Effect of acceptor carbohydrates on oligosaccharide and polysaccharide synthesis by dextransucrase DsrM from Weissella cibaria

- α-Glucans are efficient acceptor carbohydrates for dextransucrase DrsM.
- The efficiency of acceptors for DsrM decreased in the order DP2 > DP3 > DP1.
- Among disaccharides, the efficiency decreased α-(1 → 6) > α-(1 → 4) > α-(1 → 3).
- Equimolar addition of isomaltose and sucrose yielded only oligosaccharides.
- Conversion of commercial IMO by dextransucrase reduced their in vitro digestibility.

The digestibility of isomalto-oligosaccharides (IMO) as well as their metabolism by gut microbiota depends on the degree of polymerization and the ratio of α-(1 → 4) to α-(1 → 6) linkages. Both parameters are influenced by the method of production. Commercial IMO are produced by transglycosylation of starch hydrolysates, or by transglycosylation with dextransucrase and sucrose as glucosyl-donor and maltose as glucosyl-acceptor. This study aimed to quantitatively and qualitatively assess the acceptor reaction with dextransucrase. α-Glucans were selected by systematic variation of degree of polymerization and linkage type; the dextransucrase DsrM from Weissella cibaria 10M was used as biocatalyst. The efficiency of α-glucans as acceptor carbohydrates decreased in the order DP2 > DP3 > DP1; among disaccharides, the efficiency decreased in the order α-(1 → 6) > α-(1 → 4) > α-(1 → 3); the α-(1 → 2) linked kojibiose did not support oligosaccharide formation. Equimolar addition of efficient acceptor molecules and sucrose shifted the dextransucrase reaction to oligosaccharides as virtually exclusive product. DsrM readily extended a commercial IMO preparation by adding α-(1 → 6)-linked glucose moieties. Conversion of commercial IMO by dextransucrase reduced their in vitro digestibility as analyzed by two different protocols. This study facilitates the synthesis of oligosaccharides produced in the acceptor reaction with dextransucrase with controlled yields and degree of polymerization, and hence with optimal functional properties in food applications.

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