A review of the enzymatic hydrolysis of mannans and synergistic interactions between beta-mannanase, beta-mannosidase and alpha-galactosidase

Mannan is an important polysaccharide found in softwoods and many other plant sources. Mannans from various sources display large differences in composition, structure and complexity. To hydrolyse mannan into its monomer sugars requires a number of enzymes working in synergy. This review examines mannan structure and the enzymes required for its hydrolysis. Several studies have investigated the effect of supplementing beta-mannanases with beta-mannosidases and alpha-galactosidases in binary and ternary combinations. Synergistic enhancement of hydrolysis has been found in some, but not all cases. In the case of mannosidases, they sometimes display an anti-synergistic effect with mannanases, most likely due to competition for binding sites. Most importantly, in the case of alpha-galactosidases, the same enzyme from different families display differences in synergistic interactions due to different specificities. An improved understanding of enzyme interactions will aid in achieving enhanced hydrolysis of mannans and higher sugar yields. This review highlights areas which require further research in order to gain a better understanding of mannan hydrolysis and utilisation. Such knowledge is very important as this can be used in the optimisation of commercial or purified enzyme mixtures to improve the economic viability of the conversion of high mannan-containing biomass such as softwoods into fermentable sugars for bioethanol production.