Department of Analytical Chemistry, Institute C-1, Faculty of Chemical Engineering and Technology, Cracow University of Technology, ul. Warszawska 24, Cracow 31-155, Poland.
J Agric Food Chem. 2011 Sep 14;59(17):9612-22. doi: 10.1021/jf2020107. Epub 2011 Aug 17.
Betanidin is a basic betacyanin with a 5,6-dihydroxyl moiety which causes its high antioxidant activity. For the purpose of structural study, the enzymatic oxidation of betanidin and betanin (5-O-glucosylated betanidin), followed by chromatographic separation of the oxidation products with spectrophotometric and mass spectrometric detection (LC-DAD-MS/MS) was performed. Within the pH 4-8 range, two main oxidation peaks of betanidin were observed, betanidin quinonoid (possibly betanidin o-quinone) and 2-decarboxy-2,3-dehydrobetanidin, whereas at pH 3 only dehydrogenated and decarboxylated derivatives were detected, suggesting different stabilities of the products at different pH values. The presence of two prominent oxidation products, 2-decarboxy-2,3-dehydrobetanidin and 2,17-bidecarboxy-2,3-dehydrobetanidin, at pH 3 indicates their generation via two possible reaction routes with two different quinonoid intermediates: dopachrome derivative and quinone methide. Both reaction paths lead to the decarboxylative dehydrogenation of betanidin. Subsequent oxidation and rearrangement of the conjugated chromophoric system results in the formation of 14,15-dehydrogenated derivatives. Betanin is oxidized with generation of a quinone methide intermediate, which rearranges to 2,3-dehydro- or neoderivatives. The products of enzymatic oxidation of betacyanins thus formed are derivatives of 5,6-dihydroxyindole and related structures known as the key intermediates in melanogenesis.
甜菜因是一种具有 5,6-二羟基部分的碱性甜菜红素，这使其具有高抗氧化活性。为了进行结构研究，进行了甜菜因和甜菜红素（5-O-葡萄糖基甜菜红素）的酶促氧化，随后通过色谱分离氧化产物，并进行分光光度和质谱检测（LC-DAD-MS/MS）。在 pH 4-8 范围内，观察到甜菜因的两个主要氧化峰，甜菜因醌型（可能是甜菜因 o-醌）和 2-脱羧基-2,3-脱水甜菜因，而在 pH 3 时仅检测到脱氢和脱羧衍生物，表明在不同 pH 值下产物的稳定性不同。在 pH 3 时存在两个明显的氧化产物，2-脱羧基-2,3-脱水甜菜因和 2,17-双脱羧基-2,3-脱水甜菜因，表明它们通过两种不同的醌型中间体：多巴色素衍生物和醌甲醚，生成两种可能的反应途径： dopachrome 衍生物和醌甲醚。两条反应途径都导致甜菜因的脱羧脱氢。随后共轭发色团系统的氧化和重排导致 14,15-脱氢衍生物的形成。甜菜红素的氧化生成醌甲醚中间体，其重排为 2,3-脱氢或新衍生物。因此，甜菜红素的酶促氧化产物是 5,6-二羟基吲哚和相关结构的衍生物，这些结构被称为黑色素生成的关键中间体。
