Conclusions
This study clarified that aspartic endopeptidases, subtilisin-like proteases, metalloendopeptidase, and serine carboxypeptidases were contained in isolated sesame OBs. In them, aspartic endopeptidases showed high activity against oleosins in a pH range of 4–6, and subtilisin-like proteases exerted sharp optimum at pH 5. Metalloendopeptidase contributed to the low proteolytic activity against oleosins at pH 7–9. At pH 5, aspartic endopeptidases and subtilisin-like proteases exerted high activity in a temperature range of 40–70 °C, and optimal at 50–60 °C. Serine carboxypeptidases exhibited high activity at pH 3–5, and optimal at pH 4. By incubating isolated OBs at pH 5 and 60 °C for 2 h, approximately 97% of total lipids were recovered as free oil. Moreover, this study clarified that the intrinsic proteins of sesame OBs were complicated. There were at least three kinds of oleosins with MWs around 17 kDa, and four kinds around 15 kDa. In addition to 27 kDa caleosin, there were four kinds of oil body-associated proteins and one kind of peroxygenase-like protein also had MWs around 27 kDa. Besides 39 kDa steroleosin, 11-beta-hydroxysteroid dehydrogenase-like 6 also had a MW around 39 kDa. In all, this study is meaningful for supplying a new strategy for efficiently demulsifying sesame OBs into free oil by directly using the endogenous proteases.