Comparison of free and bound phenolic compositions and antioxidant activities of leaves from different mulberry varieties

Mulberry leaves are used in traditional Chinese medicine and contain numerous active substances that are known to be beneficial for human health. The aim of this study was to investigate the phenolic compositions and antioxidant activities of the leaves from 23 mulberry cultivars. Qualitative LC-ESI-QTOF analysis revealed the presence of 11 phenolic compounds in the free phenolic extracts and 10 phenolic compounds in the bound fractions. Chlorogenic acid and caffeic acid were the major components in the free and bound fractions, respectively. The results revealed that the changguosang cultivar from Taiwan contained the greatest content of phenolic compounds as well as the highest antioxidant activity among the 23 cultivars examined, as determined using three separate antioxidant assays. The isoquercitrin, chlorogenic acid, and rutin contents of the free phenolic extracts displayed significant correlations with the antioxidant activities, while syringic acid and rutin were the main contributors to the antioxidant activities of the bound phenolic fractions. The obtained results demonstrate that mulberry leaves contain a variety of beneficial phenolic substances and may be suitable for further development as a herbal medicine.