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I . . . - . _ i . . u. .. . I A . .0. ‘ I u — on O — . A . . I o .a _ . A. . . . . ‘ . A uh. - n . u .4 n . . . . . a .A I . A a O - . .I. .. s O . . v A .o I A A v i - . a . .. o . 2 . . . . u . . . . . .n . . .. o . i.. . . . .uv o i v . 5.3. . .A O . . . . . . .4: 0.54. , . _... .r...... v.3. .0 z. s ‘3... .. .‘ a, Ly. . \I .. .,¢ fr: 4. 9:. o. .l . . A. . . A . . , 0., . - .. ,. .4}: . ~ . :3... _ .f». ~.1?......(.'......l . g... .4..&.<...>.~_..... .3331... . .. minis}. 3.... 1 Ruin.” .oflyhrk .Lrwe a. L . I .: 3.. a, 9 . . A . . . . . . t F [A I? {E y> NY 0 HUAG & SB ABSTRACT THE EFFECT OF SEVERAL ANTIOXIDANTS ON THE STORAGE STABILITY OF DEHYDRATED POTATO FLAKES BY Shahram Dokhani Two types of potato (clone 709 and variety Russet Burbank) were processed to mash, treated with two pro- prietary antioxidants, Tenox 20 and Tenox 26, and dried on a small double-drum drier to produce dehydrated mashed potatoes. The small flakes were packed in nitrogen or air and stored at two different storage temperatures, 21 i 2 and 37 i 1°C., for 16-18 weeks. The fatty acid composition of the dried flakes was determined by gas liquid chromatography. Lipid oxidation and nonenzymatic browning were determined initially and during storage. Storage at 21 i 2°C. resulted in less deterioration of the dried flakes. Samples containing antioxidant were also superior to the controls. Atmospheric oxygen and high storage temperature accelerated autoxidation of the flakes. A notable browning was demonstrated in air or nitrogen packed Shahram Dokhani samples of clone 709, especially at 37 i 1°C. No brown- ing was observed in the flakes prepared from Russet Bur- bank and stored under these conditions. Antioxidants provided good initial stability in the air-packed Russet Burbank flakes up to six weeks' storage. The Clone 709 flakes were stable for ten weeks. However, at the con- clusion of the storage experiments, the air—packed clone 709 flakes had oxidized to the greatest extent. Tenox 26 improved the shelf-life of both types of potato flakes throughout 16-18 weeks of storage; samples containing Tenox 20 were much less stable. THE EFFECT OF SEVERAL ANTIOXIDANTS ON THE STORAGE STABILITY OF DEHYDRATED POTATO FLAKES BY Shahram Dokhani 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 1975 ACKNOWLEDGMENTS The author extends sincere appreciation to his major professor, Dr. Charles M. Stine, for his helpful suggestions and counsel throughout the course of this study and during preparation of this manuscript. Thanks and appreciation are extended to the guidance committee: Dr. C. L. Bedford, Department of Food Science and Human Nutrition, for his assistance to provide the raw material and processing; and Dr. H. A. Lillevik, Department of Biochemistry. The author also wishes to acknowledge those friends who made many helpful suggestions and gave up substantial amounts of their time to assist in the pilot plant processing. The author desires to acknowledge his parents for their constant support and stimulation and encourage- ment to pursue a higher degree of education. ii TABLE OF CONTENTS INTRODUCTION 0 O O O C O O O 0 LITERATURE REVIEW . . . . . . . Potato Flakes Processing (Dehydrated Mashed Potatoes). . . . . . . . . Nonenzymatic Browning . . . . . The Maillard Reaction. . . . The Ascorbic Acid Browning Mechanism. The Active Aldehyde Theory or "Caramelization" Autoxidation of Lipids . . . . . EXPERIMENTAL METHODS . . . . . . Raw Material . . . . . . . . Preparation of Additive Mixtures. . Processing Procedures . . . . . Analytical Procedures . . . . . Moisture Content . . . Quantitative Analysis of. Fatty Acids. TBA Value Determination . . . . 'Nonenzymatic Browning Measurements RESULTS AND DISCUSSION. . . . . . Raw Materials . . . . . . . . Additives Mixture. . . . . . . Processing . . . . . . . . . Moisture Content . . . . . . Fatty Acid Composition of Potato Samples The TBA Test . . . . . . . . Nonenzymatic Browning . . . . . SUMMARY AND CONCLUSIONS . . . . . BIBLIOGRAPHY O O O C O O O O 0 iii Page 11 15 15 15 17 19 l9 19 21 23 25 25 25 26 27 27 30 37 52 55 Table II. III. IV. VI. VII. VIII. IX. LIST OF TABLES THE COMPOSITION OF THE TENOX 20 AND 26 ANTIOXIDANTS . . . . . . . . . . MOISTURE CONTENT OF AIR-PACKED DEHYDRATED MASHED POTATOES DURING STORAGE AT 21 i 2 AND 37 : 1°C. 0 O O O O O C O . FATTY ACID COMPOSITION IN TOTAL MIXED FATTY ACIDS OF POTATO LIPIDS. . . . . . . TBA VALUES OF DEHYDRATED MASHED POTATOES (CLONE 709) DURING STORAGE, AIR- OR NITROGEN-PACK, AT 21 i 2 AND 37 i 1°C. . TBA VALUES OF DEHYDRATED MASHED POTATOES J (VAR. RUSSET BURBANK) DURING STORAGE, AIR- OR NITROGEN-PACK, AT 21 i 2 AND 37 i 1°C. 0 O O O O O O O O O O MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (CLONE 709) DURING STORAGE, AIR-PACK, 21 i 2 AND 37 i 1°C. BY THE HUNTER LAB COLOR DIF- FERENCE METER. . . . . . . . . . MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (CLONE 709) DURING STORAGE, NITROGEN-PACK, 21 i 2 AND 37 i 1°C. BY THE HUNTER LAB COLOR DIFFERENCE METER. . . . . . . . . MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (VAR. RUSSET BURBANK) DURING STORAGE, AIR-PACK, 21 i 2 AND 37 i 1°C. BY THE HUNTER LAB COLOR DIFFERENCE METER. . . . . . . MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (VAR. RUSSET BURBANK) DURING STORAGE, NITROGEN-PACK, 21 i 2 AND 37 i 1°C. BY THE HUNTER LAB COLOR DIFFERENCE METER. . . . . . . iv Page 16 28 29 31 32 39 4O 41 42 Table X. MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (CLONE 709) DURING STORAGE, AIR- OR NITROGEN-PACK, 21 i 2 AND 37 i 1°C. BY AGTRON 500 . . XI. MEASUREMENT OF NONENZYMATIC BROWNING OF DEHYDRATED MASHED POTATOES (VAR. RUSSET BURBANK) DURING STORAGE, AIR- OR NITROGEN-PACK 21 i 2 AND 37 i 1°C. BY AGTRON 500 . . . . . . . . . . Page 44 45 Figure II. III. IV. VI. LIST OF FIGURES TBA Values of Dehydrated Mashed Potatoes (Clone 709) During Storage, Air-Pack, 21 