Antibaterial Activity And Antioxidant Activity Of Different Form Phenolics From Defatted Rice Bran

Rice bran, a by-product of rice processing which accounts for 5% to 5.5% of the rice weight, is a mixture of cortex, a small amount of rice embryo and debris when the brown rice is grinded. Rice bran is rich in active substances, such as protein, polysaccharides and polyphenols. Rice bran is honored as “God-given nutrient source”. Polyphenols in rice bran has anti effects to oxidation, virus, bacteria, cancer and could lower serum lipids in vivo. In this research, five different forms of polyphenols were extracted from defatted rice bran,namely free, soluble ester, soluble glycosides, insoluble ester and insoluble glycosides polyphenols. The content of total phenols, flavonoids and monomer phenolic acids of the five different forms of polyphenols was determined. Antibaterial activities and antioxidant activities were studied. Results showed as follows:(1) Defatted rice bran contained 6.99 mg GAE/g total phenols and 0.61 mg Rutin/g flavonoids. The content of total phenols decupled the flavonoids in defatted rice bran. The insoluble covalent binding polyphenols was the major form which accounted for 53%, and ester bond was the most frequently observed. As for the monomer phenolic acids, obvious differences were determined in types and quantities among these five different forms polyphenols. The main ingredients of the free polyphenols wasp-coumaric acid; ferulic acid,gallic acid and protocatechuic acid consisted of soluble ester polyphenols; the soluble glycosides polyphenols was mainly composed of protocatechuic acid; ferulic acid and p-coumaric acid accounted the insoluble ester polyphenols; the insoluble glycosides polyphenols largely existed in the form of protocatechuic acid.(2) When the concentration was ranging from 200 to 800 μg/mL, soluble ester, soluble glycosides and insoluble glycosides polyphenols all had great antibaterial activities to E.coli O157, Staphylococcus aureus Rosenbach and Pichia carsonii. The antibacterial activity of the soluble ester polyphenols was most remarkerable. However, insoluble ester combined polyphenols only had weak antibacterial effect on E. coli O157. Free polyphenols had no antibaterial activities. The five different forms of polyphenols had no effects on Aspergillus niger.(3) When the concentration was ranging from 10 to 100 μg/mL, the five different forms of polyphenols all showed some antioxidant activity in vitro, Fe3+ reduction capability, DPPH and ABTS radical scavenging activity. The antioxidant activity of the soluble ester polyphenols was most remarkerable. As a whole, the antioxidant effect of ester combined polyphenols was better than that of glycosides combined polyphenols. The soluble combinedwas better than insoluble combined polyphenols. These results indicated that the combination of the key ways, existing forms and different monomer phenolic acids would affect the antioxidant activity.(4) When the concentration was ranging from 6.25 to 125 μg/mL, the five different forms of polyphenols significantly inhibited erythrocyte hemolysis. The following order was accorded to its function from strong to weak, that is insoluble ester, free polyphenols, soluble ester polyphenols, insoluble glycosides polyphenols, soluble glycosides polyphenols. The anti-hemolysis activities of free, insoluble ester and soluble ester polyphenols were significantly higher than that of insoluble glycosides polyphenols, soluble glycosides. The anti-hemolysis ability induced by AAPH would have relation with total phenolic content and individual monomers phenolic acids.(5) Five different forms of polyphenols were able to eliminate ROS effectively and inhibit lipid peroxidation. They would protect red blood cells from being oxidation with CAT,SOD and GSH-PX.