Stability Evaluation And Interaction Of Betacyanins From Red-purple Pitaya On Bayberry Anthocyanins

Bayberry（Myrica rubra Sieb.et Zucc）is a characteristic fruit in Southern China.Bayberry juice has bright colour,sweet and sour taste and attractive flavor.It is deeply loved by consumers and is the most important deep processing product of bayberry at present.Anthocyanins are the chromogenic substances of bayberry juice,contributing to the bright red colour.However,anthocyanins have poor stability and are easy to degrade under the influence of processing conditions,resulting in the deterioration of the colour of bayberry juice.Betacyanins are another group of natural pigments whose structures are different from anthocyanins.They have bright and stable colour and have the value of application in the field of food colouring.Red-purple pitaya is rich in betacyanins.Therefore,it is of great significance to purify betacyanins from pitaya fruit and carry out its auxiliary colour effect on bayberry anthocyanins,which can provide a theoretical basis for the interaction between the two natural red pigments.Based on the bayberry-pitaya compound juice system,this paper studied the content changes of anthocyanins and betacyanins under different treatment conditions and the external colour changes of the compound juice.The purification process of betacyanins from pitaya was optimized,and the comprehensive utilization from this source was studied.Through the bayberry juice and fermented bayberry wine system,the copigmentation effect of pitaya betacyanins on anthocyanins was evaluated.The interaction mechanism between anthocyanins and betacyanins was analyzed through structural characterization and molecular simulation,so as to provide reference for the application of anthocyanin-betacyanin compound pigment in beverage system.The main findings are as follows:（1）Determination of physicochemical indexes and colour stability of bayberry-pitaya compound juice.Through the determination of the main indexes,it was found that the compound juice was rich in flavonoids and had stronger FRAP antioxidant activity.Betacyanins in compound juice was easy to undergo structural transformation when suffering long-time heating,for example,the decarboxylation at position C-17 of betanin happened and showed orange-red colour.The addition of pitaya juice could enhance the p H stability in the range of 3.0-5.0,showing better colour.Besides,the content of both betanin and isobetanin increased during p H adjustment.（2）Extraction,purification and identification of betacyanins from red-purple pitaya.Taking betacyanins yield as indicator,the extraction process of pitaya pulp was optimized by response surface experiment.The optimum conditions were as follows:solid-liquid ratio was 1:64（w/v）,p H of extraction solvent was 6.0,extraction time was32 min and ultrasonic power was 420 W.Under this condition,the betacyanins yield was 18.68(10^-1 mg·g^-1).The conditions of betacyanins purification with HPD100macroporous resin were optimized as:the p H of the crude extract was 3.0,the adsorption and desorption time was both 4 h,and the desorption solution was 50%ethanol aqueous solution with p H 5.0.Seven structures of pitaya betacyanins were identified by QTOF-MS（Quadrupole Time-of-Flight Mass）method,and the three main structures were betanin,phyllocactin and isobetanin.After heat treatment,betacyanins would produce decarboxylation products of betanin and phyllocactin.（3）Stability evaluation and interaction mechanism of betacyanins from red-purple pitaya on bayberry anthocyanins.Betacyanins purified from pitaya enhanced the stability of bayberry juice in the p H range of 4.0-5.0 and protected anthocyanins from degradation.It could also enhance the anthocyanin stability of fermented bayberry wine during a room temperature storage,and the colour enhancement effect was obvious.It was found that the O-H stretching vibration absorption peak in the FTIR spectrum narrowed and shifted to the low frequency,and the absorption peak in the C-O stretching vibration region decreased.The SEM profile showed that the average particle size of betacyanins became smaller and combined with anthocyanins According to the electrostatic potential analysis,it was inferred that betacyanins and anthocyanins would combine by intermolecular hydrogen bond force,which could protect anthocyanins from nucleophilic attack and thus improve its stability.