Melanins of Vitex mollis fruit with differences in water-solubility show high inhibition of carbohydrate digestive enzymes and antioxidant activity

作者：Fernando Pio Leon Juan; Montes Avila Julio; Lopez Angulo Gabriela; Paz Diaz Camacho Sylvia; Vega Rios Alejandro; Angel Lopez Valenzuela Jose; Delgado Vargas Francisco^*

来源：Journal of Food Biochemistry, 2018, 42(3): e12509.

DOI：10.1111/jfbc.12509

• alpha-glucosidase
• antioxidant
• melanins
• Vitex mollis

The fruit of Vitex mollis Kunth contains water-soluble melanin (SM), whose properties have been poorly described. This study determined physicochemical characteristics, the inhibition of carbohydrate digestive enzymes (amylase and alpha-glucosidase), and antioxidant activity (ABTS, DPPH, ORAC, and beta-carotene bleaching) of SM (partially purified, aqueous extraction), water-insoluble melanin (IM) (pure, alkali-acid extraction), and organic (i.e., methanol, ethanol, and methanol : water 8:2 vol/vol) and aqueous extracts of V. mollis fruit. SM and IM were characterized by UV and IR spectroscopy, and their spectra showed signals characteristic of melanins. They also showed similar antioxidant (1,321-2,664 mu mol TE/g), and alpha-glucosidase inhibitory (IC50 1.48-0.022 mg/mL) activities, values that were better than those of the organic extracts (ABTS<746 mu mol TE/g and IC50>4.87 mg/mL, respectively). In addition, SMs showed higher extraction yields than IMs. Therefore, SM shares nutraceutical properties with IM and can be obtained by simple and environmentally friendly methods.
Practical applications
Melanins show biological activities (e.g., antioxidant, immunostimulatory, UV-, and radiation-protective) and their consumption has been associated with health benefits. However, studies of plant melanins are scarce because their extraction involves harsh pH conditions and the yields are usually low. The results showed that melanin was the main pigment in Vitex mollis fruit and water-soluble. Moreover, the extraction method was simple, ecological, and produced high yields. Both water-soluble and water-insoluble melanins showed similar biological activities (antioxidant and glucosidase inhibition). Species of Vitex are commonly employed as food and in folk medicine (e.g., premenstrual and gynecological disorders, gastrointestinal problems and inflammation, bacterial infections). Soluble melanins of V. mollis could be used as food supplement or in pharmaceutical preparations.

• 出版日期2018-6