Rheological behaviour, fatty acid composition and pigment content of Moroccan Picholine virgin olive oil during three harvest periods

Abstract

The physicochemical, rheological, and fatty acid composition of six virgin olive oils extracted from the Picholine variety in the Beni Mellal-Khénifra region (Morocco) were studied and compared over three harvest years: 2018-2019, 2019-2020, and 2020-2021. These results show that all samples are rich in oleic acid, with the lowest amount observed for samples harvested in 2018-2019, followed by samples from 2019-2020 and finally those from the 2020-2021 harvest. It was also shown that all virgin olive oil samples exhibited Newtonian behaviors at shear rates between 60 and 120 s-1 and that the average dynamic viscosity of the 2018-2019 samples was 0.045 ± 1.14.10-4 Pa.s, below that observed for the 2019-2020 period (0.063 ± 4.92.10-4 Pa.s). The latter was in turn lower than the viscosity recorded for the 2020-2021 harvest (0.071 ± 1.90.10-4 Pa.s). Analysis of fatty acid composition shows that olive oils with a high oleic acid content have a higher viscosity than those with a low content. Finally, multivariate statistical analyses (Principal Component Analysis and Hierarchical Cluster Analysis) showed good classification between samples according to their physicochemical properties and year of harvest. The olive oils produced in 2018 were significantly different from those harvested in 2020, probably due to their viscosities and fatty acid profiles.