Vacuum pyrolysis of chia flour residues: An alternative way to obtain omega-3/omega-6 fatty acids and calcium-enriched biochars

Abstract

The consumption of chia (Salvia hispánica L.) seeds products has increased recently and it has been suggested that the inclusion of this functional food in a daily human diet could contribute to improving consumers’ health. The present study focuses on the extraction of omega-3 and omega-6 fatty acids from chia flour residues using the vacuum pyrolysis (VP) technique as an alternative free-solvent extraction method. The pyrolysis conditions and their effects on the quality of the bio-oil containing the fatty acids were evaluated. VP experiments were carried out in a nitrogen atmosphere between 300 and 700 °C under vacuum for 20 min. The best results were achieved at 400 °C, where the oil fraction (38% yield) was enriched in high proportions of omega-3 and omega-6 fatty acids. 1H NMR analysis of the oil indicated 67.5% of α-linolenic acid and 18% of linoleic acid in the bio-oil, which are recovery values similar to those found in the literature. Moreover, extraction of fatty acids from chia flour waste with organic solvents was carried out in order to compare these procedures with the VP technique. On the other hand, XRPD analysis of the carbonaceous solid obtained as a subproduct from the VP of chia flour showed that this material was rich in attractive calcium crystalline compounds, such as calcite and calcium oxalate. These results indicate that pyrolysis products of chia flour residues, i.e., oil as well as biochar, have important properties that can be exploited in different fields.