During alcoholic fermentation yeasts of Saccharomyces cerevisiae are exposed to rapid changes in the fermentative environment. High temperature, high concentration of substrates and products, lack of nutrients and oxygen are stress factors from which yeasts require protection. Microencapsulation is a technique that is gaining an increasing role in food industry and biotechnology. Research has shown that microencapsulation can protect yeasts from stress factors in the fermentative environment. In this master's thesis, we prepared microcapsules from alginate, chitosan, and pectin with a BÜCHI 395–Pro Encapsulator. Yeast strain S. cerevisiae ZIM 2155 from the Collection of Industrial Microorganisms of the Biotechnical Faculty was used for encapsulation. The course of alcoholic fermentation with encapsulated yeasts was monitored in media with high glucose concentration at high temperature. Yeast cell release from the microbeads was monitored by measuring the OD values at 650 nm, the amount of ethanol produced, and glucose consumption were analyzed by HPLC method. We found that encapsulation successfully protected yeasts from the high concentration of glucose and ethanol in the medium, as the encapsulated yeasts achieved better yields. Encapsulation only partially successfully protected the yeasts from the fermentation temperature of 37 and 42 °C. The encapsulated yeasts achieved better yields than free at 8 % glucose and 37 °C, and at 24 % glucose at 37 and 42 °C, but still produced lower ethanol concentration than at 24 °C. Encapsulation affected the kinetics of glucose consumption and ethanol production. Of the three polysaccharides used, alginate microbeads proved to be the most effective. When using alginate microbeads (240 ± 27 µm), the yeasts achieved the best yields and produced the highest concentrations of ethanol (up to 13,1 vol. %. of the resulting ethanol).
|
