Enrichment Of Black Tea Aroma By Resin Adsorption Or Pervaporation

The preparation of tea essence though enriching tea aroma components has provided a great new way for the utilization of the low-grade tea in the tea market.The aim of this study is to develop and optimize the preparation process of tea essence,using lapsang souchong black tea(LSBT),a typical Fujian black tea,as the raw material.The tea aromatic compounds of LSBT were first extracted by distillation,followed by a concentration step either using macroporous resin adsorption or pervaporation,to produce tea essence.The main results and conclusions are as follows:(1)Black tea aromatic compounds extraction.The volatile aromatic compounds of LSBT were extracted either by atmospheric distillation or vacuum distillation.The extracts were analyzed by using headspace solid phase microextraction combined with gas chromatography-mass spectrometry(HS-SPME-GC-MS).The results showed that the amount extracted by atmospheric distillation and by vacuum distillation were 26.466?L/L and 14.239?L/L,respectively.And the number of volatile components were identified from the extracts obtained by atmospheric distillation and by vacuum distillation were 66 and 52,respectively.Although the total amount of volatile compounds extracted by atmospheric distillation was more,the extraction efficiency was lower.According to sensory evaluation,the aroma water sample of atmospheric distillation showed obvious burnt flavor,while the sample of vacuum distillation was closer to the original tea soup.(2)Concentration of the black tea aroma extracts by dynamic adsorption of macroporous resin.The LSBT aroma extracts obtained by vacuum distillation were dynamically adsorbed by macroporous resin LX-8,and subsequently desorbed by ethanol to obtain condensed tea essence.The optimum conditions are as follows:the packed column volume of the macroporous resin LX-8 was 5 m L(5 m L=1 BV),and the packing diameter ratio was 1:4.7and the loading volume was 400 BV with the loading flow rate of 80 BV/h,elution was performed with 5 BV ethanol for 2.5 h and then collected in 5 tubes,1 BV per tube.Under the optimum conditions,the concentration factor of tea essential oil was approximately 190 times.The aroma components were analyzed by HS-SPME-GC-MS.The results showed that the characteristic aroma substances in LSBT could be enriched and largely reserved in the tea essence,including cis-3-Hexen-1-ol,linalool,phenylethyl alcohol,geraniol,damascene,jasmone and benzene acetaldehyde,etc.The results of activity assay indicated that the tea essence had antioxidant and bacteriostatic activities.(3)Enrichment of tea aroma by pervaporation.The LSBT aroma water prepared by vacuum distillation were enriched by pervaporation method,and the enrichment effects of two different pervaporation membrane materials of Al₂O₃/PDMS and PVDF/PDMS were compared.The results indicated that pervaporation membrane could selectively enrich tea aroma,PVDF/PDMS membrane was better than that of Al₂O₃/PDMS membrane.After optimizeation of the feed temperature,flow rate and solid-liquid ratio,the seperation factors of the characteristic aromatic components of LSBT,including phytol phenylacetaldehyde,linalool,geranic acid and nerol were 9.74,7.89,15.67,8.76 and 4.84,respectively.