Microbial polysaccharides

Microbial polysaccharides represent a class of biopolymers that has been the object of much study in the biotechnological field. Being obtained from renewable sources, they bear specific features such as biocompatibility, biodegradability, non-toxicity, wide availability and low cost. These features form the basis for the continuous increase in the search for product formulation in such diverse areas as foodstuffs, biomedical, cosmetics, pharmaceutical, chemical, petroleum and some areas of the textile industry. These microbial gums are able to work as emulsifiers, stabilizers, binders, gelling agents, coagulating agents, flocculating agents, film-forming substances, lubricants and thickening agents.  

These biopolymers are naturally formed macromolecules during the growing cycle of the organisms, and therefore are referred to as natural polymers. Their synthesis generally involves enzymatic catalysis, with chain increase through polymerization reactions of activated monomers, those being typically formed within the cells through complete metabolic processes. 

The structure and composition of the microbial polysaccharides depend on several factors, such as the composition of the culture medium, kind of carbon source, kind of microbial system utilized, fermentation conditions (pH, temperature, oxygen concentrations) as well as the control. In bench scale or in commercial fermentations, these factors are offered so as to simulate the natural conditions. For the production of microbial gums it is required to establish the optimal composition of the medium and the fermentation parameters. Several ions are added to the medium so as to provide the synthesis of exopolysaccharides, and those should be present in suitable amounts. For several microbial species, K^+,, Mg⁺⁺, and in lesser amounts, Ca⁺⁺ are essentially required for optimum growth. Other ions, in lesser amounts, are required as well.

Nitrogen-fixating bacteria such as Rhizobium sp. tend to produce a large amount of polysaccharides so as to control the O₂ entrance within the cell. This group is thoroughly studied and has been associated to a high production and diversity of polysaccharides.

Experimental design and statistical analysis

Recent studies have demonstrated that the planning of experiments as well as the response surface method are valuable tools for the optimization of process parameters in fermenting processes. Through said method, factors and interactions affecting the desired response and that can be experimentally controlled are tested according to their efficiency for optimization of important fermentation process parameters, this being done by a limited number of experiments.

The statistical data interpretation obtained from an experimental planning can be carried out according to various statistical criteria and of significance, among which we point out the p Test, the t Test, the variance analysis and the adjustment of the mathematical model to experimental data, through determination coefficient.

In the experimental planning, the p Test comprises a tool that provides, for a certain confidence level, the probability of discarding the main effects and the interaction effects of the studied variable. The choice of the confidence level occurs as a function of the desired accuracy level. The most common value for the accuracy level is 95%.

And for a certain confidence level, the Student t Test is used for evaluating if the calculated effects are significantly different from zero.

The determination factor measures the approximation between the experimental points and a certain curve. When this value is close to 1, a good adjustment of the points to the curve is obtained, meaning that the curve can describe continuously the phenomenon established by the points, at the desired confidence level and at the interval. 

Final considerations

Due to their large application in several areas, microbial polysaccharides are being extensively studied in order to obtain materials of microbian source showing high industrial potentiality. The utilization of statistically based experimental projects is a powerful tool for the preparation of products showing improved features and has aided to locate the optimum levels of the most significant parameters for exopolysaccharide production by Rhizobium sp., through minimum efforts and time.