Study On The Development Of The Fermented Tea Beverage By Lactic Acid Bacteria And Its Functional Research

Probiotics are a class of active and beneficial microorganisms which can play a beneficial role in the host.Lactic acid bacteria as an important representative of probiotics are favored by more and more people because of their widespread scope and their special function.In the food industry,lactic acid bacteria fermented food is considered to be a good functional food.In recent years,lactic acid bacteria fermented beverage have been developing rapidly,new products are emerging constantly,showing the unique nutritional value and the vast market space.At present,there are a variety of lactic acid bacteria products on the market,such as lactic acid bacteria fruit and vegetable juice,lactic acid bacteria milk tea,lactic acid bacteria plant beverage and so on,but the breeds of lactic acid bacteria fermented tea beverage are rare.In order to enrich the market demand,screening high-quality strains for tea fermentation and developing new beverage products will become an inevitable trend.The main contents and conclusions are as follows:(1)Two strains were screened from the tea leaves and identified as Lactobacillus plantarum by morphological,physiological,biochemical characteristics and molecular biological identification,were named NCU177 and NCU178 respectively.The tea fermentation performance test showed that NCU177 was the dominant strain and selected as the experimental strain;(2)Study on growth,metabolism and properties of L.Plantarum NCU177.The growth curve of L.Plantarum NCU177 was determined,delay period was 0-2 h,logarithmic period was 2-16 h,while 16-32 h was the stationary phase and it began to enter into decline phase after 32 h.The strain metabolized glucose into lactic acid in the fermentation process.The viable cell number of the strain was 6.97 Log(CFU/mL)after 3 h in MRS medium with PH 2.0 and could still maintain 9.65 Log(CFU/mL)after 12 h in the artificial gastrointestinal fluid.In the high bile salt environment for 4 h,the survival rate was 80.7 %.In addition,the strain maintained for more than 9.4 Log(CFU/mL)under hyperosmotic condition after 24 hours.The strain had good inhibitory effect on the common pathogenic bacteria,and the antibacterial activity was not only lactic acid produced by its own metabolism,but also other antibacterial substances.(3)Study on the technology of lactic acid bacteria fermented oolong tea and black tea beverage.Extraction process was determined by orthogonal experiment with sensory evaluation and tea polyphenols content as index.For oolong tea,ratio of tea to water was 1:80,80 ? extraction 12 min and the ratio of tea to water was 1:100,80 ? extraction 12 min for black tea,respectively.The fermentation conditions were optimized by orthogonal experiment with sensory evaluation,PH and acidity as index.The result of oolong tea was 8 % syrup,1 ‰ inoculum concentration,fermented at 37 ? for 36 h and the result of black tea was 8 % syrup,3 ‰ inoculum concentration,fermented at 32 ? for 48 h,respectively.The optimum sugar degree was 2 % to fermented oolong tea and 1 % to fermented black tea.The final products were in line with GB/T 21733-2008 tea beverage standards.(4)Quality analysis of beverage fermented by lactic acid bacteria.Compared the changes of tea components before and after fermentation,the PH value and caffeine content of the beverage decreased significantly,the acidity and the soluble solid content increased significantly as well as the tea polyphenols decreased slightly.The content of theanine in the oolong tea was not significantly changed,while the black tea increased significantly.The main aroma components species and content of two kinds of fermented tea beverages were significantly increased,which enhanced the flavor formation.The storage stability of the fermented tea beverage at 4 ?,room temperature and 37 ? was measured by different indexes.It was found that the high temperature had a great influence on the light transmittance,color change and some components.Therefore,the products were not suitable for storage at high temperature.(5)Study on antioxidant activity of lactic acid bacteria fermented tea beverage in vitro.Although the scavenging ability about some free radical has decreased slightly after fermentation,it still has a strong antioxidant capacity.The scavenging ability to hydroxyl radical and DPPH radical of the fermented oolong tea and black tea were 97 %,76.8 % and 80 %,53.9 %,respectively.In the total antioxidant study of ABTS,TEAC values of the beverages were all higher than 1.2 mM and there was no significant effect before and after the fermentation.FRAP antioxidant capacity about two beverages were both higher and no significant changes before and after fermentation.