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In this study, the content, structure, antityrosinase activity, and mechanism of longan bark condensed tannins were evaluated. The findings obtained from mass spectrometry demonstrated that longan bark condensed tannins were mixtures of procyanidins, propelargonidins, prodelphinidins, and their acyl derivatives (galloyl and p-hydroxybenzoate). The enzyme analysis indicated that these mixtures were efficient, reversible, and mixed (competitive is dominant) inhibitor of tyrosinase. What's more, the mixtures showed good inhibitions on proliferation, intracellular enzyme activity and melanogenesis of mouse melanoma cells (B). From molecular docking, the results showed the interactions between inhibitors and tyrosinase were driven by hydrogen bond, electrostatic, and hydrophobic interactions. In addition, high levels of total phenolic and extractable condensed tannins suggested that longan bark might be a good source of tyrosinase inhibitor. This study would offer theoretical basis for the development of longan bark condensed tannins as novel food preservatives and medicines of skin diseases.

Using social network theory as a theoretical root, this study introduces the concept of peer engagement behaviors and discusses its characteristics in relation to customer, employee, and actor engagement behaviors. This study identifies several sets of foundational research questions related to peer engagement behaviors that focus on unique attributes such as role duality, role fluidity, platform centrality, tie strength, and multidirectionality of peer engagement behaviors. Directions for broad areas of future research are also discussed to encourage theory-building on topics related to measurement, classification, subjective experiences, antecedents, and consequences of peer engagement behaviors.

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