«if-..» an“ . Amwmfinhrvmhxr A 95.3 ‘53.... , ‘1‘ . .vavfiv . m. .wnfiwnlfi ...ww.... @nfiqfi. \l maybe 3233:1232 v » v A 31’“) RR", \ ‘ It \Iv ‘ K . ulnufinv'fl‘v. ‘ A v . X . L. If 4‘ . ‘ , .. “.Qral Y3)? .v I 1. . . . m: -.IV:‘. I kl u. 1 , .d.,_r.;._.x Wang.» u-k.. 51W. memo»: ATE UNNE Will Milli“ as LIBRARIES \\ \ll\l\\\\\\ll\ll\| ‘1 019 2031 Will 31293 0 This is to certify that the thesis entitled Microstructure, Sensory and Textural Characteristics of Cheddar Cheese As Influenced by Milkfat presented by Anita Corinne Bryant has been accepted towards fulfillment of the requirements for _Mas.tex:s__ degree in 51: i ence Department of Food Science & Human utrition Major professor ”a 3 Date all? 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARV Michigan State University I ,/ PLACE IN RETURN BOX to romovo this checkout from your record. TO AVOID FINES mum on or before date duo. DATE DUE DATE DUE DATE DUE ___JC:J___J -l I- |l__l- MSU lo An Affirmative Action/Equal Opportunity Institution m m1 MICROSTRUCTURE, SENSORY AND TEXTURAL CHARACTERISTICS OF CHEDDAR CHEESE AS INFLUENCE!) BY MILKFAT By Anita Corinne Bryant A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science and Human Nutrition 1993 ABSTRACT MICROSTRUCTURE, SENSORY AND TEXTURAL CHARACTERISTICS OF CHEDDAR CHEESE AS INFLUENCED BY MILKFAT By Anita Corinne Bryant Cheddar cheese was manufactured with varying fat levels (34, 31.5, 26.8, 20.5. 12.6, and 4796), a soft pasty body is obtained [Johnson and Chen (1991)]. Fat occupies the interstitial spaces within the protein network of the cheese. Removal of the fat causes the protein network to be more compact and rigid, yielding a hard cheese. The increased moisture occupies some of the space previously occupied by fat and loosens the protein network, thus it is thought to improve texture. Production of a Cheddar-type cheese with 33% fat reduction yields cheeses that are acceptable, but reductions in fat of 50% or greater produce cheeses that are of lower flavor quality and physical properties [Olson and Johnson (1990)]. In general, quality reduced fat cheeses cannot be made using conventional manufacturing procedures. Methods for improving quality of reduced fat cheeses have been suggested. These include, alteration of typical make schedules [Chen et al. (1992a); Chen (1991); Banks er a1. (1989)], processing of the cheese milk prior to cheese manufacture by ultrafiltration or homogenization [McGregor and White (1990a; 1990b); Metzger and Mistry (1993)], suitable starter culture selection [Chen et al. (1992b); Simard (1991)], and the use of fat substitutes [El-Newshawy et a1. (1986)]. One of the main goals of altering the cheese make schedule is to improve texture by increasing moisture retention Chen (1991) reported on 9 increasing moisture of reduced fat Cheddar cheeses by cooking the curd at lower temperatures, and cutting the curd using larger knives, 3/8" as opposed to 1/4", and milling at pH 5.9. These changes in manufacturing procedures, produced a Cheddar cheese with about a 44—4 5% moisture [Chen (1991)]. Banks er al. (1989) increased moisture retention in Cheddar cheese by decreasing cook temperature and reducing cheddaring and stirring time. They produced a low fat cheese (16.8%) with 47.2% moisture and an intermediate fat cheese (25.6%) with 42.9% moisture. The curd of the low fat cheese was cooked at 3 5°C and the curd of the intermediate fat cheese was cooked at 37°C. Both cheeses were cooked for 30 minutes and cheddared for 60 minutes. The curd of the control cheese (33.1% fat, 37.9% moisture) was cooked at 39°C for 60 minutes and cheddared for 90 minutes. The intermediate fat cheese (25.6%) had a flavor and textm'e quality comparable to the full fat cheese. The low fat cheese (16.8%) lacked Cheddar flavor and was judged to be over firm. Chen et ai. (1992a) studied the effects of altering various manufacturing parameters on the quality of a 33% reduced fat Cheddar cheese. The parameters studied were milk pasteurization temperatures, starter culture levels, rennet levels, drain pH and mill pH. Higher pasteurization temperatures (77. 7°C) produced a higher moisture cheese, and higher starter culture levels (2.0%) produced higher flavor intensity in young cheeses. However the quality of these cheeses deteriorated with age. They concluded that a higher curd pH at 10 drain and mill pH, 6.37 drain pH as opposed to 6.13, produced cheeses of higher flavor and texture quality. They concluded pH control was a critical factor in producing a quality reduced fat Cheddar cheese. Washing the cheese curd, or diluting the whey with water will help control pH. High pH values at drainage will assist in water retention Washing the curd also reduces lactose and lactic acid concentration in the cheese maintaining a higher pH, thus aiding in moisture retention [Simard (1991)]. Tunick et at. (1991) showed that moisture retention improves the texture of reduced fat Mozzarella cheese. Moisture of Mozzarella cheese was increased by eliminating a cooking step (459°C for 15 min) in the procedure. Cheeses produced with a higher moisture, 57.4% vs. 51.8%, were softer. Moisture retention improved texture by resulting in a softer Mozzarella cheese. Processing of the milk or cream for cheese manufacturing is another method for improving the quality of reduced fat cheeses. Emmons et a1. (1980) produced a reduced fat Cheddar cheese using homogenized milk. The cheese was slightly softer, less elastic and had a slightly higher moisture content than cheese made from non-homogeniz ed milk. Tunick et a1. (1992) produced reduced fat Mozzarella cheese, 22% fat on dry basis (PDB), using milk homogenized at 10300 and 17200kPa. At the higher homogenization pressure, adverse affects were noticed in the rheological and melting properties of the cheese. At the lower pressure, the textural and melting properties were improved. Metzger and Mistry (1993) 1 1 improved the texture of reduced fat Cheddar cheese by homogenization of the cream. Homogenization of the milk caused shattering of the curd. Therefore, they separated the milk into cream and skim. When skim milk was standardized to 1.9% fat with cream homogenized at 176/35 kg/cm’, curd shattering did not occur. The cheese had an improved texture when compared to the non-homogeniz ed control. Ultrafiltration(UP) has been used as a method for improving quality of reduced fat cheeses [Dao and Renner (1988); Green (1990); McGregor and White (1990a; 1990b)]. The UP process increases the retention of whey proteins and enhances the removal of calcium. Increasing whey proteins may improve texture by increasing the water holding capacity of the cheese. Reduction of calcium may reduce firmness [McGregor and White (1990a)]. UP milk gels rapidly, taming a coarse protein network, which tends to lose fat and water. Heating the UP milk above pasteurization temperatures will cause it to gel more slowly and form a finer protein network which retains fat and water [Green (1990)]. Dao and Renner (1988) increased Cheddar cheese yield by 22% using heated UP milk. The cheese made from heated UP milk had an improved flavor over cheese made from non-heated UP milk. McGregor and White (1990a; 1990b) improved the texture of reduced fat Cheddar cheese using UP milk. The cheeses made from UP milk had an improved body and texture over the reduced fat cheese made from non-UP milk. However, ultrafiltration of the milk did not improve the flavor of the 12 cheeses. Anderson et a1. (1992) suggested that condensing cheese milk will improve quality of reduced fat Cheddar cheese. Condensing cheese milk to 15.4% and 18.3% total solids (TS) improved the body, texture and flavor of the cheeses. Condensation of milk by evaporation may increase fat retention and reduce the amount of fat loss in the whey [Poster et ai. (1990)]. Starter selection is important for production of a quality reduced fat cheese. In manufacture of reduced fat cheeses, cultures that are less proteolytic and slow acid producers are desirable. Starters that are used for full fat cheeses produce meaty/brothy flavors in reduced fat cheeses [Johnson and Chen ( 1991)]. Chen et al. (1992b) studied the effects of four different starter cultures on ripening of reduced fat Cheddar cheese. Streptococcus salivarius susp. thermophilus produced acceptable Cheddar cheeses, but the cheese developed less flavor and exhibited less protein and body breakdown Lactococcus strains produced more typical Cheddar cheeses. The strains used were Lactococcus lactis subsp. lactis and cremoris. The use of adjunct cultures may improve the texture and flavor of reduced fat cheeses. The use of Lactobacilius case! casei as an adjunct culture to increase protein and peptide breakdown improved the texture and flavor of low fat cheese [Simard (1991)]. Johnson et ai. (1993) improved the texture and flavor of reduced fat cheeses using attenuated bacterial cultures. Adjunct cultures, Lactobaciilus heiveticus CNR232 were 13 attenuated by freeze drying or freeze shocking. The addition of the cells accelerated body development without causing bitterness and excessive softening. The use of fat replacers is a method for improving the texture of reduced fat cheese, specifically processed cheeses. Fat mimetics mimic the mouthfeel of fat and fat substitutes have some chemical and physical properties related to fat. Pat replacers do not contribute to flavor [Olson (1991)]. El-Neshawy et al. (1986) produced a low fat Cephalotyre (Ras) cheese using stabilizers as fat replacers. Low fat Ras, a hard Egyptian type cheese was produced from milk standardized to 1%, 1.5% and 2% fat. Carboxymethylcellulose (CMC) and carrageenan were added after addition of the culture and prior to renneting. The fat levels of the cheeses were 13%, 19% and 23% PDB, made from milk containing 1%, 1.5% and 2% fat, respectively. Addition of the stabilizers increased the softness and smoothness of the cheese. The cheese with 23% PDB had a mild flavor. The flavor of the two remaining cheeses (13% and 19%) was described as being flat. Low fat Ras cheeses made with the same fat content, without the addition of the stabilizers were hard, tough and lacked flavor. CMC and carrageenan react with milk proteins forming complexes that have high water binding capacity and enhances moisture retention of the curd. 14 CHEESE TEXTURE AND RHEOLOGY Texture of cheese may be one of the most important characteristics in determination of quality and type of cheese. Rheology is the science of the defamation of matter. Texture and rheology are related because the texture of a product affects the rheological properties of that product. Rheological and fracture properties affect the eating quality, usage (ease of cutting, melting etc.) and handling of cheese [Walstra and Peleg ( 1991)]. Rheological characterization of cheese is important as an index for determining body, texture, quality and identity. Determination of the rheological properties of cheese provides a means of studying the structure of a product as a function of its composition [Konstance and Holsinger (1992)]. The final texture of a Cheddar cheese is determined by its pH and ratio of intact casein to moisture. The breakdown products of casein are water soluble and are not able to contribute significantly to texture [Lawrence et al. (1983)]. After the cheese is manufacured, texture development of the cheese takes place mainly during the ripening process. Conditions during cheese manufacture and ripening promote the necessary microbial and enzymatic activity for degradation of proteins, which is required for proper development of the textural characteristics. Proteolysis is influenced by pH, salt to moisture ratio, moisture to casein ratio, and ripening temperature [Cooper (1987)]. Two phases of texture development 15 occur during ripening; (1) Transformation of the rubbery curd into a smooth, homogeneous product, occurs 1-2 weeks after manufactm'e and about 20% of the cal-casein is hydrolyzed to yield a,,-I casein; (2) Breakdown of remainder of the urn-casein causes a more gradual change in texture, which may continue for months [Creamer and Olson (1982)]. Cheese is considered a viscoelastic material, exhibiting both fluid and solid like properties. During short time spans of defamation, with law strain levels, its behavior is elastic. The sample almost regains its original shape once the applied stress is removed. During long time spans of deformation its behavior is viscous. The cheese remains deformed after the deforming stress is removed. Cheese shows very little yield stress. Even a small amount of stress can cause a permanent deformation [Walstra and Peleg (1991)]. The three main components of cheese, casein, fat and moisture, all contribute to the rheological properties of cheese. The rheological role of casein is to provide a continuous elastic frame—work for the individual fat globules and moisture. The properties of the fat are determined by the ratio of solid to liquid (protein: moisture). Water acts as a low viscosity lubricant between the surface of the fat and protein Def omation of the protein causes defamation of the fat. The movement of the protein relative to the fat is lubricated by the presence of the moisture. The whole complex system and the interaction of the major components gives cheese its viscoelastic properties [Lee et a1. (1992)]. 