Bulk Protein Concentration Influences Lipid Oxidation in Emulsions through the Initial Hydroperoxide and Radical Concentration

Abstract

Lipid oxidation poses a significant challenge in food emulsions, as it deteriorates texture, flavor, and shelf life. In this study, we varied the bulk protein concentration and investigated its effect on lipid oxidation in whey protein isolate (WPI)-stabilized oil-in-water emulsions, in which oxidation was induced by an iron/EDTA catalyst. Oxygen consumption was measured in the headspace, and oxidation products were quantified using nuclear magnetic resonance (NMR), focusing on primary (hydroperoxides) and secondary (aldehydes and epoxides) compounds. Oxygen concentration decreased more rapidly in samples containing higher protein levels, although the differences were small. At the onset of oxidation, hydroperoxide concentration ranged from 5 to 10 mmol/kg oil, with 5 mmol/kg for high protein concentration and 10 mmol/kg for low protein concentration. Epoxide concentrations ranged from 2 to 4 mmol/kg oil. Modeling indicated an initial radical concentration of 300–335 μmol/kg oil, consistent with lower hydroperoxide formation and reduced lipid oxidation, suggesting reduced catalytic iron availability, although this mechanism was inferred rather than directly demonstrated.