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.     

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.     

STUDY ON BACTERIAL LOAD DURING GELATIN MANUFACTURING PROCESS AND ITS EFFECT ON FOOD GRADE GELATIN

A total of 138 samples from different stages of gelatin manufacturing process were analyzed to detect bacterial contamination of food grade gelatin and to see its effect on the quality of gelatin. The isolated bacterial species included Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Clostridium perfringens, which exhibited gelatinase activity and caused depletion in the nutritional quality of food grade gelatin. Marked changes in the amino acid content with incubation days indicated degradation of food grade gelatin because of the secretion of gelatinases that were depicted by paper chromatography. Because these isolated species are known pathogens and have gelatinolytic properties, their occurrence in food grade gelatin can make it an unsafe and unsuitable for food applications.     

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。     

ANTIOXIDANT ACTIVITY OF BENE HULL OIL COMPARED WITH SESAME AND RICE BRAN OILS DURING THE FRYING PROCESS OF SUNFLOWER OIL

The antioxidant activity of Bene hull oil (BHO) was compared with that of sesame oil (SEO) and rice bran oil (RBO) during the frying process of sunflower oil (SFO) at 180C. The ratio between the polyunsaturated and saturated fatty acids and calculated oxidizability were statistically greater for the SFO (4.26 and 6.48, respectively), followed by the SEO (3.18 and 6.27, respectively), RBO (1.53 and 4.37, respectively) and BHO (0.37 and 1.67, respectively). Peroxide and acid values of the oils studied ranged from 0.34 to 3.07 mEq/kg and from 0.19 to 5.20 mg/g, respectively. Total tocopherols and phenolics contents of the SEO (1093.28 and 1042.43 mg/kg, respectively) were significantly higher than those of the SFO (740.27 and 38.68 mg/kg, respectively), BHO (573.41 and 276.67 mg/kg, respectively), and RBO (832.98 and 67.98 mg/kg, respectively). In total, based on the conjugated diene value and carbonyl value measurements during the frying process, the BHO showed an antioxidant activity higher than those of the SEO and RBO at the level of 2%, and the levels higher than 2% of the antioxidative oils caused to decrease the oxidative stability of the SFO, indicating the pro-oxidant effect of the oils added at these levels.

PRACTICAL APPLICATIONS

This research introduces the oil obtained from the hull of Bene, a species of pistachio growing wild in Iran, as a new source of vegetable oil for human nutrition with antioxidant activity significantly higher than sesame and rice bran oils, which are considered as very stable and antioxidative vegetable oils because of the presence of very strong indigenous antioxidants, during the frying process.     

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.     

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.     

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).     

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.     

FILTRATION AND FILTER SYSTEM FOR TREATED FRYING OIL

Used canola oil was treated with commercially available adsorbents (HB 600, Magnasol, and Frypowder) and a UGA blend for flow rate study and oil quality improvement. Viscosity measurements of fresh and used oil indicated that the oil temperature >140C was best suited for active filtration. One percent adsorbent gave better flow rates than 2% except for Frypowder, which showed no difference in flow rates. All the adsorbents significantly improved the oil quality. Most significant improvement was observed in FFA values (15–20% and 24–35% for 1% and 2% adsorbent level, respectively) except for Frypowder, which resulted in least improvement (4 to 7%). Neither increasing the duration of treatment, prior to filtration, from 3 to 6 min, with 3% UGA blend, nor the multipass filtration treatment showed any significant improvement in oil quality. Pressure system was more promising for active filtration than vacuum and gravity systems.     

THE EFFECT OF EDIBLE FILM ON OIL UPTAKE AND MOISTURE RETENTION OF A DEEP-FAT FRIED POULTRY PRODUCT

The recent trend in reducing the fat content in fried foods is leading to the development of low-fat products using batter and breading formulations from protein and other hydrocolloids. The functionality of many of these edible ingredients on moisture retention and fat barrier properties during deep-fat frying is not clearly understood. The objective of this study is to evaluate the effectiveness of hydroxypropyl methylcellulose edible film coating on chicken balls for moisture retention and fat reduction during deep-fat frying. Two sizes (35 and 47 mm) of uncoated and coated chicken balls were fried in peanut oil at 175C for five different frying periods ranging from 30 to 180s for small and 30 to 300s for large balls. The moisture and fat content from the surface layer and core were determined. In comparison to the control, moisture retention up to 16.4% and fat reduction up to 33.7% were observed.     

EFFECT OF FRYING AND OTHER COOKING CONDITIONS ON NITROSOPYRROLIDINE FORMATION IN BACON

Nitrosopyrrolidine (NO-Pyr) formation in bacon is primarily dependent on frying temperature and not time. Cooking methods affect the amount of NO-Pyr formed: pan frying produces the highest level of NO-Pyr with variable concentrations formed on baking, broiling and cooking in a "baconer." Microwave oven treatment produced the lowest amount of NO-Pyr. A model system study of the decarboxylation of nitrosoproline shows this precursor, which may be present in bacon, is maximally converted to NO-Pyr at 185°C near the recommended temperature for frying.     

EFFECT OF DEGUMMING PROCESS ON CHROMATOGRAPHIC SEPARATION OF CAROTENES FROM CRUDE AND DEGUMMED PALM OIL

Carotene from crude palm oil (CPO) and degummed palm oil (DPO) was separated using synthetic polymer adsorption chromatography. Diaion HP-20 adsorbent was used for reverse-phase chromatography and column temperature was kept at 50C. Both 2-propanol and n-hexane were used as the first and the second eluting solvents, respectively. Phosphoric acid was used to remove the minor components in CPO in the degumming process. The turbidity of DPO was lower than that of CPO and the retention time in the column for DPO was shorter (21.3 min) compared to CPO (29 min) due to the removal of the minor components by phosphoric acid. Degumming process caused a reduction of 1.67 mg of total carotene content and 55.67 ppm of carotene concentration in CPO. This is probably due to the removal of carotenoids during the degumming process. After column chromatography, carotene recovery for CPO was 30.23% and 54.82% for the first and second fractions, respectively. On the other hand, carotene recovery for DPO was 33.91% for the first fraction and 46.25% for the second fraction. This indicated that the separation of carotene in CPO was more efficient than DPO in the column chromatography due to the longer retention time in the column.     

QUALITY CHANGES OF REFINED-BLEACHED-DEODORIZED (RBD) PALM OLEIN, SOYBEAN OIL AND THEIR BLENDS DURING DEEP-FAT FRYING

The quality changes of refined, bleached and deodorized palm olein (RBDPO) and soybean oil (SBO) and their blends were investigated in this study. The oils were studied during intermittent frying of potato chips at 180PT5C for 5 h per day for 5 consecutive days. The indices used for assessment of changes in quality of the oils were fatty acid composition (FAC), peroxide value (PV), anisidine value (AnV), % free fatty acid (FFA), iodine value (IV), % polar component, polymer content, color, viscosity, smoke point and foaming tendency. The results showed that RBDPO was superior to SBO in frying performance in terms of resistance to oxidation, changes in IV, AnV, foaming tendency, % polar component and polymer content. However, SBO performed better than RBDPO with respect to color, viscosity, FAA content and smoke point. Sensory evaluation showed that potato chips fried in both RBDPO and SBO were equally acceptable by the panelists.     

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.