmee, S. (2012). Combined modification of zeolite NaY by phenyl trimethyl ammonium bromide and potassium for ethylene gas adsorption. Microporous and Mesoporous Materials , 153 , 30 34. 31. P uziy, A. M., Poddubnaya, O. I., Martínez - Alonso, A., Suárez - García, F., & Tascón, J. M. D. (2002). Synthetic carbons activated with phosphoric - Acid I. Surface chemistry and ion binding properties. Carbon , 40 (9), 1493 1505. 32. Salamanca, F.A., Balaguera - Lóp ez, H.E. & Herrera, A.O. ( 2014 ) . Effect of potassium permanganate on some postharvest characteristics of tomato. Acta Horticulturae . 171 - 175 33. Saltveit, M. (1999). Effect of ethylene on quality of fresh fruits and vegetables. Postharvest Biology and Technolo gy , 15 (3), 279 292. 34. Shorter, A. J., Scott, K. J., Ward, G., & Best, D. J. (1992). Effect of ethylene absorption on the storage of Granny Smith apples held in polyethylene bags. Postharvest Biology and Technology , 1 (3), 189 194. 35. Soliva - Fortuny, R. C., & M artín - Belloso, O. (2003). New advances in extending the shelf - life of fresh - cut fruits: A review. Trends in Food Science and Technology , 14 (9), 341 353. 36. Sothornvit, R., & Sampoompuang, C. (2012). Rice straw paper incorporated with activated carbon as an e thylene scavenger in a paper - making process. International Journal of Food Science and Technology , 47 (3), 511 517. 31 37. Suslow, T. (1997). Performance of Zeolite Based Products in Ethylene Removal. Perishables Handling Quarterly , (92), 32 33. 38. Sue - aok, N., Srit hanratana, T., Rangsriwatananon, K., & Hengrasmee, S. (2010). Study of ethylene adsorption on zeolite NaY modified with group I metal ions. Applied Surface Science , 256 (12), 3997 - 4002. 39. Szczerbanik, M. J., Scott, K. J., Paton, J. E., & Best, D. J. (2005). Effects of polyethylene bags, ethylene absorbent and 1 - methylcyclopropene on the storage of Japanese pears. Journal of Horticultural Science and Biotechnology , 80 (2), 162 166. 40. ka, Anna. (2015). Development of a poly (lactic acid) packaging material able to scavenge carbon dioxide and ethylene by incorporation of zeolites. PhD Thesis. Michigan State University, East Lansing, USA 41. Taechutrakul, S., Netpradit, S., & Tanprasert, K. ( 2009). Development of recycled paper - based ethylene scavenging packages for tomatoes. In Acta Horticulturae , 837, 365 370. 42. Wilson, C. T., Harte, J., & Almenar, E. (2018). Effects of sachet presence on consumer product perception and active packaging accept ability - A study of fresh - cut cantaloupe. LWT Food Science and Technology , 92, 531 - 539 43. Zagory, D., 1995. Ethylene - removing packaging , in: Rooney, M.L. (Ed.), Active Food Packaging , Springer, Boca Raton, pp. 38 - 54. 44. Zagory, D., & Kader, A. A. (1988). Modifi ed Atmosphere Packaging of Fresh Produce. Food Technology , 49 (9), 70 74 & 76 77. 45. Southwick, F.W. and Smock, R . (1943). Lengthening the storage life of apples by removal of volatile materials from the storage atmosphere. Plant Physiology , 18 (4), 716. 46. Zhang, B. and Luo, Y. (2017). Tackling Food Waste Challenge with Nanotechnology: Controllable Ripening via Metal Organic Framework. Internationa l Journal of Nutrition and Food Engineering 4(8) 47. Zhang, B., Luo, Y., Kanyuck, K., Bauchan, G., Mowery, J., & Za valij, P. (2016). Development of Metal - Organic Framework for Gaseous Plant Hormone Encapsulation to Manage Ripening of Climacteric Produce. Journal of Agricultural and Food Chemistry , 64 (25), 5164 5170. 48. Dilley, D. R., Wang, Z., Kadirjan - Kalbach, D. K., Ve rveridis, F., Beaudry, R., & Padmanabhan, K. (2013). 1 - Aminocyclopropane - 1 - carboxylic acid oxidase reaction mechanism and putative post - translational activities of the ACCO protein. AoB Plants, 5. 32 CHAPTER 3 Identif ication of ethylene scavenger and packaging material for development of a tray with ethylene removing capacity 3.1 Materials 3.1.1. S cavengers M etal organic framework (M OF s) (Basolit e® C300) was obtained from the G erman branch of BASF (Ludwig, Germany). Powdered activated carbon ( PAC ) (100 mesh particle size ) and potassium permanganate (KMnO 4 ) were obtained from Sigma - Aldrich (St. Louis, Missouri , USA ). Granulated activated carbon ( GAC ) ( 8 - 12 mesh particle size) derived from coconut was obtained from Capi tal Scientific (Austin, Texas , USA ). Clinoptilolite (CL) was procured from Liquid Zeolite Company Inc. ( Cedar Grove, NJ, US A ), 4A zeolite was obtained from UOP LLC . , A Honeywell Company ( Des Plaines, IL, US A ) . These scavengers are shown in Figure 3 . 1 and t he ir properties as claimed by the manufacture r s are listed in Table 3 . 1 . D esiccant was obtained from W.A. Hammond Drierite Co. LTD (Xenia, OH, USA). Certified gas cylinders containing 500 ppm of ethylene balanced in N 2 and a gas mixture of 40% O 2 , 40% CO 2 balanced in N 2 were provided by Airgas (Radnor, PA, US A ) . 3.1 .2. Films Low density polyethylene ( LDPE 0.030 - m m thickness ) , linear low density polyethylene ( LLDPE 0.025 - mm thickness ) , polypropylene (PP 0.020 - mm thickness ), nylon (0.012 - m m thickness ) , and polyethylene terephthalate (PET 0.013 - m m thickness ) films were donated to the School of Packaging by Dow Chemicals (Midland, MI, USA). Polylactic acid (PLA) film ( 0.040 - mm thickness) was obtained from EVLON EV - HS1 (BI - AX International Inc., Wingham, O N, Canada). 33 Table 3. 1 Properties of scavengers used in the study . Scavengers Metal Constituents Pore radius (Å) Langmuir surface area (m 2 /g) BET surface area (m 2 /g) PAC - 4 - 10 1 1070 2 741 2 GAC - 4 - 10 1 1252 2 747 2 MOF Cu 5.0 3 1520 3 1470 3 CL K, Ca, Na 5.5 4 169.8 ± 17.8 4 31.4 ± 5.4 4 4A Na 2.3 4 171.3 ± 79.4 4 48.0 ± 26.0 4 Sources: 1 Ding et al. (2008); 2 Yener et al. (2008); 3 Kathuria (2013); 4 Figure 3 .1 Images of scavengers used for the study . 34 3.2. Methods 3.2.1 Activation of scavengers MOF ( Basolite® C300 ) was subjected to a vacuum oven ( VWR, Pennsylvania, USA) and set at 140 °C between 10 and 20 mm Hg for at least 8 hours. A ctivated carbons (PAC, GAC) and zeolites (CL and 4A) were activated in the aforementioned oven at 110 °C and 25 mm Hg for at - mL glass with polypropylene caps , Fisher Scie ntific , Pittsburgh, PA, USA) until use. 3.2.2 Assay system s About 0.5 g rams of scavenger was placed into 250 - ml glass jars with aluminum closures containing a central hole covered with a septum . The jars were then injected using a gastight syringe ( Supelc o Analytical, California, USA ) with 500 ppm of ethylene balanced in N 2 to obtain 5 µl of ethylene . R elative humidity (RH) conditions of <5 %, 55 % and 100 % RH were generated inside the jars by using a desiccant, ambient RH, and a small vial with deionized water , respectively . In another study, the jars were flushed with a mixture of 40 % O 2 , 40 % CO 2 , and 20 % N 2 prior to closure and injection with ethylene (same as above) and only high RH conditions were generated. 3.2.3 Storage conditions Two temperatures, 23 ± 2 o C and 5 ± 2 o C were used to mimic the produce supply chain. The different temperatures were attained by placing the jars in an environmental chamber (Environmental growth chambers, Chagrin , Ohio, USA). 35 3.2. 