Synthesis and characterization of new oligosaccharides with prebiotic activity

Abstract

The importance of human intestinal microbiota in maintaining host health is well-known and in the past few decades, the consumer’s awareness for healthier foods has increased. There are several strategies to stimulate the proliferation of beneficial intestinal bacteria, including the consumption of prebiotics. Currently, there is a range of prebiotic carbohydrates on the market, most of them isolated from plant polysaccharides such as inulin and fructooligosaccharides (FOS) but there is an increasing interest in the development of new prebiotics, with added functionality. In this sense, chitosan, which is a polysaccharide composed of glucosamine (GlcN) and N-acetyl glucosamine (GlcNAc) units, linked by β (1→4) bonds, presents a structure very similar to prebiotic glucooligosaccharides. The main difference is the presence of amino groups, which are the cause of antimicrobial effect of chitosan. Chemical modification of chitosan by substitution of its amino groups could eliminate the antimicrobial effect and convert chitosan in a new interesting prebiotic ingredient. Thus, the objective of the present work is to chemically modify chitosan to be used in the food industry as prebiotic ingredient. In order to achieve this objective, the optimization of the synthesis of chitosan derivatives with glucose by the Maillard reaction and enzymatic hydrolysis, was conducted and the obtained purified derivatives were assayed for molar mass distribution and structural characterization by Size Exclusion Chromatography (SEC), Fourier Transform Infrared Spectroscopy (FT-IR), Proton Nuclear Magnetic Resonance (1H-NMR) and colloid titration. The purified product was assayed for its prebiotic potential by means of in vitro fermentability assays performed with individual microbial strains and human faecal inocula. The experimental data showed that the refined chitooligosaccharide (COS) derivatives obtained in this work had potential prebiotic effects, inducing changes in both the pattern of generated metabolic products and the count of Bifidobacterium, which might contribute to a healthy intestinal environment. Finally, the in vitro cytotoxicity of the COS derivatives synthesized was performed by flow cytometry. The results obtained demonstrated that the COS derivatives are biocompatible molecules. Also, the assay showed that the substitution of the amino groups decreased the cytotoxicity of the COS derivatives when compared to unmodified COS. Nevertheless, further studies are recommended, mainly in vivo tests, to eventually confirm these in vitro results.

Date of Award	11 Apr 2014
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Maria Manuela Pintado (Supervisor)