Antioxidant, antibacterial properties and the light barrier assessment of raw and purified melanins isolated from Citrullus lanatus (watermelon) seeds

Abstract

Summary Introduction: The nutritive value and terapeuthic activity of watermelon seeds is known, but up to day no studies on isolation and characterisation of their melanin were conducted. Objective: The aim of the study was to evaluate the antioxidant, antibacterial and light barrier properties of raw and purified melanins isolated from watermelon seeds. Methods: Native melanin was isolated from seeds by alkaline extraction. Obtained pigment was purified by acid hydrolysis. Chemical tests and FT-IR analysis were conducted to determine the melanin nature of the isolated pigments. UV-Vis, transmittance and colour properties were evaluated spectrophotometrically. Antioxidant activity was determined using ABTS and antibacterial activity through a well diffusion method. Results: The results of the study demonstrated that melanins isolated from watermelon seeds had antioxidant, light barrier and antibacterial properties. A purified form of melanin had higher antioxidant activity and light barrier properties than the raw form. Both melanins inhibited the growth of Enterococcus faecalis and Pseudomonas aeruginosa. Conclusions: Watermelon seeds may be considered as a promising source of natural melanin which possess remarkable therapeutic action that can support the traditional use of this plant in the ethnomedicine.