Antioxidant Character and Levels of Polyphenols in Several Tea Samples

Area of Science:

• Food Science
• Analytical Chemistry
• Nutraceuticals

Background:

• Tea possesses significant antioxidant properties attributed to various compounds like catechins and gallic acid.
• Quantifying tea's antioxidant capacity using methods like Oxygen Radical Absorbance Capacity (ORAC) and Ferric Reducing Antioxidant Power (FRAP) is crucial for understanding its health benefits.

Purpose of the Study:

• To measure the antioxidant properties (ORAC hydro, ORAC lipo, FRAP) of 15 commercial tea samples.
• To analyze the content of specific antioxidant compounds (gallic acid, four common catechins) and caffeine.
• To determine the correlation between measured antioxidant activity and the calculated activity based on individual compounds.

Main Methods:

• Assayed antioxidant properties using ORAC (hydrophilic and lipophilic) and FRAP methods.
• Quantified gallic acid and four major catechins (epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate) using chromatography.
• Calculated expected ORAC and FRAP values based on individual compound content and their known activities.

Main Results:

• Correlations between experimental and calculated antioxidant values were poor (R² for ORAC hydro=0.3657, ORAC lipo=0.2794, FRAP=0.6929).
• This poor correlation indicates that catechins alone do not fully account for the observed antioxidant capacity of tea.
• The study confirmed previous findings of poor correlation for ORAC and presented new findings for FRAP.

Conclusions:

• The antioxidant character of tea is more complex than solely attributed to the analyzed catechins and gallic acid.
• Other unmeasured compounds likely contribute significantly to the overall antioxidant power of tea.
• Further research is needed to identify and quantify all relevant antioxidant compounds in tea.