Determination of Limonene Chirality in Oils Obtained from Different Types of Citrus Waste Peels in Türkiye

Abstract

Limonene constitutes a significant amount in citrus oils. It has a chiral structure and has two different optically active isomers, R-limonene and S-limonene, which are symmetrical to each other. Determining the chiral configurations of limonene plays an important role in determining the beneficial use areas of essential oils. Citrus oils are used in a wide variety of industrial areas, depending on their limonene content. This paper presents the analytical method optimization, validation, and chirality studies of limonene in the citrus oils acquired from different citrus waste peels in Türkiye. An inlet temperature of 250 °C and an injection volume of 2 µL were decided as the optimal conditions for the most accurate measurement of both limonenes in the citrus oil. This method produced results for linearity, sensitivity (LODs and LOQs), repeatability, and reproducibility that were acceptable within the scope of the validation studies. The chirality of limonene was investigated in twenty-six citrus oils (fifteen orange oils, six lemon oils, four mandarin oils, and one grapefruit oil) in Türkiye. While the content of R-limonene in orange oil varied between 56.39% and 72.85%, the content of S-limonene changed from 2.53% to 5.71%. Whereas the constituent of R-limonene in lemon oils ranged from 54.73% to 73.99%, the content of S-limonene varied between 3.78-4.79%. In mandarin oils, the content of R-limonene was determined to be 58.02% and 65.05%, while the content of S-limonene was found as 3.05% and 4.87%. In single grapefruit oil, R-limonene content was 60.69% and S-limonene content was 3.12%.