Physico-chemical characteristics and fermentative activity of the hydrogel particles based on polysaccharides mixture with yeast cells immobilized, obtained by ionotropic gelation

- The hydrogel particles are obtained from gellan, i-carrageenan and CMCNa.
- The cations Mg2+, Ca2+, Zn2+ derived from acetates are effective cross-linkers.
- The yeast cells can be immobilized in hydrogel particles for obtaining bioreactors.
- The polymer matrix preserves in time the cell viability at optimal values.
- The bioreactors allow obtaining higher yields in glucose fermentation.

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 water 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 × 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.

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