Effect of UV-C and UV-B treatment on polyphenol oxidase activity and shelf life of apple and grape juices

• PPO activity can be affected by UV-C energy and mechanical stress.
• No effect of UV-B energy on PPO activity could be detected at the applied doses.
• UV-C treatment enhanced the microbial shelf life of apple and grape juices.
• The UV-C inactivation of PPO in apple juice prevented further browning during storage.

In order to minimize quality losses due to enzymatic browning and spoilage reactions during the storage, the effect of a flow through UV-C and UV-B technology on the activity of polyphenol oxidase (PPO) as well as on the shelf life of apple and grape juices was investigated. The absorption of soluble compounds led to smaller effects of UV-C energy on PPO activity in juice than in buffer. Moreover, the pumping and the flow conditions in the coiled tube reactor had additional effects on the activity of the enzymes studied. In contrast, no effect of UV-B energy on PPO activity could be detected at the applied doses. An up to 2 log10 reduction of total aerobic plate count as well as yeasts and molds was reached at a dose of 100.47 kJ L− 1 leading to an extended shelf life of the UV-C treated juice. The high reduction of PPO activity at this dose prevented further browning of apple juice during the refrigerated storage.Industrial relevanceSince enzymatic reactions can lead to quality losses during storage, the inhibition of enzyme activity is almost as important as the microbial inactivation in order to prevent spoilage reactions. As shown by the results of this study, browning reactions in juices may be minimized by the UV-C inactivation of polyphenol oxidase providing a product of extended shelf life.