Mechanisms Of The Color Deterioration And Anthocyanin Degradation In Chinese Bayberry Wine

Chinese bayberry wine,a deep-processed product of Chinese bayberry,has attractive color,unique taste,rich aroma,and great market potential.However,serious color deterioration occurs during the storage process,that is to say,the red color fades within three months with browning occurring,and thus causing reduced commercial value.At present,there are few researches on Chinese bayberry wine,so the mechanism of the color deterioration is not clear,and there is no effective method to improve the color stability of Chinese bayberry wine.To solve the above problems,the study of this dissertation first explored the relationship between the changes of color-related composition and color deterioration during storage to identify that the main reason for the color deterioration is the degradation of anthocyanins,the main coloring substance in Chinese bayberry wine,then three main influencing factors were investigated successively,including the effect of oxygen on the color deterioration and anthocyanin degradation in Chinese bayberry wine,the effect of iron on the degradation of anthocyanins in the presence of organic acids,and the anthocyanin degradation resulted from antioxidants.The above results indicate that the hydration at position 2 of C ring in anthocyanin is one of the main reasons for the oxidative degradation of anthocyanins.Published literatures have shown that the copigmentation can protect the anthocyanin from the nucleophilic attack of water.Therefore,this dissertation finally explores the effect of copigments on color deterioration in Chinese bayberry wine.Main research contents and results are as follows:It was found that anthocyanins were highly unstable in Chinese bayberry wine,whose degradation could be well described by first-order kinetic model and the half-life was 138.63 d,26.87 d,and 9.00 d,respectively.As the L*,a*,b*,total anthocyanins,total phenols and total flavonoids decreased,small polymeric pigments(SPP)and large polymeric pigments(LPP)increased positively correlated with storage temperature during storage.5-hydroxymethylfurfural(5-HMF),an indicative product of Maillard reaction,increased linearly only during the storage at 37°C,not at lower temperatures;however,serious color deterioration occurred even in Chinese bayberry wines stored at 25°C,indicating other,more important factors leading to color deterioration.The color difference(?E)was significantly correlated with anthocyanins as well as SPP,and the correlation coefficient is high,indicating that anthocyanin probably underwent oxidative degradation and then participated in the generation of SPP,thereby leading to the color deterioration in Chinese bayberry wine.Results showed that oxygen accelerated the color deterioration,accelerated the degradation of anthocyanins,promoted the content of acetaldehyde and polymer pigments,and increased the content of total volatile easters and acids by 19.74%and 41.03%,respectively.The molar ratio of produced protocatechuic acid to degraded anthocyanins increased from 5.08%to 25.14%during storage as package oxygen inceased.Compared with the oxidative condensation pathway of anthocyanins,oxygen was more likely to accelerate the degradation of anthocyanins by promoting the cleavage pathway of anthocyanins.Nitrogen filling and deoxygenation weakened the adverse effects of oxygen on the color and anthocyanins of Chinese bayberry wine,and had a weaker effect on the flavor composition.Results showed that the oxidation rate of Fe(?)in different organic acid systems was oxalic acid<citric acid<malic acid<tartaric acid,but it cannot be oxidized in succinic acid systems.Fe(?)and Fe(?)could produce unstable complex with cyanidin-3-O-glucoside(C3G),leading to the oxidative degradation of anthocyanins in the succinic acid system,while citric acid prevented the reaction.The rate of iron-mediated degradation of anthocyanins in different organic acid systems was citric acid<oxalic acid<succinic acid<malic acid<tartaric acid,and the half-life of C3G was 23.34 d,9.48 d,6.52 d,and 4.88 d,respectively.The stability of Fe-organic acid complex could not explain the effect of organic acid on iron-mediated degradation of C3G and it could be related to the steric hindrance of organic acid.The degradation products were analyzed by LC-MS,and were found to be 