Digestion and Metabolism of Pectin
The key stages of digestion and metabolism of dietary fibre throughout the gastrointestinal tract is presented with a focus on the digestion of pectin. Increasing evidence shows that pectins are not simply an inert viscosity enhancing agent but possess a
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Digestion and Metabolism of Pectin Kathrin Haider and Peter Wilde
8.1 Introduction 8.1.1 P ectin as a Source of Soluble Fibre and Influence on Digestion Pectin is considered as a dietary fibre which are generally defined as carbohydrate polymers with three or more monomeric units, which are not hydrolysed by the endogenous enzymes in the small intestine of humans and are either naturally occurring in the food as consumed or have been shown to have a beneficial physiological effect (Codex Alimentarius Commission 2009). When isolated and added to food during processing, pectin is approved as dietary fibre by the FDA due to its ability to maintain normal blood cholesterol levels and additionally by EFSA due to its proven ability to reduce post-prandial rise in blood glucose (EFSA Panel on Dietetic Products, U.S. Food and Drug Administration 2018). Soluble dietary fibres are regarded as beneficial for health for a number of reasons, firstly their ability to retain water and to resist digestive enzymes in the upper gut, which is thought to slow down the digestion and absorption of glucose and lipids. In the lower gut, they are fermented by the gut microbiota to produce beneficial metabolites such as short chain fatty acids (SCFA). This fermentation can lead to the proliferation of beneficial microbiota, and the metabolites provide nutrition for the gut epithelium, are thought to mitigate the development of colon cancer and act as immunosuppressors. They also act as signalling molecules to improve a range of physiological functions including insulin sensitivity, lipid metabolism and satiety. The molecular structure of pectin is thought to be important for its ability to interact with cell surface proteins such as lectins, which are important for cell signalling and anti-cancer activity. K. Haider · P. Wilde (*) Quadram Institute Bioscience, Norwich Research Park, Norwich, UK e-mail: [email protected] © Springer Nature Switzerland AG 2020 V. Kontogiorgos (ed.), Pectin: Technological and Physiological Properties, https://doi.org/10.1007/978-3-030-53421-9_8
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K. Haider and P. Wilde
Low molecular weight, unbranched glycan chains with the appropriate sugar composition are more able to interact with surface bound proteins and trigger responses (Maxwell 2015). Even though pectins are not metabolised by humans per se, they interfere with physiological processes at many stages of the digestion like gastric emptying, entero-hepatic circulation, absorption of nutrients and intestinal permeability and fermentation products (Popov 2016). Since intrinsic digestive enzymes will not hydrolyse pectin, pectin gels find use in the delivery of probiotics (Cabrera et al. 2011; Naqash et al. 2017).
8.1.2 Sources of Pectin Pectins are very common in a normal western diet with consumption reported as around 4–5 g each day (Willats et al. 2006) or 2.5 ± 1.2 g/day in postmenopausal women aged 50–79 years in the US (Navarro et al. 2016). This is not only due to a high abundance in fruits and vegetables, but also because
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