Study On Extraction And Composition Of Anthocyanins From Purple Corn Cob And Analysis Of Their Stability

In this paper,optimization of the conditions for extracting and purifying anthocyanins from purple corn cob was carried out and the effects of pH,heating,light,vinegar fermention and some food additives on the stability of anthocynains was investigated.The composition and structure of purple sweet cron anthocyanins wcrc analyzed and identified. The methords and mechcism for increasing the stability of anthocyanins were researched, aiming to provide basement for the application of purple corn cob anthocyanins and gain the following results:1,The results of optimization of the conditions for extracting anthocyanis purple corn cob indiactcd that the maximum anthocyanins yield(5.90 mg/g dw) was obtained with the combination of 80%methanol and 1%citric acid.A negative correlation(r=-0.645) was found between the yield of anthocyanis and Lightness(L~*),the positive correlations were found between anthoycanins yield and Chroma(C~*)(r=0.795),and between the yield of anthocyanins and Hun angle(h~o)(r=0.922);correlations between the Hunter color parameters were rather lower in this study.2,Four kinds of macroporous resins(HP-10,LSA-10,AB-8 and NKA-Ⅱ) to purple corn cob anthocyanins were used to carry out static adsorption dynamics,adsorption isotherm and desorption,so as to find a better resin.It was indicated that the macroporous resin of HP-10 was the suitable resin for adsorption to purple corn cob anthocyanins with the maximal velocity constant of absorption equilibrium(0.7777),higher than that of the other three resins.The maximal adsorption and desorption were 9.349 mg/g and 7.523 mg/g, respectively.The result shows that suitable temperature for adsorption was 25℃,and that 80%ethanol solution is the optimum solution for dcsorption to purple corn cob anthocyanins.The color value of purified purple corn cob anthocyanins solutions was 3.7 times than that of before purifying one.3,The results of HPLC-DAD-MS indicated that the majority of anthocyanins are non-acylatcd cyanidin-3-glucoside,pclargonidin-3-glucosidc and pconidin-B-glucoside, which account for 90%.The others were acylated anthocyanins with one molecur malonic acid.4,Doing research on some physico-chemical properties of purple corn cob anthocyanins,and investigation some these factors such as pH,temperature,lighting,vinegar fermation,oxidation and reducing agent and food additives on the stability of anthocyanins.The results show that keeping the pH at a range of 1.0-3.0;it has a bright color and can keep stability very well.With the pH increasing,the degradation index increased.When temperature over 70℃,the stability of anthocyanins touchdown quickly. After accepting 10 day's successive light,the conservative rate was only 14.30%.The thermal degradation of anthocyanin and Hunter color parameters C~*,a~*和ΔE followed the first-order reaction kinetics,while Hunter color parameters b~*和h~o followed zero-order reaction kinetics.The degradation of anthocyanins showed high correlation with Hunter color parameters.Salt and sugar can increase the color stability of anthocyains.Except for malic acid,purple corn cob anthocyanis has higher stability in others three kinds of acids. The anthocyanins content could be preserved by reduing the fermention time.5,The stability enhancing effect of copigments on purple corn cob anthocyanins was investigated in this study.The calculated results illustrated that the activation energy(E_a) of test samples(addition of ferulic and caffeic acid) were higher than that of control samples, and the pigment has a more color stability to storage.The stability of anthocyanins was increased by copigments in semi-solid system.After 60 days of storage,new kinds of anthocyanin-derived pigments(Pyranoanthocyanins) were detected and identified by HPLC-MS.