Extraction,Isolation And Antioxidant Activity Of Melanin From The Ovum Of Rana Chensinensis

With the rapid development of Rana chensinensis industry,the market demand for the refined products of Rana chensinensis is increasing gradually.The ovum of Rana chensinensis is one of the byproduct in the production of ovidutus ranae,which has been more attention because of its large annual output and insufficient utilization.The ovum of Rana chensinensis?OORC?is rich in melanin.The melanin has enormous potentiality colorant.It has a lot of healthful functions,such as immunomodulatory activity,antioxidation and Anti-radiation.The melanin is widely used in the fields of food,medicine,cosmetics,and chemical industry,but its physicochemical characterization and structure are not clear.In this study,response surface methodology utilized to optimize extraction process and protein removal process,and study on physicochemical properties and antioxidant activity of melanin from ovum of Rana chensinensis.The main results were shown as follows:1.A single factor test was used to determine the level range of enzymatic hydrolysis temperature,raw material ratio to PBS solution,enzymatic hydrolysis time and papain addition of the melanin extraction process.Response surface methodology was utilized to optimize extraction process.Results showed that the optimum conditions for protein removal were as follows:enzymatic hydrolysis temperature of58?,raw material to PBS solution ratio of 1:16 g/mL,enzymatic hydrolysis time of2.1 h,papain addition of 3.0%.Under the optimal conditions,the maximum predicted melanin yield was 13.74%,which corresponded fairly well with that of melanin yield?13.62%±0.22%,n=3?.2.Response surface methodology was utilized to study the effects of various NaOH solution treatment conditions on melanin isolation.Results showed that the optimum conditions for melanin isolation were as follows:0.65 mol/L NaOH,extraction temperature of 50?,extraction time of 1.45 h and raw material to NaOH solution ratio of 1:21.Under the optimal conditions,the maximum predicted melanin content was 0.6987 g/g,which corresponded fairly well with that of real protein removal ratio(?0.689 g/g±0.023 g/g,n=3?.3.The OORC melanin was examined by UV–VIS absorption spectroscopy,infrared spectrometry,and elemental analyzer.Results showed that Infrared spectroscopy indicated that OORC melanin was composed of OH,NH₂,C=C,C=N,C=O,C-N and aromatic ring groups.S:N ratio of the melanin was 0.05.he melanin from ovum of Rana chensinensis consists mostly of eumelanin.The OORC melanin contains some protein.4.The concentration of an antioxidant needed to decrease the initial DPPH concentration by 50%?IC50?is a parameter widely used to measure antioxidant activity.OORC melanin exhibited significant clearance ability on hydroxyl radical,superoxide-radical,DPPH radical and their IC50 values were 0.662 mg/mL,1.250mg/mL and 0.404 mg/mL.The OORC melanin had significant stronger antioxidant abilities by hydroxyl radical scavenging activity and determining reducing power than BHT.