Thiol S-Conjugate Profiles: A Comparative Investigation on Dual Hop and Grape Must with Focus on Sulfanylalkyl Aldehydes and Acetates Adducts
Cysteinylated and glutathionylated precursors of sulfanylalkyl alcohols have been extensively studied in hop and grape matrices, in contrast to those of sulfanylalkyl aldehydes and sulfanylalkyl acetates. Here, cysteinylated and glutathionylated adducts of 3-sulfanylpentanal (Cys-3SPal and G-3SPal), 3-sulfanylhexanal (Cys-3SHal and G-3SHal), 3-sulfanylpentyl acetate (only Cys-3SPA), and 3-sulfanylhexyl acetate (Cys-3SHA and G-3SHA) were first synthesized. Next, the occurrence of these compounds was studied by RP-HPLC-ESI(+)-MRM and apotryptophanase-GC-PFPD in a few dual hops and Belgian grape must samples. None of the Cys-adducts of 3-sulfanylalkyl aldehydes were detected in hop or grape extracts, while G-3SPal was identified for the first time in a natural matrix. Concentrations ranging from 3 to 15 mg/kg were found in several hop varieties, including Citra, Mandarina Bavaria, Mosaic, Nelson Sauvin, Polaris, and Saaz, whereas G-3SHal was detected (below the quantitation limit) only in the four latters. As for esters, Cys-3SPA was found in hop (4 mg/kg in Mosaic), while G-3SHA was detected only in grape extracts (Belgian Chardonnay and Johanniter). Besides the ubiquitous G-3SHol, G-3SPol was identified here for the first time in grape must (up to 7 mg/kg in Johanniter).