Severe browning often occurs in Multivitamin Iron Oral Solution during storage, which directly leads to the decline of product quality. To clarify the main mechanism of browning in this preparation, the contents of 5-hydroxymethylfurfural (5-HMF) and carbohydrates, as well as the relevant characteristic parameters such as color and fluorescence, were determined at different storage times in this study. Subsequently, four reaction models, namely sucrose-lysine, sucrose-citric acid, sucrose-niacin, and sucrose-folic acid, were constructed according to the formulation of the preparation to systematically investigate the effects of each system on browning. The results showed that the sucrose-lysine model was the main color-forming reaction system of the preparation. Citric acid could significantly promote the hydrolysis of sucrose to produce two reducing sugars, glucose and fructose, which not only provided sufficient substrates for the Maillard reaction (MR), but also led to the massive accumulation of 5-HMF. Further analysis revealed that heating temperature and heating time were significantly positively correlated with the contents of 5-HMF, browning index (BI), color density (CD), and reducing sugars in the solution, while significantly negatively correlated with sucrose content (p < 0.05). Two fractions, P1 and P2, were isolated by Sephadex LH-20 column chromatography. Among them, P1 with a molecular weight of 61,660 Da was identified as the key fluorescent color-forming component, whose ultraviolet and fluorescence characteristics were basically consistent with those of Multivitamin Iron Oral Solution. Ultra-performance liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry (UPLC-Q-TOF-MS/MS) analysis confirmed that P1 contained characteristic fragments of conjugated unsaturated structure, which was the key chromophore responsible for its fluorescence properties. In summary, this study explored the main browning mechanism of Multivitamin Iron Oral Solution. It was found that after citric acid catalyzed the hydrolysis of sucrose, the generated reducing sugars underwent Maillard reaction with lysine to produce fluorescent color-forming substances, and heat treatment significantly aggravated the browning process. The results of this study not only provide a solid theoretical basis for optimizing the preparation process and improving the storage stability of Multivitamin Iron Oral Solution, but also offer an important reference for the research on the browning mechanism and stability of other sugar-containing liquid preparations.
Su et al. (Thu,) studied this question.