Enhancing in vitro digestibility of plant proteins using a novel supercritical carbon dioxide drying approach

The demand for novel and sustainable approaches to generating plant proteins with enhanced functionality is increasing. Sorghum, a drought-tolerant crop, is underutilized due to its limited physicochemical properties. Thus, in this study, an innovative approach based on supercritical carbon dioxide (SC-CO₂) drying was developed to generate sorghum protein concentrates/isolates with enhanced functional properties (i.e., increased digestibility and improved aroma profile). Briefly, Sorghum protein concentrates were extracted from white whole-grain sorghum flour and dried in two ways: freeze drying and SC-CO₂ drying. The dried proteins were characterized for their in vitro digestibility, volatile compound content, and amino acid composition. The collected proteins were also characterized for their morphology, color, crystallinity, surface hydrophobicity, and emulsifying activity index. A more porous structure was observed for the SC-CO₂-dried sorghum proteins compared to their freeze-dried counterparts. The SC-CO₂-dried sorghum proteins showed significantly higher digestibility (47.1%) compared to the freeze-dried sorghum proteins (33.7%) upon simulated sequential oral, gastric, and intestinal digestion. The amino acid compositions of both samples were similar. The levels of alcohols, esters, and organic acids in SC-CO₂-dried proteins were significantly lower than in the freeze-dried ones. In addition, a similar approach was applied to rice bran protein aerogels upon SC-CO₂ drying, which improved their in vitro digestibility. Overall, the developed SC-CO₂ drying approach possesses the potential to generate plant protein concentrates with enhanced digestibility and volatile compound profile.