How do the water-soluble cell wall polysaccharides contribute to formation of complexes with condensed tannins during processing?

Consequences of polyphenol-polysaccharide interactions are far reaching in food processing, which could cause astringency loss in fruits and produce non-extractable polyphenols, and their complexes can be fermented by colon microbiota. Water-soluble polysaccharides (especially pectins) have a high affinity for polyphenols. Procyanidins, condensed tannins, are polymers and oligomers of flavan-3-ol units, which presence in fruit and vegetables is related to protective health effects. While water-soluble cell wall polysaccharides share structural determinants and interaction mechanisms with procyanidins, a systematic study of the effects of their macromolecular structure and composition is still missing. To study the structure/property relationships, we modulated the structures of these water-soluble polysaccharides, that is, pectins and hemicelluloses from different sources were prepared and further modified under different conditions to obtain different glycosidic composition, molecular weights, branching patterns and degrees of substitution. The interactions between polysaccharides and procyanidins are described by UV-visible spectroscopy, isothermal titration calorimetry, HPSEC and computational simulation. Pectins with high linearity and homogalacturonan content, had higher affinity and aggregation capacities with procyanidins. On the contrary, rhamnogalacturonan I rich in side-chains and ferulic acid limited pectins' affinity for procyanidins. Hemicelluloses are second only to pectins in affinity for procyanidins in cell walls. Xyloglucan and xylan exhibited respectively the strongest and weakest interactions with procyanidins. The different types of arabinoxylans interacted with procyanidins in a similar way. Neither viscosity, molar mass nor side-chains influenced strongly arabinoxylan-procyanidin interactions. All water-soluble cell wall polysaccharides preferentially interact with procyanidins with higher degree of polymerization. This work promotes the design of more rational processing conditions for healthier and more nutritious foods, which provide guidance on the nutritional security, sustainability and quality of food systems. By degrading and solubilizing polysaccharides that show different structures, processing can modulate the formation of soluble complexes with procyanidins and thus influence their sensory and nutritional properties.