Changes In Bacterial Community Structure During Noni(Morinda Citrifolia L.)Natural Fermentation And Effects Of Dominant Strains On The Quality Of Fermented Noni Juice

Noni(Morinda citrifolia Linn),mainly distributed in the South Pacific islands,Southeast Asia,Hainan,Taiwan and Paracel Islands in China,has a long history as a traditional health food and medicine.Fermented noni juice(noni jiaosu)is popular due to the unique flavor and nutritional benefits.However,its industrial production and application is faced with many problems.As a natural fermentation product,its fermentation is essentially a co-fermentation system with various microorganisms.The changes in microbial community structure during fermentation may bring about different kinds and levels of nutrients and active substances in fermented noni juice.In this study,we used high-throughput sequencing to elucidate the changes of bacterial community structure during natural fermentation,and isolate the dominnant microorganisms to be applied to noni fermentation to test the effect on the quality of the fermented juice,and therefore provide a theoretical basis and guidance for the industrialization,standardization production and technical upgrading of fermented noni juice,and also we can obtain some new ideas for the development of new noni products with specific health functions.The main results were as follows:(1)The results of Illumina HiSeq high-throughput sequencing showed that the bacteria were classified into 17 phylum and 365 genera in all the fermented noni juice samples,mainly including Proteobacteria(82.33%),Cyanobacteria(14.29%)and Firmicutes(1.39%)during noni natural fermentation.Acetobacter and Gluconobacter were dominant in the Proteobacteria.With the progress of natural fermentation,the content of Cyanobacteria reduced,while the content of Proteobacteria increased sharply,and on 6th d,Proteobacteria were dominant(90.71%),of which the relative abundance of Gluconobacter reached the highest(84.75%).As fermentation preceded,the content of Gluconobacter began to decrease,and the content of Acetobacter increased gradually.On 80th d,Proteobacteria was 98.57%,of which Acetobacter was 93.06%.During the fermentation process,Acetobacter and Gluconobacter were always dominant,which indicated that acetic acid bacteria were the dominat microorganisms in natural noni fermentation process.(2)67 strains were isolated from the samples of naturally fermented noni juice in different fermentation stages.24 strains of acetic acid bacteria were identified through traditional physiological and biochemical tests and 16S rRNA sequence homology analysis.They were Acetobacter fabarum(9 strains),Acetobacter syzygii(7 strains),Acetobacter pasteurianus(2 strains),Acetobacter tropicalis(1 strains),Acetobacter lambici(1 strains)and Gluconobacter japonicus(4 strains),respectively.The rich diversity of acetic acid bacteria in naturally fermented noni juice was indicated.Acetobacter fabarum and Acetobacter syzygii were dominant strains in noni natural fermentation process.In terms of fermentation properties,Acetobacter fabarum N17 could resist 40 ℃ and 7%ethanol,and the acid production was the maximum of 17.16 g/L under the 30℃ and 5%ethanol.The optimum growth temperature of Acetobacter syzygii was 34 ℃,and the acid production was the maximum of 27.52 g/L,which was still to a certain degree of growth at 40 ℃,but was more sensitive to ethanol and the volume fraction of ethanol increased to 7%,it basically stopped growing.In addition,Acetobacter tropicalis N21 still grew well at 40 ℃and the acid production was 14.85 g/L.At the alcohol concentration of 7%,the acid production still reaches 23.60 g/L,its ability of resistance to high temperature and ethanol were superior to other strains.(3)The quality of the fermented noni juice by single strain was better than that of natural fermentation.However,the quality of fermented noni juice by different strains was different.Acetobacter lambici N10 fermented juice has the highest acidity.The content of reducing sugars in Gluconobacter japonicus N11 and Acetobacter fabarum N17 fermented noni juice were significantly higher than other samples.The fermented noni juice by Gluconobacter japonicus N11 and Acetobacter pasteurianus N4 performed better in oxidation resistance.The scopoletin content of fermented noni juice by Acetobacter syzygii N5 was the highest content of scopolamine,compared to natural fermentation juice samples increased by 45.598%.(4)The indexes of fermented noni juice from different producing area showed obvious difference.The Thailand product(TL)had the lowest pH value and the highest total acid content.The Fiji product(FJ)had a high protein content,but not significantly different between the New Zealand product(NZ)and the Hainan Haihou product(HNH)(P>0.05).New Zealand product(NZ)exhibited the highest contents of reducing sugar,total phenol and total flavonoids among the other region.The free radical scavenging ability of NZ was the strongest,and FJ had the best performance in reducing capacity.Among the organic acids of all the fermented noni juice,galacturonic acid was the highest,while fumaric acid the lowest,with the organic acids being the highest in TL.The contents of scopoletin and deacetylasperulosidic acid in NZ and FJ were higher than the other product.According to the principal component analysis,the comprehensive nutritional quality of FJ was relatively better.