| Chinese yam is tubers of Dioscorea plants in Dioscoreaceae. Chinese yam is consumed as nutritious health care products and also is commonly used as herbs. Yam is nature, sweet, and is good for lungs and kidneys. China's ancient pharmacopoeias had documented a lot about yams. Local studies focused on yam's cultivation techniques, activity of yam polysaccharide, yam processing and many other fields. However, the study on the proteins in yam species of China mainland has not been reported. Therefore, this study took domestic varieties of yams as raw material, and foucused on extraction, purification and in vitro antioxidant activity of protein in yams, looking forword to fill gaps in the field of protein research of yams.First of all, after examing six classic Henan's yams:Dioscorea oppsita.Taigu, Dioscorea oppsita. Tiegun, Dioscorea oppsita. Jicheng, Dioscorea oppsita. Jinchengyihao, Dioscorea oppsita. Baiyu. We measured the basic chemical composition of the yams. We selected water content, soluble protein content, total nitrogen content values as a reference standard, and selected the most suitable one for further research. Dioscorea oppsita. Tiegun's moisture content reached the lowest to 79.01% and its total nitrogen content as well as soluble protein content were the highest, which were 19.91% and 3.09% seperately. We choose Dioscorea oppsita.Tiegun-a valuable food medicine used as food and medicine as a raw material for subsequent experimental of proteins.Secondly, we optimized the extraction rate of protein in the yams. We selected such four factors as extraction time, liquid ratio, pH value and extraction times and compared the yield of yam proteins. After the single factor experiment, we carried out three factors and three levels of the Box-Behnken, based on the three parameters extraction time, liquid ratio and pH value. We optimized the experimental combination and obtain the optimum extraction conditions as time 67 min, solid to liquid ratio 5.5 ml/g, pH 7.5. And in predicting the optimal conditions for 3 validation experiment, the protein extraction rate was 3.72%, slightly lower than the predicted maximum results, which meant extraction conditions is feasible.Thirdly, we focoused on the extraction and purification of proteins in the yam. Using DEAE-cellulose anion exchange column chromatography-52, we extracted proteins from yams on the initial separation. Recycling dextran G-100 gel filtration column chromatography on F1 and F2 fractions were separated for further purification. Yam protein purification products are named as P-1 and P-2. Protein content of P-1, P-2 were 85.86% and 81.62%; And their sugar content were 7.72% and 8.23%. P-1 and P-2 may be both glycoproteins. By SDS-PAGE electrophoresis, we found that the molecular weight of proteins in yams ranged in 20,31,50 and 66 kDa. After determination by amino acid composition, we can see P-1 and P-2 contained at least 16 amino acids, namely aspartic acid, glutamic acid, arginine, histidine, alanine, valine, Su ammonia acid, serine, tyrosine, methionine, phenylalanine, isoleucine, leucine, lysine, tryptophan, and glycine. In the P-1 and P-2 among the aspartic acid, glutamic acid, arginine content is relatively high, as the main amino acids. The yam contains 8 essential amino acids in the P-1 and P-2 both.Finally, the sections were measured antioxidant activity in vitron of crude protein components of yam P-1 and P-2. After analyzing the crude protein, P-1 and P-2 antioxidant activity among the different conditions, results showed that crude protein, P-1 and P-2 had high antioxidant activity. Among them, the crude protein has a higher antioxidant activity than the P-1 antioxidant and P-2, which may be attributed to containing impurities, such as polyphenols and flavonoids. |
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