Evaluation of Model Food Emulsion Stability by Hygrometric Measurements

Abstract

Many natural and formulated foods, such as milk, cream, mayonnaise, butter and margarine, consist of an intimate mixture of at least two non-miscible phases in the form of finely or coarsely dispersed systems defined as emulsions. Emulsions are not thermodynamically stable systems. In fact, after a time, the droplets of the inner phase can recombine and ‘coalesce’, or cluster toghether (flocculation) and ultimately give two separate phases due to a density difference between the inner and the outer phase [1–2]. The stability of an emulsion depends on different factors (degree of dispersion of the inner phase, outer phase viscosity, a single phase volume to total volume ratio, specific gravity of the phases and temperature), and on the presence of emulsifying agents able to form an interfacial layer between the two phases. In literature numerous methods have been proposed to estimate the emulsion stability: they evaluate the chemical, physico-chemical and physical changes that in the global emulsion volume occur spontaneously or -in the aging tests- due to thermal (heating or freezing) or mechanical stress [3–6). In this work, the measurement of the rate to reach the Equilibrium Relative Humidity (%ERH) expressed as d(%RH)/dt vs %RH was used to evaluate the degree of dispersion between aqueous and lipidic phase in a model food emulsion.