Odorants quantitation in high-quality cocoa by multiple headspace solid phase micro-extraction: Adoption of FID-predicted response factors to extend method capabilities and information potential

Abstract

This paper focuses on several methodological aspects in the quantitation of volatiles in solid samples by headspace solid phase micro-extraction (HS-SPME) combined with gas chromatography and parallel detection by flame ionization detector and mass spectrometry (GC-FID/MS). Informative volatiles, including key odorants and process markers, from single-origin cocoa samples (Colombia, Ecuador, Mexico, Sao Tomè, and Venezuela) were captured at two processing stages along the chocolate production chain (nibs and cocoa mass). Accurate quantitation was achieved by multiple headspace extraction (MHE) in headspace linearity conditions and by external calibration. Quantitative results on selected analytes (3-hydroxy-2-butanone, 2-heptanol, 2,3,5-trimethylpyrazine, 2-ethyl-3,6-dimethylpyrazine, ethyl octanoate, benzaldehyde, 2-methylpropionic acid, 3-methylbutyric acid, ethyl phenylacetate, 2-phenylethyl acetate, guaiacol, 2-phenylethanol, and (E)-2-phenyl-2-butenal) provided reliable information about the key sensory notes of cocoa intermediates (odor activity values) and their origin specificities. Additional information about analytes release by the solid environment (cocoa nibs, mass, and powders) was achieved by modeling decay curves. Parallel detection by MS and FID enabled quantitative cross-validation, and FID-predicted relative response factors (RRFs) extended method quantitation capabilities to additional compounds that were not subjected to an external calibration procedure: 3-methylbutyl acetate (isoamyl acetate), 2-heptanone, heptanal, 2-nonanone, γ-butyrolactone, octanoic acid, 2-ethyl-5(6)-methylpyrazine, phenylacetic acid, phenol, 2-acetyl pyrrole, and 2,3-dihydro-3,5-dihydroxy-6-methyl(4H)-pyran-4-one. This procedure extends method capabilities and information potential with great consistency.