| Black corn is a new corn species, which color is different from other corn, mainly because there is a plenty of black pigment in its epidermis. It is rich in water-soluble black pigment , a variety of essential amino acids and various trace elements. Taking black corn as experimental material, studied the extraction and composition of black corn pigment, evaluated antioxidative activities of corn by a series of antioxidative tests and determined the contents of amino acids in black corn epidermis. The thesis mainly includes the following three parts :1. study on extraction technology and composition of black corn pigment. 2. study on the antioxidative activities of extracts from black corn and yellow corn. 3. determination of three amino acids in black corn epidermis by capillary electrophoresis with electrochemical detection (CE-ED).Firstly, black corn pigment is a natural anthocyanin pigment. The effects of different factors on extraction of pigment with orthogonal test were investigated. The optimal parameters of extraction of black corn pigment were as fellows: ethanol–water (95:5, v/v) as extracting solvent, solid-liquid ratio 1:30, extracting time 45 min. Liquid chromatography-mass spectrometry (LC-MS) were applied to determine the components of black corn pigments. The results showed that there were two major anthocyanins in ShanDong sample: cyanidin and pelargonin, and three major anthocyanins in ShanXi sample: cyanidin, pelargonin, and paeonidin.Secondly, to compare the antioxidative activity with other common corn, we chose yellow corn and black corn as the raw materials to carry on a series of antioxidative tests. The different fractions of corn antioxidative extracts were obtained using solvents with different polarities. The antioxidative activity of these extracts were assessed for 1,1-Diphenyl-2-picrylhydrazyl(DPPH)free radical scavenging activity to find the strongest antioxidative fractions in both corns. Taking the strongest antioxidative fractions as experimental objects, their antioxidiative activities were investigated by two different methods in scavenging superoxide anion (O2-) generated by pyrogallol autoxidant system and restrainning lard oxidation. The total flavonoids contents of ethanolic extract from the both corns were determined. The results showed that ethanol-water antioxidative extract fraction had the strongest antioxidative capacities among the five fractions in both corns .The total flavonoids contents of ethanolic extract were 16.2 mg/8g and 51.5 mg/8g for yellow corn and black corn, respectively. Three antioxidative experiments shown that the antioxidative activity of black corn was better than that of yellow corn.Finally, using o-phthaldehyde (OPA) as a pre-column derivative agent, the contents of leucine, valine and alanine in black corn epidermis were determined by CD-ED in this paper. A 300μm diameter carbon disk electrode was used as the working electrode, the effects of several factors such as pH of running buffer, separation voltage, injection time, and detection potential were investigated to acquire the optimum conditions. The optimum CE-ED conditions were as fellows: applied potential to the working electrode at 0.95V (vs.SCE), 100 mmol/L borate solution (pH 7.8) as running buffer, injection time 6s, the analytes could be well separated within 18 min at a separation voltage of 18 kV in a 100 mmol/L borax running buffer . The detection limits (S/N=3) were 2.5×10-4 g/L,2.5×10-4 g/L,5.0×10-4 g/L, for leucine, valine and alanine, respectively. This method is accurate and feasible, the sample preparation is simple, which provided a fast and sensitive determination method for amino acids. |
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