Production of fatty acid methyl esters and bioactive compounds from citrus wax

Abstract

Citrus wax is a waste generated during the purification process of the citrus essential oil. A lot of citrus wax wastes are globally produced, despite this, its composition and properties are not well known. Here we present comprehensive results proving the chemical composition and the physical properties of citrus wax. Additionally, our study provides the basis for obtaining value-added products from citrus wax wastes. The qualitative/quantitative analysis revealed the presence of different compounds, which range from flavonoids, saponins, carbohydrates, unsaturated compounds, phenolic hydroxyls, and long-chain fatty acid esters. Given that citrus wax is a source of many bioactive compounds, they were preferably extracted with ethanol. The ethanolic extracts demonstrated the presence in citrus wax of different bioactives, such as 5–5′-dehydrodiferulic acid, 3,7-dimethylquercetin, 5,6-dihydroxy-7,8,3′,4′-tetramethoxyflavone, tangeretin, and limonene. After the extraction of bioactives from citrus wax, a washed waxy material with high content of long-chain fatty acid esters was obtained. It was shown that this washed wax can be used for the production of biodiesel. The transesterification reactions in acid media was the preferred process because higher content of fatty acid methyl esters (such as hexadecanoic acid methyl ester and 9,12-octadecadienoic acid (Z,Z)-, methyl ester) were obtained. Currently, citrus wax does not have any industrial application, here we shown that under the concept of waste biorefinery, the citrus wax wastes are useful sources for producing value-added products such as bioactive compounds and biodiesel.