Isomaltulose from sucrose

Scheme 2.17 Generation of isomaltulose from sucrose, and the foUow-up products with industrial potential.

Isomalt, a mixture of a-D-glucopyranosyl-l,l-D-mannitol dibydrate and a-D-glucopyranosyl-l,6-D-sorbitol, is obtained by hydrogenating isomaltulose which is en2ymatically derived from sucrose (102). 

Disaccharides such as isomaltulose (6-a-D-glucopyranosyl-D-fructo-furanose), obtained in one step from sucrose by bioconversion (Scheme 12),44 Isomalt , the hydrogenated derivative of isomaltulose and trehalulose (1-a-D-glucopyranosyl-D-fructopyranose) have been shown to be interesting substrates for chemistry.45... 

Another, industrially relevant foUow-up reaction of isomaltulose comprises its ready conversion into 5-(a-D-glucosyloxymethyl)-furfural ( a-GMF ) by acidic dehydration of its fructose portion under conditions (acidic resin in DMSO, 120°C ) that retain the intersaccharidic linkage (Scheme 2.17). As this process can also be performed in a continuous-flow reactor,a most versatile building block is available from sucrose in two steps, of which the first is already industrially realized, and the second simple enough to be performed on a large scale. 

Isomaltulose (a-D-glucopyranosyl-(1 6)-D-fructofuranose) and the related trehalulose (a-D-glucopyranosyl-(l—>l)-D-fioictofuranose) are both accessible from sucrose by enzyme-catalyzed rearrangements (Fig. 11). 

Palatinose/ Isomaltulose OS [Glc(al-] 6)Fru Enzymatic synthesis from sucrose... 

In the context of the strong commercial interest in alternative sweeteners, in particular isomaltulose (which is produced industrially by the conversion of sucrose with the sucrose isomerase SmuA from Protaminobacter rubrum, a GH 13 enzyme), the complex with 1-deoxynojirimycin (2, 10 pM) was investigated (PDB 3GBE)278... 

Disaccharides analogous to isomaltulose, but containing other sugars in place of ot-D-glucose, can be obtained by similar bioconversions from different disaccharides.234 Sucrose analogues (galactose-fructose, xylose-fructose, fucose-fructose) have also been prepared by isomerization, catalyzed by an engineered fructosyltransferase.235,236... 

Isomalt is produced from food-grade sucrose in a two-stage process. Beet sugar is converted by enzymatic transglucosida-tion into the reducing disaccharide isomaltulose. This undergoes catalytical hydrogenation to produce isomalt. 

Focus is also put on the third pathway which includes reactions of sucrose which lead to carbohydrate structures different from the starting carbohydrate sucrose. This includes the inversion of sucrose to the monomers o-glucose and o-fmctose but also enzymatic rearrangements of the two sucrose building blocks to other carbohydrates, e.g., isomaltulose and trehalulose. 

Isomalt is a mixture of two isomeric polyols which result from hydrogenation of the keto group of isomaltulose. The starting material, isomaltulose, is obtained by bacterial conversion of sucrose (Scheme 1). 

It was shown for the sucrose isomerases of more than one strain that the enzyme catalyzes the reaction to both products, whereas isomaltulose (Palatinose ) is the kinetically and trehalulose the thermodynamically preferred product.111,134,157,169 difference in the reaction mechanism between the isomaltulose (Palatinose ) and trehalulose formation is an additional tauto-merization step of the fructose from the fructofuranose to the fructopyranose form in the catalytic pocket of the enzyme, which finally results in the trehalulose formation. ... 

Isomaltulose, also known as Palatinose (lUPAC name (2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[[(2R,3R,4S)-3,4,5-trihydroxy-5-(hydroxymethyl)oxolan-2-yl]methoxy] oxane-3,4,5-triol), and sucrose have similar physical and organoleptic properties. Isomaltulose (Palatinose ) is a reducing, free-flowing, non-hygroscopic crystalline compound which can be crystallized easily from aqueous solutions with one mole crystal water. Crystalline isomaltulose (Palatinose ) melts at 123-124 The crystal structure and... 

C -NMR spectrum were identified. The water solubility at 20 °C is about one-quarter compared to that of sucrose. The viscosity of aqueous isomaltulose (Palatinose ) solutions is in the same range as that of sucrose. Isomaltulose (Palatinose ) shows a neutral sweetness like sucrose without any aftertaste, but it is only 42% as sweet as sucrose. ° " Apart from lower sweetness, isomaltulose (Palatinose ) is non-cariogenic. " 156,158 Isomaltulose (Palatinose ) has a low glycaemic index therefore the insulin release is correspondingly reduced compared to other sugars. 

In addition to saccharose, numerous other disaccharides and higher oHgosaccharides derived from glucose and fructose are present in foods as natural components. An overview of relatively commonly occurring oligosaccharides is shown in Table 4.14. Turanose, maltulose (4-108) and isomaltulose (4-116) are examples of reducing disaccharides (sucrose isomers). 

Most f. is found as a component of - sucrose, from which it is obtained by inversion (-+invert sugars). There are many other f-containing di-and trisaccharides, e.g., ->isomaltulose, - leu-crose. 

---