Heat-induced dissociation and association of proteins in hempseed protein bodies

Abstract

Protein bodies (PBs) are naturally occurring storage organelles in seeds. In hempseeds, the major storage proteins, including edestin (11S globulin) and albumin, are primarily located in the crystalloids and proteinaceous matrices of hemp protein bodies (HPBs), respectively. The retention of native PB structures in flours and dry-fractionated protein ingredients has important implications for protein functionality and digestibility, especially when heat treatment is applied during processing. While the thermal behaviour of hempseed proteins has been studied in protein isolate systems, to the best of our knowledge, it has not yet been explored in HPB systems. In this study, we isolated native HPBs using an enzymatic method. Aqueous suspensions of HPBs (4 % protein, w/w) were heated at selected temperatures (60–100 °C) and pH 7 for 20 min, followed by hydrolysis with trypsin at pH 7 and 37 °C for 120 min. The thermal aggregation of proteins in HPBs was characterised using confocal laser scanning microscopy (CLSM) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The hydrolysis of HPBs by trypsin was monitored over 120 min by measuring the degree of protein hydrolysis (DH) and analysing SDS-PAGE. Aggregation of edestin in HPBs, primarily driven by disulfide bond formation, occurred upon heating, most noticeably at temperatures above 80 °C. Heating increased DH and altered protein degradation patterns of both acidic and basic subunits of edestin. This may be related to conformational changes in the HPB structure resulting from heat-induced dissociation-association of multiple HPB protein fractions, including 11S edestin, 7S globulin, and 2S albumin. These findings contribute to our understanding of the structure-hydrolysis relationships of HPBs, potentially leading to their use as a new plant-based material for food applications.