Isomalt

Description

Isomalt is an equimolar mixture of oc-D-glucopyranosyl-1,6- D-sorbitol (GPS) and α-D-glucopyranosyl-l,l-D-mannitol (GPM). The production process of isomalt involves two essential steps. In the first step, the 1,2 -glycosidic linkage between the glucose and the fructose moiety of sucrose is rearranged by an immobilized enzyme system to a 1,6 -glycosidic linkage, which is more stable and characteristic for the cross linkage in the amylopectin fraction of native starch. In the second step, the rearranged sucrose molecule, i.e., isomaltulose, is hydrogenated to the corresponding sugar alcohols. Isomalt is commercially available as a dry, white crystalline powder which is about half as sweet as sucrose.
In vitro studies with intestinal disaccharidases from mammals demonstrated that isomalt is cleaved much more slowly than sucrose or maltose. A slight inhibitory effect on maltose hydrolysis and on the active transport on glucose has also been observed.
Ingested isomalt is partly hydrolyzed in the small intestine and slowly absorbed in the form of glucose, sorbitol, and mannitol. The intact portion of isomalt, as well as some unabsorbed sorbitol and mannitol, reaches the distal parts of the gut where these products are fermented to volatile fatty acids.

Chemical properties

White or almost white powder or granules.

Chemical properties

Isomalt is a more or less equimolar mixture of 1-O-a-D-glucopyranosy-D-mannitol- dihydrate and 6-O-a-D-glucopyranosyl-D-sorbitol. Different production conditions, however, allow variations in the ratio of the two products. The solubility in water is about 24.5 % (w/w) at room temperature, but varies with the composition and increases with increasing temperature. In addition to the dry isomalt, a syrup is available.
Isomalt is, depending on the concentration, approximately 45–60 % as sweet as sucrose, stable under normal processing conditions of foods, and noncariogenic.
In the European Union, isomalt is approved as E 953 for a large number of food applications. It is GRAS in the United States and also approved in many other countries.
Owing to its low glycemic index, isomaltulose, an intermediate of the production, has found increasing interest as a food ingredient in recent years.

Chemical properties

Isomalt is a sugar alcohol (polyol) that occurs as a white or almost white powder or granular or crystalline substance. It has a pleasant sugarlike taste with a mild sweetness approximately 50–60% of that of sucrose.

History

It is claimed that isomalt is odorless, white, crystalline, and sweet tasting without the accompanying taste or aftertaste. Sweetening power is from 0.45 to 0.6 that of sucrose. A synergistic effect is achieved when isomalt is combined with other artificial sweeteners and sugar substitutes. Principal applications are in confections, pan-coated goods, and chewing gum. The substance was approved for use in most European countries in 1985. Classification of isomalt as a GRAS substance was petitioned in the United States. (GRAS = generally regarded as safe.)

The Uses of Isomalt

analgesic, NSAID

Production Methods

Developed in Germany, isomalt is described as an energy-reduced bulk sweetener and marketed in Europe under the tradename Palatinit? mark. The compound is produced from sucrose in a two-step process. In the first step, the easily hydrolyzable 1-2 glucoside linkage between the glucose and fructose moieties of sucrose are catalyzed by immobilized enzymes to produce isomaltulose, Palatinos mark After crystallization, the isomaltulose is hydrogenated in a neutral aqueous solution using a nickel catalyst.

Definition

ChEBI: (2xi)-6-O-alpha-D-glucopyranosyl-D-arabino-hexitol is a glycosyl alditol consisting of alpha-D-glucopyranose and (2xi)-D-arabino-hexitol residues joined in sequence by a (1->1) glycosidic bond. It is functionally related to an alpha-D-glucose.

Production Methods

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

Biotechnological Production

For the production of isomalt sucrose is converted to isomaltulose which is then hydrogenated to yield a mixture of the two components of isomalt. Although the production of isomalt itself from isomaltulose is a chemical hydrogenation, transformation of sucrose into isomaltulose requires enzymatic transformation. The enzyme sucrosemutase is sensitive to glutaraldehyde, therefore crosslinking is not possible. For industrial use it is, however, not necessary to isolate the enzyme, as immobilized cells of the organism can be used. Addition of sodium alginate to the cultivated cells and subsequent addition of calcium acetate immobilizes the cells. This allows for the use of the cells in a bed reactor, and also facilitates the separation of the product from the reaction mixture. The long-term stability of the immobilized organism is high and can exceed 5,000 h, even if high sucrose concentrations of 550 g/L are used. The yields are about 80–85 % with 9–11 % of trehalulose and small quantities of other saccharides as by-products.
Prior to hydrogenation, free sucrose has to be removed. This is carried out by nonviable cells of Saccharomyces cerevisiae. Remaining by-products of the reaction are converted to the respective sugar alcohols. Although the hydrogenation of isomaltulose theoretically should yield an equimolar mixture of the two constituents of isomalt, the share of each component may vary between 43–57 % depending on the conditions of hydrogenation. An alternative possibility is the direct cultivation of suitable microorganisms such as P. rubrum on sucrose-containing juices obtained during the production of beet and cane sugar. It is claimed that glucose and fructose produced during the transformation are consumed by the microorganisms which results in lower amounts of by-products.

Pharmaceutical Applications

Isomalt is a noncariogenic excipient used in a variety of pharmaceutical preparations including tablets or capsules, coatings, sachets, and suspensions, and in effervescent tablets. It can also be used in direct compression and wet granulation.
In buccal applications such as chewable tablets it is commonly used because of its negligible negative heat of solution, mild sweetness, and ‘mouth feel’. It is also used widely in lozenges, sugar-free chewing gum, and hard-boiled candies, and as a sweetening agent in confectionery for diabetics.

Safety

Isomalt is used in oral pharmaceutical formulations, confectionery, and food products. It is generally regarded as a nontoxic, nonallergenic, and nonirritant material.
Toxicological and metabolic studies on isomalt have been summarized in a WHO report prepared by the FAO/WHO Expert Committee (JECFA), resulting in an acceptable daily intake of ‘not specified’.
The glycosidic linkage between the mannitol or sorbitol moiety and the glucose moiety is very stable, limiting the hydrolysis and absorption of isomalt in the small intestine. There is no significant increase in the blood glucose level after oral intake, and glycemic response is very low, making isomalt suitable for diabetics. The majority of isomalt is fermented in the large intestine. In general, isomalt is tolerated very well, although excessive consumption may result in laxative effects.
Isomalt is not fermented by bacteria present in the mouth; therefore no significant amount of organic acid is produced that attacks tooth enamel.

storage

Isomalt has very good thermal and chemical stability. When it is melted, no changes in the molecular structure are observed. It exhibits considerable resistance to acids and microbial influences. Isomalt is non-hygroscopic, and at 25°C does not significantly absorb additional water up to a relative humidity (RH) of 85%; paracetamol (acetaminophen) tablets based on isomalt were stored for 6 months at 85% RH at 20°C and retained their physical aspect.
If stored under normal ambient conditions, isomalt is chemically stable for many years. When it is stored in an unopened container at 20°C and 60% RH, a re-evaluation after 3 years is recommended.

Regulatory Status

GRAS listed. Accepted as a food additive in Europe.