Enhanced production of bioethanol and ultrastructural characteristics of reused Saccharomyces cerevisiae immobilized calcium alginate beads
Department of Wood Science and Landscape Architecture (BK21 Program), Chonnam National University, Gwangju 500-757, Republic of Korea.Bioresource Technology (Impact Factor: 4.49). 09/2011; 102(17):8191-8. DOI: 10.1016/j.biortech.2011.06.063
Yeast immobilized on alginate beads produced a higher ethanol yield more rapidly than did free yeast cells under the same batch-fermentation conditions. The optimal fermentation conditions were 30°C, pH 5.0, and 10% initial glucose concentration with 2% sodium alginate beads. The fermentation time using reused alginate beads was 10-14 h, whereas fresh beads took 24h, and free cells took 36 h. All bead samples resulted in nearly a 100% ethanol yield, whereas the free cells resulted in an 88% yield. Transmission electron microscopy (TEM) showed that the shortened time and higher yield with the reused beads was due to a higher yeast population per bead as well as a higher porosity. The ultrastructure of calcium alginate beads and the alginate matrix structure known as the "egg-box" model were observed using TEM.
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- "Immobilization techniques can be categorized as follows: (1) immobilization on solid carrier surfaces, (2) entrapment within a porous matrix, (3) mechanical containment behind barriers, and (4) cell flocculation (aggregation). Bioethanol fermentation using immobilized cells can increase cell density, shorten fermentation times, increase ethanol and inhibitor tolerances, and improve the feasibility of using continuous fermentation, resulting in higher bioethanol production efficiency . Lee et al.  used sodium alginate beads immobilized with Saccharomyces cerevisiae for bioethanol fermentation. They found that immobilized yeast cells converted glucose into alcohol http://dx.doi.org/10.1016/j.procbio.2015.06.006 1359-5113/© 2015 Elsevier Ltd. "
ABSTRACT: Cell immobilization is a way to isolate or localize intact cells in a certain space and maintain their catalytic activity. Immobilized cells can effectively reduce the negative effects of inhibitors and the processing cost of inoculum preparation for continuous or fed-batch fermentation of microorganisms. In this study, a novel yeast immobilization technique using renewable poly-l-lactic acid (PLLA) microtube array membrane (MTAM) was thoroughly evaluated for bioethanol fermentation. PLLA-MTAM was shown to be stable in 15% (v/v) ethanol solution during shaking cultivation. A yeast encapsulation efficiency of 67–70% was obtained, and the yeasts in MTAMs with greater porosity showed greater bioethanol productivity. The MTAM-immobilized Kluyveromyces marxianus, prepared using in situ and siphon methods, were evaluated using 5% (w/v) glucose fermentation. Improved glucose consumption and bioethanol production were observed in batch bioethanol fermentation. In 7 cycles during repeated-batch fermentation, the immobilized yeasts prepared using the in situ method showed a maximum CEtOH of 24.23 g/L, maximum YP/S of 0.48 g/g, and r PEtOH of 2.69 g/L h. Our data indicated that the PLLA-MTAM immobilized yeasts significantly enhanced bioethanol productivity and was a novel, promising technology for bioethanol fermentation.
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- "Different microbial species have been encapsulated in various matrices for different applications. On many, one might mention the encapsulation of the fungal strains for biocontrol and other applications (Lee et al. 2011; Cruz et al. 1998); the thermophilic and methanogenic bacteria encapsulation (Kanasawud et al. 1989) has also been investigated for potential commercial uses. "
ABSTRACT: A bacterial strain E21 was isolated from a sample of water collected in the salt lake located close to Ain Salah, Algeria. The analysis of 16S rRNA gene sequence had indicated that the strain had 93 % sequence similarity with the genus Natrialba sp. strain E21 (GenBank, FR750525.1) and was considered extremely halophilic. Production of biosurfactant by the strain E21 with free and entrapped cells was investigated using soluble starch in the saline conditions. Biosurfactant synthesis was followed by measuring the surface tension and emulsifying index 9 days under optimal conditions (40 °C, pH 7). Some diffusional limitations in alginate and agar beads affected the kinetics of biosurfactant production when compared to that obtained with free cells culture. The minimum values of surface tension were 27 and 30 mN m−1 achieved after 9 days with free and immobilized cells, respectively, while the corresponding maximum E24 values were 65.3 and 62.3 %, respectively. The re-use of bacterial cells along with the limited cell losses provided by the immobilized system might lead to significant reduction of the biosurfactant production cost.
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- "After the formation of beads, 0.1 M sterile CaCl 2 solution was replaced with 0.05 M sterile CaCl 2 solution and the cells were allowed to harden for 12 h. Beads were then washed with sterile 0.85% NaCl solution to remove nonadherent cells and CaCl 2 ions (Lee et al., 2011; Razmovski and Vučurovic´, 2011). "
ABSTRACT: In this study, optimization of ethanol production from carob pod extract was carried out by immobilized Saccharomyces cerevisiae. Results showed that Ca-alginate concentration and the amount of immobilized cells had significant effects on yield. Optimum conditions for ethanol fermentation were determined to be 2% Ca-alginate concentration, 150rpm agitation rate, 5% yeast cells entrapped in beads and pH 5.5. After validation experiments; ethanol concentration, yield, production rate and sugar utilization rate were respectively 40.10g/L, 46.32%, 3.19g/L/h and 90.66%; and the fermentation time was decreased to 24h. In addition, the immobilized cells were shown to be reusable for five cycles, though a decrease in yield was observed. Finally, carob pod extract was used for ethanol fermentation by controlled and uncontrolled pH without any enrichment, and the results suggest that carob extract can be utilized effectively by immobilized-cell fermentation without the use of enrichments to facilitate yeast growth.
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