4 Adsorption measurements 3.2 .4.1 Ethylene adsorption Ethylene levels were measured by withdrawing an amount of 100 µL from each jar using the gastight syringe and septum described in section 3.2.2 . The gas was injected into the splitless port of a gas chromatograph ( HP 6890 ser ies GC ) equipped with a Carboxen TM 1010 Plot fused silica capillary column (30 m X 0.53 mm) (Supelco, Bellefonte, California, U SA) and a flame ionization detector . The oven and injector temperatures were set to 150 °C and 220 °C, respectively. Ethylene le vels in µl were quantified using a standard curve with the following regression equation: y = 6E - 14x 2 + 3E - 08x + 5E - 05. Ethylene sorption was tested every 24 hours until maximum sorption was reached or there was a suspicion of leakage . Otherwise, ethylene withdrawal was carried out for five days. Three replicates of each scavenger type were used. % ethylene ad sorption was calculated as shown below and was then normalized for the weight of the scavenger. w here: Initial concentration indicates the c oncentration of ethylene in µ l at t=0 and Final concentration indicates the c oncentration of ethylene in µ l at a specific time t . 3.2. CO 2 and O 2 adsorption The amounts of O 2 and CO 2 in the jar headspace were measured using the Check Point 3 (Mocon , Ametek Instruments , Minneapolis, USA ) . 1 ml of gas sample from each jar was 36 withdrawn through the septum of the lid every 24 hours for 5 days. Three replicates of each scavenger type were used. % O 2 and CO 2 adsorption were calculated similarly to ethylene . 3.2.5 Barrier properties Water vapor transmission rates (WVTR) of the film s listed in section 3.2.2 were measured in accordance with ASTM F1249 - 05 (ASTM, 2005) using a Permatran W Model 3/33 water permeability a nalyzer (MOCON, Minneapolis, MN, US A ). Three films of each material were tested at 23 °C and 100 % RH . A setup was cre ated to measure ethylene permeation ( Figure 3. 2 ) . A permeation cell was used . T he film was mounted separating the cell into two halves. The system consisted of test gas ( 15 , 000 ppm of ethylene + air ) flowing at 0.125 ml/sec through the upper half of the cell (donor chamber) while the carrier gas (air) flowed at 0. 667 ml/sec through the lower portion (receiver chamber) . The ethylene permeated into the receiver chamber was withdrawn using a 1 - ml gas syringe and was injec ted into a GC ( Carle Series 400 AGC; Hach Co., Loveland, CO, USA ) equipped with a flame ionization detector and coupled with a 6 - m - long x 2 - mm - i.d. stainless steel column packed with activated alumina. The ethylene detection limit of the GC was 0.005 µl/l. Ethylene concentrations were calculated relative to a certified standard (Matheson Gas Products, Chicago, I l, USA ) with a concentration of 0.979 µl/l. Three films of each material were tested at 23 °C and 55 % RH . 37 Figure 3.2 Schematic representation of the system used to measure ethylene permeation . 3.2. 6 Statistical analysis To compare the effect of type of scavenger, time, temperature , and relative humidity the statistical model included these parameters and their interactions as fixed factor s, and the replicates used for the analysis as a random factor. There was a minimum of three replicates per treatment. All evaluated factors and their interactions were determined through a general linear model using the statistical software Minitab 17 (St ate College, PA , USA ) and Tukey at 0.05 level was used for statistical significance. In all analyses, the assumptions of normality of statistical errors and homogeneity of variances were checked and met for avoiding biasing results from uncontrolled find i ngs . For the adsorption study in presence of O 2 and CO 2 and for barrier properties the statistical analyses was performed using a univariate analysis of variance (ANOVA) with the statistical software Minitab 17 (State College, PA) and T ukey at 0.05 level for statistical significanc e. 38 3.3 Results and d iscussion 3.3.1 Effects of temperature and relative humidity on the sorption capacity of ethylene scavengers The results obtained by subjecting the scavengers (KMnO 4 , MOF, PAC, GAC, CL, 4A) to the temperatures 4 ± 2 o C and 23 ± 2 o C and the relative humidity conditions <5 % RH, 55 %RH, 100 %RH are shown in Figure 3 . 3 3.3.1.1 KMnO 4 At RH conditions of 55 % and higher , KMnO 4 had a greater ethylene oxidizing capacity at 23 o C than at 4 o C un til day 3, after which no statistically significant results were obtained. Lidster et al. ( 1985 ) also reported that ethylene removal by KMnO 4 increase s with time and temperature. After 5 days, KMnO 4 oxidized 97 % of the ethylene at RH of 55 % and higher, while it showed lower activity in the range of 60 % ( 4 o C) and 70 % (23 o C) at < 5 % RH. Lidster et al. ( l 985) also reported higher ethylene removal cap acity for KMnO 4 at high RH (90~96 %), which was attributed to the moisture requirement for reaction between ethylene and KMnO 4 crystals. In comparison with all other scavengers, KMnO 4 had the highest ethylene removing capacity at 100 % RH and 23 o C. These conditions are prevalent for a few climacteric fruits but not for most. 3.3.2.2 Activated carbon Temperature influence d the ethylene removing capacity of both GAC and PAC. H igher adsorption was observed at 5 o C than at 23 o C regardless of the RH . The difference was much larger when RH increased. In contrast, Mart i nez - Romero et al. ( 2007 ) reported that temperature (2 o C vs. 20 o C ) does not affect the ethylene adsorption of activated carbons. Ethylene adsorption was about 80 % at 4 o C regardless of the RH. However, ethylene adsorption decreased with increasing RH at 23 o C. This is most likely due to more water molecules surrounding the scavenger 39 at 23 o C compared to 4 o C as water pressure increases with increasing temperature ( Kessler, 2006 ). Furthermore , water instead of ethylene adsorption was favored due to the smaller kinetic diameter of water (2.65 Å ) compared to ethylene (3.9 Å) . Nature of activated carbon ( GAC and PAC ) showed differences in the first 24 hours only at 100% RH , with GAC be ing able to adsorb more ethylene . In agreement with these results, Bailen et al. (2007) found that PAC (40%) had a lower ethylene adsorption compared to GAC (70%). However, the authors reported the difference happening at ambient RH instead of at high RH l ike in this study. The difference between the two studies could be the use of different sources of activated carbon that led to different BET surface areas and/or the use of different activation conditions. Both activated carbons desorbed more than half of the trapped ethylene after 48 hours at 100 % RH and 4 o C but not at other combinations of temperature and RH. Among the scavengers considered in this study, the ethylene removing capacity of activated carbon was the highest at 4 o C and RH of 55 % and high er (conditions surrounding climacteric fruits and other types of commodities) for the first 48 - 72 h. At 23 o C, activated carbon still showed more ethylene removing capacity than zeolites but not than KMnO 4 at RH of 55 % and higher and MOF at RH of 55% and lower. GAC was the second best ethylene remover at high RH regardless of the RH. 40 4 ± 2 o C 23 ± 2 o C Relative h umidity 100 % RH Relative humidity 55% RH Relative humidity <5 % RH Figure 3.3 Impact of temperature and relative humidity on the ethylene removing capacity of six scavengers. 