Study on the interactions between oral mucin and cyanidin 3-O-glucoside: the effect of oxidized quinone

Abstract

Abstract Cyanidin 3-O-glucoside (C3G) is believed to combine with oral mucin, thus impairing oral lubrication and leading to the development of oral astringency. When C3G is oxidized into cyanidin 3-O-glucoside quinone (C3GQ), it might covalently interact with cysteine of mucin to enhance astringency. Herein, their detailed interactions at the molecule level were characterized through spectroscopy, isothermal titration calorimetry and determination of free amino and sulfhydryl groups. The results showed that hydrogen bond and van der Waals force were the predominant non-covalent interactions. Furthermore, C3GQ could additionally bind to mucin by forming C-N and C-S bonds since the amino and sulfhydryl groups of mucin decreased by 0.48 mmol/g and 4.14 µmol/g after reacting with C3GQ. Besides, C3GQ had stronger interaction with mucin as the exothermic value of Muc-C3GQ (2513 KJ/mol) was larger than Muc-C3G (60.4 KJ/mol). These findings may explain the phenomenon of increased astringency of anthocyanins after being oxidized into quinones.