Stability of target polyphenols of leaf-added virgin olive oil under different storage conditions over time

Abstract

The degree to which olive oil is protected against oxidation and rancidity is highly reliant on the presence and quantities of antioxidant polyphenols in the oil. On this account, the principal polyphenols need to be intactly available (withstand oxidation) in large numbers over the shelf-life of the oil, which often comes with a challenge as the oil is generally exposed to various atmospheric conditions during domestic, or even, throughout manufacturing and commercial situations, and consequently, a drastic depletion of endogenous antioxidants may occur in the oil before being consumed. That being the case, this study examined the stability of target polyphenols of virgin olive oil (VOO) enriched with olive leaf powders (0.3 mm particle size), compared to the non-enriched VOO (control),after oxygen and light exposures over time points. The main purpose was to observe the magnitude of depletions of the chief polyphenols in the leaf-added oils upon the given storage conditions. For each storage condition, there were relatively similar trends of changes in both leaf-added and leaf-free oils (from the same malaxation: 30 and 60 min). However, quantitatively, the leaf-added oils (particularly 30 min malaxation) contained significant proportions of oleuropein and verbascoside over a six-month period; with final concentrations of 5.03 and 4.15 mg kg⁻¹ oil (for oleuropein) and 3.50 and 2.88 mg kg⁻¹ oil (for verbascoside) when exposed to light and oxygen, respectively. On the other hand, only trace levels of these compounds were found in leaf-free oils. Overall, the outcome of this study support the inclusion of olive leaves in the oil because considerable levels of polyphenols, and correspondingly antiradical capacity, remained having been exposed to oxygen and light over the course of time.