Influence of Harvest Time on Biologically Active Compounds and the Antioxidant Activity in Leaves of Mulberry Grown in Lithuania

Abstract

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. Mulberry leaves contain a wide range of bioactive compounds, such as flavonoids and phenolic acids, which are responsible for beneficial effects on human health. 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. 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). The highest accumulated rutin, nicotiflorin, and chlorogenic acid contents and the greatest antioxidant activity were found in the leaves of ‘Plodovaja 3’. 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 antiradical activity was highest in September. There were a very strong positive correlations between the antiradical 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).