S-Methylmethionine is sometimes referred to as vitamin U,[3] but it is not considered a true vitamin. The term was coined in 1950 by Garnett Cheney for uncharacterized anti-ulcerogenic[4] factors in raw cabbage juice that may help speed healing of peptic ulcers.
The biological roles of S-methylmethionine are not well understood. Speculated roles include methionine storage, use as a methyl donor, regulation of SAM.[2] A few plants use S-methylmethionine as a precursor to the osmolytedimethylsulfoniopropionate (DMSP). Intermediates include dimethylsulfoniumpropylamine and dimethylsulfoniumpropionaldehyde.[5]
Beer flavor precursor in barley malt
S-Methylmethionine is found in barley and is further created during the malting process. SMM can be subsequently converted to dimethyl sulfide (DMS) during the malt kilning process, causing an undesirable flavor. Lightly kilned malts such as pilsner or lager malts retain much of their SMM content while higher kilned malt such as pale ale malt has substantially more of the SMM converted to DMS in the malt. Darker kilned malts such as Munich malt have virtually no SMM content since most has been converted to DMS. Other crystal malts and roasted malts have no SMM content and often no DMS content since the kilning also drives that compound out of the malt.[6][7]
