EFFECT OF ROSEMARY EXTRACTS ON THE STABILIZATION OF FRYING OIL DURING DEEP FAT FRYING

Rapeseed oil and a mixture of rapeseed oil with palmolein containing silicone oil were used for preparation of french fries. The intermittent frying was continued for 5 days in a household fryer with replenishment of used oil. The decomposition of polyunsaturated triacylglycerols, formation of polar substances, polymers, colored products and conjugated dienes, but also of several sensory attributes, correlated with frying time. Polymers, dienes and coloration were closely intercorrelated and correlated with sensory characteristics of oil and fries, particularly when multiple regression was applied for prediction. Rosemary extracts inhibited the formation of polar substances, polymers and decomposition of polyunsaturated triacylglycerols, especially in the case of rapeseed oil and improved the sensory attributes of french fries.     

KINETICS OF ACRYLAMIDE FORMATION DURING TRADITIONAL AND VACUUM FRYING OF POTATO CHIPS

Acrylamide is considered a carcinogen in animals and a possible carcinogen in humans. It has been found in starch‐rich foods cooked at high temperatures. Vacuum frying (10 Torr) was investigated as a possible alternative to reduce acrylamide formation in potato chips. The cultivar Atlantic was used to determine the kinetics of acrylamide formation during traditional and vacuum frying at different temperatures. There was a 94% decrease in acrylamide content when potatoes were fried to the same final moisture content (1.5% ± 0.3% w.b.) under vacuum compared to those fried under atmospheric conditions. Acrylamide accumulation under vacuum frying was modeled using first‐order kinetics (during traditional frying, the logistic kinetic model was used). The behavior of the kinetics of acrylamide content in potato chips fried under the two processes was different mainly because of the different temperatures used. During traditional frying, higher temperatures are used (150 to 180C) and acrylamide after some time is produced but starts degrading, producing a constant level of acrylamide content at longer times. During vacuum frying (10 Torr), acrylamide increased exponentially (but at lower levels) for all frying times.     

棕榈油在煎炸过程中的劣变及对生物机体的影响

介绍了从营业餐厅煎炸实际中所得的油样在煎炸过程中的化学变化及生物学效应方面的最新报道，具有代表性和实际指导意义，可供有关科技工作者参考。     

EVALUATION OF OLEIC SAFFLOWER OIL IN FRYING OF POTATO CHIPS

SUMMARY– A recently introduced variety of safflower, UC-1, produces an oil in which oleic:linoleic acid ratios of ordinary safflower oil are reversed, giving an oil with iodine value 90. This oil was compared with cottonseed oil and hydrogenated vegetable oil (HVD) for frying potato chips. After accelerated storage at ambient temperature under fluorescent light, the quality of chips fried in oleic safflower oil was ranked equal to that of chips fried in hydrogenated oil, Chips fried in either oil were more stable than those fried in cottonseed oil. Effect of propyl gallate antioxidant was negligible.     

EFFECT OF POLYDIMETHYL SILOXANE ON RAPESEED OIL TRANSFORMATION DURING DEEP FRYING

During deep fat frying a series of undesirable transformations occur. These include oxidation, polymerization, and hydrolysis. Use of additives to reduce the access of air to the frying oil may be one of the preventive methods. Such additives reduce the amount of foam formed. In this work, polydimethyl siloxane (PDMS) at 3 ppm was added to the frying rapeseed oil for frying potato fritters. It was found that oxidation was significantly limited as it reduced peroxide, anisidine, E^1%_lcm values and oxidized triacylglycerol (TAG) contents. Polymerization was also limited as a reduction in the contents of TAG polymer and dimer occurred. Addition of PDMS also reduced degradation of polyenoic acids of the frying oil. Oil without PDMS was less resistant to these transformations.     

OPTICAL ASSESSMENT OF CORN OIL DETERIORATION DURING FRYING

The ultraviolet (UV), visible and near-infrared (NIR) absorption changes in corn oil were measured during processes simulating deep fat frying. Corn oil, maintained at 185C, was exposed to various treatments with nitrogen, air, water injection, air with water injection, and steam. Autoxidation due to a combination of air and high temperature in the simulated frying trials caused visible absorption changes between 400 and 580 nm as the oil deteriorated similar to those observed in potato frying experiments. These absorption changes were found to be associated with changes in an ultraviolet absorption band with a maximum near 270 nm. Second-derivative calibration equations developed at various visible and NIR absorption wavelengths successfully predicted the percentage of total polar materials (%TPM) which accumulated in the corn oil during simulated trials of autoxidation (R values from 0.93 to 0.98). Using spectral data from repetitive potato frying experiments, the predicted %TPM calculated with these equations correlated well with kinematic viscosity measurements (R values from 086 to 0.97).     

