Research On Extraction And Purification, Stability And Structure Identification Of The Pigment From Peels Of Purple Yam

Purple yam, also as know Dioscorea alata Lirm sp., is an annual vegetable varieties. The tube of purple yam have an irregular shape, look like baseboard, so it was common known as the common yam rhizome. Now it was only growed in small parts such as Guangxi and Jiangxi provinces. The rich variety of purple yam, starch, mucilage gule, vitamins, saponins and other nutrients and has the function of nourishing stomach, refreshes breath, nourish the liver and kidney. Purple yam's pulp with purple-red and the peels of purple yam with purple-black, which is full of nature pigments and is an ideal material to produce nature edible pigments. At present, the research on the pigment of purple yam has been very little and limited to the extract pigments from purple yam's pulp. In this paper, it is the first time study the nature pigment extracted from the peel's of purple yam, and the major contents of the research encompasses the following four parts:extraction pigments from the peels of purple yam, purifying purple yam pigment by macroporpous adsorption resin method, the stability of purple yam pigment and the structure intinal analysis. The main conclusions are as follows:1) The effects of different parameters such as extracting reagent concentration, temperature, time and the ratio of sample to reagent were studied for the optimal pigment extraction from the purple yam by single factor experiment and orthogonal test. The optimum conditions were obtained as follows:extracting reagent 40% ethanol,70℃, rate of sample to reagent 1∶10,and 2h.2) The purple yam pigment was purified by macroporous adsortion resin. Methods with adsorption and desorption rate as the markers, comparing the specialities of 6 kinds of resins(AB-8,D101,X-5. LSA-10,XDA-6,XDA-7), the XDA-7 resin was the optimum integrated estimate. Through the dynamic adsorption and desorption experiments, we obtained the optimum technological process to purify purple yam pigment by XDA-7 resin. The optimum adsorption conditions were as follows:concentration of sample was 2.0mg/mL, flow rate was 2.5mL/min, pH of sample was 3.0, under those conditions, the adsorption rate was 92.78%. The optimum desorption conditions were as follows:60% alcohol as the eluent, elution rate 2.5mL/min, the volume of elution was 2.5BV. and the desorption rate was 92.21% under those conditions. After purification, pigment solution was dried to purple black powder by vacuum drying oven, the color value is 51.2, which was 7 times as much as which was not purified.3) Purple yam pigment was anthocyanins and water soluble. Purple yam pigment was influenced distinctly by pH values and stable under acid conditions. It shows a better heat stability while sensitive to light, but due to long time under high temperature and direct sunlight, leading to decrease stability evidently. Thus the purple yam pigment should be stored in cool/dry place under room temperature or low temperature (4℃refrigerator), and protect from sunlight. Fe2+ had hypochromic effect on the purple yam pigment, while Fe3+, Cu2+, Ca2+, K+, Zn2+, Mg2+ and Al3+ had weak influences. In addition, the purple yam pigment were more sensitive to ascorbic acid, Na2SO3 and H2O2, and during use should avoid.4) The structure of the purple yam pigment was initial identified by UV, IR and LC-MS. Purple yam pigment was anthocyanins through the scanning spectrum of UV. There was only one main component in purple yam pigment through analyzing the result of HPLC.That could be preliminary identified that the pigment was delphinium-glucoside through spectrum of IR and MS.