Identification of Thiols in Yellow Onion (Allium cepa L.) Using Solvent Vented Large Volume Injection GC‐MS

Abstract

Thiols are often highly odor active molecules and as such can significantly contribute to aroma while being present at extremely low concentrations. This paper details the identification of thiols in yellow onion juice by solvent extraction followed by thiol enrichment using a mercuric agarose gel column. Due to the inherent thermal instability and low concentrations of thiols in onion, chromatographic analysis utilized larger volume solvent elimination injections. New sulfur compounds in onion included 1,1-propanedithiol, bis-(1-sulfanylpropyl)-sulfide, 1-methylsulfanyl-1-propanethiol, 1-propylsulfanyl-1-propanethiol, and 1-allylsulfanyl-1-propanethiol. A discussion on the potential route of formation for each compound is included along with the orthonasal and retronasal evaluations of the synthesized molecules. This work investigated and identified 5 newly identified compounds present in onions that can impart onion character at low concentrations levels.

Mechanisms underlying the formation of main volatile odor sulfur compounds in foods during thermal processing

“…The characteristic pungent odor of garlic and the tear‐inducing properties of onion primarily result from S ‐alkyl cysteine and its oxidation product, S ‐alkyl cysteine sulfoxide (like alliin) (Ferioli et al., 2022). S ‐Alkyl cysteine sulfoxide is the oxidation product of S ‐alkyl cysteine, which is synthesized inside plant bodies through cysteine by γ‐glutamyl transpeptidase, as illustrated in Figure S1 (Wermes et al., 2017). During processing, the two compounds are interconverted by oxidation (Fenton reaction, ferrous ions, and hydrogen peroxide) or reduction (thiols, R‐SH) (Figure 2b).…”

“…Nucleophilic substitution is a key pathway by which hydrogen sulfide generates thiols, alkyl sulfurs, and thiophenes. The common reactants (functional groups) in substitution reactions are alcohols (C–O), sulfenic acid (S–O), and furans (C–O) (Wermes et al., 2017). Oxygen is a common element in these groups due to the large difference in electronegativity between oxygen and carbon or sulfide.…”