Study On Extraction, Purification And Stability Of Purple Sweet Potato Pigment

Purple sweet potato (convolvulaceae) was an annual herb. It was rich in anthocyanin with nutrition and health function, etc. Therefore, it was a natural pigment resource to be exploited. In the present thesis, extraction, purification, stability and stablization of purple sweet potato pigment (PSPP) were studied and the results were as follows:On the basis of single factor experiment, reponse surface methodology(RSM) was employed to optimize the extraction conditions of PSPP. The results were: temperature 60℃, time 1h, solid-liquid ratio 1:30, acidified ethonal concentration 80%, and the extraction yield was 12.47mg/g.The optimum extraction frequency was twice. Lots of impurities were existed in the crude PSPP. Based on experiment, AB-8 macroporous adsorption resin(MAR) was chosed to purify PSPP, and the purification conditions were: the concentration, pH and flow velocity of the sample were 1.80mg/mL, 3 and 3mL/min, respectively. The eluent was 70% ethanol aqueous with 1% hydrochloric acid and its flow velocity was 3mL/min. Elution volume was 700mL. The purification recovery percent was 62.37%. The color value and rate of purification of PSPP after purification was 21.45 and 9.22%, respectively.PSPP was unstable. In ultraviolet lamp, outdoor/indoor natural light and dark chamber for 7h, the retention of PSPP were 50.64%,71.98%, 82.22%, 89.90%, respectively. Based on this, the stability of PSPP was bad in the presence of light, especially ultraviolet lamp. With full wavelength scanning in differenet pH values from 2 to 11, the color of PSPP changed from deep red to blue, andλ_max moved to the longer wavelength with its CI decreasing firstly and then increasing as the increasing of pH. With the rise of the heating temperature and prolong of heating time,its stability decreased. Al³⁺ could increase the stability of PSPP, but Fe³⁺, Cu²⁺, Zn²⁺, Pb²⁺ would decrease the stability of PSPP. Oxidant would decrease the stability of PSPP and the PSPP solution would fade as the rise of the concentration of oxidant and prolong of oxidation time.Na2SO3 did harm to the stability of PSPP. Sodium benzoate and potassium sorbate showed little influnce on the stability of PSPP. Tannin, p-hydrobenzoic acid and coffeic acid could effectively increase the stability of PSPP, and itsλ_max moved to the longer wavelength. Carbohydrate could increase the stability of PSPP, and the higher the concentration of carbohydrate was, the more stable PSPP was.Sorbic acid potassium, sodium sulfite and ascorbate acid sodium added in PSPP could stablized its stability. After experiment, the rate of sorbic acid potassium and the sodium sulfite added in PSPP was 1:1(m/m), and its dosage was 5ppm with 1ppm ascorbate acid sodium in it. Effects of light, temperature, oxidative and pH were studied to prove that it was correct.