Bioactivity And Microbial Diversity Analysis Of Red Raspberry During The Natural Fermentation Process

The fermented Red raspberry product has broad market prospects due to uts riched nutrients and active substances.In this experiment,the changes of metabolites and antioxidant activities during the natural fermentation process of raspberry were analyzed,the succession of microbial community structure during fermentation was researched using the high-throughput sequencing technology,and the correlation between bioactive components and microbial communities was analyzed in order to provide a comprehensive understanding of the natural fermentation process of raspberry.And meanwhile,to the excellent fermentation strains of raspberry were screened,which can finally provide a theoretical basis for the automatic,modernized and standardized production and management of the raspberry industry.The main findings are as follows:1.The changes of metabolites from the raspberry fermentation samples CD and CX during the fermentation process were basically the same that the pH value did not change significantly,the soluble solids and reducing sugar content decreased,and was stable after 30 days,the protein content was highest at the 20 th day of fermentation.the content of lactic acid,citric acid and tartaric acid increased,and the content of malic acid and succinic acid decreased.After fermentation,the type and content of amino acids in the fermentation product of raspberry increased,TAA The increase of 29.11% and 33.91% respectively,EAA increased by 2.11 times and 1.51 times respectively.During the fermentation process,the total phenol content reached the highest at 20 d,and the flavonoid content reached the maximum at 60 d.Except for protein and amino acid,other metabolite contents of CD sample were higher than that of CX sample.2.Compared with the raspberry juice,the antioxidant activity of the raspberry fermentation is significantly increased.The antioxidant activity of raspberry broth gradually increased with the progress of fermentation,and then decreased slightly.At 120 days of fermentation,the DPPH free radical scavenging rate of CD and CX raspberry fermentation was 1.53 times and 1.34 times higher than that of raspberry juice,respectively.The ABTS free radical scavenging rate was 1.23 times and 1.09 times that before fermentation,respectively;the total reducing power was 1.53 times and 1.54 times that of unfermented,respectively.The DPPH free radical scavenging rate was significantly positive synergistic with pH,lactic acid,citric acid and various amino acids.The ABTS free radical scavenging rate showed a significant negative correlation with pH.The total reducing power had a high positive correlation with lactic acid,flavonoids and various amino acids..3.The high-throughput sequencing was used into studying the microbial community during the raspberry fermentation.A total of 65 different genus fungi were detected,among these genus,3 dominant species with more than 1.00% in the CD sample were found,including Saccharomyces,Hanseiaspora and Kazachstania,Saccharomyces was mainly presented in the early stage of fermentation,and,Kazachstania was changed into the dominant bacteria with the fermentation process.However,there are only two species in CX samples,namely Saccharomyces and Hanseiaspora.And as the fermentation progresses,the abundance of Saccharomyces gradually decreasesand Hanseiaspora increased.The bacterial content in the sample was lower,but the community diversity of the bacteria is higher.The dominant bacteria more than 1% in the CD sample were norank-c-Cyanobacteriaa,norank-f-Mitochondria and Rhodococcus.In addition to the dominant genus as well as CD samples,the dominant bacteria in the CX sample also contained other dominant genus such as Rosenbergiella,Bacillus and Acetobacter.4.Correlation analysis between microbes and bioactive components during raspberry fermentation has been conducted.The results showed that Saccharomyces had a significant positive correlation with reducing sugar and protein components,and a negative correlation with tartaric acid,malic acid,threonine and leucine.Hanseiaspora had a significant positive correlation with tartaric acid and leucine,and a significant negative correlation with reducing sugar.Kazachstania had a significant positive correlation with citric acid,threonine and total reducing power,and a significant negative correlation with glutamic acid.The bacteria during the raspberry fermentation had a significant positive correlation with the citric acid content and valine content in the sample,and a significant negative correlation with the ABTS free radical scavenging rate.Hanseiaspora produce the tartaric acid,Gly,Ile,Leu and Phe by using reducing sugars and proteins for growth and metabolism.The growth of Kazachstania increased the content of lactic acid,citric acid,Thr,Pro,Ala,etc.,which further lead to the improvement of the DPPH free radical scavenging ability and total reducing power.The growth and reproduction of Saccharomyces might improve the synthesis of succinic acid,and as the content of reducing sugars and proteins in the system gradually decreased,the growth and metabolism of Saccharomyces was hindered,and resulted in the content of succinic acid decreases,and also showed an upward trend on the DPPH free radical scavenging rate and total reducing power.5.A total of 11 fungi and 2 bacteria were screened from the raspberry fermentation.Strains S1,F211,3-1,4-1,4-2,4-3,6-1 and 6-2 were identified as Saccharomyces cerevisiae.P21,Z3 were Pichia kudriavzevii,B31 was Pichia manshurica,R1 was Brevibacillus laterosporus,and RS13 was Lactobacillus plantarum.