Chemical changes in oils rich in non-conjugated and conjugated linoleic acid under simulated gastric conditions

Abstract

Chemical changes occurring to dietary lipid oxidation compounds throughout the gastrointestinal tract are practically unkown. In this regard, the first site for potential chemical modifications is the stomach due to the strong acidic conditions (1). The objective of this study was the evaluation of potential chemical changes during simulated digestion of safflower oil (SO), a vegetable oil rich in linoleic acid (LA) and of the oil obtained after its alkaline isomerization and commercialized as Tonalin (TO). TO contains about 80% conjugated linoleic acid (CLA) and it is added to a number of commercialized dairy products as a functional lipid especially for its attributed effect of body fat reduction. It is well-known that oils rich in linoleic acid are highly susceptible to oxidation and the compounds formed may be found in the diet at considerable amounts (2). In the case of CLA-rich oils, mechanisms of oxidation are different and lead to formation of polymerization compounds from the beginning of the oxidation process (3). In this study, samples of SO and TO oxidized at 40 ºC and fractions concentrated in oxidized compounds were subjected to in vitro gastric conditions. A simulated gastric fluid (SGF) containing 0.03 M NaCl and 3.2% w/v pepsin in 0.1 M HCl (pH 1.0) was used and samples were stirred with SGF for 3 hours at 37 ºC. Changes in peroxide values, oxidized triacylglycerol monomers, dimers and polymers were evaluated. Results showed that unoxidized samples remained practically intact, while oxidized samples showed significant changes in peroxide values and polymerization compounds. Peroxide values decreased after digestion in highly oxidized samples and such a decrease seemed more pronounced as oxidation was greater. Particularly relevant were the depolymerization effects observed in oxidized TO samples, thus converting the complex high-molecular weight polymeric molecules formed into monomers susceptible to enzymatic hydrolysis and absorption. Overall, results showed that significant modifications may occur to dietary oxidized lipids under gastric conditions, giving rise to structural changes and/or differences in the amounts of the oxidized compounds originally ingested.