Cooxidation of proteins and lipids in whey protein oleogels with different water amounts

Protein- and lipid oxidation were investigated in whey protein based oleogels with varying water addition. Lipid oxidation was low (~30 mmol O₂/kg lipid hydroperoxides after 6 weeks) in gels with < 0.23% water and a high (>1,000 mmol O₂/kg lipid hydroperoxides after 4 weeks) in gels with > 2.4% water addition. In systems with > 2.4% water addition fluorescence (excitation 325 nm / emission 410 nm) as indicator of tyrosine oxidation and carbonyl content significantly increased and remained at low levels in oleogels with < 0.23% water addition. Primary amines as indicator for protein backbone breakage increased in early stages of oxidation in high water oleogels and decreased after 28 days. Degradation has been suggested to occur through interactions with reactive secondary lipid oxidation products and was confirmed by spiking experiments using respective compounds. The results suggest that secondary lipid oxidation markers are masked dependent on water addition in the presence of proteins.