Influence of postharvest UV-B treatment and fermentation on secondary plant compounds in white cabbage leaves.

The influence of postharvest UV-B on its own and in combination with fermentation (e.g. sauerkraut production) on formation and degradation of bioactive compounds was investigated in white cabbage, processed according to traditional Chinese fermentation methods. The pattern of polyphenols was affected by postharvest UV-B: Newly formed coumaroylglycoside, feruloylglycoside, caffeoylglycoside (up to 1 mg/g dry matter; 4 days) and quercetintriglycoside (0.4-0.5 mg/gdm; 4 days) might be related to postharvest increase in enzyme activity in the biosynthesis. Decreasing contents were observed for the glucosinolates glucobrassicin and 4-methoxyglucobrassicin, but the formation of the degradation products dihydroascorbigen and dihydro-4-methoxyascorbigen, which might be related to cell shrinking as mechanical damage. Fermentation resulted in deglycosidation of hydroxycinnamic acids. Newly generated cinnamic acid from coumaric acid aglycone was detected in fermented plant material combined with UV-B (50 μg/g). Glucosinolates and dihydroascorbigens were completely degraded. This study shows exemplary UV-B as a supplemental step to improve the nutritional quality of processed plants.