Functional properties of hemp protein concentrate obtained by alkaline extraction and successive ultrafiltration and spray-drying

Hemp protein concentrates were obtained from hemp seed cake by extraction at high alkaline pH (10 and 12) followed by an ultrafiltration/diafiltration (UF) purification step and spray-drying. The composition, thermal, nutritional, and functional properties of the resulting protein samples were evaluated. The UF treatment increased protein purity of the protein extracts recovered at pH 10 and 12, from similar to 61% and similar to 70% to similar to 85% and similar to 88%, respectively. This protein enrichment did not change the polypeptide composition, as well as the protein solubility profile at each respective pH of extraction. However, the pH 12-extracted proteins showed higher solubility (>85%) notably at alkaline pH (7-9) compared with the pH 10-extracted samples (similar to 40-80%). The highest in vitro protein digestibility values were obtained for the crude protein sample resulting from the extraction at pH 10 (similar to 89%) and the pH 12-extracted protein sample after heat treatment (similar to 96%). The pH 12-extracted hemp proteins presented excellent emulsifying properties, producing submicromic emulsions with high stability even after protein heating, whereas the emulsions prepared from the pH 10-extracted proteins tended to be easily destabilised by flocculation and coalescence. The particular properties of the former protein sample could be explained by the denaturing polymerisation of protein during the extraction at pH 12 involving complexation with polyphenols.