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Antioxidants, ORAC and Astringency

March 29, 2012

Recently, it was published that a South African company have produced the world’s first 1 000 000 (one million) ORAC value plant extract. What is the implication of this? and what exactly is ORAC?
We’ll try and answer below!

ORAC = Oxygen Radical Absorbance Capacity.

ORAC is a method for measuring antioxidant capacities in biological samples.

ORAC is a standardised test adopted by many agencies, labs and organisations and measures the Free Radical destroying or neutralising power (i.e. Antioxidant Power) of a particular food.

The ORAC unit has become an accepted industry standard for measuring antioxidants.

ORAC of Green Tea (The score is for 100 grams):
• Green tea brewed 1,253

The assay measures the oxidative degradation of a fluorescent molecule (beta-phycoerythrin or fluorescein) after being mixed with free radical generators such as azo-initiator compounds. Azo-initiators produce the free radical by heating, which damages the fluorescent molecule, resulting in the loss of fluorescence. Antioxidants protect the fluorescent molecule from the oxidative degeneration. So the degree of protection is quantified using a fluorometer (measurement of fluorescence).

Fluorescein is currently used most as a fluorescent probe. The fluorescent intensity decreases as the oxidative degeneration proceeds.

“The recommended daily antioxidant dose should add up to 3000 to 5000 ORAC units each day. It is clear that one has to be quite selective in the foods chosen so as to easily achieve this. For example, if you ate bananas alone, you would need to eat 2.4 kilograms of bananas to get your daily ORAC dose! However, you only need to eat 87 grams of prunes. In a study of 36 people, boosting fruit and vegetable intake to reach 3,200 ORAC units a day increased the antioxidant potential of the blood by 10 to 15%; enough to have an impact on disease prevention (Holly, 2003).”

Also remember, taste is important too. In this article on astringency we described the mouth drying or puckering effect of antioxidants.

Saliva contains proteins that lubricate the surface of the mouth. When we drink an infusion or a tea, salivary proteins can react with the phenolics found in these drinks.

When a protein reacts with certain phenolics (e.g. tannin), they form a larger structure….effectively glued together by bonds which can react with more proteins and phenolics and like a snowball form even bigger molecules. These large structures are so heavy that they precipitate. The lubricating proteins therefore are no longer doing there job of lubricating – they are effectively tied up with the phenolics and the mouth ”feels” dry. The receptors in the mouth signal to the brain the existence of this “rough”, drying sensation known as astringency. So, the more reactive a polyphenolic is (i.e. the more antioxidant) the stronger the astringency.


ORAC looks like a fairly good measure of Antioxidant power of a food. Looking at a list of typical food types (see below) it looks like a million ORAC figure is probably excessive.

Additionally, huge antioxidant potential (High ORAC score) may be, from a taste point of view, too astringent and possibly unpleasant from a sensory point of view. Take a look at Clove oil at over 10 million! Nice in small doses maybe but not too much.
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