and 37°C. 0 O O O O O O O 0 TBA Values of Dehydrated Mashed Potatoes (Var. Russet Burbank) During Storage, Air-PaCk, 21 and 37°C. 0 o o o 0 Development of Nonenzymatic Browning in Dehydrated Mashed Potatoes (Clone 709) During Storage, Air-Pack, 21 and 37°C. Development of Nonenzymatic Browning in Dehydrated Mashed Potatoes (Clone 709) During Storage, Nitrogen-Pack, 21 and 37°C. 0 O O I O O O O O O O Browning of Clone 709 Dehydrated Potato Flakes after 15 Weeks' Storage at 21 and 37°C. 0 O O O O I O O O O O Browning of Russet Burbank Dehydrated Potato Flakes after 15 Weeks' Storage at 21 and 37°C. . . . . . . . . vi Page 34 35 46 47 49 50 INTRODUCTION Potatoes were first cultivated and processed by the natives of South America at about 200 A.D. Potatoes were dehydrated by being allowed to freeze at night, thawed during daylight, and squeezed by foot to extract the juice from the thawed potatoes (Talburt & Smith, 1967). Rapid changes have taken place in the production and processing of potatoes in the United States in the past 20 years. The increase in potato processing is illustrated by the following data: in 1956, 14% of all potatoes were processed for food use, while by 1966, this figure was increased to 41% (Smith, 1968). Potato flakes are defined as mashed potatoes which have been dehydrated on a drum drier by the process deve10ped at the Eastern Utilization Research Division of the Agricultural Research Service (Talburt & Smith, 1967). Browning and lipid oxidation deteriorations in mashed potato powder at certain storage conditions were reported by Burton (1945 & 1949). The development of brown color and off flavors have been ascribed to non- enzymatic browning. Off flavors also have been described as rancid, stale, or haylike; and these may be due to the autoxidation of unsaturated potato lipids. The purpose of this study is to determine the extent of lipid autoxidation and nonenzymatic browning in two varieties of dehydrated mashed potatoes containing antioxidants and stored at two temperatures in air or nitrogen. LITERATURE REVIEW Potato Flakes Processing (Dehydrated MaShed Potatoes) The use of a drum drier was suggested by investi- gators in 1940 to reduce the moisture content of mashed potatoes to a range between 40 and 65%, followed by a final drying step (Talburt & Smith, 1967). Below 45% moisture, damage to cells and cell integrity could occur; and above 50%, there was claimed to be no damage (Barker, 1941). Cording et a1. (1954) used a small double drum drier with six-inch diameter rolls to produce a dehydrated mashed potato with a bulk density of 7.0 lbs./cu. ft. for 1/2-inch flakes. They could be rehydrated to a mash of good texture, color, and flavor. At least two impor- tant conditions were required: first, an arrangement of potato cells to be put together in a dehydrated form which could permit the.rehydrating liquid to penetrate quickly; second, the maintenance of cell structure so that starch remained within the cell. By the use of a single drum drier with applicator rolls, the bulk density of l/2-inch flakes was raised to about 14.0 lbs./ cu. ft. (Cording et al., 1959). The relationship of drum speed and solids content of potato flakes has been studied on a single drum drier by Cording et a1. (1957). The use of a single drum drier rather than a double drum drier produced a denser flake, 14 to 23 lbs./cu. ft. Potatoes of higher solids content not more than 22% increased both the production rate and the sheet density. At solids content less than 22%, poor adherence to the roll and reduced output were noted. Increasing drum speed was demonstrated to yield flakes of higher moisture content. Selection of potato variety for processing was considered by Cording et a1. (1954). Potatoes such as Russet Burbank with high dry matter, which have a better texture or mealiness after cooking, are also desirable for drum drying (Iritani & Weller, 1973). Certain methods of washing, peeling, and slicing are necessary in potato flake processing. All of the peel and eyes must be removed from the potato before drying. The highest starch fraction of a potato lies directly below the skin, and excessive peel loss not only results in reduced yield but also damages the texture of reconstituted flakes (Cording et al., 1954). There are abrasion, lye, steam, brine, flame, and oil peeling methods; and among them, flame peeling losses are generally quite low. The abrasion method results in somewhat higher loss (Talburt & Smith, 1967). Cording et al. (1954 & 1956) observed that dilution of very high solids mashed potatoes, for example, from 24% to a range between 20 and 22% resulted in lower moisture content in the final dried flake. This was due to a better adherence to the drums and hence, higher heat transfer efficiency. Moreover, flakes from mash diluted to this range exhibited improved texture and tolerance to higher temperature of reconstitution. Dilution past this range caused increasing cell rupture and a pasty reconstituted mashed potato. The clearance between the drying rolls is very important in potato dehydration: a clearance below 0.007 inches causes more cell rupture and 0.013 inches gives an incompletely dried product in one stage. The 0.17-inch clearance was found to be satisfactory in the second stage, but did not result in a mash of suitable texture after reconstitution (Willard & Cording, 1957). To increase the storage stability of dehydrated mashed potatoes without damage to texture or flavor, it is desirable to reduce the moisture content of potato flakes as much as possible. Flakes can be dehydrated to 4% or lower moisture content on a double drum drier in one stage. A drum temperature of 318°F. at a drum speed of 3.0 r.p.m. was shown to be a desirable combi- nation (Cording et al., 1954). Eskew and Drazga (1962) processed a new dense product from flakes, called potato flakelets, with higher absorption of liquid on reconstitution and bulk