Purification,Composition Analysis And Stability Of Anthocyanins From Purple-Fleshed Potato

Purple-fleshed potato is a new type of hybrid potato,which is rich in anthocyanins,making its skin and tuber purple.Anthocyanins is a kind of compounds formed by the combination of anthocyanins and various sugars.They are the most important natural water-soluble pigments in vascular plants.Anthocyanins is one of the natural pigment widely used in food industry.It not only gives food attractive color,but also plays an important role in maintaining human health.Anthocyanins has many beneficial effects on human health,such as anti-oxidation,anti-cancer,regulating blood pressure,preventing obesity and improving insulin resistance and diabetes.However,because anthocyanins are not easy to extract,and the purified monomer anthocyanins are very unstable,its stability is seriously affected by external factors,these characteristics limit the application of potato anthocyanins in the food industry,so that there is no Purple-fleshed potato anthocyanins related products on the market.In this study,Purple-fleshed potato anthocyanins was extracted by ultrasonic assisted method,and its components and relative contents were identified after separation and purification.The antioxidant and stability of anthocyanins were studied comprehensively.On this basis,the effect of pH on the degradation and polymerization of anthocyanins was further studied.It is hoped that the experiment can provide theoretical basis and reference for the application of anthocyanins in food industry.The main results are as follows:1.Optimization of extraction conditions of anthocyanins from purple-fleshed potato.Taking the anthocyanins extraction amount of purple-fleshed potato as the index,single factor and Box-Behnken test was carried out.The best extraction conditions were obtained by response surface analysis:the ratio of material to liquid was 1:51.64(M/V),extraction power was 307.07 W,extraction temperature was 50.49℃,extraction time was 14.97 min,under which the maximum extraction amount was predicted to be 1.44 m g/g.In order to facilitate the test,the extraction conditions were adjusted as the ratio of material to liquid was 1:51,the extraction power was 300 W,extraction temperature was 50℃,extraction time was 15 min,validation test was carried out,and extraction amount was 1.36 ± 0.05 mg/g.Through the interaction analysis of factors,it can be seen that the influence of the factors on the response value is material liquid ratio,extraction power,extraction temperature and extraction time.2.The separation and purification technology of anthocyanins from purple-fleshed potato was analyzed.The results showed that AB-8 macroporous resin had the best adsorption and resolution ability,and the recovery was 83.38±4.2%.The adsorption isotherms of the samples at 25℃,30℃ and 35℃ were measured.The experimental data were fitted with the Langmuir model and the Freundlich model.R2 showed that the isotherms of this experiment fit well with the Langmuir model.The model data showed that the optimal temperature of adsorption was 25℃,and the adsorption of anthocyanins by resin was exothermic.Ethanol with 60%concentration can achieve good elution effect.The results of dynamic adsorption and elution showed that when the concentration of purified sample was 0.29 mg/ml,the maximum purification amount of sample was 9 BV,and most anthocyanins could be eluted by 6 BV eluent.The concentration of anthocyanins in the purified sample was 6.43 ± 0.37 mg/g.3.The composition and relative content of anthocyanins in purple-fleshed potato were identified.The composition and relative content of anthocyanins in purple-fleshed potato was analyzed by UPLC-ESI-MS/MS.The results showed that there were 28 different anthocyanins in anthocyanins of purple-fleshed potato,covering all kinds of common anthocyanins.Among them,petunianin is the main component of purple-fleshed potato anthocyanins,followed by peonidin,malvidin and cyanidin,the proportion of four anthocyanins is 52.35:49.75:37.96:25.62,in addition to a small amount of delphinine and pelargonidin.There are a lot of acylated anthocyanins in purple-fleshed potato anthocyanins,which are mainly produced by acylation of p-coumaroyl,ferulic acid,erucic acid,caffeic acid and malonic acid.4.The antioxidant activity of anthocyanins of purple-fleshed potato was analyzed.The results showed that the content of total phenol in the freeze-dried Purple-fleshed potato anthocyanins powder was 218.5 ± 1.26 mg GAE/g DW,and the content of total flavonoids was 131.69±1.84 mg RE/g DW,which had a certain reducing power.The IC50 of DPPH free radical scavenging was 183.37μg/ml,that of ABTS+free radical scavenging was 224.52 μg/ml,and that of hydroxy radical scavenging was 115.86μg/ml.The results showed that anthocyanins of purple-fleshed potato had good antioxidant and free radical scavenging effects.5.The stability of anthocyanins of purple-fleshed potato was analyzed.The relationship between the stability of anthocyanins and the external environment was studied.The results showed that the stability of anthocyanins decreased with the increase of illumination time.The higher the pH value of the solution,the faster the storage rate of anthocyanins decreased.When the pH value was lower than 6,T1/2 was more than 300 min,when the pH value was 8.0,T1/2 was only 51.37 min.The higher the pH value,the worse the stability of anthocyanins.When the temperature is less than 90℃,T1/2 is more than 5 h,while when the temperature is 90℃,T1/2 is only 3.26 h,indicating that the higher the temperature,the worse the stability of anthocyanins.Purple-fleshed potato Anthocyanins is stable in the solution containing Mg2+,K+,Na+,Zn2+,Ca2+.Precipitation occurs in the solution containing Cu2+.Al3+can protect it.Preservatives have some influence on the stability of anthocyanins,but common food additives such as sucrose,glucose,maltose,fructose,xylitol,phytate and salt have little influence on the stability of anthocyanins.6.The effects of heating time and pH value on the degradation of anthocyanins,polymer formation and color change of purple-fleshed potato were studied.The degradation of anthocyanins in purple-fleshed potato follows the first-order reaction kinetic.At pH7.0,the degradation rate of anthocyanins increased,and the pH value had a significant effect on the degradation rate of anthocyanins.In the process of heat treatment,the degradation of anthocyanins is accompanied by the polymerization reaction,resulting in a large number of brown polymerization products.In the process of solution,the rule of polymer color formation also accords with the zero order kinetic model.During the heat treatment,the color of the sample also changed obviously,the higher the pH value,the faster the color change.It is suggested that pH value plays an important role in the color retention of anthocyanins during heat treatment.