0 20 40 60 80 100 % adsorption MOF GAC PAC CL 4A KMnO4 Control 0 20 40 60 80 100 % adsorption MOF GAC PAC CL 4A KMnO4 Control 0 20 40 60 80 100 0 1 2 3 4 5 % adsorption Days 0 20 40 60 80 100 0 1 2 3 4 5 % adsorption Days 0 20 40 60 80 100 % adsorption 0 20 40 60 80 100 % adsorption 41 3.3.2.3 Zeolite According to Figure 3 , CL has ethylene removing capacity. This is in agreement with et al. ( 2008 ) but not Peiser & Suslow ( 1998 ) . In fact, CL had higher ethylen e removing capacity than 4A. This could be attributed to its larger pore diameter compared to 4A . Furthermore, the two zeolites differ in metal constituents and these seem to play a role in ethylene removal. CL consists of K + , Ca + and Na + ions whereas 4A consists of Na + ions. The adsorption of ethylene by CL has been attributed to the interactions between the K + ions and ethylene and strong quadropole moment and interaction between divalent Ca 2+ ions with the ethylene double bond ., 2008). Tem perature and RH influenced the ethylene removing capacity of CL but did not of 4A . Ethylene adsorption by CL was lower at 4 o C than at 23 o C and decreased with increasing RH. Ethylene adsorption was expected to be lower at 23 o C because of more water mole cules. This could be explained by zeolites being able to remove ethylene by adsorption and absorption instead of only adsorption like the other scavengers. The details of this mechanism can be found in Chapter 2 (literature review). Among all compared scav engers, zeolites exhibited the lowest ethylene removing capacity. The evaluated zeolites were in their natural form and not modified . H owever, an improvement in their ethylene removing capacity can be obtained when treated with cationic agents and surfacta nts ( Sue - aok et al. , 2010 , Patdhanagul et al . , 2010 , et al. , 2008 ). 3.3.2.4 MOF Temperature d id not have a consistent impact on ethylene r emoving capacity of MOF but RH did . increasing RH, which can be attributed to more water molecules competing for the same adsorption sides as ethylene. The ethylene removing capacity of M OF at low relative humidity ( ~ 96 %) was comparable to that of KMnO 4 at high RH ( ~ 93 %) at both temperatures . At ambient and low RH, 42 equilibrium was reached within the first 24 hours. At high RH, ethylene adsorption was ~ 9 5 % at 4 o C and ~15 % at 23 o C after 24 hours. However, the trapped ethylene was then desorbed and reach ed values of less than 5 % at both temperatures. In agreement with these results, Chopra et al. (2017) reported a high affinity of MOF towards ethylene in the absence of water and l ow ethylene adsorption by MOF in the presence of water. The authors also reported that ethylene removing capacity was more than KMnO 4 , activated carbon, and zeolite s at < 5 % RH. Based on the results discussed above, the ethylene removing capability of the scavengers is highly diminished with increasing RH except for KMnO 4 , which was able to retain its high ethylene removing capacity at high RH due its oxidative mec hanism compared to an adsorption mechanism. However, as mentioned in the literature review, certain drawbacks of KMnO 4 , such as its caustic nature and need for careful handling during storage require the study of alternative scavengers (e.g., adsorption - ba sed scavengers) to replace KMnO 4 . Among the studied adsorption - based scavengers, zeolites have a low ethylene adsorption capacity compared to activated carbon and MOF. Consequently, zeolites and KMnO 4 were excluded and MOF and PAC were shortlisted for a f urther study on competitive adsorption of ethylene in the presence of competing molecules like CO 2 and O 2 . The study was carried out because CO 2 , and O 2 not only can compete for the same adsorption sites but are also present in produce surroundings (e.g., package headspace). 3.3.2 Effect of competitive adsorption (CO 2 , O 2 and water) on ethylene adsorption The ethylene adsorption of PAC and MOF was studied in the presence of competing molecules such as CO 2 , O 2 , and water. Three replicates of jars were used for the study, however leakage was suspected in one set of jars and hence the reported data is only for two sets of jar samples. The % ethylene and % CO 2 , were calculated using the formula mentioned in 3.2.4. No 43 adsorption of O 2 was observed by MOF and PAC . The results obtained for ethylene and CO 2 after 5 days of storage at 23 o C and 100 % RH are presented in Table 3 . 2. Both scavengers were able to adsorb ethylene and carbon dioxide simultaneously. Both MOF and PAC adsorbed CO 2 in the presence of water and ethylene. It could be that the co - adsorbed water molecules enhanced CO 2 adsorption . Yaza y diyan et al. ( 2009 ) and Burtch et al. ( 2014 ) both reported an enhancement of CO 2 adsorption in the presence of water. Both scavengers we re able to adsorb ethylene when CO 2 and water w ere present . However, the effect of CO 2 on ethylene adsorption was different depending on the scavenger type. CO 2 had no effect on the adsorption of ethylene by PAC. However, the competing molecule increased the adsorption of ethylene by MOF. This could be attributed to different host - guest affinities that depend on host sides (Li et al., 2011). This variability in e thylene adsorption among scavengers in the presence of competing molecules has already been reported. Chopra et al. (2017) reported a decrease in the amount of ethylene adsorbed by Baseolite® C300 but not by Baseolite® A520 and Zeolite Z13X, which showed t he same capability to adsorb ethylene. 44 Table 3. 2 Competitive adsorption of CO 2 and ethylene of MOF and PAC at 23 o C and 100% RH Scavenger Ethylene adsorption (%) CO 2 adsorption (%) Condition: 5 µ l of ethylene and high RH Condition: 40% CO 2 , 40% O 2 , 5 µ l ethylene and high RH Condition: 40% CO 2 , 40% O 2 , 5 µ l ethylene and high RH MOF 3.28 9.98 9.01 PAC 8.54 7.21 8.32 3.3.3 Barrier properties From Figure 3. 3 and Table 3 . 2, it can be inferred that PAC and MOF have more affinity towards water than CO 2 and ethylene. So, for developing an ethylene - removing packaging, it is essential to have a packaging material with good barrier properties to water as produce generates a high RH condition inside the package . On the oth er hand, a weak permeability to ethylene is also desired. It is important that the gas permeates through the film to reach the scavenger. Hence, several petroleum - based and bio - based films were tested for their permeability to water and ethylene and the re sults are presented in Table 3 . 3 . The petroleum - based polyolefin films (LDPE, LLDPE, PP) had lower permeability to water than the other petroleum - based and bio - based films. PET had moderate permeability to water while nylon and the bio - based films (PLA, carbohydrate - based and protein - based ) have poor water barrier properties. Ethylene was only detected in the case of the LDPE, LLDPE, and PP films indicating they are relatively poorer barrier s to ethylene than the other films. The none detection of ethylen e in case of the other films shows that these have good barrier to ethylene. 45 Table 3. 