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FOOD SCIENCE 8 HUMAN degree in NUTRITION gawk /%Wk Major professor 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES \— RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. DO NOT CIRCULAT!’ ROOM USE or“ EVALUATION OF CERTAIN NUTRITIONAL AND SENSORY QUALITIES 0F FRENCH FRIED POTATOES By Ioannis Evangelou 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 1983 ABSTRACT EVALUATION OF CERTAIN NUTRITIONAL AND SENSORY QUALITIES 0F FRENCH FRIED POTATOES By Ioannis Evangelou Two Greek potato cultivars were par-fried, frozen, and finish-fried with 7 different frying oil combinations. Moisture, ash, fat, Kjeldahl N, non-protein N, free amino acids and ascorbic acid were determined in raw, par-fried and finish-fried potatoes. Individual sugars were assayed in raw potatoes. Total and free fatty acids were deter- mined in olive oil and kernel olive oil. These oils, along with cottonseed oil, corn oil, sunflower oil, and palm oil were used in the trials. Par-frying and finish-frying resulted in the following respective losses: moisture 5% and 28%; ash 22% and 55%; Kjeldahl N 2l% and 31%; non—protein N 4l% and 62%; free amino acids 42% and 74%; and ascorbic acid 39% and 49%. Non-protein N losses were approximately double those in total Kjeldahl N. Both cultivars contained less than 1% reducing sugars, dry basis. The fat content was: raw potatoes O.l%; par-fried 4%; and finish-fried ll%. A sensory panel evaluation of the finish-fried potatoes indicated that par-frying with kernel olive oil, and finish-frying with olive oil results in the best product. DEDICATION to my family ii ACKNOWLEDGMENTS The author wishes to express his sincere appreciation to Dr. Pericles Markakis for his guidance during the course of this study and his advice in the preparation of this manuscript. D Appreciation and thanks are also extended to the guidance committee, Drs. R.C. Herner, C.M. Stine, and M.A. Uebersax, for their help in reviewing the manuscript. The author especially thanks Dr. J.I. Gray and Miss Susan Cuppett for the laboratory facilities in fatty acid analysis, and Ms. Doris H. Bauer of the Biochemistry Department for the amino acid analysis. The author feels deeply grateful to the Greek Govern- ment, for the NATO fellowship granted to him, for his studies at Michigan State University. Acknowledgments are extended to Aristotelian Univer- sity of Thessaloniki, Greece, to Greek Institute of Cereals, and the Cooperative Food Industry in Xanthi, Greece for the offered facilities to complete this study. The author expresses his appreciation and gratitude to his friend Stratos Kiranas for his moral support and the offered laboratory facilities in the Institute of Food Technology in Thesaloniki. iii Appreciation is also extended to Nick Leventis and Michael Kondilis, graduate students in the Chemistry Department, M.S.U., and Dr. Nayini Reddy, post doc in Biochemistry, M.S.U., for their sincere friendship. Finally, the author is indebted tohis parents, Evangelos and Sophia, for their constant encouragement and support during the course of this study, iv TABLE OF CONTENTS LIST OF TABLES. LIST OF FIGURES INTRODUCTION. LITERATURE REVIEW A. French Fries Commercial Processing. 8. Nutrient Composition. . Specific Gravity- -Dry Matter Mineral Content . . Fat Content Sugars. Nitrogen. Ascorbic Acid C. Frying Fats MATERIALS AND METHODS A. Potato Processing . 8. Analytical Methods. . Moisture Content Determination. Ash Content Determination Fat Content Determination Sugar Analysis by HPLC. Total Nitrogen Determination. . Non-Protein Nitrogen Determination. Free Amino Acid Determination Total Ascorbic Acid Determination C. Fatty Acid Analysis of Frying Oils. Total Fatty Acid Composition. Free Fatty Acid Determination Free Fatty Acid Composition . Total Free Fatty Acid Content D. Frying Quality of Oils. . . RESULTS AND DISCUSSION. A. Nutrient Analysis Specific Gravitlery Matter- Moisture. Ash Content Page NOQJCJCDNO‘IONQ) (A) NN—" Fat Content. Sugar Content. Nitrogen Content Ascorbic Acid Content: B. Frying Fats. SUMMARY. BIBLIOGRAPHY vi Table 10 11 LIST OF TABLES Proximate analysis of potatoes (wet basis) (Kroner et al., 1950; Watt et al., 1963). Nitrogen containing compounds (crude protein) of the potato (Schreiber, 1961) Relationship between sp. gravity (G) and dry matter (DM) in cv. Jaerla and cv. Spunta. Moisture content in raw, par-fried and finish- fried potatoes (% with fat, % fat-free, and % retention . . . . . . . . . . . . . . . Ash content in raw, par-fried and finish-fried potatoes (% wet and fat-free dry basis, and as % retention). . . . . . . . . . . . Fat content in raw, par-fried and finish-fried potatoes (% wet and fat—free dry basis) Sugar content in cv. Jaerla and cv. Spunta potatoes stored at 4 5° C for 2 months and conditioned for 15 days at 14°C (% wet and dry basis . . . . . . . . . . . . . . . Crude protein content in raw, par-fried and finish-fried potatoes (Kjeldahl N % x 6.25, % wet and fat-free dry basis, and % retention). Total nitrogen (Kjeldahl) and non-protein nitrogen (NPN) contents in Jaerla potatoes (in mg N/lOO 9 potatoes, wet, and fat- free dry basis and as % retention) . Total