| With the rapid socio-economic development, tea beverage especially pure tea beverage is preferred by consumers with their distinctive health-care function. Tea beverage has become the interested R&D fields in tea further processing industry. However, it is liable to undergo browning during the production and storage of green tea beverage, which shortens the shelf life and affects the external appearance. Attempted to dissolve this problem, this paper focus on the components as flavonols glycosides and oxidized products of catechins in green tea which play a vital role in the formation of tea beverage color. With the investigation of the beverage color variation at the room temperature storage, this paper was attempted to explore an efficient technology to keep the color of green tea beverage. The major results acquired in this paper were as follows:1. A HPLC method assaying for flavonol in green tea infusion has been achieved by using the mobile phase system of phosphate– methanol. The protocol could be described as following: using phenomenex-c18(150×4.60mm) column, mobile phase A was phosphate/water in ratio of 2/998(v/v),mobile phase B was methyl alcohol and phase B decreased gradiently from 55% to 20% in early 20 minutes, then increased gradiently from 20% to 55% for next 1minutes. The linear gradient elution with the flow rate of 1mL?min-1 was detected at the wavelength of 360nm. The hydrolyzed flavonols were further separated successfully with the HPLC method.With the orthogonal design, the optimal hydrolytic conditions of flavonol glycosides in green tea infusion (5mL) were explored by 2 hours hydrolysis at 75℃in the hydrolytic solution of methyl alcohol(15mL) supplemented with 6 mol?L-1 hydrochloric acid(5mL). Quercetin,myricetin and kaempferol from the hydrolytic system of tea infusion were detected by using the HPLC.2. The correlations between flavonol and its glycosides and color of tea infusion during storage were investigated. The results showed that the redness(a)and yellowness (b) increased as the decrease of myricetin glycosides in green tea infusion, which suggested that myricetin glycosides have a significant relation to the redness(a)and yellowness(b) of green tea infusion with -0.9821** and -0.8826* of the correlation coefficients, respectively. The correlations between the color of tea infusion and quercetin, myricetin, kaempferol and their glycosides were not remarkable.3. Simulated model in vitro of catechins in green tea infusion comparatively studied on auto-oxidation and enzymatic oxidized of catechins and detected their oxidized products using HPLC. As a result, the model of the standard solution of catechins at room temperature storage, catechins underwent auto-oxidation and the solution color varied from colorless into light yellow. However, the model of the standard solution of catechins with polyphenol oxidase, catechins underwent enzymatic oxidation and the solution color varied from colorless into redish brown. The auto-oxidation products of catechins were different from their enzymatic oxidized products too.During the storage of green tea infusion at room temperature, catechin esters in tea infusions decreased significantly while gallic acid and theabrownins (TBs) increased gradually. However,enzymatic oxidized products were not found. It is supposed that catechin esters have degallated to simple catechins and catechins have underwent enzymatic oxidation during the storage of green tea infusion.4. The color of green tea infusion can be stabilized at the initial storage with the supplement of ascorbic acid (Vc), which led to the minimal changes of the glycosides of myricetin, quercetin and kaempferol and catechins as EGCG, ECG and EGC. With the elongation of tea infusion's storage, the color changes were similar to those without the Vc supplement. The protective method of the color of tea beverage is still under exploration. |
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