Synthesis of glucooligosaccharides by glucansucrases from fructophilic lactic acid bacteria from honey bee Apis mellifera

In the present work, we report synthesis of glucooligosaccharides (GOSs) by glucansucrase enzymes from fructophilic lactic acid bacteria Lactobacillus pentosus AG8, Lb. kunkeei AG9, AG10 and AG11 isolated from the gut of honey bees Apis mellifera. As an acceptor of glucose units from sucrose was used maltose and maltose to sucrose ratios (M/S) 1, 2, 4, 6, 8, 0.12, 0.16, 0.25 and 0.5. GOSs with degrees of polymerization (DP) ranging from 3 to 7 were obtained. The yields of GOSs and their composition according to DP were strongly influenced by the concentrations of the acceptor and sucrose. The highest yields of GOSs were obtained at М/S=1 – 45 to 53 g/L with predomination of DP3 fraction of oligosaccharides – 47 to 53%. The further increase of M/S ratios led to gradual decrease of the amounts of GOSs and also of their diversity according to DP. At М/S=8 were achieved yields of 13 to 15 g/L, composed only by DP=3 and DP=4 GOSs. In the opposite, the increase of sucrose concentrations at the expense of maltose ones led to more even distribution of the synthesized GOSs according to their DP up to 7, and yields of 40 to 42 g/L at M/S=0.5. Thus by varying the acceptor/donor ratio we were able to produce GOSs preparations with more controlled composition.

               In addition, GOSs preparations synthesized with glucansucrases from the four strains were subjected to dextranase hydrolysis in order to determine the content of α-(1→6) linkages. The results showed content of α-(1→6) linkages that decreases towards the lower maltose concentrations and is between 71 and 96%. Knowing that the enzymes from the four strains introduce 16 to 22% α-(1→3) linkages in the synthesized glucan polysaccharides such type of linkages could be expected also in the oligosaccharide products and this is promising for their prebiotic potential.