Effects of Harvesting Time and Isolation Techniques on The Physico-chemical Characteristics of Grapefruit (Citrus paradisi, Macfadyen), Bitter Orange (Citrus aurantium, Linnaeus) and Kumquat (Fortunella margarita, Swingle) Essential Oils

The essential oil (EO) yield and physicochemical parameters of four grapefruit cultivars, a bitter orange, and a kumquat cultivar were evaluated in relation to harvest time and isolation technique. EO samples were obtained by hydrodistillation (HD) and cold pressing (CP). The chemical composition of the EOs was determined by gas chromatography-mass spectrometry (GC-MS/FID). EO yield across the samples ranged from 1.24% to 2.83%. The isolation method significantly influenced the relative density, optical rotation, and refractive index of the oils. The cultivar also had a statistically significant effect on refractive index and optical rotation. Oils obtained by CP had higher relative densities (0.8473-0.8524) compared to those obtained via HD (0.8385-0.8413). CP oils also exhibited higher refractive index values (1.4749-1.4765) than HD oils (1.4721-1.4733). In contrast, HD-isolated oils had higher optical rotation values (95.48-99.13°) than CP (91.55-94.50°). While some variation in EO composition was observed based on cultivar, harvesting time, and extraction method, these differences were mostly insignificant. Limonene was identified as the major component, ranging from 93.7% (Rio Red as grapefruit) to 96.0% (Nagami as kumquat). Cultivar and harvest time effects on limonene content were statistically significant, whereas the effects of the isolation method were not (p>0.05). β myrcene was the second main component, ranging from 1.9% to 2.1%. While harvest time and isolation method had a significant impact on its concentration, the cultivar effect was not important. The study demonstrated a small variation in the composition of these citrus essential oils. Harvest time appears to be a less critical factor for these specific properties.