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.     

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.     

EFFECTS OF OHMIC PRETREATMENT ON OIL UPTAKE OF POTATO SLICES DURING FRYING AND SUBSEQUENT COOLING

The effect of ohmic pretreatment on the oil uptake of potato slices during frying and subsequent cooling was investigated. The treated potato slices were heated by either directly sandwiching the slices between two electrodes or by heating them in a 0.11% salt solution. The treatment was carried out using an alternating current field of 35.5 V/cm. Results of this study indicate that oil uptake during frying and subsequent cooling of potato slices was decreased by the ohmic pretreatment without involving a liquid medium (direct sandwiching). However, when the ohmic pretreatment was carried out in a liquid medium, the effect was not evident. This might be due to water absorption during the treatment, which increased initial moisture content as well as porosity of the treated samples.     

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).     

EFFECT OF TEMPERATURE ON THE QUALITY OF MUSCLE FOODS

Heating/cooking alters a food's flavor precursors yielding a product with a new pleasing taste. While heating to a high temperature destroys most pathogens thereby enhancing safety, it also alters the food's flavor by changing the precursors and final flavor components of the food. For example, heating meat to above 77C not only destroys many foodborne pathogens but also causes major changes in level of desirable flavor precursors. Many of these changes are due to alteration in activity of endogenous hydrolytic enzymes as well as heatinduced structural and functional changes. Heating induces differential production and distribution of flavor principles and flavor precursors. A secondary effect of temperature on food-flavor is its direct affect on analysis of flavor volatiles, i.e., high purge temperatures bias analysis of flavor components by production of new and destruction of existing components. This paper focuses on the structure/function relationship of meat proteins and their proteolytic products as they relate to meat flavor and end-point cooking temperature. The paper also will address the effect of analytical temperature on meat flavor analysis.     

CHANGES IN THE FRYING MEDIUM DURING DEEP-FRYING OF FOOD RICH IN PROTEINS AND CARBOHYDRATES

Changes in the frying medium (rapeseed oil) during controlled deep-frying of sliced potatoes and cod fillets and oil heated without them were compared. Fifteen frying cycles were conducted each day for five days. Results showed that oil after frying of cod fillets contained 10% less triacylglycerol (TAG) polymers and 40% less TAG dimers than other oils. Other parameters (iodine and anisidine values and absorption value at 233nm) showed that less thermooxidative products formed during frying of food rich in proteins. Oil after frying of cod fillets was darker and its acid value was significantly higher than that for other oils. Content of TAG polymers and dimers for oil after frying of sliced potatoes and oil heated without food was equal. The relative loss of C18:2 acid and decrease in iodine value showed that oil after heating without food underwent more intensive thermooxidative transformation than other oils.     

EFFECT OF STORAGE ON THE RHEOLOGICAL BEHAVIOUR OF BABY FOODS

The effect of storage temperature on rheological behaviour of four varieties of baby foods was studied. After 24-month storage at 15C and 25C, the constant A in Weltman model increased significantly for the vegetables, meat and fish samples, and decreased significantly for the fruit samples. After 24-month storage at 5C and 15C there were no significant changes in flow behavior index, consistency index and yield stress of the Herschel-Bulkley model for the vegetables, meat, fish and fruit samples. Increase in storage temperature decreased the consistency index and yield stress of the fruit samples.     

THERMOXIDATIVE AND HYDROLYTIC CHANGES IN OILS USED FOR FRYING OF FROZEN PREFRIED FOODS

Palm olein with 22.9 h of stability at 100 C (by the Rancimat method) and low acid and peroxide values of 0.184% and 1.33 meq/kg, respectively, was used to study the deteriorative effect of frying of frozen prefried potatoes and chicken and compared it with the effect of frying the same fresh foods. Quality characteristics of palm olein were monitored by following the changes in physical and chemical properties; foam height (FH), smoke point (SP), refractive index (RI), viscosity (Vis), acid value (AV), peroxide value (PV), polymer content (%Pol.), oxidized fatty acids (%OFA), thiobarbituric acid (TBA) value and, conjugated acids (absorbance at 232 nm for conjugated dienes and at 268 nm for conjugated trienes) with the progress in frying time of up to 20 h. Results revealed that frying the frozen prefried foods express more deteriorative effect than the fresh foods throughout the frying process.     

CONTRIBUTION OF AIR-AND BONE-CONDUCTION TO THE CREATION OF SOUNDS PERCEIVED DURING SENSORY EVALUATION OF FOODS

The noises perceived during sensory evaluation of foods are transmitted to the innerear by both air and bone conduction. The contribution of the two conductions was studied for six foods "croquant" (crunchy), "craquant" (crackle) and "croustillant" (crispy), by six panelists. It was studied by reconstituting the attenuation of the air and bone conduction records needed to imitate sound actually heard during sensory evaluation of foods. The eating technique (bite or chew) modified the contribution of air- and bone-conduction to auditory sensation. Differences were shown between foods, but they could not clearly distinguish between the kinds of food. Modifying the attenuation of the air- and bone-conduction records was not enough. The bone-conduction records had to be attenuated over a frequency range around 160 Hz, which is the resonance frequency of the mandible. The air-conduction records had to be attenuated at a frequency range around 160 Hz and amplified at a frequency range around 3,500 Hz in order to match the action of the middle-ear muscles which behave differently when sounds were generated inside or outside the mouth.     

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.     

EFFECT OF GAMMA RAY IRRADIATION AND FRYING ON THE THIAMINE CONTENT OF BACON

The effects of ionizing irradiation and frying on the thiamine and riboflavin content of bacon were determined. Significant destruction of thiamine but not riboflavin occurred during both the irradiation and frying. The destruction of thiamine was found to be directly related to the dose of ionizing radiation or the degree of cooking. Frying before irradiation, reduction of water content by lyophilization, and irradiation at - 40°C rather than 2°C produced significantly greater retention of thiamine. Frying the bacon following irradiation produced radiation dose-related, nonadditive, increased destruction of thiamine. The protective effect of frying before irradiation was not directly linked with the reduction of moisture by frying.     

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.     

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.