Extraction of Polyphenols in Tea with Lemon Juice

For thousands of years, tea has been one of the most popular drinks around the world. Not only is tea delicious, it is also full of health benefits. Tea is an abundant source of antioxidants called polyphenols. One of these polyphenolic compounds, catechins, are found mostly in green tea. Catechins have been studied thoroughly and have been found to reduce free radical stress, they have also been found to be anti-inflammatory as well as potentially therapeutic for cancer cells.

Since catechins are phenolic compounds, their ideal extraction condition is an acidic environment. A simple way to make the extraction solvent (the boiling water in this case) acidic, is to add lemon or lemon juice. Lemon juice is very acidic (approximately pH 2), so adding just a teaspoon can drastically drop the pH of your cup of tea. This allows more of the catechins to be extracted which allows your body to absorb more of them – plus, lemon juice makes the tea taste great!

This principle is applied in the extraction method outlined in EPA Method 8270. This method is used to extract and quantitate a full suite of semi-volatile compounds from multiple different sample matrices, including aqueous samples. This method outlines the separation of 3 separate classes of compounds – acidic, neutral and basic. Like in the example above, the phenolic compounds come out during the acidic portion of the extraction. The pH of the sample is brought to approximately 1 or 2 using either sulfuric or hydrochloric acid. The sample is then subjected to an extraction solvent, such as dichloromethane, where the semi-volatile compounds are extracted from the water sample.

As you might guess, separating and quantifying all 3 classes of compounds can be complicated and time-consuming. Making multiple pH adjustments and selectively eluting your acids separately from your bases and separately from your neutrals must be done carefully. And if you want to do this type of extraction on a regular basis, you have to learn how to do it precisely. Fortunately, solid phase extraction (SPE) (read our blog post “Solid Phase Extraction – What is That?”) is a technique that’s well-suited for this type of sample preparation. For extra precision and accuracy – as well as convenience – you can automate your SPE! That’s exactly what was done in this application note and the results are great for all 3 compound classes.

And to think, it all started with a cup of tea and a lemon wedge.

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