Comparison of sanitizing technologies on the quality appearance and antioxidant levels in onion slices

Background A Portuguese landrace onion variety grown in Póvoa do Varzim (Northwest of Portugal) was selected for this study. It is a red onion known as “vermelha da Póvoa”. The effect of different chemically- and irradiation-based disinfectant procedures of fresh-cut onions on their flavonoid content was compared. Amongst the chemical treatments the most used were selected: sodium hypochlorite, amukine, hydrogen peroxide, and sodium dichloroisocyanate. UV-C irradiation was also selected amongst all irradiation treatments. Results The main effect contributing to the loss of flavonols in fresh-cut onion slices is their solubility in immersion water (17–23% both at 4 or 50 °C). The acidification of sodium hypochlorite with sulphuric acid is also rendering losses (6–19%) vs. the use of citric acid. Anyway, in dry decontaminantion treatments, like UV-C irradiation, the natural levels of flavonoids in fresh-cut onion slices significantly increase at 35% for flavonols, and at 29% for anthocyanins. Conclusions Onion flavonoids decreased by chemically disinfectant procedures of fresh-cut onion by solubility in immersion water. UV-C irradiation does not only maintain the initial levels of flavonoids but increases them; therefore, this is the recommended treatment.