Stability, Antioxidant Activity And Identifyication Of Anthocyanins Of Pomegranate Juice

The attractive red color of pomegranate juice is the important commercial character anddetermined by its anthocyanins.Anthocyanins which are unsteady and easy to degrade inproducing and storage are important functional components of pomegranate juice.It hasimportant realistic meaning and theory value to study the stability and degradation ofpomegranate anthocyanins.In this paper pomegranate planted in Lintong of shanxi province was took asexperimental material.Stability and degradation kinetics of pomegranate juice anthocyanins,the effect of many copigments on stability of anthocyanins and color of pomegranate juice,characteristics of polyphenoloxidase(PPO)and the role in anthocyanins degradation,enzymatic clarification of pomegranate juice and the effect of several production procedureson the stability of its anthocyanins,antioxidant activity of pomegranate juice andanthocyanins extract were studied.Anthocyanins of pomegranate juice were purified bymacroporous resin and Sephadex LH-20 and identified by HPLC-DAD-MS.The main resultswere as follows:(1)Anthocyanins in pomegranate juice is instable to heat,its Hunter a* value has adowntrend with increases of heating time and temperature,while the Hunter b* has anincreased trend.The stability of pomegranate juice anthocyanins is influenced deeply by pHvalue and light.It can induce degradation of anthocyanins when pH＞5 or presence of light.The degradation of anthocyanin in pomegranate is followed first-order reaction kinetics,andthe thermal degradation activation energy of anthocyanins in pomegranate juice is46.1602kJ/mol,and the rate constant (k₀)is 6.37×10⁶.The theoretical value and experimentalvalue are propinquity,which indicate that the model is appropriate.(2)EDTA,SDS and phytic acid have certain copigment effects and could increaseheating stability of anthocyanins of pomegranate juice,and phytic acid whice concentration is20mg/mL has best effct.Tween-80,amino acids and rutin have no copigment effect and donot affect the heating stability of pomegranate juice anthocyanins.Tannic acid has copigmenteffect but has no effect on stability of anthocyanins of pomegranate juice.Vc decrease thestability of pomegranate juice anthocyanins significantly when the concentration is over 1.06mg/L.Glucose and fructose increase the Hunter a* value of the pomegranate juice whilesucrose decrease the value.Sucrose and low concentration glucose have no effect on heatingstability of pomegranate juice anthocyanins.Glucose has protecting effect on anthocyaninswhen the concentration is 150mg/L.Fructose shows a disadvantage impact and the higher theconcentration is the more disadvantage effect is.(3)The PPO of pomegranate juice could katalyze monohydric phenol,dihydric phenoland polyhydric phenol.PPO has maximum activity when substrate is catechol.At thecondition of pH7&30℃PPO activity is biggest.PPO loses activity when temperature is over80℃.PPO of the pomegranate juice can directly catalyze degradation of pomegranate juiceanthocyanins and Phenolic compounds may also have certain catalysis in the process of PPOcatalytic degradation of anthocyanins.(4)Cleaning time of arils (seed sacs)has little effect on the pomegranate juiceanthocyanins content.Cold squeezing has advantage effect on content of anthocyanins whileheat squeezing has disadvantage effect.EDTA,Vc,L-cysteamine has certain effect of colorpreservation,L-cysteamine was the best.The optimum concentration was 0.025%.Theoptimum condition for clarification by a two-factor central composite design was as following:pectinase quantity was 0.98 ml/L,hydrolyze temperature is 40.5℃,Hydrolyze time is 127min,under the conditions,the light transmittance of the pomegranate juice was 95.31%,theretention rate of anthocyanins was 82.5%.It is observed that the retention rate ofanthocyanins was almost 100% and Hunter L*,Hunter a* has no change in rotary vacuumconcentrating process.The retention rate of anthocyanins,Hunter L* and Hunter a* reducedsignificantly in microwave and atmospheric heating concentrating process.There isremarkable degradation effect in microwave concentrating process.(5)HPD-100 is the suitable macroporous resin in purifying pomegranate juiceanthocyanins.The optimal adsorbing time is 3h and optimal concentration of acid ethanol is80%.The color value is 19.96 after purifying by HPD-100.HPLC-DAD-MS was used topurify and identify the pomegranate juice anthocyanins.The composition of pomegranatejuice anthocyanins are delphinidin-3-glycoside,delphinidin-3,5-di-glycoside,cyanidin-3-glycoside,cyanidin-3,5-di-glycoside,pelargonidin-3-glycoside,and pelargonidin-3,5-di-glycoside.Cyanidin-3-glycoside,cyanidin-3,5-di-glycoside are the main anthocyanins in thejuice.(6)The contents of anthocyanins and polyphenol in pomegranate juice ranged from2.1mg/L to 146.09mg/L and 1.10g/L to 1.70g/L respectively.All varieties of pomegranatejuice show good effect on scavenging capacity to DPPH·.There was significant positivecorrelation between total phenol content and reducing power.There was also good correlation between the total phenol and scavenging rate of DPPH·and O₂^-·.Anthoeyanins andscavenging rate of·OH shows good correlation but shows little correlation with other indices.Among the 4 antioxidation indices,besides scavenging rate of DPPH·and reducing power,scavenging rate of O₂^-·and scavenging rate of·OH show significant correlation both,there isno significant correlation each other.The extract of pomegranate juice anthocyanins showsgood antioxidant activity.Reducing power and scavenging rate of·OH,O₂^-·,DPPH·ofanthocyanins extract increase with the increase of the concentration,and there are significantdose-effect relationship between them.The IC₅₀of·OH,O₂^-·,DPPH·are 135mg/L,72.3mg/L,8.56mg/L.