Investigation on the formations of volatile compounds, fatty acids, and γ-lactones in white and brown rice during fermentation.

Volatile compounds, including γ-lactones, in brown and white rice fermented by Lactobacillus paracasei, were compared using gas chromatography-mass spectrometry (GC-MS) with stir-bar sorptive extraction (SBSE). The contents of most esters, alcohols, lactones and some aldehydes were higher in brown rice samples containing higher amount of free fatty acids after fermentation. In particular, the contents of γ-lactones increased more in fermented brown rice containing high amounts of fatty acids than in fermented white rice, suggesting that γ-decalactone and γ-nonalactone were formed from oleic acid and linoleic acid during rice fermentation. In addition, the contents of γ-decalactone in fermented brown rice samples with added 4-hydroxydecanoic acid and ricinoleic acid were determined. The content of γ-decalactone in fermented brown rice samples with added 4-hydroxydecanoic acid was considerably higher than that in the control after fermentation, indicating that 4-hydroxydecanoic acid could be an effective intermediate for the formation of γ-decalactone in rice during fermentation.