Effect of ultraviolet-B irradiation on antioxidative properties of aqueous extracts from shiitake (Lentinus edodes) mushrooms

Antioxidant properties of aqueous extracts from Lentinus edodes treated with UV-B irradiation were examined in vitro systems including DPPH, ABTS and oxygen radical absorbance capacity (ORAC) assays and in riboflavin-photosensitised oil-in-water (O/W) emulsions. Changes in total phenolics, total flavonoids and vitamin C were also analysed. Lentinus edodes receiving 25 kJ m(-2) UV-B treatment showed high radical scavenging ability based on DPPH and ABTS assays compared with samples with 0, 50 and 75 kJ m(-2), while those with 50 kJ m(-2) had higher antioxidant capacities than other samples from ORAC assays. Samples with 25 kJ m(-2) UV treatment had significantly 7.1% higher total phenolic content, 12.0% higher total flavonoid content and 8.0% higher vitamin C content than UV-B-untreated sample (P < 0.05), respectively. In O/W emulsions under riboflavin photosensitisation, 25 and 50 kJ m(-2) UV treatment significantly increased the oxidative stability compared with other samples based on headspace oxygen content and lipid hydroperoxide analyses (P < 0.05). Aqueous extracts of UV-B-treated mushrooms possessed enhanced antioxidant properties compared with untreated mushrooms.