Factors Involved in the Formation of Two Precursors of Dimethylsulfide During Malting

Abstract

L-Methionine S-methyltransferase (SMM synthetase) was found to be present in barley, and its activity increased almost two-fold during germination. The level of this enzyme in barley was positively correlated with the levels of S-methylmethionine (SMM) in green malt (r = 0.79, P ≤ 0.01), kilned malt (r = 0.85, P ≤ 0.01), and the level of dimethylsulfoxide (DMSO) in kilned malt (r = 0.76, P ≤ 0.05). SMM primarily was synthesized during germination. The level of SMM in green malt seemed to determine the level of SMM (r = 0.97, P ≤ 0.005) and DMSO (r = 0.80, P ≤ 0.01) in kilned malt. Barley genotype, row type, and malt modification also were major factors associated with the levels of SMM and DMSO in malt. Steeping and germination temperature influenced the synthesis and levels of SMM in green malt, but kilning temperature determined the final levels of SMM and DMSO in malt. SMM started to degrade into dimethylsulfide (DMS) at 70°C. DMSO formation began at the same time. SMM was almost completely degraded at 110°C, while levels of DMSO increased under these higher temperatures. It was concluded that the level of SMM synthetase activity in barley determined the level of SMM in green malt, which in turn influenced the concentrations of both SMM and DMSO in kilned malt.