| Noni(Morinda citrifolia Linn.),a plant of the rubiaceae family for the homology of medicine and food.The Polynesians have been using the noni plant to treat various diseases for more than 2000 years.They believe that noni has a good preventive and therapeutic effect on diseases such as diabetes,hypertension,heart disease and arthritis.As the most concerned noni products,fermented noni juice generally adopts the traditional fermentation method,and the whole fruit is femented under dark and sealed conditions.The juice obtained by this fermentation method has a low juice yield and the fermentation time is long.At the same time,because of the widespread microbial pollution and unstable product quality in the production process,the quality and value of fermented noni juice are difficult to be improved.Therefore,in order to improve the juice yield and antioxidant activity of noni juice,we used exogenous pectinase and cellulase to hydrolyze noni fruit efficiently and optimize enzymatic conditions.Apply the excellent strains to the noni fennentation process those selected from fermentation noni natural juice.Then we used metabolomics technology combined with principal component analysis(PCA),partial least squares-discriminant analysis(PLS-DA),orthogonal partial least squares discriminant analysis(OPLS-DA)and other statistical analysis methods to analyze the main active substances and their changes in the inoculation fermentation process,and the volatile components in noni fruit and fermented juice,and evaluated the fermentation system of noni juice.This study can initially explore the mechanism of action of microorganisms in the fermentation of noni fruit,and reveal the impact of main strains on the quality of fermented products.We can obtain some new ideas for the development of new noni products with specific health functions.The main results were as follows:(1)Using noni as the material,the effects of enzymatic hydrolysis conditions on the juice yield and ABTS free radical scavenging rate of noni juice were studied by single factor experiment and Box-Behnken response surface experiment.And then,we analyzed the antioxidant capacity of enzymatic noni juice.The results showed that pectinase and cellulase complex enzymes were better than single enzyme enzymatic hydrolysis.The optimal conditions for the hydrolysis of noni pulp enzyme are as follows:ratio of pectinase to cellulase of 2:3,total enzyme concentration of 0.46%,enzymatic hydrolysis temperature of 49.43?,and nzymatic hydrolysis time of 4.2 1h.Under this enzymatic hydrolysis condition,the noni juice yield was 65.48%,and the ABTS free radical scavenging rate was 62.76%,which was 82.30%and 18.48%higher than that before enzymolysis.Compared with the enzymatic hydrolysis of the former noni juice,its OH scavenging ability,DPPH scavenging ability,total reducing ability and total phenolic content were significantly increased(P<0.05).(2)Selecting Lactobacillus plantarum A33 and Acetobacter lambici C20-14 those were separated from noni juice after natural fermentation and have excellent fermentation performance,and Metschnikowia agaves P3-3 who was isolated from papaya peel.Applying these domesticated strains to noni fermentation to find the best strain suitable for noni fermentation.The active ingredients(scopolamine and deacetyl levulinic acid)and antioxidant capacity of each strain of fermented noni juice tend to be stable after fermentation for 15 days.After inoculate fermentation,the content of organic acids in noni juice after fermentation by different strains was significantly different.The content of galacturonic acid,lactic acid,acetic acid and formic acid accumulated after fermentation,and the succinic acid content did not change significantly.The lactic acid bacteria A33 is superior to other strains in terms of total phenolic content,antioxidant capacity in vitro,and active ingredients such as noni's own scopolamine and deacetyl levulinic acid.And it is more suitable for use in noni fermentation,providing a new direction for further development of noni products with health care functions.(3)In order to further analyze the changes in the quality of noni juice before and after fermentation by lactic acid bacteria A33,we used solid phase microextraction-gas chromatography-mass spectrometry(SPME-GC-MS)to analyze the changes in the aroma components and its contents in noni juice before and after fermentation.The results showed that the types and contents of volatile substances in the noni juice after fermentation increased significantly.A total of 109 volatile components were detected,among which esters,acids and alcohols contributed a lot to the aroma components of noni juice,and the esters was the highest content.There are 85 volatile substances were detected in fresh noni juice,and the total content of esters was 12162.15 ?g/kg(relative content 56.90%).After fermentation,we detected a total of 105 volatile compounds in the noni juice,the content of esters was 25257.11 pg/kg(relative content 55.36%).There are 29 kinds of volatile components methyl formate,methyl 3-pentanoate,2-methyl-3-buten-2-ol and methyl phenyl acetate are newly formed,and the total content of esters is also significantly increased,which is the main reason for the change in the flavor of noni juice.(4)In this study,we used liquid chromatography and mass spectrometry(LC-MS)for metabolomics research on noni juice before and after fermentation by lactic acid bacteria A33.PCA,PLS-DA and OPLS-DA were used for multivariate statistical analysis to investigate the effects of fermentation processes on metabolites.As a result,a total of 74 differential metabolites with significant changes were screened after fermentation,including alkaloids,organic acids,amino acids,glycosides,and other metabolites.Among them,the content of 54 substances increased significantly,accounting for 72.97%of the total amount of significant metabolites.The most important substances are alkaloids,such as 6"-O-acetylxanthine,candidopsis,isorhamnetin,quercetin,kaempferol,soybean meal,3-hydroxycoumarin,epicatechin,soy bean flavin. |
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