Isolation, purification, identification of melanin from grape pomace extracts, and its application areas

Abstract

Background: In recent years, natural pigments have gained increasing interest across various industries. Melanin is a versatile pigment with many biological effects, including antioxidant, antimicrobial, antiradical, immunostimulatory, antitumor, anti-inflammatory, and bio-stimulatory effects. Melanin can absorb heavy metal ions and remain stable over a broad pH range, with temperatures up to 130°C. These properties are primarily attributed to the high concentration of unpaired electrons (10¹⁷–10¹⁹ spin/g). Water-soluble melanin has many applications. This compound serves as an antioxidant, an antimicrobial, an anticancer agent in medicine, a neutralizer of free radicals in tobacco production, a bio-stimulant in agriculture, a food additive, a semiconductor in solar battery production, and a radioprotector in nuclear power plants.

Objective: This study aims to develop an efficient method to isolate and purify melanin from grape skin seeds. Once collected, its physicochemical and biological properties were determined to assess the purity yield, allowing researchers to explore this product's potential applications.

Methods: Melanin was extracted from grape pomace under static conditions (65°C, 2.5–3.0 h) using 0.7 M sodium hydroxide as an extractant. Following centrifugation, melanin was isolated by acidifying the alkaline extract with HCl to a pH of 2.0. The resulting amorphous precipitate was purified through repeated re-precipitation. To obtain water-soluble melanin, the precipitate was dissolved in NaOH, vacuum-evaporated to a viscous form, and dried at 60°C.

Results: Grape varieties analyzed (white Itsaptuk, red Karmir Itsaptuk, black Armenia) yielded melanin at rates of 0.114%, 0.164%, 0.148%, respectively. Infrared spectroscopy (IR) confirmed similar valency deformation vibrations across all varieties studied. HPLC analysis revealed a single symmetrical peak for each sample, indicating chromatographic purity and uniform composition. Studies concluded that melanin was effective as a food-coloring agent in beverages, baked goods, and confectionery. When applied to vegetable melon seeds, low-concentration melanin solutions exhibited high bio-stimulating activity, enhancing root development and improving crop yields.

Conclusion: The extraction method within this experiment efficiently produces affordable, pure, water-soluble melanin from grape pomace. Due to its chromatographically pure composition, melanin has the potential to be used in medicine, food production, and tobacco processing. Notably, melanin can reduce the production of free radicals in tobacco smoke.

Keywords: melanin, grapes, production, identification, application