Concentrated Tea Soup Produced By Pulsed Electric Field And Freeze Concentration

In order to solve the key difficulty problems of tea aroma loss due to thermalprocessing of tea beverage production, a new technology for keeping tea aroma at lowtemperature was researched. In this paper, the application of integration of pulsedelectric field (PEF) and freeze concentration technology on concentrated tea soup wasstudied. With pulse electric field (PEF) extraction instead of hot water extraction andfreeze concentration instead of vacuum evaporation, the two processings of pulsedelectric field (PEF) and freeze concentration were studied respectively.Low-temperature extraction and concentration was achieved in the tea soupprocessing. With the combination of gas chromatography mass spectrometry andsolid-phase micro-extraction, the differences on aroma composition was investigatedin the tea soup extracted by pulse electric field (PEF) and hot water and in theconcentrated tea soup by freeze concentration and vacuum evaporation respectivelyThe brief introduction of whole research was as follows:(1) Tea polyphenols extraction rate was the index when green tea soup was extractedby PEF. The effects of electric field strength, pulse number and pulse frequency on theextraction rate of tea polyphenols were researched under the conditions thatsolid-liquid ratio1:30, pulse width2.5μs. On the basis of the most suitable singlefactor experiments, response surface methodology was used to optimized experimentscheme, and the most suitable experiment conditions for PEF extraction were electricfield strength merely37kV/cm, pulse number10and pulse frequency2700Hz.(2) Compared with hot water extraction, extraction of tea polyphenols by PEF was notmuch different. The method of GC-MS with solid-phase micro-extraction was used toanalyze aroma compounds of tea soup extracted by PEF and hot water respectively.The results indicated that PEF extraction technology could effectively keep the mainaroma of tea soup, which was better than hot water extraction and was a kind of newtechnology to produce tea soup.(3) With the amount of ice and ice phase concentration as the index, suspension crystallization was selected to concentrate tea soup. The effects of initial temperatureof tea soup, scraper speed and coolant temperature on concentration were researched.Experimental results showed that the results of freeze concentration were best underthe conditions of solution initial temperature4℃,scraper speed150r/min and coolanttemperature-15℃～-18℃. Two grade freeze concentration of tea soup was alsostudied, and the kinetic equation of freeze concentration was constituted by thecomputer software MATLAB. The kinetic equation of first grade freezeconcentration: and the loss rate of solublesolids was2.417％. The kinetic equation of second grade freeze concentration:and the loss rate of soluble solidswas1.978％. Values obtained from first grade and second grade of the kinetic equationof freeze concentration were closed to the results from experiment. Degree of fittingwas higher.(4) The method of GC-MS with solid-phase micro-extraction was used to analyzearoma compounds of tea soup concentrated by freeze concentration and vacuumevaporation respectively. The results showed that freeze concentration technologycould effectively keep most aroma compounds of tea soup. It was better than vacuumevaporation and could be a kind of new concentration technology to preserve aroma.