Extraction, Deodoirzation, Stability And Initial Structure Identification Of Anthocyanins From Purple Sweet Potato

Purple sweet potato is riched in acylated anthocyanin, which has antioxidant,anti-inflammatory, anti-tumor and other healthy physiological effects and shows broadapplication prospects in food, cosmetics, pharmaceutical and other fields. Purple sweet potatohas good characteristic of adaptability, high and stable yields. Meanwhile it can overcomeproblems, such as seasonal and high cost like arbutus berries. The extract residues can be usedas feed and chemical raw materials to drive value. So there are advantages of raw materialsused for extracting natural anthocyanins. Deodorised purple sweet potato anthocyanin (PSPA)has characteristic of less impurities and unpleasant odor. It not only can be directly added intoproducts to improve red color, prevent browning and increase nutrition, replacing othernatural or synthetic pigments, but also can be as raw materials used for refining high-purityanthocyanin as standard. But vulnerable to varieties of factors from environmental, it willshow polymerization or degradation. For high development and utilization of PSPAs, the keyprocess of extraction, deodorization, stability and initial structural identification about PSPAshad been studied.Firstly, extract effects of MASE and UASE for PSPAs had been investigated. Throughsingle factor and response surface methods, the optimum conditions of MASE were asfollows:60mmol/L hydrochloric acid as extract agent, microwave power471.87W,treatments for3.54min, liquid-solid ratio47.42:1ml/g. The maximum predicted value of totalanthocyanin yield was183.60mg/100g, and actual value measured was182.56mg/100g inverification test. The optimal extraction conditions for UASE by orthogonal experiment were:ultrasonic power360W, liquid-solid ratio40:1ml/g, treat time35min, ultrasonic temperature65°C, and total anthocyanins yield was176.13mg/100g. After comparison with PSPAs yieldsof MASE, UASE and CSE, the results showed that MASE was best, which significantlyshortened extraction time and improved extraction rate with UASE followed and CSE worst;ultimately MASE method used were determined.Secondly, the key processes of macroporous resin separation coupled with chitosanadsorption used for deodorization was investigated. The results showed that pretreatment ofultrasonic assisted-alcohol precipitation could remove most of impurities. Compared toNKA-II, NKA-9, D101, D4020, HPD-300and X-5, AB-8resin was best for removal ofimpurities. The best conditions were: static adsorption under40°C, pH3.0, the amount ofresin50mL/g; desorption conditions were:75%acidified ethanol as desorption agent with pH3.0, sample flow rate2BV/h. The impacts of deodorization with chitosan on qualities ofPSPAs were studied. The results showed that the content of protein, total sugar, soluble solidsand degradation index decreased; L*, a*, C*and sensory score value increased, reflecting animprovement in stability and purity by resin coupled with chitosan adsorption. However,chitosan absorption could slightly reduce anthocyanin content. Consideringly, the optimalcondition of pH3.2, amount of1.5%chitosan, adsorption for2.5h was determined with10.52%of loss rate of anthocyanin. Detected by SPME-GC/MS, the types and contents ofvolatile compounds with bad odors were reduced. Chitosan can be used for deodorization of PSPAs as an adsorption agent.Thirdly, the stability of PSPAs were studied. The results showed that pH-value had greatinfluence on color characteristics and stability; Ultraviolet and natural light cause degradation;The product should be stored in condition of low temperature, dark and near pH3.0. Fe3+inlow concentration has hyperchromic effect, but caused degradation of anthocyanin in highconcentration with time. Not only Fe2+has no hyperchromic effect, but also led to degradation;Ca2+, Mn2+and Cu2+in low concentration had copigmentation effect. H202made anthocyanindegradation and fade, Na2SO3had bleaching effect; Sodium benzoate and potassium sorbatehad almost no effect on stability of PSPAs; ascorbic acid made it subtractive. Oxalic acid,malonic acid and L-malic acid had copigmentation effect and could improve the thermalstability. Oxalic acid was best, but ferulic acid and citric acid was not obvious; phytic acid,EDTA and leaves glycosides rutin had copigmentation effects; the effect of phytic acid wasbest, followed by glycosides rutin leaves, but leaves glycosides rutin made a*value decreased;the copigmentation effect of SDS and Tween-80was not obvious.Finally, the structure of PSPAs was initially identified by LC-MS, which revealed thatmaybe there exist ten components, namely cyanidin-3-sophoroside-5-glucoside,pelargonidin-3-sophoroside-5-glucoside, peonidin-3-sophoroside-5-glucoside,cyanidin-3-p-hydroxybenzoyl sophoroside-5-glucoside, cyanidin-3-(6"-feruloylsophoroside)-5-glucoside, peonidin-3-(6"-feruloyl sophoroside)-5-glucoside,cyanidin-3-(6"-caffeoyl-6’"-feruloylsophoroside)-5-glucoside,peonidin-3-caffeoyl-p-hydroxybenzoylsophoroside-5-glucoside, peonidin-3-(6"-caffeoyl-6’"-feruloylsophoroside)-5-glucoside,peonidin-3-feruloyl-p-hydroxybenzoyl sophoroside-5-glucoside.