ARS | Publication request: Improved Folin-Ciocalteu assay of “total phenolic content” by removal of ascorbate and dehydroascorbate

Submitted to: Gordon Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 17, 2010
Publication Date: N/A

Technical Abstract: The venerable and operationally simple Folin-Ciocalteu (F-C) assay for total phenolics can have severe limitations due to interference by ascorbic acid (AsA). For common fruit juices AsA interference can easily exceed the magnitude of the total phenolic signal itself. Ascorbate oxidase (AO) has been a promising approach to eliminating the AsA interference, but the oxidation product of AsA digestion by AO is dehydroascorbic acid (DHA) which is itself a F-C reductant, giving an apparent signal implying a molar strength of 10 to 20% of the original AsA. We have successfully used hydrogen peroxide (H2O2) to degrade this residual DHA into products that are not themselves F-C reductants. Using a model orange juice we have examined the apparent impact of this small amount of (~600 ppm) of H2O2 on actual orange and non-orange phenolics in the model juice. The best that can be said is that conditions can be easily set so that the alteration in phenolics represents less than a 10% perturbation in the untreated model juice F-C signal. This is much better than the large errors originally seen from AsA (100% or more of a typical orange juice phenolic signal) or from the residual DHA (20 to 40% error). These modifications of F-C applied to actual orange juice samples gives readings of total phenolic levels much more consistent with HPLC readings from the same samples.