Wastewater from hydrodistillation can be reused for various sequential extractions: A study using Corymbia citriodora leaves

Abstract

The most common essential oil extraction method is hydrodistillation by steam distillation, which is efficient but results in a large volume of by-products, which are underused within industries, such by-products are the aqueous extract and residual biomass, that representing more than 95% of the extracted material. The aqueous extract consists of the fraction of chemical compounds soluble in hot water extracted from the leaves during hydrodistillation process, such as polyphenols, sugars, and their derivatives. These bioactive compounds can be exploited for a wide range of applications with higher commercial value as in reagent standards or in functional foods with antioxidant activity. Here, we characterised the by-products of the hydrodistillation industry of Corymbia citriodora leaves, through sequential extractions with reuse of the extract for concentration of bioactive compounds envisage further application. It was possible to reuse the aqueous extract up to seven times to obtain maximum solids of 49.94 g L−1 without loss of essential oil yield, of which 17.19 g L−1 are polyphenols and 7.31 g L−1 are sugars, amino acids and organic acids were also found in abundance in the extract. However, degradation of some compounds was observed as a function of the time they were exposed to a boiling point temperature (ca. 100 °C) and a more detailed study was conducted to understand their effects on the composition of the extract. The subsequent extraction by hydrodistillation of C. citriodora can increase the wastewater's tannins, and flavonoids. The alteration is mainly attributed to the sugars that decrease sucrose quantity in favour of fructose and glucose. This work demonstrates that the reuse of wastewater can not only be a promising for byproducts with potential commercial interest, but also yielding a stable essential oil without compromise its quality.