2-(3,4-Dihydroxyphenl)-dihydroxybenzofuran-3-carboxylic acid glucose ester and{2-[(3,4-Dihydroxybenzoyl)oxy]-4,6-dihydroxyphenyl}acetic acid,the same as the anthocyanin degradation products caused by active oxygen,indicating that iron may promote the degradation of anthocyanins by increasing the level of active oxygen in Chinese bayberry wine.Studies have found that antioxidants including AA,CYS,and GSH had no effect on the absorbance spectra of C3G at room temperature;however,CYS and GSH significantly changed the cyclic voltammograms of C3G.AA,CYS and GSH promoted the degradation of anthocyanins during storage,and their promoting effect was positively correlated with the concentration of antioxidants and temperature.AA,CYS and GSH at 1 m M decreased the half-life of C3G from 28.52 d to 3.11 d,14.09 d,and 7.36 d respectively at p H 3.1 and 37°C.Compared with the hemiketal and chalcone forms,when the anthocyanins exist in the form of flavylium cations,the degradation rate caused by antioxidants was lower.Mercaptoethanol,CYS,and GSH decreased the half-life of C3G to 11.83 d,11.07 d,and 10.16 d,respectively;however,dithiothreitol at the same concentration decreased the half-life of C3G to 1.05 d,indicating that the promoting effect of thiols on the degradation of anthocyanins was highly positively correlated with the number of thiol groups.Antioxidants had the ability to reduce anthocyanin quinone back to anthocyanin,but this reducing ability was invalid due to the high instability of C3G quinone at flavylium cations form in Chinese bayberry wine.CYS can undergo an addition reaction with anthocyanin quinone to generate anthocyanin-cysteine adducts,namely dihydroxy benzothiazine carboxylic acid derivatives as chalcone form.Results showed that gallic acid,ferulic acid and tannic acid had significant copigmentation with Chinese bayberry wine anthocyanins.The absorbance at maximum absorption wavelength of anthocyanins(A_max)were increased by up to 66%,112%,and 27%in Chinese bayberry wine with pre-fermentative addition of gallic acid,ferulic acid,and tannic acid,respectively;the A_maxincreased by up to 56%,70%,and 22%in post-fermentative group respectively.However,rutin had hypochromic effect on Chinese bayberry wine and the A_max of pre-and post-fermentative wines decreased by up to 51%and 25%.Gallic acid,rutin,and tannic acid had bathochromic shift effect on Chinese bayberry wine and the bathochromic shift was up to 6 nm,8 nm,and 5nm.Ferulic acid drmatically increased the ability of anthocyanins to resist the bleaching of SO₂.Although the pre-and post-fermentative addition of gallic acid,ferulic acid and tannic acid accelerated the degradation of C3G(the half-life of C3G decreased from 15.54 d to 9.93 d,5.97d,and 8.03 d,respectively),it can significantly improve the color performance of Chinese bayberry wine during storage.In summary,the degradation of anthocyanins and the formation of SPP are the main reasons for the color deterioration of Chinese bayberry wine during storage.Many factors could affect the degradation of anthocyanins.Among them,oxygen could accelerate the loss of anthocyanins by promoting the cleavage of anthocyanins(more than oxidative condensation of anthocyanins);Fe(?)can be oxidized by oxygen to Fe(?),forming the Fe(?)/Fe(?)redox cycle in the presence of organic acids,which could enhance the generation of reactive oxygen,and promote the degradation of anthocyanins in Chinese bayberry wine.Antioxidants including AA,CYS and GSH cannot reduce C3GQ back to C3G,but have prooxidative effect and accelerate the degradation of C3G.The promotion effect of thiols on C3G degradation depends on the sulfhydryl group.It is speculated that thiols promotes the level of reactive oxygen through the redox of the sulfhydryl group,thereby accelerating the degradation of C3G.In addition,CYS could react with C3GQ(hemiketal or chalcone forms)to produce C3G-CYS adducts,which could be one of the ways to promote the degradation of anthocyanins.Finally,although the copigments promote the degradation of C3G,they significantly improve the color performance of Chinese bayberry wine during storage.These findings are helpful to understand the mechanism of the color deterioration in Chinese bayberry and the degradation of anthocyanins,and can provide references for solving the problem of color deterioration of fruit wine including Chinese bayberry wine.