Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA.
Food Funct. 2019 Sep 1;10(9):5707-5717. doi: 10.1039/c9fo01053j. Epub 2019 Aug 22.
Polymethoxyflavones (PMFs) are found almost exclusively in citrus peel and have attracted much attention due to their potential health benefits. Dried citrus peel is an important ingredient for applications in food and traditional Chinese medicine. However, the structural changes of PMFs during drying processes of citrus peel remain unknown. In this study, for the first time we discovered that four major permethoxylated PMFs, i.e. sinensetin, nobiletin, heptamethoxyflavone and tangeretin, underwent demethylation at the 5-position on the A ring of their flavonoid structures to yield corresponding 5-demethylated PMFs during the drying process of citrus peel. Our results further demonstrated that the aforementioned PMF demethylation was through two mechanisms: acid hydrolysis and enzyme-mediated catalysis. PMF demethylation in citrus peels was systematically characterized during hot-air drying (HAD), vacuum-freeze drying (VFD) and sun drying (SD). The highest PMF demethylation was obtained in SD followed by HAD and VFD. This study provided a solid scientific basis for rational control of PMF demethylation in citrus peels, which could facilitate the production of high-quality citrus peel and related products.
多甲氧基黄酮（PMFs）几乎只存在于柑橘皮中，由于其潜在的健康益处而受到广泛关注。干柑橘皮是食品和中药应用的重要原料。然而，柑橘皮干燥过程中 PMFs 的结构变化尚不清楚。在这项研究中，我们首次发现，四种主要的多甲氧基 PMFs，即橙皮素、川陈皮素、七甲氧基黄酮和桔皮素，在柑橘皮干燥过程中，其黄酮结构的 A 环 5 位发生脱甲基化，生成相应的 5-脱甲基 PMFs。我们的结果进一步表明，上述 PMF 脱甲基化是通过两种机制实现的：酸水解和酶介导的催化。在热空气干燥（HAD）、真空冷冻干燥（VFD）和自然干燥（SD）过程中，系统地研究了柑橘皮中的 PMF 脱甲基化。SD 处理得到的 PMF 脱甲基化程度最高，其次是 HAD 和 VFD。这项研究为柑橘皮中 PMF 脱甲基化的合理控制提供了坚实的科学依据，有助于生产高质量的柑橘皮及相关产品。