16 Textm'e measurement of cheese involves measurement of its fundamental rheological properties. These properties are characteristic of the material and independent of the test instrument. Some fundamental properties are elastic modulus (E), shear modulus (G’), Poisson's ratio ([1), bulk modulus (K) and viscosity (0/8) [Bourne (1982)]. Fundamental tests typically used to evaluate cheese include farce-compression, creep and stress relaxation tests [Tunick and Nolan (1992); Prentice (1992)]. Fundamental tests can be performed using the Instron Universal Testing Machine. The Instron is a multiple measm'ing instrument that can also be used to measm'e multiple textm‘al parameters. These parameters are hardness, fracturability, adhesiveness, cohesiveness, springiness, gumminess and chewiness [Tunick and Nolan (1992)]. There are many factors to be considered when evaluating the rheological properties of cheese. These factors include, sample shape and size, ratio of defamation, surface friction and sample lubrication [Sherman (1989)]. All of these factors will affect the measurement of its rheological properties. Ak and Gunasekaran (1992) evaluated the effect of sample lubrication and defamation rate on the rheological properties of Cheddar cheese. In this study, cheeses were subjected to six different defamation rates and were either lubricated or not lubricated. Lubrication did not affect the parameters studied. However the data from the non lubricated samples had a higher coefficient of variation This suggests that lubrication of the 17 cheeses produced more reproducible results. Tunick et ai. (1990) detemined the viscoelastic properties of Cheddar and Cheshire cheeses as a method for distinguishing these two cheeses. The properties determined were the two components of shear modulus(G'), elastic or storage modulus (G'), and viscous or loss modulus(G"), complex viscosity (n') and frequency (a). The Cheshire showed G', G" and 11‘ values almost half those of the Cheddar cheese after 60 weeks of ripening. The inflection point, which is the point at which the cheese begins to fracture, was also lower for the Cheshire cheese. The Cheddar cheese did not break down under the same conditions. This was expected because, Cheshire cheese has a more crumbly texture than Cheddar. Lee et ai. (1992) evaluated the rheological properties of cheese using an ultrasonic technique. Storage and loss modulus were measured by propagation of an ultrasonic wave through the material. The results were compared with those obtained from a Rheometer. Good qualitative agreement was found between the two measurements. This suggests that there is potential for developing this technique as a method for an on-line, non-destructive method for rheological evaluation of foods. Creamer and Olson (1982) evaluated the effect of proteolysis on texture using rheological measurements. The force at yield point of the cheeses was measured and they found that the yield strain decreased linearly with the logarithm of days aged. This suggests that the texture of 18 the cheese softens during aging. Bertola et ai. (1992) analyzed the changes in rheological behavior of Tybo Argentina cheese during ripening. Tybo Argentina is a semi-hard cheese with 40% PDB. Uniaxial compression tests were performed using the Instron, to obtain values for hardness, adhesiveness and cohesiveness. Viscoelastic parameters, elastic moduli and relaxation times, were also obtained. Hardness decreased, adhesiveness increased and cohesiveness remained unchanged during ripening. The rheological changes correlated with water soluble nitrogen and trichloroacetic acid (TCA) soluble nitrogen Hardness was highly correlated with viscosity. Green et a1. (1981) analyzed textural characteristics of Cheddar cheese made from concentrated milk, using the Instron Instrumental firmness, cohesiveness, force required for fracture and adhesiveness increased as the concentration factor of the milk increased. Elasticity did not change. Metzger and Mistry (1993) analyzed the rheological characteristics of reduced fat Cheddar cheese made with skim milk standardized with homogenized cream (176/ 35 kg/cm’). The cheese made with the homogenized cream (4 7.7% moisture) was significantly harder than cheese made with non-homogenized cream (46% moisture). The hardness values, determined by the Instron, were 9.02 kg and 11.59 kg respectively. Stampanoni and Noble (1991a & 1991b) used the Instron to evaluate the effect of fat, acid and salt on textural attributes of cheese analogs. The fat 19 levels used were 10, 17.5 and 25 %, acid levels, 0.1 and 1.2% citric acid and salt levels, 0.5 and 2.0% sodium chloride. Cheese analogs containing higher amounts of fat were softer, less springy, more cohesive and adhesive. Increasing acid or salt increased firmness, but decreased cohesiveness and springiness as detemined by the Instron Adhikari et a1. (1992) analyzed the relationship between the textural properties of Chhana and Rasogalla. These are two Indian—style cheeses. Chhana is similar to Cottage cheese and Rasogalla is a sweetened product made from Chhana. Analysis of the texture of the cheeses using the Instron showed that as Chhana was transfomed to Rasogalla, hardness, gumminess and chewiness of the cheese decreased, while springiness increased. One of the main goals of analyzing the textural properties of cheese is to detemine the relationship between instrumental and sensory properties. This relationship is usually determined by observing the correlation between instrumental and sensory parameters [Zoon (1991)]. Lee et ai. (1978) evaluated the texture of several cheeses including Cheddar, Cream, Mozzarella and Swiss using the Instron and a sensory panel. The panelists ranked the various samples for each of the following characteristics, hardness, brittleness, chewiness, springiness, adhesiveness and lumpiness. Hardness, chewiness, springiness and adhesiveness all correlated highly with Instron measurements. Chenetal (1979) analyzed six textural characteristics of eleven different cheese varieties. The 20 characteristics measured were, hardness, cohesiveness, adhesiveness, elasticity, gumminess and chewiness. Hardness, cohesiveness, chewiness and adhesiveness were correlated with measurements from a trained sensory panel, composition and pH of the cheese samples. The panel did not evaluate gumminess and elasticity. Stampanoni and Noble (1991a) observed a positive correlation between sensory and instrumental measurements as determined by a trained sensory and the Instron, of cheese analogs with varying fat, salt and acid contents. Correlations were observed between firmness and a 55% compression force, sensory and instrumental adhesiveness and springiness with modulus of elasticity. Lakhani et ai. (1991) were not able to correlate instrumental and sensory characteristics of Cheddar cheese made from ultrafiltered milk. A trained sensory panel judged the UP cheese to be harder, more rubbery and chewy than the control cheese. The Instron was not able to distinguish among the cheeses. To obtain a correlation between instrumental and sensory measurements testing conditions must be as close as possible. CHEESE M ICROSTRUCTURE Microstructure is the microscopic structure of a material. It is a result of the combination of chemical components and physical forces of the food [Stanley and Tung ( 1976)]. Microstructure is determined by the composition and processing of the product. Microstructure in turn, affects 21 the sensory and mechanical properties of the food [Heertje (1993)]. Microstructure of dairy products may be based on fat such as in ice cream, cream cheese, butter, or on protein such as in buttermilk, yogurt, cottage cheese, or on both, as in most cheeses [Kalab (1979)]. Lawrence et a1. (1983) stated that the basic structure of cheese largely may be determined by the acidity at draining. This controls the mineral content of the cheese and the proportions of rennet and plasmin that remain in the curd. The structure of cheese develops as the casein micelles come together to fom chains, and then a protein network which entraps fat globules and moisture. As the network foms, the curd clusters together and foms an amorphous mass [Glaser et ai. (1980); Green et a1. (1981)]. The basic structure of the protein network is famed during the curd firming process and does not change significantly throughout the remainder of the cheesemaking process [Green et a1. (1981)]. The microstructure of cheese has been studied extensively using Scanning Electron Microscopy [Emmons et a1. (1980); Green et a1. (1981); T‘Lmick et a1. (1990); Adhikari et a1. (1992)] and Transmission Electron Microscopy [Kimber et a1. (1974); Green et ai. (1981); Kalab et a1. (1991)]. The resolving power of electron microscopes enables the visualization of minute particles in dairy products, such as casein micelles and fat globule membranes [Kalab (1993)]. The research in this area has studied the changes in the milk and curd throughout the cheesemaking process, as well 22 as throughout the ripening stage. Electron microscopy is a method of imaging and magnifying specimens using electrons to carry the necessary infomation, because electrons have greater resolving power than visible light. The Scanning Electron Microscope (SEM) has a resolving power of 36 nm and magnification range of 20X—150,000X [Klomparens et ai. (1992)]. The SEM also had a great depth of focus which enables one to visualize three dimensional objects, including the protein networks of cheese [Kalab (1993)]. Evaluation of cheese structure using SEM shows an open irregular protein matrix in which the lipid has been intermeshed. Young Cheddar cheeses exhibit an open irregular network, with spherical shaped openings. Initially, the structure of the cheese has a fibrous appearance. During ripening, there is a loss of the fibrous appearance and the development of a more compact, amorphous structure, as if the proteins contracted or pulled together [Stanley and Emmons (1977)]. The fat globules separate initially, but are forced together by the compacting of the casein network to fom clumps. Starter cultures are typically trapped at the fat-protein interface, areas high in moisture [Kimber et a1. (1974)]. Emmons et ai. (1980) observed the microstructure of full and reduced fat cheeses made from homogenized milk. The fat globules in the homogenized cheeses were drastically reduced in size. In the full fat 23 cheese, the fat globules were clustered together and associated with the protein network forming a ”lace-like" structure [Emmons et ai. (1980)]. The structure of the cheese made from reduced fat homogenized milk was not as compact as the structure of the cheese made from whole non- homogenized milk. Metzger and Mistry (1993) observed the microstructure of reduced fat Cheddar cheese made from skim milk standardized with homogenized cream. In these cheeses the microstructure showed a large number of small, evenly dispersed fat globules. In the cheeses made with non-homogenized cream, there was a small number of large, tmevenly dispersed fat globules. Green er a1. (1981) observed microstructural changes in Cheddar cheese made from concentrated milk. In the cheeses made from the more concentrated milk, the protein was packed in larger, more compact areas and the fat was more segregated. Mistry and Anderson (1993) observed a reduction in fat globule distribution with a reduction in fat content. The microstructure of full and reduced fat, natural and processed cheeses was compared. Pull fat cheese had a smooth protein matrix, with large fat globules. In the reduced fat cheeses, the protein matrix became more dense and rougher. Kiely er al. (1993) observed large cavities of irregular dimensions in the microstucture of Mozzarella cheese. The cavities were dispersed randomly throughout the paracasein matrix. These observations were made 24 3 days after cheese manufacture. After 50 days of ripening, the porosity of the paracasein matrix decreased. The microcavities were larger in diameter. The grth of the cavities was attributed to proteolytic destruction of the protein Taneya et a1. (1992) observed the structure of string cheese. Stringiness, an important characteristic in string cheese, was found to be associated with a uniform, longitudinal orientation of the protein matrix Pat, also in a longitudinal direction was dispersed between the protein strands. The diameter of the subunits in the casein matrix were equivalent to the diameter of casein submicelles. Adhikari et a1. (1992) compared the relationship between the microstructure in Chhana and Rasogalla, two Indian style cheeses. SEM showed that the structure of Chhana consisted of a compact, conglomerated matrix with embedded fat globules. Rasogalla, a sweetened product made from Chhana, had a ragged, porous protein matrix with collapsed and ruptured fat globules embedded in the matrix. Ideally, a correlation between microstructure and rheological measurement is desirable. This will allow the prediction of the functional properties of a product from its microstructure. Quantitative correlation of textural and structural properties has been attempted recently and is an area of much interest to food scientists. Preliminary research has been conducted using image analysis as a method for establishing correlation [Holcomb et al. (1992)]. Rosenberg et ai. (1991) used magnetic resonance 25 imaging (MRI) as a method for viewing cheese structure. MRI is a non- destructive method which provides images of the inner structure of cheeses. This allows one the ability to determine cheese quality at any stage in the ripening process. There are many factors involved in the development of the textural and microstructural properties of cheese. These properties are related and are important for quality determination of cheese. This research further investigates the effect fat has on the microstructural, textural and sensory properties of Cheddar cheese. CHAPTER HI EXPERIMENTAL PROCEDURES MILK STANDARDIZATION Raw skim milk (0.03% milkfat) and cream (40.0% milkfat) were obtained from Michigan Milk Producers Association (Ovid, Michigan). The skim milk was pasteurized at 74°C for 18 sec. and the cream was pasteurized at 63°C for 30 min The skim milk and cream were stored at 2°C until use. The milk for cheese manufacture was standardized to, 4.0%, 3.2%, 2.4%, 1.6%, 0.8%, and 0.03% fat. The final fat content of the milk was determined using the Babcock method for fat determination [Marshall (1992)]. Table 1 shows the composition of the milk used for cheese manufacture. MANUFACTURE OF CHEDDAR CHEESE Cheddar cheese was manufactured according to the procedure outlined by Kosikowslci (1982) using pilot plant equipment. The milk was warmed to 31°C and ripened for one hour using Redi Set DVS (Direct Vat Set) cheese culture (DVS #980, Chr. Hansens Laboratory, Milwaukee,WI). The milk was set in 30 minutes using Chymax-Double Strength (Pfizer, Milwaukee,WI). The curd was salted at a 2.3% level, 26 27 (weight of the curd), hooped and pressed for 18 hours. The cheeses were vacuum sealed and allowed to ripen for four months (16 weeks) at 7°C. Table 1. Composition of milk for cheese manufacture. TREATMENT 'lo MILKFAT 7. MILK PROTEIN TOTAL SOITDT- 1 l 4.0 3.00‘ 12.30‘ 2 3.2 2.91‘I 1 1.60” 3 2.4 2.93a 10.91c 4 1.6 2.92‘ 10.19‘1 S 0.8 2.82a 9.3 1" 6 <0.1 2.96a 8.76f (p<0.05) n=4 for all treatments. — “' Means with the same superscript within a column do not differ significantly. ANALYTICAL PROCEDURES Babcock Fat Test The fat content of the milk, cream and cheeses was determined using the Babcock method outlined by Marshall (1992). 