densities of 48-52 1bs./cu. ft. The storage properties of potato flakelets were studied by Drazga et a1. (1964). They found no significant differences between nitrogen packs with or without antioxidants, BHA + BHT, but there was a notable difference between samples stored in air or nitrogen. Nonenzymatic Browning The browning phenomenon whose purely chemical nature is not involved with enzymatic catalysis is referred to as nonenzymatic. This complex series of. reactions may occur_during processing and storage of food products and causes deterioration of flavor and nutri-' tional value in foods (Braverman, 1963; Eskin, 1971). Water has a profound affect on the rate of nonenzymatic browning and causes acceleration of the reactions up to a suggested maximum in the range of intermediate moisture (foods, moisture content between 20 and 40% (Labuza et al., 1970). Three distinct mechanisms have thus far demon- strated in nonenzymatic browning (Braverman, 1963). 1. The Maillard Reaction: This is considered the most important type of nonenzymatic browning in foods (Reynolds, 1969). The reaction was first studied by the French chemist Maillard (1912), who observed the formation of dark brown products when simple amino acids were heated in the presence of certain carbohydrates (Ellis, 1959). Similar reactions were shown between aldehydes, ketones, and reducing sugars with amines, amino acids, peptides, and proteins (Hodge, 1953; Ellis, 1959; Reynolds, 1963 & 1965). The following steps are involved in the Maillard reaction (Braverman, 1963). (a) Amino-Carbonyl Reaction: a-amino groups of amino compounds are readily condensed with free carbonyl groups of carbohydrates to form a Shiff's base and then N-substituted glycosyl amine. Important reactions between amino compounds and reducing sugars have been discussed by Reynolds (1965). A slow combination has been shown between the open chain aldehydic form of sugars with sulfites to form hydrosulfonic acids and decreasing the rate of this reaction (Katchalsky, 1941; Braverman, 1963). Although the carbonyl-amino reaction can occur in both acidic and alkaline media, the rate is enhanced when PH is increased (Lea & Hannan, 1949; Underwood et al., 1959). A linear relationship has been demonstrated between the rate of reaction and temperature over the range of 0°C. to 90°C. for a casein-glucose system (Lea & Hannan, 1949). Reducing sugars are of major importance in the carbonyl- amino reaction (Eskin, 1971). (b) Amadori Rearrangement: this is a transition of an aldose to a ketose sugar derivative by isomerization of the N-substituted glycosylamine to the N-substituted l-amino-l-deoxy-Z-ketose (Hodge, 1955; Braverman, 1963). This reaction is acid catalyzed (Weygand, 1940). The products of this reaction are stable in a moist, acidic atmosPhere and undergo browning decomposition at alkaline PH (Hodge, 1953). Up to this point all the reactions are reversible and the products are colorless with no absorp- tion in near ultraviolet and up until this stage, it is called the induction period (Hodge, 1953; Ellis, 1959; Eskin, 1971). (c) Condensation Reactions: following the forma- tion of N-substituted-l-amino-l—deoxy-Z-ketose deriva- tives, brown pigments may be formed in any of the follow- ing distinct pathways (Hodge, 1967): (i) Methyl-a-dicarbonyl intermediates are formed. They either undergo a series of polymerization and condensations with amines to form nitrogeneous dark brown pigments or are converted to reductones following the formation of melanoidines (Hodge, 1953; Hodge et al., 1963; Simon & Heuback, 1965). (ii) D-glucosones and 3-deoxyhexasones are formed from the Amadori products after a series of hydrolyzing reactions. Then, these intermediates undergo polymerization and condensations with amines to nitro- geneous brown pigments, or formation of S-hydroxymethyl-Z- furfuraldehyde following the development of melanoidines (Anet, 1960 & 1964; Kato, 1962 & 1963). (iii) A Strecker degradation may occur, which is the oxidative degradation of an amino acid in the presence of a-dicarbonyls or other conjugated dicarbonyl compounds by releasing one molecule of carbon dioxide. This reaction is not directly responsible for pigment production, but is for odor and flavor (Eskin, 1971). Maillard (1912) concluded that the liberating CO2 from his browning system must have come from the carboxyl groups of the a-amino acid. Tracing methods have shown that 90 to 100% of the liberated CO2 originates from the amino acid moiety (Wolform et al., 1953). Some reactions could take place at this point, like an aldol conden- sation, aldehyde amino polymerization and the formation of heterocyclic substances, as pyrrols, pyridines, amidaloses, etc. (Braverman, 1963). 2. The Ascorbic Acid Browning Mechanism: this type of browning results from the decomposition of ascorbic acid to furfural, accompanied by the formation of carbon dioxide. Furfural is known to undergo polymeri- zation to brown pigments (Braverman, 1963). Tracing experiments have revealed that evolved carbon dioxide 10 originates from ascorbic acid degradation, and not from amino compounds (Lalikainen et al., 1958). The degradation products from ascorbic acid decomposition in orange and grapefruit powders have been identified by Tatum et a1. (1969). By using gas liquid chromatography and spectrosc0pic methods, they identified eight nonenzymatic browning products out of 15 isolated compounds. The type of compounds were furans, lactones, and 3-hydroxy-2-pyran. A notable change in the production of carbon dioxide to pigment formation was observed at 37°C. and 50°C. At lower temperature a linear relationship has been revealed between gas and pigment formation (Lalikai- nen et al., 1958). The rate of ascorbic acid degradation in fruit juices and concentrates is very much dependent on PH and the concentration of the juice. The rate of this browning is inversely proportional to the PH over a range of 2.0 to 3.5. The juices with higher PH, there- fore, are less subject to this type browning (Braverman, 1963). 