Polydextrose is a synthetic, low-calorie polysaccharide designed as a soluble dietary fiber and bulking agent, produced through thermal polymerization of glucose with minor amounts of sorbitol and citric acid to mimic the functional properties of sugar and fat in processed foods.
Molecular Structure
Polydextrose is a highly branched, non-digestible glucose polymer characterized by random glycosidic linkages, predominantly α/β-(1→6), with additional 1→2, 1→3, and 1→4 bonds. It exhibits an average degree of polymerization of approximately 12 (range 2–120; Mw ≈ 2000 Da). This structural irregularity, in contrast to the crystalline organization of starch, includes less than 6% free glucose and sorbitol monomers and approximately 0.3% citric acid residues. As a result, polydextrose is resistant to hydrolysis by human pancreatic enzymes but remains fermentable by intestinal microbiota.
Production and Functional Properties
Industrial production is based on bulk melt polycondensation at 160–200 °C under reduced pressure, typically using a formulation of 89% glucose, 10% sorbitol, and 1% citric acid as a catalyst. Water is removed during the reaction to yield an amorphous, off-white powder, which is subsequently purified by ion-exchange and hydrogenation steps to obtain food-grade products. Polydextrose is highly soluble in water (>80 g/100 mL), exhibits low solution viscosity, and has a neutral sensory profile. It is stable over a broad pH range (3–7) and at temperatures up to 150 °C, displays humectant properties useful for water activity control, and shows a glass transition temperature above 120 °C, contributing to chewy or soft textures in food matrices. Its physiological energy value is approximately 1 kcal/g, derived mainly from partial colonic fermentation.
