Introducing inulin-type fructans

Abstract

Inulin is a generic term to cover all beta(2-->1) linear fructans. Chicory inulin is a linear beta(2-->1) fructan (degree of polymerisation (DP) 2 to 60; DPav=12), its partial enzymatic hydrolysis product is oligofructose (DP 2 to 8; DPav=4), and by applying specific separation technologies a long-chain inulin known as inulin HP (DP 10 to 60; DPav=25) can be produced. Finally, a specific product known as oligofructose-enriched inulin is obtained by combining chicory long-chain inulin and oligofructose. Because of the beta-configuration of the anomeric C2 in their fructose monomers, inulin-type fructans resist hydrolysis by intestinal digestive enzymes, they classify as 'non-digestible' carbohydrates, and they are dietary fibres. By increasing faecal biomass and water content of the stools, they improve bowel habits, but they have characteristic features different from other fibres. They affect gastrointestinal functions not because of their physico-chemical properties but rather because of their biochemical and physiological attributes. In the colon, they are rapidly fermented to produce SCFA that are good candidates to explain some of the systemic effects of inulin-type fructans. Fermentation of inulin-type fructans in the large bowel is a selective process; bifidobacteria (and possibly a few other genera) are preferentially stimulated to grow, thus causing significant changes in the composition of the gut microflora by increasing the number of potentially health-promoting bacteria and reducing the number of potentially harmful species. Both oligofructose and inulin are prebiotic. They also induce changes in colonic epithelium stimulating proliferation in the crypts, increasing the concentration of polyamines, changing the profile of mucins, and modulating endocrine as well as immune functions. From a nutrition labelling perspective, inulin-type fructans are not only prebiotic dietary fibres; they are also low-calorie carbohydrates [6.3 kJ/g (1.5 kcal/g)]. Supported by the results of a large number of animal studies and human nutrition intervention trials, the claim 'inulin-type fructans enhance calcium and magnesium absorption' is scientifically substantiated, but different inulin-type fructans have probably a different efficacy (in terms of effective daily dose), the most active product being the oligofructose-enriched inulin. A series of animal studies demonstrate that inulin-type fructans affect the metabolism of lipids primarily by decreasing triglyceridaemia because of a reduction in the number of plasma VLDL particles. The human data largely confirm the animal experiments. They demonstrate mainly a reduction in triglyceridaemia and only a relatively slight decrease in cholesterolaemia mostly in (slightly) hypertriglyceridaemic conditions. Inulin appears thus eligible for an enhanced function claim related to normalization of blood triacylglycerols. A large number of animal data convincingly show that inulin-type fructans reduce the risk of colon carcinogenesis and nutrition intervention trials are now performed to test that hypothesis in human subjects known to be at risk for polyps and cancer development in the large bowel.