Concentrated green tea soup produced by pulsed electric field and freeze concentration

Abstract: Instant tea powder is completely soluble solid. It has emerged as a new and fast growing product in the world.. The tea powder basically keeps the original color, aroma, and taste of the tea. It has advantages of convenience, health, nutrition, elegance, quality control, and high stability, which is deeply favored by consumers at home and abroad as well as tea beverage manufacturers. However, tea aroma losses during thermal processing of tea beverage production. In this paper, the application of integration of pulsed electric field (PEF) and freeze concentration technology on tea soup was studied. The hot water extraction was substituted by the PEF extraction to extract green tea soup, vacuum evaporation was substituted by freeze concentration to concentrate the tea. The optimum conditions of the above two technologies were investigated. Using the combination of gas chromatography(GC-MS) mass spectrometry and solid-phase micro-extraction (SPME), the differences of the tea soup extracted by pulse electric field (PEF) and hot water on the aroma composition were investigated respectively, the same analysis was done for concentrated tea soup by freeze concentration and vacuum evaporation,. The optimal conditions of PEF extraction were given as; pulse width of 2.5 μs, electric field strength of 37 kV/cm, pulse number of 10, pulse frequency of 2 700 Hz and solid-liquid ratio of 1:30. The results of freeze concentration were best under the following conditions: initial solution temperature at 4℃, scraper speed at 150 r/min and coolant temperature at -15～-18℃. Compared with the hot water extraction, extraction of tea polyphenols by PEF was almost the same. The method of GC-MS with SPME was used to analyze aroma compounds of tea soup extracted by PEF and hot water respectively. The results indicated that PEF extraction technology could effectively keep the main aroma of tea soup. It was better than hot water extraction. The results of SPME /GC-MS indicated that freeze concentration technology could effectively keep most of aroma compounds of tea soup. It was better than vacuum evaporation. Both methods have potential applications in industrial production.