oils during frying take the polar fraction and perform an analytical method known as high-performance size exclusion chromatography. But this technique can be time- and solvent-intensive.
So the team developed what they describe as a more simple
and rapid test for monitoring oil quality, which involves the use
of the less expensive and nondestructive analytical technique,
Fourier transform near-infrared spectroscopy.
The researchers deep- and pan-fried raw potato pieces in
the four different refined oils and reused each oil sample 10
times. After frying, each sample was examined for fatty acid
composition, trans fatty acid contents, oxidative stability, and
several other parameters.
The most stable frying conditions involved the use of
refined olive oil in a deep fryer at 320°F and 374°F (160°C and
190°C). The least stable conditions involved sunflower oil pan-fried at 356°F (180°C). The team concluded that for domestic
frying applications, refined olive oil maintains quality and nutrition better than refined seed oils.
cold-pressed oils vary
in antioxidant activity
Cold-pressed vegetable oils, which are obtained through press-
ing and grinding fruits or seeds at temperatures below 49°C,
exhibit a range of antioxidant activity, as reported by Anna
Prescha (Wroclaw Medical University, Poland) et al. in the
Journal of the American Oil Chemists’ Society ( http://dx.doi.
The researchers analyzed a variety of cold-pressed oils to
determine their antioxidant activity, fatty acid composition, and
oxidative stability over time. They characterized oils from macadamia, avocado, sesame, safflower, pumpkin, rose hip, Linola
(the trade name of a low-linolenic flaxseed oil), flaxseed, walnut,
hempseed, poppy, and milk thistle. Using an assay involving
the molecule 1,1-diphenyl-2-picrylhydrazyl (DPPH), the team
determined the radical scavenging activity of the nonfraction-ated fresh oil and both the lipophilic and hydrophilic fractions.
In general, higher antioxidant activity was found in the lipophilic fractions, and the oxidative stability parameters of the oils
were only slightly affected by shelf life. Using gas chromatography, the researchers also found the fatty acid composition was
the same whether the oil was fresh or near the end of its shelf
life, when kept under conditions mimicking domestic storage.
Prevalence of trans fat
in US processed foods
In the United States, manufacturers are permitted to label products containing between 0.0 and 0.5 g of trans fat per serving
as “0 grams,” which may lead people to consume more trans
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