A rheological characterisation of an olive oil/fatty alcohols organogel

Abstract

Policosanol is a mixture of fatty alcohols well known for its nutraceutical effects on consumers' health. In the present paper, the potential ability of this food-grade additive to organogel vegetable oils has been investigated by preparing samples based on virgin olive oil at different policosanol concentrations. The onset of crystallisation temperature (Tco) and the gelation temperature (Tg) were evaluated by carrying out dynamic temperature ramp tests, whereas the rheological characteristics of samples at temperatures lower than the crystallisation onset were studied with frequency sweep tests at 25°C. Experimental data have shown that crystallisation occurs for policosanol concentration larger than 0.1% w/w whereas gelation (i.e. the formation of a structured 3D network) can be observed only for concentrations larger than a critical value ranging between 0.3% and 0.5% w/w. The onset of crystallisation temperature increases nonlinearly with organogelator amount even if an asymptotic trend seems to be present for concentrations larger than 50% w/w. A fractal model was used to fit experimental storage modulus data, G′, as a function of policosanol amount, and a fractal dimension equal to 2.75, in agreement with literature values, was found. Finally, a phenomenological equation based on a modified fractal model, was proposed to fit, with a good agreement, the experimental Tco values as a function of the policosanol fraction.