Supercritical CO2 Technologies for the Recovery and Use of Terpene Ketones as Biopesticides

Abstract

Terpene ketones are botanical compounds involved in natural defense mechanisms of numerous plant species, making part of a group of substances that play an important role protecting the plant from pest attack, with specific activities against several microorganisms and insects. These biodegradable compounds generally show a high selectivity with low toxicity for mammals, fish, and birds, and therefore they could be very useful as biopesticides in agroindustrial pest management, to protect crops, seeds, and related food products with low environmental risks [1, 2]. Notwithstanding these advantages, terpene ketones are highly volatile, thermolabile and sensitive to UV radiation, which constitutes a limitation for their use as biopesticides. Besides, they are normally extracted from vegetable matrices as a mixture of various volatile compounds known as essential oil, and they must be further processed in order to obtain a purified extract with the desired specific activity. Consequently, some technological solutions are needed before their application could be achieved at a great scale. In this sense, supercritical fluid technology appears as an innovative tool to overcome these limitations.On one hand, supercritical fluid extraction using CO2 (pure or mixed with cosolvents) is a well-known technology with interesting advantages over other extraction techniques for the obtention of essential oils and/or other extracts from plants, as well as for the valorization of agronomical residues [3]. This technique yields high-quality extracts, since the raw materials are not exposed to high temperature and other degrading agents (such as oxygen, radiation, etc.), and has been applied to a great number of plants and vegetable materials for obtaining aromas, nutraceuticals, bioactive compounds and other natural compounds of interest. In addition, the different solubility behavior of polar and nonpolar substances in supercritical CO2 (scCO2) allows the fractionation of mixtures (such as essential oils) and the purification of target compounds or families. In particular, ketone-rich essential oils can be treated with scCO2 in order to remove the more volatile nonpolar compounds and increase or purify the fraction of ketones. Two cases of interest are presented and discussed in this chapter: i) the purification of tagetenones from Tagetes minuta essential oil [4], and ii) the recovery of piperitenone from dementholized peppermint oil [5]. The main interest of these α,β-unsaturated ketones is based on their potential use as biopesticides and precursors for chemical synthesis.On the other hand, scCO2 is also a suitable solvent for the incorporation of low molecular weight compounds into polymer matrices [6]. In this sense, the supercritical impregnation of biopesticides into commercial polymer materials appears as an innovative and environmentally friendly tool to develop food active packaging and/or gradual release devices. In this chapter, the impregnation of polymer materials with two different ketones with known activity against the main pest of stored products (thymoquinone and R-(+)-pulegone) is presented, and the effect of the process variables on ketone loading and the final activity of the impregnated materials is discussed [7?10]. Overall, supercritical fluid technology is proposed as a promising tool to develop environmentally friendly processes for encouraging the use of terpene ketones as biopesticides at a commercial scale.