Physicochemical and functional property changes in soy protein isolates stored under high relative humidity and temperature.

The effects of water activity (aw) and temperature during storage on the physicochemical characteristics and functional properties of soy protein isolate (SPI) were investigated. SPI was stored with two different temperatures (25, 45 °C) and two levels of water activity (0.25, 0.75) for 224 days. During the 224-day storage period, all the samples showed decreases in gel hardness, emulsifying stability, foaming properties, viscosity, solubility, and color alteration, but increased in surface hydrophobicity (RSo). These alterations were stronger when stored at 45 °C than at 25 °C and in 0.75 aw than 0.25 aw, and most pronounced at 45 °C and 0.75 aw. Our results revealed that storage conditions - temperature and water activity - will indeed affect the functional properties of soy protein isolates.