Edwin N. Frankel

Bio: Edwin N. Frankel is an academic researcher from University of California, Davis. The author has contributed to research in topics: Hexanal & Lipid oxidation. The author has an hindex of 56, co-authored 97 publications receiving 15865 citations. Previous affiliations of Edwin N. Frankel include California State University, Chico & Spanish National Research Council.

The problems of using one-dimensional methods to evaluate multifunctional food and biological antioxidants

Abstract: The activity of antioxidants in foods and biological systems is dependent on a multitude of factors, including the colloidal properties of the substrates, the conditions and stages of oxidation and the localisation of antioxidants in different phases. When testing natural antioxidants in vitro, it is therefore important to consider the system composition, the type of oxidisable substrate, the mode of accelerating oxidation, the methods to assess oxidation and how to quantify antioxidant activity. Antioxidant effectiveness is also determined by the heterogeneity and heterophasic nature of the system, the type of lipid substrate, including its physicochemical state and degree of unsaturation, the types of initiators, notably transition metals, other components and their possible interaction. For this reason there cannot be a short-cut approach to determining antioxidant activity. Each evaluation should be carried out under various conditions of oxidation, using several methods to measure different products of oxidation. Because most natural antioxidants and phytochemicals are multifunctional, a reliable antioxidant protocol requires the measurement of more than one property relevant to either foods or biological systems. Several recent studies on natural phytochemical compounds produced conflicting results because non-specific one-dimensional methods were used to evaluate antioxidant activity. There is a great need to standardise antioxidant testing to minimise the present chaos in the methodologies used to evaluate antioxidants. Several methods that are more specific should be used to obtain chemical information that can be related directly to oxidative deterioration of food and biological systems.

Principal Phenolic Phytochemicals in Selected California Wines and Their Antioxidant Activity in Inhibiting Oxidation of Human Low-Density Lipoproteins

Abstract: The phenolic antioxidant phytochemicals in wines have been implicated for the lower rates of cardiac disease mortality among people drinking wine regularly in certain European populations. The activities of 20 selected California wines in inhibiting the copper-catalyzed oxidation of human lowdensity lipoproteins (LDL) were determined. This antioxidant activity was related to the major phenolic compounds and not to resveratrol analyzed in wines by HPLC and GC-MS. The relative inhibition of LDL oxidation varied from 46 to 100% with the red wines and from 3 to 6% with the white wines. When compared at the same total phenol concentration, the inhibition of LDL oxidation varied from 37 to 65% with the red wines and from 27 to 46% with the white wines. The relative antioxidant activity correlated with total phenol contents of wines (r = 0.94) and with the concentrations of gallic acid (r = 0.921, catechin (r = 0.761, myricetin (r = 0.701, quercetin (r = 0.681, caffeic acid (r = 0.631, rutin (r = 0.50), epicatechin (r = 0.451, cyanidin (r = 0.431, and malvidin 3-glucoside (r = 0.38). Therefore, the activity of wines to protect LDL from oxidation appeared to be distributed widely among the principal phenolic compounds.

Interfacial Phenomena in the Evaluation of Antioxidants: Bulk Oils vs Emulsions

Abstract: Antioxidants have been difficult to evaluate in oils and food emulsions due in part to the complex interfacial phenomena involved. Lipophilic and hydrophilic antioxidants were evaluated with corn oil stripped of natural tocopherols in bulk and in emulsion systems. Oridation was followed by determining formation of hydroperoxides and hexanal. The lipophilic antioxidants α-tocopherol and ascorbyl palmitate were more effective in an oil-in-water emulsion system than in bulk oil, while the opposite trend was found for the hydrophilic antioxidants Trolox and ascorbic acid. The oil-insoluble ascorbic acid was a particularly efficient antioxidant in suspension in the bulk oil system

The Chemistry behind Antioxidant Capacity Assays

Abstract: This review summarizes the multifaceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Depending upon the reactions involved, these assays can roughly be classified into two types: assays based on hydrogen atom transfer (HAT) reactions and assays based on electron transfer (ET). The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentrations. ET-based assays include th...

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Abstract: Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements

Abstract: Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.