Essential Science Indicator Feature

Essential Science Indicator Feature

Published by the Institute for Scientific Information (ISI) , Philadelphia, PA

Dr. Edwin Frankel of the University of California at Davis discusses his highly cited work on lipid oxidation and antioxidants in both an interview and an essay. In our analysis of high-impact agricultural research, 13 of Dr. Frankel's papers were cited a total of 586 times, placing him among the 2 most-cited scientists of the 1990s in this field. Another of his highly cited papers is "Inhibition of oxidation of human low-density-lipoprotein by phenolic substances in red wine," (Lancet, 3418443:454-7, 20 February 1993). Because Lancet is not categorized by ISI as an agricultural journal, this paper was not included in our analysis of the field, but ISI's Web of Science© indicates that this paper has been cited 498 times to date.

*Note: The 2008 list of highly cited papers from ISI indicates a citation of 1012 times.

“ISI In-cites” published an editorial: "An Interview with Dr. Edwin Frankel" on  http://in-cites.com/scientists/dr-edwin-n-frankel.html

Interfacial Lipid Oxidation and Antioxidants.

“The subject of natural antioxidants continues to captivate the interest of food and biomedical scientists, because of the reports that diets rich in plant antioxidants derived from fruits and vegetables are associated with lower risks of coronary heart disease and cancer. The public is also catching on to the possible health promoting effects of antioxidants found in fruits and vegetables. However, there is much confusion among food and nutrition scientists about the potential health effects of antioxidants in our diet.

We found that the activity of antioxidants in model food systems was significantly influenced by different lipid substrates according to their hydrophilic or lipophilic character. For example, a-tocopherol and ascorbyl palmitate are lipophilic antioxidants that behaved quite differently from Trolox (a carboxylic acid analog of a-tocopherol) and ascorbic acid, which are hydrophilic. In bulk corn oil triglycerides, Trolox and ascorbic acid were better antioxidants thana-tocopherol and ascorbyl palmitate, but the opposite trend was observed in the corresponding oil-in-water emulsions. The physical states of lipid systems affect the distribution of antioxidants and influence their activity. Lipophilic and hydrophilic antioxidants exhibit complex interfacial properties between air-oil and oil-water interfaces that significantly affect their relative activities in different lipid systems. These studies led us to define the novel concept of "Interfacial Oxidation," which affects the stability of a large number of multi-phase foods and biological systems. Interfacial oxidation involves the interactions of antioxidants and prooxidants distributed in different compartments of colloidal systems.

My basic antioxidant studies at the University of California at Davis led us to a fertile field of research with plant phenolic antioxidants and phytochemicals. For many years, natural phenolic compounds have been known to be effective antioxidants in model food systems. By actively evaluating the effects of natural antioxidants in foods we developed more reliable testing methods for measuring lipid oxidation in foods. We were thus able to extend our research to evaluate the activity in inhibiting oxidation of various biological lipid systems, including human low-density lipoproteins (LDL), which are implicated in the initiation and development of atherosclerosis.

We were intrigued by the epidemiological studies on the French Paradox correlating the unusual low rate of mortality in certain parts of France with consumption of wine. This paradox sent many research teams looking for the health benefits of alcohol. In our laboratory at UC Davis we were all set up to test a hypothesis that perhaps all the speculation about the health effects of wine may have little or nothing to do with alcohol, and may be mainly due to the polyphenolic compounds present in relatively high levels in wine, especially in red wine. From our experience with polyphenolic antioxidants in foods, we expected the corresponding polyphenolic compounds in red wine to be active antioxidants in inhibiting lipid oxidation in LDL. By developing and using a very sensitive test to measure lipid oxidation, we observed a significant decrease in oxidation when wine phenolics were added to human LDL. We tested the antioxidant activity of 20 different California wines, which showed a wide range of total phenolic compounds. The antioxidant activity of these wines in inhibiting LDL oxidation in vitro correlated well with their total phenolic contents and the principal phenolic components.

We also found that flavonoids in commercial white and red grape juices significantly inhibited the oxidation of LDL, as well as in extracts of rosemary, green tea, berries, and peaches. Therefore, grape extracts and juices, especially red grape juices, many fruits and green tea provide significant sources of flavonoid antioxidants that like wine may have potential beneficial health effects in protecting against atherosclerosis and other degenerative human diseases. They represent a positive potential in our diet that requires further research to improve our understanding of their mechanism of action.

I believe that food and nutrition scientists have to be concerned about the nutritional value of plant flavonoid compounds because we consume them in substantial amounts in our diet. Our research on wine antioxidants led to a sudden increase in the number of publications and industrial developments exploiting the potential nutritional benefits of phytochemicals and natural antioxidants. Unfortunately, several recent studies on natural phytochemical compounds produced conflicting results on their antioxidant activities because of the wide and diverse methodologies used to evaluate them. There is a great need to standardize antioxidant testing using more specific methodology to minimize the present chaos in the literature.”

NEWS ITEM 

UCDavis – News & Information (February14, 2002)

UC Davis Leads the Nation for Ag and Environmental Publications, Citations

…. “In a decade-survey, UC Davis researchers also led the nation in agricultural sciences citations. From 1991 to June 2001, 1520 papers published by UC Davis researchers were referenced in 10,602 other journal articles. Following UC Davis in the agricultural sciences were the University of Wisconsin and Cornell University.

In this 10-year survey, three UC Davis food scientists were ranked among the top 20 most referenced of more than 1500 agricultural science researchers. They are Edwin Frankel, second; Bruce German, 16th; and the late John Kinsella, 17th.

Quoting Dean Neal Van Alfen, College of Agricultural and Environmental Sciences: “This reaffirms our belief that research in the college and elsewhere on campus has impact and is a good investment in advancing the frontiers of knowledge.”

Media contact(s): Pat Bailey, (530) 752-9843, pjbailey@ucdavis.edu