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 Citrus and Other Subtropical Products Research: Fort Pierce, FL
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ARS Home Southeast Area Fort Pierce, Florida U.S. Horticultural Research Laboratory Citrus and Other Subtropical Products Research Research Publications at this Location





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Title:   Author  item
                                            FORD, BRYAN - Former ARS Employeeitem
                                            Bai, Jinheitem
                                            Manthey, Johnitem
                                            Baldwin, Elizabeth

                                                         - *Liz*
  Submitted to: Proceedings of Florida State Horticultural Society
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 12/5/2010
                                    Publication  Date: 12/29/2010
                                    Citation: Ford, B.L., Bai, J., Manthey, J., Baldwin, E.A. 2010. Improved removal of ascorbate interference in the folin-ciocalteu assay of “total phenolic content”. Proceedings of Florida State Horticultural Society. 123:220-222.Interpretive Summary:
                                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 substantially exceed the magnitude of the total phenolic signal. Ascorbate oxidase (AO) has been a promising approach to eliminating the AsA interference, but the oxidation product of AsA by AO is dehydroascorbic acid (DHA) which is an F-C reductant that gives an apparent signal implying a molar strength of 15% to 30% of the original AsA. We have successfully used hydrogen peroxide (H2O2) to degrade this residual DHA into products that are not F-C reductants. Using a model orange juice we have examined the impact of this small amount of (~450 ppm) of H2O2 on the orange and non-orange phenolic measurements. We sought chemical means to quench the H2O2 oxidative activities shortly after it destroyed the DHA, or to otherwise prevent interaction with the phenolics present without altering the F-C signal. Some promising candidates were identified, but none protected the 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 (15 to 30% error), we strive to develop an approach to the point that it predictably causes no more than a 5% artifactual error.


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