3. The Active Aldehyde Theory or "Caramelization": this mechanism of nonenzymatic browning involves the dehydration of sugars in the absence of amino compounds, resulting in the formation of very active aldehydes such as hydroxy methyl furfural. This compound is capable not only of polymerization into brown products but also, 11 in the presence of amino compounds, can combine readily to form further brown pigments (Wolform et al., 1948; Braverman, 1963). Not only sugars, but also polysaccharides, poly- hydroxy carboxilic acid, reductones, a-dicarbonyl com- pounds and quinones will undergo this type of browning in the absence of amino compounds at a very high tempera- ture (Hodge, 1953). This reaction can take place either in acidic or alkaline conditions and is associated with changes in flavor. The uncontrolled reaction will produce unpleasant, burned, bitter products. The desirable products of this reaction, caramels, have extremely complex compositions (Eskin, 1971). Heyns and Klier (1968) studied on a whole group of mono-, di-, and polysaccharides for carameli- zation, and found that similar volatile compounds formed at high temperatures. Autoxidation of Lipids The process of the spontaneous reaction between atmospheric oxygen and many types of organic compounds is referred to as autoxidation. Rancidification or off flavor of many fats and fat-containing materials is due to autoxidation (Swern, 1962). Labuza (1971) has defined the rancidity of foods as the development of an off flavor that makes the food unacceptable on a consumer market level. It has been 12 well established that unsaturated fatty acid moieties are the major cause in the develOpment of most off flavors in foods. Autoxidation mechanisms of fatty acid materials had been studied over 100 years ago. One of the most important theories has involved the role of hydroperoxides and this theory has been reviewed in detail by Swern (1962).. The main consequence is the formation of free radicals having unpaired electrons from unsaturated fatty acids, or other olefinic compounds. A shift of double bonds on these products has been found to produce isomers (Farmer et al., 1943a). The free radicals combine readily with oxygen, bringing a rapid conversion to peroxides and hydrOperoxides. The hydroperoxides are the primary pro- ducts of autoxidation of food fats (Farmer et al., 1942, 1943b, 1946). These are very unstable and will break down to produce more free radicals and initiate a chain reaction (Labuza, 1971). Although the hydroperoxides are the major product of autoxidation, they are not responsible for off flavors (Lundberg, 1962). The rancid flavors and odors are due to many secondary substances such as aldehydes, ketones, and hydrocarbons. These are formed by peroxide decom- position through different reactions (Lundberg, 1962; Pokorny, 1971). 13 A chemical test which is widely used for measuring oxidative changes in foods unsaturated fatty acids is the 2-Thiobarbituric acid (TBA) test. Kohn and Liversedge (1944) observed a complex color when animal tissues were incubated aerobically with 2-Thiobarbituric acid. This impure red color was found to form from oxidation products of unsaturated fatty acids and 2-Thiobarbituric acid (Bernheim et al., 1947). The red color of the TBA reaction has been identi- fied as the condensation product of one molecule of malonaldehyde with two molecules of 2-Thiobarbituric acid (Sinnhuber & Yu, 1958a). Since malonaldehyde has been believed to be derived from some decomposition products of oxidized unsaturated fatty acids, the spectrophotometric measure- ment of TBA reaction is thought to be a quantitative measurement of fat oxidation (Tarladgis et al., 1960; Yu & Sinnhuber, 1957; Sinnhuber & Yu, 1958b). Interfering yellow and orange colors with absorp— tion maxima at 450 - 460 nm were found, associating with the red color of the TBA test in certain foods (Yu & Sinnhuber, 1962). These interfering colors had been attributed to the presence of sugars in digest (Biggs & Brayant, 1953). The separation of these colors from the red color of TBA reaction has been achieved by absorption 14 chromatography and elution from cellulose (Caldwell & Grogg, 1955; Yu & Sinnhuber, 1962). The relationship of autoxidative reactions by antioxidants was observed over 170 years ago>‘ Antioxi- dants are defined as "substances that in small quantities, are able to prevent or greatly retard the oxidation of easily oxidizable materials as fats" (Chipault, 1962). An active antioxidant reacts with free radicals to form products which cannot take part in autoxidation. The antioxidant molecule may react either with a free fatty acid radical or with the free hydroperoxide radical. In these reactions the free radicals are deactivated and free antioxidant radicals produced cannot undergo another autoxidation chain. They react with other free radicals or further oxidized to quinones (Everson et al., 1957). Phenolic antioxidants are very active, but also they may promote autoxidation under unfavorable conditions (Pokorny, 1971). The rate of these pro-oxidative reactions would be low, if the concentration of anti- oxidants in fat is between 0.001 and 0.02%. Commercial blends of antioxidants for use in food products to retard oxidation in oils, fats, and fat- containing foods are readily available. The proper use of such mixtures in approved foods may assist in extending the practical shelf-life of such food. EXPERIMENTAL METHODS Raw Material The potato samples used for this study, clone 709 and var. Russet Burbank, were obtained from the Department of Crops and Soil Science at Michigan State University. The potatoes were preconditioned at 65°F. and at 90-95% relative humidity for three weeks before processing. Preparation of Additive Mixtures The following procedure was used for preparing