Comparison of physicochemical characteristics, functional properties and biological activities of hemp seed proteins by different extraction methods

Objective: Protein extraction methods play a crucial role in the quality, functionality, and recovery efficiency of protein products, and directly affect their subsequent applications. Hemp seeds are rich in proteins and oils; however, the process of hemp seed protein extraction has rarely been studied. To bridge this knowledge gap, we aimed to explore the effects of the extraction conditions on the yield, physicochemical characteristics, functional properties, and biological activities of hemp seed proteins. Methods: Alkaline extraction (AE), AE combined with ultrasonication (AEU), salt extraction (SE), and SE combined with ultrasonication (SEU) were used to extract the hemp seed proteins. The protein yields of SE and SEU were significantly higher than those of AE and AEU. All four types of protein extracts showed no obvious differences in protein purity, which was higher than 95%; however, significant differences were observed in protein physicochemical properties, functional properties, and biological activities among the proteins obtained by the four extraction methods. The hemp seed proteins extracted by the SE (designated as HPS) and SEU (designated as HPSU) methods possessed better nutritional quality, digestion properties, higher fat absorption capacity, and a lower water-holding capacity. Moreover, we found that the proteolytic products of HPS and HPSU exhibited superior biological activities, including 2,2-diphenyl-1-picrylhydrazyl scavenging capacity and dipeptidyl-peptidase IV inhibitory activity, but similar anti-inflammatory activities. We concluded that SE was more suitable for the extraction of hemp seed protein because the SE method maintained the high nutritional value for the proteins. We believe that these findings contribute to a better understanding of the effects of extraction methods on protein quality.