Antioxidant and α-glucosidase inhibitory properties of soluble melanins from the fruits of Vitex mollis Kunth, Randia echinocarpa Sessé et Mociño and Crescentia alata Kunth

• Soluble melanins were extracted from the edible dark pulp of three fruits
• Melanins were partially purified (PMe) by environmentally-friendly methods.
• All PMe showed better α-glucosidase inhibition than acarbose.
• The spectroscopic analyses (UV-Vis and IR) corroborated their identity as melanins.
• Melanins could be forming complexes with carbohydrates, which make them soluble.

Melanins have important pharmacological properties with limited applications due to their poor solubility. Soluble melanins have been reported in different organisms, but not in plants. In this study, aqueous soluble melanins, Impure (IMe) and Partially Purified (PMe), were prepared from the edible pulp of fruits native to Mexico (i.e. Vitex mollis, VM; Randia echinocarpa, RE; and Crescentia alata, CA). IMe and PMe were tested for their phenolics content (TPC), antioxidant activities (AA), α-glucosidase inhibition (αGI) and spectroscopic features (UV-Vis and IR). Melanins of VM showed the highest TPC (222.23 mg GAE/g) and AA (ABTS 2779.30 μmol TE/g; FRAP 1203.70 μmol TE/g). Purified melanins (PMe) showed better αGI than acarbose (IC50 = 8.38 mg/mL). The spectroscopic features of IMe and PMe corresponded to melanins and solubility may be by their complexation with carbohydrates. For the first time, plant-based soluble melanins and their remarkably high antioxidant and α-glucosidase inhibitory characteristics are presented.