Abstract
The solubility of quercetin and its thermal degradation was studied in CO2-expanded ethanol and ethyl lactate. An equipment setup was constructed that enabled the separation of the products of degradation while quantifying the solubility of quercetin. Three different conditions of temperature were analyzed (308, 323, and 343 K) at 10 MPa. Higher solubility and thermal degradation of quercetin were observed for CO2-expanded ethyl lactate in comparison with CO2-expanded ethanol. At the same time, as the amount of CO2 was increased in the CO2-expanded liquids mixtures, the thermal degradation of quercetin decreased for almost all the conditions of temperature considered in this work. The importance of considering thermal degradation while performing solubility measurements of compounds that are thermally unstable such as quercetin was highlighted.
Highlights
Quercetin is one of the most abundant flavonoids observed in many types of fruits, vegetables, leaves, and grains
Higher solubility and thermal degradation of quercetin were observed for CO2 -expanded ethyl lactate in comparison with CO2 -expanded ethanol at the studied conditions of temperature and pressure in this work
For CO2 -expanded ethanol, the maximum solubility of quercetin was obtained at the highest temperature considered (343 K) and for 30% mol CO2 in the mixture
Summary
Quercetin is one of the most abundant flavonoids observed in many types of fruits, vegetables, leaves, and grains. Quercetin can be extracted from natural matrices, and different techniques for the extraction can be found in literature, such as solid-liquid extraction [3], and pressurized liquid extraction [4], among others. Extraction is generally limited by solubility, mass transfer resistance, and partitioning [5]. Quercetin presents low stability, suffering from rapid hydrolysis in aqueous solution [6], being thermally unstable [7], and unstable in the presence of oxygen [8] and light [9]. It is important to use a method for the extraction of quercetin that provides high solubility in the solvent and that favors fast mass transfer and partitioning, resulting in quicker extraction with low residence time and thereby less risk of degradation
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