Effect of kinematic viscosity over the dynamic properties of an extra-virgin olive oil

Abstract

Previous studies 1,2 have shown that kinematic viscosity values of food oils depend on the presence of added solvents and on the nature of the oil under investigation (e.g., geographical origin and treatments prior to oil production). However, to the best of our knowledge, only one paper 3 dealt with the correlation between viscosity values and relaxation times of simple pure alkyl compounds. Up to now, no papers have been found in literature dealing with viscosity of complex mixtures and their relaxometric properties. In this study, we intended to investigate the effect of kinematic viscosity over the dynamic properties of an extra-virgin olive oil which is known as a very complex mixture of lipophilic triglycerides (more than 98%) and waxes, and hydrophilic secondary metabolites (around 2%) such as chlorophyll, salts and sterols. The relaxometric model 2,4 applied for the analyses of the NMRD profiles of the oil added with increasing amounts of n-hexane, split the correlation time in two contributions. The first one, modulated by an amplitude indicated as AD, was assigned to translational motions (D). The second component of the correlation time, also modulated by an amplitude indicated as AR, was due to the rotational motions (R). Results revealed that all the relaxometric parameters had a diametric trend. A possible explanation for such a behavior was found in the aggregative properties of the inverse micelle-like 1 components of the food oil. In fact, in the absence of n-hexane, all the inverse micelle-like systems, in which triglycerides are shrink together, aggregate, thereby forming large sized units which are subjected to very slow rotations but fast translations. Conversely, as the amount of n-hexane was increased, kinematic viscosity decreased and rotations became preponderant over translations. In fact, n- hexane has the effect to separate the inverse micelle-like systems and to increase rotational freedom degrees over the translational ones. This study confirmed the inverse micelle-like nature of food oils reported in a previous paper 1 .