SIMULTANEOUS HEAT and MASS TRANSFER DURING the DEEP FAT FRYING of TORTILLA CHIPS

The heating and water loss of a single tortilla chip during deep fat frying was investigated experimentally and the data were analyzed by writing two heat and mass transfer balances. the equations were solved using explicit finite difference technique. Oil uptake as a function of frying time was described by a first order exponential equation. the empirical and theoretical heat and mass transfer agreed well.
The effect of oil temperature on the moisture loss and oil uptake as a function of frying time was analyzed. Moisture loss rate increased as temperature increased. the effects of temperature on oil uptake were not significant during the first 15 s of frying, however, the final oil content was higher for the tortilla chip fried at 190C than at 150C for 60 s.     

PHYSICAL PROPERTIES OF GRAM AS A FUNCTION OF MOISTURE CONTENT

This study was carried out to determine the effect of moisture content on some physical properties of gram. Six levels of moisture content ranging from 10.83 to 31.20 percent (dry basis) were considered for this study. Length, width, thickness, diameter of equivalent sphere, mass of 1000 grains and porosity increased linearly from 7.968 to 8.758 mm, 5.864 to 6.554 mm, 5.713 to 6.359 mm, 6.770 to 8.795 mm, 137.97 to 172.73 g, and 33.17 to 35.85% respectively with the increase of moisture content from 10.83 to 31.20%. The angle of repose increased from 27.03 to 33.27° with the increase of moisture content. Bulk density and true density decreased linearly from 787.31 kg/m³ to 712.61 kg/m³ and 1398 kg/m³ to 1250 kg/m³, respectively. Static coefficient of friction was determined over plywood, galvanized steel, celluloid sheet, and glass sheet. Static coefficient of friction varied from material to material and depended on the roughness and wetness of the true. The highest coefficient of static friction was found over plywood and lowest for glass sheet among the materials tested.     

PHYSICAL and THERMAL PROPERTIES of GORGON NUT

Bulk density, true density, angle of repose, coefficient of friction on metal surfaces, specific heat, thermal diffusivity and conductivity of gorgon nut were determined using standard techniques for different sizes of nuts at moisture contents and temperatures ranging from 15 to 60% (dry basis) and 25 to 55C, respectively. the physical properties varied quadratically with moisture content. Specific heat increased with moisture and temperature but decreased with the size of the nut; whereas, the thermal diffusivity showed a reverse trend. Thermal conductivity increased with moisture content but did not follow any trend with temperature within the range of the study. the physical and thermal properties data at various moisture contents and temperatures were used to develop equations for different sizes of gorgon nuts.     

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.     

ASCORBYL PALMITATE AS AN ANTIOXIDANT FOR DEEP FAT FRYING OF POTATO CHIPS IN PEANUT OIL

The antioxidative properties of ascorbyl palmitate (AP) alone and in combination with other known antioxidants were investigated during deep fat frying of potato chips in peanut oil. Their effect on the quality of the frying oil and shelf-life of the fried product were studied. The other antioxidants tested were butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl gallate (PG). The characteristics evaluated for the frying oil were color development, viscosity, peroxide value (PV) and polymerization of the oil during deep fat frying; AP was found to reduce these values. It also helped to prevent the degradation of the oil by retaining the unaltered triacylglycerols during the frying period. Addition of AP to the frying oil reduced the PV of the extracted fat, doubled the shelf-life of the fried product and improved the quality of frying oil with increase in frying time. However, AP did not show any synergistic effect with other antioxidants examined.     

COMPARATIVE STUDIES ON PHYSICAL PROPERTIES OF VEGETABLE OILS AND THEIR BLENDS AFTER FRYING

Physical properties of six commonly used oils and three blends consisting of three oils in each blend were studied after three successive frying of 'poories'(fried snack from flattened dough of refined wheat flour). The changes in viscosity, CIE trans-reflectance color and related parameters, UV-Visible spectra and UV-spectra of oil samples in solvent system (chloroform:methanol; 2:1, v/v) were studied. The results showed that viscosity and color of the oils changed to a much higher extent after first frying than subsequent fryings. The hue angle followed a similar trend. Changes in the UV-spectra in the solvent system indicated an increase in the formation of conjugated compounds after successive fryings. Peroxide values (PV) also increased after frying. Principal Component Analysis (PCA) plots of the data indicated that among oils examined groundnut oil and soy oil in combination with other oils were preferred for frying. Use of small amounts of unrefined oils (filtered) such as mustard oil or sesame oil which have a high content of natural antioxidants was beneficial as formation of conjugated compounds and increase in peroxide value was minimized after successive frying using blended oils.     

THERMAL BEHAVIOR OF PORCINE COLLAGEN AS RELATED TO POST-MORTEM TIME

SUMMARY: DTA (differential thermal analysis) thermograms of epimysial connective tissue from normal and low quality porcine muscle were compared at 0 and 24 hr post-mortem. In addition, the melting characteristics of intramuscular collagen were determined at 0 hr post-mortem. In all tissues studied, collagen from low quality muscle consistently gave slightly lower peak melting points than that from normal muscle. Epimysial collagen had a significantly ( P < .05) lower peak melting point at 24 hr than at 0 hr post-mortem (64.24 vs. 65.77°C). Using epimysial collagen, a significantly ( P <.01) greater proportion of the total melting range occurred at lower temperatures at 24 hr post-mortem as compared to 0 hr (4 1.1 vs. 30.9%). The thermal behavior of intramuscular collagen at 0 hr post-mortem was similar to that of epimysial collagen at 0 hr, but peak melting temperatures were slightly higher for intramuscular connective tissue.     

