Structural characteristics, functional properties and in vitro digestibility of rice protein prepared from rice wine lees via an alkaline extraction process or carbohydrate-lipid removal process

Abstract

Rice wine is a traditional beverage in Asian countries, and rice wine lees, a by-product resulting from the fermentation process, generate substantial amounts annually. To promote the sustainable utilization of such product, this research presents the optimization of rice protein extraction processes. An optimized alkaline extraction process (pH 12, 45 °C, 6 h and solid-liquid ratio 1:8), and an optimized carbohydrate-lipid removal process (α-amylase plus cellulase for a 2-h reaction at pH 5 and 50 °C, then heating to 60 °C for 1 h; followed by lipid removal twice at 50 °C for 3 h) were established, resulting in a protein content of 70.80% and 82.52%, respectively. FT-IR and SDS-PAGE indicated a prevalence of β-sheet and α-helix structures in both protein products, and analogous protein subunits, but protein product post carbohydrate-lipid removal showcased superior stability and orderliness. Functional properties and in vitro digestion studies indicated that alkaline extraction improved solubility, foaming ability, emulsifying ability and gastrointestinal digestibility, but presented lower oil-holding capacity, foam stability and emulsion stability. These findings suggest that carbohydrate-lipid removal process is an efficacious technique for extracting rice protein from rice wine lees.