Enzymatic release of odourant polyfunctional thiols from cysteine conjugates in hop

Polyfunctional thiols are contributors to the hop varietal aroma of beer. Besides free thiols, a cysteine-S-conjugate has recently been shown to be an additional component of the thiol potential of hop. Such cysteine adducts investigated here in four hop cultivars and in different hop forms. Hop hydroalcoholic extracts were purified on a cation exchanger and subjected to apotryptophanase beta-lyase activity. The Cascade hop variety exhibited the highest bound 3-sulphanylhexan-1-ol (grapefruit-like) potential, while both Tomahawk and Nelson Sauvin cultivars were confirmed to be important sources of bound 3-methyl-2-butene-1-thiol (skunky-like), 3-sulphanylpentan-1-ol and 4-sulphanyl-4-methylpentan-2-one (box-tree-like). Surprisingly, hop CO2 extracts proved to contain cysteine conjugates. Although related, the concentrations of cysteine-bound thiols in hop are not strictly correlated to the amounts of free volatiles found in the derived beers. Copyright (C) 2013 The Institute of Brewing & Distilling