Nutritional assessment and effects of heat processing on digestibility of Chinese sweet potato protein

The amino acid composition, in vitro and in vivo digestibility as well as trypsin inhibitor activity (TIA) of sweet potato protein (SPP) were evaluated. The effects of different types of heat processing on the in vitro digestibility and TIA of SPP were also investigated. The results showed that SPP was deficient in lysine, but rich in threonine, valine, tryptophan and aromatic amino acids. SDS-PAGE analysis showed that native SPP was not easily digested by pepsin-pancreatin enzyme system, whereas commercial soy protein isolate (SPI) displayed a good in vitro digestibility. Autoclaving (127 °C for 20 min, 0.145 MPa) significantly improved in vitro and in vivo digestibility of SPP. The in vivo digestibility of autoclaved SPP was 95.1%, which was comparable to that of SPI (96.1%) and casein (97.4%), and remarkably higher than that of native SPP (50.4%). PDCAAS of native SPP and autoclaved SPP were 0.36 and 0.66, respectively. In addition, autoclaving also markedly decreased TIA of native SPP from 67.8 to 2.0 mg trypsin/g protein. Autoclaving enhanced in vitro digestibility and decreased TIA of native SPP, thereby improving its food qualities. Although SPP was deficient in lysine, autoclaved SPP could be utilized as a good protein source for human consumption.