Health aspects of oxidized dietary fats - Oxidation in Foods and Beverages and Antioxidant Applications - page 150

CFAM in specific are only formed to a significant extent at temperatures
exceeding 200 ëC. Oils rich in linoleic acid or linolenic acid are more easily
polymerized during deep-fat frying than oils rich in oleic acid (Takeoka et al.,
1997; Tompkins and Perkins, 2000; Bastida and Sanchez-Muniz, 2001).
Similarly, the formation of CFAM increases as the amount of linoleic acid
and linolenic acid increases (Tompkins and Perkins, 2000; Rojo and Perkins,
1987; Christopoulou and Perkins, 1989). Hence, heated vegetable oils contain
significant amounts of CFAM accounting for up to 0.66% of total fatty acids
(Sebedio and Grandgirard, 1989; Sebedio and Juaneda, 2007).
7.5 Bioavailability of lipid oxidation products
Numerous studies in both, humans and animals provided indication that lipid
oxidation products are readily absorbed from the diet. This indication is based
on the observation that lipid peroxidation products (TBARS, conjugated dienes)
were found at increased levels in plasma, lipoproteins, tissues, and urine of
humans and animals following ingestion of thermally treated fats or foods
(Brown et al., 1995; Naruszewicz et al., 1987; Staprans et al., 1994; 1996a;
1996b; 1999; Suomela et al., 2004; 2005a; 2005b).
Strong evidence for the absorption of lipid oxidation products from the diet
was provided from Wilson et al. (2002). These authors observed an increase in
the plasma concentrations of [U- 13 C]-labeled hydroxy and dihydroxy fatty acids
in healthy women following consumption of 30 g fat containing 15 mg [U- 13 C]-
labeled hydroxy and dihydroxy triglycerides. Noteworthy, the authors of this
study noticed differences in the absorption rates of monohydroxy and dihydroxy
fatty acids. The increase in plasma concentrations of [U- 13 C]-labeled hydroxy
fatty acids was much higher that of labeled dihydroxy fatty acids, and the
calculated absorption rate of labeled monhydroxy fatty acids was 21%, whereas
that of labeled dihydroxy fatty acids was less than 4.5% (Wilson et al., 2002).
This indicates that substantial differences exist in the absorption rates of certain
lipid oxidation products.
Whereas certain lipid oxidation products such as dihydroxy fatty acids are
obviously only poorly absorbed in the intestine, other lipid oxidation are not
absorbed at all. Namely, several studies observed that, in contrast to hydroxides,
epoxides, ketones and aldehydes, hydroperoxides were not found in lipoproteins
and tissues of animals fed oxidized fat (Suomela et al., 2004, 2005a; 2005b).
This is, however, probably not due to an inability of enterocytes to take up
hydroperoxides ± the uptake of 13-HPODE by cultured enterocytes has been
demonstrated (Penumetcha et al., 2000) ± but rather due to an effective
reduction or degradation of hydroperoxides in the gastrointestinal tract. It was
demonstrated that hydroperoxides are efficiently reduced to hydroxides by
reducing agents such as glutathione and detoxifying enzymes present in the
mucus layer of small intestine (Glavind, 1970; Bergan and Draper, 1970;
Kowalski et al., 1990; Aw et al., 1998; Kanazawa and Ashida, 1998; Mohr et al.,