A wide number of Lactic Acid Bacteria (LAB) species produce alpha-glucans with their ability to synthesize glucansucrases (GS) which use sucrose as substrate for the glucan production. Recently another group of enzymes in LAB gained special interest for their ability to produce alpha-glucans targeting the substrates containing alpha 1-4-linkages and synthesizing new (alpha 1-6) or (alpha 1-3)-linkages as alpha-glucanotransferases. In this study, a putative 4,6-a-glucanotransferase (GTFB) from sourdough isolate Lactobacillus reuteri E81 was identified and expressed in Escherichia coli. The biochemical characterization of the GTFB-E81 confirmed its function as it cleaved the alpha 1-4-linkages in different substrates and produced new gluco-oligomers/polymers containing al 6 linkages together with the alpha 1-4-linkages detected by NMR analysis. GTFB-E81 produced maltooligosaccharides targeting maltose and maltoheptaose as substrates with up to DP 8 detected by TLC and ESIMS/MS analysis. The functional roles of these malto-oligosaccharides were determined by testing their immune-modulatory functions in HT29 cells and they triggered the production of anti-inflammatory 1L-4 and pro-inflammatory IL-12 cytokines. (C) 2018 Elsevier B.V. All rights reserved.