3 Water and ethylene permeability of various petroleum - based and bio - based films. Film Thickness (mm) Water vapor permeability * 10 - 16 (Kg. m/m 2 sec Pa) @ 23 o C and 100%RH Ethylene permeability *10 - 17 (Kg. m/m 2 sec Pa) @ 23 o C and 55%RH LDPE 0 .030 4.55 1 ± 0.145a 2.775 ± 1.388a LLDPE 0.025 2.849 ± 0.078a 2.111 ± 1.065a PP 0.020 1.754 ± 0.031a 1.533 ± 1.387a PET 0.013 10.484 ± 1.50a Below measurable quantity Nylon 0.012 104.012 ± 4.33b Below measurable quantity PLA 0.040 221.007 ± 7.99c Below measurable quantity Yam - based 1 0.070 20827 ± 3184d Below measurable quantity Egg white - based 2 0.110 21458 ± 8790d Below measurable quantity 1 Pranata et al. (2018); 2 Guimarães et al. (2018). Means within the same column with a same letter are not statistically different at p < 0.05. Wang et al. (1998) studied ethylene permeation for LDPE and LLDPE and reported similar range s for the two polymers in terms of ethylene permeation results. For developing ethylene - removing packaging, a plastic with poor barrier to ethylene and a decent barrier to water would be ideal. Based on these criteria, plastics like LDPE, LLDPE, and PP could be used for creation of ethylene - removing packaging . 46 REFERENCES 47 REFERENCES 1. Martínez - Romero, D., Bailén, G., Serrano, M., Guillén, F., Valverde, J.M., Zapata, P., Castillo, S. , & Valero, D. (2007). Tools to maintain postharvest fruit and vegetable quality through the inhibition of ethylene action: a review. Critical R eviews I n F ood S cience A nd N utrition , 47 (6), 543 - 560. 2. Saltveit, M. E. (1999). Effect of ethylene on quality of fresh fruits and vegetables. Postharvest B iology A nd T echnology , 15(3), 279 - 292. 3. Zagory, D. (1 995). Ethylene - removing packaging. In Active F ood P ackaging (pp. 38 - 54). Springer US. 4. Keller, N., Ducamp, M. N., Robert, D., & Keller, V. (2013). Ethylene removal and fresh product storage: a challenge at the frontiers of chemistry. Toward an approach by p hotocatalytic oxidation. Chemical R eviews , 113 (7), 5029 - 5070. 5. scavenge carbon dioxide and ethylene by incorporation of zeolites. PhD Thesis. Michigan State University , East Lansing, USA. 6. Kathuria Ajay (2013). Functional properties and stability of plla - metal organic framework based mixed matrix membranes. PhD Thesis. Michigan State University, East Lansing, USA. 7. haracterization and ethylene adsorption of natural and modified clinoptilolites. Applied Surface Science , 254 (8), 2450 - 2457. 8. Peiser, G., & Suslow, T. V. (1998). Factors affecting ethylene adsorption by zeolite: the last word (from us). Perishable Handling Quarterly Issue , (95), 17 - 19. 9. Lidster, P. D., Lawrence, R. A., Blanpied, G. D., & McRae, K. B. (1985). Laboratory evaluation of potassium permanganate for ethylene removal from CA apple storages. Transactions of the ASAE , 28 (1), 331 - 0334. 10. Chopra, S., Dhumal, S., Abeli, P., Beaudry, R., & Almenar, E. (2017). Metal - organic frameworks have utility in adsorption and release of ethylene and 1 - methylcyclopropene in fresh produce packaging. Postharvest Biology and Technology , 130, 48 - 55. 11. Zhang, B., Luo, Y., Kanyuck, K., Bauchan, G., Mowery, J., & Zavalij, P. (2016). Development of metal organic framework for gaseous plant hormone encapsulation to manage ripening of climacteric produce. Journal of Agricultural and Food Chemistry , 64 (25), 5164 - 5170 . 12. Singh, P., Abas Wani, A., & Saengerlaub, S. (2011). Active packaging of food products: recent trends. Nutrition & Food Science , 41 (4), 249 - 260. 48 13. Vermeiren, L., Devlieghere, F., Van Beest, M., De Kruijf, N., & Debevere, J. (1999). Developments in the acti ve packaging of foods. Trends in F ood S cience & T echnology , 10 (3), 77 - 86. 14. Almenar, E., Siddiq, M. , & Merkel, C. ( 2012 ) . Packaging for processed food and th environment. In: M.S. Rahman and J. Ahmed, eds. 2012. Handbook of F ood P rocess D esign. Oxford: Wiley - Blackwell Publishing Limited, pp.1369 - 1405. 15. Almenar, E., Hernández - Muñoz, P., Lagarón, J.M., Catalá, R., & Gavara, R. (2006). Advances in packaging technologies for fresh fruit and vegetables. In: Noureddine, B., Norio, S.(Eds.), Advances in Postharv est Technologies of Horticultural Crops. Research Signpost, Kerala, India, 87 112. 16. Bailén, G., Guillén, F., Castillo, S., Serran o, M., Valero, D., & Martínez - Romero, D. (2006). Use of activated carbon inside modified atmosphere packages to maintain tomato fruit quality during cold storage. Journal of Agricultural and Food Chemistry , 54 (6), 2229 2235. 17. Kuppler, R.J., Timmons, D.J., Fang, Q. - R., Li, J. - R., Makal, T.A., Young, M.D., & Zhou, H. - C., ( 2009 ) . Potential applications of metal - organic frameworks. Coo rdination Chemistry Reviews , 253 (23 24), 3042 3066. 18. Li, J. - R., Kuppler, R.J., & Zhou, H. - C., (2011) . Selective gas adsorption and separation in metal organic frameworks. Chemical Society Reviews 38 (5) , 1477 1504 . 19. Patdhanagul, N., Srithanratana, T., Rangsriwatananon, K., & Hengrasmee, S. (2010). Ethylene adsorption on cationic surfactant modified zeolite NaY. Microporous and Mesoporous Materials, 131 (1 3), 97 102. 20. Sue - aok, N., Srithanratana, T., Rangsriwatananon, K ., & Hengrasmee, S. (2010). Study of ethylene adsorption on zeolite NaY modified with group I metal ions. Applied Surface Science, 256 (12), 3997 - 4002. 21. Burtch, N. C., Jasuja, H., & Walton, K. S. (2014). Water stability and adsorption in metal organic framew orks. Chemical R eviews , 114 (20), 10575 - 10612. 22. R. Q. (2009). Enhanced CO 2 adsorption in metal - organic frameworks via occupation of open - metal sites by coordinat ed water molecules. Chemistry of Materials , 21 (8), 1425 - 1430 . 23. Modification of water vapour transfer rate of low density polyethylene films for food packaging. Journal of Food Engineering, 63 (1) , 9 - 13. 24. Yener, J., Kopac, T., Dogu, G., & Dogu, T. (2008). Dynamic analysis of sorption of methylene blue dye on granular and powdered activated carbon. Chemical Engineering Journal , 144 (3), 400 - 406. 49 25. Ding, L., Snoeyink, V. L., Marinas, B. J., Yue, Z., & Economy, J. (2008). Effects of powdered activated carbon pore size distribution on the competitive adsorption of aqueous atrazine and natural organic matter. Environmental S cience & T echnology , 42 (4), 1227 - 1231. 26. Pranata, M. P. , González - Buesa , J., Kikyung, K., Chopra, S., Pietri, Y., Perry, N., Matuana, L., & Almenar, E. (2018). Effects of temperature and relative humidity on the properties of egg white protein - based films obtained through extrusion and calendering processes . Food and B ioproducts P rocessing (submitted). 27. Guimarães, G.H., Silvanda, M.S., Antônio, A.M.R., Beaudry, R.M ., & Almenar, E. (2018). Precise targeting of processing temperature is essential for optimizing properties of starch - based films from different biological sources. Polymer Carbohy drates (submitted). 28. Ghaani, M., Cozzolino, C. A., Castelli, G., & Farris, S. (2016). An overview of the intelligent packaging technologies in the food sector. Trends in Food Science & Technology , 51 , 1 - 11. 29. Kessler, H. G. (1988). Lebensmittel - und Bioverfahrenstechnik. Molkereitechnologie. Technische Universität München - Weihnstephan. 50 CHAPTER 4 Develop ment and characteriz ation of an ethylene removing tray and its validaton for produce packaging applications 4.1 Materials Low density polyethylene (LDPE) resin (melt flow index of 24 g/10 min , density 0.913g/cm 3 ) were procured from LyondellBasell and LDPE film (0.04 - mm thickness) w as supplied by Dow Chemicals (Midland, MI, USA). Powdered activated carbon (100 mesh particle si ze) was purchased from Sigma Aldrich (St Louis, MO, USA). Cherry tomatoes ( Solanum lycopersicum var. cerasiforme ) were purchased from a local grocery store (East Lansing, MI, USA). They were transported to the School of Packaging and were then sorted by color and size and any damaged or rotten fruits were removed, all at ambient conditions . Certified gas cylinder containing 500 ppm of ethylene balanced in N 2 was provided by Airgas (Radnor, PA, US A ) . 