Evaluation of phenolics and cysteine sulfoxides in local onion and shallot germplasm from Italy and Ukraine

Onions (Allium cepa L.) are the most important Allium vegetables whose increasing popu- larity is related to their pungent taste and richness in non-nutrient bioactive compounds. Many diverse local types are present and valued in several areas, although still poorly characterized. In the present study, fresh edible parts from Italian and Ukrainian bulb onion, potato onion, and shallot populations were analyzed for their phenolic and cysteine sulfoxide content and antioxidant capacity. Fifteen phenolic compounds, belonging to flavonols and anthocyanins, and two cysteine sulfoxides, methiin and isoalliin, were quan- tified. Total phenolics and cysteine sulfoxides were in the range 2595–9840 and 6777–18,916 mg kg-1 d.m., respectively. On average, potato onion phenolic con- tent was 55 and 59 % higher than in bulb onion and shallot accessions, respectively. Bulb and potato onions showed a similar cysteine sulfoxide content, whereas in shallots sulfoxide level was about 17 % lower. Flavonols were related to antioxidant capacity in both low and high anthocyanin types; however anthocyanins gave a prominent contribution to total antioxidant capacity in red onions. Quantitative vari- ations of some components allowed a clear discrimi- nation among the three groups of onions, highlighting the possibility of selection for both low or high content of specific components.