Rheological characterization under shear of a fraction of polymer produced via ...

• Author(s): Pintado, M. E. ; Silva, J. A. Lopes da ; Pintado, A. I. E. ; Malcata, F. X.
• Date: 1998
• Persistent ID: http://hdl.handle.net/10400.14/5929
• Origin: Veritati - Repositório Institucional da Universidade Católica Portuguesa
• Subject(s): Lactan; Rahnella aquatilis; Polysaccharide
• Document Type: Article
• Language: English

Description

Production 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