the additives mixture for 10 lbs. of mashed potatoes (Anon., 1963). To 90 ml. of distilled water heated to 150-155°F. was added 5.0 g. of Myverol distilled mono- glyceride type 18-07 (Eastman Chemical Company). The mixture was stirred continuously until the temperature dropped to 130°F. Quantitatively, 0.375 g. of either Tenox 20 or Tenox 26 antioxidants (Eastman Chemical Company) were added. Finally, 2.0 g. nonfat dry milk, 0.3 g. sodium sulfite, and 0.1 g. sodium bisulfite were added to the mixture. Stirring was continuous in all of the above steps. The composition of the Tenox anti- oxidants is shown in Table I. 15 16 TABLE I THE COMPOSITION OF THE TENOX 20 26 ANTIOXIDANTS Composition Tenox 20 Tenox 26 Mono-tertiary- butylhydroquinone (TBHQ) 20% 6% Butylated-hydroxy- toluen (BHT) -- 10% Butylated-hydroxy- anisole (BHA) -- 10% Citric acid 10% 6% Corn oil -- 28% Glycerolmono-oleate -- 28% Propylene Glycol 70% 12% 17 Processing Procedures The procedure used for processing the potatoes was essentially that of Pope (1969) with only slight modification. 1. The potatoes were washed and preheated at 170°F. for two minutes. They were transferred to 12-15% lye solution at 165-170°F., soaking with constant turning for 3 t 0.5 minutes. The peels and lye were washed off with a cold water Spray. After the tubers were trimmed, they were held for three minutes in 1,000 ppm. 802 solution prepared from sodium bisulfite. The potatoes were then cut into 3/8-inch slices with a Qualheim slicer machine Model 101 and washed with running water for 1-2 minutes. The slices were precooked for 20 minutes at 160- 165°F. and then cooled to 70-80°F. in a cold water bath. After removal, they were allowed to stand for 20 minutes. The slices were cooked in a retort at 212°F. and at atmospheric pressure for 30 minutes. Ricing was done using an electric Hobart Kitchen Aid Model 3-C with a coarse rotary grater attachment. 10. 18 The additive mixture and diluting water were added to each 10 lbs. mash in a Hobart Mixer Model A-200 and then thoroughly mixed. The con- trols contained every additive except Tenox antioxidants. The mash samples were dried on an Overton Machine Company Model P—36 double drum drier, equipped with drums 12 inches in diameter and 19 1/8 inches long. One drum was kept unheated and used as an applicator roll; the other was heated and served as the drying roll. All samples were dried with 75-80 psi steam pressure in the drums and a 3/16- inch nip between rolls. However, different drum speed and doctor-blade simulations were used: for clone 709 samples, the drum speed was 8.0 r.p.m. and 4 layers of dried sheets were taken for each simulation, whereas for Russet Burbank, 6.5 r.p.m. and 3 layers were used. The dried sheets were kept in moisture-proof plastic bags for 24-48 hours to equalize the moisture content and finally were comminuted to very small flakes with a comminuting machine Model D, using screen No. 2. 19 , . 11. Samples for nitrogen packing were canned(in 8 02. No. 1 cans. The air-packed samples were kept in 250 g. glass jars covered with aluminum foil. 12. The cans were evacuated in a vacuum chamber at 29.5 inches of mercury with a water aspirator and were double gassed with pure nitrogen. The samples were stored at two different temper- atures, 21 i 2 and 37 i 1°C. for 18 weeks, and samples were removed for appropriate analyses. Analytical Procedures 1. Moisture Content. A Mettler moisture balance, Model P160, with drying unit attachment, Model LPll, was used. Approximately 3.0 9. samples, accurated weighed, were dried to constant weight. The temperature regulator was adjusted on step No. 4. After turning on the heat source, the weight loss was recorded every minute until a constant weight was obtained. The percentage of moisture content was determined by the amount of moisture removed, divided by the initial weight of the sample and multi- plied by 100. 2. Quantitative Analysis of Fatty Acids. (a) Fat Extraction. Ten-gram samples of the initial controls were extracted overnight with petroleum ether on a soxhlet extractor. 20 (b) Preparation of Fatty Acid Methyl Esters. Fatty acid methyl esters were prepared by treatment of fat samples with borontrifluoride-methanol reagent (Morrison & Smith, 1964). Samples of potato lipids were evaporated to dryness under nitrogen. Borontrifluoride- methanol reagent was added in the proportion of one m1. reagent per 4-16 mg. of lipid to each tube. The tubes were heated for 2.0 minutes in a boiling water bath with a closed screw cap. After cooling, the esters were extracted by adding two volumes of pentane, then one volume of water. The tubes were shaken briefly and cen- trifuged until both layers were clear. (c) GLC Analysis. Methyl esters were chromato- graphed on a F & M Model 810 gas chromatograph equipped with a dual flame ionization detection system. A stain- less steel 300 x 0.31 cm. column was packed with 20% stabilized diethylene glycol succinate on 80/100 mesh acid washed chromosorb W., packing being accomplished using pressure and mechanical vibration. Methyl esters of the fatty acids of potatoes were analyzed by GLC using the following conditions: Injection port temperature, °C. . . . 270 Detection block temperature, °C. . . . 280 Hydrogen flow, ml/min. . . . . . . 63 Air flow, ml/min. . . . . . . . 500 Nitrogen carrier gas flow, ml/min. . . 25 21 Range setting . . . . . . . . . 103 Attenuation lower limit. . . . . . 4 Column temperature, °C. . . . . . 190 Esters were identified by a comparison of their retention time to a series of pure standard methyl esters (K & K Laboratories, Inc., Plain View, New York). Esters were quantitated by disk integration. Correction factors were derived as described by Bills et a1. (1963). The correction factors were based on the response of a given ester to that of the appropriate internal standard, laurate: c12’ Standard fatty acids were obtained from the Hormel Foundation, Austin, Minnesota. 