Santi R. Bhowmik

Thermal kinetics of color changes in pea puree

Abstract Change in food color is associated with heat treatment of the food. Retention of food color after thermal processing may be used to predict the extent of quality deterioration of food resulting from exposure to heat. Samples of green pea puree were heat treated for different lengths of time at several temperatures to determine thermal destruction of color. Hunter color scale values (L, a, and b) from heat treated samples were analyzed to determine the kinetics of color change due to heat treatment. Color changes followed first-order reaction kinetics. Reaction rate and activation energy, as well as D and z values of color degradation, were determined experimentally. The determined D and z values for ( − La b ) were 31.10 min and 42.87 °C, respectively. These values were used to estimate the color change of pea puree processed in cylindrical plastic cans. The estimated colors were compared with experimentally determined color values under identical processing conditions. Good agreement was found between the estimated and experimental color retentions.

Effective moisture diffusivity of plain yogurt undergoing microwave vacuum drying

Abstract The effective moisture diffusivity of yogurt was estimated by the method of slopes of the drying curve and the regular regime technique using the isothermal drying data obtained by microwave vacuum drying. The use of microwave vacuum drying seemed advantageous for obtaining the isothermal data. The method of slopes of the drying curve was found useful for estimating effective moisture diffusivity from the drying data of yogurt, because the model obtained from this method simulated the drying curve better than the one from the regular regime technique and because the method of slopes is simple to handle.

Moisture sorption isotherms of concentrated yogurt and microwave vacuum dried yogurt powder

Abstract Moisture sorption isotherms of yogurt, concentrated yogurt and microwave vacuum dried yogurt were determined and compared with those of freeze dried and spray dried yogurts, using the GAB and Halsey models. The GAB model showed better fitness than the Halsey equation for the moisture sorption isotherms of yogurt products. The temperature shift of isotherms could be expressed using GAB parameters m0, c1, and c2. Yogurt showed higher sorption energy levels than those of concentrated yogurt at moisture contents of 0.025 kg water/kg solid or higher. Three yogurt powders processed from the concentrated yogurt showed very similar heat curves. Concentrated yogurt showed a lower level of equilibrium moisture content than yogurt, which implied structural changes of yogurt during preconcentration. Microwave vacuum dried concentrated yogurt powder showed a lower level of equilibrium moisture content than freeze dried and spray dried yogurts. However, the differences were not significant when concentrated yogurt was used as a raw material for the three drying methods. The differences between sorption isotherms of the three powders may be ascribed to the different surface structures.

Thermophysical properties of plain yogurt as functions of moisture content

Abstract Plain yogurt was prepared, concentrated and then microwave vacuum dried to obtain samples of different moisture content (0·04–0·85 kg water/kg sample). The yogurt samples were used to determine the thermophysical properties. Bulk density was determined with the water displacement method, shrinkage by measuring the thickness, specific heat according to the calorimetric method, and thermal conductivity with the line-source probes. Both specific heat and shrinkage were linear with moisture content, but bulk density changed nonlinearly with moisture content. Thermal conductivity was linear with temperature (25–55 °C) but changed logarithmically with moisture content.

Computer simulation to evaluate thermal processing of food in cylindrical plastic cans

Abstract A computerized mathematical model was developed to evaluate the thermal processing of low acid foods in cylindrical plastic cans with various values of thermal diffusivity for the can wall. The model was based upon the solution of heat conduction equations by the modified alternating direction implicit technique, the Douglas algorithm. This method was used successfully in estimating the time-temperature profile at various locations in the can wall and the food. The program was capable of running on a high speed personal computer. The sterilizing values were found to be more affected by wall thickness than the thermal diffusivity of the wall.

Heat transfer in canned foods undergoing agitation.

An apparatus was developed that allowed for end-over-end rotation of cans during processing in a modified still retort. Cans were rotated in a horizontal and vertical position using a variety of guar gum solutions and rotating speeds. Average values of heat transfer coefficient (h) were found to increase with rotational speed. An increased viscosity caused a decrease in the average h value. Can orientation showed a moderate effect on h. Horizontally positioned cans yielded higher average h values. In 0·4% guar solutions, the average increase in h was 7%. A 0·5% solution resulted in a 14% increase in h while the 0·75% guar solution increased h to a lesser degree of only 4%. Statistical analysis determined that each of the individual variables was significant (P<0·01) in affecting the heat transfer coefficient. Interactions among variables were also found to affect the h value significantly (P<0·02).

Isolation and Determination of Soy Bean Trypsin Inhibitor by Using HPL-Affinity Chromatography

Abstract Trypsin was immobilized on silica support. The bonded phase thus obtained was used to analyze trypsin inhibitors from soybeans. Deactivation study of soybean trypsin inhibitor was conducted after heating at 75°C as such and also in the presence of N-acetyl cysteine and sodium sulfite.