CORRELATION OF QUALITY OF FRYING OIL AND OIL EXTRACTED FROM POTATO FRITTERS FRIED IN LIQUID AND PARTIALLY HYDROGENATED RAPESEED OILS

The increase in consumption of food fried in the so-called 'deep-frying-oil'entails the necessity of knowledge of both thermooxidative transformation occuring in the frying medium and chemical composition of oil absorbed by the fried product. The aim of this study was to correlate the quality of frying medium and oil extracted from potato fritters fried under rigorously controlled laboratory conditions in liquid and partially hydrogenated rapeseed oils. Oxidation and polymerization reactions predominated during deep frying of potato fritters in both frying media, but hydrolysis occured only to a small degree. The peroxide value was not a suitable quality control indicator for monitoring the thermooxidative transformation during deep frying. The most suitable method for examining such transformations was to study the content and composition of the polar fraction. A correlation existed between the amount of polymers and oxidized triacylglycerols (TAGs) and the amount of polar fraction. Small differences existed in the content of thermooxidative transformation products in the frying medium and the oil extracted from potato fritters. By monitoring anisidine value (AnV), E^1%_1cm and the content and composition of the polar fraction in the frying medium, it was possible to evaluate the quality of the fat in the fritters. Thus, the use of partially hydrogenated compared to liquid rapeseed oil in deep frying process may be preferred because at the same content of polar fraction and its components partially hydrogenated rapeseed oil contained a lesser amount of secondary oxidation products.     

COLOR AND TEXTURE DEVELOPMENT OF POTATO CYLINDERS WITH LIQUID SMOKE DURING BAKING, FRYING AND MICROWAVING

The rate of color and texture development in partially fried before freezing potato cylinders processed by deep fat frying, microwaving and baking was determined. The effect of 0, 1, 3 or 5% wt/wt solution containing 30% liquid smoke was measured at intervals during thermal processing and the reaction order and rate determined. Also, five different wood and dextrose‐derived browning agents were compared at 1% wt/wt addition. The processing method had a significant effect on the reaction rates of color and texture development during processing. Microwaving was faster than frying, which was faster than baking. The addition of liquid smoke led to a significant increase in the rate of color production but had no statistically significant effect on texture. The addition of 1% liquid smoke increased the reaction rate by adding carbonyls, which limit the reaction rate in potatoes. Higher levels of liquid smoke did not change the reaction rate because the carbonyls were no longer limiting the reaction. The processing method and the addition of the browning agent had no effect on the reaction order which remained a pseudo zero‐order reaction. Thus, liquid smoke could be used to reduce processing times, potentially saving money and decreasing acrylamide formation.     

EFFECTS OF AERATION DURING THE CULTIVATION OF PITCHING YEAST ON ITS CHARACTERISTICS DURING THE SUBSEQUENT FERMENTATION OF WORT

The characteristics of cultivated yeast were studied after continuous aeration, aeration for the first hour and without aeration. The fatty acid content increased under aerobic conditions, while the level of storage sugars increased under anaerobic conditions. In a fermentation test, total number of cells and their viability and also the intracellular level of storage sugars and fatty acids were higher in yeast cultivated under aerobic conditions than in yeast cultivated under anaerobic conditions. Since there were no significant differences between the performance of yeast cultivated under continuous aeration and those with aeration for the first hour, the latter offer the best economic choice.     

INFLUENCE of OIL TEMPERATURE ON CONVECTIVE HEAT TRANSFER DURING IMMERSION FRYING

The relationship between oil temperature, convective heat transfer coefficient, and heat flux during immersion frying was investigated. Potato cylinders were fried in 120, 150, and 180C oil and convective heat transfer coefficients and heat flux measurements were made. These measurements followed the expected trends predicted by fundamental heat transfer calculations. the maximum convective heat transfer coefficient and heat flux reached during frying increases as oil temperature increases. the process time to reach these maxima decreases as oil temperature increases. This research provides fundamental knowledge relevant to the effects of oil temperature on the coupled heat and mass transfer problem present during immersion frying. This knowledge will provide a first step towards better understanding the frying process, and eventual process optimization through manipulation of the time-temperature regime of the frying processes.     

非油炸型速冻马铃薯预处理加工工艺参数的研究

传统的速冻马铃薯产品大部分都采用了油炸工艺，而马铃薯高温油炸时会产生致癌物质丙烯酰胺，对人体有害。为了开发食用安全的速冻马铃薯新品种，采用正交试验和综合评分，对非油炸型速冻马铃薯的预处理加工工艺条件进行了研究。研究了马铃薯品种（A）、热烫温度（B）、热烫时间（C）和马铃薯直径（D）对速冻后产品的失重率、硬度、多酚氧化酶活性和过氧化氢酶活性的影响。结果表明：试验因子对其影响的主次顺序为B〉C〉A〉D；最佳方案为A4B3C2D2即以中薯3号为原料．马铃薯直径为4．5cm，110℃热烫3min。产品的品质最佳。     

DYNAMICS of FAT/OIL DEGRADATION DURING FRYING BASED ON PHYSICAL PROPERTIES

The dynamics of fat/oil degradation were studied by measuring the concentrations of major degradation products, polymers, decomposition products, free fatty acids and total polar materials. Regression models were fitted to predict the changes in physical properties, specific gravity, viscosity, surface tension, specific heat, dielectric constant and capacitance with fat degradation. Fat degradation affected specific heat, specific gravity and viscosity. the dielectric constant or capacitance predicts fat degradation, independent of the food fried. A parallel plate capacitor of larger capacitance was found to produce better correlation with total polar materials in the high polar region.