Effects of UV-C treatment on browning and the expression of polyphenol oxidase (PPO) genes in different tissues of &ITAgaricus bisporus&IT during cold storage

Polyphenol oxidase (PPO) is the key enzyme leading to browning of Agaricus bisporus (A. bisporus). In order to determine the influence of UV-C treatment on polyphenol oxidase (PPO) of A. bisporus (Cv, 192), the visual quality and color, degree of browning, PPO activity and the expression of PPO genes in different tissues of A. bisporus during cold storage after 1.0 kJ/m(2) UV-C treatment were analysed. Results showed that the degree of browning and PPO activity of A. bisporus increased during 21 d of storage at 4 degrees C. UV-C treatment increased the PPO activity and exacerbated the browning of cap surface of A. bisporus during the beginning period of the storage. However, the degree of browning and the PPO activity in pileus, stipe and gill of A. bisporus were reduced by UV-C treatment. The expression of PPO genes (AbPPO2, AbPPO3 and AbPPO4) in the peel of A. bisporus was stimulated by UV-C treatment during storage at 4 degrees C, while they were inhibited in pileus, stipe and gill. The patterns of AbPPO2, AbPPO3 and AbPPO4 transcription level in different tissues of A. bisporus were similar to that of the degree of browning and PPO activity. AbPPO1 gene transcription was not in accordance with the degree of browning and PPO activity. UV-C treatment inhibited browning of A. bisporus fruit body (pileus, stipe and gill) and the expression of AbPPO genes.