Influence of rosemary (Rosmarinus officinalis, L.) on plant sterol oxidation in extra virgin olive oil

The objective of this study was to investigate the potential role of rosemary compounds in inhibiting the plant sterol oxidation in extra virgin olive oil during heating. The stability of plant sterols was measured by quantification of plant sterol and sterol oxide formation upon 6 h of heating in both the extra virgin olive oil and its respective oil at 10% rosemary concentration (ROE). The total sterol and sitosterol oxide contents were determined by GC‐flame ionization detection (GC‐FID) and GC‐MS techniques, respectively. Heating experiments were carried out at 180°C for 0, 1, 3 and 6 h. The total sterol content in the extra virgin olive oil was 255 mg/100 g and that in the ROE 270 mg/100 g. Sitosterol was the most abundant sterol in both samples (50% of total sterol). The ROE showed a lower content of sitosterol oxides with respect to the extra virgin olive oil during heating: after 6 h of heating only 6.1% of sitosterol oxides were formed, while up to 11.5% of sitosterol oxidized in the extra virgin olive oil. Our findings suggested that rosemary compounds were able to counteract the oxidation of plant sterols in the extra virgin olive oil during heating, preventing formation of potentially harmful compounds to human health.