The marine psychrophilic and endemic Antarctic yeast Leucosporidium antarcticum strain 171 synthesizes intracellular b-fructofuranosidase, and intra- and extracellular a-glucosidases. Each enzyme is maximally produced at 5°C , while the strain’s optimum growth temperature is 15°C . Invertase biosynthesis appeared regulated by catabolic repression, and induced by sucrose; the enzyme was extremely unstable ex vivo, and only EDTA, Mn2+, and BSA stabilized it for up to 12 h after yeast cell lysis. Thermal stability of the invertase was also low (30 min at temperatures up to 12°C). The optimum temperature for invertase activity was 30°C , and optimum pH was 4.55 to 4.75. The extracellular a-glucosidase was maximally active at 35°C and pH 6.70–7.50, and stable for 30 min up to 20°C.
The measured rate of release of intercellular protein from yeast cells by ultrasonication was applied for evaluating the effects of sonication reactor geometry on cell disruption rate and for validation of the simulation method. Disintegration of two strains of Saccharomyces cerevisiae has been investigated experimentally using a batch sonication reactor equipped with a horn type sonicator and an ultrasonic processor operating at the ultrasound frequency of 20 kHz. The results have shown that the rate of release of protein is directly proportional to the frequency of the emitter surface and the square of the amplitude of oscillations and strongly depends on the sonication reactor geometry. The model based on the Helmholtz equation has been used to predict spatial distribution of acoustic pressure in the sonication reactor. Effects of suspension volume, horn tip position, vessel diameter and amplitude of ultrasound waves on the spatial distribution of pressure amplitude have been simulated. A strong correlation between the rate of protein release and the magnitude of acoustic pressure and its spatial distribution has been observed. This shows that modeling of acoustic pressure is useful for optimization of sonication reactor geometry.
The removal of organic dyes from industrial wastewater remains a problem, both technically and economically. In this study, Yarrowia lipolytica yeast cells were isolated from poultry meat and immobilized using alginate. The immobilized Yarrowia lipolytica yeast was used as biosorbent to remove methylene blue (MB) dye from synthetic effl uent water. The results show that maximum adsorption capacity under optimum conditions was 66.67 mg∙g-1. The equilibrium adsorption data fi tted well onto the Freundlich adsorption isotherms with R2 >0.99. Adsorption kinetics was of pseudo-second order process suggesting that the adsorption was a chemisorption. FTIR spectra identifi ed typical absorption bands of a biosorbent. Sorption of MB dye on Yarrowia lipolytica yeast cells was exothermic with weak sorption interaction.
Saccharamyces cerevisia known as baker’s yeast is a product used in various food industries. Worldwide economic competition makes it a necessity that industrial processes be operated in optimum conditions, thus maximisation of biomass in production of saccharamyces cerevisia in fedbatch reactors has gained importance. The facts that the dynamic fermentation model must be considered as a constraint in the optimisation problem, and dynamics involved are complicated, make optimisation of fed-batch processes more difficult. In this work, the amount of biomass in the production of baker’s yeast in fed-batch fermenters was intended to be maximised while minimising unwanted alcohol formation, by regulating substrate and air feed rates. This multiobjective problem has been tackled earlier only from the point of view of finding optimum substrate rate, but no account of air feed rate profiles has been provided. Control vector parameterisation approach was applied the original dynamic optimisation problem which was converted into a NLP problem. Then SQP was used for solving the dynamic optimisation problem. The results demonstrate that optimum substrate and air feeding profiles can be obtained by the proposed optimisation algorithm to achieve the two conflicting goals of maximising biomass and minimising alcohol formation.