Study Of The Extraction,Purification By Membrane Technology And Stability Of Anthocyanin Pigment From Purple Sweet Potato

Purple sweet potato (Ipomoea batatas), a Convolvulaceae annual herb with rich antioxidative natural pigment, is a recommendable resources for anthocyanin pigment extraction, has caused universal concern.The present thesis was focused on the detection method of pigment from purple sweet potato, technology conditions of extraction and extraction assisted by enzymolysis, technology of purification by membrane, stabilities of anthocyanin pigment from purple sweet potato.Bleaching technology, a rapid method for determination of anthocyanins pigment from purple sweet potato by bleaching, has been researched in this paper. Sodium sulfite used as bleaching agent, the appropriate detecting condition of bleaching was: pH value 3, detection wavelength of 528 nm, linear range of absorbency 0.2～2.9, the dosage of Na₂SO₃ 0.3 g/10 mL, bleaching time 10 min. the equation of linear regression of amaranth standard curve was: y=42.767x+0.8947;y---concentration of amaranth, ppm; x---absorbency of amaranth solution. The concentration of anthocyanin in purple sweet potato is 368.53 mg/100 g detected by bleaching.By contrast, citric acid was better than alcohol and acidulated alcohol as extractant. Then the optimum extraction conditions have been obtained, which included temperature 60℃, 2% hydrochloric acid, the ratio of sweet potato powder to the extraction reagent 1:40, extracting time 1 hour twice (the second time 30 min). under the optimum extraction conditions, the color calue of anthocyanins pigment solution was 0.8013, the extraction ratio was 93.9%.Pectinase and cellulose were used to assisted extraction of anthocyanins pigment from purple sweet potato; the result showed that it was not beneficial to extraction when pectinase added in. The optimum enzymolysis-extraction conditions were: enzyme concentration 1 g/kg, temperature 35℃, pH 4.5, taking time 30 min. The crude pigment was purified by ceramic membranes with 0.1μm pore size, the interception ratio of anthocyanidins and removal rates of impurity have been determined. The interception ratio of anthocyanidins was 27.4%, the removal rates of impurity was 38% and the concentration of anthocyanins pigment increased from 32 mg/g to 37.42 mg/g after process of membrane filtration.The stabilities of anthocyanin extracting from purple sweet potato were conducted. The results showed that the pigment had better stability to be kept in low pH value, and was sensitive to temperature, the stability of the pigment dropped notably in heating. Metal ions had little influence to this anthocyanins pigment, among them; Cu³⁺ deepened the color more than Pb²⁺, while Fe³⁺ deepened the color little based on combining of the disruptive and protective properties of Fe³⁺ to anthocyanins pigment.The effects of Food Additives on stabilities of anthocyanins pigment have been researched, the result shown that D-isoascorbate can protected the anthocyanins pigment, while Na₂SO₃ and NaNO₂ breakdown it, and Sodium Benzoate has no harmful effects on anthocyanins pigment from purple sweet potato.