28 Kjeldahl Protein Determination The protein was estimated by determining the total nitrogen content of the samples using the Kjeldahl nitrogen determination method [Marshall (1992)]. The nitrogen determination system used consisted of the Buchi 342 control unit, the Tecator 40/ 1016 digester, the Buchi 322 digestion unit, the Metrohm 614 impulsomat, the Metrohm 623 pH meter and the Metrohm 655 Multi-Dosimat unit [Buchi Laboratories, Flawil, Switzerland]. The % total nitrogen was detemined from the volume of HCl used to titrate the sample to an endpoint using the following equation: (HCI, - HCIJ 96 TN :- x A x Normality HCi x 6.38 x 100 Sample weight where: HCL a volume HCl used to titrate sample to the endpoint(ml) HClb = volume HCl used to titrate blank to the endpoint(ml) Sample weight = weight of sample (g) A = 1.4007 (g/mol) 6.38- nitrogen conversion factor f or dairy products Atmospheric Oven Moisture Determination The total solids of the milk and moisture of the cheese was determined using an atmospheric oven method outlined by Marshall (1992). 29 TEXTURAL EVALUATION The tenure of the Cheddar cheese manufactured was evaluated after 16 weeks of ripening using the Instron Universal Testing Machine Model 4202,#537 (Livonia, MI) (Figure 1). Cylindrical samples of 20x20 mm size at 9°C were used for analysis. The cheeses were cut the day before testing and stored at 9°C. The cheeses were held at this temperature until the test was performed. A two-bite compression test was performed at 80% compression lOKN load cell, crosshead speed of lOOmm/min and chart speed of 20 cm/min Adhesiveness, cohesiveness and hardness was determined from the Textm'e Profile Analysis curve Figur' e 2 . ( ) : FIRSTVBITE ; : SECOND BITE ——_. ,..__ 00w~snoxr ——. .— ursnoxr ——+ o—DOWNS "OK! —> +UPSHOKE > HAIDNESS m U C! 0 LL rec 1 Area 2 c/ v TIME -9 Figure 2. Texture Profile Analysis curve from Instron Universal Testing Machine. 30 Figure l. Instron Universal Testing Machine 3 l The samples were lubricated by placing one drop of vegetable oil on the top and bottom surfaces of the sample. The compression plate and surface of the Instron was cleaned with a paper towel after measuring each individual sample. Hardness was determined from the height of the force peak from the first compression A is the beginning of the first compression and B is the beginning of the second compression (Figure 2). Cohesiveness was determined by taking the ratio of the areas A2 and Al (AZ/A1). Adhesiveness was determined from the area A,. The Instron gives a force-time curve as well as a force-distance curve, which enables the parameters obtained from it to have the dimensions listed in Table 2. Table 2. Dimensional Analysis of TPA parameters'. _ Mechanical Measured Dimensions of parameter variable measured variable Hardness Force ml!” Cohesiveness Ratio Dimensionless Springiness Distance 1 Adhesiveness Work mFt" ‘ Reprinted from Bourne( 1967) J. Food Sci. 32, 154. Copyright by Institute of Food Technologists. mamass, l=length, t=time 32 Springiness was detemined using a 55% compression test similar to Stampanoni and Noble (1991a). The height of the sample was measured before and after compression and springiness was expressed as percent the sample returned to its original height, using the following eqation (Figure 3). where: L - AL Springiness - ----- L - height of sample before compression (mm) AL - change in height of sample after compression (mm) FLAT l Fl / PLATE \ I I] [.___ SAMPLE i I. L COMPRESSION BEFORE Ll}. SAMPLE i LOAD /1 CELL 1 AFTER COMPRESSION Figure 3. Textural definition of springiness (elasticity). (Reprinted from Chen et al. (1979) J. Dairy Sci. 62(6), 903. Copyright by Journal of Dairy Science) 33 MICROSTRUCTURAL EVALUATION The microstructure of the cheeses manufactured was evaluated using the Scanning Electron Microscope (SEM) following the method outlined by Tunick et al. (1990) with modifications. Small samples of each cheese were cut and primary fixed in 4% buffered glutaraldehyde for 1 9‘: hours, washed in 0.1M phosphate buffer for 30 minutes, past fixed in buffered Osmium tetroxide for 2 hours and washed for 30 minutes in 0.2 M phosphate buffer. The samples were dehydrated in increasing ethanol and water solutions, 25%, 50%, 75% and 100% for 30 minutes in each solution The samples were quick frozen and fractured in liquid nitrogen to expose an uncut surface and placed in fresh 100 % ethanol. The samples were critical point dried in a Balzers Critical Point Dryer (Figure 4) and coated with a thin layer of gold in an Emscope Sputter Coater EM 500 (Figure 5). The samples were viewed on a JEOL Scanning Electron Microscope (Figure 6) at 15 KV accelerating voltage. SENSORY EVALUATION The texture of the six cheeses manufactured was evaluated at 16 weeks of ripening using a trained sensory panel. The panel consisted of faculty and graduate students at Michigan State University, East Lansing, MI. The panel evaluated four textural characteristics, adhesiveness, cohesiveness, hardness and springiness. A trained panel was used .\ \i)\l\r/\I\I\I\I\I\I\l\l\i\i\,\i\i\i\ll\i\i\l\,\i\\;\J\I\I\I\\,\\, 34 Figure 4. Balzers Critical Point Dryer _, ‘ »—-~-»-.r*~.“\»-’W 35 Figure 5. Emscope Sputter Coater EMSOO 36 Figure 6. JEOL Scanning Electron Microscope 3 7 because most individuals are not familiar with the specific characteristics measured and would perceive each characteristic in a different manner. Training provides a sensory panel that is famfliar with the attributes tested and have similar perceptions of each attribute. Panel members were selected first by participating in a primary screening process. Approximately 20 people participated in the screening. Each participant was screened for his or her ability to distinguish the four desired characteristics, adhesiveness, cohesiveness, hardness, and springiness. The panelists initially attended a brief orientation in which the goal and purpose of the experiment was explained as well as the definitions and procedure f or evaluating each characteristic [Civille and Szczesniak (1973)]. Before evaluating the samples, the panelists signed a consent fom (Appendix A, Table A2) and completed a questionnaire to assist the panel selection process (Appendix A, Table A1). The tests were conducted in a sensory room, room temperature (25°C) under fluorescent lighting. Testing took place in individual testing booths. The panelists were presented a tray, containing three cheese samples that ranged in their degree of each characteristic (adhesiveness, cohesiveness, hardness, springiness), crackers, a pencil for scoring, a score sheet and a cup of water at room temperature. The panelists were asked to rank the samples from least to most for each characteristic (Appendix A, Table A3) [Lamond (1987)]. 38 The cheeses were cut into 20x20 mm cylinders the day before testing and refrigerated. The temperature of the samples during the testing was 9°C. The samples used for training were commercial Cheddar and Colby cheeses purchased from the local grocery store. Panelists who were able to correctly determine the order of the samples were selected to be a part of the trained sensory panel. Fifteen panelists were selected to undergo panel training. The fifteen selected members participated in four panel training sessions. In each session, the panelists were given a tray containing five cheese samples and instructed to assign a specific value to the sample based on which characteristic was being judged (Appendix A, Table A4- A7). Each of the five samples corresponded to a specific value on a 9 point scale, either 1.3.5.7 or 9. 1 being least. 5, being moderate and 9' being most of each characteristic eg. least adhesive, moderately adhesive etc. The panelists were also instructed as to how to evaluate each sample. To determine adhesiveness, the panelists were asked to place sample between molars; chew sample five times; press sample to the roof of mouth with tongue; evaluate the force required to remove the sample from the roof of the mouth with tongue. To detemine cohesiveness, the panelists were asked to place sample between molars; compress fully; evaluate the degree to which the sample deforms rather than crumbles, breaks or falls apart. To detemine hardness, the 39 panelists were asked to place sample between molars; bite through once; evaluate for hardness, and to determine springiness, the panelists were asked to place the sample between the molars; compress partially without breaking the sample structure [Civille and Szczesniak ( 1973)]. This portion of the training session took place in panel booths, the panelists judged the samples individually and no discussion took place. After evaluating the samples, the panelists were seated around a table and given the same samples. The panelists were told the correct responses, allowed to taste the samples again and compare the correct response to their original response. During this portion of the panel training, panelists were allowed to discuss their responses as well as give suggestions to the panel leader. After 16 weeks of ripening the trained panelists evaluated all six cheeses manufactured for this study for the four characteristics: adhesiveness, cohesiveness. hardness and springiness. The samples were cut into 20x20 mm cylinders the day before testing and stored at 9°C until testing. The samples were coded with three digit numbers (Appendix C, Table CI). The panelists were presented with a tray containing four cheeses of same treatment (one sample to evaluate each characteristic), four score sheets, one for each characteristic. a pencil for scoring, crackers and a cup of water. The samples were presented to the panelists in a random order (Appendix B). The panelists evaluated each 40 cheese for each characteristic using a nine point intensity scale (Appendix A, Table A3). The panelists were allowed to evaluate 3 treatments. a total of 12 samples per session to reduce fatigue. Overall texture acceptance was also detemined. This was investigated using an untrained sensory panel, consisting of faculty, staff, graduate and undergraduate students at Michigan State University. The untrained panel evaluated treatments 1-5 (34%, 31.5%, 26.8%, 20.5%, 12.6% fat cheeses) after 36 weeks of ripening. The panelists completed a short questionnaire to obtain inf omation about their dietary habits (Appendix A, Table A8). The panelists were presented a tray containing all five cheeses labeled with a 3-digit code in a random order (Appendix C, Table C.2) and instructed to taste each sample and indicate their degree of likeness of the texture of the cheese using a nine point hedonic scale ranging from l-dislike extremely to 9=like extremely (Appendix A, Table A9) [Meilgaard et al.(1987)]. The panelists were also given crackers and water and instructed to rinse their mouths between samples. Twenty-five panelists evaluated each replicate of all five cheeses, giving a total of 100 panelists for the entire experiment. STATISTICAL ANALYSIS A randomized block design was used consisting of six treatments, with four replicates of each treatment. The data was analyzed using the 41 Microcomputer statistical program (MST AT) (Crop & Soil Sciences, Michigan State University). A one-way Analysis of Variance (AN OVA) and Student-Neuman—Keul's test was conducted to determine the treatment means and differences between the treatment means at the 0.05 probability level CHAPTER IV RES UL TS AND DISCUSSION CHEESE QQMPOSITION The composition (fat, protein and moisture) of the cheeses are listed in Table 3. Composition was determined to evaluate the effect of changing the milkfat content on final cheese composition As expected, reduction in milk fat, resulted in a reduction in fat content (p<0.05) and thus an Table 3. Cheese composition TREATMENT '/a MILKFAT '/a FAT %MOISTURE %PROTEIN 1 4.0 34.0“ 38.5' 22.3' (2.94) (1.34) (1.74) 2 3.2 31.50” 39.7a 24.3' (2.35) (1.89) (1.06) 3 2.4 26.8c 40.8a 27.9b (1.44) (1.35) (1.53) 4 1.6 20.50d 40.8a 32.7c (1.96) (1.81) (1.26) 5 0.8 12.6.3 44.7b 36.4‘I (1.93) (2.16) (1.06) 6 <0.01 <0.lf 49.6c 423' (--)Z (1.29) (1.69) ‘ Means with standard deviations in parentheses, n=4 for all treatments 2 % Pat not detectable "' Means with the same superscript within a column do not differ significantly (p<0.05). 