Microbial treatment approaches for high-purity fructo-oligosaccharides production

Abstract

The production of high-purity fructooligosaccharides (FOS), known as prebiotics, by sucrose fermentation using whole microbial cells has been recently explored. At the end of the fermentation process, FOS are present in mixture with small saccharides that are known to have an inhibitory effect of transfructosylating enzymes and to decrease the prebiotic activity of the mixture. This issue can be overcome by reducing the small saccharides present in FOS broth, which can be done using a combined microbial treatment, among others, improving as well the further purification of FOS by Simulated Moving Bed (SMB) chromatography. The main goal of this work was the use of combined microbial treatment approaches to improve FOS production and enhance a high purity FOS content. Aureobasidium pullulans and Saccharomyces cerevisiae were used combined to produce FOS and reduce the small sugars in the culture, respectively. FOS-producing microorganism was used free, immobilized to a non-conventional carrier or encapsulated in Ca-alginate beads, in mixture with the non-oligosaccharides consuming microorganism, free or encapsulated in Ca-alginate beads. A factorial design, considering three different variables, was performed, to select the microbial treatment approach through which increased FOS levels and yields can be obtained. The 38 assays were performed in shaken-flasks and the most suitable one was scaled-up to a 3L bioreactor. The inoculation time of S. cerevisiae showed to be the most relevant variable for FOS production, and the use of immobilized A. pullulans, mixed with encapsulated S. cerevisiae inoculated after 20h of fermentation, was the best combination, with statistical relevance (p<0.01), to obtain enhanced FOS concentration, percentage in the medium, yield and productivity. Results in bioreactor showed a higher fermentation time (20 to 25h) needed to obtain an increased maximal production of FOS (around 132 g.L-1) and yielded 0.70 ± 0.05 g of FOS per gram of initial sucrose. Also, the approach selected improved the percentage of FOS in the medium throughout the fermentation time, providing a pre-purified broth, with lower levels of mono-saccharides for further purification by SMB.