Effect of temperature on the dynamic and steady-shear rheology of a new microbial extracellular polysaccharide produced from glycerol byproduct Vítor D. Alves a, * , Filomena Freitas b , Nuno Costa b , Mónica Carvalheira b , Rui Oliveira b , Maria P. Gonçalves a , Maria A.M. Reis b a REQUIMTE-Department of Chemical Engineering, Faculty of Engineering, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal b REQUIMTE/CQFB, Chemistry Department, FCT/Universidade Nova de Lisboa, 2829-516 Caparica, Portugal article info Article history: Received 8 July 2009 Received in revised form 22 September 2009 Accepted 13 October 2009 Available online 17 October 2009 Keywords: Rheology Temperature Extracellular polysaccharide Glycerol-rich product Pseudomonas oleovorans abstract The effect of temperature on the dynamic and steady-shear rheology of aqueous solutions of an extracel- lular polysaccharide produced by microbial fermentation using Pseudomonas oleovorans NRRL B-14682 and glycerol byproduct, was studied. The biopolymer solutions have shown a pseudoplastic fluid behav- iour and no gel formation was detected for all temperatures studied. As expected, the steady shear and dynamic parameters decreased with increasing temperature, due to the increase of polymer chain mobil- ity. The EPS solutions were thermorheologically simple and stable, since the rheological parameters were successfully superimposed to and arbitrary reference temperature using the Time–Temperature Superpo- sition principle, and the Cox-Merz rule was satisfactorily applied. In addition, the rheological properties were maintained under consecutive oscillatory and steady-state tests at 25 °C, after exposing the sample to increasing temperatures up to 80 °C. This polymer is a good candidate to be used in industrial pro- cesses involving temperature variations, at least in the range from 15 to 80 °C. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Polysaccharides from natural sources are a class of compounds that are broadly used in many areas of application, such as in the food, pharmaceutical and cosmetic industries (as thickeners, gel- ling agents, texture modifiers, stabilizers and binding agents), in the paper industry (as strengthening agents), in oil well fracturing and drilling, in water treatment and mining industry (as flocculat- ing agents), and in biodegradable films for agricultural purposes and packaging. Natural biopolymers have been recovered from plants, e.g. galactomannans, starch, and pectins (Cerqueira et al., 2009; Nwokocha & Williams, 2009a; Wang et al., 2007); from algae, e.g. carrageenan, alginate and agar (Gomez, Lambrecht, Lozano, Rina- udo, & Villar, 2009; Hilliou et al., 2006; Villanueva, Sousa, Gonçal- ves, Nilsson, & Hilliou, 2009); and animal sources, e.g. chitosan (Abdou, Nagy, & Elsabee, 2008). However, the characteristics and availability of the recovered products are dependent on the season of the year and climate conditions. As an alternative, polysaccha- rides may well be obtained by microbial fermentation, e.g. xanthan gum, bacterial alginate, levan and succinoglycan (Bae, Oh, Lee, Yoo, & Lee, 2008; García-Ochoa, Santos, Casas, & Gómez, 2000; Peña, Trujillo-Roldán, & Galindo, 2000; Simsek, Mert, Campanella, & Reu- hs, 2009), since they are naturally produced by several microor- ganisms. Microbial fermentation is a more controlled process depending only on manipulated variables that, under optimized conditions, enables the production of key compounds at a constant rate and with unchanged properties over time. Besides the polysac- charide physicochemical characterization, the evaluation of the influence of different parameters, such as temperature and poly- mer concentration, on the rheological properties of their aqueous solutions, is essential (Arvidson, Rinehart, & Gadala-Maria, 2006; Bae et al., 2008; Nickerson, Paulson, & Speers, 2004; Simsek et al., 2009; Xu, Liu, & Zhang, 2006). The production of a new extracellular polysaccharide (EPS) by microbial fermentation with a Pseudomonas oleovorans strain has been previously reported, using pure glycerol (Freitas et al., 2009a) and glycerol byproduct from the biodiesel manufacture without any pre-treatment (Freitas et al., 2009b). The EPS pro- duced in both cases is a high molecular weight heteropolysaccha- ride (1.0–5.0  10 6 ) with good viscous enhancing properties, and composed by neutral sugars and acyl groups, the later conferring a small charge density to the polymer chains. From the study of the properties in aqueous solutions of the EPS produced from pure glycerol, the zero-shear rate scaling with concentration in salt free solutions revealed to follow a typical polyelectrolyte behaviour in a bad solvent, while at high ionic strength the rheological properties 0144-8617/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2009.10.026 * Corresponding author. Present address: CEER – Biosystems Engineering, Instituto Superior de Agronomia – UTL, Tapada da Ajuda, 1349-017 Lisboa, Portugal. Tel.: +351 213653546; fax: +351 213653200. E-mail address: vitoralves@isa.utl.pt (V.D. Alves). Carbohydrate Polymers 79 (2010) 981–988 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol