Comparative Analysis of Volatile Compounds and Antioxidant Activity of Kefir Produced by Thai Black Jasmine Rice

Abstract

Volatile compounds and antioxidant activity of kefir produced from Thai black jasmine rice (Hawm nil) were investigated and compared. Thai black jasmine rice milk was prepared by ultrasonication for 24 hours, and then subjected to nine different inoculum percentages of kefir grains and fermentation temperature conditions. Volatile compounds were detected by gas chromatography-mass spectrometry (GC-MS) analysis, while antioxidant activity was determined by DPPH free radical scavenging and ferric reducing/ antioxidant power (FRAP) assays. Metabolic pathway analysis was also conducted. Results indicated that Hawm nil rice milk kefir contained 27 volatile compounds, including four organic acids, four fatty acids, six alcohols, four esters, four ethers, three amines, one ketone and one amide. The GC-MS profile of volatile compounds differed significantly between fermentation conditions; however, antioxidant capacity of Hawm nil rice milk kefir remained constant. Metabolism of pyruvate, sulfur and glycerolipid were identified as pathways affected by fermentation. Results indicated that volatile compounds in fermented Hawm nil rice milk contributed to its antioxidant property. Varying temperature and inoculum conditions were crucial factors that affected the release of these volatile compounds. Rice milk kefir showed potential as supplementary food that was effective in ameliorating multiple human diseases and could serve as a valuable tool in promoting sustainability of human health.