Structural analysis of rebaudioside A derivatives obtained by Lactobacillus reuteri 180 glucansucrase-catalyzed trans-α-glucosylation

The wild-type Gtf180-Delta N glucansucrase enzyme from Lactobacillus reuteri 180 was found to catalyze the alpha-glucosylation of the steviol glycoside rebaudioside A, using sucrose as glucosyl donor in a transglucosylation process. Structural analysis of the formed products by MALDI-TOF mass spectrometry, methylation analysis and NMR spectroscopy showed that rebaudioside A is specifically alpha-D-glucosylated at the steviol C-19 beta-D-glucosyl moiety (55% conversion). The main product is a mono-(alpha 1 -> 6)-glucosylated derivative (RebA-G1). A series of minor products, up to the incorporation of eight glucose residues, comprise elongations of RebA-G1 with mainly alternating (alpha 1 -> 3)- and (alpha 1 -> 6)-linked glucopyranose residues. These studies were carried out in the context of a program directed to the improvement of the taste of steviol glycosides via enzymatic modification of their naturally occurring carbohydrate moieties. (C) 2017 Elsevier Ltd. All rights reserved.