nitrogen (Kjeldahl) and non-protein nitrogen (NPN) contents in Spunta potatoes (in mg N/lOO 9 potatoes, wet, and fat- free dry basis and as % retention) . . Free amino acid (FAA) content in raw, par-fried and finish- fried Jaerla potatoes (in mg FAA/ 100 g potatoes, fat- free dry basis, and as % retention). . . . . . vii Page 15 15 42 42 44 44 49 51 52 53 55 Table 12 13 14 15 16 17 18 19 20 21 22 23 Free amino acid (FAA) content in raw, par-fried and finish- fried Spunta potatoes (in mg FAA/ 100 9 potatoes, fat- free dry basis, and as % retention). . . . . . Percentage free amino acid distribution in raw and processed potatoes (cv. Jaerla and cv. Spunta) . Total ascorbic acid (AA) content in raw, par- fried and finish- fried potatoes (in mg AA/ 100 9 potatoes, wet, and fat- free dry basis, and as % retention) . . . Percentage composition of raw potatoes (peeled2 stored at 4.5°C for 2 months and conditioned at 14°C for 15 days (wet and dry basis). Percentage composition of French fries commer- cially prepared from tubers, stored at 4.5°C for 2 months, and conditioned at 14°C for 15 days (wet, dry-with-fat and dry-without-fat basis) . . . . . . . . . . . . . . . . . Percentage distribution of fatty acids in Greek kernel olive oil. . . . . . . . . . . Percentage distribution of fatty acids in Greek olive oil . . . . . . . . . . . . . . . Percentage distribution of free fatty acids (FFA) in Greek kernel olive oil (total FFA content as oleic is 0.4%) . . . . . Percentage distribution of free fatty acids (FFA) in Greek olive oil (total FFA content as oleic is 0.7% . . . . . . . . . . . . . Sensory evaluation of French fries prepared with different frying oils (averages of six scores by six panelists) Kramer's method for determining significance of differences in frying oils, from rank sums. Kramer' 5 Rank Sum Method. Rank totals for significance - any treatment. . viii Page 56 57 59 61 63 64 65 67 68 69 70 72 LIST OF FIGURES Figure 1 Unit operations in the production of French fries. . . . . . . . . . . Structural features of potato tuber sections Flow diagram of sugar analysis Elution of fructose, glucose and sucrose from a potato extract (Figure 3) through an HPLC column (Waters C-l ), with acetonitrile-water, 80:20 v/v. . . . . . . . Reference curves for the quantitative estima- tion of fructose, glucose and sucrose in raw potatoes by HPLC (Figure 4). . . ix Page 14 3O 46 47 INTRODUCTION Historians mniarcheologists trace the cultivation of potato (Solanum tuberosum), to at least 200 A.D. on the Andean mountains. Potato, with a total yearly production in excess of 10 billion bushels, is one of the major food crops in the world. The potato is one of the few crops that is capable of nourishing large populations with energy, high quality protein, minerals and vitamins. A hectare (2.47 acres) produces 226 kg of potato protein, a yield greater than that in wheat grain protein (200 kg/ha) or rice grain protein (168 kg/ha) (FAO, 1972). In addition to their good nutritional quality, potatoes can be abundantly, quickly and economically produced in temperate zones. Today, there is a significant trend of increasing the per capita consumption of potatoes, worldwide, as a result of the rapid increases in processing and the greater availability of a larger variety of processed products. Frozen potato products are the fastest growing category of processed potatoes, accounting for almost one-half of all processed potatoes. In the U.S. per capita consump- tion of processed potatoes increased from 4.1 kg in 1940, to 51.5 kg in 1956, and reached 147.5 kg in 1972. Commercial production of frozen French fries has increased about 800 times since 1947. Since 1970, frozen potato products have constituted 45 to 48 percent of all processed potatoes, or nearly 1/4 of the food use of potatoes in the United States (AFFI, 1969-1972). The frozen French fry industry provides a convenient product for institutional and home use, which is dependable regardless of the season of the year. The objective of this study was a) to investigate the nutrient changes in two potato cultivars during the commer- cial processing of frozen French fries, and b) to conduct a sensory evaluation of the finish-fried potatoes prepared with different frying oil combinations. LITERATURE REVIEW A. French Fries Commercial Processing The French fry commercial operations can be divided into the preparative and the preservative ones (Talburt and Smith, 1975), as shown in Figure 1. The preparative group includes the following: Storage-Conditioning Potato tubers, immediately after harvest, are stored first at 14°C for 10 days, and then they are transferred to about 4°C, with 92-94% RH and treated with sprouting inhibi- tors. Before processing they are conditioned, by transfer- ring them to 14°C for 2-3 weeks to decrease the reducing sugar content. Washing-Peeling Unpeeled tubers are washed and then dipped in a 10-20% NaOH solution at 88°C for 60-90 sec., followed by removal of peel with high pressure streams of water, or by exposure of the tubers to infrared radiation. Trimming;Sorting-Cutting Peeled potatoes are conveyed over trimming and inspec- tion belts, and then to the strip cutters where they are