THE THERMAL PROPERTIES OF POTATOES AND CARROTS AS AFFECTED BY THERMAL PROCESSING1

The effects of processing on the thermal properties of white potatoes and carrots were studied. The test samples were blanched, boiled, cooked and canned. Whole potato tubers were baked to study the effects of starch gelatinization. The thermal conductivity (k) and density (ρ) were measured and the specific heat (c_p) and thermal diffusivity (α) were calculated. Results showed that in general, α initially decreased and then increased during processing. Test samples were found to have a gain in α when their moisture content increased by more than 9%. The α of potatoes decreased after canning and increased after boiling. In carrots, a similar trend was also observed but to a lesser degree. The k of potatoes was unaffected after blanching or cooking. In all the processing baking study showed that gelatinization significantly decreased the k of potatoes.     

DYNAMIC VISCOELASTIC PROPERTIES OF PASTA AS A FUNCTION OF TEMPERATURE AND WATER CONTENT*

Pasta samples were tested in the linear viscoelasticity range using a dynamic mechanical thermal analyzer over the temperature range of 25 to 95C and the water content range of 12 to 20% (weight of water/weight of solids). To obtain wholesome pasta samples at different moisture levels, the intermittent sorption technique was used. The behavior of G′ and tanδversus temperature curves exhibited a transition, which was determined to be the glass transition by making comparisons to the literature values of glass transition for starch and semolina extrudates. At 12.5% water content, glass transition initiated at 48.7C. With increase in water content values, the initiating glass transition temperature decreased. At 19.7% water content, glass transition was observed in the temperature range of 36.9 to 57.3C. Although pasta contains about 13% protein fraction, it did not seem to affect the major part of glass transition range because the pasta proteins become mobile at temperatures greater than 80C and water content greater than 17%.     

CHANGES OF SOME THERMAL AND PHYSICAL PROPERTIES IN MODEL SYSTEMS SIMULATING AN ALCOHOLIC FERMENTATION

Highly simplified model systems, simulating the fermentation of 25.00% sugar-water mixture into a 12.78% ethanol-water mixture, were considered in order to study their thermo-physical properties. Calorimetric data, viscosity and water activity determinations showed that important thermal and physical changes are associated with the steps of a fermentation process. Besides the increase in ethanol content, other concomitant changes are a strong increase in ethanol vapor pressure and a decrease in water activity and viscosity. DSC measurements of the models during scanning from -140C to 25C showed three peaks: peak 1 (exotherm) covered a temperature range from -110C to -80C and was attributed to the recrystallization of the ethanol monohydrate; peak 2 (endotherm), with peak temperature around -70C, was attributed to the melting of the alcoholic monohydrate; peak 3 (endotherm) in the higher temperature range from -30C to OC, was due to ice melting. The alcoholic monohydrate appeared only in the final simulated step of the fermentation, where only ethanol and water were present. The inhibitory effect of even small amounts of sugars on the formation of the monohydrate might be related to the increase in viscosity. This would confirm the formation of the ethanol hydrate as kinetically hindered, as it is reported in the literature.     

MICROSTRUCTURE AND PHYSICAL PROPERTIES OF QUARG CHEESE AS AFFECTED BY DIFFERENT HEAT TREATMENTS

The effects of different heat treatments on the rheological properties, microstructure and yield of production of quarg cheese were investigated. Three levels of time–temperature combination were used: 72C–16 s, 82C–5 min, 90C–5 min. Rheological properties were studied by means of frequency sweep experiment with the measurement of elastic modulus ( G' ). Microstructures of samples were observed by scanning electron microscopy (SEM). Maximum and minimum G' and cheese yield were obtained at 90 and 72C, respectively ( P <  0.05). Yield at 82 and 90C was higher than 72C but difference between heat treatment at 82 and 90C was not significant ( P <  0.05). G' values at 82 and 90C were higher than that at 72C. The difference between 82 and 90C was initially low; subsequently increase in frequency made G' at 90C higher than 82C. SEM micrographs of samples at 82 and 90C were closely similar and no differences were observed between them. Micrographs showed the regular microstructure with branched clusters and numerous small pores at 82 and 90C, whereas micrographs of heat treatment at 72C had larger protein aggregates and fewer but larger pores. This study showed that heat treatments at 82 and 90C were more suitable for quarg cheese making than that at 72C.

PRACTICAL APPLICATIONS

Quarg cheese is one of the most popular acid-coagulated cheeses. This study shows that heat treatment at 82C–5 min is preferred for quarg production compared with other heat treatments. Contribution of denatured whey proteins in gel network led to higher cheese-making yield as well as high nutrition value. Heat treatment at 82C is also suggested in economic and energy consumption aspect.