Impact of water pH on essential oil yield and quality in aromatic crops

Abstract

This study aimed to investigate the effects of using water with varying pH levels (pH 4, 7, and 9) instead of normal water during hydrodistillation. Four aromatic plants, Palmarosa, Eucalyptus citriodora, Lemongrass, and Citronella, were freshly distilled using a Clevenger apparatus with water at different pH levels. The study revealed that essential oil yields were significantly influenced by the distillation process. Soaking the plant material in water with varying pH levels overnight prior to hydrodistillation resulted in higher yields compared to distillation without soaking. In Palmarosa, geraniol was most abundant in the pH 7 sample (83.426%), while the yield increased by 0.2% when using pH 9 (soaked) water. It was concluded that pH 9 (soaked) water maximised essential oil yield, whereas pH 7 water was ideal for obtaining higher geraniol content. For E. citriodora, a notable yield increase (0.88%) was observed between pH 7 and pH 7 (soaked) samples, with the primary aldehyde Citronellal being most abundant in the pH 9 sample (84.432%). Similarly, Citronella showed higher essential oil yields (2.5%) when transitioning from pH 7 (soaked) to pH 9 (soaked), though Citronellal content was highest in the pH 7 sample (39.054%). In Lemongrass, the total citral content (86.702%) and essential oil yield (0.4%) were highest in the pH 7 (soaked) sample. These findings suggest that hydrodistillation with pH-adjusted water can optimise essential oil yields and quality, depending on the desired chemical constituents.