Polyphenoloxidase inactivation by light exposure in model systems and apple derivatives

The effect of UV-C and visible light on the enzyme polyphenoloxidase was studied in model systems and food. Enzyme inactivation under non thermal conditions was achieved following both UV-C and visible light exposure. UV-C light promoted enzyme inactivation in the entire range of irradiance and exposure time tested whilst visible light was effective only at high doses since lower intensity treatments were associated to enzyme activation. Polyphenoloxidase inactivation upon UV-C light exposure occurred as a consequence of protein aggregations other than those derived from thermal denaturation. The possibility to apply UV-C light exposure to achieve enzymatic stability of clear apple juice and fresh-cut apple slices was studied. Polyphenoloxidase inactivation in apple juice occurred to the detriment of natural occurring phenols which independently underwent photo oxidation. However, UV-C light exposure for few min prevented enzymatic browning during storage of refrigerated apple slices. The latter resulted comparable to the untreated apple slices from the sensory point of view. Industrial relevance: Light irradiation is very effective in promoting poly phenoloxidase inactivation. UV-C light treatment has a good potential of successful application to achieve enzymatic stability in fresh-cut vegetables under non thermal conditions. (C) 2009 Elsevier Ltd. All rights reserved.