Interaction between black mulberry pectin-rich fractions and cyanidin-3-O-glucoside under in vitro digestion

Pectic polysaccharides are potential candidates to enhance the stability of anthocyanins, and the interactions between pectin and anthocyanin are structure-dependent. In this study, mulberry pectic polysaccharides, extracted through different methods, and mulberry cyanidin-3-O-glucoside (C3G) were used to prepare complexes whose characterization and in vitro digestive properties were then investigated. The extracted mulberry polysaccharides were mostly made up of the monosaccharides galacturonic acid, glucose, mannose, galactose and rhamnose. The ratio of rhamnose to galacturonic acid (Rha/GalA) for the samples ranged from 0.06 to 0.56. The results showed that the main component of mulberry polysaccharide was pectin, and that the different preparation methods changed its chemical structure. Subsequently, different polysaccharide-C3G complexes were prepared: hot water-extracted polysaccharide-C3G (HWC), high temperature and pressure-extracted polysaccharide-C3G (HTPC), pectinase-extracted polysaccharide-C3G (PEC), cellulase-extracted polysaccharide (CEC)-C3G, pectin lyase-extracted polysaccharide-C3G (PLC) and compound enzyme-extracted polysaccharide-C3G (MC). Physicochemical analysis showed that the six pectic polysaccharide complexes bound to C3G to different degrees and in different ways. The binding affinities occur through ionic force, hydrogen bonding and hydrophobic interaction during digestion. Cellulase-assisted extraction greatly improved the binding capacity of obtained mulberry polysaccharides to C3G. High temperature and pressure-extracted mulberry polysaccharide, which was constituted of high proportion of galacturonic acid, greatly improved the bio-accessibility of C3G in small intestine. This study provides a theoretical basis from which to investigate the interaction mechanisms of anthocyanin and mulberry pectins during gastrointestinal digestion. The consequent influence of the interactions on fermentation patterns of the complex remains to be elucidated.