Microbial fructo-oligosaccharides as emergent prebiotics

Abstract

Introduction. Fructo-oligosaccharides (FOS) have been associated to prevention and treatment of many XXI centurys diseases. There is therefore a huge interest in successfully developing bioprocesses for their production. FOS have been industrially produced via fermentation, by several microorganism enzymes, with low yields and purities in a two-step bioprocess. To obtain high-content FOS we explored an integrated strategy using a co-culture of an Aspergillus ibericus as FOS producer strain, with Saccharomyces cerevisiae, with the gene responsible for sucrose hydrolysis disrupted, as small saccharides removal. The functionality of the microbial FOS produced as prebiotics was further assessed. Methodology. The wholecell microorganisms were used in a one-step bioprocess. Parameters such as initial yeast concentration, inoculation time, fermentative broth composition, temperature and pH were optimized in shake-flask previously scale-up to a lab bioreactor size. FOS prebiotic potential was evaluated in anaerobic batch cultures for 24 h using human faeces from 5 healthy volunteer individuals. The dynamic bacterial populations changes were assessed by PCR-real time, as well as the production of short chain fatty acids (SCFA) by HPLC. Sugars were analysed by HPLC. Results. Fermentations run under 30 ºC, initial pH of 6.0 and 17 g.L-1 yeast extract led to FOS mixtures with 97.4 ± 0.2% (w/w) purity in shake-flask. The scaledup fermentations in bioreactor yielded 64 ± 2% of FOS, after 141 h, with a FOS content of 118 ± 5 g.L-1 and a purity of 93.0 ± 0.5% (w/w). The microbial FOS triggered a beneficial effect on gut microbiota composition. SCFA including succinate, acetate, propionate and valerate were produced by the five faecal inoculum tested, at high concentrations. Lower amount of formate and butyrate were also produced. Conclusions. The one-step fermentation using the specific co-culture studied showed to be more efficient, economical and fast than the conventional two-step bioprocesses, thus avoiding the need of the conventional downstream treatments. The microbial FOS produced exhibited promising potential as nutraceutical ingredients for gut microbiota modulation with likely prebiotic features.