3. TBA Value Determination. A modification of the 2-thiobarbituric acid test which had been suggested for baked products by Caldwell and Grogg (1955) was used to determine the extent of autoxidation. The test was run every two weeks for air-packed and every month for nitrogen-packed samples. (a) Reagents.’ (i) TBA reagent was prepared as described by Kohn and Liversedge (1944). A 1% TBA solution was obtained by dissolving 2.0 g. of TBA (Eastman Chemical Company) in 193 ml. distilled water and 6.6 ml. of 2N NaOH. The solution was placed in a hot water bath for several minutes and then 0.7 ml. of 4N NCL was added. 22 The complete reagent was made by mixing 2 parts of TBA solution with one part of citrate buffer. The citrate buffer was prepared by mixing 29.5 g. sodium citrate and 25‘m1. concentrated HCL in 200 ml. volumetric flask. The PH of the completed reagent was adjusted to 2.6. The TBA reagent was prepared freshly every week. (ii) Aqueous pyridine was prepared by diluting 100 ml. of fresh reagent quality pyridine to 500 ml. with distilled water. \ (b) Preparation of Adsorption Columns. The \, \ tips of 9 x 250 mm. glass columns were plugged with coarse porosity fritted disks and glass wool. They were filled with cellulose powder (Whatman Standard grade) to a packed height of 50 mm. above the plug and were packed by tapping and using 10-15 psi nitrogen pressure. (c) Procedures. Twenty grams of samples were extracted overnight with petroleum ether in a soxhlet apparatus equipped with 250 m1. flat bottom flask. The solvent was evaporated using steambath and under nitrogen. After cooling the flasks, 7.5 m1. dis- tilled water, 6.0 m1. TBA reagent, and 3.0 ml. 20% trichloroacetic acid were added to each flask. They were refluxed for exactly 10 minutes from the incidence of boiling, followed by removing and chilling in ice- water. Ten-m1. quantities of the aqueous layers were - transferred to centrifuge tubes and 3.0 m1. chloroform 23 added. The tubes were stoppered, shaken vigorously and centrifuged for about 2 minutes. Aliquots of 7.0 ml. were then transferred to the adsorption columns and forced through with 9.0 psi nitrogen pressure. Each column was washed successively with three l-ml. portions of distilled water. A lO-ml. volumetric flask was then placed under each column and the adsorbed red fraction eluted with aqueous pyridine. Exactly 10 m1. of each solution were collected. Using a Beckman DU-2 spectrophotometer, absorbence was read at 532 nm. against a reagent blank, carrying an extra flask without fat sample through all parts. 4. Nonenzymatic Browning Measurements. Browning of the samples was measured with a Hunter Lab Color Dif- ference Meter Model D-25 and Agtron-SOO. The procedures were followed as directed in the manual. The results were obtained every two weeks for air-packed and every month for nitrogen-packed samples. (a) The Hunter Lab Color Difference Meter. The instrument was standardized with a yellow tile, color standard No. 2814 with L = 83.0, a = -3.5, bL = 26.5 at L each trial. The samples were placed in the dishes and tapped gently to a depth that minimized light trans- mission. Two readings were taken on each sample and the average was computed. 24 (b) The Agtron-SOO. The instrument was cali- brated by standard Reflectance disks at each trial. The disk range, 63-90, was chosen and the calibration was done in so that these ranges were extended to between 0 and 100% spectral reflectance. The relative spectral reflectance was made directly after calibration in yellow color mode. RESULTS AND DISCUSS ION Raw Materials The two types of potatoes which were chosen for processing had different specific gravities. Pope (1969) has reported 1.089 specific gravity for Russet Burbank and 1.075 for clone 709. The correlation between specific gravity and solids content or reducing sugars of potatoes has been shown by the same author; for Russet Burbank, the average percentages of solid content and reducing sugars are 22.9 and 0.2; and for clone 709, 19.5 and 0.5. The reducing sugars in potatoes are increased when they are stored at low temperatures, such as 34-36°F. This is not desirable for processing and storage. The potatoes were preconditioned at 65°F. and 90-95% relative humidity because they had been stored before precon- ditioning at those low temperatures. Therefore, pre- conditioning for three weeks before processing was suitable to bring the reducing sugar content down to a level suitable for processing and storage stability. Additives Mixture Sodium sulfite and bisulfite were added to inhibit browning of the samples during processing. 25 26 Nonfat dry milk was added to improve whiteness. Myverol (type 18-07) emulsifier was incorporated into the mash to improve texture and also served as a convenient vehicle for adding the antioxidant mixtures. When antioxidants were used, either Tenox 20 or 26 (Table I) was added to the emulsifier and the mixture was blended into the mash. Processing Precooking of the potatoes produced better texture in the dehydrated mashed potatoes. The precooked potato slices were then cooled to reduce the "blue value," which is a measure of free starch (Talburt & Smith, 1967). The slices were maintained at room temperature for a constant period of time to equalize the temperature of the slices which is important in the subsequent cooking process. The time and temperature for cooking, 30 minutes at atmospheric pressure and 212°F., were sufficient to make the potatoes soft enough to rice. Talburt and Smith (1967) have reported that the cooking time for lower solids varieties should be longer than higher solids varieties: 30 minutes for high solid starchy types and 40 minutes for lower solid varieties. Employ- ment of higher times and temperatures may be detrimental to texture. Ricing was accomplished in a manner to minimize cell rupture. 