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.