PREPARATIVE OPERATIONS STORAGE/CONDITIONING (4.5°C, 92-94% RH/140C for 2-3 weeks) 1 WASH/PEEL (lo-20% NaOH Dip, 88°C, 60-90 sec) 1 TRIM/SORT/CUT (l.3x1.3x9.6 cm) 1r BLANCH (80°C, 8 min) + PAR-FRY . (175°C, 60 sec) 1 DEFAT/COOL (vibration system) PRESERVATIVE OPERATIONS FREEZE (I.Q.F. system, -30°C, 5-10 min) 1r PACK/STORE (-l8°C) + FINISH-FRY (182°C, 2 min) 1 Figure 1. Unit operations in the production of French fries. cut into strips 1/2 or 3/8 in. square. Hot Water Blanching Strips are usually blanched in water of 80°C, for 8 min. Blanching has several advantages including color improvement of the fried product, by decreasing the reducing sugar on the surface, and inactivating undesirable enzyme systems, improved texture of the final product and reduction of fat absorption. The disadvantage of blanching is the high nutrient losses, due to leaching (Dry blanching prevents these losses.) Par Frying Potato strips are fried with various frying fats, at 175°C for 60 sec. Par-frying removes any surface water adhering to the strips, so they will not stick together or onto conveyors when placed into the freezing tunnel. It also completes the enzyme inactivation. Defatting-Cooling Product passes over a vibrating screen, in order to drain off excess fat. Cooling reduces the load on the freezer. The preservative operations include the following: Freezing The I.Q.F. (Individual Quick Freezing) is a popular system by which strips are conveyed on perforated belts and frozen in a chamber of -30°C for 5-10 min. Packing-Storage The product is automatically packed in either cartons or poly bags and stored at -180C. Finish-Frying French fries are fried intact at 180°C for 2 min. B. Nutrient Composition Specific Gravity - Dry Matter The specific gravity and the total solids content of the potato tuber are very important criteria in selecting varieties, especially for the crisp product industry. Varieties have significant differences in specific gravity level, which is genetically controlled. Differences exist within the same variety, due to cultural and environmental conditions such as date of planting, soil type, soil moisture and temperature, location, type and amount of fertilizers, plant emergence and harvesting, pesticides, vine killing, etc (Findlen and Glaves, 1964). The earlier the planting, the longer the growing season, the higher the specific gravity. High soil moisture, excessive nitro- gen applications, high temperatures and earlier harvesting decrease specific gravity. Harvest temperatures below 8°C reduce specific gravity (Findlen and Glaves, 1964). Specific gravity affects the yield and oil content of crisps and to some extent it also influences their color. The higher the specific gravity the lower the oil accumu- lation in the crisps. Oily crisps are undesirable as well as costly to producg. Correlation coefficients for crisp yield and specific gravity have been reported in the literature (Findlen, 1964). Relationships between specific gravity, dry matter (DM) and starch content of the tuber have also been reported (Simmonds, 1977; Vakis, 1978; Orphanos, 1980). Specific gravity is determined in several ways. The potato hydro- meter is most widely used for potato sp. gravity determi- nation, as it is rapid, accurate and inexpensive method. Simmonds (1974) compared the DM content of potatoes from different countries and when allowance was made for a strong relation between maturity and DM, the following sequence, in ascending order of DM, was found: USA < Germany < Britain < Netherlands Mineral Content Potatoes provide practically all essential dietary factors including minerals (USDA, 1982). True et a1. (1978, 1979) found that fresh potatoes contribute significantly to the U.S. Recommended Dietary Allowance. The factors which affect the mineral content of potatoes are: soil type, mineral content of the soil and potato variety (Augustin, 1975). In addition, the outer cortical region has higher mineral concentration than the pith region within the same tuber. Cooking has a negligible effect on mineral content of potato flesh, regardless of the cooking methods (True et al., 1979; Mondy et al., 1983) and potato peel contains signifi- cantly higher amounts of ash (16% of the whole tuber ash) than potato flesh (Augustin et al., 1979). Fat Content Surveys of the literature (Sayre et al., 1978; Lee et al., 1979) indicate that the average fat content (ether- extractible matter) of the potato is around 0.1 percent on a wet basis, with a range of 0.02 to 0.2 percent. Early potatoes contain more lipids than late varieties. The lipid concentration of outer tuber layers is greater than of inner ones (Talburt and Smith, 1975). The fatty acids present consist of about 40% linoleic, 30% linolenic, 5% oleic, and 25% saturated acids, mainly as palmitic acid (Lee et al., 1979). Sugars The sugars in the potato tuber are glucose, fructose (reducing sugars) and sucrose, as well as traces of maltose, xylose, sugar phosphates, raffinose, melibiose, heptulose and melezitose (Habib and Brown, 1957; Schwimmer et al., 1954). The reducing power of potato extracts is not solely attributable to glucose and fructose. Chromatographic results indicate that there are several