Extraction, Purification Of Anthocyanins Pigment From Purple Sweet Potatoes (Ipomoea Batatas)

Anthocyanins pigment from purple sweet potatoes has many characteristics, such as attractive bright colours, great stability, heat-resistant and light fastness,and has many physiological and pharmacological activities. Purple Sweet potatoes are so facile and cheap that they can meet the expectation of industry. There are great potential applications of anthocyanins in food and medicine fields.Aiming at increasing extraction efficiency, ultrasonic method and freezed-melt method were used in extracting anthocyanins pigment from purple sweet potatoes.The result of experiments showed that the optimal conditions of extracting anthocyanins pigment with ultrasonic method were: the extractant was consisted of 0.1%HCl : 95% ethanol(40:60,v/v), the powder of purple sweet potatoes were soaked in extractant for 30 minutes at 60℃ under ultrasonic condition, the ratio of raw material and extractant was 1:40 (g/ml). The rate of extraction was 89.45%. The result of experiments showed that the optimal conditions of extracting anthocyanins pigment with freezed-melt method combined with ultrasonic method were: the powder of purple sweet potatoes were soaked in 15% citric acid 160 time as much as the weight of raw material, after freezed in refrigerator, thawed for 40 minutes at 70℃ under ultrasonic conditions. The rate of extraction was 17.92%.In order to determinate the content of anthocyanins in pigment, the pH differential method was studied. The anthocyanins content of purple sweet potatoes was 872.9mg/100g calculated by the pH differential method.Two methods to purify anthocyanins pigment were studied. The colour characteristic of anthocyanins pigment purified by precipitation method was 1. Then the anthocyanins pigment was further purified by macroporous resins. Through comparisons among three kinds of resins' adsorption, desorption property and adsorption dynamic, 8# resin was selected as the adsorbent. Effects of pH value, salting–out, flow rate on adsorption and effects of eluent, flow rate, pH value on desorption were also studied. The result was as follow: when the pH value in solution of pigment was 4.0, the concentration of sodium chloride was 40mg/ml, the flow rate was 1.0ml/min, the adsorption content was 9.326mg/g(resin); while 80% ethanol with pH2.0 as eluent, flow rate at 0.5ml/min, the desorption rate was 91.25%. The color characteristics of purified anthocyanins pigment was 10.At the same time, the adsorption kinetics and thermodynamics of 8# resin for anthocyanin pigments were studied. It was found that the adsorption isotherms at different temperatures could be described with equations Langmuir. The purified pigment was judged by UV and IR, the result indicated that the main component of pigment was acylated anthocyanins.