Influence of malt modifications on the concentrations of free phenolic acids in wheat and barley malts

Process induced changes in free phenolic acids (caffeic-, cinnamic-, p-coumaric-, ferulic-, sinapic-, and vanillic acid) in wheat and barley grain, green malts, and kiln-dried malts were analysed by means of stable isotope dilution assays (SIDAs) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Different steeping degrees, germination temperatures, and germination times were applied for malt production to study their influence on the concentrations of free phenolic acids. The most abundant free phenolic acid in wheat grain was ferulic acid (1.43 mg/kg dry mass) and vanillic acid (1.03 mg/kg dry mass) in barley grain. In wheat and barley green malts as well as in the corresponding kiln-dried malts, the amounts of some free phenolic acids increased in comparison to the grain, while others declined. Variation of the steeping degree, germination temperature, and germination time to manipulate the proteolytic and cytolytic degree of malt modification did not have a clear influence on the concentrations of free phenolic acids in kiln-dried wheat malts. However, in kiln-dried barley malts, a clear influence of the malt modifications on the concentrations of the acids was found. Especially the application of a higher steeping degree (48 %), germination temperature (18 °C), and germination time (7 days) yielded higher amounts of free phenolic acids in comparison to a lower steeping degree (42 %), germination temperature (12 °C), and germination time (5 days). Quantitation experiments revealed, for example, 1.54 mg of cinnamic acid and 4.09 mg of ferulic acid per kg dry mass of kiln-dried barley malt (highly modified malt) vs. 0.67 mg of cinnamic acid and 2.62 mg of ferulic acid per kg dry mass (undermodified malt), respectively.