non-sugar components present which could conceivably react as reducing sugars. These include tyrosine, ascorbic acid, cysteine, and glutathione (Schwimmer et al., 1954). The sugar content of potatoes varies from only traces to as much as 10 percent (dry weight). The two main factors which influence the sugar content of potatoes during post- harvest storage are variety and temperature. Also sugar content is affected during the storage by the maturity stage and pre-storage conditions (Sowokinos, 1978). Potatoes high in sugag taste sweet and have a poor texture after cooking. The poor texture is probably related to the Jew starch content associated with high sugar content. Isherwood (1973) found that a starch-sugar interconversion occurs by transferring potatoes stored at 10°C to 2°C and reverse, as the following schematic pathways show: Transfer from 10°C to 2°C Starch :Glucose-l-P etelucose-6-P ATP-rUTPl UTP-Glucose Fructose-6-P LA I Sucrosee——-Suérose-6-P Pressey and Shaw (1966) found that the rapid conversion of starch to hexoses, at low temperatures, occurs due to a 10 rapid increase in invertase enzyme activity. Transfer from 2°C to 10°C ATP ——»Glucose aGlucose-O-P Sucrose—————A ADP: ATP [‘ LgFructose———————+Fructose-6-P I ; ATP ADP—Glucose: ‘Glucose-l-P Starch In the manufacture of French fries, potato chips and dehydrated potatoes, the sugar content is closely related to the color produced during the processing procedure. The source of the yellow to brown color of these products is attributed to so—called Browning Reactions which are illustrated in the following Scheme: Tyrosinase Enzymatic (Tyrosine «—:Melanin) Browning Caramelization (sucrose polymerization) Reactions Maillard (Carbonyl-Amine reaction) reaction Non-Enzymatic——Ascorbic acid reaction (carbohyl- amine reaction) Metal-phenol (phenolic compound-metal) reaction Fat deterioration Dicarboxylic acid - sugar reaction It has become increasingly clear in the last 20 years that the controlling factor in determining the amount of 11 browning is the reducing rather than the total sugar content. This suggests that the main mechanism in browning is one involving the Maillard reaction between the carbonyl groups of reducing sugars and the amino groups of the free amino acids and, perhaps to a lesser degree, of the proteins of the potato (Schwimmer et al., 1957; Hoover and Xander, 1961). As a rule, potatoes containing more than 2.0% reducing sugars on a dry weight basis are considered to be unaccep- table for processing. The correlation between reducing sugar content and browning tendency although generally good, is by no means perfect. This suggests that the already mentioned browning reactions,other than Maillard reaction,may be involved in the browning of processed potato products (Wisler, 1968). In order to secure suitable raw material of low browning tendency, it is general practice to use potatoes which are poor sugar formers and to process potatoes in storage at periods during which they are at low sugar level and have notsprouted (Ewing et al., 1981). The extension of storage life of potato tubers up to 10 months can be accomplished by maintaining optimum storage conditions such as temperature 3-4°C, relative humidity 85-95 percent, efficient cooling, drying and heating facili- ties. The excessive sugar formation can be reduced by conditioning cold-storage tubers for 2 to 3 weeks at room 12 temperature, prior to processing; blanching of potatoes prior to frying decreases the reducing sugar content on the surface. Prediction of the storage potential of tubers can be made based on their sucrose content at harvest time (Ewing et al., 1981; Wilson et al., 1981; Rastovski, 1982; Califano and Calvelo, 1983). Individual determination of glucose, fructose, and sucrose, the major sugars in potatoes, is becoming essential as more studies are being conducted on genetic and bio- chemical mechanisms of carbohydrate formation and degrada- tion in potato tubers. Previous methods of determination include colorimetric procedures which do not distinguish between the monosaccharides, glucose and fructose, directly. Della Monica et a1. (1974) quantified fructose by subtract- ing glucose,determined enzymatically from total reducing sugars. Sucrose was determined as the increase in glucose content,after acid hydrolysis of sucrose. Chromatographic procedures include gas chromatography which determines the individual sugars, but requires a time-consuming derivatization step (Shaw, 1969). Currently High Performance Liquid Chromatography (HPLC) methods are the most preferable ones, since they determine the individual sugars without derivatization, and they are accurate, reproducible as well as sensitive to the 0.01 percent level (Wilson et al., 1981). l3 Nitrogen Nitrogen content is not distributed equally in the potato tuber; it is highest in the periderm, and then decreases sharply in the cortex and rises again towards the pith (Herrera, 1979) (Figure 2). Throughout the tuber, total and soluble nitrogen are inversely related to specific gravity (Monday and Rieley, 1964). It is generally agreed that variations in environmental factors exert a greater influence on nitrogen content than does variety,except