29C-14 |
Evaluation of the variability of the WLF constants of extruded soy flour with processing parameters and storage conditions |
B. K. ASHOKAN and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Williams, Landel and Ferry (WLF) equation is a useful tool in predicting the temperature induced changes in foods and hence knowledge of the WLF constants, which are known to be material properties rather than ‘universal values’, and their variability is essential. Adequate information on the observed variation of the WLF constants as a function of various processing parameters and storage conditions is not available in food literature. The objective of the present study is to determine the variation of the WLF constants of extruded soy flour with the degree of cross-linking in the food polymer and the influence of the water activity of the polymeric matrix on the WLF constants. Roasted, defatted soy flour was extruded at 95°, 115° and 145°C and the extrudate was then stored at various water activities. The degree of cross-linking was semi-quantitatively estimated by the preferential solubility of the extrudate in various solvents. WLF constants were determined using time-temperature superposition principles and Ferry’s reduction method. The WLF constants (C1, C2) of soy flour extruded at 95° and 145°C were (46.76, 186.9°C) and (49.4, 198.370C) respectively at a water activity of 0.973. The constants at a water activity of 0.75 were determined to be (210.32, 1178.22°C) and (167.74, 930.930C) at 95° and 145°C respectively and the variation of the constants was correlated with the degree of cross-linking. The WLF constants for extruded soy flour were found to be different from the universal values reported for synthetic polymers and show differences across water activities and extrusion temperatures. The present study allows a quantitative determination of the effect of water activity and degree of cross-linking on the WLF constants of extruded soy flour and will lead to a better understanding of the variability of the WLF constants in food polymers.
Session 29C, Food Engineering: Rheology and texture
|