Aims: The effects of kefir fermentation were investigated on antioxidation activities (in vitro) and antioxidative stress (in vivo) for different Thai rice; Hawm Nil rice, Red Hawm rice and Khao Dawk Mali 105 rice. Methodology: Antioxidant activity (in vitro) was investigated using ferric reducing antioxidant power and 2, 2´-diphenyl-1-picrylhydrazyl assays. In addition, antioxidative stress (in vivo) was performed using colitis rat models to study nitric oxide (NO), lipid peroxidation (LPO) and superoxide dismutase (SOD) compared with rats treated with prednisolone and cow's milk kefir. Results: Antioxidant activity of rice kefir powder from both assays had higher antioxidant activity than cow's milk kefir powder. NO levels of colitis rats received Hawm Nil rice kefir powder (HNKP) was reduced when compared to phosphate buffered saline (PBS) group. Moreover, colitis rats received HNKP did not differ in NO levels from colitis rats that received prednisolone and non-colitis rats. The result of LPO product malondialdehyde (MDA) indicated that colitis rats treated with HNKP had reduced TBARS compared to PBS group, and did not differ in TBARS levels from rats that received prednisolone and non-colitis rats. Surprisingly, increase in SOD activity was observed in colitis rats that received HNKP compared to PBS, with similar results of increased SOD in rats that received prednisolone and cow's milk kefir powder. Conclusion: Hawm Nil rice kefir may offer a protective effect for antioxidative stress resulting from chemical induction; it has potential as a supplementary food with high antioxidant activity and is regarded as safe for consumer health.

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.