Malolactic fermentation of wines with immobilised lactic acid bacteria - influence of concentration, type of support material and storage conditions.

Corn cobs, grape skins and grape stems were evaluated as support materials for immobilization of the lactic acid bacteria Oenococcus oeni. The support materials with immobilized cells were further used in malolactic fermentation (MLF) of white wine. Viability of using the immobilized supports was evaluated in consecutive batch fermentations under different conditions of temperature, ethanol and SO(2). Additionally, the possibility of storage and operational stability of the immobilized supports was also studied. All the three supports presented large potential for immobilization of O. oeni cells. The consecutive batches of MLF were successfully conducted for a total period of around 5 months with the possibility of storage of the biocatalyst for 30 d in wine at 25°C.

Decolorization of salt-alkaline effluent with industrial reactive dyes by laccase-producing Basidiomycetes strains.

The discharge of highly coloured synthetic dye effluents into rivers and lakes is harmful to the water bodies, and therefore, intensive researches have been focussed on the decolorization of wastewater by biological, physical or chemical treatments. In the present study, 12 basidiomycetes strains from the genus Pleurotus, Trametes, Lentinus, Peniophora, Pycnoporus, Rigidoporus, Hygrocybe and Psilocybe were evaluated for decolorization of the reactive dyes Cibacron Brilliant Blue H-GR and Cibacron Red FN-2BL, both in solid and liquid media. Among the evaluated fungi, seven showed great ability to decolorize the synthetic textile effluent, both in vivo (74-77%) or in vitro (60-74%), and laccase was the main ligninolytic enzyme involved on dyes decolorization. Pleurotus ostreatus, Trametes villosa and Peniophora cinerea reduced near to 60% of the effluent colour after only 1 h of treatment. The decolorization results were still improved by establishing the nitrogen source and amount to be used during the fungal strains cultivation in synthetic medium previous their action on the textile effluent, with yeast extract being a better nitrogen source than ammonium tartarate. These results contribute for the development of an effective microbiological process for decolorization of dye effluents with reduced time of treatment.

beta-Fructofuranosidase production by repeated batch fermentation with immobilized Aspergillus japonicus.

The fungus Aspergillus japonicus ATCC 20236 was immobilized in vegetal fiber and used in repeated batch fermentations of sucrose (200 g/l) for the production of beta-fructofuranosidases (FFase). The assays were performed during eight consecutive cycles that were completed in a total period of 216 h. After each 24-h cycle of fermentation (except for the first cycle, which lasted 48 h), the fermented broth was replaced by fresh medium, and the FFase activity was determined in the replaced medium. The average value of FFase activity was a constant 40.6 U/ml at the end of the initial seven cycles, but had decreased by 22% at the end of the eighth cycle. Concurrent with these high and constant FFase values, the hydrolyzing activity of this enzyme increased during the cycles, while the transfructosylating activity decreased. As a consequence, the maximum production of fructooligosaccharides of 134.60 g/l observed in the initial 30 h of fermentation (first cycle) had gradually decreased by the end of the subsequent cycles, reaching approximately 23% of this value during cycles 4-8. Based on these results, we conclude that the present immobilization system has a great potential for application in a semi-continuous process for the production of FFase, but further studies are necessary to maintain the FFase transfructosylation activity at high levels during the overall process.

Xylitol production from high xylose concentration: evaluation of the fermentation in bioreactor under different stirring rates.

AIMS: To investigate the production of xylitol by the yeast Candida guilliermondii FTI 20037, in a bioreactor, from rice straw hemicellulosic hydrolysate with a high xylose concentration. METHODS AND RESULTS: Batch fermentation was carried out with rice straw hemicellulosic hydrolysate containing about 85 g xylose l(-1), in a stirred-tank bioreactor at 30 degrees C, under aeration of 1.3 vvm (volume of air per volume of medium per min) and different stirring rates (200, 300 and 500 rev min(-1)). The bioconversion of xylose into xylitol by the yeast depended on the stirring rate, the maximum xylitol yield (YP/S = 0.84 g g(-1)) being achieved at 300 rev min-1, with no need to pretreat the hydrolysate for purification. CONCLUSIONS: To determine the most adequate oxygen transfer rate is fundamental to improving the xylose-to-xylitol bioconversion by C. guilliermondii. SIGNIFICANCE AND IMPACT OF THE STUDY: For the microbial production of xylitol to be economically viable, the initial concentration of xylose in the lignocellulosic hydrolysate should be as high as possible, as with high substrate concentrations it is possible to increase the final product concentration. Nevertheless, there are few reports on the use of high xylose concentrations. Considering a process in bioreactor, from rice straw hemicellulosic hydrolysate, this is an innovator work.