Studies on the Stability of Ascorbic acid in Tea Infusion

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  • 茶浸出液中のアスコルビン酸の安定性の解明
  • チャシンシュツエキチュウ ノ アスコルビンサン ノ アンテイセイ ノ カイメイ

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The average losses of ascorbic acid (AsA) in green tea infusions were about 10.3% at 50°C for 60 min and about 47.9% at 70°C for 60 min. The activation energy for ascorbic acid degradation in tea infusion ranged from 12 to 17 kcal/mol. The average value was 14.7 kcal/mol. AsA in the first infusion was more stable than that in the third infusion. The stability of AsA in the third infusion increased when sodium cyanide was added to the infusion.<BR>Since AsA in tea infusion was more stable than AsA dissolved in distilled water, it was suggested that tea infusion contained protect-ing compounds of AsA. Polyphenol fraction extracted with ethyl acetate, pectin fraction precipitated with 50% ethanol, and water soluble fravonoid fraction precipitated with aceton from tea infusion depressed the degradation of AsA. When authentic catechins were added to the AsA solution, epicatechingallate and epigallocatechin gallate depressed the degradation of AsA. However, epicatechin, epigallocatechin and catechin did not show the effects on the stabilty of AsA. Copper ion and ferrous ion accelerated the degradation of AsA. Chelating agents such as sodium cyanide and ethylenediamine tetraacetic acid depressed the degradation of AsA in the solution containing Cu+2 and+2 Fe. Moreover AsA in the solutions containing chelators was more stable than that of tea infusion.<BR>From these results, it is speculased that AsA in tea infusion is stabilized by the compounds that have an interaction with metal ion, such as gallate of catechins.

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