| Color browning is the frequent problem during the processing and storage of green tea beverage. It has a great influence upon customers' purchasing behavior, although it has little effect on beverage nutrition. Anti-browning or green color-keeping is one of the most important areas in developing and processing green tea beverage. In this work, we have made some progresses in analysis of trace pigments in tea liquor with HPLC equipment. Change of pigments and its effect on liquor color in green tea beverage were studied during short-time heat treatment and long-time storage. According to the mechanic of color browning, some attemption to green color-keeping has also been made. Details of achievements were described as followings:①A HPLC method for assay of trace liposoluble pigments in tea liquor was achieved by using different mobile phase with acetonitrile based solution. The optimized protocol could be described as following: mobile phase A was acetonile/acetic acid/water in ratio of 3/0.5/96.5 (v/v/v), mobile phase B was acetonile /methanol /chloroform in ratio of 75/15/10 (v/v/v), and phase B increased gradiently from 80% to 100% in early 20 minutes, then held 100% for next 15 minutes. The main pigments, i.e. neoxanthin, violaxanthin, lutein, chlorophyll b, chlorophyll a, phaeophytin b,β-carotene and phaeophytin a, could be separated upto baseline under that condition. Verification test showed that the protocol with good repeatability and low detection limits was suitable for measurement of trace pigments in ready-to-drink tea.②The threshold of different pigments in water solution was investigated by dissolving and dilution of standard compounds purchased from company and pigments monomer separated by thin layer chromatograph. It showed that the volunteers could distinguish difference between distilled water and the solution with 50ng/ml chlorophyll a or b, and that with 100ng/ml phaeophytin b orβ-carotene, and that with 200ng/ml neoxanthin, lutein or phaeophytin a. HPLC Analysis showed that the concentration of chlorophyll a or b in general fresh juice of green tea was higher than the threshold, while phaeophytin a or b were lower than the threshold. The sum of yellow pigments (likeβ-Carotene, neoxanthin, lutein) was above the threshold. The ratio of total green pigments to yellow pigments was basically consistent with color of tea liquor, i.e. the higher the ratio, and the greener the liquor color.③The results of short-term (15-120min) heat treatment (55-95℃) showed that the higher the treating temperature, the longer the time, and the yellower in liquor color was observed. Chlorophyll a could be detected in the beverage within 30 minutes at 55℃, Chlorophyll b was more stable than chlorophyll a and after 120 minutes treatment it was still about 25% of the initional concentration. The concentration of phaeophytin b increased with increasing of treatment time, while the concentration of phaeophytin a was significantly lower than the control. Yellow pigments and catechins changed unconspicuously. The color changed dramatically when the liquor was subjected to heat treatment at 95℃. Chlorophyll a was undetectable even within 15 minutes, while chlorophyll b could be detected at that time. The concentration of phaeophytin b, lutein and other yellow pigments reduced with increasing of the time. Nonepi-catechins which transformed from epi-catechins were increased gradually during the heat treatment at 95℃. Upto 120min, the total concentration of epi-catechins was almost equal to total nonepi-catechins. But the total volume of catechins decreased significantly in the treatment duration. It indicated that catechins were destroyed at high temperature because of oxidation and polymerization.④The color of tea beverage turned yellower and redder with increasing of aging time(7-57d) compared with the initial control. Addition with 100mg/L Vc-Na could not maintained the color of the green tea beverage, but deepen it. EGCG, EGC, EC, ECG, epi-catechins and total catechins decreased gradually during aging treatment. Significant change of these components was observed at 21d compared to the initial control.⑤Addition of metal ion to improve the color of green tea beverage were attempted. The results showed that the color of green tea beverage with addition of ZnCl2 or CaCl2 could maintain green after the heat treatment. The best addition concentration of ZnCl2 or CaCl2 was 0.1mg/L and 0.15mg/L, respectively. The better green color-keeping effect of ZnCl2 than CaCl2 was also observed.
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