Antioxidant And Anti-tyrosinase Activities Of Bioactive Compounds In Fermented Rice By Aspergillus

Bioactive compounds are high-value nutrients existing in plant and food products with smallamount. The most common bioactive compounds include secondary metabolites, such asantibiotics, alkaloid, eatable colorants and phenolic compounds[1-3]. Phenolic compoundsconsist of isoflavones, phenolic acids, and tannin. Phenolic compounds, also namedpolyphenol, are a group of natural antioxidants. They are considered as very importantbioactive compounds in food. Aspergillus is an imperative microorganism used by theindustry of fermentation and food processing. So far, more than60Aspergillus strains havebeen applied in these two industrial areas. Aspergillus has been widely used for solid-statefermentation of grains and legumes with an aim to improve the antioxidant activities of theseculture mediums[4]. Some Aspergillus strains are able to synthesize kojic acid as thesecondary metabolite during fermentation. Kojic acid is an effective anti-tyrosinasecompound, which can be used in food preservation[5]. In addition, natural phenoliccompounds in rice have been indicated to have tyrosinase inhibitory effects, such as vanillicacid, coumaric acid, ferulic acid, and syringic acid[6-9].Aspergillus oryzae M-1, A. oryzae MC-01, A. oryzae SP-01, and A. sojae have been selectedfor strain screening for further investigation of antioxidant activity of Aspergillus-fermentedrice. The enzymatic activities of α-amylase, cellulose, and β-glucosidase, DPPH radicalscavenging activity, reducing power, metal chelating capacity, and total phenolic content offermented-rice by the four strains have been determined. Based on the results of the aboveparameters, A. sojae has been selected for further investigation. Online HPLC analysis(post-column) was adopted to identify the major phenolic compound in fermented-rice by A.sojae. The oxygen radical absorbance capacity and β-carotene bleaching inhibition have beendetected to evaluate the antioxidant activity of fermented-rice by A. sojae. Moreover, theDNA protective effect has been demonstrated by using fenton reagents for radical productionand supercoil plasmid as the substrate.As for anti-tyrosinase activity of phenolic compounds in fermented-rice, A. oryzae M-1, A.oryzae MC-01, A. oryzae SP-01, and A. sojae have been used for solid-state fermentation ofrice under the conditions of35°C and humidity>90%. The metal chelating, polyphenoloxidase inhibitory activity, oxygen radical absorbance capacity, and total phenolic content offermented rice during fermentation were analyzed. The rice fermented by A. orgzae SP-01had higher metal chelating, polyphenol oxidase (PPO) inhibitory activity and oxygen radical absorbance capacity (ORAC) than that of other three stains. These four parameters offermented rice tended to be stable at the fourth day of fermentation. Therefore, rice fermentedby A. orgzae SP-01for four days was selected for the evaluation on its anti-tyrosinase activity.Lineweaver-Burk Plot was employed to investigate the inhibitory effects of bioactivecompounds in fermented rice by A. orgzae SP-01on the oxidation of L-DOPA catalyzed bymushroom tyrosinase (M-PPO). The potential mechanism of the anti-tyrosinase activity wasestimated based on the results of Lineweaver-Burk Plot. The IC50and inhibitory constant (KI)of the extract of fermented-rice by A. oryzae SP-01indicated that its inhibitory effect washigher than positive control-kojic acid and ferulic acid. Spectrophotography and ImageJ wereused to quantitatively analyze the preventive effects of the extract of fermented-rice by A.oryzae SP-01on browning of shrimp hemolymph and apple slices, respectively. In addition,the direct application of fermented-rice by A. oryzae SP-01on anti-melanosis shrimp furthersupported that fermented-rice by Aspergillus possessed an effective inhibitory activity ontyrosinase.