In vitro biodegradation study of acetyl and methyl inulins by Bifidobacteria and inulinase

The purpose of this study was to investigate if acetylated and methylated inulins can be degraded by inulinase from Aspergillus niger and by Bifidobacteria, in order to determine their potential in colonic drug delivery. Methyl and acetyl inulins were synthesized by the reaction of inulin (Raftiline HP) with methyl sulfate and acetic anhydride, respectively. The degree of substitution (DS) and the structure of the reaction products were confirmed by 13C-NMR. Degradation by inulinase was investigated in a citrate buffer (0.05 M, pH 4) or with a mixture of citrate buffer and DMSO at 37 degrees C. Biodegradation by Bifidobacteria was investigated under anaerobic conditions using an in-house prepared broth at 37 degrees C for 2 days. The resulting products were analyzed chromatographically; the formation of short chain fatty acids was followed by measuring the pH of the incubation media. The results obtained suggest that acetylated and methylated inulins are not biodegradable, since no degradation product could be detected after incubation; a decrease in pH was clearly observed in control samples (pure fructose and inulin), but not in the derivatized inulin samples. The results can probably be explained by a change in conformation of inulin due to derivatization.