Research On Submerged Fermentation Technology By Aspergillus Niger And Lipid-lowing Effect Of Instant Dark Tea

Dark tea creates a unique sensory experience,with a brownish-red color,a marked fragrance,and a full-bodied flavor,possibly due to natural fungal inoculation and fermentation.According to modern pharmacological research showed that dark tea had many pharmacological activities,such as improving oral hygiene,lowering hypertension,serving as antioxidants and antibacterial agents,and by countering obesity,hyperlipidemia,hyperglycemia,allergies,and mutagens.and it had wide application and development prospects.However,traditional dark tea preparation usually takes 1-2 months,from sun-dried tea leaves through solid-state fermentation and dehydration.Most of this process is not automated,resulting in low productivity and quality consistency,thus limiting to its used in the food industry.The method of submerged fermentation to product instant dark tea by Aspergillus niger in present work,while summer and fall tea was chosen as row material.Response surface methodology combined with a desirability function was used to optimize the parameters for submerged fermentation.Then the main chemical components of instant dark tea during fermentation process were analyzed.To discuss the possibility for production of instant dark tea by submerged fermentation,the anti-obesity effect of the instant dark tea in vitro digestion and on C57BL/6J mouse were analyzed.The results as follows:1.The preponderant fungus was separated and purified from Anhua dark tea in the plate method,and it was Aspergillus niger(accession number: KY607770)through the use of molecular identification.2.Design the single factor experiment of redness,turbidity and theabrownins content of tea infusion influenced by fermentation time,inoculum size,liquid-solid ratio,and rotation speed.On the basis of the result of the single factor experiment,instant dark tea preparation parameters were optimized using response surface methodology combined with a desirability function.The result suggested that the optimized conditions were 5.3%(v/v),a liquid-solid ratio of 27.78 m L/g and a rotation speed of 182 r/min.Using the modeled optimized conditions,the predicted redness value,turbidity and theabrownins content of the produced instant dark tea infusion were 40.78,90.98 NTU and 140.92 g/kg respectively.3.The change of chemical components and testing were carried out during the fermentation process.When fermented to 144 h,tea polyphenols,free amino acids and soluble sugar content decreased significantly,respectively decreasing by 88.81%,92.13%,50.24%;The growing rate of caffeine and theabrownins contene were increased to 18.51%and 6.18,respectively;The turbidity value and p H of fermentation infusion were decreased and then increased;The dry weight of mycelium offered upgrade firstly than descending latter tendency;The content of catechins were completely oxidized.With the fermentation of continued,the redness and yellowness values of tea fermented infusion were rised,while the brightness was decreased.Compared with commercial instant pu-erh tea,instant dark tea sample was better in color,which reached the quality of traditional dark tea.4.We investigated whether instant dark tea can attenuate the activity of pancreatic lipase,results showed that IC50s(the inhibition concentration at 50%)of instant dark tea was122.7 ± 5.67 ?g/m L,which was lower than two commercial instant pu-erh tea(167.26 ±4.92 ?g/m L and 295.45 ± 9.59?g/m L).Compared with the effects of two commercial instant pu-erh tea,the overall concentration of free fatty acids in the sample treated with instant dark tea was clearly lower,indicating that the instant dark tea markedly inhibited lipolysis.5.The anti-obesity function of submerged fermented instant dark tea was discussed.The results indicated that instant dark tea have reduced body weight,visceral weight,liver weight,TC,TG and so on,compare with the obesity model group.Histological analysis showed that instant dark tea had suppressive effects on the number and size of the adipose tissue fat cell.Significant effects were observed on the serum concentration of leptin and Neuropeptide Y(NPY)in the C75BL/6J mouse treated with instant dark tea.Expression levels of the genes related to obesity in the mouse liver were evaluated by RT-q PCR.The results showed that the gene expression of enzymes involved in lipogenic metabolism and adipose differentiation including FAS and SREBP-1c expression was attenuated by instant dark treatment.In contrast,instant dark tea increased the gene expression of hepatic CPT-1a and LDLR,which is related to energy expenditure and lipodieresis.6.In order to investigate the influences of dietary instant dark tea on intestinal microbial communities in high fat diet induced obesity mice,the V4 hypervariable 16 S r RNA region were selected for sequencing based on Thermofisher Ion S5 TMXL paltform.Instant dark tea intervention decreased the ratio of Firmicutes to Bacteroides.The relative abundance of butyrate-producing bacteria,within Bacteroidales S24-7 group,Ruminococcaceae and Bifidobacteriaceae families were increased after instant dark tea interventions.This study has a guiding effect for instant dark tea on modulating intestinal microbiota in mice,as well as understanding the occurrence and prevention of obesity.