Consumers demand healthy, natural and fresh foods, which require only a minimum amount of effort and
time for preparation. This was the reason for comparing the effects of different mild preservation technologies
on onion flavonoids. Onions were minimally processed to produce fresh-sliced onions, which
were packed either in closed plastic cups or under vacuum conditions, taking into account the effect of
light exposure. In all cases, the commodity was acceptable after the storage period, with the exception
of vacuum packaging (score 5, fair/poor, on a 1–9 scale), due to water loss (about 4%) colour loss and a
glassy appearance. In general, after storage in the dark, a slight increase in flavonols was observed,
whereas a clear decrease in the relatively low amounts of anthocyanins was evident. However, the best
performance was obtained when the more transparent polystyrene cups were stored under light. Both
types of flavonoids increased, with an enhanced increase of total flavonols by 58%, and an increase in total
anthocyanins of 39%.