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Polyalcohol arabitol can be used in the food and pharmaceutical industries as a natural sweetener, a dental caries reducer, and texturing agent. Environmental samples were screened to isolate effective yeast producers of arabitol. The most promising isolate 27RL-4, obtained from raspberry leaves, was identified genetically and biochemically as Candida parapsilosis. It secreted 10.42– 10.72 g l-1 of product from 20 g l-1 of L-arabinose with a yield of 0.51 - 0.53 g g-1 at 28°C and a rotational speed of 150 rpm. Batch cultures showed that optimal pH value for arabitol production was 5.5. High yields and productivities of arabitol were obtained during incubation of the yeast at 200 rpm, or at 32°C, but the concentrations of the polyol did not exceed 10 g l-1. In modified medium, with reduced amounts of nitrogen compounds and pH 5.5-6.5, lower yeast biomass produced a similar concentration of arabitol, suggesting higher efficiency of yeast cells. This strain also produced arabitol from glucose, with much lower yields. The search for new strains able to successfully produce arabitol is important for allowing the utilization of sugars abundant in plant biomass.

L-arabitol, a polyol with applications in the food and pharmaceutical industries, is secreted by different yeasts, e.g., Candida spp., Pichia spp., and Debaryomyces spp. The process of its biotechnological production is highly dependent on the physical and chemical conditions of culture. The aim of this study was to use statistical response surface methodology (RSM) to optimize the biotransformation of L-arabinose to arabitol by Candida parapsilosis, a yeast species able to assimilate pentoses. Batch cultures of the yeast were prepared following a Plackett-Burman design for seven variables. Following this, rotation speed, temperature, and L-arabinose concentration were chosen for a central composite design (CCD) experiment, which was carried out to optimize the production L-arabitol. The results showed that the optimal levels for the three factors were: rotation speed 150 rpm, temperature 28°C, and L-arabinose concentration 32.5 g/l. The predicted concentration of arabitol after two days of incubation of C. parapsilosis under the above conditions was 14.3 g/l. The value of R=0.8323 suggested that this model was well-fitted to the experimental data, and this was confirmed during a verification experiment. [ABSTRACT FROM AUTHOR]

A proteinase produced by the human gastrointestinal isolate Lactobacillus rhamnosus strain OXY was identified and characterized. The prtR2 gene coding for proteinase activity was detected in the examined strain. The PCR primers used were constructed on the basis of the sequence of the prtR2 proteinase gene from Lactobacillus rhamnosus GG. The enzyme was purified by fast protein liquid chromatography (FPLC) using CM-Sepharose Fast Flow and Sephacryl S-300 columns. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the enzyme had a relatively low molecular mass of 60 kD. Protease activity was observed at a pH range from 6.5 to 7.5 with optimum kcat/Km values at pH 7.0 and 40°C. Maximum proteolytic activity (59 U mL−1) was achieved after 48 hr of cultivation. The activity of the enzyme was inhibited only by irreversible inhibitors specific for serine proteinases (PMSF and 3,4-dichloro-isocumarine), suggesting that the enzyme was a serine proteinase. Proteinase activity was increased by Ca2+ and Mg2+, and inhibited by Cu2+, Zn2+, Cd2+, and Fe2+. [ABSTRACT FROM AUTHOR]

An evaluation was made of the ability of 9 low-protease mutants of Trichoderma reesei M-7 to produce extracellular enzymes on a medium with whey enriched with mineral salts. Cultures were carried out using batch and continuous culture methods. Inversely proportional relationships between the activity of cellulases and xylanases as well as the activity of proteases in filtrates obtained from cultures of low-protease mutants of Trichoderma reesei M-7 were not found unambiguously in batch cultures. In continuous cultures, in turn, the highest activities were shown by filtrates of mutants of Trichoderma reesei M- 7 which exhibited the lowest ability to produce extracellular proteases in batch cultures. [ABSTRACT FROM AUTHOR]

Comparing the production of extracellular enzymes by the examined mutants Trichoderma reesei RUT-C30, Trichoderma reesei 18/14, Trichoderma reesei 18/15 under continuous cultivations in a medium containing undiluted whey with mineral salts fortification, it was found that the strain Trichoderma reesei 18/15 showed the highest FPU and xylanolytic activities with low proteolytic activity after continuous cultivation. [ABSTRACT FROM AUTHOR]