Tailoring the natural rare sugars D-tagatose and L-sorbose to produce novel functional carbohydrates

This multidisciplinary study details the biosynthesis of novel non-digestible oligosaccharides derived from rare sugars, achieved through transfructosylation of D-tagatose and L-sorbose by levansucrase from *Bacillus subtilis* CECT 39 (SacB). The characterization of these carbohydrates using NMR and molecular docking elucidated the catalytic mechanism and substrate preference of SacB. Tagatose-based oligosaccharides were more abundant, with β-D-Fru-(2-6)-β-D-Fru-(2-1)-D-Tag and β-D-Fru-(2-1)-D-Tag being most representative. *In vitro* studies demonstrated resistance to intestinal digestion and prebiotic properties of tagatose-based oligosaccharides, particularly β-D-Fru-(2-1)-D-Tag. This disaccharide showed a higher bifidogenic effect than unmodified tagatose. Bioconversion of rare sugars into β-fructosylated species enhances bioavailability and gut microbiota interaction, offering potential as prebiotics and low-calorie sweeteners.

Oswaldo Hernandez-Hernandez, Carlos Sabater, Inés Calvete-Torre, Elisa G. Doyagüez, Ana M. Muñoz-Labrador, Cristina Julio-Gonzalez, Blanca de las Rivas, Rosario Muñoz, Lorena Ruiz, Abelardo Margolles, José M. Mancheño, F. Javier Moreno