Concepts Important in Understanding the Health Benefits of Phenolics in Fruits and Vegetables: Extractable and Non-Extractable Phenolics and the Influence of Cell Wall Polysaccharides.

The health benefits associated with a diet high in fruits and vegetables are well established and fruits and vegetables are a key source of phenolic compounds. Phenolic compounds have been shown to demonstrate antioxidant, anti-inflammatory, and anti-carcinogenic activities. However in order to provide health benefits , these compounds must be bioaccessible and bioavailable in the body after ingestion. Evidence is emerging that demonstrates the importance of plant cell wall polysaccharides as a key factor affecting the bioaccessibility and consequent bioavailability of phenolics. Also, the health benefits of phenolics does depend on their concentration in fruits and vegetables and the phenolic content in fruits and vegetables has been commonly under-reported due to the aqueous organic extraction method typically used. Determination of the extractable and non-extractable phenolics content using a more complete extraction method is necessary to obtain accurate measurements of phenolics in foods. This review discusses the following: the concepts of extractable and non-extractable phenolics in fruits and vegetables; the influence of cell wall polysaccharides on the bioaccessibility of phenolic compound including a discussion of the types of polysaccharide-phenolic interactions; an examination of the release of phenolics from polysaccharides during simulated gastrointestinal digestion; and an examination of how polysaccharides may influence the uptake/bioavailability of phenolics. The aim of the review paper is to stimulate increased research efforts in the area of polysaccharide-phenolic interactions and their consequences on human health.