42 43 increase in moisture and protein content of the cheeses. The fat contents of the cheeses were 34.0%, 31.5%, 26.8%, 20.5%, 12.6% and <0.1%, when manufactured from milk containing 4.0%, 3.2%, 2.6%, 1.8%, 0.8% and 0.03% fat, respectively. The moisture content of these cheeses ranged from 38.5% - 49.6%, and the protein ranged from 22.3% - 42.3%. It was also noted that removal of fat from Cheddar cheese affected the overall appearance of the cheeses. Fat reflects light. When fat was removed, the cheeses became more translucent and darker in color (Figure 7). MICROSTRUCTURE EVALUATION The effect of fat content on the microstructure of the Cheddar cheeses was studied using Scanning Electron Microscopy (Figures 813). Scanning Electron micrographs show the basic protein network of the cheese. The fat, which was removed during the fixation process, occupied the open regions within the protein network. The effect of fat on the microstructure of Cheddar cheese is apparent when examining the micrographs. Figures 8 8: 9 Show the microstructure of cheeses containing 34.5% and 31.5% fat. As observed by the SEM, these cheeses had an open, lacy, irregular network, suggesting that the fat is distributed in an uneven pattern throughout the matrix. The fat appeared to have been present as clusters or aggregates of fat globules. The gradual decrease in fat is ._ r-.._-,va‘-‘\ 44 Figure 7. Cheddar cheese manufactured with varying fat contents. Fat content ('/a): A=34°/a B=3l.5'/a C=26.8°/a D=20.5% E=12.6°/a F=<0.l°/a 4 5 evident when comparing the micrographs of the different cheeses. The microstructure of treatment 3, containing 26.8% fat, (Figure 10) still has the open microstructure, but not as open as that of the higher fat Cheddar cheeses (34.0 and 31.5%). The openings observed were more spherical in shape and more defined. Areas existed in the protein matrix that weren't broken up by fat, resulting in strong protein bridges. The structure became more dense and compact. The Cheddar cheese containing 20.5% fat cheese was similar in its microstructure to the cheese containing 26.8% fat (Figure 11). However, the fat was distributed in a more regular pattern giving the microstructure a sponge like, but more defined appearance. The lower fat Cheddar cheese containing 12.6% fat had very few openings (Figure 12). The openings were spherical in shape and scattered evenly throughout the protein matrix. The majority of the microstructure appeared to be dense, compact protein The skim milk cheese, with <0.1% fat contains no openings in its structure (Figure 13). The structure has a almost flat, rock like appearance. This cheese is essentially a solid block of protein Without the fat present to disrupt the protein network, the protein famed a compact, very rigid microstructure. Tunick er al. (1991) used Scanning Electron Microscopy as a method to distinguish differences between Cheddar and Cheshire cheeses. The two cheeses were purchased locally and analyzed at 60 weeks and 20 weeks 46 Figure 8. Scanning Electron micrograph of Cheddar cheese with 34% fat. Magnification soox C=casein F- area previously occupied by fat globule. Figure 9. Scanning Electron micrograph of Cheddar cheese with 31.5% fat. Magnification soox C=casein F= area previously occupied by fat globule. I, l L J. J‘ 47 Figure 10. Scanning electron micrograph of Cheddar cheese with 26.8% fat. Magnification soox C=casein F= area previously occupied by fat globule. Figure 11. Scanning electron micrograph of Cheddar cheese with 20.5% fat. Magnification soox C=casein F=area previously occupied by fat globule. Figure 12. Scanning electron micrograph of Cheddar cheese with 12.6% fat. Magnification soox C=casein F= area previously occupied by fat globule. Figure 13. Scanning electron micrograph of Cheddar cheese with <0.1% fat. Magnification soox C=casein F=area previously occupied by fat globule. 49 respectively. The Cheddar and Cheshire cheeses, containing between 30- 33% fat were described as having a smooth, continuous network surrounding irregular lipid inclusions, similar to observations in this study. The microstructure of the Cheddar cheese was similar, however the protein matrix in the Cheddar cheese was more dense, than that observed in Cheshire cheese. The size of the lipid inclusions in Cheddar cheese ranged from 1-5u in diameter and the lipid inclusions in the Cheshire cheese ranged from 230]; in diameter. The microstructure of the two cheeses were diff erent, however the microstructure of the Cheddar was similar to the microstructure observed in Mozzarella cheese. The microstructure of Mozzarella cheese has been described as a dense, homogenous paracasein matrix, with a large number of microcavities of irregular dimensions [Kiely et al. (1993)]. Mistry and Anderson (1993) compared the microstructure of commercial full and reduced fat, processed and natural cheeses. Similar to the results observed in this experiment, the protein matrix became more dense and compact as the fat content of the cheese decreased. In the reduced fat cheeses, the protein dominated the structure. The full fat cheeses had a smooth protein matrix interlaced with aggregated fat globules. 50 W Adhesiveness is defined as the work necessary to overcome the attraction forces between the surface of the sample and the surface of the other materials with which the food comes in contact, in this case the compression plate [Civille and Szczesniak (1973)]. The adhesiveness from the Texture Profile Analysis is a measure of the negative force or curve A3 on the TPA (Figure 2). This is a measure of how much the sample sticks to the plunger plate, as the plunger begins its upstroke. The adhesiveness of the cheese increased as the fat in the cheese increased (Figure 14). The higher fat cheeses (34%, 31.5%), with scores of 1.15 and 1.13 N.mm, were more adhesive than the lower fat cheeses(20.5%. 12.6%) with scores of 0.53 and 0.49 N .m respectively (Table 4). However these differences were not significant. There was no curve produced with the skimmilk cheese (Table 4). The adhesiveness results obtained from the Instron were not very conclusive. A high variation was observed. One factor that may have affected the adhesiveness results and contributed to the variation was lubrication of the compression plates. With samples containing fat, the cheese sample stuck to the plunger without lubrication and prevented the production of an accurate TPA curve. Once the plate was lubricated, the cheeses did not produce very high adhesiveness scores. The fat in the cheese also contributed to lubrication of the plate. As the sample is compressed, fat is exuded contributing to lubrication Similar to the results Adhesiveness (N.mm) 51 O 5 1 O 1 5 20 25 3O % Fat in cheese Figure 14. Influence of fat on adhesiveness of Cheddar cheese as determined by the Instron Universal Testing Machine. 52 obtained in this experiment, Adhikari et al. (1992) failed to obtain a curve for adhesiveness when evaluating the texture of Chhana and Rasogalla, two Indian style cheeses. However the fat content of the Chhana was 22.4% and the fat content of the Rasogalla was 7.8%. Therefore other factors such as manufacturing procedures or components of the cheese other than fat affected the lack of adhesiveness of these cheeses. Chhana is manufactured by direct acidification of cow's milk and is similar to cottage Table 4. Textural characterization of Cheddar cheese as influenced by fat content: Results from Texture Profile Analysis __ TREATMENT ADHESIVENESS COHESIVENESS HARDNESS SPRINGINESS (% rat)l Nauru (Ratio) (N) (“/0 34.0 1.15a 0.135“ 193.7“ 58.1' (0.62)2 (0.03) (66.55) (13.26) 31.5 1.13“ 0.131“ 260.7' 57.8‘ (0.80) (0.03) (105.37) (7.25) 26.8 1.18“ 0.154a 280.0“ 71.5b (0.36) (0.02) (60.25) (6.04) 20.5 0.52 5“b 0.192“ 468.7" 78.9c (1.44) (0.03) (129.96) (8.19) 12.6 0.492“b 0.216b . 762.3c 88.1“ (0.82) (0.04) (186.36) (6.52) <0.1 0.0c 0.271c 960.3“ 94.6“ H3 (0.06) (168.97) (2.52) l % Pat in cheese 2 Standard deviations in parentheses n=4 for all treatments 3 Adhesiveness not detectable " Means with the same superscript within a column do not differ significantly (p<0.05). 53 cheese. Rasogalla is produced from Chhana by cooking kneaded Chhana in concentrated syrup. The physical description of cohesiveness is the extent to which a material can be deformed before it ruptures [Civille and Szczesniak (1973)]. The cohesiveness results are strongly due to the way cohesiveness is measured on the Instron Cohesiveness is related to the hardness and springiness of the cheese when measured by the Instron since it is determined as a ratio of curve A2 to A1 of the TPA curve (Figure 2). If an extremely hard, springy cheese is being measured then the ratio of Az/Al will be large, because the height of both peaks will be high. The sample has a tendency to recover, generating a high A2 peak. If the cheese is relatively soft, the recovery of the sample is not as great and the height of peak A2 will be shorter, relative to peak Al decreasing the overall ratio. Cohesiveness of Cheddar cheese decreased as the fat content of the cheese increased (Figure 15). In this evaluation the higher fat cheeses with 34, 31.5, and 26.8% fat were similar in their cohesiveness, with cohesiveness values of 0.135, 0.131 and 0.154 respectively (Table 4). At 20.5% fat, a significant increase (p<0.05) in cohesiveness was detected among the cheeses. The intemediate (20. 5%) and low fat (12.6%) cheeses were similar in their cohesiveness, with scores of 0.192 and 0.216. The skim milk cheese (<0.1%) with a value of 0.271 was the most cohesive cheese (p<0.05) as determined by the Instron 54 Cohesiveness O N 0.15 0.1 L L l 1 l 1 0 5 1O 15 20 25 30 % Fat in cheese Figure 15. Influence of fat on cohesiveness of Cheddar cheese as determined by the Instron Universal Testing Machine. 55 These results are consistent with those obtained by Stampanoni and Noble (1991a). Cheese analogs made from rennet casein deionized water and melted vegetable fat, became more cohesive as the fat content of the analog was decreased. The cheese analogs were cut into 13x10 mm cylinders and evaluated with the Instron at 9°C. The objective of the experiment was to detemine the effect of fat, acid or salt levels on the texture of cheese analogs. Cohesiveness was also related to the salt and acid levels in the analog. Cheese analogs containing higher levels of acid or salt were less cohesive. These results suggest that fat alone does not effect the cohesiveness of cheese, the composition and interaction of the other components contribute to cheese cohesiveness as well Hardness is defined as the force necessary to obtain a given defamation [Civille and Szczesniak (1973)]. Hardness on the Instron is measure of the force in Newtons required to compress the samples to 80% of their original height with a flat plate plrmger. Hardness of the Cheddar cheese decreased (p<0.05) as the fat content if the cheese increased (Figure 16). The higher fat cheeses (34%, 31.5% and 26.8%) were softer (p<0.05) than the lower fat cheeses. These cheeses were similar in their hardness with scores of 193.7, 260.7 and 280 N respectively (Table 4). Differences in hardness became apparent when fat was reduced to 20. 5% in Cheddar cheese. The cheese containing 12.6% fat was harder (p<0.05) Hardness (N) 56 1 200 1000; J. 800 600 400 200 % Fat in cheese Figure 16. Influence of fat on the hardness of Cheddar cheese as determined by the Instron Universal Testing Machine. 57 than the cheese containing 20.5% fat with a value of 762.3 N. The skim milk cheese (<0.1% fat) was the hardest, requiring 960.3 N for compression When the fat is removed from cheese, the protein becomes more compact and rigid as observed in the scanning electron micrograph discussed previously (Figure 13). The skim milk cheese with <0.1% fat was essentially a rigid block of casein and very firm and rigid in its microstructure since there wasn't enough fat present to loosen the protein network. This cheese was very compact and dense, therefore very hard as observed with Instron values. High variation in the data among the replicates was observed when measuring hardness. The textural evaluation of the hardness or firmness of cheese is very complex. Hardness is affected by the composition of the cheese as well as the conditions of the experiment. Hardness is also affected by the size of the sample, % def omation and the amount of surface friction [Shaman (1989)]. The variation in this experiment most likely arose from surface friction When cylindrical shapes are deformed, they assume a barrel shape. This results from the surface friction between the compressing plate and the surface of the sample and hinders lateral movement of the upper and lower surfaces of the cheese. Some of the compressing force is used to overcome the surface friction and not all the force is used to compress the food. Barrel defamation can be eliminated by lubrication of the sample with oil, or bonding the sample to the compression plates [Sherman (1989)]. The cheeses in this study were 58 lubricated, however, lack of uniform lubrication among samples may have caused the variation observed in this experiment. Another factor that may have contributed to the variation is the presence of openings within the cylindrical cheese samples. If there were openings in the sample, this would have resulted in a lower force required for def omation These results are consistent with those obtained by Stampanoni and Noble ( 1991a & 1991b). Cheese analogs manufactured with rennet casein deionized water and melted vegetable fat, became more firm as the fat content of the analog was decreased. Firmness was measured with a 80% flat plate compression force as well as a 80% prmcture force using a U- shaped probe. In contrast to the results obtained in this experiment. Tunick et al. (1991) observed little change in the hardness of Mozzarella cheese when fat content was decreased. Low fat, high moisture (2 2.3% PDB, 57.4% moisture) Mozzarella cheeses had hardness values comparable to high fat, low moisture (47.6% PDB. 47.3% moisture) Mozzarella cheeses. Springiness is the rate at which a deformed material goes back to its undefomed condition after the deforming force is removed. Springiness of the cheeses decreased as the % fat in the cheese increased (Figure 17). Cheddar cheese containing 34 and 31.5% fat had similar springiness with scores of 58.1% and 57.8%, respectively. When fat was reduced to 26.8%, significant differences (p<0.05) in springiness were detected. This cheese Springiness [96) 59 100 50 L 1 1 ’ J l L o 5 1o 15 20 25 30 % Fat in cheese Figure 17. Influence of fat on springiness of Cheddar cheese as determined by the Instron Universal Testing Machine. 