What It Is and How It's Made
Polydextrose is built from roughly 90% glucose, 10% sorbitol and a small amount of citric acid, heated together under vacuum in a process called melt polycondensation. The result is a highly branched polymer with glucose units joined by a mix of different bond types, rather than the single repeating bond type found in ordinary starch. That randomness in how the bonds form is what makes the finished molecule resistant to digestion.
Structure and Chain Length
Polydextrose chains vary considerably in length, from as few as two glucose units up to around 120, with an average chain length of around 12. This variability, rather than a single consistent structure, is part of why it's described as "randomly bonded" rather than built to a specific repeating pattern.
How It's Classified as Dietary Fibre
Polydextrose has its own dedicated method in Schedule 11 of the Food Standards Code (AOAC section 2000.11), alongside its own specific energy factor: 5 kJ per gram, lower than the general 8 kJ/g factor the Code assigns to dietary fibre generally. This is one of the few fibre types with a bespoke energy value written into the Code, rather than using the general dietary fibre figure.
How It Behaves in Food
Polydextrose dissolves in water and has a relatively neutral taste, used in food manufacturing partly as a bulking agent, replacing the volume that sugar or fat would otherwise provide in a reduced-sugar or reduced-fat product, while also contributing fibre.
Sources
- Australia New Zealand Food Standards Code, Schedule 11, Calculation of Values for Nutrition Information Panel
- Australia New Zealand Food Standards Code, Standard 1.2.8, Nutrition Information Requirements