that early varieties tend to contain more nitrogen than do late varieties. Schuphan (1970) found that during the growth of potato tubers, the nitrogen content decreases gradually on a dry matter basis and the portion of protein is higher in the immature tuber. Protein N decreases in sprouting tubers. The total nitrogen content can be broken down into a) true protein fractions soluble in various extracting solu- tions; b) insoluble protein residue, and c) non-protein nitrogen (NPN) which includes inorganic nitrogen, amide nitrogen, free amino acid (FAA) nitrogen, and basic nitrogen such as alkaloids, purines, pyrimidines, choline, enzymes, certain vitamins, quaternary ammonium compounds, etc. Table 1 shows that potato tuber contains on the average 2.0% total protein (% Nx6.25) on a fresh weight, and it represents approximately 10.3% of the total solids of the potato (Kroner et al., 1950; Watt et al., 1963). According to Table 2, the true protein nitrogen is approximately 50% 14 Lateral bud Periderm J Cortex . Parenchyma Pith Q -- -- BUD END 0 --o -c‘ ---Q -‘c ‘ ’---- ‘ --------~‘- -O-‘-- Apical bud Figure 2. Structural features of potato tuber section. 15 Table l. Proximate analysis of potatoes (wet basis) (Kroner et al., 1950; Watt et al., 1963). Average % Range % Water 77.5 63.2-86.9 Total solids 22.5 13.1-36.8 Protein 2.0 0.7-4.6 Fat 0.1 0.02-0.96 Carbohydrate Total 19.4 13.3-30.53 Crude fiber 0.6 0.17-3.48 Ash 1.0 O.44-1.9 16 Table 2. Nitrogen containing compounds (crude protein) of the potato (Schreiber, 1961). N Fraction % of Total N True protein N 50 Non-protein N 50 Inorganic N Nitrate N l Nitrite N trace Ammonia N 3 Amide N Asparagine N 13 Glutamine N 10 Remaining N Free amino acid N 15 Basic N ea aAlkaloids, certain vitamins, purines, pyrimidines, quaternary ammonium compounds, etc. i-( 17 of the total nitrogen (Schreiber, 1961) but may vary from ‘ 37% to 74% (Schuphan, 1960; Li and Sayre, 1975). In rela- tion to Table 2, Markakis (1975) stated that it is doubtful that there is so much free ammonia (3%) in potatoes; ammonia is formed from glutamine during acid hydrolysis. Kapoor et a1. (1975) measured the protein fractions present in potatoes, as percentages of total protein nitrogen expressed on a freeze-dry basis, and found that globulin I (tuberin) accounted for 71.3%; globulin II, 3%; albumin (tuberinin), 6.6%; prolamine, 1.7%; glutelin, 7.6%; and insoluble residue, 9.8%. It is known that heavy nitrogen fertilization results in a total protein increase, mainly by increasing the contents of aspartic and glutamic acids and amides asparagine and glutamine. Lysine content increases proportionally with fertilization, but methionine content drops significantly (Hoff et al., 1971). However, Leuscher (1972) found that a high free methionine content (2.07 g/l6 g NPN) was obtained with 185 ng/ha. Quantitative differences for total protein, free and total amino acids, ratio of free to total nitrogen and methionine are attributed to differences in variety, year, location, fertilization and very highly to genotype x environ- mental conditions (Augustin, 1975; Davies, 1977). Essential amino acids in the NPN fraction are present at a much lower level than in the protein fraction and no free 18 tryptophan or free cysteine could be detected in the NPN “ fraction. The methionine content of potato families varies and free methionine is responsible for 93% of the variation in available methionine. Free methionine ranges from 0.34 to 2.2 g/16 g non-protein N. Free methionine contributes from 12 to 62% of all methionine present in the total protein (Leuscher, 1972; Kaldy and Markakis, 1972; Herrera, 1979). The free amino acids occurring in the NPN fraction are subject to variations affected by storage, nutrition of the plant, year, location and treatment with chemicals such as ethylene chlorohydrin (Talley et al., 1970). In general, the most abundant free amino acids are valine, arginine, aspartic acid, glutamic acid, and the amides asparagine and glutamine. However,in addition to the above Kaldy (1971) reported a very high serine content in six cultivars. He reported that 11% of the total N of potatoes was present in the form of free amino acids, 69% in the form of bound amino acids, and 20% was unaccounted for. Nitrogen changes also have been studied in cooked potatoes, chips, canned, drum dried and french fried potato samples. The nitrogen losses occurring during processing are attributed to leaching of non-protein nitrogen. Free amino acid losses occur as a result of both leaching and the Maillard reaction. Retention values of nitrogen and other constituents like minerals, water soluble vitamins and crude fiber are affected 19 by the cooking methods involved and specifically by the individual unit operations, e.g. blanching, deep-fat frying, mashing, dehydration etc. Water blanching is the chief contributor toward the reduction of nutrients. (Retention values of nitrogen and other constituents are significantly greater with hot air blanching). The leaching losses in peeled potatoes or potatoes cut into small pieces are higher than in whole potatoes or potatoes cut into large pieces (Augustin et al., 1979; Herrera, 1979; Kozempel et al., 