Chemistry Reference
In-Depth Information
13.9 INULIN
Inulin is present in a wide range of plants, including common vegetables, fruits, and cereals.
It is a polydisperse mixture of oligomers and polymers of β-(2-1)-fructose from the fructan family
(Figure 13.4; De Leenheer and Hoebregs 1994). Native chicory inulin is extracted industrially from
the root of the chicory plant (
Cichorium intybus
) by diffusion in hot water. In general, its structure
can be represented by GF
n
, in which G stands for the glucosyl unit, F presents the fructosyl unit,
and
n
is the number of linked fructosyl units linked by β-(2-1) linkages. The DP or number of fruc-
tose units of native chicory inulin varies between 3 and 60, with an average DP of 10. Inulin can be
partially hydrolyzed by an endoinulinase, resulting in OFs, which the DP varies from 2 to 8 (average
DP = 4). OF is composed of the same fructose monomers as inulin and is a mixture of both GF
n
(the
inulin fraction containing the sucrose part) and F
n
molecules (Niness 1999).
The extensive use in the food industry is based on the nutritional and technological properties
of inulin. The technological use of inulin is based on its properties as a sugar replacer (especially in
combination with high-intensity sweeteners), a fat replacer, and a texture modiier. Inulin has very
minimal inluence on the sensory properties of a product due to its neutral taste and absence of
color. A neutral taste is colorless. The solubility of inulin increases signiicantly with temperature,
reaching 34% (w/v) at 90°C (Kim et al. 2001). The functionality of inulin depends on its effect on
water solutions at various solid levels. At lower concentrations, it can be used as a rheology modi-
ier, because it causes signiicant increase in viscosity while at a concentration of 40%-45%. An
inulin gel or crème that is irm but with a fatty creamy feel is formed. In this form, inulin is stable
in acidic conditions and at high temperatures (Murphy 2001). Upon complete dissolution in water,
inulin forms a particle gel characterized with a white creamy structure and short-range spreadabil-
ity. For these reasons, inulin is frequently used to almost completely replace fat. The created gel
is composed of a tridimensional network of insoluble submicron particles of crystalline inulin in
water. The gel is very stable due to the inulin's ability to immobilize large amounts of water (Franck
2002). As a fat mimetic in low-fat dairy products, inulin appears to contribute to an improved
mouthfeel (Guggisberg et al. 2009; Paseephol et al. 2008). The physicochemical properties of inulin
appeared to be linked to the DP. OF is much more soluble and sweeter than native and long-chain
inulin and can contribute to improve mouthfeel, because its properties are closely related to other
sugars. Long-chain inulin is less soluble, enhances viscosity, and, as such, can act as a texture
modiier (Coussement 1999). Additionally, the DP affects melting (Blecker et al. 2003) and glass
transition temperature (Schaller-Povolny et al. 2000, 2001), gel formation and gel strength (Meyer
CH
2
OH
O
H
H
H
OH
H
HO
O
H
OH
CH
2
OH
O
H
HO
H
CH
2
OH
H
O
CH
2
OH
O
H
HO
H
CH
2
OH
OH
H
Figure 13.4
Structure of inulin.
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