| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 93 === The Green tea, Oolong tea and GABA tea made by two farmers in Ming-Chien with two different packing forms, tea leaves and tea bags, were used as materials. The purpose of this study is to investigate the changes in the color of tea infusion, pH value, total catechins, total polyphenols, total free amino acids, GABA contents, individual catechins and caffeine of 4oC cold-water steeped tea infusions with different time as compared with hot-water steeped one as the control. Using 7-point hedonic scoring, the consumer preference of cold-water steeped tea infusion by 100 consumer-type panelists was evaluated as compared with hot-water steeped one.
The analysis results of color of tea infusion with these three kinds of tea samples showed that the color of cold-water steeped samples was brighter than that of hot water steeped ones and the color of tea infusion using tea leaves were brighter than that of tea bags. The pH value of hot-water steeped tea infusion was found lower than that of cold-water ones, and the pH value of cold-water steeped tea infusion of tea bags at the same steeping time was lower than that of tea leaves.
The contents of total catechins and total polyphenols in cold-water steeped tea infusion for 12 hr were equal to or higher than those steeped in hot water for 5 min, but the contents were only half of those steeped by hot water for 5 min three times in total. The total free amino acid contents of tea steeped with cold water for 2 hr were already equal to or even higher than those steeped in hot water for 5 min. The GABA contents in the GABA tea showed the similar tendency with the total free amino acid contents of GABA tea. It indicates that cold-water steeping has better extraction than that the hot-water steeping.
For the individual catechins, the extraction effectiveness of steeping with cold water was found quite different among different degree of fermentation and types of packing. However, the contents of free-type catechins in tea steeped with cold water for 12 hr were higher than those steeped in hot water for 5 min. The caffeine contents of tea steeped with hot water were significantly higher than those with cold water. The content of caffeine in 12-hr cold-water steeped tea infusion was only 1/2 to 2/3 of those with hot water steeped.
Except GABA tea samples, the contents of all constituents in tea infusion with tea leaves packing type were only reached to 50 - 60 % of those with tea bags packing type. The contents of total catechins, total polyphenols, and total free amino acids in GABA tea samples were found no significant difference between two different packing types, because the tea leaves did not go through the ball rolling step.
Using the tea samples steeped with cold water for 4 hr and 12 hr, and with hot water for 5 min as materials, the results of the consumer preference teat showed that the aroma score of tea steeped with hot water for 5 min was the highest. The taste score of tea steeped with 12-hr cold water were higher than those of other two tea samples. However, there was no significant difference between the 12-hr cold-water steeped tea infusion and the one with 5-min hot-water steeping.
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