39B-10

J. DE LA CRUZ¹, G. Vela, D. M. Leon, and H. S. Garcia. (1) UNIDA, Instituto Tecnologico de Veracruz, M.A. de Quevedo # 2779, Col. Formando Hogar, Veracruz, Ver, 91897, Mexico

Mangoes are climacteric fruits which suffer from a physiological disorder known as chilling injury (CI) when exposed to low but non-freezing temperatures. Although a number of symptoms have been associated to CI in mango fruits, one that has been recognized as important in that it affects the visual quality of the fruits is pulp and peel discoloration caused by polyphenoloxidase (PPO) acting on a variety of substrates as terpinols and polyphenols. Enzyme and substrates come in contact upon tissue breakdown caused by CI.

Our objective was to measure changes in PPO activity that occur during normal ripening and chilling-stress conditions.

PPO activity in pulp and peel of Manila mangoes was measured using 4-methylcathecol as substrate. Fruits were stored at 6 or 12 °C, including a control lot that was ripened at 25 °C. Physical parameters of ripening were monitored (textural hardness, pH, acidity, soluble solids and color), and CI was assessed by visual inspection.

Our results showed that PPO activity increased in refrigerated mangoes but those fruits that were stored at 6 °C displayed greater activity than those stored at 12 °C. Both temperatures produced a peak in enzyme activity at day 16 of storage. Browning of mango peel. Additionally, severity of CI symptoms was also correlated to PPO activity (r2=0.82). After the PPO peak observed at day 16, refrigerated mangoes showed smaller enzyme activities; however browning became more pronounced.

There was a direct correlation between CI symptoms in the peel and increased PPO activity. Enzyme activity was significantly smaller in control mangoes. The greatest PPO activity measured at day 16 that was followed by a concomitant discoloration suggest that the PPO peak of activity coincided with the point at which tissue breakdown occurred.