Study On Extraction,Bacteriostasis And Bacteriostatic Mechanism Of Tea Polyphenols

Tea has a very long application history both as food and as medicine in China,and there are many good effects and functions of tea in healthcare or therapy field.Therefore,the research and utilization of the functional and active components in tea,is very significant and beneficial.In this paper,the optimum extraction conditions of tea polyphenols were studied by using green tea as the raw material,based on the results of single factor(temperature,time and liquid to material ratio)and orthogonal experiments.And by Oxford cup method,the antimicrobial activity of tea polyphenols had been studied.The inhibitory spectrum and minimum inhibitory concentration had been investigated on bacteria,yeasts and molds;The influences of pH,temperature and polyphenoloxidase on the antibacterial effects in green tea had also been examined;Furthermore,the antibacterial mechanism of tea polyphenols was discussed from the aspects of inhibition of enzyme and change of total amino acid and glucose concentration.The results are as follows:1.The best extraction conditions of tea polyphenols:The extraction technology process is: green tea ? hot water extraction ? filter ? hot water extraction for the second time ? combine the twice filtrate ? centrifugation ? detection and analysis.Through the single factor and orthogonal experimental analysis,the optimum extraction conditions of tea polyphenols were as follows: extraction temperature 85 ?,extraction time 40 min,ratio of material to liquid 1:20.The extraction rate of tea polyphenols was 18.84%.2.The antimicrobial activity of tea polyphenols was studied by Oxford cup method.It was found that it had outstanding antibacterial activity,especially against bacteria,even at low concentration.The inhibition effects,arranging from high to low,are as follows: Staphylococcus aureus > Bacillus subtilis > Escherichia coli.The minimum inhibitory concentrations(MIC)are 0.25 mg/ml,8mg/ml and 10mg/ml,respectively.However,tea polyphenols showed no obvious effect against lactic acid bacteria and fungi.3.Tea polyphenols exhibit good thermal stability,and still has a good antibacterial effect,even if at very high temperature for the long time treatment,which characteristic can provide a guarantee for the high temperature treatment of tea polyphenols in food.The results indicate that tea polyphenols have excellent pH stability,at the range of pH from 3 to 9,shows strong antibacterial activity.Under treatment of polyphenol oxidase,the antibacterial activities of tea polyphenols have no effect.These stability experiments provide a theoretical basis for the application of tea polyphenols as natural antibacterial agents.4.Tea polyphenols have not only antibacterial activity,but also broad enzyme inhibition on protease and amylase.Through the experiment of trypsin,?-amylase,neutral protease and pepsin,it was found that with the increase of tea polyphenol concentration,the inhibition rates of the enzymes increased accordingly,and the enzyme activities decreased significantly.5.Effects of total amino acids(i.e.hydrolyzing casein)and glucose on the bacteriostasis of tea polyphenols: at concentration of 50 g / L glucose and more than 20 g / L hydrolyzed casein,antimicrobial activity of tea polyphenols weakened;when the concentration of hydrolysis casein reached greater than 30 g / L,the tea polyphenols lost completely their antibacterial effects.Therefore,a possible bacteriostatic mechanism is: through inhibiting protease and amylase of microbial cell(bacteria),and thereby results in that bacterial cells can not obtain and intake the nutrients needed for growth and reproduction by proteolysis of protein and hydrolysis of carbohydrates.