Screening Of Citric Acid-degradation Strain And Application In Fermented Red Raspberry Juice

In order to obtain strains with high citric acid-degrading ability and apply it to reduce acidity of red raspberry juice,the high rate of deacification strains were isolated from the soil and fruit of the red raspberry orchard.Strain with high citric acid-degrading ability was used to reduce acidity of red raspberry juice and its degrading characteristics were studied.Yeast and lactic acid bacteria were used to ferment the red raspberry juice after bio-deacidification.Determined the most suitable fermentation conditions,antioxidant activity of fermented juice under in vitro stimulated digeston was studied.A strain with high efficient citric acid degradation ability and one kind of high-quality fermented red raspberry juice were obtained.Strains were isolated from the soil and fruit of the red raspberry orchard.Fermentation is carried out by stationary and agitation culture,the strain T2 from the soil and the strain G4 from red raspberry fruit behaved with good deacidification capability.Strains T2 and G4 stationary fermented in red raspberry juice,the total acid degradation rates were 55.32%and 60.41%,respectively.Agitation fermented in red raspberry juice,the total acid degradation rates were 89.82%and 94.66%,respectively.According to the morphological features,physiological and biochemical characteristics and molecular identification,strain T2 and G4 were identified as Issatchenkia terricola,renamed Issatchenkia terricola WJL-T2 and Issatchenkia terricola WJL-G4,respectively.To study the effect of fermentation conditions on the acid-degrading of Issatchenkia terricola WJL-G4 and the active components and aroma components of red raspberry juice during acid-degrading culture.The results showed that the conditions for degrading the acidity of red raspberry juice were 28? for fermentation temperature,36 to 60 h for fermentation time,4%(v/v)for inoculum size,120 r/min for rotation speed and 20%(v/v)for broth content.The contents of total phenolics and anthocyanins in treatment group and control group were decreased,the total flavonoids significantly increased in treatment group.10 kinds of phenolic acids,9 kinds of flavonoids and one kind of aromatic compound were identified by high performance liquid chromatography.The contents of p-hydroxybenzoic acid,chlorogenic acid and erucic acid in the culture showed a downward trend.The contents of syringic acid,p-coumaric acid,raspberry ketone,isovitexin,rutin,quercetin and kaempferol increased and were higher than the control juice.Gas chromatography-mass spectrometric identified 46 kinds of aroma components,including 8 kinds of alcohols,16 kinds of esters,6 kinds of aldehydes and ketones,6 kinds of olefins,8 kinds of alkanes and 2 kinds of other species.During acid-degrading culture,the relative contents of aldehydes and ketones gradually decreased and esters significantly increased.Using the red raspberry juice after acid-degrading culture,yeast and lactic acid bacteria were mixed to ferment.According to the contents of total phenols,total flavonoids and anthocyanins,the fermentation sequence and fermentation species are determined.On the basis of the single factor experiment,orthogonal experiment was used to optimize the fermented parameters.The results showed that,the optimal fermentation process conditions for fermented red raspberry juice were obtained:adjust the initial sugar content of the juice to 12°Bx,after fermentation of Saccharomyces cerevisiae 2323 for 60 h,Lactobacillus plantarum fermented for 60 h,the inoculum size was 4%(yeast:lactic acid bacteria,1:1),fermentation temperatures of yeast and lactic acid bacteria were 24? and 37?.Simulate gastrointestinal digestion of red raspberry fermented juice in vitro,investigate the changes in active ingredients and antioxidant properties during the digestion process.The results showed that during simulated gastric digestion,the contents of active ingredients and antioxidant activity fluctuated at different digestion times.During the simulated digestion of red raspberry fermented juice in vitro,the content of total phenols in the gastric digestion group increased first and then decreased.The total flavonoids content showed a stable tendency after rising.The content of anthocyanins was no significant change.The DPPH free radical scavenging activity increased first and then decreased.There is no significant change in the ABTS+free radical scavenging activity.The total reductive ability increased first and then kept stable.The superoxide free radical scavenging activity increased first and then kept stable.The hydroxyl free radical scavenging activity gradually decreased and lower than the control group.In the intestinal digestion group,the contents of total phenols and total flavonoids increased first and then decreased.Anthocyanins content was gradually decreased.The DPPH free radical scavenging activity gradually decreased.The ABTS+free radical scavenging activity kept stable and then decreased.The total reducing ability and the hydroxyl free radical scavenging activity increased first and then decreased.The superoxide free radical scavenging activity increased first and then kept stable.The active components have certain correlation with antioxidant activity during in vitro simulate gastrointestinal digestion.