4 .2 Methods 4.2.1 Tray development Activated carbon (A C) was conditioned prior to processing using a vacuum oven (VWR, Pennsylvania, USA) for 4 h at 110 °C followed by 4 h at 200 °C and was then stored in a desiccator until use. Specific quantities of LDPE resin and AC (5%, 10%, and 20% w/w) (Step 1; Figure 4 . 1) were weighed and mixed (Step 2 ; Figure 4 . 1) using a three - piece mixer (Brabender, Duisburg, Germany) at 160 °C for 3 min. Amounts of ~11g of each of the LDPE/ AC mixtures were compression molded into sheets with thicknesses between 350 µm and 420 µm using a hydraulic press (model 0L488 - C, PHI, City of Industry, CA, USA) at a pressure of 20,000 psi and a temperature of 1 2 0 °C for 7 min (Step 3 ; 51 Figure 4 . 1). The formed sheets (Step 4; Figure 4 1) were stored in a desiccator at 23°C (Step 5 ; Figure 4. 1) until these were shaped into trays using a vacuum thermoforming machine (LABFORM® Model 1620, Hydrotrim thermoformer, New York , NJ, USA). The heating phase was carried out for 1 min ute and the t hermoforming phase for about 45 s econds . A temperature of 1 20 o C was maintained during the whole thermoforming process (Step 6; Figure 4 . 1). A minimum of six trays containing only LDPE (controls) and six trays containing AC in concentrations of 5%, 10 % , and 20 % were produced. Figure 4 . 2 shows a control tray and a tray containing AC. Figure 4 .1 Schematic representation of the preparation of the thermoformed tray s 52 Figure 4.2 Control tray (left) and a tray containing AC (right). 4.2.2 Tray selection The trays containing AC produced in section 4.2.1 were tested for their ethylene adsorption capacity. The assay systems consisted of 250 - ml mason jars with one tray each, it was flushed with N 2 containing 20 ppm of ethylene for 1 min prior to their closure. The lids were previously modified by cutting a central piece out that was covered with a snap - fit rubber septum. The assay systems were stored at 23 o C and 100 % RH. Amounts of 100 µL of jar headspace were withdraw n throu ghout the lid septum every 24 h for 5 days using the gastight syringe (Supelco Analytical, California, USA). The gas was injected into the splitless port of a gas chromatograph ( HP 6890 GC, Agilent Technology, Palo Alto, California, USA) equipped with a fl ame ionization detector and a Carboxen TM 1010 Plot fused silica capillary column (30 m X 0.53 mm) (Sup elco, Bellefonte, California, US A). The ove n temperature was 150°C and injector and detector temperatures were set to 150 °C and 220 °C, respectively. Th e splitless flow was 3.0. Ethylene 53 levels were quantified using a previously prepared standard curve with the following regression equation: y = 6E - 14x 2 + 3E - 08x + 5E - 05 . The results are presented as adsorbed ethylene/g of tray . 4.2.3 Tray characterizatio n The control trays (LDPE) and the trays containing AC selected in section 4.2. 2 were compared in terms of thickness profile and thermal, mechanical, and barrier properties. 4. 2 . 3. 1 Thickness Sheet t hickness (Step 4, Figure 4. 1) w as determined with a TMI 549 M micrometer ( Testing Machines Inc., Amityville, NY , USA) in accordance with ASTM D374 - 99 (ASTM, 2016 ). The thickness profiles (wall, edge, bottom, and trim) of the trays (Step 7, Figure 4. 1) were obtained using a Magna - Mike Mo del 8000 thickness ga u ge ( Panametrics, Waltham, MA. USA). At least six samples of each type of tray were measured. The results are presented in mm. 4. 2. 3.2 Thermal c haracterization The t hermal transitions of the neat LDPE and LDPE/ AC sheets (Step 4; Figure 4. 1) were determined using a Q100 Differential scanning calorimeter (TA Instruments, New Castle, DE, US A ). The temperature calibration of the equipment was performed in accordance with ASTM E967 - 03 (ASTM, 2003a) and the heat flow calibration was performed in ac cordance with ASTM E968 - 02 (ASTM, 2002). D egree of crystallinity (% X c ) was obtained from the ratio between the heat of fusion samples ( ) and heat of fusion 100% crystalline LDPE (277.1 J/g) as reported by Brandrup, Immergut, & McDowell ( 1975) but tak ing into consideration the percentage w eight of the LDPE present in the sheets ( : 54 B etween 5 mg and 8 mg of LDPE and LDPE/ AC sheets w ere used for each run . Samples were heated from 5 ° C to 210 ° C at a rate of 10 ° C/min. Three replications of each type of sheet were tested. The results are presented as % crystallinity. 4. 2. 3.3 Mechanical characterization The control trays and the trays containing AC selected in section 4.2. 2 were subje cted to compression test s in order to determine the effect of the addition of the AC on the mechanical properties of the material since the trays did not differ in design . Measurements w ere carried out using an Instron Universal Testing Machine (Model 5565 , Instron, Norwood, MA, US A ) with a crosshead speed of 5 mm/min and a gauge length of 30 mm. Ten trays of each type were used and the results are presented as compressive force (N) and extension (mm). 4.2.3.4 Barrier properties Water vapor transmission rates (WVTR) of the aforementioned sheets were measured in accordance with ASTM F1249 - 05 (ASTM, 2005a) using a Permatran W Model 3/33 water permeability analyzer (M ocon , Minneapolis, MN, US). Three sheets of each type were tested a t 23 o C and 100 % RH. Oxygen transmission rates ( OTR) of the sheets were measured in accordance with ASTM D3985 - 05 (ASTM, 2005b) using an 8001 Oxygen p ermeation a nalyzer (Mocon, Minneapolis, MN, US). Three sheets of each type were tested at 23 o C and 0 % RH. All samples were masked with an adhesive type aluminum foil (McMaster - Carr, Aurora, Ohio, US), leaving an uncovered test area of 3.14 cm 2 . The results are presented as permeability units ( k g. m/m 2 sec Pa). 4.2.4 Shelf - life study Quantities of approxi mately 75 g rams of cherry tomatoes precision balance, OHAUS, Pine Brook, NJ, USA) and placed in side the control trays and the trays 55 containing AC selected in section 4.2. 2. T he trays were wrapped with LDPE film that had all its sides heat sealed u sing an impulse sealer (Ceratek, Sencorp SystemsInc., Hyannis, MA, USA) for 5 seconds . A silicone septum was attached to the corner of each package to withdraw the headspace gases. Fig ure 4. 3 shows the developed packaging systems. All pa ckages were kept at 23 o C and 55% RH for 9 days. Physiological, p hysico - chemical , and microbial evaluations were performed every 3 days. Six packages of each material were evaluated at each testing day. Figure 4.3 Packaging systems with and without trays containing AC . 4. 2.4 . 1 Physiological evaluations The in - package headspace composition (CO 2 and O 2 ) was measured using Check Point 3 (Mocon , Ametek Instruments , Minneapolis, USA). 1 - ml syringe of the gas headspace was withdrawn through the septum patched o n the package . The concentration of the headspace gases 56 CO 2 and O 2 is reported in percentage. Ethylene content was measured according to the method described in 4.2.2 but using packages instead of glass jars. The weight of each package of cherry tomatoes was measured on day 0 and on each sampling day using a balance haus , NJ, USA). Weight loss was determined by subtracting the final weight from the initial weight divided by the result from the subtraction of the packaging material weight from the initial weight . Weight losses are reported in percent. 