| Ferulic acid is a phenolic acid widely found in plant cell walls. Because of its outstanding antioxidant capacity and free radical scavenging effect, it became the new research focus in medicine, food and especially cosmetics industries in last decades. Ferulic acid shows good stability in solid-state form, while it can easily degrade in aqueous solution when exposed to light or stored at high temperature/pH. In earlier studies, we found that the introduction of ferulic acid into the cosmetics formulas could have serious impact on the system, which would not only make the formulas unstable but also ferulic acid itself would degrade soon enough into byproducts with dark color and off flavor. These greatly affect the aspect and the quality of the cosmetics formulas, and the production of the by-products would probably induce serious safety problems, thereby limiting the application of ferulic acid in cosmetics industry. To our knowledge, no researches on stability or dgradation pathways of ferulic acid in cosmetics environment were ever reported. This study was undertaken to observe the stability of ferulic acid in cosmetics formulas and to find out the influence of different factors, like light, pH and temperature, on its degradation. High-performance liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) were used to mesure ferulic acid’s degradation products. These results provided evidences to elucidate the mechanism of ferulic acid’s degradation, and then might help us to find out a way to stop the degradation progress in formula.There are four addresses in my study:1. Studies on the stabilities of ferulic acid in cosmetics formulasStability studies of whitening active-ferulic acid in cosmetics environment were effectuated according to L"Oreal standard stability test protocol. The compatibilities of ferulic acid with different formulas were evaluated according to the changes of aspect, pH, viscosity and microstructure in 2 months. The results showed that 1% of ferulic acid could have serious impact to the stabilities of formulas. Different types of formulas have no significant differences. The stabilities were much improved after the water phase of the formulas were meliorated, and the yellowing and off flavor problems were ameliorated to acceptable levels.2. Studies of influences of different factors on ferulic acid’s degradationThe influences of different factors, like light, pH and temperature, on ferulic acid’s degradation in cosmetics environment were observed. We used HPLC method to quantitate the concerntrations of ferulic acid under different conditions at different time points, and different concerntration-time curves were obtained. The results showed that high pH and high temperature favored the degradation of ferulic acid, and different solvents had different influences on its decomposition. It was observed that ferulic acid had a better stability in alcoholic solutions than in the aqueous ones, which was consistant with the results of earlier studies. By studying these results, we further defined the stabilization conditions and formulation guidelines of ferulic acid in formulas.3. Separation and characterization of ferulic acid’s degradation productsBy simulating water phase of cosmetics formula, we prepared several different ferulic acid solutions. Their degradation products were separated by column chromatography and then characterized by NMR respectively. The results obtained were that the degradation products of ferulic acid in different solutions or at different pH were approximately the same. The two main degradation products were 4-hydroxy-3-methoxystyrene and its dimer 1,3-bis (4-hydroxy-3-methoxyphenyl)-1-butene. Therefore we hypothesized that one possible degradation pathway of ferulic acid was:ferulic acid was heated to decarboxylate into 4-hydroxy-3-methoxystyrene, and its dimer 1,3-bis (4-hydroxy-3-methoxyphenyl)-1-butene. The characterization of degradation products is very helpful to the research on the mechanism of ferulic acid’s degradation.4. Studies on the degradation pathways of ferulic acidA specific and stable high-performance liquid chromatography method which can respectively quantitate the trans-ferulic acid, cis-ferulic acid,4-hydroxy-3-methoxystyrene and its dimer 1,3-bis (4-hydroxy-3-methoxyphenyl)-1-butene in one injection was developed in this part of study. By studying the dynamic patterns of ferulic acid and its degradation products, we better understood the degradation mechanism of ferulic acid in solutions. The results showed that alkaline environment would speed up the decarboxylation process, while different types of bases have different influences on the degradation. In this part of study, we compared three differnet bases which were commonly used in cosmetics, the sodium hydroxide, potassium hydroxide, and triethanolamine, and found that sodium hydroxide, potassium hydroxide and metal ions could promote the formation of 1,3-bis (4-hydroxy-3-methoxyphenyl)-1-butene, while the triethanolamine had no such exclusive catalysis. And the triethanolamine had a higher acceleration effect on ferulic acid’s degradation than the other two bases. Therefore, we concluded that when we formulated with ferulic acid, the pH of the formula should be as low as possible, and at the same time, adding bases or metal ions into the formula should be avoided. |
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