When we examined the antioxidant activities of different
fractions after butanol extraction, we found that supplementary
butanol extracts exhibited decreasing antioxidant activity (+1
butanol > +2 butanol > +3 butanol extract). To better understand
this observation, we investigated the compositions of all 3 extracts
with UPLC–MS analysis. Several peaks were eluted between 0.8
and 1.8 min; these peaks correspond to oligosaccharides (di- and
trisaccharides) and vanillic acid. These hydrophilic compounds
were present as minor fractions; a main peak was eluted at
8.93 min corresponding to sesaminol triglucoside; a sesaminol diglucoside
peak was also detected at 9.55 min. In addition, UPLC–MS
analysis of +2 and +3 butanol extracts showed that sesaminol triglucoside
peak intensity decreased gradually and sesaminol diglucoside
was not detected in the two extracts (Supplementary
data 3). These results suggest that sesaminol glycoside content in
supplementary butanol extracts gradually decreased, in a manner
that was correlated with the decrease in antioxidant activity.