γ-PGA對紅茶色澤及茶乳生成量之影響

Effect of γ-PGA on the color and tea cream formation of black tea

陳文彬(Wen-Bin Chen)

指導教授 ： 吳瑞碧

國立臺灣大學/生物資源暨農學院/食品科技研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00752

摘要

γ-PGA為納豆菌發酵產物，是一種天然存在、具有強烈陰電性的homo-polyamide，在低添加量下即具有良好的助懸作用，可能有助於阻止茶湯中的多酚類彼此鍵結形成茶乳。本研究主要目的為開發γ-PGA的應用範圍，並提供茶飲料工業一個較為省時省能的加工方式。
經測試過不同鹽類(鈉、鉀)、分子量型態(高、低)以及添加量(0.05~0.25 %)之後，發現鈉鹽高分子型、鈉鹽低分子型、鉀鹽高分子型三種γ-PGA皆可抑制紅茶茶乳生成，並且能夠提高茶湯的紅色度，其中以鈉高分子型抑制茶乳的效果最好，鈉低分子型提升紅色度的效果最好。由於鈉高分子型γ-PGA的黏度過高，對茶湯的口感會有不良影響，因此以鈉低分子型γ-PGA較適合作為茶飲料的添加劑。實驗結果發現在以2%茶葉、100℃去離子水萃取5分鐘的茶湯中添加0.15%的鈉低分子型γ-PGA可將茶乳生成率降低至50%左右，且黏度與市售樣品相近，因此選擇作為儲藏實驗的條件。經4℃儲藏實驗後，證實γ-PGA抑制茶乳生成的效果至少可以維持4週。
為了解γ-PGA抑制茶乳生成的機制，分別以添加CMC與碳酸氫鈉作為對照組來探討黏度與pH值效應的影響。在相同的黏度下，CMC組的茶乳生成量為γ-PGA組的2.8倍。而在相同的pH值下，碳酸氫鈉組的茶乳生成量為γ-PGA組的1.8倍，顯示γ-PGA並非以提高茶湯的黏度或pH值來達到抑制茶乳生成的效果，與市面上常用的茶乳抑制劑不同。
進一步分析茶湯、上清液與茶乳中的成分變化後，發現γ-PGA降低了茶乳中總茶紅質所佔的比例。推測γ-PGA與茶紅質之間可能產生電荷間交互作用(charge-charge interaction)，因此抑制了茶乳的生成。氯化鈉電荷干擾實驗證實此一作用的存在。

關鍵字

紅茶 ； 茶乳 ； 聚麩胺酸 ； 色澤

並列摘要

γ-PGA is a product of natto bacteria fermentation. It is a naturally occurring homo-polyamide with strong electronegativity that might inhibit the cream formation in tea infusion resulted from polyphenol linkages. The aims of this study are to develop new applications for γ-PGA and to offer a more economical way in tea drink manufacture.
Different salt (sodium and potassium) and molecular weight (high and low) forms of γ-PGA and additions (0.05~0.25%) were tested. The results showed that all of the tested three forms of γ-PGA (sodium form high molecular weight, sodium form low molecular weight and potassium form high molecular weight) inhibit the cream formation and enhance the redness of black tea infusion. Among them, sodium form high molecular weight is the best cream inhibitor and sodium form low molecular weight is the best redness enhancer. Due to the high viscosity of sodium form high molecular weight γ-PGA, sodium form low molecular weight γ-PGA is more suitable for tea infusion concerning bad mouth feel. The 0.15% sodium form high molecular weight γ-PGA decreased cream formation to 50% in tea infusion that was made by 2% tea leaf, 100℃ deionic water and 5 minutes extraction to a viscosity close to the commercial products. The optimum condition was thus chosen. In 4℃ storage, the effect of cream inhibition by γ-PGA could last for at least 4 weeks.
To understand the mechanism of cream inhibition of γ-PGA, CMC and NaHCO3 are added to tea infusion to investigate the effects of viscosity and pH value. At the same viscosity, CMC produced 2.8 times cream formation as compared to γ-PGA. At the same pH value, NaHCO3 produced 1.8 times cream formation as compared to γ-PGA. It shows the mechanism for γ-PGA is different from that for common commercial cream inhibitors.
After analyzing the contents of whole tea infusion, supernatant and cream, it was found that γ-PGA decreases the ratio of total thearubigins in cream. Charge-charge interaction may exist between γ-PGA and thearubigins that inhibits the formation of cream. The interaction was proven by sodium chloride interfering test.

並列關鍵字

black tea ； tea cream ； γ-PGA ； poly-γ-glutamic acid ； color

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