60 exhibited 71.5% recovery. The Cheddar cheese became more springy (p<0.05) with 20.5% fat exhibiting 78.9% recovery. The lower fat cheeses. 12.6% and <0.01% fat, exhibiting 88.1 and 94.6% recovery. these values were statistically similar. As with the hardness, the high variation observed when measuring springiness is most likely due to surface friction Consistent with the springiness results obtained in this experiment, Stampanoni and Noble (1991a) observed an increase in the springiness of cheese analogs manufactured with rennet casein deionized water, and melted vegetable fat, with increased levels of fat. In contrast to the results obtained in this experiment, Tunick et al. (1991) did not observe a change in the springiness of Mozzarella cheese when the fat content was reduced. SENSORY EVALUATION Trained sensory panelists evaluated the six Cheddar cheeses of varying fat contents for four textural characteristics (adhesiveness, cohesiveness, hardness, springiness) (Table 5). The results from the trained panel texture evaluation followed a distinct pattern Generally adhesiveness and cohesiveness increased as the % fat content of the cheese increased and hardness and springiness decreased as the % fat in the cheese increased (Figure 18). Adhesiveness in sensory applications refers to the force required to remove the material that adheres to the mouth (generally the palate) during the nomal eating process. The method used in the 61 1O intensity -P. O 5 1 O 1 5 20 25 30 % Fat in cheese ‘°' Adhesiveness + Cohesiveness * Hardness + Springiness Figure 18. Influence of fat content on the textural characteristics of Cheddar cheese as determined by a trained sensory panel. 62 adhesiveness evaluation involved the panelists physically forcing the cheese sample to the roof of their mouth with the tongue and evaluating the f orce required to remove the sample from the roof of the mouth [Civille and Szczesniak (1973)]. Adhesiveness scores increased as the fat content of the cheese increased. Adhesiveness scores were significantly different (p<0.05) for all cheeses with the exception of the two higher fat cheeses containing 34 and 31.5% fat. The score for these cheeses were 6.89 and 6.29 respectively and were similar in their adhesiveness as determined by the Table 5. Adhesiveness, cohesiveness, hardness and springiness of Cheddar cheese as influenced by fat content. determined by a trained sensory panel. TREATMENT ADHESIVENESS COHESIVENESS HARDNESS SPRINGINESS ('/o flt)’ 34.0 6.89a 5.68'l 2.70“ 2.61“ (1.63)2 (2.68) (1.29) (1.49) 31.5 6.29“ 4.96“” 2.89“ 2.52'l (1.68) (2.22) (1.60) (1.49) 26.8 5.26“ 5.2 5'“ 4.14b 3.55b (1.87) (2.03) (1.70) (1.84) 20.5 3.96c 4.68“be 5.61c 5.30c (2.12) (1.63) (1.47) (1.93) 12.6 2.14“ 4.45““ 6.98“ 6.91“ (1.27) (2.15) (1.39) (1.72) <0.l 1.27“ 3.86c 8.25“ 7.96“ (0.62) (2.67) (1.12) (1.74) ‘ % Pat in cheese 2 Means with standard deviations in parentheses n=4 replicates x 14 judges " Means with the same superscript within a column do not differ significantly (p<0.05). 63 trained senSory panel The values for these cheeses (34 and 31.5% fat) fall between S-moderately adhesive and 9-very adhesive. Both of these cheese were perceived as adhesive, in that their scores were higher than 5 which is the midpoint of the scale. The remaining cheeses (26.8%, 20.5%. 12.6%, <0.1% fat) were all different from each other in their adhesiveness (p<0.05). Cheddar cheese with 26.8% fat with a score of 5.29 was perceived as moderately adhesive. The intermediate (20. 5%) and low fat (12.6%) cheeses received scores of 3.96 and 2.14, respectively, which fall between moderately and not adhesive. The skim milk cheese (<0.1%) was not perceived as adhesive by the sensory panel, receiving a low score of 1.27. The above results suggest that the amount of fat in the cheese affected the cheese adhesiveness. However, this data also suggests that human perception of adhesiveness does not change up to a certain level fat. In this study, it was observed that trained panelists could not detect differences in adhesiveness of up to 4%. Only when fat levels were increased greater than 4% differences in adhesiveness were detected by the panelists. The fat in cheese adds to the lubricity and softness of the cheese, making the cheese easier to compress to the roof of the mouth, but more difficult to remove with tongue. Panelists commented that the higher fat cheeses were very difficult to remove, and once the sample was removed, a film remained on the roof of the mouth. The cheeses containing 26.8 and 20. 5% fat stuck to the roof of the mouth easily, but 64 they were able to be removed easily, with no remaining film on the palate. The low fat cheese (12.6%) stuck to the roof of the mouth slightly and was removed easily. The skim milk cheese (<0.1%) did not stick to palate at all, therefore it was judged to be not adhesive. These results are similar to those obtained by Stampanoni and Noble (1991a). A trained sensory panel evaluated cheese analogs made with rennet casein deionized water and vegetable fat. The trained panel detected an increase in adhesiveness in the cheese analogs with an increase in fat content. Increasing the acid concentration of the cheese analog resulted in a decrease in adhesiveness as detemined by the trained sensory panel Cohesiveness in sensory applications refers to the degree to which a substance is compressed between the teeth before it breaks. The cohesiveness evaluation involved compressing the sample between the molars and evaluating the degree to which the sample def arms, rather than crumbles, breaks or falls apart (Appendix A, Table A6). Cohesiveness of Cheddar cheese decreased as the fat content decreased. Table 4, column 3 lists the cohesiveness scores. The sensory panel failed to detect many differences in the cohesiveness of the Cheddar cheeses. Cheddar cheeses containing 34%, 31.5%. 26.8% and 20. 5% fat were all judged to have a similar cohesiveness. Likewise, cheeses with 31.5%, 26.8%, 20.5% and 12.6% fat were also similar in their cohesiveness and cheeses with 3 1.5%, 20. 5%, 12.6% and <0.1% were also judged to be similar by the trained sensory panel All 65 of the cheeses tended to fall within the mid range of the scale ranging from 3.86-5.68. corresponding to moderately cohesive. The fat in the cheese is dispersed in the protein matrix, and contributes to the cohesiveness of the cheese, or to the ability of the cheese to stick to itself. As the fat is removed, the protein matrix becomes more compact and rigid. A rigid structure crumbles and breaks more easily than a soft structure, making the cheese less cohesive as observed in this study. Cohesiveness is a difficult characteristic to evaluate, because as the fat is removed from the cheese, the cheese becomes more springy. A springy cheese resists defamation Since a springy cheese does not break as easily, panelists may tend to judge this characteristic as cohesive, therefore, extremely springy cheeses may be given a higher cohesiveness score. These results are consistent with those obtained by Stampanoni and Noble (1991a). A trained sensory panel evaluated cheese analogs made with rennet casein deionized water and vegetable fat. The trained panel detected an increase in cohesiveness of the cheese analogs with an increase in fat content. Hardness in sensory applications is defined as the force required to compress a substance between the molar teeth. The hardness evaluation involved compressing the sample through the molar teeth once, and evaluating the force required to achieve this. No significant differenCes in hardness existed between the higher fat cheeses containing 34 and 31.5% fat (Table 4). However all four remaining treatments were different in their 66 hardness (p<0.05). The higher fat samples. treatments 1 (34.5%) and treatment 2 (31.5%), received scores of 2.70 and 2.89 for hardness (Table 5). A score of 1 represents not hard. The 3% difference in fat did not result in a significant difference in the hardness of the cheese as perceived by the trained sensory panel The cheese with 26.8% fat received a score of 4.14, which is one point below moderately hard, and the cheese with 20. 5% fat received a score of 5.61, which is slightly above moderately hard. The low fat cheese (12.6%) fell between moderately hard and very hard with a score of 6.98, and skim milk cheese was perceived as very hard with a score of 8.2 5, less than the one point below the maximum of 9 on the scale. These data further support. the statement that fat level affects the hardness of the cheese consistent with the Instron data. These results are consistent with those obtained by Stampanoni and Noble (1991a). A trained panel detected an increase in the hardness of the cheese analogs with a decrease in fat content. Also consistent with the results obtained in this Study, Banks et al. (1989) observed an increase in the hardness of Cheddar cheese when the fat content of the cheese was reduced and moisture content was increased. Reduced fat Cheddar cheeses were manufactured with 2 5% and 16% fat. The moisture of the cheeses were 42.9% and 47.2%, respectively. Springiness in sensory applications refers to the degree to which a product returns to its original shape after it has been compressed between the teeth The evaluation involved compressing the sample partially 67 between the teeth without breaking the sample structure and evaluating the degree to which the sample returned to its original height. Significant differences did not exist between the springiness of the two higher fat cheeses (34, 31.5%). The scores were 2.61 and 2.52, for the cheeses containing 34% and 3 1.5% fat, respectively (Table 5). The remaining cheeses (26.8%. 20.5%, 21.6%,<0.1%) were all different (p<0.05) in their springiness. The 26.8% fat cheese, with a score of 3.55, fell between not springy and moderately springy, and the 20. 5% fat cheese was moderately springy with a score of 5.30. The low fat cheese (12.6% fat) was springier with a score of 6.91 and the skim milk cheese (<0.1% fat) was the springiest (p<0.05) among the cheeses with a score of 7.96, as perceived by the trained sensory panel The rigid structure of cheese without fat or a reduced amount of fat prevents the sample from breaking easily. The sample resists defamation and a higher force is required to break the sample structure. These results are consistent with those obtained by Stampanoni and Noble (1991a). In their study, a trained sensory panel evaluated cheese analogs manufactured from rennet casein deionized water and vegetable fat. Springiness of the cheese analogs increased with an increase in the fat content of the cheese analog as determined by the trained panel Fat is very important to the texture of Cheddar cheese. As fat is removed from the cheese, it losses its adhesiveness, and cohesiveness and 68 becomes more springy and hard. The data presented from the Instron and sensory study supports this statement. An ideal Cheddar cheese would receive a moderate score for each of these characteristics. An ideal Cheddar cheese should have moderate adhesiveness. A very adhesive cheese would be sticky and pasty and a cheese with no adhesiveness would be very dry [Olson and Johnson (1990)]. Cheddar cheese should be moderately cohesive, a low cohesive cheese would have crumbly texture like that of a Cheshire cheese and a very cohesive cheese like a Havarti would have a texture too soft for Cheddar cheese. Cheddar cheese is considered a hard cheese, however the hardness of the cheese with <0.1% fat in this experiment was similar to that found in Pamesan cheese, an unacceptable texture f or Cheddar cheese. Springy or rubbery cheese is not a desirable characteristic for Cheddar cheese. This characteristic is typically found in reduced fat cheeses. The hardness and springiness scores for each treatment were very similar. for example, the cheese with 34% fat received a hardness score of 2.70 and a springiness score of 2.61. These results suggest that the hardness or firmness of cheese is related to, or affects the springiness or elasticity of cheese. A harder cheese is more likely to be more springy, and exhibit higher elastic recovery. Fat is not solely responsible for the alteration of these characteristics. Cheese texture is affected by many parameters, such as protein and water interactions and interactions of f at, water and protein However removal of 69 the fat significantly alters cheese composition and the textural characteristics of cheese. The removal of the fat affected adhesiveness, hardness and springiness after differences of 4% or greater. Treatments 1 and 2. 