1982). Kozempel et a1. (1982) reported that hot water blanching at 770C for 16 min resulted in significant losses of several amino acids, specifically glutamic acid, aspartic acid, valine, phenylalanine, arginine, methionine, tryptophan, as well as gamma- aminobutyric acid. Potato protein is being recognized for its nutritional quality. The evaluation of the potato protein has been tested chemically by amino acid analysis and biologically by animal feeding experiments, human feeding experiments, and microbial growth. According to several investigators the potato protein has a good amino acid composition and balance for maintenance and growth promotion in humans. A protein score of 70 was reported by Markakis (1975) for the "pure" potato protein; this value compares favorably with other foods which have the following protein scores: beef 80, fish 75, soyflour 70, milk 60, wheat flour 50, 20 maize 54, rice 65 (FAD/WHO, 1965; Payne, 1976). Potatoes have a high content in the amides,asparagine and glutamine, 13% and 10% of the total nitrogen content, respectively (Schreiber, 1961). It has been suggested that some compounds of the potato, such as amides, have a substantial influence upon the efficiency of the utiliza- tion of the amino nitrogen, by preventing the antagonism between certain amino acids; their role in human nutrition could be important subject for further investigations (McCay, 1959). Ascorbic Acid Potatoes have been reported to be a good source of several water soluble vitamins (Augustin et al., 1975). One hundred and fifty grams of raw potatoes can supply as much as 90% of the Recommended Dietary Allowances (RDA) for ascorbic acid, 12% for thiamin, 8% for riboflavin and folic acid each, as well as up to 20 and 30% for niacin and vitamin B6,respective1y (Augustin et al., 1978). The American Medical Association (1974) claims that- potatoes continue to be an important vitamin C source, particularly for individuals who do not regularly consume other fresh or frozen vegetables and fruits. The initial level of ascorbic acid in raw potatoes vary, as it is dependent on several factors, such as potato cultivar, production, harvest and storage conditions, 21 as well as length of storage. Long storage decreases ascorbic acid significantly. Potato products contain from 3-21 mg of vitamin C per 100 g (wet basis) depending upon initial concentrations of vitamin C in the raw potatoes and the method of processing (Augustin et al., 1978, 1979; Shekar et al., 1978). Thermal processes such as blanching, soaking, and frying have been reported to result in losses of ascorbic acid in potato products (Augustin et al., 1978). Leaching and thermal degradation have been found to be the two main process parameters involved in ascorbic acid losses of potatoes and other vegetables. Some investigators (Lathrop and Leung, 1980) attribute ascorbic acid loss during hot water blanching of vegetables, almost entirely to leaching. Swartz and Carroad (1979) showed that, in the absence of leaching, thermal degradation accounts for ascorbic acid loss. However, Rognerud (1972) reported significant losses in ascorbic acid, during blanching of vegetables due to leaching. The leaching losses in some cases were two to three times greater than losses due to thermal degradation. Kozempel et a1. (1982) reported a leaching model, with diffusion as the rate controlling step, which successfully predicted losses of the water soluble vitamins of hot water blanched potatoes, as a function of process parameters. 22 Retention values of ascorbic acid during potato processing are dependent on several factors including peeling, temperature and duration of blanching, circulation of blanching water, as well as time and tem- perature of processing steps following blanching. Pelletier et a1. (1977) reported ascorbic acid retentions of 66 to 80% for fried potatoes while Artz et a1. (1983) reported retention values ranged from 83.2 to 54.1% for water blanched French fries. C. Frying Fats In the recent decades there is a worldwide trend to consumption of oils at the expense of solid fats. The increased consumption of fluid fats is related to the wider use of frying techniques. In the culinary process known as "saute" only a small quantity of animal or vegetable fat is used in the vessel, while in "deep frying” food is submerged in a bath of oil. In the U.S. oil consumption has increased by a factor of 14, during 1910-1976, the last ten years showing a much higher rate (Friend et al., 1979). This is related to the rapid growth of the pre-cooked food industry, primarily the pre-fried foods (potatoes, chicken, fish, etc). In general, the significance of the frying process is the same as of all thermal processes: a) notable increment of palatability 23 b) decrease of the preparation time c) small oxygen influence Nutritionally, frying affects the palatability, diges- tibility and metabolic utilization of both food and frying fat (Varela, 1980). The frying fats commonly used in commercial production line of French fries are hydrogenated vegetable oils such as cottonseed, soybean, palm, sunflower, coconut, peanut corn oil, either alone or in combinations, depending upon price and availability. The vegetable oil is hydrogenated, a process of adding hydrogen to the unsaturated fatty acid component of the fat, to increase its stability against rancidification. Hydrogenated shortenings usually have a high smoke point, and are also resistant to foaming and gum formation during frying. Olive oil is particularly palatable due to its organo- leptic properties, which are mainly attributed to a number of pleasant flavoring compounds, such as aliphatic and aromatic hydrocarbOns, aliphatic and terpenoic alcohols, aldehydes, ketones, ethers, esters, furan and thiopene derivatives (Fedeli, 1977). In the frying of potatoes olive oil forms a thin crust of high fat concentration, while other fats form a thicker and less dense crust (Varela, 1980). 