Changes in microstructural, thermal, and rheological properties of olive oil/monoglyceride networks during storage

Abstract

Effects of storage at 25 °C on microstructural, thermal, and rheological characteristics of olive oil/monoglyceride (MG) gel networks were studied. Polarized light micrographs revealed rod-shaped aggregates whose crystalline intensity increased with storage time. Coagel melting temperature decreased with storage time and this was explained in terms of the Gibbs–Thompson equation. Upon storage for about 9 weeks, the olive oil/MG networks displayed a progressive increase in hardness. An empirical model was used to describe this isothermal hardening process, and a hardening rate constant of 0.358 week −1was obtained. Creep-compliance behavior of stored mixtures all conformed to a discrete retardation spectrum consisting of two Kelvin–Voigt elements in the Burger's model implying two major modes of creep mechanisms. The retardation times and retarded compliances associated with each mechanism increased in the initial storage period and subsequently decreased. A linear regression analysis revealed statistically significant ( r=0.81, α=0.05 ) relationship between creep viscosity and hardness during the first five weeks of storage. These findings have important implications on storage stability and spreadability of olive oil/monoglyceride-based spreads.