Inhibitory Effects of ‘Enokitake’ Mushroom Extracts on Polyphenol Oxidase and Prevention of Apple Browning

Abstract

‘Enokitake’ mushroom (Flammulina velutipes) extracts were prepared by three different solvents: 70 mL/100 mL acetone, 70 mL/100 mL ethanol as well as hot water. Effects of the extracts on mushroom tyrosinase activity and browning of apple were investigated. Mushroom tyrosinase activities assayed spectrophotometrically and by oxygen uptake were found to be inhibited significantly by all three extracts. Lyophilized ‘enokitake’ fruit body powder inhibited the browning of fresh apple. Immersing sliced apple into the acetone extract was found to prevent effectively the browning development. Freshly squeezed apple juice with added hot-water extract showed the concentration-dependent inhibition of browning. No browning was observed on the apple juice when mixed with the extract containing 1.0 g wet ‘enokitake’/mL in a mixture. Under the same conditions, no significant changes in color in terms of a* and b* values of the mixture were observed for up to 6 h. These observations suggested that ‘enokitake’ mushroom contained certain compounds which inhibited mushroom tyrosinase activity and the development of browning induced by the catalytic oxidation due to polyphenol oxidase.