Modification of the interactions between β-casein stabilised oil droplets with calcium addition and temperature changing

Abstract

Milk caseins are natural emulsifiers widely used in food processing applications. Four different caseins exist in milk. β-casein, the more abundant, is present in solution in a molecular or aggregated state depending on concentration, temperature and calcium content. Varying these three parameters, four aggregation states of β-casein were previously characterised: a molecular state at 4 °C, a micellar state at 37 °C, a “polymeric” state at 4 °C with calcium and an aggregated state at 37 °C with calcium. In this paper, we have studied the influence of these β-casein aggregation states on perikinetic flocculation of an oil-in-water emulsion, using rheological and microscopic tools. We have verified that in the absence of calcium, the molecular or micellar state of β-casein in the aqueous phase did not lead to depletion flocculation in the condition used. In contrast, in the presence of calcium added after emulsification, the emulsions flocculated when the aggregated β-casein were present in the aqueous phase. At low temperature, bridging flocculation of emulsions decreases when β-casein concentration increases, but at higher temperature, we have observed the opposite behaviour. Moreover, this flocculation was totally reversible with temperature and calcium content. In fact, emulsions stabilised by β-casein present a behaviour in term of aggregation close to that observed for β-casein in solution with temperature and calcium changes. Hence, the aggregation state of non adsorbed β-casein in the aqueous phase plays an important part in perikinetic emulsion flocculation.