Abstract: The in vitro digestibility of soy protein isolates (SPI) and the effects of thermal treatments were investigated. SDS- PAGE analysis showed that, glycinin of SPI was the most easily digested by pepsin, andβ-conglycinin was the most difficult. In all the subunits of β-conglycinin, theα-subunits were the most susceptive subunits. TCA-NSI analysis indicated that, at a certain protein concentration, the nitrogen release of SPI by pepsin during the enzyme incubation was dependent upon the enzyme concentration applied. In addition, the in vitro digestibility of SPI was affected by different thermal treatments. The dry heat-treatment (i.e., at 80℃ for 30～60min) nearly did not affect the in vitro digestibility by pepsin, while under the same conditions, the wet heat-treatments could remarkably improve the digestive extent of pepsin and trypsin upon SPI. This result suggested that the in vitro digestibility of SPI depended on its extent of denaturation.

Key words: soy protein, in vitro digestibility, thermal treatment, digestibility