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In order to explore the effect and the corresponding physiological mechanisms of UV-C irradiation on browning of fresh-cut apples, both whole and sliced apple were irradiated with UV-C (254 nm) for 5 min before or after processing. The browning index (BI) of slices was immediately measured, while other relevant physiological parameters were evaluated on quick-frozen samples during refrigerated storage. Results indicated that both pre-and post-processing UV-C treatments effectively delayed browning of apple slices; nevertheless, post-processing UV-C treatment was more efficient. BI significantly negatively correlated with non-enzymatic capacities, and activities of catalase, ascorbate peroxidase, and glutathione reductase (GR). BI was positively correlated with the contents of H 2 O 2 and malondialdehyde (MDA). These findings suggested that UV-C treatment delayed browning of apple slices during cold storage by improving the antioxidant system. Post-processing UV-C treatment was more efficient than pre-processing. Practical applicationsUV-C treatment is a technique of preservation for fresh-cut fruits. It is widely applied in food processing and many other fields due to its convenience, safety, low cost, etc.In the present study, both pre-and post-processing UV-C (254 nm) irradiation for 5 min could (1) delay the browning of fresh-cut apple, (2) improve the polyphenol oxidase activity and reduce the phenylalanine ammonia-lyase (PAL) activity and total phenolic content (TPC), and (3) reduce the accumulation of H 2 O 2 and malondialdehyde, and increase the antioxidant activities of fresh-cut apples. Thus, UV-C treatments maintain the fresh-cut quality of fresh-cut apple slices and extend their shelf life.

Firmness is an important indicator to evaluate post-harvest apple quality, because firmer fruit is considered to have better quality than softer fruit (Harker et al., 1997), and softer fruit is more susceptible to physical damage and fungal infections during preservation and processing (Wei et al., 2010). Maintaining firmness and extending the storage life of fruit are often achieved by storing fruit at low temperature so as to reducing their biological reaction rate. It is generally believed that the optimum temperature for slowing down the quality deterioration of apple is often 0-3°C (depending on the sensitivity of cultivar to chilling damage; Johnston et al., 2001). However, fruit is often exposed to different temperatures (most of the time are nonoptimal temperatures) during storage, transportation, distribution,