Chemical stability and reaction kinetics of two thiamine salts (thiamine mononitrate and thiamine chloride hydrochloride) in solution

Abstract

Two types of thiamine (vitamin B) salts, thiamine mononitrate (TMN) and thiamine chloride hydrochloride (TClHCl), are used to enrich and fortify food products. Both of these thiamine salt forms are sensitive to heat, alkali, oxygen, and radiation, but differences in stability between them have been noted. It was hypothesized that stability differences between the two thiamine salts could be explained by differences in solubility, solution pH, and activation energies for degradation. This study directly compared the stabilities of TMN and TClHCl in solution over time by documenting the impact of concentration and storage temperature on thiamine degradation and calculating reaction kinetics. Solutions were prepared containing five concentrations of each thiamine salt (1, 5, 10, 20, and 27 mg/mL), and three additional concentrations of TClHCl: 100, 300, and 500 mg/mL. Samples were stored at 25, 40, 60, 70, and 80 °C for up to 6 months. Degradation was quantified over time by high-performance liquid chromatography, and percent thiamine remaining was used to calculate reaction kinetics. First-order reaction kinetics were found for both TMN and TClHCl. TMN degraded significantly faster than TClHCl at all concentrations and temperatures. For example, in 27 mg/mL solutions after 5 days at 80 °C, only 32% of TMN remained compared to 94% of TClHCl. Activation energies and solution pHs were 21-25 kcal/mol and pH 5.36-6.96 for TMN and 21-32 kcal/mol and pH 1.12-3.59 for TClHCl. TClHCl degradation products had much greater sensory contributions than TMN degradation products, including intense color change and potent aromas, even with considerably less measured vitamin loss. Different peak patterns were present in HPLC chromatograms between TMN and TClHCl, indicating different degradation pathways and products. The stability of essential vitamins in foods is important, even more so when degradation contributes to sensory changes, and this study provides a direct comparison of the stability of the two thiamine salts used to fortify foods in environments relevant to the processing and shelf-life of many foods.

Amorphization of Thiamine Chloride Hydrochloride: Effects of Physical State and Polymer Type on the Chemical Stability of Thiamine in Solid Dispersions

“…Sample pH has been reported to be an important factor affecting thiamine stability in solutions [ 12 , 18 ]. As shown in Table 4 , the pH levels of pre-lyophilized solutions of 5TClHCl:95PVP and 5TClHCl:95PEC were 3.8 and 3.5, respectively, which are both below the food-relevant pK a of thiamine (4.8).…”

“…As shown in Table 4 , the pH levels of pre-lyophilized solutions of 5TClHCl:95PVP and 5TClHCl:95PEC were 3.8 and 3.5, respectively, which are both below the food-relevant pK a of thiamine (4.8). A speciation plot of thiamine illustrates that the more stable protonated (pyrimidine N1) species was dominant at both of these pH values [ 12 ]. Although the fraction of protonated species was slightly higher in 5TClHCl:95PEC solutions (~95%) than in 5TClHCl:95PVP solutions (~91%), this slight difference in fraction of protonated species was not likely to have caused the substantial difference in chemical stability between PEC- and PVP-based dispersions, with the dispersions containing 96% and 76% thiamine, respectively, following 56 days of storage at 11% RH and 60 °C ( Figure 4 ).…”

“…The following temperature and RH conditions were chosen as storage treatments: 11% RH and 30, 40, 50, and 60 °C. Increasing temperature conditions at 11% RH were chosen in order to enable reaction kinetics calculations of thiamine degradation, similar to studies by Voelker, Miller, Running, Taylor, and Mauer [ 12 ]. RH was controlled by using saturated salt solutions in desiccators, with the water activity of the salt solutions verified by measurement using an AquaLab 4TE water activity meter (Decagon Devices Inc., Pullman, WA, USA).…”

“…Both natural and synthetic salt forms of thiamine are known to degrade via oxidation/reduction reactions and interactions with other ingredients [ 7 , 9 , 10 ]. In addition to loss of vitamin activity, thiamine degradation is also known to produce sulfur-containing degradation products that can contribute significant odors, thereby negatively affecting sensory perception, with one known degradation compound, bis(2-methyl-3-furyl) disulfide, having one of the lowest odor thresholds of any organic compound in water (0.02 parts per trillion) [ 11 , 12 ]; thus, nutritional availability is not the only consideration when monitoring thiamine degradation, even when present in relatively low amounts in food or supplement products.…”

Degradation Products of Tryptophan in Cell Culture Media: Contribution to Color and Toxicity

“…The color change associated with the degradation of some cell culture media components has been reported, such as for the Maillard reaction of amino acids (AAs) and glucose, which leads to highly oxidized, highly colored organic compounds [9][10][11]. Other common organic CCM components shown to produce colored degradation products are thiamine [12,13] and tryptophan [14,15]. The instability of CCM components is not only an issue for color production, but also for the potential production of toxic degradation products, which would be detrimental to cell culture.…”