Effect of γ-PGA on the color and tea cream formation of black tea
Date Issued
2005
Date
2005
Author(s)
Chen, Wen-Bin
DOI
zh-TW
Abstract
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.
Subjects
紅茶
茶乳
聚麩胺酸
色澤
black tea
tea cream
γ-PGA
poly-γ-glutamic acid
color
Type
thesis
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