Search

The purpose of this study is to obtain ionically cross-linked gellan particles containing immobilized yeast cells. The zinc acetate was chosen as a cross-linking agent due to its beneficial role in the growth and nutrition of yeast cells and also due to the advantages of its use in fermentation processes. The physicochemical and morphological properties as well as the fermentative activity of the obtained particles were studied. The zinc acetate concentration has an influence on particles stability in water, on the mechanical stability and also on the swelling degree. The morphology of the obtained particles was analyzed by SEM and proves that the yeast cells are immobilized in large numbers in the polymeric matrix. The cell viability is maintained at high values after several fermentation cycles. These obtained micro-bioreactors were tested in terms of fermentative activity and the fermentation process was optimized by studying the influence of several factors. The gellan gum particles can be easily recovered by filtration and they can be reused in repeated fermentation cycles. The results obtained in the presence of these cross-linked particles are comparable to those achieved in the free yeast fermentation. [ABSTRACT FROM AUTHOR]

The paper reports the preparation of particles, having a hydrogel behavior, with immobilized yeast cells from a mixture of polysaccharide based on gellan, i-carrageenan, and carboxymethyl cellulose sodium salt. These particles were ionically cross-linked, using the extrusion method, with magnesium acetate, calcium acetate and zinc acetate and were characterized, by FTIR and SEM, in terms of some physicochemical properties, morphology, stability in water, and w ater retention capacity. These properties are influenced by the composition of polysaccharide mixture, which determines the number of cross-linkable functional groups, and also by the type and the concentration of the cross-linking agent. Analysis, by scanning electron microscopy, reveals that the yeast cells are well immobilized and in high amounts in the polysaccharides matrix. This matrix maintains the cell viability at high levels in aqueous media. High fermentation yields were obtained and the specific productivity in ethanol was equal to 0.79 g ethanol/h x g yeast cells. Highest ethanol yield was obtained for the sample cross-linked with Mg2*, and the lowest for the sample cross-linked with Zn2+. Polysaccharides matrix provides structural stability to yeast cells and maintains the cells viability, at values higher than 82% even after 10 fermentation cycles, as well as their ability to proliferate. Moreover, the obtained particles are stable, can be readily recovered by filtration from the fermentation medium and can be reused for at least 10 fermentation cycles. The obtained bio-reactors could represent a new approach to solving the problem of producers in the alcoholic beverages industry concerning the deficit of mineral nutrients. [ABSTRACT FROM AUTHOR]

In this paper we report on the production of microbioreactors using ionically cross-linked gellan containing immobilized yeast cells with potential application in glucose fermentation. Cross-linking was achieved through a novel extrusion process in capillary by ionotropic gelation under the action of magnesium acetate. Compared to commonly used methods, this provides a host of practical advantages. The particles were physico-chemically and morphologically characterized as their mechanical stability, behavior in aqueous media, and bio-catalytic activity are influenced by the amount of cross-linker used. This demonstrated their ability to be reused in a large number of fermentation cycles without losing their bio-catalytic activity. Our results are wholly comparable with the behavior of free yeast. We show that fermentation cycles can succeed either immediately or at variable intervals, ensuring high yields of glucose transformation, comparable-if not superior-to results currently obtained using free yeast. [ABSTRACT FROM AUTHOR]