24 Phenols, sterols and primarily tocopherols are natural antioxidants responsible for the stability of vegetable oils. Olive oil is relatively high in natural antioxidants, particularly in tocopherols (Sherwin, 1976). The basic criteria for evaluation of olive oil quality are the free fatty acid (FFA) content, the peroxide value, the ultra- violet absorption values, and the organoleptic characteris- tics (taste and odor). The reason olive oil is not used commercially in frying industry is its high price. Nevertheless it is very popular in home prepared fried stuff, particularly for the finish-frying of commercially frozen "par-fried" foods, all over the world. Kernel olive oil is oil extracted from olive fruit kernels after the extraction of olive oil from pressed fresh olives. Commercially,it is subjected to refining. by decolorization (clarification), neutralization of FFA excess (acidity reduction), and deodorization. It can be used in the par-frying step of French fries production, since it bears some of the olive oil organoleptic proper- ties, which keep it in very competitive position, as compared to other vegetable oils; on the other hand, it is inexpensive, fact that supports its position, particularly in countries where it is available. Fat may break down or deteriorate in several ways during frying, including: 25 Hydrolysis Reaction with water or steam which breaks the fat into its component fatty acids and glycerol. Free surface water should be removed from French-fry slices to reduce fat hydrolysis. The FFA content of the commercial shorten- ing should be kept below 1%. Oxidation Atmospheric oxygen reacts with fat and causes darkening, foaming, and development of off-odors and off-flavors during frying. An oxidized fat reduces the storage sta- bility of the fried product. Fat oxidation ends up as rancidity, although fats do not reach this stage in the frying operation. Excessive oxidation may be avoided by preventing aeration during filtering and circulating of the frying fat. Polymerization Formation of gum or gummy deposits in frying fats is attributed to polymerization. Oxidation may or may not be involved. MATERIALS AND METHODS A. Potato Processing Two potato cultivars were chosen for this study: cv. Jaerla (Spherical, medium solids content) and cv. Spunta (oblong, medium solids content). These cultivars are of Dutch origin, but they have been cultivated for more than two decades in Greece. Potatoes were grown on the NE region of Greece, called Xanthi. They were fertilized with 115 kg/ha N, 50 kg/ha P205 and 120 kg/ha K20. After harvest, tubers were stored at 14°C for 10 days and then they were transferred to 4.5°C with 92% RH. Chloro-isopropyl-phenylcarbamate (CPC) was used for sprouting inhibition. A potato hydrometer was used for the specific gravity determination of the tubers. After 2 months storage, the tubers were conditioned at 14°C for 15 days, before processing. Approximately 50 kg of tubers, from each cultivar, were washed, peeled by a 10% NaOH solution at 88°C for 90 sec, cut to pieces of 14 4: mm z_ om: :»_z mzauo> omu\> omuom .cwpmzrmpwgpwcopmom saw: Am mgamwav uumsuxm canyon m Eogm mmo .Awpto mcwpmzv cszpoo Una: cm smzocgg Loam ucm mmoozpm .mmouozcw we :owuzpm .cwE .meH m b e . N o :m 3 14 I: n a U 1 : . .d 5 3 Lu P a. U. a 60 U. nl? ucw>—Om .q mczm_d .Aw mczmwmv and: xn mmoumpoa 2m; :- mmosuzm ucm mmoozpm .mmouozce we cowpmswumm w>vumpwpcmzc mgu com mm>czu mucmcmemm .m mczmwu _E\me .cowumgpcmocoo 47 mmouoscw mmogozm mmoo:_m o _. m. m. w a 9 m; w L. (z a. p._ 48 §l£££. Intercept Correlation Glucose 0.91185 0.03428 0.99902 Fructose 0.84130 -0.03317 0.99614 Sucrose 0.85038 -0.00365 0.99654 Table 7 shows the percent content of fructose, glucose and sucrose in cv. Jaerla and cv. Spunta tubers, stored at 4.5°C for 2 months and conditioned at 14°C for 15 days. Results show that cv. Jaerla forms a little higher sugar content than cv. Spunta. Both cultivars can be considered as low sugar formers, since they did not contain more than 1% dry basis, reducing sugars (2% reducing sugar content, dry basis, is the upper limit acceptable for processing). In fact, they showed a low browning tendency, even when they were fried immediately after storage at 4.5°C for 2 months, without any conditioning at higher temperature. The results are in accordance with those reported by Wilson et a1. (1981) for Kennebec, Katahdin and Russet Burbank tubers stored at two storage temperatures (3.3°C and 7.2°C) and analyzed by similar HPLC method. The sensi- tivity of the method of this study was up to 0.01 percent level. Nitrogen Content The analyzed cultivars showed a closed N composition as well as similar N retention values during the processing. 