Quantitation Method for Polyfunctional Thiols in Hops (Humulus lupulus L.) and Beer Using Specific Extraction of Thiols and Gas Chromatography–Tandem Mass Spectrometry

Abstract

A method for the quantitation of six polyfunctional thiols, 4-methyl-4-sulfanylpentan-2-one (4MSP), 3-sulfanyl-4-methylpentan-1-ol (3S4MP), 3-sulfanyl-4-methylpentyl acetate (3S4MPA), 3-sulfanyl-3-methylbutan-1-ol (3S3MB), 3-sulfanylhexan-1-ol (3SH), and 3-sulfanylhexyl acetate (3SHA), in hops and beer without organic mercury compounds was developed. The method employed specific extraction of thiols using a silver ion solid phase extraction (SPE) cartridge and gas chromatography-tandem mass spectrometry (GC-MS/MS). For all thiols analyzed, good linearity was achieved by adding thioglycerol as an analyte protectant. Recoveries for both hops (74-100%) and beer (79-113%) were acceptable, and the repeatability for both was also good (relative standard deviations of 2.8-8.4%). The limits of detection for the six polyfunctional thiols were below their odor thresholds in beer. The method was applied to quantitation of hops and beer flavored with thiol-containing hop varieties. Due to their detected levels and level variations in different beers, 4MSP and 3S4MP are thought to be important polyfunctional thiols for the characteristic flavor of hop varieties.

Analysis of Potent Odour-Active Volatile Thiols in Foods and Beverages with a Focus on Wine

“…For example, the potential of novel molecularly imprinted polymer SPME fibres for volatile analysis keeps growing [80], and it seems plausible that SPME fibre coatings could also be customised for volatile thiol extraction. The same can be suggested for SPE sorbent materials, given the recent example of an Ag + based SPE cartridge that has been proposed for volatile thiol analysis [28].…”

“…Another selective extraction method is based on the high affinity between thiols and Ag + (Table 1, Entry 5) [28]. Using commercially available Ag + based SPE cartridges (Meta-Sep IC-Ag), volatile thiols in the organic extracts of beer and hops were retained and then eluted with thioglycerol in CH 2 Cl 2 [28]. Ag + extraction is advantageous when compared to Hg + , because it avoids the use of toxic mercury and the SPE cartridges can be commercially obtained.…”

“…PTI has great extracting and concentrating ability for relatively large volumes of sample (8 mL) [21,56], and cool-on-column injection is preferred for labile analytes [56], hence they are both suitable for the analysis of trace to ultra-trace volatile thiols. The enhancement of thermal stability of analytes after derivatisation allows for the use of conventional injectors and injection modes for thiols, including splitless [18,19,32], large volume (20 µL) [29,30], splitless to split [33,35], TDU in splitless mode [26], and pulsed splitless [28] injection programs. After injection, most of the separations are performed in a one-dimensional GC system installed with fused silica capillary columns, either with non-polar (e.g., BPX-5 [22], DB-5ms [32]) or polar (e.g., HP-Innowax [19], DB-Wax [35]) stationary phases.…”

“…Taking 3-SH, which is probably the most evaluated thiol in wine and beer, as an example, many methods have used MS for its detection. When detected in the native form, SIM ions at m / z 134, 100, 82, and 67 [19,60] were chosen as the qualifiers and quantifier for single stage MS, whereas transitions m / z 134→82 and 100→82 were the pairs used for MRM with MS/MS [28]. If 3-SH has been derivatised, ions that were selected in EI–MS have higher m / z , for instance, 314, 181, and 133 for the PFBBr derivative [32] and 232, 187, and 132 for the ETP derivative [19].…”

“…If 3-SH has been derivatised, ions that were selected in EI–MS have higher m / z , for instance, 314, 181, and 133 for the PFBBr derivative [32] and 232, 187, and 132 for the ETP derivative [19]. The reported LOD values for 3-SH when using single stage MS were 30 ng/L [32], 69 ng/L [60], 7 ng/L [29], and 2 ng/L [30], which were higher than those values that were obtained with MS/MS (1.9 ng/L [28] and 0.7 ng/L [25]).…”