Interactions Between Dietary Antioxidants and Plant Cell Walls

Dietary antioxidants are a chemically diverse group of compounds, however most of them are of plant origin, with major classes being polyphenols, vitamins notable vitamin C (ascorbic acid) or E (tocopherols) and carotenoids. Other molecules may carry an antioxidant effect (e.g. amino-acids, sterols, many secondary metabolites) but are not used as such in foods. Most antioxidants are naturally present in tissues where plant cell walls play an important role in structure and texture, but also lead to encapsulation and compartimentation. Interactions withplant cell walls therefore occur in extraction processes, during food processing operations that lead to tissue destructuration, or during digestion, where they may limit bioaccessibility. Five mechanisms can be identified in interactions between polyphenols and antioxidants: protection of plant cells, limit to diffusion (of soluble molecules or enzymes), bio-encapsulation, affinity for specific molecules, and chemical reactions. Bio-encapsulation of lipophilic antioxidants, and specific interactions between polyphenols, specially tannins, and polysaccharides (mechanisms detailed in chapter “Interactions between polyphenols and macromolecules: effect of tannin structure”) will be descried in more details. Among the cell wall components, pectin is particularly relevant, due to its sensibility during processing and its affinity for some antioxidants.