Effects of extraction temperature and preservation method on functionality of soy protein

The effects of extraction temperature and preservation method on the functional properties of soy protein isolate (SPI) were determined. Four extraction temperatures (25, 40, 60, and 80 degrees C) were used to produce SPI and yields of solids and protein contents were determined. Three preservation methods were also tested (spray-drying, freeze-drying, and freezing-thawing) and compared to fresh (undried) samples for each extraction temperature. No differences in yields of solids and protein were observed among SPIs extracted at 25, 40, and 60 degrees C; however, SPI extracted at 80 degrees C yielded significantly less solids and protein. Extraction temperature significantly affected SPI functionality. As extraction temperature increased, solubility and emulsification capacity decreased; surface hydrophobicities, emulsification activities and stabilities, and dynamic viscosities increased; and foaming properties improved. Preservation method also significantly affected SPI functionality. Drying method did not affect the denaturation enthalpies of SPIs, but spray-dried SPIs had higher solubilities, surface hydrophobicities, and emulsification stabilities, and lower viscosities, emulsification activities and rates of foaming than freeze-dried SPI exhibited. Emulsification and foaming capacities and foaming stabilities were similar for both methods of drying. There was significant interaction between extraction temperature and preservation method for all functional properties except emulsification capacity.