Transglycosylation by β-mannanase TrMan5A variants and enzyme synergy for synthesis of allyl glycosides from galactomannan

•β-Mannanase TrMan5A variants catalysed synthesis of reactive allyl β-mannosides.•The substitutions R171 K/E205D increased the transglycosylation capacity two-fold.•TrMan5A can use galactomannan as donor for synthesis of allyl glycosides.•The yield increased four-fold using enzyme synergy by addition of α-galactosidase.