Effect of the presence of protein on lipolysis and lipid oxidation occurring during in vitro digestion of highly unsaturated oils

- The impact of proteins on lipid digestion was studied by 1H NMR and SPME-GC/MS.
- Protein hydrolysates provoked higher hydrolysis of TG, but delayed lipid oxidation.
- Amino acids/peptides released during digestion showed antioxidant activity.
- The reduction of lipid hydroperoxides to hydroxides was clearly enhanced.
- The selection of lipid oxidation markers during digestion is a crucial decision.

The effect of the presence of ovalbumin and soy protein isolate on lipolysis and oxidation taking place during in vitro gastrointestinal digestion of slightly oxidized sunflower and flaxseed oils was addressed. The extent of lipolysis, the molar proportions of acyl groups/fatty acids after digestion, and the oxidation products formed were studied by Proton Nuclear Magnetic Resonance. The presence of proteins provoked a higher hydrolysis in triglycerides, a lower decrease of polyunsaturated chains, and a lower generation of oxidation compounds (conjugated dienes in chains having also hydroperoxy/hydroxy groups, epoxides and aldehydes); the formation of hydroxides was clearly favoured over that of hydroperoxides. Study of headspace composition by Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry confirmed that oxidation advanced to a lesser extent in the presence of protein. Thus, amino acids/peptides released during digestion may show antioxidant properties, affecting not only the extent of lipid oxidation, but also reactions pathways.