Antioxidant evaluation-guided chemical profiling and structure-activity analysis of leaf extracts from five trees in Broussonetia and Morus (Moraceae)

Abstract

Morus and Broussonetia trees are widely used as food and/or feed. Among 23 phenolics identified from leaves of five Moraceae species using UPLC-QTOF-MS/MS, 15 were screened using DPPH/ABTSguided HPLCs, including seven weak (flavonoids with one hydroxyl on B-ring) and eight strong (four caffeoylquinic acids and four flavonoids, each with a double hydroxyl on B-ring) antioxidants. We then determined the activity and synergistic effects of individual antioxidants and a mixture of the eight strongest antioxidants using DPPH-guided HPLC. Our findings revealed that (1) flavonoid glucuronide may have a more negative effect on antioxidant activity than glucoside, and (2) other compounds in the mixture may exert a negative synergistic effect on antioxidant activity of the four flavonoids with B-ring double hydroxyls but not the four caffeoylquinic acids. In conclusion, the eight phenolics with the strongest antioxidant ability reliably represented the bioactivity of the five extracts examined in this study. Moreover, the Morus alba hybrid had more phenolic biosynthesis machinery than its cross-parent M. alba, whereas the Broussonetia papyrifera hybrid had significantly less phenolic machinery than B. papyrifera. This difference is probably the main reason for livestock preference for the hybrid of B. papyrifera over B. papyrifera in feed.Morus and Broussonetia tree species (family: Moraceae) have high economic value; among other uses, their leaves are widely used as feed to improve meat quality. The genus Broussonetia comprises five species: B. papyrifera, B. kazinoki, B. zeylanica, B. kaempferi, and B. kurzii 1 , some of which are used as folk medicinal plants and/or for making bark paper 2 . The bark, fruits, leaves, and roots of B. papyrifera and B. kazinoki exhibit antioxidant, anti-inflammatory, antinociceptive, and anti-tyrosinase activity 3-6 . In China, B. papyrifera and B. kazinoki leaves, from which several bioactive components such as polyphenols, flavonoids and alkaloids have been isolated 7 , are widely used to feed livestock for meat quality improvement. Methanol extracts from B. papyrifera leaves have greater inhibitory effects on mushroom tyrosinase and 2,2-diphenyl-1-picrylhydrazyl/(DPPH)• scavenging activity 8 , and ethanol extracts from B. papyrifera roots inhibit both acetyl-and butyl-cholinesterases 2 . Papyriflavonol A, isolated from the root bark of B. papyrifera, exhibits strong antimicrobial activity against different pathogenic bacteria and fungi 9 , whereas a 70% ethanol leaf extract of B. kazinoki was reported to dramatically reduce ear and dorsal skin thickness and other clinical symptoms in mice with atopic dermatitis, possibly via the downregulation of immunoglobulin E (IgE) and interleukin-4 (IL-4) plasma levels 5 . Broussonone A extracted from B. kanzinoki stem bark displays noncompetitive inhibitory activity against pancreatic lipase 10 . However, data on the antioxidant activity and bioactive composition of B. kanzinoki remains limited.The genus Morus comprises 10-16 species 11 , of whic...

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