| Summer-autumn tea is a large class of tea compared to spring tea.Because of its bitter taste and poor quality,its utilization rate is low and resources are wasted.Summer-autumn broken tea is a by-product of tea processing,which still contains rich nutrients and functional ingredients,and has good potential for development and utilization.In this thesis,the summer-autumn broken green tea was used as the main raw material,while yeast and acetic acid bacteria were used as the strains.Tea vinegar,a new fermentation product with the characteristics of tea and vinegar,was prepared by liquid fermentation.The fermentation conditions,clarification methods,product quality indexes,aroma components and functionalities of the tea vinegar were comprehensively studied to provide an effective way for the comprehensive development and utilization of summer-autumn tea and its by-products.The main results of the study are as follows:（1）Study on the alcoholic fermentation process of tea vinegar:the summer-autumn broken green tea was extracted with hot water and then added with sucrose and yeast for alcohol fermentation.The effects of yeast strain,feed-liquid ratio,comminution number,sucrose addition and inoculation amount of yeast on alcohol fermentation were studied.The best process conditions for the alcoholic fermentation of tea vinegar were as follows:strain BV818,4:100 ratio for the feed liquid,60 number of crushed mesh,15%amount of added sucrose,and 0.9%amount of the yeast inoculation.（2）Study on the acetic fermentation process of tea vinegar:firstly,the effect of adding glucose,rice saccharification solution and Anqi fermented nutrient salt on acidity was studied for the problem of low acidity during acetic acid fermentation.The results had shown that the best acid production effect was obtained by using Anqi fermented nutrient salt.Based on this,the effects of fermentation time,fermentation temperature,inoculation amount of acetic acid bacteria and initial alcohol content on acetic acid fermentation were further studied.The optimum conditions for the acetic fermentation of tea vinegar by orthogonal test were as follows:6%vol of the initial alcohol content,12 d of the fermentation time,9%of the inoculation amount of acetic acid bacteria.28°C of the fermentation temperature.And the acetic acid fermentation verification test was carried out.The acidity of tea vinegar wsa 62.2 g/L and the tea polyphenol content of tea vinegar was 3.23 g/L.（3）Study on clarification process of tea vinegar:clarification test of fermented tea vinegar was carried out by using five clarifying agents of gelatin,activated carbon,chitosan,diatomite and bentonite.The results had shown that diatomite had the best clarification effect,acidity and tea polyphenols lose their value less.Further orthogonal optimization experiments were carried out on the diatomite addition,standing time and standing temperature.The optimum clarification conditions for diatomite were as follows:2.4 g/L amount of added diatomite,10 h standing time,and 20°C standing temperature.（4）Analysis of tea vinegar quality and aroma components:the sensory indexes,physical and chemical indicators and health indicators of the clarified tea vinegar were all tested to meet the requirements of relevant products.During the detection and analysis of amino acid of tea vinegar,17amino acids were found,and the total content was 2.17mg/mL,which contains 7 kinds of essential amino acids.Taking tea infusion as a comparison,GC-MS analysis of the aroma components in tea vinegar had shown that 44 kinds of aroma substances were detected in the tea infusion,among which,13 kinds of alcohols,17 kinds of aldehydes,1 kind of acid,9 kinds of ketones,dimethyl sulfide,2-ethane-3,5-dimethylpyrazine,2-acetylpyrrole and indol.The 51 kinds of aroma substances were detected in the tea vinegar,including 7 kinds of esters,13 kinds of alcohols,13 kinds of aldehydes,3kinds of alkanes,4 kinds of alkenes,6 kinds of acids,3 kinds of ketones,1 kind of phenol,and 1kind of amine.After the tea infusion was fermented into tea vinegar,its aroma components were richer.（5）Study of tea vinegar’s function:The antioxidant and antibacterial properties of tea vinegar were studied separately,and compared with vinegar and tea infusion,the results had shown that tea vinegar had good antioxidant and antibacterial properties.The DPPH free radical scavenging effect ranking was:tea vinegar>tea infusion>vinegar,and the removal rates were 98.7%,93.4%and92.3%,respectively.The effect of OH free radical scavenging rate ranking was:tea vinegar>tea infusion>vinegar,and the clearance rates were 64%,53%and 52%,respectively.The superoxide anion（O2-·）clearance rate ranking was:tea vinegar>tea infusion>vinegar,and the removal rates were 98.3%,97.7%and 76.4%.The iron reducing power ranking was:tea vinegar>tea infusion>vinegar,and the absorbance values were 1.99,1.97 and 1.23,respectively.In the antibacterial test,all three products could inhibit Escherichia coli,and their bacteriostatic effect ranking was:tea vinegar>tea soup>vinegar.For Staphylococcus aureus,all three products had certain inhibitory effect,their antibacterial effect ranking was:tea infusion>tea vinegar>vinegar.For Candida albicans,the above three products had no obvious antibacterial effect. |
