Abstract :
[en] Isomaltooligosaccharides (IMOs) are non-digestible oligosaccharides, considered as prebiotics and therefore aim to selectively feed probiotics indigenous to the human colon.
IMOs consists of glucose monomers linked by at least one α-1-6, or in a lower proportion α -1-3 (nigerose family) or α -1-2 (kojibiose family) glucosidic linkages.
In our case they are produced from either corn, tapioca, or rice hydrolyzed starch. The enzymatic reaction is achieved using an Aspergillus niger transglucosidase (EC 2.4.1.24). It results in a very complex mixture with molecules characterized at the same time by their DP value (from 2 to ~15), linkages types (α-1-2, 3 or 6) and the proportion and position of each type of linkage (only α -1-6 or combined types).
However, the reaction only permits to reach yields between 50-75 % in IMOs. Impurities are composed of residual maltooligosaccharides (glucose with exclusively α -1-4 linkages) from the starting vegetal material and glucose released during the transglucosylation step. These digestible saccharides are deleterious for the prebiotic preparation.
Therefore, these compounds must be eliminated from the medium or converted in prebiotic species.
Residual maltooligosaccharides are thus specifically hydrolyzed by a thermostable α-glucosidase (EC. 3.2.1.20) in order to produce glucose as the only unwanted specie. This glucose can then be converted to gluconic acid and/or its salts using a glucose-oxidase (EC. 1.1.3.4) in combination with a catalase.
Gluconic acid (C6H12O7) is a saccharide derivative which has been recognized as a prebiotic compound. It is also known for its purgative action and proved to be effective for lipid peroxidation prevention.
A first option can then be chosen, leaving gluconic acid in the product in order to obtain an original prebiotic product enjoying new prebiotic potential properties due to the combination of both types of prebiotic compounds (IMO and gluconic acid).
The second option is to eliminate the gluconic acid from the prebiotic mixture. This separation doesn’t present the same difficulties than for glucose as gluconic acid is charged and can therefore be separated on anion-exchange resins (Dowex AcO-).
This overall process, fulfilling the principles of green chemistry and being applicable to produce organic prebiotic, is an elegant solution, from an economical, an environmental, a nutri-functional and a techno-functional point of view.
Indeed, it can lead to original prebiotic preparations, with yields close to 100%, by avoiding product loss, as the digestible saccharides portion is converted to gluconic acid. Furthermore, the presence of gluconic acid can provide many functional properties to the prebiotic preparations for their incorporation in food products.
