Manno-oligosaccharide preparation by the hydrolysis of konjac flour with a thermostable endo-mannanase from Talaromyces cellulolyticus

Aims: A thermostable endo-mannanase from the fungus Talaromyces cellulolyticus was identified to facilitate manno-oligosaccharide preparation from Konjac (Amorphophallus konjac) flour.

Methods and results: A putative endo-1,4-β-mannanase from the T. cellulolyticus was obtained and efficiently expressed by improving its gene dosage in the genome of the host. After cultivation in a bench-top bioreactor for about 120 h, the protein content and enzyme activity of mannanase increased to 3·4 g l^-1 and 17 500 U ml^-1 respectively. Enzymatic characterization showed that this enzyme has an optimal temperature of 80°C, optimal pH of 5·0. Under the optimized hydrolysis conditions of pH 5·0, 70°C, and an enzyme concentration of 200 U l^-1 solution, this enzyme could efficiently hydrolyse 0·5% konjac flour into manno-oligosaccharides (MOSs) with the degree of polymerization range from 3 to 7. The possible mechanism by which the enzyme produced MOSs was also discussed.

Conclusion: Talaromyces cellulolyticus endo-mannanase is thermostable and has a broad pH range adaptability. Method of improving the dosage of mannanase gene in the genome could realized its high-level impression. This enzyme could efficiently hydrolyse konjac flour into manno-oligosaccharide products.

Significance and impact of the study: This study has enriched endo-mannanase resources, facilitated its bulk production and provided a strong reference for its application in manno-oligosaccharide preparation from the natural glucomannan of konjac flour.