Effect of extraction pH on functional properties, structural properties, and in vitro gastrointestinal digestion of tartary buckwheat protein isolates

The tartary buckwheat protein isolates (TBPIs) were extracted by different pH combined with isoelectric precipitation. The impacts of extraction pH on Osborne-type protein fractions, functional properties, structural properties, and in vitro gastrointestinal digestion were investigated. The result showed that alkaline extraction was effective to increase yield of TBPI. With increase of extraction pH, the content of albumin in TBPI gradually decreased, while content of glutenin was increased. The solubility of TBPIs extracted by pH above 12 were significantly decreased while emulsion stability was significantly increased, which was related to significant increase of surface hydrophobicity. The digestive rate of TBPIs of pH 7 and 8 were high. With increase of pH from 8 to 10, digestive rate of TBPIs decreased. It was related to the compact structure of TBPIs, which had higher alpha-helix content, higher disulfide bonds, and lower intrinsic fluorescence intensity. Continuous increase of pH increased digestive rate of TBPIs. It was associated with unfolded and denatured structure of TBPIs (pH > 12), as evidenced by breakdown of disulfide bonds, lower alpha-helix structure, red-shift in intrinsic fluorescence, and dissociation of subunits. Overall, extraction pH during protein extraction has great impacts on TPBIs.