Study On Purple Potato Anthocyanins: Extraction, Isolation And Identification

Purple potato (Solanum tuberosum L.) is one of the new varieties brought into China in recent years containing anthocyanins which give it the function of both medcine and food. The natural colorants have received increasing interests to substitute synthetic colorants due to the worldwide tendency towards the consumption of natural products. Anthocyanins have enormous interests as natural colorants because of their color attributes and their potential health benefits associated with their antioxidant capacity, vaso-protective and anti-inflammatory properties and enhancement of sight acuteness. The well established techniques of agricultural production, harvest and storage as well as the low production cost with high yield, make the purple potato a great potential source of natural anthocyanin pigments. In order to develop anthocyanins source in purple potato, the anthocyanins extraction technology was studied by using the orthogonal expeirment on the basis of single factor experiment and an efficient method was developed for the purification and enrichment of Purple Potato Anthocyanins (PPA) using macroporous resin. This paper also evaluated the antioxidant acitivities and identified the structure of the two main anthocyanins in purple potato. The results were as follows:(1) The anthocyanins yield from the purple potato was determined by the pH differential method. The alternate action of ultrasonic power, extraction temperature, time and the ratio of sample weight to solvent volume were investigated. Results showed that the ratio of sample weight to solvent volume, extraction time, temperature had notable effects on the anthocyanins yield while the ultrasonic power had little effects on it. The optimum extraction conditions were as follows:the ratio of sample to solvent volume(W/V)1:40, extraction time 5 min, extraction temperature 35℃, and ultrasonic power 350W. Citric acid solution was taken as extractant to reduce the hydrolysis of anthocyanins while at the same time the production cost was greatly reduced and safety issue of the extraction solvent was eliminated.(2) The adsorption and desorption characteristics of nine widely used macroporous resins were evaluated and the purification process of the PPA on the selected resin was optimized. Among all the resins investigated, D-101 resin presented the best adsorption capacity for PPA and its adsorption data well fitted to both the Langmuir and Freundlich models at 25℃,30℃and 35℃. The highest desorption ratio was obtained using ethanol-water (80∶20, v/v). In the dynamic adsorption and desorption, 8 g (dry weight) D-101 resin could successfully process 900 mL PPA solution with a anthcyanins concentration of 0.2380 mg/mL. And 120 mL desorption solution could completely desorb the PPA from the column. The results presented the feasibility of D-101 resin for the separation and purification of PPA. The optimized conditions could be used for a base for further scaled up.(3) The contents of the antioxidant components in the lyophilized Purple Potato Anthocyanins powder were measured. Total phenolic acid content is 406.9∞±1.2mg gallic acid equivalent (GAE) per gram, total flavnoids content 397.8±2.3mg rutin per g and anthocynins 259.0±1.9mg per gram. The testing results show that Purple Potato Anthocyanins presented antioxidant acitivity and it can be seen that the antioxidant abililities of PPA and ascorbic aicd are quite similar in terms of total reducing power and DPPH·radical-scavenging acitivity. The ABTS+ radical-scavenging ability of PPA is higher than that of ascorbic acid with the IC50 value of PPA 202.0μg/mL and ascorbic acid 606.1μg/mL. The hydroxyl radical-scavenging ability of PPA is pretty close to that of ascorbic acid but the scavenging ability of ascorbic increases much faster than that of PPA. Both PPA and ascorbic acid possess little metal chelating acitivity, much lower than EDTA.(4) Two main types of anthocyanins were tentatively identified via the method of HPLC-DAD-ESIMS and UV-Vis analysis. It was deduced that the two main anthocyanins in purple potato could be petundidin-3-O-(p-coumaric acid-rhamnopyranosyl-glucopyranosides)-5-O-glucopyranosides and peonidin-3-(p-coumaric acid-rhamnopyranosyl-glucopyranosides)-5-O-glucopyranosides. These two anthocyanins are both acylated and thus relatively stable.