Effect of milling and long-term storage on volatiles of black rice (Oryza sativa L.) determined by headspace solid-phase microextraction with gas chromatography-mass spectrometry

Abstract

Although black rice has gained popularity, the changes in volatiles produced during black rice storage remain unclear. Herein, the volatile composition of unmilled and milled black rice stored at 25 °C or 35 °C for 0-12 months was investigated by headspace solid-phase microextraction with gas chromatography-mass spectrometry. Fifty-four volatiles were identified, 15 of which were not previously identified in black rice, including 4-propylbenzaldehyde, methyl 2-hydroxybenzoate, methyl 2-methylpentanoate, 2,5-dimethylnonane, 5-methyldecane, and 2-methylundecane. In this study, octanal increased at a high rate during early storage compared with hexanal, a traditional oxidation marker; thus, octanal may be an early oxidation marker in black rice. The results suggested that high temperature is not appropriate for storage of unmilled or milled black rice because it promotes lipid oxidation, producing volatile compounds. At 25 °C, black rice stored for short times such as 3 months should be milled, whereas for 6 months, black rice should be stored without milling.

Keywords: Black rice; GC–MS; Headspace solid-phase microextraction; Lipid oxidation; Storage; Volatiles.