Synthesis and in vitro digestion and fermentation of acylated inulin

The objective of this project was to develop a method for the synthesis of acetylated, propionylated, and butyrylated inulins as designer dietary fibers for enhanced gut health. High purity (HP) inulin was acylated with acetic anhydride, propionic anhydride, or butyric anhydride. Degrees of substitution [mol short chain fatty acid (SCFA)/mol fructosyl equivalents] were 0.313±0.013, 0.152±0.005, and 0.371±0.003. Acylation decreased the molecular weight of inulin. No SCFAs were released when the acylated inulin conjugates were subjected to an in vitro model of digestion, suggesting that they would be able to travel through the upper gastrointestinal tract intact. In a 24 h in vitro fermentation experiment acylation reduced the rate of fermentation and resulted in enhanced SCFA production in the latter half of fermentation compared with control inulin. Acylation changed the types of SCFA that were produced during fermentation, although this did not always correspond to the SCFA that had been acylated to inulin. Acylation of the inulin reduced the growth of bifidobacteria compared to the inulin control, but the addition of fructooligosaccharides to the acylated inulin during fermentation partially alleviated this issue. Thus, acylation of inulin may be beneficial for delivering high concentrations of SCFA to more distal regions of the colon, but fructooligosaccharides should be included in the preparation to maintain bifidogenicity.