Inulin
Category: Heterogeneous fructose polymer
Chemical Structure: Chain-terminating glucosyl portion + repeating fructosyl portion, linked by β(2,1) bonds
Degree of Polymerization (DP): Standard inulin (DP 2–60); High-performance inulin (DP ≥10)
Plant Attribute: Alternative energy storage form besides starch
Core Applications: Functional food ingredient; Raw material for oligofructose, high fructose syrup, crystalline fructose
Introduction Of Inulin
Inulin is a heterogeneous collection of fructose polymers with a unique molecular structure: it is composed of a chain-terminating glucosyl portion and a repeating fructosyl portion, and the two parts are connected by specific β(2,1) bonds.
In terms of classification based on the degree of polymerization (DP):
- Standard inulin: Has a DP range of 2–60
- High-performance inulin: A refined product obtained by removing fractions with a DP below 10 during the manufacturing process
- Note: Some academic articles classify fractions with a DP below 10 as short-chain oligofructose, and only refer to long-chain molecules as inulin
In nature, inulin is another form of energy storage in plants besides starch. The commercial inulin products we use are extracted and refined from inulin-rich plants, which are mixtures of various fructans with a DP range of 2–60. This characteristic makes inulin an ideal functional food ingredient; it is also a high-quality raw material for producing downstream products such as oligofructose, high fructose syrup, and crystalline fructose.
Function Of Inulin
The β(2,1) bonds in the molecular structure of inulin determine that it cannot be digested by enzymes in the human digestive system, which is the core basis for its diverse functional properties, including low calorie value, dietary fiber characteristics, and prebiotic effects.
In addition to its functional advantages, inulin also has excellent application performance in food processing:
- Sensory characteristics: It is colorless and tasteless, and has little impact on the original sensory properties of food. Oligofructose has 35% of the sweetness of sucrose and a taste similar to sugar; standard inulin has a slight sweetness, while high-performance inulin is completely tasteless.
- Physical properties: Its solubility is higher than that of classic fibers. When fully mixed with liquids, inulin can form a gel and a white, creamy structure similar to fat. This structure is supported by a three-dimensional gel network composed of insoluble submicron crystalline inulin particles, which can immobilize a large amount of water and ensure good physical stability of the product. It can also improve the stability of foams and emulsions in food systems.
- Chemical properties: Different from starch, inulin is soluble in warm water and does not produce an iodine reaction. It can be hydrolyzed by acid or inulase (inulinase) to mainly produce D-fructose. Its structure is inferred to be a polysaccharide formed by the dehydration condensation of D-fructofuranose and the fructose part of sucrose through β-1,2 bonds, with a polymerization degree of 32–34.
In the medical field, inulin is also used to test the glomerular filtration capacity of the kidneys, playing an important role in clinical diagnosis.
