11-7 |
Effect of stabilization method on functionality of soy protein isolates |
N. A. DEAK, Dept. of Food Science & Human Nutrition, Iowa State Univ., 2312 Food Sciences Bldg., Ames, IA 50010 and L. A. Johnson, Center for Crops Utilization Research, Iowa State Univ., Dept. of Food Science & Human Nutrition, 1041 Food Sciences Bldg., Ames, IA 50011. Soy protein isolates (SPI) are widely used in the food industry and their applications are based upon their functional properties (i.e. solubility, emulsification and viscosity control). These applications make SPI a high value-added product. SPI is usually stored as a dry powder and the drying is done to enhance shelf life and ease of distribution. The drying method of choice in industrial plants is spray-drying while the usual method used at bench-scale isolate production for research purposes is freeze-drying. The purpose of this study was to determine the functional properties of SPI after both methods of drying and to relate them to the functionality of fresh (undried) SPI and frozen-thawed SPI. Four extraction temperatures were used to produce these isolates, 25, 40, 60, and 80°C, for each stabilization method and the effects on solubility, surface hydrophobicity, emulsification, foaming, thermal, and rheological properties were determined. The rheological studies were conducted by using a cone-and-plate viscometer and the relative native state of the soy proteins were monitored by differential scanning calorimetry. There was a slight loss of the native state of proteins during both freezing and freeze-drying. These losses were even less with spray-drying. Emulsifying capacity was improved by all stabilization methods, but the emulsions obtained were less stable when the SPI was stabilized. Viscosity decreased by spray-drying, but increased by freezing or freeze-drying. Foaming capacity decreased but foam stability was greatly improved by stabilizing, freeze-drying being the best. Solubility significantly decreased by freeze-drying but no significant decrease was observed when spray-drying. Surface hydrophobicity was significantly affected by all stabilization methods tested. Functionality is significantly changed during drying. Each method of drying gives unique characteristics and these are difficult to relate to one another.
Session 11, Food Chemistry: Proteins I
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