Optimization of extractions of eumelanin from cuttlefish ink and the hypoglycemic effects: In vitro enzyme inhibitory activity and glucose consumption in HepG2 cells

Abstract

In 1,840, Swedish researcher Berzelius first used the name melanin (Roy et al., 2019). Melanin is a polymer biopigment formed by oxidative polymerization of phenols and terpenoids with sugars and proteins. Melanin, a substance ranging from dark brown to black that can protect the skin from ultraviolet rays, is a well-known component of human hair (Riley, 1997;Xiao et al., 2018). Melanin is insoluble in water, acidic solutions, and common organic solvents (d'Ischia et al., 2013), which is characteristic of natural melanin. However, eumelanin can be extracted by dissolving in 10% sodium hydroxide aqueous solution, filtering, and precipitating with dilute hydrochloric

Melanin: insights into structure, analysis, and biological activities for future development

“…(3) 1400-1300 cm À1 corresponds to C-H in-plane bending vibrations, C-O stretching vibrations and C-C single bond skeleton vibrations. 52,53 And the CQO stretch in the carboxyl group shows a significant unique peak at around 1710 cm À1 . 50,51 Pheomelanin is composed of sulfur-containing units, mainly phenprothiazine and benzothiazole, which are shown to have a strong absorption of 1535 cm À1 on the infrared spectrum, and there are characteristic bands of aromatic rings and sulfur at both 800 cm À1 and 678 cm À1 .…”

“…63 When eumelanin is dissolved in alkaline solution and analyzed by UV-vis in the range of 180-900 nm, eumelanin produces a maximum absorbance peak at 220 nm and a broad absorption at other wavelengths. 48,53 Pheomelanin and eumelanin both show strong absorption in the wavelength range of 300-450 nm with attenuation behavior extending into the infrared region. 54 In general, pheomelanin exhibits higher absorption in the full spectrum, becoming more pronounced in the visible region, with the highest absorption wavelength near 233 nm.…”

“…220 nm: maximum absorbance. 48,53 1400-1300 cm À1 : C-H in-plane bending vibrations, C-O stretching vibrations and C-C single bond skeleton vibrations 52,53 300-450 nm: show strong absorption, extending into the infrared region. 54 Pheomelanin 1535 cm À1 : strong absorption; 1280 cm À1 : weak, corresponds to the (COH) phenolic stretch.…”

“…59 The EPR signal of allomelanin extracted from oat hulls showed a single peak 80 without any fine structure similar to the EPR spectra of other synthetic and natural melanin from different sources. 53,81 The g value of this signal was calculated as 2.0051, typical of a carbon-centered organic radical with a conjugated structure. 80 Mekala et al 78 performed ESR analysis of pyomelanin produced by photosynthetic bacteria and found that pyomelanin had a characteristic signal of 325 mT.…”

“…Studies have tried enzymatic extraction methods for melanin in hair, where some studies started to use proteinase K, papain or trypsin to extract melanin by hydrolyzing keratin. 104,105 Eumelanin from squid ink was extracted by alkaline protease by Song et al, 53 the extraction rate was found to be 88.3% for enzymatic extraction and 16.82% for the alkaline acid precipitation extraction.…”