34% and 31.5% fat cheeses were only different in their fat content by 3% and there were no perceived differences in these characteristics as observed in this study. The differences in the textural characteristics of the cheeses can be explained by their microstructure. The higher fat cheeses which were softer, less springy and more cohesive and adhesive than the other cheeses, had a very open irregular protein matrix (Figures 8 and 9). The protein network was not very rigid due to disruption of the matrix by the fat present. As the sample was deformed, the fat was present to act as a lubricant, allowing the structure to move freely. As the fat content of the cheese was decreased. the structure became more compact, dense and rigid with fewer openings in the protein matrix. The microstructure of the intermediate fat cheeses (26.8% and 20.5%) was not as open as that of the higher fat cheeses. This closed compact structure resulted in harder, more springy cheeses. The adhesiveness and cohesiveness of these cheeses decreased due to a decrease in the amount of fat present to act as an adhesive force. In the lower fat cheese (12.6%) the structure was even more compact and the bridges connecting proteins were thicker, resulting in the rigid texture of this cheese. The skim milk cheese with <0.1% fat. and an 70 almost completely closed Structure resulted in a very hard, springy cheese, with very little cohesiveness and adhesiveness. The rigid structure required a very high force f or def omation and would regain much of its original height when compressed at low forces. This cheese had no fat present to act as an adhesive force. Once the sample structure was broken it fell apart very easily without the fat present to contribute to the cohesiveness of the cheese. Adhikari er al. (1992) explained the characteristics of Chhana and Rasogalla, two Indian cheeses using SEM. The Chhana, the more firm of the two cheeses. had a conglomerated matrix, with small numerous rmiformly distributed pores. The structure contained thick protein bridges which reduce the mean free path of the casein micelles, limiting movement of the fat phase relative to the protein phase. Likewise in this study, the lower fat samples with strong protein bridges (20.5% and 12.6% fat) were more firm than the higher fat cheeses (26.8%, 31.5% and 34% fat) that lacked the strong thick protein bridges. The Rasogalla had a ragged, porous, loose protein matrix. Large voids were present between the proteins allowing the protein bodies to move freely. resulting in a lower firmness than the Chhana. Also consistent with the results observed in this study, Mistry and Anderson (1993) observed that reduced fat cheeses with a firm, rubbery texture had a dense, rough microstructure, dominated by protein as determined by SEM. 71 ORRELATION BETWEEN INSTRON AND EN RY MEASUREMENTS The results from the sensory and Instron measurements were correlated. The Instron and sensory measurements show a linear relationship for all textural parameters studied (Figure 19 and 20). A strong correlation existed for determination of hardness (r=0.95) and springiness (r=0.94) as measured by the Instron and a trained sensory panel Table 6. Regression statistics for relationship between Instron and sensory measurements. I Characteristic r' a b Adhesiveness 0.73' -0.25 0.21 I Cohesiveness 0.41“ 0.27 0.02 I Hardness 0.95' -192.55 132.66 I Springiness 0.94' 42.87 6.56 I ‘rs correlation coefficient as line intercept b= line slope ' significant at p<0.001. "' significant at p<0.05. A positive correlation (r=0.73) also existed between adhesiveness determined by the Instron and the trained sensory panel Overall, the sensory panel was better able to detect the differences in adhesiveness of the cheese with a change in fat content compared to the Instron However the trend of instrumental and sensory adhesiveness, was an increase in 72 I-adhssivsnsss ‘ . s-edhestvonoss I-cohosivensss 0.121 S-eoboslvonoss Figure 19. Relationship between textural characteristics (adhesiveness and cohesiveness) as determined by the Instron Universal Testing Machine and a trained sensory panel. I-Instron S-Sensory 73 I-springlnoss 3 6 7 l S'springlnoss 1 2 3 4 Figure 20. Relationship between textural characteristics (hardness and springiness) as determined by the Instron Universal testing Machine and a trained sensory panel. I-Instron S-Sensory. 74 adhesiveness with an increase in fat content. The negative correlation for cohesiveness (r-0.41) was not significant. Correlation between instrumental and sensory cohesiveness was not significant. Cohesiveness determined by the Instron increased with a decrease in fat content and decreased with a decrease in fat content as determined by the trained sensory panel This is most likely the result of differences in measurement. Instron cohesiveness is a ratio of the height of two peaks. Sensory determination of cohesiveness is a measure of how much the sample deforms or falls apart. To obtain a good correlation the types of measurements must be similar or measuring the same type of property. The Instron was able to distinguish differences in the cohesiveness of the cheeses whereas the scores from the trained panel tended to overlap. The relationship between sensory and instrumental measurements is typically linear, however some characteristics such as firmness may exhibit a curvilinear relationship, with the instrumental firmness increasing more than the sensory firmness. However, this relationship for cheese is typically non-linear unless the parameters are not too wide [Zoon (1991)]. In this study, a high positive linear correlation was observed between the two measurements for adhesiveness, hardness, and springiness (Figure 19A and 20 A&B). A low negative correlation was observed between sensory and Instron cohesiveness. Chen et al. (1979) obtained a positive correlation 75 coefficient between instrumental and sensory determination for hardness (r=.845). consistent with these results. They observed a high negative correlation between instrumental and sensory adhesiveness(r=—.837). and in contrast to these results, a high positive correlation (r=.849) for cohesiveness. The uperiment evaluated rectangular cheese samples of various varieties including Cheddar cheese at 126°C. Hardness, cohesiveness and adhesiveness were evaluated using a plrmger probe as opposed to a flat plate. Springiness or elasticity was determined using a flat plate. A trained sensory panel evaluated the samples using a 1 5-point scale. Stampanoni and Noble (1991) observed a negative correlation (r-.66) between springiness and modulus of elasticity f or cheese analogs as detemined by the Instron in contrast to these results. Firmness as determined by a trained sensory panel correlated (r=.89) with 80% puncture force and 55% compression force (r=.93), consistent with these results. Adhesiveness as determined by a trained sensory panel correlated (r=.72) with adhesiveness as determined by the Instron A trained sensory. panel evaluated 13x10 mm cylindrical cheese analogs using an unstructured 100 mm scale. TEXTURE ACCEPTANCE TESTS An rmtrained sensory panel evaluated the five cheeses with 34%, 31.5%, 26.8%, 20. 5% and 12.6% fat, for overall texture acceptance. The skim 76 milk cheese (<0.1%) was an inedible mass of casein and was not evaluated by the untrained sensory panel Before the evaluation of the cheeses the panelists were instructed to fill out a brief questionnaire to obtain infomation regarding their concern f or dietary fat intake, to determine whether or not the panelists were consumers of reduced fat cheeses, and what their expectations of a reduced fat cheeses were as compared to full fat cheeses (Appendix A, Table A8). Table 7 lists the results from the questionnaire regarding the dietary fat concerns of the panelists. Forty four percent of the panelists were moderately concerned about their dietary fat intake. Six percent of panelists were extremely concerned about their intake of dietary fat. Seven percent of the panelists were not concerned about dietary fat consumption Table 7. Results from questionnaire - dietary fat concerns — I EXTREMELY CONCERNED 696 . VERY CONCERNED 27% MODERATEIX CON CERNED 44% SOMEWHAT CONCERNED 1696 NOT CONCERNED 796 77 Of the panelists who have any concern(extreme1y, very, moderately and somewhat total 93%) regarding their fat intake, 43% percent of the panelists choose to reduce fat intake by consuming low fat cheese as recommended by the dietary guideline that suggest people reduce their dietary fat intake. Fifty-seven percent of the panelists were not reduced fat cheese consumers. Table 8 lists the results from the final question on the questionnaire. This question asked the panelists what they etpected from a reduced fat cheese, did they expect it to be better than full fat, the same as a full fat of worse than full fat. Table 8. Untrained panelists expectations of the quality of a reduced fat cheese compared to a full fat cheese. Better than full fat 12% Same as full fat 50% Worse than full fat 35% No idea _ 3% i Fifty percent of the panelists expected a reduced fat cheese to be the same as a full fat cheese, 12% expected it to be better and 35% expected it to be worse. These results are from a small group relative to the entire population of cheese consumers. However, they do suggest that consumers want products that are lower in fat, but they expect these products to have 78 the same quality flavor and texture of a full fat counterpart. Reduced fat Cheddar cheese has been marketed as a Cheddar cheese, therefore consumers expect the same type of product, and are greatly disappointed when it does not perform as well as regular Cheddar [Hise (1991)]. Twelve percent of the panelists expected a better product. This suggests that the consumer expects that if any factor of the product is improved le. less fat is better f or your health, this will improve the overall quality of the product, not taking into account the functional properties fat has in cheese and not realizing some of these functional properties may be eliminated by removal of fat. Thirty five percent of the panelists expected the product to be worse. This expectation may stem from previous experience with eating reduced fat cheeses, or other products reduced in fat that did not compare to their full fat counterparts. Three percent of the panelists did not know what to expect from a reduced fat cheese. Table 9 lists the results from the overall texture acceptance tests. Cheeses receiving a score of 5 or higher were judged to be acceptable. A score of 5 corresponded to neither like nor dishke on the scale. As expected, the acceptance of the cheese increased as the fat in the cheese increased. suggesting that an increase in fat content makes a cheese more desirable (Figure 21). The panelists did not judge the three higher fat cheeses differently. These cheeses contained fat levels of 34.5%, 31.5% and 26.8% and were similar in their overall texture acceptance by the untrained 79 Table 9. Overall texture acceptance of Cheddar cheese as influenced by fat content, determined by an untrained sensory panel. TREATMENT RESPONSE (“/0 f“)1 (acceptance) 34.0 6.782“ (2.03) 3 1.5 6.70“ (1.8 5) 26.8 6.79a (1.68) 20.5 5.07b (2.00) 12.6 3.72c (2.20) ‘ % Pat in cheese 2 Means with standard deviations in parentheses n= 4 replicates x 25 judges '“ Means with the same superscript within a column do not differ significantly (p<0.05) panelists. These cheeses received mean scores of 6.78, 6.70 and 6.79 respectively. indicating that their textures were liked and acceptable to the panelists. The individual scores for the cheese with 34% fat ranged from 1-9, and cheeses with 26.8% and 20.5% fat ranged from 2-9. Panelists who gave these treatments lower scores, commented that, the samples left a film on the roof of their mouth At 20. 5% fat level the acceptability of the cheeses began to decrease. This Cheddar cheese sample received a score of 5.6 7, which is between like slightly and neither like/dislike, was still 80 acceptance 6! 01 3 J J l l I l l l l l l 1 1O 12 1416 18 20 22 24 26 28 30 32 34 96 Fat in cheese Figure 21. Influence of fat content on the overall texture acceptance of Cheddar cheese. 81 acceptable, suggesting that the texture was not preferred by the untrained panel, but was not necessarily unacceptable. The low fat cheese (12.6% fat) with a mean score of 3.72, was no longer acceptable. A score of 3.72 falls between dislike moderately and diser very much Many panelists commented that this sample was waxy and dry, and the texture was unacceptable. A list of the panelists comments are in Appendix D. The majority of the panelists disliked the sample as the mean indicates, however there were panelists who did prefer the hard texture of this sample. Fat influences the acceptance of Cheddar cheese. Consumers enjoy dairy foods because of their sensory characteristics, specifically flavor and texture [Jameson (1990)]. The results obtained in this study are consistent with those obtained by Madsen et al. (1970). Cheddar, Swiss and Colby cheeses with reduced fat contents were evaluated by consumers to determine the effect of fat on the preference of the cheeses. Preference for Cheddar and Colby cheeses decreased with a decrease in fat content. Cheddar cheese with 35.5% FDB and Colby with 24.4 % FDB were preferred the least while Cheddar and Colby cheeses with 54.3% and 52.6% PDB, respectively were preferred the most. However, the consumer preference for Swiss cheese increased with a decrease in fat content. Swiss cheese with 36.1% PDB was preferred more than cheese with 45.9% PDB. Banks er al. (1989) produced several Cheddar cheeses with varying fat levels (33.1%, 25.6% and 16.8%). 