Influence of harvest time on bioactive composition and antioxidant activity of the white mulberry leaves

Abstract

Our results may help to select the best cultivar and harvest month in order to produce better quality mulberry leaves. Mulberry tree, a plant of the family of Moraceae and genus Morus. Mulberry leaves contain a wide range of bioactive compounds, such as flavonoids and phenolic acids, which are responsible for beneficial effects on human health. The aim of this study was to establish the influence of harvest time on the contents of flavonoid compounds (rutin, isoquercetin, nicotiflorin, and astragalin) and chlorogenic acid, as well as the antiradical activity in white mulberry (Morus alba L.) leaves grown in Lithuania. Leaves from two mulberry cultivars were collected from July to September in 2015-2016. Quantitative determinations of four flavonoids and chlorogenic acid were conducted by HPLC method and antiradical activity using the 2.2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method. This study showed that the mulberry leaves from both cultivars were nutritionally rich. The results showed that the total flavonoid contents of mulberry leaves in the two cultivars ranged from 921.92 to 1512.02 mg 100 g−1 dry matter (DM). The highest accumulated rutin, nicotiflorin, and the greatest antioxidant activity were found in the leaves of ‘Plodovaja 3’. The highest chlorogenic acid contents were found during July in ‘Plodovaja 3’ (223.00 mg 100 g−1 DM) and during September in ‘Turchanka’ (177.32 mg 100 g−1 DM). The bioactive compounds in the leaves of the mulberry cultivars varied over a period of time, where ‘Turchanka’ and ‘Plodovaja 3’ accumulated the highest total flavonoid contents in September and August, respectively. In both cultivars, the antioxidant activity was highest in September (15.34-16.50 μmol TE g−1 DM). There were a very strong positive correlations between the antioxidant activity as determined using the DPPH method and the chlorogenic acid contents (r = 0.887, p < 0.05) and the isoquercetin contents (r = 0.848, p < 0.05).