Study On Iactic Acid Bacteria Fermentation On Phenolic Composition And Antioxidant Activity Of Blueberries

Previous studies have found that enzymes secreted by lactic acid bacteria during fermentation may change the chemical structure of substances and produce various kinds of metabolites that promote health(biotransformation).In addition,some lactic acid bacteria fermentation showed positive effects on the transformation of polyphenols in fruits and vegetables and the bioavailability of antioxidant activities.In this paper,the optimum fermentation conditions for six common lactic acid bacteria fermenting blueberries were studied based on the antioxidation index.The results obtained from single factor and response surface tests showed that: The optimum fermentation conditions for lactobacillus rhamnosus are fermentation temperature 33?,fermentation time23 h,and initial inoculation 3.6%;the optimum fermentation conditions forbifidobacterium animalis are fermentation temperature 39?,fermentation time 35 h,and initial inoculation3.2%;the optimum fermentation conditions for lactobacillus plantarum are fermentation temperature 42?,fermentation time 47 h,and initial inoculation 4.2%;the optimum fermentation conditions for leuconostoc mesenteroides are fermentation temperature 29?,fermentation time 36 h,and initial inoculation 2.2%;the optimum fermentation conditions for pediococcus pentosaceus are fermentation temperature 37?,fermentation time 49 h and,initial inoculation 3.2%;the optimum fermentation conditions for streptococcus lactis are fermentation temperature 37?,fermentation time 49 h,and initial inoculation 3.2%;After extracting the free phenol and combined phenol from fermented blueberries under these fermentation conditions,the antioxidant ability of free phenol and combined phenol was detected by ABTS and DPPH.The results showed that the antioxidant capacity of the samples was improved after fermentation compared with that before fermentation(p<0.05).By combining the results of the two antioxidant methods,the fermentation samples of pediococcus pentosaceus and streptococcus lactis were considered and selected for subsequent experiments.This study investigated the effect of phenols of blueberries on antioxidant activity after fermentation by different lactic acid bacteria.Phenolic compounds were identified in blueberry pulp fermented by different lactic acid bacteria,of which 16 phenolic substances were identified as free phenol and 6 phenolic substances were identified as combined phenol.The study found that the levels of phenols in blueberries changed after fermentation,in which the content of anthocyanins decreased significantly while phenolic acids increased to differentdegrees.Compared with the control group,the antioxidant capacity of free phenol ABTS increased by 10.63%,binding phenol 7.05%,DPPH free radical scavenging capacity increased by 17.63% and binding phenol increased by 41.04% after fermentation by Streptococcus lactis.After fermentation by pentose tablets,the antioxidant capacity of free phenol ABTS increased by 10.47%,binding phenol by 7.78%,DPPH free radical scavenging capacity by 18.38%,and binding phenol by 42.8%.It indicates that anthocyanins are converted into phenolic compounds under the action of lactic acid bacteria during fermentation and the free and combined phenols of blueberries after fermentation had a higher antioxidant activity than that before fermentation.It was found that the antioxidant capacity was highly correlated with catechin,epicatechin,p-Coumaric acid,and ferulic acid.Moreover,the content of these substances increased after fermentation,which was the main reason for the enhancement of antioxidant activity.The antioxidant activity of blueberries fermented by Streptococcus lactobacillus was the strongest.This study also explored the impacts of changes in phenolic compounds onantioxidant activity of blueberries fermented by different lactic acid bacteria after in vitro simulating digestion.The identification of the free phenol by stimulating in vitro digestion of phenols found a total of 16 phenolic compounds.The identification of the combined phenol by stimulating in vitro digestion of phenols found a total of 7 phenolic compounds.The results showed that the antioxidant activity increased continuously during simulated gastrointestinal digestion.The antioxidant ability of the free phenol after in vitro digestion was maximumly correlated with catechin and ferulic acid while the antioxidant ability of the combined phenol after in vitro digestion was maximumly correlated with chlorogenic acid and syringic acid.The content of these substances increased during digestion,which may be the main cause for the increase of antioxidant capacity.The free phenol and combined phenol from streptococcus lactis fermented blueberries showed the strongest antioxidant activity during gastrointestinal digestion.After the fermentation of free phenol by Streptococcus lactis,the antioxidant capacity of ABTS is the strongest in intestinal digestion,reaching 96.82 Trolox equivalent,and the antioxidant capacity of binding phenol in gastric digestion is the strongest,reaching97.59 Trolox equivalent.After simulated digestion in vitro,the bioavailability of polyphenols and flavonoids in samples fermented by the two bacteria increased.The bioavailability(PAV)and bioaccessibility(PAC)of free phenol and combined phenol in samples fermented by Streptococcus lactis were the highest.Compared with the control group,PAC increased by28.82% and PAC increased by 5.23%.PAC increased by 17.2% and PAV increased by37.37%.Compared with the control group,the PAC increased by 48.79%,the PAC increased by 26.7%,the PAC increased by 34.23%,and the PAV increased by 52.68%.In conclusion,streptococcus lactis is the best lactic acid bacteria for blueberry fermentation.It provides a valuable choice for the food industry in blueberry fermentation.