Study On Release And Transformation Of Phenolics In Monascus Fermented Oats And Their Bioactivity

Oat(Avena sativa L.),one of the major crops in China,is produced in various countries around the world.Oat is one of the highest nutritional values of cereal grain.A wide range of functional components like carbohydrates,proteins,avenanthramides,flavonoids and phenolics have been reported from A.sativa and they have been widely used in food.Solid state fermentation has been employed to increase the resource utilization and nutritional valve in oat products.This paper is aimed at the mechanism for improving phenolic compounds of oat fermented by Monascus.The composition of free,conjugated and bound phenolic fractions in Monascus fermented oat were investigated,and we analyzed the three phenolic fractions'antioxidant activities.The correlation between phenolic contents and carbohydrate-hydrolysis enzyme activities in Monascus fermented oat were analysed,in order to explore the enzymology mechanism of polyphenols release.Moreover,the enzymatic hydrolysis and microbial fermentation were used to further improve the efficiency of polyphenol release and conversion.The major conclusions are as follow:(1)Constructing the polyphenol composition system in Monascus fermented oat to find the relationship between three separated phenolic fractions.Results revealed that the fermentation process significantly increased total phenolic content(6.04 GAE mg/g DW),especially the free phenolic content increased with an 26-fold rise.Moreover,the dominate phenolic compositions of free,conjugated and bound phenolic fractions from oats varied with fermentation.Chlorogenic acid in free phenolic fraction was enhanced 40-fold,ferulic acid in bound fraction was enhanced 100-fold,while the amount of newly generated rutin was up to355.07 mg/kg in conjugated fraction.All three phenolic fractions from fermented oats demonstrated greater DPPH and ABTS~+radical scavenging abilities than that of unfermented oats.And this high antioxidant activity may be due to a high content of antioxidant compounds,such as chlorogenic acid,catechin and ferulic acid.(2)Based on the relationship between phenolics and carbohydrate-hydrolysing enzymes in fermented oat,to clarify the enzymology mechanism of phenolics release.There were good correlations between phenolic content and?-amylase,xylanase and FPase activities.A high level of?-amylase activity(141.07 U/g)was observed in the fermentation system.The phenolic content of oat powder treated with crude enzyme from fermented oats significantly increased,free phenolic content increased from 0.042 to 0.23 mg GAE/g DW while bound phenolic content increased from 0.089 to 0.48 mg GAE/g DW.The content of ferulic acid in insoluble fraction and the vanillic acid in the soluble fraction increased significantly.The surface SEM morphology of the oats showed that the cell wall structure was damaged by the crude enzyme treatment,which led to the release of phenolics.(3)Further improve the efficiency of polyphenol release and conversion in fermented oat with enzymatic hydrolysis and microbial fermentation.The results revealed that the cellulase could release great quantities of insoluble phenolics from 166.78 to 86.32 mg/kg in oat,and the ferulic acid in insoluble fraction decreased by 54.54%.Compared to the traditional fermentation system,the system of fermentation following enzymatic hydrolysis further increased the soluble and insoluble phenolic contents(24.38%and 31.05%,respectively)and shortened the fermentation time from 14 days to 12 days.Moreover,the soluble phenolic fraction exhibited significantly higher?-glucosidase inhibition,while the insoluble phenolic fraction had significantly(p<0.05)higher?-amylase inhibitory activity.This study explored the mechanism of phenolic release and conversion in Monascus fermented oat,which provided a classic example for solid-state fermentation with cereal to improve their phenolic content.It also provided guidance for a new processing technique for oats rich in phenolics.