Synthesis of long-chain isomaltooligosaccharides from tapioca starch and an in vitro investigation of their prebiotic properties

Abstract

The recombinant wild-type (WT) or Y101S-mutated amylomaltase prepared from the gene screened from soil DNA was used in combination with Aspergillus niger transglucosidase to produce isomaltooligosaccharides (IMOs) from tapioca starch. The highest IMO yield was obtained when 30% (w/v) soluble tapioca starch was incubated with 120 Units of both amylomaltases and 6 Units of transglucosidase at 40°C for 30min with WT or for 1h with Y101S-mutated enzymes. Mass spectrometry and 1H NMR analysis of the IMOs synthesized from WT and Y101S-mutated enzymes showed the presence of α-1,4 and α-1,6 glycosidic bonds with a polymerization degree of ≤9. HPAEC-PAD analysis showed that the sizes of the IMOs synthesized from both enzymes were significantly larger than those of commercial IMOs. A smaller proportion of long-chain IMOs was observed when Y101S-amylomaltase was used. As for physical and biological properties, the degree of sweetness of both synthesized IMOs was lower than those of sucrose and commercial IMOs, while the brown color from the Maillard reaction, the viscosity and the hygroscopicity were higher than those of commercial IMOs. The prebiotic properties of both synthesized IMOs showed that they were able to tolerate acidic conditions, heat, and human digestive enzymes. In addition, these IMOs could stimulate the growth of Lactobacillus casei and resulted in a decrease of the culture pH, similar to the effect of commercial IMOs.