Characterization of Polyphenol Oxidase Activity in Juices from 12 Underutilized Tropical Fruits with High Agroindustrial Potential

Polyphenol oxidase activities of lulo, mangosteen, Castilla blackberry, mango, apple guava, tree tomato, papaya, soursop, banana passionfruit, giant granadilla, sweet granadilla, and passion fruit were determined and related to their physicochemical properties. Mangosteen and lulo showed the highest activities (0.1435 and 0.1298 U mL −1 , respectively), while passion fruit and banana passionfruit had the lowest ones (0.0101 and 0.0093 U mL −1 ). The two fruits with highest PPO activity were also the ones in which highest color differences (ΔE) during the first 90 min after fruit crushing were achieved. The Principal Component Analysis revealed a high correlation between PPO activity and total phenolic content for the compounds that are susceptible to act as enzyme substrate. These two variables were also highly correlated with the decrease produced in brightness (measured with the CIELab parameter L*).