Chemical stability and reaction kinetics of thiamine mononitrate in the aqueous phase of bread dough

Thiamine is a water-soluble essential micronutrient, and grains are the main source of thiamine in the human diet. Refining processes reduce thiamine content; therefore, many flours are enriched with thiamine. Further processes, such as heating (baking), destabilize thiamine. In doughs, thiamine partitions into the aqueous phase (dough liquor). The objective of this study was to document temperature effects on thiamine degradation reaction kinetics in dough liquor. Two concentrations of thiamine mononitrate (1 and 20 mg/mL) were added to dough liquor (the supernatant of centrifuged bread dough) and control solutions (water and pH 6-adjusted water). Samples were stored at controlled temperatures (25, 40, 60, 70, and 80 degrees C) for up to 6 months, and thiamine degradation was quantified over time using high-performance liquid chromatography. Thiamine degradation kinetics, including the observed reaction rate constant (k(obs)) and activation energy (E-a) of degradation, were calculated. Dough liquor ingredients stabilized thiamine in most cases when compared to the pH 6 control solutions, especially in the samples containing more thiamine. Thiamine degradation in dough liquor generally followed similar trends to those in the controls: thiamine degraded more quickly in the 20 mg/mL solutions than in 1 mg/mL solutions (with one exception), and increasing temperature led to increased thiamine degradation. However, kobs ranged from 0.0019-0.22 days(-1) in dough liquor and 0.0003-0.46 in control solutions, with differences attributed to interactions with components in the dough liquor. The E-a of thiamine degradation was similar to 90 kJ/mol in the control samples regardless of vitamin concentration but differed between vitamin concentrations in the dough liquor (95 and 60 kJ/mol in 1 and 20 mg/mL solutions, respectively), indicating that a different degradation pathway may have occurred in dough liquor. The different thiamine stability trends in dough liquor compared to control solutions indicate that food formulation has a substantial impact on the chemical behaviors of thiamine.