Changes In Antioxidant Activity And Volatile Compounds During The Probiotic Fermentation Of Citrus Juice

Fruit juices fermented by probiotics have been attracted more attention in recent years.The probiotic fermention can integrate the functional characteristics of juice and probiotics,and also improve the flavor of juice.Citrus is one of abundant fruits in China.In this paper,lactic acid bacteria and yeast were used in citrus juice fermentation.The effects of lactic acid bacteria species,citrus varieties and lactic acid bacteria/yeast coinoculation on antioxidant activity and volatile substances of fermented juices were evaluated.This study would provide theoretical basis and technologic support for the processing of citrus fruits.(1)The effect of lactic acid bacteria species,such as L.plantarum,L.acidophilus and L.paracasei,on antioxidant activity and volatile substances of Mandarin juice was investgated.As compared with the other lactic acid bacteria,L.plantarum showed better growth in Mandarin juice.Flavonoids and polyphenols contents in juice fermented by L.plantarum were significantly higher than those by L.acidophilus and L.paracasei,but vitamin C content in all fermented juices was decreased obviously.Higher antioxidant activity was found in juice fermented by L.plantarum,followed by L.acidophilus and L.paracasei.Alkene relative contents in juices fermented by L.plantarum and L.paracasei were increased along with the increase in those of ethanol and ethyl acetate,but that of aldyhydes in all the fermented juices was decreased significantly.Based on principal component analysis(PCA),the volatile substances of Mandarin juice were affected by lactic acid bacteria species and fermentation time.Among the three specices,L.acidophilus had a great impact on the flavor of fermented Mandarin juice.(2)The effects of citrus varieties including Mandarin,Huyou,Newhall and Harumi on primary components,antioxidant activity and volatile substances of juice fermented by L.plantarum were investigated.As compared with the other citrus juices,Mandarin juice was more suitable for the growth of L.plantarum.The contents of total sugar,reducing sugar and flavonoids were decreased at the early stage,while increased at the later stage.And higher content of flavonoids was found in fermented Huyou juice.Antioxidant capacity of all the above fermented juices were increased first and then decreased.Relative contents of β-myrcene and γ-terpinene were increased,indicating the enhancement of citrus aroma;those of hexanal,octanal and furfural were decreased,meaning the weakening of faint scent;while those of ketones and esters have not been obviously changed.PCA indicated that the volatile substances in fermented citrus juice mainly depended on the citrus species,and only affected to some extent by the fermentation of lactic acid bacteria.(3)The effect of S.cerevisiae on antioxidant activity and volatile substances of L.plantarum-fermented Mandarin juice was studied.The growth of L.plantarum in Mandarin juice was promoted by the addition of S.cerevisiae,suggested by the significant decrease in the p H.Low content of ethanol in fermented juice was found.Total phenolic content in co-fermented juice was improved,while the contents of total flavonoids and vitamin C were obviously reduced.There was no significant difference between antioxidant activities of Mandarin juice fermented by L.plantarum with and without the addition of S.cerevisiae.Relative contents of alcohols,esters and acids in the co-fermented juice was increased by 1.37%,1.05% and 0.16%,as compared with L.plantarum-fermented juice,meaning the enrichment of ethanol and ester’s flavour.The results indicate that the addition of yeast such as S.cerevisiae is beneficaial to improve the quality of lactic acid bacteria-fermented juice,especially in terms of flavour.