Fructo-oligosaccharides (FOS) obtained by fermentation of sucrose may be purified at large-scale by continuous chromatography (Simulated Moving Bed: SMB). In order to improve the efficiency of the subsequent SMB purification, the optimization of the fermentative broth composition in salts and sugars was investigated. Fermentations conducted at reduced amount of salts, using Aureobasidium pullulans whole cells, yielded 0.63 ± 0.03 g of FOS per gram of initial sucrose. Additionally, a microbial treatment was proposed to reduce the amount of small saccharides in the mixture. Two approaches were evaluated, namely a co-culture of A. pullulans with Saccharomyces cerevisiae; and a two-step fermentation in which FOS were first synthesized by A. pullulans and then the small saccharides were metabolized by S. cerevisiae. Assays were performed in 100mL shaken flasks and further scaled-up to a 3 L working volume bioreactor. Fermentations in two-step were found to be more efficient than the co-culture ones. FOS were obtained with a purity of 81.6 ± 0.8% (w/w), on a dry weight basis, after the second-step fermentation with S. cerevisiae. The sucrose amount was reduced from 13.5 to 5.4% in total sugars, which suggests that FOS from this culture broth will be more efficiently separated by SMB.

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In this study, a low-cost RGB sensor is developed to measure online the microalgae concentration within a photo-bioreactor. Two commercially available devices, i.e., a spectrophotometer for offline measurements and an immersed probe for online measurements, are used for calibration and comparison purposes. Furthermore, the potential of such a sensor for estimating other variables is illustrated with the design of an extended Luenberger observer.

Fructo-oligosaccharides (FOS) are non-digestible sweeteners with improved functional and technological properties for food and pharmaceutical industry applications. The immobilization of FOS-producing microorganism's whole cells can be used to improve the production of FOS and so, an accurate choice of the carrier is of crucial importance. Here we present a screening and selection of carriers for immobilization of Aureobasidium pullulans cells with potential for yielding high FOS production. Synthetic, agro-industrial by-products and mineral materials were tested and selected regarding their ability to immobilize cells, as well as their potential to produce FOS, through shaken-flask fermentations. Increased amounts of immobilized cells were found for carriers with higher porosity observed at the microscope, higher water absorption index (WAI) and lower critical humidity point (CHP). Reticulated polyurethane foam was one of the most efficient synthetic carriers immobilizing cells (over 75% (w/w) of the total cells were immobilized). Also, high FOS production was obtained: FOS concentration, purity and yield increased in 15, 8 and 12% (w/w), respectively, as compared to free cells conditions. Although walnut shell had a much lower immobilization efficiency, the high amount of cells grown while using this carrier led to a highest increment of FOS concentration, purity and yield, namely, 27, 10 and 25% (w/w). Cells immobilization with the selected carriers holds great promise for FOS production on a larger scale.