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- Production of polysaccharide by Rahnella aquatilis with whey feedstockPublication . Pintado, M. E.; Pintado, Ana I. E.; Malcata, F. X.The rates were monitored on biomass increase, polysaccharide production and viscosity development of whey broth and a control synthetic broth during fermentation by Rahnella aquatilis and organic acids, lactose, peptides and free amino acids were measured. Growth curves were similar and characterized by maximum specific growth rates of 0.61 h−1 for whey and 0.63 h−1 for synthetic medium. The yields of polysaccharide were 0.59 g/glactose for the synthetic medium and 0.56 for whey. Small peptides (<4,000 Da) and most free amino acids in both fermentation media were consumed within 24h.
- Rheological characterization under shear of a fraction of polymer produced via fermentation of whey-related media by Rahnella aquatilisPublication . Pintado, M. E.; Silva, J. A. Lopes da; Pintado, Ana I. E.; Malcata, F. XavierProduction of lactan, a polysaccharide composed of mannose, galactose and galacturonic acid (at the ratio of 5:3:2), starting from a semidefined medium containing lactose via fermentation with Rahnella aquatilis was described previously. In this communication, such polysaccharide was produced from five alternative fermentation media: (1) a synthetic (defined) medium, plain whey (under (2) aerobic and (3) anaerobic conditions), (4) whey permeate and (5) whey with 2% NaCl (w/v). The effect of the concentration of polysaccharide, pH and ionic strength at harvest on the rheological properties of the polysaccharide was studied using lactan-enriched fractions recovered from each medium and analysed in solution under steady shear flow. Lactan solutions showed a shear-thinning behaviour in all cases, and increases in viscosity were observed at increasing concentrations of polysaccharide, as expected. The polysaccharide fraction produced from whey with 2% (w/v) NaCl and plain whey under anaerobic conditions exhibited lower viscosity than that produced from the other media, an observation that is associated with the lower concentration of polysaccharide. Post-harvest addition of salts (KCl or CaCl2) and changes in pH (3–11) affected slightly the viscosity of the polysaccharide solutions. q1998