Inclusion of tributyrin during enzymatic synthesis of cyclodextrins by β-cyclodextrin glycosyltransferase from Bacillus circulans

Tributyrin is a precursor of butyric acid, which is beneficial to intestinal health. Due to its unpleasant odor and poor solubility, tributyrin is usually used after inclusion complexation with suitable wall materials. In this paper, tributyrin was creatively added to the enzymatic synthesis of cyclodextrins catalyzed by beta-cyclodextrin glycosyltransferase from Bacillus circulans STB01. The tributyrin formed inclusion complexes directly during enzymatic cyclodextrins synthesis and increased the yield of cyclodextrins from 25.84% to 44.01%. This process was investigated by determining inclusion complex stability constant and by using molecular modeling and H-1 NMR. The inclusion complexes stability constants of tributyrin with alpha-, beta-, and gamma-cyclodextrin were 25.11, 58.56 and 6.93 L/mol, respectively. beta-Cyclodextrin had the largest stability constant and the most significant increase in yield (72.80%). Molecular modeling of the three-dimensional structures of the tributyrin-cyclodextrin inclusion complexes indicated that the morphology of the complexed groups was related to the size of the cyclodextrin cavity. Finally, the supramolecular structures were verified with H-1 NMR through the chemical shift changes of protons at key positions. This study created a new method and a new inclusion wall material, instead of single pure cyclodextrin for complexing guest molecules. These advances are important because they may expand the application of cyclodextrins due to significant cost reduction.