EFFECTS OF DRYING METHOD ON PHYSICOCHEMICAL AND FUNCTIONAL PROPERTIES OF SOY PROTEIN ISOLATES

Three soy protein isolates (SPIs) were obtained by different drying methods, including freeze-drying, spray-drying and vacuum-drying. These SPIs were found to be significantly different in color of CIELAB L*, a*, b*values, enthalpies of denaturation (ΔH) in differential scanning calorimetry, 1-anilino-8-napthalene-sulfonate surface hydrophobicities and total sulfhydryl group contents (P < 0.05). The solubility of spray-dried SPI was significantly higher than that of freeze-dried SPI and vacuum-dried SPI (P < 0.05), except at pH 4-5. Spray-dried SPI had much lower turbidity, higher solubility, and better emulsifying and foaming properties than freeze-dried and vacuum-dried SPIs. These results suggested that drying methods could influence the functional properties of SPIs. The utilization of soy protein isolates (SPIs) in various foods is based on their highly desirable functional properties such as solubility, emulsification and foaming. These functional properties may be affected by different drying methods such as freeze-drying, spray-drying and vacuum-drying. This study explains the effects of drying methods on the physicochemical and functional properties of SPIs, which is useful for SPI researchers and manufacturers. Additionally, freeze-drying is usually used in laboratory experiments, while spray-drying is utilized in industrial processes and vacuum-drying is applied in both cases. Hence, the research results on functional properties of freeze-dried SPI in laboratory experiments may not have practical applicability. The direct evidence of the effects of various drying methods on the functional properties of SPIs is based on experiments using the same drying method that is consistent with industrial practice. It is very important that the drying method must be taken into consideration in the research of the functional properties of soy proteins.