Controllable and complete conversion of agarose into oligosaccharides and monosaccharides by microwave-assisted hydrothermal and enzymatic hydrolysis and antibacterial activity of agaro-oligosaccharides

Hydrolysis of agar or agarose can yield two types of oligosaccharides: agaro-oligosaccharides (AOS) and neoagaro-oligosaccharides (NAOS). These oligosaccharides have various biological activities and promising applications in the future food industry and pharmaceuticals. In this study, we prepared AOS from agarose by microwave-assisted hydrothermal hydrolysis and then used a commercial beta-galactosidase to treat AOS for producing NAOS. A complete conversion from agarose to AOS or NAOS can be achieved by microwave hydrothermal treatment and one-step enzyme reaction, and the production process was completely green. In addition, we combined beta-galactosidase and alpha-neoagarobiose hydrolase from Saccharophagus degradans 2-40 (SdNABH) to treat AOS, and AOS was completely converted into monosaccharides. Then the results of the inhibitory activity of AOS on the growth of Streptococcus mutans showed that AOS might be a good potential sugar substitute for dental caries prevention. This study provides an efficient approach for the production of multiple mixed degrees of polymerization (DP) of pure AOS and NAOS without requiring acid catalyst and agarases while simplifying the production processes and reducing costs.