Inactivation Behavior of Enzymes and the Changing Pattern of Some Physicochemical Properties During Steam Blanching of Banana Slices before Further Processing

Abstract

Setagaya-ku, Tokyo 156 The gradual changing pattern of lightness (L), saturation color index and ΔE during storage of unblanched and blanched banana slices were found to conform to heat inactivation performances of peroxidase isozymes and polyphenoloxidase fractions. At 10min steam blanching of the slices all the isozymes of peroxidase were inactivated, whereas, at 5min blanching polyphenoloxidase were completely inactivated; and the inactivation time and rate of each isozyme and fraction were found to be different until being completely inactivated, although 90-96% of the peroxidase activity and 99% of polyphenoloxidase activity were lost at 1min blanching. To clarify this inactivation pattern the D-values for peroxidase isozymes and polyphenoloxidase fractions were calculated. All the fractions of pectinesterase exhibited zero residual activity at 10min blanching and the order of heat stability was found to be fraction-III>fraction-I>fraction-II at 30s blanching, at 1-4min blanching it was fraction-II>fraction-III>fraction-I and after that the order was fraction-II>fraction-III>fraction-I. After one minute of blanching only 66.3% of fraction-I, 55.4% of fraction-II and 30.3% of fraction-III were inactivated and during 6min blanching 96.4%, 82.7% and 91.8% activityies of the respective fractions were lost. Hardness were positively correlated with the pectinesterase activity and with the pectin behavior of versene and HCl-soluble fractions both in terms of pectin and methoxyl content of the fractions. There was an increase of water soluble pectin and its methoxyl content with the increase of blanching time, whereas, these values decreased in versene and HCl-soluble fractions. There was no remarkable change in phenolic content and acidity values.