1. Introduction: Materials: Methods: Results : Conclusions:
9th International Conference on Materials Science and Engineering – BRAMAT Immobilized yeast cells in spherical gellan matrices: a comparative study C.E. IURCIUC (TINCU)1,2, C.L. SAVIN1, A. SAVIN1, M. POPA1, P. MARTIN2 1 ”Gheorghe Asachi” Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Natural and Synthetic Polymers, 73 Prof. Dr. Docent Dimitrie Mangeron, , Iasi, Romania 2 Université d’Artois, IUT Béthune, Département Chimie, CS20819, Béthune, France
Introduction:
Many researchers use physical entrapment in granular matrices among various immobilisation of living cells techniques. This method provides a valuable protection to the immobilized biocatalyst. It can be carried out under very mild conditions and it is suitable to produce spherical microparticles that can be used in continuous fermentation processes, in columns. [1, 2]
This paper represents a comparative study of immobilization of yeast cells in a gellan matrix (anionic polysaccharide). The matrix ionic crosslinking was performed using as crosslinking agents two acetates of divalent metals: Mg and Zn
Materials:
Gellan from Kelkogel food grade type.
Magnesium acetate
Zinc acetate
Baker’s yeast, was purchased from Pakmaya–Romania.
Glucose monohydrate.
Methods:
The particles for yeast immobilization were prepared by extrusion, through capillaries of a suspension obtained by mixing gellan solution and yeast cells. The final mixture was then dropped in a bath containing the crosslinking agent (certain concentration).
The influence of some factors (the concentration of the polysaccharide solution, the concentration of the crosslinking agent, the chemical nature of the crosslinker) on the physical-chemical characteristics and their fermentation ability was analyzed.
Biocatalytic activity of the new products was evaluated during the glucose fermentation in an aqueous solution ( 8% glucose in the presence of 0.5% magnesium acetate or 0.01% zinc acetate, at a temperature of 30 °C).
Results :
Figure 1:
Preparation technique of gellan particles
Figure 2: Ionically crosslinked gellan matrix containing yeast cells into the meshes, using as crosslinked agent (a) magnesium acetate and (b) zinc acetate
Table 1: Experimental program and obtained results
a b
Figure 3: Variation of the swelling degree in time for particles without yeast using as a cross-linking agent (a) magnesium acetate and (b) zinc acetate.
a b
Figure 5: Evolution of glucose fermentation yield in time for several cycles, in the presence of particles of gellan with yeast cells cross-linked with (a)magnesium acetate, sample P2 or (b) zinc acetate, sample L4 (b).
Figure 4:Amplitude sweep of the samples (a) P2, P4, P2+Y, P4+Y and (b) A4, L4, N4, A4+Y, L4+Y, N4+Y
Frequency sweep of the samples (c) P2, P12, P2+Y, P12+Y and (d) A4, L4, N4, A4+Y, L4+Y, N4+Y
Conclusions:
It was found that lower amounts of zinc acetate in the crosslinking bath are required for obtaining stable particles with high fermentation capacity.
The degree of swelling varies to the cross-linking density: the gellan particles cross-linked with (CH3COO)2Mg agent showed a lower cross-linking density than the ones cross-linked with (CH3COO)2Zn . This fact was demonstrated by the swelling degree and is in the good agreement to the rheology tests.
The rheology tests showed that the gellan particles with and without immobilized yeast cells are stable depending on the cross-ling density. The particles containing yeast cells and cross-linked with (CH3COO)2Mg are more stable than the others without yeast cells while in the case of the particles cross-linked with agent (CH3COO)2Zn were more stable without yeast cells.
Both types of particles can be used in a large number of fermentation cycles being stable and easy to recover from the fermenter. A possible explanation is that zinc and magnesium ions increase yeast cells proliferation.
Acknowledgement:
This work was supported by the strategic grant POSDRU/159/1.5/S/133652, co-financed by the European Social Fund within the Sectorial Operational Program Human Resources Development 2007 – 2013.
References:
1. I. Calinescu1, P. Chipurici, E. Alexandrescu, Adrian Trifan, Saccharomyces cerevisiae yeast immobilized on marrow stem sunflower and polyacrylamide hydrogels+, Cent. Eur. J. Chem., 12, 2014,
2. S.M. Tan, P.W.S. Heng, L.W. Chan, Development of re-usable yeast-gellan gum bioreactors for potential application in continuous fermentation to produce bio-ethanol, Pharmaceutics, 3, 2011,