4.2.4.2 Physico - chemical evaluations The c herry tomatoes of each package were blended for 30 s using a common blender (Hamilton Beach, NC , USA ). Soluble solids in the tomato juice were determined using a refractometer (RHB - 32ATC , Cole - Parmer Instruments, IL, USA). The refractometer was calibrated prior to each measurement. Three measurements were taken for each sample and the results are reported in o Brix. 4. 2.4.3 Microbiologi cal evaluations Fungal growth was visually estimated on each individual fruit immediately after opening the packages. Any cherry tomato with visible fungal growth was considered to be decay ed . The results were expressed as percentage of decayed cherry toma toes . 4. 2.5 Statistical analysis All statistical analyses were performed using univariate analysis of variance (ANOVA) with the statistical software Minitab 17 (State College, PA) and T ukey at 0.05 level for statistical significance. In all analys es, the assumptions of normality of statistical errors and 57 homogeneity of variances were checked and met for avoiding biasing results from uncontrolled 4.3 Re sults and discussion 4.3.1 Tray selection The developed trays differing in AC concentrations (0 %, 5 %, 10 %, 20 % w/w) are shown in Figure 4 . 4 . The ethylene removing capacity of these trays present in the jars after 5 days is shown in Figure 4 . 5. The control tray (LDPE tray) was able to adsorb 1.105 ppm/g of tray when exposed to an ethylene concentration of 20 ppm. Similarly, García - García et al. ( 2013 ) reported that thick LDPE films (0.07 mm) adsorb ed 2.755 ppm of ethylene in 15 days. Significant diff erences ( P < 0.05) in ethylene adsorption capacity were observed between the LDPE tray and the LDPE/10% AC and LDPE/20% AC trays. The latter two absorb ed twice as much ethylene as the LDPE tray. The LDPE/10% AC and LDPE/20% AC trays did not differ in ethyl ene adsorption capacity but in uniformity. The trays with 20% AC developed some micro - cracks and small voids. These could have resulted from the formation of clusters and agglomerations by the AC due to its high concentration that restricted the LDPE chain mobility during thermoforming. Development of cracks and voids was also reported by Chodak & Krupa (1999) when the authors studied the addition of carbon black to polyethylene. Based on the higher ethylene adsorption capacity and the even trays, the LDPE/ 10% AC trays were selected for further characterization . 58 LDPE tray LDPE / 5% AC tray LDPE/ 10% AC tray LDPE /20% AC tray Figure 4.4 Trays developed with LDPE and 0%, 5%, 10%, and 20% activated carbon . 59 Figure 4.5 Ethylene adsorption after 5 days by developed trays containing 0%, 5%, 10% and 20% of AC. and a shelf - life study. Furthermore, the selection of this type of tray led to the use of a tray where 10% of the LDPE resin is replaced with a material obtained from agricultural waste . 4.3 .2 Tray characterization 4.3.2.1 Thickness As shown in Table 4. 1 , the thickness of both trays varied significantly ( P < 0.05) based on the part of the tray. Wall thickness was higher than corner and bottom thicknesses in both LDPE and LDPE/10% AC trays. Buntinx, et al. ( 2014 ) and Throne (2008) attributed the non - uniform thickness of a tray to a variety of processing parameters in the thermoforming process including sheet temperature, type of mold, depth of mold, mold temperature, heating time, thermoforming pressure, and differential stretching. Also, the authors mentioned that the thinning observed in the 0 1 2 3 4 0 5 10 20 Adsorbed ethylene/g of tray (ppm/g) Activated carbon (%) 60 corners and bottom of a tray is a major dr awback for thermoforming. No differences were observed between the thicknesses of sheet and trim indicating that the non - uniformity in thickness occurs when the heated sheet is deformed into the mold. The addition of 10% AC did not affect the thickness in sheet, trim, and corner. However, differences ( P < 0.05) were observed in the thicknesses of the walls and bottoms, which thinned with the addition of the AC. This could be explained by different levels of deformation that parts of the sheet have to underg o to reach the furthest ends of the mold (Martin & Duncan 2007). Due to the mold design , as the tray becomes deeper, thinning is observed in the corners and the bottom 4.3.2.2 Thermal characterization The % crystallinity of the LDPE and LDPE/10 % AC sheets are shown in Table 4. 2 . These thermal properties were not altered due to the presence of AC. This could be due to the saturation of the nucleating action of AC occurring at higher loading (10 %). At such high amounts, AC interferes with the crystal growin g process and hence an increase in crystallinity was not observed ( Trujillo et al., 2007). Karsli & Aytac (2011) observed a decrease in crystallinity for short carbon fiber reinforced polypropylene composites. The difference could be attributed to the lowe r concentration of carbon (2.5 - 5%) and the increased interfacial interaction between polymer matrix and the carbon due to the use of a fiber format. 4.3.2.3 Mechanical characterization The compressive force (N) and extension (mm) of the tray did not change with the addition of AC as shown in Table 4 . 2 . The compressive force was approx. 7.90 N and the extension was 15 mm. The identical mechanical properties of the trays can be attributed to their same % crystallinity and corner thickness. Contrary to w hat one might expect, differences in wall thickness did not lead to different compressive forces and extensions. There are not results for trays loaded 61 with AC in the literature for comparison purposes. For films, Khalil et al. (2007) observed higher tensi le strength for cast polyester resin loaded with 10% AC compared to the neat casted material. 4.3.2.4 Barrier properties The water permeability and oxygen permeability of the trays were determined due to their effect on the concentration of water and oxyg en inside the package headspace. As reported in Table 4 . 2, t he LDPE/10% AC and LDPE trays had the same permeability to water (approx. 5 x 10 - 16 kg.m/m 2 s Pa). Zagory (1995) reported that polymers with open pore spaces created by addition of compounds such as zeolites can alter the gas/vapor exchange properties of the polymers. Dirim et al. (2004) showed that LDPE films with embedded zeolites had less permeability to water than the neat films, which was attributed to the porous structure and water sorption c apacity of zeolites. Although AC is porous and has water sorption capacity ( Bailen et al. , 2006 ), a decrease in water permeability was not observed due to no differences in crystallinity between the LDPE/10% AC and LDPE sheets . Similar to water permeability , the developed LDPE/10% AC and LDPE trays did not show differences in oxygen permeability (approx. 5 x10 - 17 kg.m/m 2 s Pa ). The reasoning is the same as that for water. 62 Table 4. 1 Thickness profile of the shee ts and the developed t ray M eans with same lowercase letters within the same column are not significantly different based on the ANOVA results at 5% significant level. Means with same uppercase letters within the same row are not significantly different based on the ANOVA results at 5% significant level . Table 4. 