Study On Phenolics,Antioxidant Capacity And Clarification Effect Of Fermented Mulberry Wine

Mulberry fruit,rich in anthocyanins,phenolic acids,flavonols,flavanones and other active substances,has high antioxidant capacity.Mulberry wine made mainly by alcoholic fermentation of mulberry juice is nutritious and has numerous health benefits.However,its phenolics and antioxidant capacity are affected during the processing of mulberry wine,and product quality changes significantly comprising color,taste and aroma.In this work,the correlation between the change in phenolics and the improvement of the antioxidant capacity,as well as the color,taste and aroma were studied.A new technological process which involved the addition of apple lactic acid fermented broth to mulberry broth was proposed.The effects of fermentation and clarification on the phenolics and antioxidant capacity of mulberry wine were explored,and changes of substances related to the phenolics directly or indirectly were also investigated.Pearson correlation among the color parameters,antioxidant capacity,total anthocyanin,total polyphenol and total flavonoids were established respectively.Principal component analysis was used to analyze the effects of the different clarifying agents on the overall quality of mulberry wine.The main research contents and conclusions were as follows:(1)The effects of different apple lactic acid fermented broth on the sensory quality of mulberry wine were compared using sensory score as an indicator.The results showed that,the amount of apple lactic acid fermented broth significantly affected the sensory score of mulberry wine,and the optimal amount of apple lactic acid fermented broth was established to 15%(v/v).A second order polynomial equation for the sensory scores of mulberry wine and fermentation parameters were established with response surface methodology.The optimum fermentation parameters for actual operation were:Inoculum concentration 0.26%(v/v),fermentation temperature 21.5?,and initial sugar degree 20%.(2)Results of changes in color,the phenolics and antioxidant capacity,as well as Pearson correlation between the phenolics and color,antioxidant capacity during mulberry wine fermentation were as follows:The L*(lightness),a*(red/green),b*(yellow/blue)and C*(chroma)value increased rapidly and then decreased.The total anthocyanin content decreased rapidly and then stabilized.The negative correlation between total anthocyanin content and L*value,a*value,b*value and C*value was the strongest with R~2 values of-0.955,-0.990,-0.934,-0.989 respectively.Within 0~3d,the hue angle H~0 value decreased first,then increased and finally decreased.The total phenols content increased and irons reducing capacity decreased firstly and then increased.After 3 d,H~0 value increased rapidly and then decreased,total phenols content and irons reducing capacity decreased.The negative correlation between total phenols content and H~0 value and the positive correlation between total phenols content and irons reducing capacity was the strongest with R~2 values of-0.920 and0.939 respectively.The total flavonoid content,DPPH free radical scavenging capacity and ABTS~+·scavenging capacity decreased firstly,then increased and finally decreased.The total flavonoid content had the strongest correlation with DPPH free radical scavenging capacity and ABTS~+·scavenging capacity,and R~2 was 0.973 and0.957 respectively.The total phenolic acid content was in dynamic equilibrium.(3)The changes of taste index and aroma components during the fermentation process of mulberry wine were studied by electronic tongue and gas chromatography-mass spectrometry.Within 0~4 d,the relative abundance of sourness and astringent increased and then decreased,bitterness,saltiness and umami decreased and then increased,while aftertaste A(aftertaste of astringent),aftertaste B(aftertaste of bitterness)and richness(aftertaste of umami)increased.After 4 d,the relative abundance of sourness,bitterness,astringent,saltiness,umami and richness was stable and maintained in a relatively stable state,at the same time,aftertaste A and B decreased first,then increased and decreased.From the whole fermentation process,the polar difference of sourness was the greatest.The contents of aroma components increased and then decreased.Alcohols,esters and acids increased significantly and then decreased,and the contents of aldehydes and ketones decreased.After the fermentation,the contents of alcohols,esters and acids increased significantly(p<0.05),which increased alcohol and ester flavors in mulberry wine,while the content of aldehydes and ketones was significantly reduced(p<0.05).(4)The effects of clarifying agent(bentonite,chitosan and gelatin)and their concentrations on the clarifying effect of the mulberry wine were studied with the light transmittance of mulberry wine clarified.The results showed that,when the concentration of clarifying agent increased,the color difference?E increased significantly(p<0.05),while the total anthocyanin content,total phenols content,total flavonoids content and antioxidant capacity decreased.The optimum addition amount of clarifying agent was established as follows:bentonite 0.7 g/L,chitosan 0.7g/L and gelatin 0.5 g/L,of which the gelatin 0.5 g/L was observed to have the best clarifying effect.Comparison of the clarifying effects suggested that gelatin 0.5 g/L was the best clarificant and concentration.(5)The mulberry wine was clarified by bentonite 0.7 g/L,chitosan 0.7 g/L and gelatin 0.5 g/L respectively.The results showed that,in the bentonite treatment group,the?L*value,?a*value,?b*value and?E value were the least color values,total anthocyanin content,total phenols content,total flavonoids content,DPPH free radical scavenging capacity,ABTS~+·scavenging capacity and irons reducing capacity were the highest,gallic acid,protocatechuic acid,chlorogenic acid,caffeic acid,p-coumaric acid,ferulic acid,hydroxycinnamic acid and total phenolic acid decreased the least,which were 4.10%,6.12%,23.90%,25.00%,2.82%,8.15%,20.80%,20.29%,respectively.Comprehensive comparison of the color,phenolics and antioxidant capacity suggested that bentonite was the best clarificant.Mulberry wine clarified by bentonite could retain maximum content of the phenolics,strong antioxidation capacity and minimal change of color.At the same time,there were no significant changes in the relative abundance of sourness,saltiness,umami and richness after clarification treatment,as well as aftertaste A and aftertaste B in chitosan treatment group.In the chitosan treatment group,the relative abundance of bitterness and astringent was the least,and the content of aroma components was significantly higher than those of bentonite and gelatin treatment group(p<0.05).Comprehensive comparison of taste quality and aroma components,suggested that chitosan was the best clarificant.Mulberry wine clarified by chitosan had little effect on the taste index,and a better the aromatic components retention.The principal component analysis on the overall quality of the mulberry wine treated with the different clarifying agents classified the clarified and unclarified samples into three clusters:The unclarified treatment was located on the positive side of PC1 and PC2,the bentonite and chitosan treatment groups were located on the negative side of PC1and PC2,while the gelatin treatment group was located on the negative side of PC1and the positive side of PC2.