Thermodynamic and kinetic aspects of the transport of small molecules in dispersed systems

Abstract

The knowledge of the behaviour of flavour compounds in complex multiphase systems with regard to their structure is of great importance in flavour perception of foods. The thermodynamic and kinetic behaviour of three selected flavour compounds belonging to a homologous series of esters, e.g. ethyl acetate, ethyl butanoate and ethyl hexanoate, were studied in simple and multiphase systems. The liquid system was composed of water (with or without sodium caseinate) and/or a lipid, Miglyol. First, the properties of the solutes were determined by means of their liquid–liquid partition at equilibrium and their diffusion in aqueous or lipid phases. This first step allowed to reveal the impact of sodium caseinate and that of the lipid on their behaviour in liquid phases. The second step consisted in the investigation of the transfer of the flavour compounds through the oil phase with a rotating diffusion cell (RDC) and the knowledge of the physico-chemical characteristics of the solutes. The data obtained with the RDC enabled the calculations of the resistances to the transfer through the aqueous phase ( R aq), through the interface ( R I) and through the oil ( R oil). The transfer of ethyl acetate through the interface was the rate-limiting step, while the transfer of ethyl butanoate and ethyl hexanoate through the oil was limited by the diffusion in the aqueous phase. The effect of sodium caseinate is different for the less hydrophobic compound (ethyl acetate) and the more hydrophobic compounds (ethyl butanoate and ethyl hexanoate); in the presence of sodium caseinate, the R aq value increases for ethyl acetate, while the R I value increases for ethyl butanoate and ethyl hexanoate. Those results show the impact of the nature of the solutes on their transfer through the aqueous layer and the oil–water interface.