Title: Improved removal of ascorbate interference in the Folin-Ciocalteu assay of “total phenolic content" Authors
Submitted to: Florida State Horticultural Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 25, 2010
Publication Date: N/A
Technical Abstract: The venerable 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. We have sought chemical means to quench the H2O2 oxidative activities shortly after they have destroyed the DHA, or to otherwise prevent interaction with the phenolics present without altering the F-C signal. Some promising candidates have been identified, but none yet appear able to protect actual orange juice phenolics completely. 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. While 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), we strive to develop an approach to the point that it predictably causes no more than a 5% artifactual error.