The Effect Of Extracted And Concentrated Processes On The Quality Of Green Tea Juice

Green tea, which was also called non-fermented tea. It is made by the non-fermented youngleaves on the tea trees after de-enzyme, roting, drying and other typical process. After brewing, itshows green and is rich in nutritions. Formation of concentrated green tea juice need experienceextraction, deslagging, and concentration processes. Because of its convenient for drinking,blending, transportation and storage, the concentrated green tea juice has became an importantprocessed products of green tea. During the concentration process, the main composition, color,aroma and antioxidant activity and other qualities of the concentrated green tea juice weresignificantly influenced by the extraction or concentration processes. In this paper, based on thewater extraction method, the influence of the ultrasonic assisted extraction and concentrationprocesses (vacuum concentration, reverse osmosis membrane concentration and freezeconcentration) on the main ingredients, sensory color, rheological properties, aroma and antioxidantactivity of the concentrated green tea juice were studied and the optimal processing parameters ofproducing concentrated green tea juice were determined. Results of the study are as follows:1. A single factor test was taken to study the difference between water extraction andultrasonic assisted extraction on the content of the tea polyphenols and caffeine. According to theratio of tea polyphenols to caffeine content, a ternary quadratic rotary combination design was usedto optimize the extraction conditions during ultrasonic assisted extraction process. Results showedthat the ultrasonic assisted extraction process was significantly superior to the water extractionprocess under the same extraction temperature. The optimal parameters of ultrasonic assistedextraction process were: ultrasonic power300W, extraction temperature80℃, extraction time15min, and solid-liquid ratio1:19(m:v). Under the optimal conditions, the ratio of tea polyphenols tocaffeine reached8.23, and the content of tea polyphenols and caffeine reached21.74%and2.64%respectively.2. The effects of temperature, concentration, and shear rate during the concentration process ofthe green tea juice on the viscosity and rheological properties of the concentrated green tea juicewas studied. A concentrated dynamics model was established.Results showed that: With theincreasing of the temperature and shear rates, the viscosity of the concentrated green tea juicereduced, showing shear thinning phenomenon. When the concentration increased, the viscosity of the concentrated green tea juice also increased. And it was found that the concentrated green teajuice belongs to pseudoplastic non-Newtonian fluid. The mathematical model which depicted theeffect of temperature and concentration on concentrated juice viscosity was defined asη=-1.7215·exp (11.7367/RT-0.0473·C+0.0014·C2), and its application temperature scope was30to60℃, concentration scope was40to65°Brix.3. Under the same concentration degree (20°Brix), the color and the main ingredients of thediluted green tea juice which came from the concentrated juice produced by different concentrationprocesses (vacuum concentration, reverse osmosis membrane concentration and freezeconcentration) was studied. And the antioxidant activities (clear DPPH·free radicals ability, clearhydroxy free radical ability, metal reduction force and total antioxidant capacity) of the dilutedgreen tea juice which came from concentrated juice produced by reverse osmosis membraneconcentration process were discussed. Results showed that taken terminal concentration point(20°Brix) of the green tea juice as the reference point, the diluted samples made by freezeconcentration process and reverse osmosis membrane concentration process showed a better colorand quality ingredients, especially the samples made by a freeze concentration gained the bestcolour. However, it caused a certain loss of the quality compositions. The clear DPPH·free radicalsability and metal reduction force showed a positive correlation with tea polyphenol content of theconcentrated green tea juice made by reverse osmosis membrane concentration process, while theclear hydroxy free radical ability and total antioxidant capacity showed a negtive correlation.4. The effect of different concentration degree and concentration processes on aromaingredients and its content of green tea juice was studied. The aroma ingredients and its content ofthe diluted concentrated green tea juice and original concentrated juice (50°Brix) was discussed inthis section. Results showed that the aroma ingredients and its content of concentrated green teajuice were significantly influenced by the concentration process and degree of concentration. Therewas s serious loss of the content of aroma with the increasing degree of the concentration. Whenthe degree of the concentration process reached20°Brix, green tea concentration juice made byvacuum concentration process showed a significant loss of aroma ingredients and content with ageneration of extraordinary fragrance. The fragrance, flora and fruit aroma features were kept wellduring reverse osmosis concentration process, although its aroma ingredients and content showed alower level compared with freeze concentration process. It was also found that concentrated tea juice showed a decreasing in aroma ingredients and content, poor aroma, and incomplete tea juiceflavor characteristics, but chestnut flavor and burnt flavor produced during concentration processbecause of the oxidative degradation and chemical conversion of the aroma precursor, whichenriched the aroma of the grean tea.