Identification of bitter compounds in whole wheat bread

Bitterness in whole wheat bread can negatively influence product acceptability and consumption. The overall goal of this project was to identify the main bitter compounds in a commercial whole wheat bread product. Sensory-guided fractionation of the crust (most bitter portion of the bread sample) utilising liquid–liquid extraction, solid-phase extraction, ultra-filtration and 2-D offline RPLC revealed multiple bitter compounds existed. The compounds with the highest bitterness intensities were selected and structurally elucidated based on accurate mass-TOF, MS/MS, 1D and 2D NMR spectroscopy. Eight bitter compounds were identified: Acortatarins A, Acortatarins C, 5-(hydroxymethyl)furfural(HMF), 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP), N-(1-deoxy-d-fructos-1-yl)-l-tryptophan (ARP), Tryptophol (TRO), 2-(2-formyl-5-(hydroxymethyl-1H-pyrrole-1-yl)butanoic acid (PBA) and Tryptophan (TRP). Based on the structures of these compounds, two main mechanisms of bitterness generation in wheat bread were supported, fermentation and Maillard pathways.