Physicochemical Properties of Extra-Virgin Olive and Soybean Oils Flavoured with Rosemary and Oregano Extracts
2025
Offia-Olua, B.I. | Usuwa, F.A. | Onwuzuruike, U.A. | Ukom, A.N. | Ndife, J.
Essential oils (EOs) from medicinal and aromatic plants (MAPs) are well-known natural antioxidants. This study was conducted to ascertain the influence of essential oils (EOs) from rosemary and oregano, on the physicochemical properties of extra-virgin olive (EVOO) and soybean oils (SBO) for culinary uses. Refined EVOO and SBO were obtained from commercial stockers and infused with EOs of rosemary and oregano using established protocols to obtain flavoured oil samples assessed for chemical, physical properties, and volatile compounds using standard methods. Data were statistically analyzed using SPSS (Statistical Package for the Social Sciences), (version 20) at a 95 % probability level. Results of the chemical composition of the oil samples showed a range of 180.80 mg/KOH/g - 212.67 mg/KOH/g for saponification value, 1.17 – 4.44meq O2/kg fat for peroxide value, 0.64 – 1.95 mg/g for thiobarbituric acid value, 73.12 to 87.09 g I2/100g for iodine value and 2.14 – 4.53% for free fatty acid value. Physical properties were significantly reduced (P < 0.05) after aromatizing with EOs of rosemary and oregano. The values ranged from 240.00 to 372.00°C, 303.00 to 380.00°C and 325.00°C to 400.00°C for smoke, flash and fire points respectively. The volatile components of the six oil samples were significantly different (P < 0.05) from each other. EVOO samples had higher squalene concentrations than SBO samples. Tocopherol was not detected in EVOO samples but was detected in soybean oil, particularly delta- and gamma-tocopherol. Cyclononasiloxane octadecamethyl, cyclooctasiloxane hexadecamethyl, cycloheptasiloxane tetradecamethyl, squalene, bis(2-ethylhexyl) phthalate, and gamma-sitosterol are similar compounds found in considerably all oil samples. Conclusively, flavoured oils not only protect the oils against lipid oxidation but also improve their sensory and health benefits.
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