82 A taste panel evaluated the texture of the cheeses. Consistent with this study. the higher fat cheeses received a more favorable texture score compared to the low fat cheese (16.8%). The lowest fat cheese was judged to be over firm and rubbery. Cheese is one of the few dairy products that a reduced fat version has not been successfully produced with texture and flavor not comparable to its full fat counterpart [Rosenberg (1992)]. Development of a reduced fat or fat free product such as ice cream is not as challenging as developing a reduced fat cheese. Ice cream contains many ingredients including milk solids, flavors, sweeteners, stabilizers and emulsifiers [Morr and Richter (1988)]. When fat is removed, the proportions of these ingredients can be altered to a certain extent without detrimental effects. Fat replacers and mimetics can be used successfully in reduced fat or fat free ice creams to improve texture (mouthfeel), and melting properties when fat is removed. Fat replacers and mimetics are starch-based, cellulose-based or protein- based and function well in frozen desserts since these ingredients are part of the fomulation and are just used in higher concentrations in reduced fat products [Olson (199 1)]. Flavor can be improved by increasing or addition of flavors and sweeteners. Cheese has a limited ingredient list, when compared to a product such as ice cream. Cheese is made from milk. Other ingredients include starter cultures. rennet and salt. Cheese is a more complex system. Texture 83 and flavor development involve many chemical and physical reactions. The flavor and texture of cheese develops through the action of the starter cultures and rennet on the fat and protein in the milk [Johnson (1988)]. Moisture of the cheese, salt, pH, manufacturing conditions and ripening parameters all contribute to the complexity of the cheese texture and flavor system Thus f ar, improvement of reduced fat cheeses has been through alteration of the manufacturing procedures and the use of various starter cultures. The use of fat replacers and mimetics in natural cheeses is a potential area for improvement of reduced fat cheese quality. Thirty-six percent of all reduced fat dairy products introduced in 1992 were cheeses, and 23% were ice cream. In 1991, only 16% of the products introduced were cheese compared to 50% being ice cream [O'Donnell ( 1993)]. These figures suggest that even though the quality of reduced fat cheeses is not comparable to full fat cheeses, the demand and consumption of reduced fat cheeses is increasing and perhaps the quality is constantly improving. CHAPTER V SUMMARY AND CONCLUSIONS Pat is a major component of cheese. Reduction of fat in cheese significantly affects the microstructure, thus affecting the textural characteristics of Cheddar cheese. 1. Reduction of fat levels in Cheddar cheese resulted in a loss of the open intricate microstructure of Cheddar cheese. As the fat level of the cheese decreased, the structure of the cheese became more closed and compact. 2. Reduction of cheese fat level resulted in an increase in hardness, springiness and cohesiveness, and a decrease in adhesiveness as detemined by the Instron Universal Testing Machine. 3. Reduction of cheese fat level resulted in an increase in hardness and springiness and a decrease in adhesiveness and cohesiveness as determined by a trained sensory panel 4. A positive linear correlation was observed between the textural characteristics determined by the Instron and the trained sensory panel for hardness, springiness and adhesiveness. 5. Reduction of cheese fat level resulted in a decrease in the overall texture acceptance as determined by an untrained sensory panel At 12.6% fat, the cheese was no longer acceptable to the panel 84 CHAPTER VI FUTURE RESEARCH Based on the results obtained in this study, areas for future for research include: 1. Correlation of microstructure data with texture data through image analysis. This will allow the prediction of textural quality by observing microstructure. Image analysis will also be a method to quantitate the inf omation obtained from Scanning Electron Microscopy. 2. Development of a method to better measure cheese adhesiveness. Measurement of adhesiveness by the Instron Universal Testing Machine produces low results with a high amount of variation 3. Selection of starter cultures and adjunct cultures that result in increased proteolysis, and improved flavor and texture quality. 4. Explore the use of fat mimetics and substitutes as a method to improve texture of reduced fat Cheddar cheese. 85 APPENDICES APPENDIX A APPENDDK A QUESTIONNAIRES FOR THE SENSORY EVALUATION TESTS A questionnaire was presented to the panelists who participated in the initial screening process to assist in panel member selection The panelists completed a simple ranking test on cheese samples, for each of the four characteristics, adhesiveness, cohesiveness, hardness and springiness. The trained panelists completed a 9-point hedonic test based on the degree of each characteristic. The panelists who participated in the texture acceptance test completed a 9-point hedonic test to determine the degree of liking for treatments 1-5. 86 87 Table A.l. Prescreening questionnaire for panel selection. PRES REENIN E TI NNAIRE NAME OFFICE PHONE 1.13—4E 1. ARE THERE ANY WEEKDAYS THAT YOU WILL NOT BE AVAILABLE ON A REGULAR BASIS? 2. WHAT PART or THE DAY ARE YOU NORMALLY AVAILABLE? MORNING(8-l 1) EARLY AFTERNOON(ll-2) AFTERNOON(2-5) 3. DO YOU PLAN TO BE ON CAMPUS DURING THE SUMMER? HEALTH 1. DO YOU HAVE ANY OF THE FOLLOWING? DENTURES FOOD ALLERGIES ORAL DISEASE 2. DO YOU TAKE ANY MEDICATIONS WHICH AFFECT YOUR SENSES? 3. ARE YOU CURRENTLY ON A RESTRICTED DIET? IF YES, PLEASE EXPLAIN. 4. WHAT FOODS CAN YOU NQT EAT? 5. WHAT FOODS DO YOU NOT LIKE TO EAT? THANK YOU 9 88 Table A.2. Consent form for panel members. CONSENT FOR TASTE PANEL MEMBERS Food Science and Human Nutrition Department Michigan State University Cheddar, cheese prepared from pasteurized milk, cultures, rennet. salt and natural color. I have read the above list of ingredients and find none that I am allergic to. I agree to participate in the sensory panel that will take place on . The panel will evaluate Cheddar cheese texture (ie. how hard, rubbery etc.) I understand that the the panel will take approximately 15 minutes and my name will not be utilized in reporting of the results. I understand that that I am free to withdraw my consent and discontinue participation in the panel at any time without penalty. Signature Date 89 Table A.3. Ranking score sheet for panel selection. MM! HAIL TYPE OF SAMPLE Cheese QHAMQERISI‘IQ §TQDIED Adhesiveness W Place sample between molars; chew five times; Press the sample to the roof of the mouth with the tongue; Evaluate the force required to remove the sample from the roof of the mouth with tongue. Rate the samples from least adhesive to most adhesive. Pxpectorate the sample; rinse mouth with water between samples. 925 123 187 Least Adhesive Most Adhesive 90 Table A.4. Adhesiveness evaluation score sheet. NAME DATE TYEE QF SAMPLE CHEESE QHARAQERISTIQ SIQDIED Adhesiveness INSTRQQIIIQNS Place sample between molars; chew five times: Press the sample to the roof of mouth with the tongue. Evaluate the force required to remove the sample from the roof of the mouth with tongue. Place an X next to the value which best describes the adhesiveness of the sample. Expectorate the sample; rinse mouth with water. 299 1 Not Adhesive 9 Very Adhesive MME 91 Table A.5. Cohesiveness evaluation score sheet. MME DATE AMP A ERISTI DIED Cohesiveness W Place sample between molars; compress fully; evaluate the degree to which the sample deforms rather than crumbles. breaks, or falls apart as cohesive. Place an X next to the value which best describes the cohesiveness of the sample. gm 1 Not Cohesive _ 2 _ 3 _ 4 _ 5 Moderately Cohesive _ 6 _ 7 __ 8 _ 9 Yea Cohesive CQMMENTS 92 Table A.6. Hardness evaluation score sheet. NAM 25:le :I:!P§ QF SAMPLE Cflfi CHARACTERISTIC SIIIQDIED Hard_ness INSTRQCIIQNS Place sample between molars; bite through once; evaluate for hardness. Place an X next to the value which best describes the hardness of the sample. Fxpectorate sample; rinse mouth with water. MME 93 Table A.7. Springiness evaluation score sheet. NAME pm r AMP E HEB W988 W Place sample between molars; compress partially without breaking the sample structure. Place an X next to the value which best describes the springiness of the sample. Expectorate sample; rinse mouth with water. M _l&5m _2 _3 _4 __ 5 Modgately Springy' __6 _7 __8 _9m_§m'mgy COMMENTS 94 Table A.8. Texture acceptance questionnaire score sheet. E TIONNAIRE NAME DATE 1. How are concerned are you about your intake of dietary fat and cholesterol? Extremely concerned _ Very concerned Moderately concerned Slightly concerned Not concerned 2. Do you frequently consume dairy products, specifically Cheddar cheese? 3. Do you frequently consume low fat dairy products, specifically Cheddar cheese? 4. What do you typically expect in a low fat cheese product as compared to a full fat cheese product, in regards to product quality. specifically texture. Better than full fat Same as full fat Worse than full fat 95 Table A.9. Texture acceptance evaluation. EVALUATION OF CHEDDAR CHEESE TEXTURE NAME DATE INSTRUCTTQNS Taste the following samples in the order presented. After tasting each sample place an X next to the line that best describes how you feel about the TEXTURE of the sample (i.e. hardness, how the sample feels in your mouth when you bite and chew it). You may expectorate the sample if desired. Rinse mouth with water between samples. Sample 604 299 486 867 352 like extremely Like very much Like moderately like slighty _ _ _ _ _ Neither like/dislike Dislike slightly Dislike moderately Dishke very much Dishke extremely ngmgntg APPENDDI B Worksheets for the sensory evaluation. F our replicates of each treatment were produced. The trained panelists evaluated each treatment and each replicate once. The samples were presented in such a way that the each sample as well as each type of evaluation was presented in a different order. Twenty-five panelists evaluated each replicate once for a total of 100 responses for the consumer acceptance test. Treatments 1-5 were presented in five different ways so each sample was evaluated in a different order. 96 APPENDIX B 97 Table B.l. Order of presentation for replicates l and 3 for trained panel texture evaluation. PIT l 2 3 4 5 6 1 1-ACHS 4-CHSA 2-HSAC 5-SACH 6-CASH 3-SHCA 2 4-ACHS 1-CHSA S-HSAC 2-SACH 6-CASH 3-SHCA I 3 6-SHCA 3-CASH 2-SACH 4-HSAC 5-CHSA 1-ACHS I 4 4-SHCA 3-CASH 2-SACH 1-HSAC S-CHSA 6-ACHS I 5 2-CHSA S-HSAC 1-SACH 3-CASH 6—SHCA 4-ACHS I o 3-CHSA 2-HSAC 4-SACH 6-CASH l-SHCA S-ACHS I 7 l-HSAC 6-SACH 3-CASH S-SHCA 2-ACHS 4-CHSA s 5-HSAC 1-SACH 6-CASH 4-SHCA 3-ACHS 2-CHSA 9 2-SACH S-CASH l-SHCA 3-ACHS 4-CHSA 6-HSAC 10 6-SACH 4-CASH 3-SHCA l-ACHS 2-CHSA S-HSAC 11 2-CASH 6-SACH 5-SHCA 4-ACHS l-CHSA 3-HSAC 12 5-CASH 2-SACH 6-SHCA 3-ACHS 4-CI-ISA 1-HSAC 13 l-SHCA 3-SACH 2-CHSA 5-HSAC 4-CASH 6-SACH 14 6-SHCA l-ACHS 4-CHSA 2-HSAC 3-_CASH S-SAcr_I_ . * Number indicates order treatment was presented to panelist. ** A=adhesiveness, C-cohesiveness, H=hardness. =springiness ***P=panelist T=Treatment 98 Table B.2. Order of presentation for replicates 2 and 4 for trained panel texture evaluation. PIT I 2 3 4 5 6 1 2'-SACH 3-CAHS 6-ASCH 4—SAHC l-HACS 5-CSAH 2 4-ACHS 6-HCAS 2-SCHA 5-ACHS 3-ACHS 1-SAHC 3 6-CHSA 2-HSCA 3-ACSH l-SHCA S-SAHC 4-AHCS I 4 1-HSAC 6-CHSA 4-AHSC 2-CASH S-SHAC 3-SACH I 5 3-SACH 4-CAHS l-ASCI-l 6-SACH 2-HACS 5-CSAH I o 5-HSCA 6-AHSC 2-SCHA l-ACHS 3-CASH 4-SAHC 7 l-CHSA S-HSCA 3-HASC 4-ASCH 2-SCHA 6-AHcs s 2-SACH 4-AHCS l-HASC 6-HSAC s-SHAc 3-CSAH 9 3-SACH 6-CAHS 2-ASCH S-SACH l-HACS 4-CSAH Io 4-ACHS l-CHSA 5-SCHA 2-HSCA 6-ACSH 3-SAHC 11 5-CHSA 3-HSCA 6-SCHA l-CHSA 2-SHCA 4-AHCS 12 6—HSAC 2-SCAH 4-HASC 3-HSAC 5-SHAC 1-HCSA 13 l-SACH 6-CAHS 2-ASCH 4-SACH 3-HACS 5-CSAH 14 2-ACHS 3-AHSC l-SCHA 6-ACHS 5-ACSH 4-SAHC * Number indicates order treatment was presented to panelist. ** A=adhesiveness, Czcohesiveness, H=hardness, S=springiness ***P=panelist T=Treatment APPENDIX C APPENDIX C CODES USED FOR SAMPLES IN SENSORY EVALUATION Table C.l. Codes used for trained panel evaluation. Table C.2. Codes used for untrained panel evaluation 99 APPENDIX D APPENDIX D COMMENTS FROM TEXTURE ACCEPTANCE TESTS Table D.l. Replicate #1 * 867 and 639 seemed dry and waxy * 378 had the best texture * Most are slightly hard. there are some tastes in 867,465,286 I don't like * 867 very hard to bite. 639. I don't like color (too yellow) and texture (hard) * 378 a little hard * 639 harder * 246 same as 639 * 465 perfect * 867 to hard and chewy * 867 is too hard to like-takes too much work to chew it * 639 seemes too hard at first, but improves * 246 is extremely good Table D.2. Replicate #2 * I preferred sample # 149 out of the batch..samples 463 and 981 were rather unpalatable * 149. 