Thermal Analysis And Baking Technology Research Of Tea

Aroma and taste are the most important indicators of the quality of tea.A series of physical and chemical reactions are occurred during baking process,which affect the formation of the characteristic quality for different tea.Paper study the thermal decomposition processing by simultaneous thermal analyzer,and oolong tea,white tea,green tea,black tea,dark tea and yellow tea,as experimental material,dectect the pyrolysis escape gas by GC-MS.Depth study the baking mechanism,so that to set the baking limit temperature value,to improve the aroma quality and taste quality.The results showed that,the pyrolysis processs could be divided into four stages.The escape of water and volatiles stage of the temperature from room to 155?,endothermic peak appeared due to evaporation,vaporization,sublimation and desorption,the pyrolysis escape gas were aroma of tea,which include alcohols,phenols,nonanal(grass aunity),piperonal(floral)and longifolene(woody),etc.Flavor changing stage and carbonization pyrolysis stage of the temperature from 155? to 410?,mainly for the pyrolysis of tea inclusions,such as the pyrolysis of tea aroma components,and the decarboxylation and oxidative deamination of various amino acids;When the temperature reached 200?,the polysaccharides,polyphenols,caffeine,chlorophyll and water-soluble vitamins will be pyrolysised and produced furan,pyrrole,etc.compounds.Burning stage of the temperature above 400?,showed exothermic peak,the pyrolysis escape gas contain catechol and tar substances(biphenyl;2,7-dimethyl-naphthalene;1-indanone)under ultra-high temperature,which are harmful to human health;the main escape gases producted by the pyrolysis of hemicellulose,cellulose and lignin of tea after 450?,with the pyrolysis products of L-glucose ketone and 1,4:3,6-dianhydro-alpha-D-glucosidase pyranose.Different teas with different baking process from different areas have different thermal effects,because of different content of hemicellulose,cellulose and lignin.The thermal analysis also showed that,the temperature of tea baking must less than 150?,processing temperature of Fen Tieguanyin should be lower than 157?,and white peony should been baked at lower than 146?.The relationship between the second baking conditions and the inclusion changes of Tieguanyin tea was studied by the means of uniform design and double-screening stepwise regression(DSSR).The involved baking conditions were baking temperature,baking time and thickness of tea.The results showed that,Fen-flavor Tieguanyin tea with high biochemical quality can be baked at 80? for 150min with 4.0cm thick or at 99? for 120min with 5.5cm thick.The data was analyzed by DSSR,which have 3 independent variables and 5 dependent variables.The analysis showed that,the baking temperature is the main influence factor.when temperature rise 1?,the catechin quality index increased 0.7424,bitter index increased 0.0126.But baking temperature and baking time have a negative impact on the tea biochemical quality,the content of GABA and L-Theanine.The best baking condition is at 85? for 300min with 1.0cm thick for enrich the functional amino acids.After verification,tea contains 1.027mg/g GABA and 7.102mg/g L-Theanine.Then the changes of volatile components in White Peony tea at different second baking process were studied by headspace solid-phase microextraction-GC-MS,the baking conditions at different temperture of 40?,60?,80?,100?,120? and 140? for3h with oxygen atmosphere.Results showed that the White Peony tea was easily oxidized in an oxygen atmosphere when baking,the aroma substances and the constitution gradually became more simple.White Peony without baking process was detected a total of 23 kinds of main components,The aroma components mainly contain linalool oxide and its cis-trans(34.34%)and other alcohols(9.75%),Ionone and its epoxide(10.49%),cedar alkenes(20.77%),esters(5.62%)and caffeine(1.13%)and 2,5-Pyrrolidinedione,1-ethyl-(9.41%).It is Fen aroma,the aroma composition is clear,which mainly conained fruity and woody,supplemented floral and grassy.The aroma components can be detected 22 kinds at 40? baked for 3h,the relative content of alcohols were increase,but ketones,hydrocarbon substances,esters were decreased,finally tea smells floral and fruity.After 60 ? baked for 3h,it still can be detected 23 kinds,the relative content of linalool oxides and its cis,ionone and its epoxide were significantly reduced,while Cedol,Geranylacetone and others were increased,so tea smells floral and fruity and woody.After 80 ? baked,ionone will be oxidized in oxygen atmosphere,only detected 15 kinds,floral was not significant,it mainly smells fruity and woody.Aroma components detected only 14 or 11 kinds after baked 100?,120? and 140?,it is roasted flavor with caffeine,etc.