| White tea with silver lime green color and taste fresh glycol,which is rich in polyphenols,amino acids,flavonoids,organic acids,caffeine and other functional ingredients.Especially,organic acids are not only involved in the formation of tea aroma and taste quality,but also they are very important hygienical components.Through the optimization of HPLC method,this study detected contents and compositions of the organic acids in white tea which is produced by using different raw material and in different years.By analyzing the changes of organic acids in white tea during the process of different ways of withering and storage,the change tendency of organic acids during this two procedures and the correlation between organic acids and white tea of different assortment and years were illustrated in this study.Holding the promise of providing scientific basis for the quality control of white tea and the consumption of health preserving,we also studied the inhibitory effects of white tea on intestinal pathogens in vitro,and analyzed the effects of total organic acids and its components on the antibacterial effect of white tea.The result as follows:1 HPLC method for the determination of organic acids in white teaA rapid and accurate determination of organic acids in white tea by high performance liquid chromatography(HPLC)was established by using Agilent-1200 HPLC equipped with UV detector and a ZORBAX SB-C18 column(5?m,4.6mmx250mm).The mobile phase was 3%methanol-0.05 mol/L KH2PO4(pH value adjusted with phosphoric acid to 2.75)with flow rate of 0.5 mL/min.Column temperature was at 25 ?,the detection wavelength was at 215 nm and 15?L sample was injected into the column.Oxalic acid,acetic acid,citric acid,lactic acid,malic acid,ascorbic acid,succinic acid,fumaric acid in white tea could be separated within 25 minutes.The recovery rate of the organic acids was 91.63%?103.34%and the relative standard deviation of the organic acids was 0.45%?2.34%.All the calibration curves for these organic acids displayed a good linear relationship with correlation coefficients above 0.9997,indicating that the method was simple,rapid and accurate.2 Variations of organic acids in white teaThe same raw materials(Fu Ding da hao)were processed by continuous heating withering,water sieve heating withering,continuous combined withering.The results showed that total organic acids in white tea decreased in fluctuations during the process,and compared with the fresh tea leaves,total organic acids in made tea produced by 3 withering processes were reduced separately by 17.76%,18.44%and 27.5%.Based on the correlation analysis,the result showed acetic acid,succinic acid and malic acid were the main components resulting in content difference of total organic acids.Ultilizing comparative analysis of the total organic acids in different grades of white tea which are produced in different years from FuDing and ZhengHe,the result showed that all the total organic acids in 4 assortments decreased with the declining of the grades of raw materials.The ranking from high to low follows as:white silver needle>senior white peony>secondary white peony>Shoumei,and the difference reached significant level.All the total organic acids in 4 assortments of white tea went down gradually with the extension of storage time.The total organic acids of white silver needle produced in 2014 is up to 21.92 mg/g,the content of Shoumei produced in 1999 is the lowest,only 4.43 mg/g left.Based on correlation analysis,the result showed that the correlation between total organic acids and intensity of freshness and sweetness in tea liquor was significantly positive and the correlation coefficient was 0.722 and 0.363,respectively.The correlation between total organic acids and freshness showed extremely significant,which is corresponding to the result of organoleptic evaluation that is the higher organic acids the tea sample contained,the fresher and sweeter the tea soup turned out to be.Some components in organic acids were alsocorrelated to the taste of tea soup,for example malic acid,acetic acid,succinic acid and fumaric acid showed positively correlated with freshness in tea soup andtheir correlation coefficients were 0.444,0.687,0.399 and 0.612,respectively;the correlation between acetic acid and fumaric acid and sweetness is significantly positively related,both correlation