Thiamine (vitamin B1) is an essential micronutrient in the human diet, found both naturally and as a fortification ingredient in many foods and supplements. However, it is susceptible to degradation due to heat, light, alkaline pH, and sulfites, among effects from other food matrix components, and its degradation has both nutritional and sensory implications as in foods. Thiamine storage stability in solution was monitored over time to determine the effect of solution pH and thiamine concentration on reaction kinetics of degradation without the use of buffers, which are known to affect thiamine stability independent of pH. The study directly compared thiamine stability in solutions prepared with different pHs (3 or 6), concentrations (1 or 20 mg/mL), and counterion in solution (NO3−, Cl−, or both), including both commercially available salt forms of thiamine (thiamine mononitrate and thiamine chloride hydrochloride). Solutions were stored at 25, 40, 60, and 80 °C for up to one year, and degradation was quantified by high-performance liquid chromatography (HPLC) over time, which was then used to calculate degradation kinetics. Thiamine was significantly more stable in pH 3 than in pH 6 solutions. In pH 6 solutions, stability was dependent on initial thiamine concentration, with the 20 mg/mL thiamine salt solutions having an increased reaction rate constant (kobs) compared to the 1 mg/mL solutions. In pH 3 solutions, kobs was not dependent on initial concentration, attributed to differences in degradation pathway dependent on pH. Activation energies of degradation (Ea) were higher in pH 3 solutions (21–27 kcal/mol) than in pH 6 solutions (18–21 kcal/mol), indicating a difference in stability and degradation pathway due to pH. The fundamental reaction kinetics of thiamine reported in this study provide a basis for understanding thiamine stability and therefore improving thiamine delivery in many foods containing both natural and fortified thiamine.

中文翻译：

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pH 值和浓度对溶液中单硝酸硫胺和氯化硫胺盐酸盐的化学稳定性和反应动力学的影响

硫胺素（维生素 B1）是人类饮食中必不可少的微量营养素，在许多食品和补充剂中天然存在，也可作为强化成分。然而，由于热、光、碱性 pH 值和亚硫酸盐以及其他食物基质成分的影响，它很容易降解，并且它的降解与食物一样具有营养和感官影响。随着时间的推移监测溶液中硫胺素的储存稳定性，以确定溶液 pH 值和硫胺素浓度对降解反应动力学的影响，而无需使用缓冲液，已知缓冲液会影响硫胺素稳定性而与 pH 无关。该研究直接比较了用不同 pH 值（3 或 6）、浓度（1 或 20 毫克/毫升）和溶液中的反离子（NO3-、Cl- 或两者）制备的溶液中硫胺素的稳定性，包括硫胺的市售盐形式（单硝酸硫胺和氯化硫胺盐酸盐）。将溶液在 25、40、60 和 80 °C 下储存长达一年，并通过高效液相色谱 (HPLC) 随时间对降解进行量化，然后用于计算降解动力学。硫胺素在 pH 3 中比在 pH 6 溶液中更稳定。在 pH 6 溶液中，稳定性取决于初始硫胺素浓度，与 1 mg/mL 溶液相比，20 mg/mL 硫胺素盐溶液具有增加的反应速率常数 (kobs)。在 pH 3 的溶液中，kobs 不依赖于初始浓度，这归因于依赖于 pH 的降解途径的差异。pH 3 溶液 (21–27 kcal/mol) 中的降解活化能 (Ea) 高于 pH 6 溶液 (18–21 kcal/mol)，表明 pH 值导致稳定性和降解途径的差异。本研究中报道的硫胺素的基本反应动力学为了解硫胺素的稳定性提供了基础，从而改善了许多含有天然和强化硫胺素的食物中的硫胺素输送。