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

Pigment compounds with hypoglycemic effects are a widely researched topic, but there is almost no research evaluation on eumelanin in ink. Melanin in cuttlefish juice is used as an antibacterial, hemostatic, and other active natural medicine and food additive. This study is the first to compare the extraction method of alkali‐extracted eumelanin and enzyme‐extracted eumelanin and to analyze their hypoglycemic activities. The structures of the extracted samples were analyzed by Fourier Transform infrared spectroscopy, Ultraviolet‐visible spectroscopy (UV‐vis), X‐ray, and scanning electron microscope (SEM). The purity of the extracted samples was determined by high‐performance liquid chromatography (HPLC). The results showed that the enzyme extraction yield and purity of eumelanin were 88.3% and 91.62%, and the alkali extraction yield and purity of eumelanin were 16.82% and 58.57%, respectively. Enzyme extraction of eumelanin can significantly inhibit α‐glycosidase enzyme and α‐amylase activity, promote the utilization of glucose in cells, and increase hepatic glycogen synthesis. Eumelanin (0.8 mg/ml) was selected as the effective concentration. This study provides a technical reference for the extraction, determination, and hypoglycemic activity of eumelanin. Novelty impact statement This study is the first to compare the extraction method of alkali‐assisted extraction of eumelanin and enzymatic‐assisted extraction of eumelanin and to analyze their hypoglycemic activities. The extraction yield and purity of enzyme‐assisted extraction of eumelanin extraction is much higher than that of alkali‐assisted extraction of eumelanin. Eumelanin from squid ink has the effect of accelerating the utilization of glucose and the effect of enzyme‐assisted extraction of eumelanin is slightly better than alkali‐assisted extraction of eumelanin.