| In recent years,in order to meet the market demand,the exogenous sucrose was added into black tea processing.The phenomenon of adding exogenous sucrose in black tea,causing the consumers can not identify,disrupting the tea market.To better identify the tea containing exogenous sucrose,the study for exogenous sucrose effect on tea quality and detection method to carry out related research.For one thing,from the sensory quality evaluation,main biochemical components,aroma compounds and chromatic aberration were analyzed to investigate the influences on exogenous sucrose of black tea,providing a theoretical basis and identification reference for exogenous sucrose black tea.For another,through inquiry tea exogenous sucrose detection methods,in order to find accurate,rapid,simple and sensitive detection methods,for identification of tea is added exogenous sucrose provide method reference.The results of this study are as follows:1 Quality characteristic of black tea was added exogenous sucroseBiochemistry,chromatic aberration,and its quality of 25 samples were analyzed.The results showed that these have significant difference between suspected added exogenous and non-added in tea polyphenols,caffeine and water extract,amino acids,flavonoids,theaflavins and total soluble sugar.The lower compounds including tea polyphenols,caffeine,amino acids,thearubigins,theaflavins and flavonoids,while the high compounds including water extract,theabrownin and total soluble sugar.The total soluble sugar in suspected added exogenous black tea,range of 11.17%?24.91%,it may reference whether exogenous sucrose was added into black tea processing when it above 10%.The value L*,a*,b*lower in suspected added exogenous than non-added,while the ratio a*/b*higher in non-added.The appearance of the adding exogenous sugar tea were tightly-embraced,shapeliness,with a few golden fuzzes,dark purple with luster,and the liquid were orange red and strong,while the liquid and taste were obvious sweet,mellow and strong.The appearance of the non-exogenous sugar black tea were tightly-embraced,shapeliness,with a few golden fuzzes,dark purple with slightly gray,and the liquid were orange red and bright,while the liquid and taste were slight fragrance,fresh and mellow.6 typical samples were analyzed,the results showed that the geraniol,benzyl alcohol,phenylethyl alcohol,nerolidol,nerol,benzene acetaldehyde,decanal,geranial,lilies of the aldehyde,anti-2-hexene aldehyde,neral,caryophyllene,methyl salicylate,2-methyl naphthalene,1-methyl naphthalene,tridecane and 2-amyl furan were lower in suspected added exogenous.While the Cedar alcohol,tau-ylang oil alcohol,beta ring citral,purple luo xi,cedrene,and 2,6-BHT were higher in suspected added exogenous.Besides,the Alpha terpineol,tau-ylang oil,alcohol,cis dihydrogen carvone,naphthalene,2,3-dimethyl naphthalene,1,4-dimethyl-2,5-methyl ethyl naphthalene,pentadecane,butyrolactone and dihydro kiwifruit lactone were only found in suspected added exogenous,while furfural,alpha and ethyl benzene acetaldehyde and hidden flower aldehyde,shun-3-nonene-1-alcohol,11 alkyl cyclopentane and n-butyl ether were found in non-added exogenous.2 Experimental studys on the impact of exogenous sucrose on black tea qualityTea processing in rolling process by adding different concentration of sucrose(1%,2%,3%,4%,5%)were analyzed by biochemical composition,color difference and organoleptic quality,The results showed that the black tea adding exogenous sugar cane,tea polyphenols,caffeine and water extract,amino acids,flavonoids,theaflavins,thearubigins and total sugar content were extremely significant differences with the non-exogenous sugar black tea.The content of tea polyphenols,caffeine,thearubigins and flavonoids of the black tea adding exogenous sugar cane were lower than the non-exogenous sugar cane black tea.But the content of water extract,amino acids,thearubigins,theaflavins and soluble sugar of non-exogenous sugar tea were lower.The content of soluble total sugar added sucrose concentration 1%?5%is in the range of 9.73%?28.35%.The content of soluble total sugar>10%could judge the tea added exogenous sugar as a reference,and the sample determination results were consistent with market.The L*value of the black tea adding exogenous sugar tea were extremely significant differences with the non-exogenous sugar black tea.The Chahe hormone(TB)content of the black tea adding exogenous sugar tea is lower than the non-exogenous sugar black tea.The L*value of the black tea adding exogenous sugar tea were higher.The content of thearubigins(TR),theaflavins(TF),thearubigins of the black tea adding exogenous sugar tea were higher than the non-exogenous sugar black tea.It's a*and b*values were lower than the non-exogenous sugar black tea.The appearance of the non-exogenous sugar black tea were tightly-embraced,shapeliness,with a few golden fuzzes,dark purple with slightly gray,and the liquid were orange red and bright,while the liquid and taste were slight fragrance,fresh and mellow.The appearance of the adding exogenous sugar tea were tightly-embraced,shapeliness,with a few golden fuzzes,dark purple with luster,and the liquid were orange red and strong,while the liquid and taste were obvious sweet,mellow and strong.3 Comparison of detection methods for exogenous sugar in black teaBy comparing anthrone-sulphuric acid colorimetry,soluble solids method and high performance liquid chromatography(HPLC)method to detect the exogenous sucrose,the results showed that using anthrone-sulfuric acid colorimetry to detect soluble total sugar content,precision RSD = 2.89%<3%(n = 5),stability RSD = 1.12%<3%(n = 5),reproducibility RSD = 2.92%%<3%(n = 5),average recovery 99.85%,indicating that the method was precision,good stability,good reproducibility,high recovery rate,and simple,rapid and sensitive.Using the method of total soluble solids,the soluble solids content of black tea added exogenous sucrose were higher than the non-exogenous sugar black tea.The higher the amount of sugar in tea samples,the more the differences of soluble solids content were obvious.But the sensitivity of this method was not high,the accuracy was low.Many influencing factors will affect the results.Using high performance liquid chromatography determination of sucrose content,when the tea did not contain exogenous sugar,the sugar content was 0.0%.When the tea contained exogenous sugar content could be detected By using high performance liquid chromatography(HPLC),with the increase of exogenous sucrose concentration,the sucrose content increased.The standard curve for sucrose was y = 0.0001176x + 0.01235207,the correlation coefficient R2 was 0.9999;the average recovery was 96.9%;the Precision RSD range from 0.2%to 3.4%;the linear range was y = 1.867x ?0.4311,the correlation coefficient R2 was 0.9998.The method was of high precision,good reproducibility and high recovery rate,sensitive and accurate,but the method needed expensive equipment and complicated operation.So,to sum up,anthrone-sulfuric acid colorimetry can be used to detect exogenous sucrose,and this method is simple,quick sensitivity,good stability and reproducibility. |
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