Potential of whey protein isolate-lactose conjugates in the in-vitro infant digestion

Abstract

Protein base modification is a notable potential method to alter the molecular structure and physicochemical and functional properties of the protein, thus affecting protein digestibility. This study investigated the protein digestibility of whey protein isolate– lactose (WPI-Lac) conjugates using an in-vitro infant gastric digestion static model. WPI was conjugated with lactose by dry Maillard reaction under optimised conditions. The following conditions were studied, WPI-Lac heated at 40°C, water activity aw = 0.80 and incubation time of 0, 1, 3, 5 and 7 days. Based on the brown colour and the conjugation rates in ortho-phthaldehyde analysis, the incubation time of day 3 of conjugation promises the extent of conjugation and prevents the formation of advanced Maillard reaction products (MRPs). Functional properties of glycated protein were found to significantly higher (p<0.05) in antioxidant activity and solubility compared with native WPI. In addition, Fourier Transform Infrared (FTIR) analysis indicated that the WPI was modified by dry MR with lactose. WPI-Lac day 3 was evaluated using the in-vitro gastric infant digestion model which undergo simulated gastric infant condition at pH 3 with 19 µL of 0.625mg/mL of pepsin. Sodium dodecyl sulfate acrylamide gel electrophoresis (SDSPAGE) analysis of digesta revealed that MRPs increased susceptibility to be hydrolysed by pepsin. The digestion product affirms dry MR conjugation can potentially improve WPI digestibility. Herein, this study of WPI-Lac conjugates contributes to an understanding of how protein–disaccharide glycates affect in-vitro infant gastric digestion.