Oxidation progress in an emulsion made from metmyoglobin and different triacylglycerols

Emulsions made using metmyoglobin as emulsifier and different synthetic and natural triacylglycerols (TAG), have been studied with respect to oxidation progress during 48 h at ambient temperature. The investigated model systems contained polyunsaturated TAGs of linolein (C18:2n-6, tri-LIN), arachidonin (C20:4n-6, tri-ARA), docosahexanoin (C22:6n-3, tri-DHA), salmon oil (SO) and cod liver oil (CLO). The synthetic TAGs were added in ratios of one part to nine parts trioctanoin (C8:0), yielding model composite oil systems. The total amount of volatiles, determined using dynamic headspace GC/MS, were relatively larger for tri-LIN and tri-ARA than for the marine systems during the first 6 h of observation. After 48 h of incubation, the marine oils had more total volatiles than had tri-LIN and tri-ARA. Hexanal and propanal were observed as the marker degradation compounds for n-6 and n-3 fatty acids, respectively. Myoglobin tended to aggregate in these model systems, and only for trioctanoin and tri-LIN could the protein monomer be recovered unmodified and subsequently observed using MALDI-TOF MS after 48 h of incubation. Myoglobin was only recovered after 4 h of incubation in the tri-DHA system, and it then appeared adducted with lipid fragments up to ∼1000 Da. Final oxidation (after 48 h) products from the marine lipids were trienes, most likely as alcohols or acids. The natural oils revealed a reaction pattern close to that of tri-DHA.