Retention of aroma compounds by proteins in aqueous solution

Retention of aroma compounds in sodium caseinate aqueous phase was investigated by measurement of vapour-liquid partition equilibrium (headspace analysis or exponential dilution). This retention depended on the nature of the aroma compounds and sodium caseinate content. For a homologous series of ethyl esters (ethyl acetate, butanoate and hexanoate), it increased with the carbon chain length from 0 to 38% and from 0 to 61 % for caseinate contents of 5 and 50 g.litre−1, respectively. Retention of diacetyl increased from 0 to 23% for the same range of protein content. Thermodynamic models were applied to evaluate the binding parameters n (number of binding sites of protein), Ka (affinity constant) and h (Hill coefficient) to both ethyl esters. These values were compared with those given in the literature: n and Ka were of the same order; h indicated a weak cooperative effect between sodium caseinate binding sites.