First Evidence of the Cysteine and Glutathione Conjugates of 3-Sulfanylpentan-1-ol in Hop (Humulus lupulus L.)

After evidence of the cysteinylated precursors of 3-sulfanyl-4-methylpentan-1-ol (Cys-26) and 3-sulfanylhexan-1-ol (Cys-23) in hop, S-glutathione precursors (G-23 and G-26) were recently discovered in different dual-purpose hop varieties. Because free 3-sulfanylpentan-1-ol (21) has also been detected in hop, the present work aimed to identify its potential precursors. The compounds S-3-(1-hydroxylpentyl)cysteine (Cys-21) and S-3-(1-hydroxylpentyl)glutathione (G-21) were first synthesized and characterized by nuclear magnetic resonance and high-resolution mass spectrometry. High-performance liquid chromatography-positive electrospray ionization-tandem mass spectrometry evidenced both for the first time in hop. Both S conjugates were further quantitated in six hop samples: the well-known Saaz, Amarillo, Citra, Hallertau Blanc, Nelson Sauvin, and Polaris. Similar to G-23, G-21 appeared ubiquitous to all varieties. Of all of the samples investigated here, Citra (harvest 2017) emerged as the richest in G-21, with 18 mg/kg of dry matter. Cys-21 was found in all samples at a much lower concentration (up to 0.2 mg/kg of dry matter in Polaris, harvest 2017). Model media spiked with Cys-21 or G-21 allowed for the confirmation that brewing yeast is able to release free compound 21 from them.