English

Abednego M Dlamini,Paul S Peiris,John H Bavor,Kasipathy Kailasapathy

doi:10.5897/ajb2007.000-2416

Abstract

Physical, chemical and rheological properties of a polysaccharide produced by an isolate of Klebsiella oxytoca were characterized. Freeze dried samples of the polysaccharide were neutral and were completely soluble in water. Samples did not form gels even in the presence of salt treatments. The major monosaccharide constituents of the polysaccharide were rhamnose (37%, w/w) and glucose (34%, w/w). Residues of cellobiose were detected, suggesting that the polysaccharide had a cellulose backbone. The gum was more comparable to broth apparent viscosities of xanthan gum than to gellan gum. The K. oxytoca polysaccharide (KOP) produced high solution viscosity at low concentrations. At a gum concentration 0.5% (w/v), an apparent viscosity of 400 cP at 24 s-1 was obtained. Rheological behavior showed that the KOP formed non newtonian fluids, indicating that it is a pseudoplastic biopolymer. Although the KOP solutions displayed pseudoplastic behavior, increases in shearing time did not result in significant changes on the apparent viscosity. This indicated that the gum is neither thixotropic nor rheopectic. The conclusion reached about the potential application of the gum was that it could be suitable for use as a stabilizing or suspending agent rather than a gelling agent.

Highlights

Over the past few decades, several microorganisms have been investigated for the production of exopolysaccharides using whey or lactose as fermentation substrate (Shams and Jaynes, 1983; Cerning et al, 1992)
The pH of the K. oxytoca polysaccharide (KOP) indicated that it may be more suitable for use in products that requires acidic or near neutral pH processing conditions. These results have shown that KOP completely lost its shear thinning behavior at higher temperatures, indicating that the polysaccharide gum could be useful in product preparations that require up to pasteurization temperatures
High performance liquid chromatography analysis revealed that the exopolysaccharide produced by K. oxytoca is composed of rhamnose, glucose and cellobiose, a combination that is unique to this biopolymer

Summary

Introduction

Over the past few decades, several microorganisms have been investigated for the production of exopolysaccharides using whey or lactose as fermentation substrate (Shams and Jaynes, 1983; Cerning et al, 1992). Over the past three decades, attempts have been made to improve the utilization of whey by using it as a fermentation substrate for producing value added products such as ethanol and microbial exopolysacchari-. Whey has very high biological oxygen demand (> 45 000 ppm) and high lactose content (4.5%, w/v). For this reason, if discharged to the environment, whey can cause severe pollution since it is poorly metabolized by most environmental organisms (Ryder, 1988)

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