27 After drying the samples from different batches, a slight.difference in initial color was observed due to varying effects of drying conditions: the batches from the clone 709 appeared to be darker than Russet Burbank. The Russet Burbank mash adhered to the drum better than the mash from clone 709. Moisture Content The moisture content of the samples is shown in Table II. The initial moisture content was between 6.6 and 7.9% which is somewhat high for optimal stability. As is shown in Table II, the Russet Burbank samples con- taining Tenox 26 (one separate batch) exhibited the lowest moisture content of the samples prepared. Commercial dehydrated mashed potatoes usually contain about 5-6% moisture. Changes occurring during storage were minimal. Fatty Acid Composition of Potato Samples The composition of the fatty acids in lipid material extracted from Russet Burbank and clone 709 is represented in Table III. The percentage of total mixed fatty acids in the lipid extract was 53.11% for Russet Burbank and 54.90% for clone 709. These values are comparable to those reported by Highlands et a1. (1954), for air and vacuum dried white potatoes. The data in Table III show that in clone 709 the lipid material 28 ’ h.m o.n ~.> m.m m.h v.b v.5 m.h ~.h N.h v.h m.h ma o.> w.n. v.n H.n v.5 m.h m.m o.n o.> v.h m.n m.h NH m.m N.h o.n H.h m.n N.b o.n m.w m.m N.h o.h ¢.> m m.m m.n 0.5 o.n m.> H.> H.n m.m m.m v.5 v.5 v.5 v m.m m.h m.> m.w m.n m.h 5.5 v.5 m.> h.h m.n m.h 0 mm om 0 mm ON 0 mm cm 0 mm cm 0 Amxmmzv B + B + B + B + B + B + B + B + OEHB .an H mm .oom H Hm .UoH H hm .UoN H Hm xcmnusm ummmsm mos OGOHU .UoH H mm 02¢ N H an 84 mwdmoam GZHMDD mmoadaom Qmmmdz Omadmflwmma omfiodmlde m0 BZMBZOU HMDBmHOZ HH m4m48 29 TABLE III FATTY ACID COMPOSITION IN TOTAL MIXED FATTY ACIDS OF POTATO LIPIDS . Percentage Fatty ACid Cogzgigion Russet Burbank 709 Myristic, Cl4:0 0.9038 2.02 3.00 Palmitic, C16:0 0.8343 13.32 17.50 Stearic, C18:0 1.1233 54.34 51.50 Oleic, C18:l 1.6200 6.21 -- Linoleic, C18:2 1.1664 12.66 17.00 Linolenic, C18:3 1.2654 6.46 11.00 30 contained little or no oleic acid. However, a higher percentage of unsaturated fatty acids was obtained in this clone than in Russet Burbank, and this might relate to storage stability of the dried flakes. Significantly higher levels of linoleic and linolenic acids were noted in clone 709. Both samples had higher content of saturated fatty acids than unsaturated, generally a cause for their being less subject to autoxidation than in any- other food materials containing a higher content of unsaturated fatty acids. The TBA Test The TBA values of the samples expressed as O.D. or absorbency, are presented in Tables IV and V. The higher the TBA value, the greater will be the degree of autoxidation. Sinnhuber and Yu (1958a) reported a main absorption maximum at 532-535 nm. and secondary maxima at 305 and 245 nm. for the pigments formed in the reaction mixture. As shown in both tables, the nitrogen-packed samples exhibited very little change in autoxidation during storage, while there was a notable change in air- packed samples. At the higher storage temperature of 37°C., the TBA values of both clone 709 and var. Russet Burbank indicated that extensive oxidation had occurred. 31 TABLE IV TBA VALUES OF DEHYDRATED MASHED POTATOES (CLONE 709) DURING STORAGE, AIR- OR NITROGEN-PACK, AT 21 i 2 AND 37 t 1°C. O.D. (Absorbency) at 532 nm. Samples in Air-Pack 21 i 2°C. 37 i 1°C. Time Con- + Tenox + Tenox Con- + Tenox + Tenox (Weeks) trol 20 26 trol 20 26 0 0.041 0.031 0.029 0.041 0.031 0.029 2 0.049 0.038 0.048 0.055 0.049 -0.053 4 0.063‘ 0.050 0.048 0.070 0.049 0.065 6 0.078 0.068 0.063 0.063 0.073 0.065 8 0.080 0.070, 0.070 0.086 0.075 0.075 10 0.080 0.060 0.058 0.086 0.065 0.055 12 0.096 0.065 0.080 0.107 0.107 0.091 14 0.088 0.075 0.075 0.102 0.116 0.091 16 0.096 0.086 0.091 0.116 0.113 0.107 Samples in Nitrogen-Pack 2 _0.043 0.033 0.030 0.045 0.035 0.038 6 0.045 0.033 0.036 0.044 0.036 0.036 10 0.043 0.031 0:036 0.050 0.036 ~ 0.038 14 0.045 0.033 0.038 0.050 0.050 0.041 18 0.070 0.060 0.068 0.080 0.065 0.083 32 TABLE V TBA VALUES OF DEHYDRATED MASHED POTATOES (VAR. RUSSET BURBANK) DURING STORAGE, AIR- OR NITROGEN-PACK, AT 21 i 2 AND 37 i 1°C. O.D. at 532 nm. Samples in Air-Pack 21 i 2°C. 37 t 1°C. Time Con- + Tenox + Tenox Con- + Tenox + Tenox (Weeks) trol 20 26 trol 20 26 0 0.036 0.031 0.029 0.036 0.031 0.029 2 0.043 0.043 0.040 0.050 0.048 0.043 4 0.045 0.050 0.045 0.050 0.048 0.043 6 0.036 0.033 0.043 0.053 0.033 0.036 8 0.060 0.055 0.053 0.070 0.060 0.065 10 0.080 0.070 0.065 0.091 0.065 0.060 12 0.091 0.080 0.075 0.088 0.078 0.077 14 0.096 0.080 0.075 0.107 0.110 0.100 16 0.096 0.091 0.080 0.102 0.110 0.100 Samples in Nitrogen-Pack 2 0.041 0.038 0.036 0.038 0.044 0.038 6 0.039 0.036 0.030 0.041 0.044 0.041 10 0.041 0.036 0.045 0.060 0.045 0.045 14 0.075 0.073 0.065 0.086 0.080 0.080 18 0.070 0.065 0.070 0.096 0.099 0.083 33 Samples containing Tenox 20 and 26 antioxidants had good initial stability. These samples at room temperature were stabilized throughout the storage period, having lower TBA values than did the controls. The data in Table IV show that after 14 weeks in storage, the nitrogen-pack samples underwent very little change in TBA values compared to initial samples. After 18 weeks' storage, there was a slight increase in the TBA values of the samples--especially at 37°C. The air-packed samples showed appreciable increases in TBA values after 10 weeks of storage and the samples contain- ing Tenox 20 antioxidant at 37°C. eventually were oxi- dized the same as the control. After longer storage these samples showed a slight greater rate of oxidation than controls. Tenox 26 improved the storage stability of all samples through 12 weeks' storage; after longer storage all of the samples held at 37°C. showed similar level of oxidation throughout the storage. The rapid increase in autoxidation of clone 709 samples is shown clearly in Figure I. It is seen that the TBA values of samples containing antioxidants are below the control values, except for Tenox 20 samples after the 10th week of storage. Of the two varieties processed, clone 709 flakes showed higher initial TBA values (Figures I and II). 