Characterization of walnut proteins extracted from meals and cakes with different oil production methods

Abstract

This study investigated the effects of three industrial oil extraction methods (solvent extraction, cold pressing, and hot pressing) on the structural, physicochemical, techno-functional, and digestive properties of walnut meal or cake protein, as well as their regulatory effects on rat intestinal microbiota. The protein contents of raw materials were 57.50% for solvent-extracted walnut meal, 48.65% for cold-pressed walnut cake, and 37.45% for hot-pressed walnut cake. The purity of the extracted proteins was 88.02% (WP), 86.51% (CWP), and 70.21% (HWP), respectively. Hot pressing induced protein unfolding and improved solubility and emulsifying activity. The total amino acid contents of the three walnut protein samples ranged from 100 to 108 mg/g, and the hydrophilic amino acid contents of CWP and HWP were significantly higher than WP. In vitro digestibility of HWP was the highest (37.40%), followed by CWP (30.05%) and WP (27.83%). Moreover, differences in digestibility further mediated the regulatory effects of walnut proteins on intestinal microbiota in SD rats. This work clarified the relationships among oil extraction processing, protein structure, techno-functionalities, in vitro digestibility, and regulation of intestinal microbiota, which would facilitate the valorization and potential food application of proteins from walnut meal and cake.