Study of phenol oxidases in fruits and vegetables:Co-occurrence of thermostable peroxidases and alkaline tyrosinase in a novel source Coccinia grandis.

Tyrosinase and peroxidase content in various fruits and vegetables was compared. Avocado pulp was found to be a rich source of tyrosinase yielding around 4.5U/g. Avocado seeds, Datura metel and Coccinia grandis were found to be the next best sources. The tyrosinase rich sources gave comparatively poor yield of peroxidase with the exception of C. grandis. Tyrosinases from Avacado (ATy) functioned optimally at pH 6.5 and was stable over a broad range of pH from 5.5-9. C. grandis tyrosinase (CTy) was an alkaline tyrosinase with an optimum pH of 9.5-10. Optimum temperature of C grandis peroxidase (CPox) was 50 °C. ATy, CTy and CPox retained 100% activity at 40 °C, 60 °C and 75 °C respectively for 30min. The K_M for Catechol was 3.2-3.3 mM for both CTy and ATy. K_M for Dopa was 3.3 and 1.27mM for ATy and CTy respectively. CPox exhibited a strong affinity for hydrogen peroxide with a K_M of 87 μM. [ABSTRACT FROM AUTHOR]