This paper presents a method to estimate the biomass of Spirulina cultivated on solid medium with sugarcane bagasse as a support, in view of the difficulty in determining biomass concentrations in bioprocesses, particularly those conducted in semi-solid or solid media. The genus Spirulina of the family Oscillatoriaceae comprises the group of multicellular filamentous cyanobacteria (blue-green microalgae). Spirulina is used as fish feed in aquaculture, as a food supplement, a source of vitamins, pigments, antioxidants and fatty acids. Therefore, its growth parameters are extremely important in studies of the development and optimization of bioprocesses. For studies of biomass growth, Spirulina platensis was cultured on solid medium using sugarcane bagasse as a support. The biomass thus produced was estimated by determining the protein content of the material grown during the process, based on the ratio of dry weight to protein content obtained in the surface growth experiments. The protein content of the biomass grown in Erlenmeyer flasks on surface medium was examined daily to check the influence of culture time on the protein content of the biomass. The biomass showed an average protein content of 42.2%. This methodology enabled the concentration of biomass adhering to the sugarcane bagasse to be estimated from the indirect measurement of the protein content associated with cell growth.

Background: The aim of this study was the production of xanthan gum from salts of volatile fatty acids, which can be generated in anaerobic processes for the production of hydrogen from organic wastewaters. Xanthan gum was produced with three different acid salts used to replace the traditional citrate, which is normally used in the culture for the production of this biopolymer. The volatile fatty acids (VFA) salts used were sodium acetate 0.0328 M, sodium propionate 0.0219 M, and sodium butyrate 0.0164 M. Results: The values of biomass yield, (Yp/x) obtained were 9.2 g/g for acetate, 11.78 g/g for citrate, 11.80 g/g for butyrate and 14.59 g/g for propionate, while the values of the product yield (Yp/s), were 0.92; 0.59; 0.71 and 0.72 for acetate, citrate, butyrate and propionate. As for the rheological characterization, the gums produced showed a consistency index (K) and flow index (n) of 9.8 dina.s-n.cm-2 and 0.34 for acetate; 6.3 dina.s-n.cm-2 and 0.39 for citrate, 5.8 dina.s-n.cm-2 and 0.45 for butyrate, 39.2 dina.s-n.cm-2 and 0.24 for propionate, that characterize the gums with good consistency and fluidity. Conclusions: It is possible to produce xanthan gum from short-chain volatile acids in replacement by the citrate that is usually used in medium composition for the gum production. These results contribute to the feasibility studies for implementation of processes for treating wastewater generating products such as volatile acids, hydrogen and consequent use of these acids for the production of xanthan gum.

Spirulina platensis is a cyanobacterium that has a high protein content and therefore, a high nutritional value. It can be cultivated either in a liquid or in a solid culture. When cultivated in aqueous culture the cell growth can be determined by following the optical density. On the other hand, when produced by solid cultivation the growth can be determined only indirectly, such as, through determination of the protein content of the fermenting solids. In this work the possibility of estimating cell growth by pH determination was verified. From the results it was concluded that pH and protein production (solid or surface culture) or cell content (liquid culture) correlate well, therefore pH determination seems to be a good method to determine cell growth.

The well-known entomopathogenic bacterium Bacillus thuringiensis (Bt) produces a spore-crystal complex which is responsible for its biocide characteristic, and the bacterium can be obtained by fermentation, either in liquid or semi-solid substrates. This paper presents a successful way to achieve solid-state fermentation of active Bt var. tolworthi (Btt) against Spodoptera frugiperda (fall armyworm) in corn. More than 10(9) CFU/g were obtained using humidified rice as substrate maintained in polypropylene bags. This active complex (substrate plus spore-crystal of Bt) was prepared in order to obtain 2 x 10(6) spores/mL; the final suspension then sprayed via tractor on corn fields. On the treated plants, mortality of neonate larvae was 100% within two days of spraying, and all larvae were found dead on leaves. During one maize crop cycle, two applications were made, and up until 70 days after emergence it was not necessary to apply any other insecticide for fall armyworm control.