Improving Phenolic Bioactivity In Double-strain Fermented Oats And Their Characteristics In Vitro Digestion

Oats are rich in soluble dietary fiber,essential amino acids,unsaturated fatty acids,polyphenols,vitamins and minerals.They have strong antioxidant,anti-inflammatory,anti-cancer and hypoglycemic activities,and play a positive role in the prevention and treatment of chronic diseases and adjuvant treatment of diseases.Microbial fermentation can not only improve the nutritional and functional characteristics of oats,but also open up the way of oats resource utilization.In this study,oat was used as fermentation medium and Monascus was used as main fermentation strain.The effects of different microbial combinations on the functional and nutritional compounds of oat were studied,and the double-strain fermentation system of oat was constructed.Further,the contents,compositions and antioxidant activities of three types of phenolics in oat during fermentation were explored,and the effects of double-strain fermentation on the characteristics of oat phenolics were clarified.Simulated digestion model was used to digest unfermented and fermented oats in mouth,stomach,small intestine and large intestine.The changes of phenolic compounds and antioxidant activities of fermented oats in vitro simulated digestion were investigated.The major conclusions are as follows:(1)Constructing and optimizing the oat phenolics release system for double-strain fermentation: the effects of different combinations of Monascus,Monascus+Saccharomyces cerevisiae,Monascus+Bacillus subtilis,Monascus+Rhizopus oryzae on oat functional nutrients were investigated.The results showed that the contents of polysaccharides,soluble proteins,total phenolics and total flavonoids in the fermentation group of Monascus+Bacillus subtilis were the highest,reaching 4.58 g/100 g,7.23 mg/g,21.16 mg GAE/g DW and 1.84 mg RT/g DW respectively,which were 2,4,30.2 and 8.3 times higher than those of the unfermented oats.The optimum fermentation conditions for co-fermentation of Monascus and Bacillus subtilis determined by single factor and orthogonal experiments were as follows: the inoculation ratio of Monascus and Bacillus subtilis was 2:1,and Bacillus subtilis was added after 4 days of fermentation,initial water content of culture medium was 40%,andfermentation time was 12 days.Under these conditions,the content of phenolics and flavonolids in fermented oats were 26.73±0.62 mg GAE/g DW and 2.97±0.24 mg RT/g DW,which were 23.87 times and 22.85 times higher than unfermented oats,respectively.(2)Changes of characteristics and antioxidant activities of oat phenolics during double-strain fermentation and their main enzymes: the contents of free,conjugated and bound phenolics in oats increased by 12,7 and 4 times respectively after double-strain fermentation.The contents of gallic acid,chlorogenic acid,vanillic acid and ferulic acid in free phenolics increased by 13.05,47.31,18.64 and 28.22 times,respectively.P-coumaric acid,sinapic acid and ferulic acid were the main components of bound phenolics,and their contents increased 44.19,51.38 and 40.35 times,respectively.Chlorogenic acid in conjugated phenolics increased nearly 100 times.During double-strain fermentation process,the changes of oat phenolic content were positively correlated with the activities of ?-amylase,cellulase and ?-glucosidase.The correlation with protease activity was not significant.Fermentation combining Monascus with Bacillus subtilis significantly improved the antioxidant capacity of free and conjugated phenolics in oats.The IC50 values for scavenging DPPH radical were30.88±0.11 ?g/mL and 59.00±0.26 ?g/mL,respectively,and the IC50 values for scavenging ABTS+ radical were 8.59±0.44 ?g/mL and 20.34±0.12 ?g/mL,respectively.Free radical scavenging ability of free phenolics in fermented oat was equal to that of VC.(3)The changes of phenolic compounds and antioxidant activities of fermented oats in vitro simulated digestion: simulated in vitro digestion significantly promoted the release of oat phenolics and flavonoids.The contents of phenolics and flavonolids released from fermented oats during simulated digestion in vitro were 10.77 and 6.77 times higher than those from unfermented oats.Chlorogenic acid,catechin acid,sinapic acid and ferulic acid were the main phenolic compounds released during digestion.In addition,the antioxidant capacity of fermented oats at different digestive stages was significantly higher than that of unfermented oats(p<0.05).The antioxidant capacity of oats at different digestive stages was significantly correlated with the amount of phenolics and flavonolids released from oats.Double-strain fermentation might be an effective way to improve the bioaccessible of oatphenolics.This study provides a new idea for the development of oat products with high nutritional added value and biological activity,and has certain theoretical significance and application value.