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 r. 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, making him the second-most-cited scientist 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, 341[8443]: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.
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What prior research or whose prior work helped to start you on your
way?
In my early career, I developed a skeptical and challenging outlook
in science that has served me well in developing my own ideas and
approaches to research and in critically evaluating the scientific
literature. By questioning and not accepting on face value the ideas
of my elder scientific leaders and many dogmatic claims in the
scientific literature, I was motivated to work hard to resolve
controversial issues.
What would you rate as your most difficult or trying professional
moment?
Some of my most difficult or trying professional moments occurred
when I had to convince my major professor at the University of
California at Davis (UC Davis) and my supervisors at the U.S. 
Department of Agriculture (USDA) to accept the results of my research
that invalidated some of their scientific beliefs.
My basic studies at USDA (1956-1989) on the oxidative stability of
soybean oil were hampered when they were interrupted several times
according to changing priorities in Washington, D.C. Around 1975
however, I was able to concentrate on my favorite subject of lipid
oxidation and antioxidants. At about the same time, important research
in this field was being conducted in many parts of the world. A
revival of the field of lipid oxidation in biological systems occurred
due to accumulating evidence that free radicals participate in tissue
injuries and the development of degenerative diseases. In 1989, I had
an opportunity to return to UC Davis, and to work again on
antioxidants in both foods and biological systems.
Which of your professional achievements brings you the most
satisfaction?
In my teaching and mentoring of graduate students, I try to
stimulate their thinking process by encouraging them to be skeptical
in reviewing published papers, and to challenge the literature and
papers presented at scientific meetings. During my research career, I
was fortunate to become associated with many foreign scholars who
worked in my labs at USDA and UC Davis and made valuable and
significant contributions to our research programs (Japan: K.
Fujimoto, K. Myashita, T. Ohshima; Norway: I. Heldal; The Netherlands:
J. Roozen; Israel: J. Kanner; France: P.L. Teissedre; Finland: A.
Hopia, M. Heinonen; Germany: K. Schwarz; Spain: M.T. Satué-Gracia, I.
Medina, C. Sánchez-Moreno; Denmark: A. Meyer; Korea: O. Yi). These
scientific associations provided me with valuable and friendly
collaborations around the world. One of my greatest satisfactions is
to work with younger and enthusiastic students and foreign visiting
scholars and to follow their progress in their professional careers.
It is also quite satisfying to
find reports in the literature from several parts of the world that
agree with and
confirm our published results.
Did you expect to become highly cited, or is this surprising to
you?
Around 1975, when I was able to concentrate on my favorite subject
of lipid oxidation and antioxidants at USDA, important research in
this field was being conducted in many parts of the world. Because a
revival of the field of lipid oxidation in biological systems
occurred, I expected our papers on lipid oxidation in foods to be
highly cited. Later, in 1989, our research at UC Davis on wine
antioxidants led to a sudden and rather unexpected increase in the
number of publications citing our work on the potential nutritional
benefits of phytochemicals and natural antioxidants.
What lessons would you draw from your work to pass on to the next
generation of researchers?
Motivate your research to resolve controversial issues by
questioning the ideas of elder scientific leaders, as well as the many
dogmatic claims in the scientific literature.
If you had the power to make a single, sweeping change in the way
that scientific research is conducted and presented, what would it be
and why?
Scientists should be given more freedom to develop and implement
their own research ideas and programs without spending an undue amount
of time and effort applying for grants. Funding decisions by
grant-giving agencies are based on inadequate reviewers’ panels
expecting the applicants to provide unreasonably specific details of
proposed research and to anticipate in advance the usefulness of the
expected results. The present refereeing process used by scientific
journals is exceedingly slow, inefficient, and inadequate because it
depends on volunteer editors and reviewers. Many editors and reviewers
are busy professionals who cannot spend the time and effort necessary
to properly evaluate scientific papers. We need to re-evaluate this
reviewing system, which slows down research, by using paid full-time
professional editors. The system should select more efficient and
competent reviewers who should be rewarded for their efforts.
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, α-tocopherol
and ascorbyl palmitate are lipophilic antioxidants that behaved quite
differently from Trolox (a carboxylic acid analog of α-tocopherol)
and ascorbic acid, which are hydrophilic. In bulk corn oil
triglycerides, Trolox and ascorbic acid were better antioxidants than
α-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.
Dr. Edwin N. Frankel
University of California at Davis
Department of Food Science and Technology
Davis, CA, USA
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