Antioxidant activity of fruit juices - Letters to the Editor - Letter to the Editor

Townsend Letter for Doctors and Patients,  April, 2004  by Rudolf E. Nobel

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Editor:

The antioxidant activity of fruits, vegetables and grain products is probably a reflection of their phenolic content. (1) We wished to ascertain this for commercial fruit juices and, hence, the in vitro antioxidant activity of various juices as well as their total phenolic content was determined. We measured the antioxidant capacity of these juices by their ability to reduce ferrictripyridyl-s-triazine to the ferrous form which absorbs light at 593 nm [Ferric Reducing/Antioxidant Power (FRAP assay]. (2) We determined the in vitro total phenols present in these juices by the Folin and Ciocalteu's Reagent using gallic acid as a standard and measuring the change in absorbance at 760 nm. (3)

The total antioxidant capacity of teas has been shown to be strongly correlated with their phenolic content and is the highest for green teas and lowest for black teas. (4) Here, we found just the opposite i.e. green (white) grape juice had the lowest antioxidant activity as compared to dark (red) grape juice and this correlated well with their total phenol content. Thus, we found:

Fruit Juice                      FRAP Content   Total Phenols--GAE *
                                [micro]m/liter        mg/liter

Santa Cruz

White Grape Juice                     290                 80

Knudsen Pear Juice                  2,681                700

Lakewood Pink Grapefruit Juice      2,788                780

Santa Cruz Apple Juice              4,387              1,020

Lakewood Pineapple Juice            5,899              1,050

Lakewood Prune Juice               12,581              2,040

Lakewood Black Cherry Juice        15,563              2,180

Lakewood Concord (Red) Grape       17,172              2,380
Juice

* GAE--Gallic Acid Equivalent

References

(1). Velioglu YS, Mazza G, Gao L, Oomah BD, Antioxidant activity and total phenolics in selected fruits, vegetables, and grain products. J Agrig Food Chem 1998; 46:4113-4117.

(2). Benzie IFF, Strain JJ, Ferric Reducing/Antioxidant Power Assay: Direct Measure of Total Antioxidant Activity of Biological Fluids and Modified Version for Simultaneous Measurement of Total Antioxidant Power and Ascorbic Acid Concentration. Methods in Enzymology 1999; 299:15-27.

(3). Singleton VL, Orthofer R, Lamuela-Raventos RM, Analysis of Total Phenols and Other Oxidation Substrates and Antioxidants by means of Folin-Ciocalteu Reagent. Methods in Enzymology 1999; 299:152-178.

(4). Benzie IFF, Szeto YT, Total Antioxidant Capacity of Teas by the Ferric Reducing/Antioxidant Power Assay. J Agric Food Chem 1999; 47:633-636.

Roudolf E. Nobel, MD, PhD

20 Gough Street

San Francisco, California 94103 USA 415-626-1464

Fax 415-626-1466

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