Inulin And Fructose

A relative newcomer in the carbohydrate field is inulin, a fructan (Figure 2.9) consisting of p-linked (2 ^ 1) fructofuranose units with an a-glucopyranose unit at the reducing end. Inulin (GFn) is obtained in Belgium and The Netherlands from the roots of chicory. The average degree of polymerization is relatively low, n ~ 12 [45]. Small amounts of purefructan Fm, are also present in unulin. Another interesting inulin-containing crop is the Jerusalem artichoke [46].

Inulin is applied as a health additive in food applications; it is claimed to improve the intestinal bacterial flora. Moreover, it is a direct source (hydrolysis) of fructose

Carboxymethylation Inulin

FIGURE 2.9 Inulin and derivatives.

that, on a weight basis, is 1.5 times as sweet as sucrose. Fructose is also the precursor of the versatile compound hydroxymethylfurfural (HMF) from which several furan-2,5-disubstituted "biomonomers" (diol, dialdehyde, dicarboxylic acid) can be derived. Furthermore, HMF is a precursor of levulinic acid (cf. Figure 2.1).

Worldwide derivatization studies on inulin are ongoing. For a review, see Stevens et al. [47]. A first successful example has been carboxymethylation leading to the new material carboxymethyl inulin (CMI). In the reaction with chloroacetate (Figure 2.9), the 4-position of the fructose units turned out to be the most reactive [48], but positions 3 and 6 contribute, too. CMI appeared to be an excellent low-viscosity inhibitor of calcium carbonate crystallization [49] and is industrially manufactured now.

Another new commercial inulin derivative is inulin lauryl carbamate [50], an efficient stabilizer of oil droplets and hydrophobic particles against coalescence or flocculation. The material is used in personal-care applications.

Other promising inulin derivatives are 3,4-dicarboxyinulin, an excellent calcium-complexing material [51] and alkoxylated inulins [52].

2.13 LACTOSE

The major source of the disaccharide lactose (a galactose-glucose combination) is cheese whey, which contains 4.4 wt.% lactose (together with 0.8% of protein and 0.8% of minerals). Lactose can be crystallized in its a- or p-form. Common grades are edible and pharmaceutical [53]. Altogether, it is admirable that the processes of collecting, transporting, concentrating, demineralization, and crystallization allows such a modest price for lactose.

Lactose is used as such in the food industry, in infant nutrition, and in the pharmaceutical industry (matrix material of pills). In view of the growing chemical network around it, lactose is developing into a key molecule (see Figure 2.10).

HOH,C HOH.C

Inulin Lauryl Carbamate

Oligosaccharides Lactitol

FIGURE 2.10 Lactose as a key chemical.

Oligosaccharides Lactitol

FIGURE 2.10 Lactose as a key chemical.

Industrial conversions include hydrogénation to the low-caloric sweetener lactitol, isomerization to the laxative lactulose (galactose-fructose combination), oligomer-ization to health supplements, and oxidation to the metal-complexing lactobionic acid. Moreover lactose serves to make chiral compounds such as (S)-3-hydroxy-y-butyrolactone. Part of the lactose molecule is sacrificed in this synthesis. Via its monomers, new vitamin-C-type antioxidants can be made from lactose [54].

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