Regulation of anthocyanin and lignin contents in postharvest ‘Fuji’ apple irradiated with UV-B

Abstract

Ultraviolet-B (UV-B) irradiation is an excellent method for enhancing the appearance of poorly colored apples after harvest. However, its application is still challenging because the relationship between enhancing apple anthocyanin and preventing lignin synthesis is not clear. We reported results of UV-B application to increase anthocyanin levels and prevent lignin hyperaccumulation. UV-B irradiation up to 5 W m−2 s−1 for 3 d did not affect apple firmness, soluble solid content, and titratable acid; over 1 W m−2 s−1 UV-B maintained adequate anthocyanin synthesis. Hyperaccumulation of lignin was observed at high UV-B (5 W m−2 s−1), producing 1.45-fold of the lignin content in artificially non-pigmented skin, whereas naturally matured red apples contained 1.15-fold lignin of the green skin. It was found that metabolic gene expressions of anthocyanin in UV-B increased faster than the expressions of lignin. Therefore, UV-B intensity application was recommended to either be below 5 W m−2 s−1 for 3 d or 5 W m−2 s−1 for 2 d.