49 Table 7. Sugar content in cv. Jaerla and cv. Spunta potatoes stored at 4.5°C for 2 months and conditioned for 15 days at 14°C (% wet and dry basis) cv. Jaerla cv. Spunta wet dry wet dry Fructose 0.08 0.396 0.06 0.308 Glucose 0.11 0.545 0.09 0.462 Sucrose 0.05 0.250 0.04 0.205 1Means of triplicates. 50 Crude protein content (Kjeldahl N% x 6.25) and percent retention values of raw, par-fried and finish-fried potatoes are shown in Table 8. Augustin et a1. (1979) measured the retention values of crude protein in the finished product as compared to the corresponding raw material, as well as the retention during water blanching. The data in Table 8 are in good agreement with those reported by those investi- gators. It is important to mention, that N retention values in large sized French fries, after par-frying, are a little lower than those after water blanching. Differences between total N retention in the finish-fried product and retention in the par-fried one were not significant. The data clearly show leachingto be the main reason of crude protein losses, occurring primarily during water blanching, and to some extent during par-frying and finish-frying of the commercial frozen potato product operation. Tables 9 and 10 show total and non-protein nitrogen (NPN) content, their retention values, and ratio (NPleOO): total N changes during processing of the two potato varie- ties. The retention values of total N (crude protein) and NPN in par-frying and finish-frying are 80, 71% and 60, 39% for cv. Jaerla and 79, 69% and 58, 38% for cv. Spunta, respectively. It is noteworthy that the retention values for NPN after finish-frying are much lower than those for total N. 51 Table 8. Crude protein content in raw, par-fried and finish-fried potatoes (Kjeldahl N% x 6.25, % wet and fat-free dry basis, and % retention)1 cv. Jaerla cv. Spunta wet fat- reten- wet fat- reten- free tion free tion dry dry Raw 2.1 10.3 100 2.0 10.3 100 Par-fried 1.9 8.2 80 2.0 8.1 79 Finish-fried 3.0 7.2 70 2.9 7.0 69 1Means of duplicates. 52 .mmumow_a:u to meow:— mm mm emm om— Om mm—F Fm¢ vwvg$uzmwcrm mm om wm¢ APP ow m—m— mom wagwugom om 00— 0mm mop oop mvm— mmm 3mm xsu xcv x z Fmpoy cowacmuoc wose-pme um: cowpcmpmc mwcw-pmw um; 00— zaz zmz z FmpOH .cowucmuws & mm vcm memos ace mwcdruew new .umz .mooumpoa m oo_\z ms :wv weepmpoa upcmcw cw mpcmpcoo Azmzv comocpwc :wmpoca-co: ucm AFgmUFwnxv cmmospv: Fmpoe .m QFDmH 53 .mmpmuwfiasu mo mcmwz— mm mm omm mm? mm mNFF cue nmwce-;mwcwa mm mm woe —NF mm cam, mFm cmvcercma mm 00— omm NoF oo_ New, omm 2mm soap zen cow“ men 00— x z Fmpou -cmums mmsw-umw um; -cmpm; mm;e-pm4 pm: zaz zaz z :38 . Acowpcmpms N we ccm memos ace mmgm-pm$ use .umz .mmOHmpoa m oop\z as :wv mmoumuoq muczam :? mucopcoo Azazv cwmocpvc cwwHoLQ-:oc vcm AFLaUmexv :mmospwc Fmpok .o— ancp 54 The ratio (NPleOO):tota1 N in raw, par-fried and finish-fried product is 50, 38 and 28% for cv. Jaerla and 52, 38 and 29% for cv. Spunta, respectively. These figures also show that NPN losses are much higher than those for crude protein. Both retention values and ratio changes following processing indicate that water soluble NPN fraction contri- butes mostly to the nitrogen losses, by leaching through the potato cell membranes. Tables 11 and 12 show free amino acid (FAA) content, retention value, and free amino acid N as % of total Kjeldahl N of raw and processed potatoes. Sixteen FAA's were determined by the Beckman 121 automatic amino acid analyzer. Free cystine and tryptophan did not appear in the chromatograms. Kaldy (1971) and Herrera (1979) also did not find these amino acids free in the American potatoes, that they analyzed. The dominant FAA's in raw and processed potatoes of both cultivars were aspartic acid, serine, glutamic acid and arginine. The FAA composition of potatoes, given in Table 13, is affected by the mineral nutrition of the plant, the environmental conditions, the variety and other factors (Davies, 1977). The two cultivars analyzed here differed slightly from each other in their FAA composition. Their serine content is higher than that reported by other workers (Davies, 1977; Herrera, 1979), but similar to that 55 .mepee__eee ee meme:- z pgeepehx &_.m &N.m &P.mp Fepep we & we 2 < om o.m mo m.mp oo_ o.om ecwce~< mm _.o mm «.m— cop m.mp mcwexpw om m.o_ mo m.mm cop o.om ecwpeca mm m.om mm ¢.PPP oop m.mom cramps-w mm m.mm mm m.m- cop o.mmm ecwcmm mm m.mp No «.mm oo— o.~o ecweewccp ow o.mm mm o.em oop o.omp ewueeem< cewueeeeg m oop\ms ee_pcmuec m oop\me coweeepes m oop\me emacwtcmwcwd emwgmrcem .FAcewueeueL a we use .mwmee age metereew .meeueuee m oo_\< am m.e Ne e.ep ee_ e.NN o=_ea_< mm m.e ee m.e ee_ m.m_ oewos_e mm m.ap oe P.em eep _.em oeepoca em m.me em e.ee_ ee_ L.ea_ oeeaespe KN L.Lm em m.mmp eep m.__N deacom em m.a Fe m.ap ee_ e._m oeecaocee am e.em mm N._~ ee_ m.mN_ beecaam< eoeecoeom m ee_\me eoeeeoeom m ee_\me =o_eeoeom a ee_\me eo_cc-;meewa eaecc-caa .eerucepmc & we use .mwmee age eegmuuee .meepepee m oop\<