Release of phenolic acids from defatted rice bran by subcritical water treatment.
BACKGROUND
Oil production from rice bran, an undervalued by-product of rice milling, produces defatted rice bran (DRB) as a waste material. Although it is considered a less valuable product, DRB still contains useful substances such as phenolic compounds with antioxidant, UV-B-protecting and anti-tumour activities. In this study the phenolic acids in DRB were extracted with subcritical water at temperatures of 125, 150, 175 and 200 °C.


RESULTS
Analysis of total phenolics using Folin-Ciocalteu reagent showed about 2-20 g gallic acid equivalent kg(-1) bran in the extracts. High-performance liquid chromatography analysis showed low contents of phenolic acids (about 0.4-2 g kg(-1) bran). Ferulic, p-coumaric, gallic and caffeic acids were the major phenolic acids identified in the extracts. Thermal analysis of the phenolic acids was also done. The thermogravimetric curves showed that p-coumaric, caffeic and ferulic acids started to decompose at about 170 °C, while gallic acid did not start to decompose until about 200 °C.


CONCLUSIONS
Subcritical water can be used to hydrolyse rice bran and release phenolic compounds, but the high temperatures used in the extraction can also cause the decomposition of phenolic acids.
Fabian
Cynthia
C
National Taiwan University of Science and Technology, Taipei, Taiwan.
Tran-Thi
Ngoc Yen
NY
Kasim
Novy S
NS
Ju
Yi-Hsu
YH
D000975:Antioxidants / Q000302:isolation & purification*; D002109:Caffeic Acids / Q000032:analysis; D002934:Cinnamates / Q000302:isolation & purification*; D003373:Coumaric Acids / Q000032:analysis; D002523:Edible Grain / Q000737:chemistry*; D005707:Gallic Acid / Q000032:analysis; D062385:Hydroxybenzoates / Q000737:chemistry / Q000302:isolation & purification*; D012275:Oryza / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry*; D014867:Water
D000975:Antioxidants; D002109:Caffeic Acids; D002934:Cinnamates; D003373:Coumaric Acids; D062385:Hydroxybenzoates; D010936:Plant Extracts; D014867:Water; D005707:Gallic Acid; C004999:ferulic acid; C017616:phenolic acid