34 O.|OO' i ' [I E ' . .3 0075- -’ .‘I ‘ r0 ‘ . I I; f '0 \\. I}; ./ t? I)! ‘9‘3 ii‘f/ o \ . 0’ )V’ 3 21:2 0 371:0 0050- Control ——a ——o t ./ +Tenox 20 --—--o —-—.-a [/4 +Tenox 26 -----<> --——---0 / r 0.025 - - - 4 ‘ 1 - - O 4 8 l2 l6 TlME(weeks) Fig. I. TBA Values of Dehydrated Mashed Potatoes (Clone 709) During Storage, Air-Pack, 21 and 37°C. 35 O.l 00 ’ 9—«0 O.D. at 532 nm - ' --J‘ In (DKCY755 /3ég:—-m ‘0’ b. \ ~~ . kit-u...» D-w/kfl'xo 50.0' 25.0- RELATIVE SPECTRAL REFLECTANCE A 4 o A - . L 4 L ' 0 4 8 l2 )6 TIME (weeks) Fig. III. Development of Nonenzymatic Browning in Dehydrated Mashed Potatoes (Clone 709) During Storage, Air-Pack, 21 and 37°C. 47 2lt2 C 371t| C Control 5 a +Tenox 20 --—-—-o _.._._.a 75.0 > + Te nox 26 --—-——--o —---—-o LIJ {iv---- ‘0- ----- o~~___‘°___ ___° 9 ~.-_-__.__-__ 4 ‘\\ ’ ’-‘0~.\. m\>‘ A. .- \V “O—-' '\\ - _"0 t3 V>~~~~~-. “K\\ _.’ o .\ \ . \\\ b 50. O I. ‘\ 0 \O m . \ z: \- 0: ° \°-— -°\ _ ts '\ E \‘\ a) ‘o g 25.0 ’ . : .< _l w 0 m 0 l I 1 1 l 1 o 2 6 lo ‘ :3 l8 TIME (weeks) Fig. IV. Development of Nonenzymatic Browning in Dehydrated Mashed Potatoes (Clone 709) During Storage, Nitrogen-Pack, 21 and 37°C. 48 temperature. The browning in nitrogen-packed samples was virtually identical to those packed in air. In Table XI, a very negligible difference in the relative spectral reflections of the samples from initial until the end of storage can be seen. No color change occurred in the samples of Russet Burbank. There was, however, an unusual change of values in samples containing Tenox 20 and stored at 37°C. The instrument indicated that these samples were somewhat darker at the end of storage. The relative spectral values decreased 12.5 units during 16 weeks of storage in air-pack, 37°C. samples containing Tenox 20. Under the same condition, samples containing Tenox 26 decreased by two units and controls by 6.5 units. In Figures III and IV the extent of browning is shown in dry samples prepared from clone 709. Air- and gas-packed samples show almost identical level of brown- ing. The terminal points of nitrogen samples are somewhat lower than those of air-packed because of the longer storage period for nitrogen packs (two weeks). This means that the browning was still increasing after 16 weeks, at which time experiments on the air-packed samples were terminated. Two photographs taken after 15 weeks of storage (see Figures V and VI) show the notable browning obtained in clone 709 samples (Figure V). No color change is 49 Fig. V. Browning of Clone 709 Dehydrated Potato Flakes after 15 Weeks' Storage at 21 and 37°C. 50 Fig. VI. Browning of Russet Burbank Dehydrated Potato Flakes after 15 Weeks' Storage at 21 and 37°C. 51 observed in Russet Burbank samples (Figure VI). The samples of clone 709, air- or nitrogen-pack, at 37°C. exhibit a darker color than the same samples stored at 21°C. (Figure VI). Also, more browning is shown in Tenox 20 samples than Tenox 26 at higher temperature of storage. SUMMARY AND CONCLUS IONS Russet Burbank and clone 709 potatoes were‘pro- cessed into drum dried flakes. Two commercial antioxi- dants, Tenox 20 and Tenox 26, were incorporated into portions of each lot to evaluate their effectiveness in extending shelf-life. The ground flakes were packed either in air or nitrogen gas and examined for evidence of browning and lipid autoxidation during 16-18 weeks of storage. GLC analysis of the two potato samples showed a higher percentage of unsaturated fatty acids in clone 709 than Russet Burbank; the former variety also oxidized to a greater extent during storage. The initial moisture contents of the samples ranged between 6.6-7.9%. This somewhat excessive moisture may reflect on the stability of the dried flakes. This range of moisture remained almost constant in the samples during storage, especially for gas-packed samples. Thiobarbituric acid values (TBA) were useful in determining the relative extent of autoxidation in the samples. Interfering pigments were separated 52 53 chromatographically before measuring the absorbence of the TBA complex associated with oxidized lipids. Two different instruments used for measurement of browning gave similar results. The Hunter Lab is more accurate than the Agtron 500 since the actual color of the samples is divided into three different vectors; this permits more precise evaluation of browning. The Agtron 500 shows the direct reflectance of the samples. The higher temperature of the storage markedly increased the rate of lipid oxidation and nonenzymatic browning. This was clearly shown in the air- or nitrogen-packed samples of clone 709. None of the Russet Burbank potato samples developed appreciable color throughout Storage. Tenox 26 stabilized the samples better than Tenox 20. The latter antioxidant stabilized both varieties at room temperature, while Tenox 26 was effective at 21 and 37°C. Samples of clone 709 con- taining Tenox 20 at 37°C. also appeared to brown to a greater extent than the samples containing Tenox 26. There appeared to be little if any benefit gained from use of antioxidants in nitrogen-packed samples, since these samples showed an excellent shelf- life, especially at room temperature. 54 Russet Burbank potatoes exhibited better texture, color, and flavor during cooking, processing, and storage than clone 709. BIBLIOGRAPHY BIBLIOGRAPHY Anet, E. F. L. T. 1960. Degradation of Carbohydrates. I. Isolation of 3-deoxyhexosones. Aust. J. Chem. M g, 396. Anet, E. F. L. T. 1964. 3-deoxyglucosuloses (3-deoxy- glycosones) and the Degradation of Carbohydrates. ; Adv. in Carbohydrate Chem. 19, 181. Anonymous, 1963. Myverol Distilled Monoglycerides Type 18-00 and 18-07 in Dehydrated Potatoes. 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