But coconut oil was not tested, so this research pretty much tells us nothing. Spain happens to be the largest producer of olive oil, so I suspect bias here.
http://www.alphagalileo.org/ViewItem.aspx?ItemId=166183&CultureCode=en
Researchers at the UPV/EHU-University of the Basque Country have
studied the changes that take place in fish lipids and in the oil during
frying processes
The frying techniques, the nature of the oil used and the fish
species have been shown to exert a great influence on the changes that
take place during the process. UPV/EHU researchers have shown that the
choice of cooking oil is hugely important owing to its impact on the
lipid profile in the fish and on the possible generation of toxic
compounds in the oil during frying, which can influence food safety and
human health.
The journal Food Research International has published the article
‘The influence of frying technique, cooking oil and fish species on the
changes occurring in fish lipids and oil during shallow-frying, studied
by H-1 NMR’, which deals with the work carried out by Bárbara
Nieva-Echevarría, Encarnación Goicoechea, María José Manzanos and María
Dolores Guillén. To conduct this research, fillets of European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata)
were shallow-fried in a frying plan and in a microwave oven using extra
virgin olive oil and refined sunflower oil. The changes that took place
in the lipid composition of the fish and of the frying oil were studied
by means of Proton Nuclear Magnetic Resonance Imaging (H-1 NMR).
Migration of lipid components between the fish and the frying oil
During the shallow-frying of the fish under domestic conditions, not
only do the fish lipids migrate to the frying oil, the components of the
oil are also transferred to the fillet of fish. As a result, the
composition of the oil used for frying is modified: firstly, it is
enriched by the acyl groups (‘fatty acids’) that are present in a higher
concentration in the fish fat than in the original oil, and secondly,
and simultaneously, it is depleted in the acyl groups present in a
higher concentration in the original oil than in the fish fat. So after
having been used for frying, the extra virgin olive oil was richer in
omega-3, omega-1 acyl groups, linoleic and saturated fats (from the
fish) and poorer in oleic, which is the main acyl group in olive oil.
Likewise, after having been used for frying, the sunflower oil was
richer in all the acyl group types (coming from the fish) except
linoleic, which is the majority acyl group in sunflower oil.
Furthermore, after frying, both types of oil were enriched by small
amounts of cholesterol (from the fish).
As regards the fat in the fish fillets, its composition also changed
during the frying process, and became enriched by the acyl groups
present in a higher concentration in the frying oil than in the fillet
(in other words, oleic if extra virgin olive oil was used, or linoleic
if sunflower oil was used) and in plant sterols. Simultaneously, during
the frying process the lipids in the fish fillets were depleted in the
acyl groups and minority components present in a greater concentration
in the raw fillet than in the original oils, such as, for example, the
omega-3 docosahexaenoic (DHA) and eicosapentaenoic (EPA) polyunsaturated
groups.
Thermal oxidation reaction
Besides the migration of lipids during frying, because these oils are
subjected to high temperatures (170 ºC) in the presence of oxygen,
certain small-scale thermal oxidation may take place in them. In the
extra virgin olive oil used for frying fish, this thermal oxidation
reaction did not occur as it is more degradation-resistant than
sunflower oil. Yet in the sunflower oil used for frying fish in the
frying pan, secondary oxidation compounds (aldehydes) were formed; some
of them are regarded as potentially toxic depending on the concentration
in which they are found. It should be pointed out that these compounds
did not form in the sunflower oil used to fry the fish in the microwave
oven. Therefore, in view of the results obtained and bearing in mind the
generation of these compounds that are potentially harmful for health,
the healthiest option for frying is to use extra virgin olive and fry in
the microwave.
Fat content of the fried fish
The fish species used was also seen to be a factor that considerably
influences the fat absorption-desorption process during frying. The fat
content of the gilthead seabream had diminished after frying while that
of the European seabass remained similar or increased with respect to
the starting level.
This study shows that the frying technique, the type of oil used and
the fish species exert a great influence on the changes that take place
during the frying process. Correctly selecting the oil is of paramount
importance owing to its impact on the final composition of the fat in
the cooked fillet and the possible generation of potentially toxic
compounds in the oil during the frying process, which will greatly
influence food safety and human health.
Gotta love sashimi.
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