Influence of Oxidised Oils on Digestibility of Caseins in O/W emulsions

Abstract

The impact of lipid oxidation on protein modifications in emulsions and the consequences on protein digestibility remains unclear. In this study, this impact was evaluated in casein (6 mg/mL) based emulsions containing oxidised soybean or fish oil (3 %) in presence (0.3 %) or absence of the emulsifier Tween 20. Emulsions were prepared using oils at three oxidation levels and subsequently the impact on protein digestibility was evaluated after 24 hours incubation at 4°C. Remarkably, protein digestibility increased in emulsions containing medium and highly oxidised fish oil: 70 ± 0.4 % and 73 ± 0.4 % of the proteins were digested respectively, whereas protein digestibility in emulsions containing low oxidised fish oil amounted to 63 ± 0.4%. Protein digestibility in emulsions containing soybean oil stabilised by Tween 20 was not influenced by the oxidation level of the oil used. A remarkable tendency is observed for the malondialdehyde content of the emulsions depending on the presence of Tween 20. For soybean oil based emulsions, malondialdehyde concentrations were consistently higher in the presence of Tween 20. On the other hand, for the fish oil based emulsions an opposite trend was observed, except at the highest oxidation level evaluated, for which no significant differences could be detected. We concluded that the composition of the interface in emulsions depends strongly upon the degree of oil oxidation and the presence of other emulsifiers. If the oil is more oxidised, less protein is present in the interface restricting the impact of lipid oxidation products on the proteins and hence their digestibility.

Practical applications: This research was done to highlight the relevance of the interfacial composition in food emulsions and its influence on dairy protein digestibility. The Food industry must be aware of the oil quality and the presence of emulsifiers in foods emulsions that allow to preserve the stability and nutritional characteristics of these food emulsions.

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