Enrichment of olive oil with sage (Salvia officinalis) leaf essential oil extracted by ultrasound pretreatment followed by hydrodistillation to increase its shelf life

Abstract

Olive oil (OO) is a valuable food product, compared with other seed oils, for its health benefits, sensory attributes and higher economic value. The demand for natural antioxidants has recently grown due to the potential toxicity and carcinogenicity of synthetic antioxidants that are utilized in food industry. This study aimed to investigate the oxidative stability of OO enriched with sage (Salvia officinalis) essential oil (EO). The sage EO was extracted from the leaves by ultrasound (US) as a pretreatment followed by hyrodistillation (HD). The effects of US power level (60 and 90 W) and time (10, 20 and 30 mins) on the EO yield, total extraction time and quality characteristics were studied. Compared to the HD extraction, the US pretreatments before HD shortened the total extraction time to ≤ 54 mins, with the same extraction yield, instead of 240 mins with HD. Various EO samples extracted by these US pretreatments followed by HD (US+HD) were analyzed for their chemical compositions by GC–MS and compared with that of EO obtained by HD. Compositional analysis revealed that the most prominent oxygenated monoterpenes of EO samples were camphor, α-thujone, 1,8-cineole, β-thujone, bornyl acetate and endo-borneol. The EO extracted by US pretreatment at 60 W for 10 mins followed by HD for 34 mins was characterized by the highest quality index [(α- + βthujone)/camphor ratio] and higher levels of antioxidant constituents (α-pinene and camphene). The sage EO obtained by this technique was selected to enrich OO at 200, 400 and 600 mg/Kg of OO. Quality criteria of the OO such as acidity, peroxide value, conjugated dienes and trienes besides chlorophyll and carotenoid contents and fatty acids composition were measured. Results revealed that the addition of sage EO at 200 mg/Kg of OO increased the oxidative stability of OO measured by Rancimat by 36% instead of 21% by using the synthetic antioxidant butylated hydroxytoluene (BHT) at the same level. Moreover, the sensory attributes of the enriched OO were maintained. From this study, it can be concluded that sage EO can be used to increase the shelf life of OO.