620,732 felt like they left a film on your teeth and tongue-too soft for my preference * 981 was by far the hardest...l graded this higher because I enjoy the hardness when chewing * 620 is a little too hard and flavor is a little different than Cheddar * 981 is felt almost as rubber * 463 is a little too chewy * 620 and 149 are the best in texture * 981 was waxy and dry * I don't like cheese and I am not really a cheese eater. but these cheese were rather good and I enjoyed them 100 101 Table D.3. Replicate #3 * 534 and 763 were very similar in their texture, 763 was a little bit more bitter in its taste * 348 seemed to stick in your mouth and to your teeth, the tase was different too * 348 is very dry but tastes good * 348 is like chewing a chunk of parafin * 534 is the texture I like the best * I like creamy smooth feeling cheese * 348 was simply too hard * 348 rubbery * 982 I liked very much, it has a good texture * 763 hard * 534 not bad * like 982 * 348 was to hard, not something you would want to take more than one bite * 534 was OK, but too smooth * 348 had no flavor and texture was bad Table D.4. Replicate #4 * 3 52 flavor-poor, 486 crumbly * 352 does not really have acheese taste * 367 seems too rigid * 604 has very strong taste at first * 867 is too dry * 352 had the best texture * 867 was hard and dry * 867 had a hard texture and crumbled in one's mouth * 352 and 486 seemed to ”melt in one's mouth” - good mouthfeel * I liked the solid, soft texture of 604 and 299... good mix between hardness and softness * 867 too hard, 486 too crumbly * 486 abd 352 are mealy-no cohesiveness * 604,299, 867-too rubbery * 867 is too rubbery to be likable- bounces back when you bite it APPENDIX E ANOVA TABLES APPENDDK E Table E.l. ANOVA table for cheese composition-fat Source of Degrees of Sum of Mean square F-Value variation freedom squares Between 5 3347.802 669.560 168.708 Within 18 71.438 3.969 I Total 23 3419.240 I Table E.2. ANOVA table for cheese composition-protein Source of Degrees of Sum of Mean square F-Value variation freedom squares Between 5 1160.530 232.106 115.406 Within 18 36.202 2.011 ‘ I Total 23 1196.732 I Table E.3. ANOVA table for cheese composition-moisture Source of Sum of variation freedom squares Between 5 339.829 67.966 24.264 Within 18 50.420 2.801 Fatal 23 390.420 102 Table E.4. ANOVA table for sensory adhesiveness Source of variation 103 Sum of squares Mean square F-Value Between 1456.265 291.253 112.731 Within 852.589 2.584 2308.854 Table E.5. ANOVA table for sensory cohesiveness Source of Sum of variation squares Between 5 1 13.634 22.727 4.449 Within 330 1685.554 5.108 Total 335 1799.188 _ _ I Table E.6. ANOVA table for sensory hardness Source of variation Degrees of freedom Sum of squares Mean square Between 1416.060 283.212 136.062 Within 330 686.893 2.081 335 2102.952 Table E.7. ANOVA table for sensory springiness Source of variation 104 Sum of squares Mean square Between 1472.310 294.462 Within 961.500 2.914 Total 2433.810 Table E.8. ANOVA table for Instron adhesiveness Sum of F-Value Source of Degrees of Mean square variation freedom squares Between 5 14.094 2.819 4.316 Within 66 43.105 0.653 Total 71 57.199 Table E.9. ANOVA table for Instron cohesiveness Source of variation Table E.10. ANOVA table for Instron hardness 105 Source of Degrees of Sum of Mean square F-Value variation freedom squares Between 5 576368378 115273676 69.628 Within 66 109267333 16555.657 Total 71 6856357.]1 _ Table E.ll. ANOVA table for Instron springiness Source of Degrees of Sum of Mean square F-Value variation freedom squares 5 13946.637 2789.327 43.957 66 4188.103 63.456 71 18134.740 Table E.12. ANOVA table for untrained panel evaluation Source of Degrees of Sum of Mean square F-Value variation freedom squares Between 4 700.66 175.167 45.611 I Within 495 1901.020 3.840 1 Total 499 2601.688 J REFERENCES 106 REFERENCES AdhikarlAK, Mathur,O.N. and PatilG.R. 1992. Texture and microstructure of Chhana and Rasogalla made from cows' milk. J. Dairy Res. 59(3):413-424. Ak,M.M. and GunasekaranS. 1991. Stress-strain curve analysis for Cheddar cheese under uniaxial compression J. Food Sci. 57(5):1078-1081. AndersonDl... Brandsma.RL, Mistry,V.V. and BaldwinKA. 1992. Reduced-fat Cheddar from condensed milk 1. Manufacture, composition and yield. J. Dairy Sci. 75(Suppl1):90. Banks.W. 1991. Milkfat. J. Soc. Dairy Tech. 44(2):31-32. BanksJ.M. Brechany,EY. and Christie,W.W. 1989. The production of a low fat Cheddar type cheese. J. Soc. Dairy Technol. 42(1):6-9. Barlow,I., Lloyd,G.T., RamshawEH., Miller, A.J., McCabe,G.P. and McCabeJ. 1989. Correlations and changes in flavor and chemical parameters of Cheddar cheese during maturation Aust. J. Dairy Tech. 44(1):7-18. Berner,L.A. and LofgrenP.A. 199 1. Symposium role of nutrition in marketing dairy products. J. Dairy Sci. 74(3):1124-1130. Bertola,N.C., Bevilacqua.A.E. and Zaritzky,N.F. 1992. Proteolytic and rheological evaluation of maturation of Tybo-Argentina cheese. J.Dairy Sci. 75(12):3273-3281. Bourne, MC. 1966. A classification of objective methods for measuring texture and consistency of foods J. Food Scl:3 1282-291. (The table in this article is incorrect. the correct table appears in J. Food Sci.32:154,1967). Bourne,M.C. 1982. Food Texture and Viscosity: Concept and Measurement, Academic Press, New York. 107 Chen.A.H., LarkinJ.W., 0ka.]. and Irwin.W.E. 1979. Textm'al analysis of cheese. J. Dairy Sci. 62(6):901-907. Chen.C. 1991. Lowfat make schedules. Reduced Fat Cheese Conference. Center for Dairy Research. Madison. WI. Chen.C.M., JohnsonME. and Olson. N.F. 1992a. Optimizing manufacturing parameters in 3 3% reduced fat Cheddar cheese. J. Dairy Sci. 7S(Suppl.1):104. Chen,C.M., Macedo,A.C., JohnsonMJE. and Olson.N.l-‘. 1992b. Analysis of four starter cultures on the ripening parameters in 33% reduced fat Cheddar cheese. J. Dairy Sci. 75(Suppl 1):103. Civille,G.V. and Szczesniak.A.S. 1973. Guidelines to training a texture profile panel. J. Texture Stud. 4(2):204-223. Cooper,H. 1987. Texture and sensory evaluation of dairy products. In: Food Texture:Instru mental and Sensory Measurement (H.R.Maskowitz eds. pp. 217-250) Marcel Dekker Inc., New York. CreamerLK. and Olson,N.F. 1982. Rheological evaluation of maturing Cheddar cheese. J. Food Sci. 47(3):631-646. Dexheimer,F. 1992. On the fat track. The pace quickens as processors race to develop tastier reduced fat products. Dairy Foods. 93(5):38-50. Dao,D.V. and RennerJ-L 1988. Studies on the application of ultrafiltration for the manufacture of Cheddar cheese. 2. Effect of heating UF milk on composition and yield. Milchwissenschaft. 43(11):708-711. El-NeshawyAA., Abdel Baky,A.A., Rabie,A.M. and Ashour,M.M. 1986. An attempt to produce a low fat Chphalotyre (Ras) cheese of an acceptable quality. Food Chem. 22(2):123-137. Emmons,D.B., Kalab,M. and Larmon.E. 1980. Milk gel structure X. Texture and microstucture in Cheddar cheese made from whole milk and homogenized low fat milk. J. Text. Stud. 11(1):15-34. Foster,S.J., Baer,R.J. and Mistry,V.V. 1990. Cheddar cheese manufactured from condensed milk. J. Dairy Sci. 73(8):19801987. 108 G1aserJ.,Carroad.P.A. and Dunkley,W. I... 1980. Electron microscopic studies of casein micelles and curd microstructure in cottage cheese. J. DairySci. 63(1). 37- 48. Green,M.L. 1990. The cheesemaking potential of milk concentrated up to four-fold by ultrafiltration and heated in the range 90-97°C. J. Dairy Res. 57(4):549-557. Green.M.L., Turvey,A. and Hobbs,D.G. 198 1. Development of structure and texture in Cheddar cheese. J. Dairy Res. 48(2):343-355 Grundy,S.M. and Denke,M.A. 1990. Dietary influences on serum lipids and lipoproteins. J. Lipid Res. 31:1149-1172. Hargrove,R.E., McDonoughFJi. and Tittsler,R.P. 1966. A new type of ripened low-fat chese. J.Dairy Sci. 49(7):?96-799. HeertjeJ. 1993. Microstrucnn'al studies in fat research. Food Struct. 12:77-94. Hise,R. 1991. Overview of lowfat cheese market. Reduced Fat Cheese Conference. Center for Dairy Research. Madison WI. Holcomb,D.N., Pechak,D.G., ChakrabartLS. and OpsahLA. 1992. Visualizing textural changes in dairy products by image analysis. Food Technol. (1):122-127. JamesonG.W. 1990. Cheese with less fat. Aust. J. Dairy Tech.45(2):93-98. JohnsonJ.A.C., Etzel. M.R., ChenC.M, and Johnson,M.E. 1993. Accelerated ripening of reduced-fat cheese using attenuated bacterial cultures. II Chemical analyses and sensory attributes. J.Dairy Sci. 76(Suppl. 1):102 Johnson.MJ-Z. 1988. Part II-Cheese chemistry. In: Fundamentals of Dairy Chemistry 3rd ed. (N.F. Wong ed. pp. 634-654). Van Nostrand Reinhold, New York. Johnson,M.E. and Chen.C.M. 1991. Making quality reduced fat Cheddar cheese. Cheese Research and Technology Conference Proc. CDR Uinversity of Wisconsin-Madison pp.35-36. 109 Kalab,M. 1979. Microstructure of dairy foods. 1. Milk products based on protein. J. Dairy Sci. 62(8):1352-1364. KalabM. 1993. Practical aspects of electron microscopy in dairy research. Food Struct. 12:95-114. Kalab,M., Modler,H.W., Caric,M., and Milanovic,S. 1991. Structure, meltability and firmness of process cheese containing white cheese. Food Struct. 10:193-201. Kiely,L.J., Kindstedt,P.S., Hendricks,G.M., LevisJ.E., YunJJ. and Barbano,D.M. 1993. Age related changes in the microstructure of Mozzarella cheese. Food Struct.12:13-20. Kimber,A.M., Brooker.B.E., Hobbs,D.G. and PrenticeJH. 1974. Electron microscope studies of the development of structure in Cheddar cheese. J. Dairy Res. 41(3):389-396. Klomparens,K., Flegler,S., and HeckmanJ. 1992. Introduction to electron microscopy. Course Packet #137. Winter pp.1-2 Konstance,R.P. and Holsinger,V.H. 1992. Development of rheological test methods for cheese. Food Technol. 46(1):105-109. Kosikowski.F. 1982. Cheese and Fermented Milk Foods. 2nd ed. EV. Kosikowski & Associates,New York. Kumar,N. and SinghaLOP. 1992. Atherosclerosis: are dairy products safe? J. Soc. Dairy Tech. 45(2):49-52. LakhanLS. Gullett, EA., Ferrier,LK., and I-IilLA.R. 1991. Texture analysis of Cheddar cheese made from ultrafiltered milk. J. Food Qual. 14(3):257-271. Larmond.E.198 7. Laboratory Methods for the Sensory Evaluation of Food. Canadian Govemmet Publishing Centre, Ottawa. Lawrence,R.C., Creamer,L.K. and GillesJ. 1983. Texture development during cheese ripening. J. Dairy Sci.70(8):1748-1769 Lee,C.H., Imoto,E.M. and Rha.C. 1978. Evaluation of cheese texture. J. Food Sci. 43(5):1600-1605. 110 Lee,H.O., LuanH. and Gaut,D.G. 1992. Use of an ultrasonic technique to evaluate the rheological properties of cheese and dough J. Food Engineer. 16:127-150. LeRoux,G.D. and Abbott,C.W. 1962. South Africa's new lowfat cheese. Dairy Engineer.79:270—2 72. Levitt,A. 1992. IDFA unveils results of cheese industry study. Dairy Foods 93(13):38. Light,A., HeymannH. and Holt,D.L 1992 Hedonic responses to dairy productszEffects of fat levels, label information and risk perception. Food Technol. 64(7):54-S7. Lindsay,R. 1991. Flavor quality of reduced-fat cheese. Reduced Fat Cheese Conference. Center for Dairy Research, Madison MadsenFM., Clark Jr.,W.S. and Reinbold,G.W. 1970. Effect of fat content in Cheddar, Colby and Swiss on consumer preference. Food Technol. 24(9):1025-1028. Marshall,R.T. 1992. Standard Methods for the Examination of Dairy Products. 16 th ed. American Public Health Association, Washington DC McGregorJ.U. and White,C.H. 1990a. Optimizing ultrafiltration parameters for the development of a lowfat Cheddar cheese. J. Dairy Sci. 73(2):314-318. McGregorJ.U. and White,C.H. 1990b. Effect of enzyme treatment and ultrafiltration on the quality of lowf at Cheddar cheese. J. Dairy Sci. 73(3):571-578. Meilgaard,M., Civille,G.V. Carr,B.T. 1987. Sensory Evaluation Techniques. CRC Press, Boca Raton Metzger,1..E. and Mistry,V.V. 1993. Effect of homogenization on quality of reduced-f at Cheddar cheese. 1. Manufacture, composition and yield. J. Dairy Sci. 76(Suppl. 1):100. Mistry,V.V. and AndersonD.I.. 1993. Composition and microstructure of commercial full-fat and reduced-fat natural and procesed cheese. J. Dairy Sci. 76(Supp1.1):145. 111 Morr,C.V. and Richter, R1. 1988. Chemistry of Processingln: Fundamentals of Dairy Chemistry 3rd ed. (N.P. Wong ed. p.749) Van N ostrand Reinhold,New York. National Dairy Council. 1989. Cheese and its role in health Dairy Council Digest 60(1):1-3. O'DonnelLCD. 1993. Cutting the fat. Dairy Foods 94(7):61-64. OlsonN. 1991. A report from the conference on fat and cholesterol reduced foods. Dairy Field Junez34-3 5. Olson,N.F. and J ohnsonM.E. 1990. Light cheese products: characteristics and economics. Food Technol. 44(10):93-97. Prentice,J.H. 1992. Dairy Rheology. A Concise Guide. VCH Publishers, New York. Rosenberg,M., McCarthy,M.J. and KautenR. 1991. Magnetic resonance imaging of cheese structure. Food Struct. 10:185-192. RosenbergM. 1992. Cheese: the toughest lowfat challenge. Dairy Foods 93(5):44-48. ShermanP. 1989. The complexity of rheological evaluation of the firmness/hardness of solid foods. Ital. J. Food Sci. 3:21-30. Simard,R.E. 199 1. Evaluation of lowf at cheese problems. Cheese Research and Technology Conference Proc. University of Wisconsin-Madison pp.3 7-40. Stampanoni,C.R., and Noble,A.C. 1991a. The influence of fat, acid, and salt on the perception of selected taste and texture attributes of cheese analogs: a scalar study. J. Texture Stud. 22(3):367-380. StampanonLCR. and Noble,A.C. 1991b. The influence of fat, acid,and salt on the temporal perception of firmness, saltiness,and soumess of cheese analogs. J. Texture Stud. 22(3):381-392. Stanley,D.W. and Tung,M.A. 1976. Microstructure of food and its relation to texture. In: Rheology and Texture in Food Quality. (J.M. Deman, Voisey, V.F. Rasper, and D.W. Stanley. eds. pp 28-78). AVI Publishing, Connecticut. 112 Stanley,D.W. and Emmons, DB. 1977. Cheddar cheese made with bovine pepsin. II Texture, microstructure, composition relationships. Can.Inst.Food Sci. Technol. J. 10(2):78-84. Taneya,S., Izutsu,T., Kimura,T. and Shioya,T. 1992. Structure and rheology of string cheese. Food Struct. 11:61-71. Tunick,M.H., NolanEJ., ShiehJ.J., Basch,J.J., ThompsonMP. and Maleef,B.E. 1990. Cheddar and Cheshire rheology. J. Dairy Sci. 73(7):1671-1675. T1mick,M.H, Mackey,K.I., Smith,P.W. and Holsinger,V.H. 1991. Effects of composition and storage on the texture of Mozzarella cheese. Neth. Milk and Dairy J. 45(2):117-120. Tunick,M.H., MalinEI... ShiehJJ, Smith,P.W., Mackey,K.I.., and Holsinger,V.H. 1992. Comparison of low-fat and full-fat Mozzarella cheese prepared from homogenized milk. J. Dairy Sci. 75(Suppl.l):130. Tunick,MHH and NolanEJ. 1992. Rheology of cheese. In: Physical Chemistry of Food Processes vol.1 Fundamental Aspects. I.C. Baianu (eds. pps.273-297). Van Nostrand Reinhold, New York. Walstra,P. and Peleg,M. 1991. Rheological and fracture properties of cheese; General considerations. Bull. Int. Dairy Fed. 268:3-4. Zoon,P. 1991. The relation between instrumental and sensory evaluation of the rheological and fracture properties of cheese. Bull. Int. Dairy Fed. 268:30-35.