2 Thermal, mechanical, and barrier properties of the LDPE tray and LDPE/10% AC tray. Sample Thermal properties Mechanical properties Barrier properties T m Crystallinity ( % ) Compressive f orce (N) Extension (mm) Water vapor permeability *10 - 16 (Kg m/m 2 s Pa) Oxygen permeability *10 - 17 (Kg m/m 2 s Pa) LDPE tray 131.12±0.222a 54.57±0.655a 7.900±2.014a 15.023±0.008a 5.037±1.734a 4.561±1.935 a LDPE /10% AC tray 130.85±0.521a 54.06±0.884a 7.839±2.597a 15.019±0.008a 5.116±3.984a 5.560±3.366a Means with same lowercase letters within the same column are not significantly different based on the ANOVA results at 5% s ignificant level . Sample Thickness (mm) Sheet Tray Wall Corner Bottom Trim LDPE 0.397±0.025aA 0.351±0.033aA 0.207±0.042cB 0.275±0.040dC 0.378±0.047aA LDPE/10% AC 0.393±0.022aA 0.311±0.013bB 0.190±0.030cC 0.227±0.042cD 0.389±0.029aA 63 Figure 4.6 Shelf - life study parameters of cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH for 9 days . 0 0.5 1 1.5 2 2.5 3 % Weight loss LDPE LDPE 10% AC 0 0.2 0.4 0.6 0.8 1 Ethylene in ppm /g of tray LDPE LDPE 10% AC 0 5 10 15 20 0 3 6 9 % Oxygen Days 0 1 2 3 4 0 3 6 9 % Carbon dioxide Days 64 4.3.3. Shelf - life study 4 .3 .3. 1 Physiological evaluations Figure 4 . 6 shows the evolution of weight loss for cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH for 9 days. In both packaging systems, weight loss was directly proportional to the storage time and was less than 1% after 9 days. This can be attributed to both packaging systems being wrapped with a good barrier to water like LDPE film and no adsorption of water by the trays containing AC. The observed results are similar to the ones reported by Bailen et al. (2006) who reported a <1% weight loss for tomatoes when packaged in bags with 5 g of sache ts containing AC. Taechutrakul et al. (2008), however, observed a weight loss of > 9% for tomatoes packaged in corrugated boxes containing AC and palm shell charcoal. They reported that the higher weight loss compared to the controls was due to the greater water absorption by AC. Transpiration in cherry tomatoes results in shriveling rendering the fruit unacceptable, which did not happen with the developed package. Figure 4 . 6 illustrates the changes in O 2 and CO 2 content within the packaging systems with L DPE trays and with LDPE/10% AC trays. In both packaging systems, O 2 content decreased and CO 2 content increased due to the respiration of the cherry tomatoes. After day 3, no further changes in gas concentration were observed due to the equilibrium reached between the respiration of cherry tomatoes and diffusion of gases through the LDPE film. F agundes et al. ( 2015 ) observed similar equilibrium in cherry tomatoes after 100 hours of storage at 5 o C. The equilibrium was attained earlier (within 72 hours) in this study due to the higher temperature (23 o C). No statistically significant differences in O 2 and CO 2 contents were observed between the two packaging systems except for a slight increase in t he CO 2 content (0.5 %) of the packaging systems with LDPE/10% AC trays at day 9. No differences in O 2 content were observed in the presence of 65 10 % AC. Salveit (1997) observed that 3 5 kPa O 2 (minimum) and 3 5 kPa CO 2 (maximum) was the best gas combination for red tomatoes under controlled atmosphere storage conditions while Ben - Yehoshua et al. ( 2005 ) recommended 3 5 % CO 2 and 3 5% O 2 f or ripe tomatoes in modified atmosphere storage. Figure 4 . 6 illustrates the evolution of ethylene in the headspace of the packaging systems with LDPE trays and with LDPE/10% AC trays. In both packaging systems, ethylene content increased due to the production of ethylene by the cherry tomatoes. No differences in ethylene content were observed in the presence of 10 % AC. Based on the results obtained in chapter 3, the ethylene adsorption by AC under medium and low RH and 23 o C occurs within the first 24 hours. Hence, the saturation of AC could have happened before day 3, when the first measurements were taken. Therefore, the in itial data on ethylene adsorption was missed and not many significant changes were observed after that . Differences were observed in the amount of ethylene adsorbed in the concentration study compared to the shelf - life study because during the former the t rays were studied in glass jars. Also, higher amounts of ethylene (20 ppm) and CO 2 (40%) were present in the jars compared to the packages. The trays have a potential to adsorb ethylene . T herefore, further studies are necessary to find correlations between the amount of AC, ethylene adsorption, and its applications in extending produce shelf life. 4 .3 .3. 2 Physico - chemical evaluations The soluble solid s content of the packaged cherry tomatoes stored at 23 o C and 85% RH for 9 days is presented in Table 4. 3 . A n increase in the total soluble solids content was observed in both LDPE and LDPE/10% AC trays. Significant differences were obtained between the two trays. An increase in soluble solids concentration is associated with ripening of fruit as the days proce ed ( Martinsen, & Schaare, 1998). 66 Table 4. 3 Changes in total soluble solids content of cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH for 9 days . Sample o Brix Day 3 Day 6 Day 9 LDPE tray 6.140±0.054a 6.880±0.044a 6.925±0.095a LDPE /10% AC tray 6.320±0.109b 6.720±0.083b 7.285±0.083b Means with same lowercase letters within the same column are not significantly different based on the ANOVA results at 5% significant level. 4 .3. 3. 3 Microbiological evaluations Figure 4 . 7 shows the fungal growth of cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH after 6 days . 2.85% of the tomatoes presented fungal growth in the LDPE 10% AC trays while a higher damag e rate of 8.57% was observed in the LDPE trays. However, no microbial growth was observed in any of the trays at days 3 and 9. The unusual fungal decay on day 6 may be due to the higher microbial load on the tomatoes tested in that day. 67 Figure 4.7 Microbiological evaluation of the cherry tomatoes packaged in LDPE and LDPE/10% AC trays and stored at 23 o C and 85% RH after 6 day 68 REFERENCES 69 REFERENCES 1. Buntinx, M., Willems, G., Knockaert, G., Adons, D., Yperman, J., Carleer, R., & Peeters, R. (2014). Evaluation of the thickness and oxygen transmission rate before and after thermoforming mono - and multi - layer sheets into trays with variable depth. Polymers , 6 (12), 3019 - 3043. 2. Throne, J.L. Understanding Thermoforming ; Carl Hanse r Verlag: Munich, Germany, 2008. 3. Trujillo, M., Arnal, M. L., Müller, A. J., Laredo, E., Bredeau, S., Bonduel, D., & Dubois, P. (2007). Thermal and morphological characterization of nanocomposites prepared by in - situ polymerization of high - density polyethyl ene on carbon nanotubes. Macromolecules , 40 (17), 6268 - 6276. 4. García - García, I., Taboada - Rodríguez, A., López - Gomez, A., & Marín - Iniesta, F. (2013). Active packaging of cardboard to extend the shelf life of tomatoes. Food and Bioprocess Technology , 6 (3), 754 - 761. 5. Soleimani, M., & Kaghazchi, T. (2007). Agricultural waste conversion to activated carbon by chemical activation with phosphoric acid . Chemical Engineering & Technology: , 30 (5), 64 9 - 654. 6. Rowell, R. M., Sanadi, A. R., Caulfield, D. F., & Jacobson, R. E. (1997). Utilization of natural fibers in plastic composites: problems and opportunities. Lignocellulosic - plastic C omposites , 23 - 51. 