coefficients were 0.348 and 0.516,respectively.3 The anti-bacterial ability of white teaOxford Cup and Double dilution method were used to study the anti-bacterial activities of old white tea on Staphylococcus aureus,Shigella and Salmonella enterica subsp.enterica.Results showed that the concentration of white tea water extract was proportional to the bacteriostatic effect.The antibacterial ability on Staphylococcus aureus was stronger than Shigella and Salmonella enterica subsp.enterica at the equal concentration of white tea aqueous extracts.The anti-bacterial activity of different assotment is:white silver needle>senior white peony>Shoumei.Based on correlation analysis,we got the result:the correlation coefficient between year and antibacterial circle diameter of Staphylococcus aureus is-0.729,the correlation coefficient between year and antibacterial circle diameter of Shigella is-0.907,the correlation coefficient between year and antibacterial circle diameter of Salmonella enterica subsp.enterica is-0.885.The correlations are negative and have reached significant level.The anti-bacterial ability of white tea produced lately is the best.This ability shows a trend of decrease with the extension of storage time.4 The relationship between main biochemical components and anti-bacterial ability of white teaTo discuss the correlation between biochemical components and antibacterial circle diameter.Results show that tea polyphenol,organic acids and b*value have high correlation with antibacterial circle diameter of Staphylococcus aureus;L*value,water extract and tea polyphenols have high correlation with antibacterial circle diameter of Shigella;tea polyphenols,L*value and organic acids have high correlation with antibacterial circle diameter of Salmonella enterica subsp.enterica.Based on path analysis,we got formulas between main biochemical components and antibacterial circle diameter:Y1=30.121+0.818X3-6.798X4+0.753X5+0.296X6;Y2=1.996-0.173X1+0.384X5+0.831X7;Y3=-9.108-0.998X1+1.146X3+0.503X5+1.104X7+0.571X9.Y1(Staphylococcus aureus);Y2(Shigella);Y3(Salmonella enterica subsp.enterica);X1(water extract);X3(tea polyphenol);X4(caffeine);X5(flavones);X6(organic acids);X7(L*value);X9(b*value).5 The anti-bacterial ability of organic acidsDetecting anti-bacterial ability of organic acids through bacteriostatic test in vitro,the results show that the organic components all have different degrees of inhibition on three tested strains,the bacteriostasis of organic acids on staphylococcus aureus is:mixed acid>oxalic acid>acetic acid>citric acid>malic acid>lactic acid>succinic acid>ascorbic acid>fumaric acid;the bacteriostasis of organic acids on Shigella is:mixed acid>acetic acid>oxalic acid>succinic acid>citric acid>malic acid>lactic acid>ascorbic acid>fumaric acid;the bacteriostasis of organic acids on Salmonella enterica subsp.enterica is:mixed acid>oxalic acid>acetic acid>lactic acid>citric acid>malic acid>succinic acid>ascorbic acid>fumaric acid.The anti-bacterial ability of mixed acids is the best,followed by oxalic acid or acetic acid,fumaric acid is the worst.6 Effect of organic acids on the anti-bacterial ability of white teaTo discuss the correlation between organic acids and antibacterial circle diameter,we got the result:the correlation coefficient between organic acids and antibacterial circle diameter of Staphylococcus aureus is 0.845,the correlation coefficient between organic acids and antibacterial circle diameter of Shigella is 0.689,the correlation coefficient between organic acids and antibacterial circle diameter of Salmonella enterica subsp.enterica is 0.864.The correlations are positive and have reached significant level,which means higher organic acids contents will bring better anti-bacterial ability in white tea.Based on correlation analysis,we got formulas between organic acids composition and antibacterial circle diameter:Y1= 18.983+3.009X1+2.554X2-3.180X3+6.139X4-1.824X5+9.947X6-2.634X7+94.636X8;Y2=20.524-8.320X1+0.452X2+3.505X3-0.373X4+0.322X5+0.462X6+0.468X7-8.966X8;Y3=16.304-6.086X1+1.782X2+3.203X3-0.350X4-0.450X5+1.145X6+0.373X7+5.254X8 X1(oxalic acid);X2(acetic acid);X3(citric acid);X4(lactic acid);X5(malic acid;X6(ascorbic acid);X7(succinic acid);X8(fumaric acid);Y1(Staphylococcus aureus);Y2(Shigella);Y3(Salmonella enterica subsp.enterica). |
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