Changes in Radical‐scavenging Activity and Components of Mulberry Fruit During Maturation

Abstract

ABSTRACT Extracts of mulberry fruits (Morus sp.) were prepared from 8 cultivars harvested at 4 stages of maturity, and their radicalscavenging activity, anthocyanin content, and total phenolic content were measured. The radical‐scavenging activity was evaluated by a spectrophotometric assay using the 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH) in a 96‐well microplate. Mulberry fruit extracts exhibited the DPPH‐scavenging activities, ranging from 2.5 to 20.3 μmol‐Trolox equiv/g‐FW. Their activities were variable during maturation, and the highest activity was observed in the fully mature mulberry fruit in all cultivars. Anthocyanin was scarcely present in the immature mulberry fruits; however, its content increased as the fruit matured in all cultivars. On the other hand, all immature mulberry fruits contained non‐anthocyanin phenolic compound. An on‐line high‐performance liquid chromatography (HPLC) method for the detection of DPPH‐scavenging compounds revealed the difference in predominant radical scavengers between the immature and fully mature stages in the Miran 5 cultivar. Four major radical scavengers in the Miran 5 cultivar were assigned to 2 caffeoylquinic acids (chlorogenic acid and its isomer) and 2 anthocyanins (cyanidin 3‐glucoside and cyanidin 3‐rutinoside) in the immature and fully mature stages, respectively, by LC‐ESI‐MS/MS analysis. The change in the content of 4 compounds in mulberry fruits during maturation demonstrated that the most likely contributors to the DPPH‐scavenging activity were caffeoylquinic acids in the immature mulberry and anthocyanins in the mature and fully mature mulberry.