7. Khalil, H. A., Noriman, N. Z., Ahmad, M. N., Ratnam, M. M., & Fuaad, N. N. (2007). Polyester composites filled carbon black and activated carbon from bamboo (Gigantochloa scortechinii): Physical and mechanical properties. Journal of Reinforced Plastics and composites , 26 (3), 305 - 320. 8. Puziy, A. M., Po - Alonso, A., Suarez - M. D. (2002). Synthetic carbons activated with phosphoric acid. I. Surface chemistry and ion binding properties. Carbon , 40 (9), 1493 1505. 9. Taechutrakul, S., Netpradit, S., & Tanprasert, K. (2009). Development of recycled paper - based ethylene scavenging packages for tomatoes. Acta Horticulturae , 837, 365 370 . 10. Agunsoye, J. O., Isaac, T. S., & Samuel, S. O. (2012). Study of mechanical behaviour of coconut shell reinforced polymer matrix composite. Journal of Mi nerals and M aterials C haracterization and Engineering , 11 (8), 774 - 779. 11. Fávaro, S. L., Lopes, M. S., de Carvalho Neto, A. G. V., de Santana, R. R., & Radovanovic, E. (2010). Chemical, morphological, and mechanical analysis of rice husk/post - consumer 70 polyethylene composites. Composites Part A: Applied Science and Manufacturing , 41 (1), 154 - 160. 12. Bailén, G., Guillén, F., Castillo, S., Serrano, M., Valero, D., & Martínez - Romero, D. (2006). Use of activated carbon inside modified atmosphere packages to maintain tomato fruit quality during cold storage. Journal of Agricultural and Food Chemistry , 54 (6), 2229 2235 . 13. Bailén, G., Guillén, F., Castillo, S., Zapata, P.J., Serrano, M., Valer o, D., Martínez Romero, D. (2007). Use of a palladium catalyst to improve the capacity of activated carbon to absorb ethylene, and its effect on tomato ripening. Spanish Journal of Agricultural Research , 5, 579 586 14. Maneerat, C., & Hayata, Y. (2008). Gas - p hase photocatalytic oxidation of ethylene with TiO2 - coated packaging film for horticultural products. Transactions of the ASABE , 51 (1), 163 168 . 15. Salamanca, F. A., Balaguera - López, H. E., & Herrera, A. O. (2014, January). Efecto del permanganato de potasio sobre algunas características poscosecha de frutos de tomate In II International Conference on Postharvest and Quality Management of Horticultural Products of Interest for Tropical Regions , 1016, 171 - 176 . 16. Tas, C. E., Hendessi, S., Baysal, M., Unal, S., Cebeci, F. C., Menceloglu, Y. Z., & Unal, H. (2017). Halloysite nanotubes/polyethylene nanocomposites for active f ood packaging materials with e thylene scavenging and gas barrier properties. Food and Bioproce ss Technology , 10 (4), 789 798. 17. AST M Standard D3417 - nthalpies of fusion and crystallization of p olymers by Differential Scanning Calorimetry ( DSC ) International, West Conshohocken, PA. 18. ASTM Standar d D 3418 - d test m ethod for transition temperatures of p olymers by thermal a ASTM International, West Conshohocken, PA. 19. AST M Standard E 968 - low calibration of differential scanning c International, West Con shohocken, PA. 20. ASTM Standard D 3985 - xygen gas transmission rate t hrough plastic film and s heeting using a c Conshohocken, PA. 21. Brandrup, J. (1975). Physical Properties of Monomers an d Solvents in Polymer Handbook, ed. by Brandrup J, Immergut EH and McDowell W. 22. Khalil, H. A., Noriman, N. Z., Ahmad, M. N., Ratnam, M. M., & Fuaad, N. N. (2007). Polyester composites filled carbon black and activated carbon from bamboo (Gigantochloa 71 scortechinii): Physical and mechanical properties. Jour nal of Reinforced Plastics and C omposites, 26(3), 305 - 320. 23. Zagory, D. (1995). Ethylene - removing packaging. In Active food packaging (pp. 38 54). 24. Fagundes, C., Moraes, K., Pérez - Gago, M. B., Palou, L., Maraschin, M., & Monteiro, A. R. (2015). Effect of active modified atmosphere and cold storage on the postharvest quality of cherry tomatoes. Postharvest Biology and Technology , 109 , 73 - 81. 25. Saltveit, M.E., 1997. A summary of CA and MA requirements and reco mmendations for harvested vegetables. University of California, Davis, CAIn: Saltveit, M.E. (Ed.), 7th International Controlled Atmosphere Research Conference, July 13 18, 1997, vol. 4. , pp. 98 117. 26. Farber, J. M. (1991). Microbiological aspects of modifie d - atmosphere packaging technology - a review. Journal of Food Protection , 54 (1), 58 - 70. 27. black filled polyethylene. Journal of Materials Science L etters, 18 (18), 1457 - 1459. 28. ASTM D374 / D374M - 16, Standard Test Methods for Thickness of Solid Electrical Insulation, ASTM International, West Conshohocken, PA, 2016, www.astm.org 29. Martin, P. J., & Duncan, P. (2007). The role of plug design in dete rmining wall thickness distribution in thermoforming. Polymer Engineering & Science , 47(6), 804 - 813. 30. Martinsen, P., & Schaare, P. (1998). Measuring soluble solids distribution in kiwifruit using near - infrared imaging spectroscopy. Postharvest Biology and Technology , 14 (3), 271 - 281. 31. Ben - Yehoshua, S., Beaudry, R. M., Fishman, S., Jayanty, S., & Mir, N. (2005). Modified atmosphere packaging and controlled atmosphere storage. Environmentally friendly technologies for agricultural produce quality. Ben - Yehoshua, S. Ed. Taylor and Francis Group LLC. Boca Raton, FL, U L, 61 - 112 . 72 CHAPTER 5 CONCLUSIONS 5.1 Conclusions The following conclusions were drawn from the study , a mong the tested scavengers ( potassium permanganate, two activated carbons, two zeolites and metal organic frameworks ) , activated carbon was selected because it had second best ethylene scavenging capacity at high RH regardless of the temperature . Activated carbon can be easily obtained from agricultural w aste and is approved for food contact by the FDA contrary to potassium permanganate, which is not used for direct contact with food products. Among the tested petroleum - based and bio - based plastics, low density polyethylene was chosen as the packaging material because of its adequate barrier to b oth water and ethylene . A thermoformed tray containing 10% activated carbon was developed. The developed tray had similar of thickness profile, thermal, mechanical , and barrier properties compared to the tray without the activated carbon and showed ethylen e removing capability. Cherry tomatoes could be packaged and commercialized in the developed trays, however , further studies on the effect of the developed ethylene removing trays on the shelf life extension needs to be carried out. 5.2 Future work Activated carbon has been proven to have ethylene removing capacity, it can be further enhanced by the treatment of certain catalysts and metal ions suc h as palladium (Pd) etc. In terms of developing a tray f urther studies are required to optimize and reach the max imum concentration of activated carbon that could replace the polymer. For tray design, t ransparent lids could be developed for the tray, also different sizes and shapes could be explored by changing the mold 73 design used in the thermoformer. Also, e xtrusio n processing instead of compression molding could be considered for forming the sheets used for tray development. Also the potential of micro perforating the sheets could be considered for balancing the gas composition and package headspace. The developed trays are black in color that gives a good contrast on packaging on produce such as cherry tomatoes. S tudies on how does color of package (transparent, white, black) influence consumer behavior could be carried out.