Isolation and characterization of bioethanol producing wild yeasts from bio-wastes and co-products of sugar factories

Purpose

Yeasts are widely used for the production of bioethanol from biomasses rich in sugar. The present study was aimed at isolating, screening, and characterizing fermentative wild yeast recovered from bio-waste and co-products of Ethiopian sugar factories for bioethanol production using sugarcane molasses as a substrate.

Method

The wild yeasts were identified according to their cellular morphology and D1/D2 and ITS1-5.8S-ITS2 rDNA sequencing. Analysis of ethanol and by-product concentration was done by HPLC equipped with a UV detector. Higher alcohols, acetaldehyde, and methanol were analyzed using GC-MS equipped with a flame ionization detector (FID).

Result

Seven strains (Meyerozyma caribbica MJTm3, Meyerozyma caribbica MJTPm4, Meyerozyma caribbica SHJF, Saccharomyces cerevisiae TA2, Wickerhamomyces anomalus MJTPm2, Wickerhamomyces anomalus 4m10, and Wickerhamomyces anomalus HCJ2F) were found tolerant to 18% (v/v) ethanol, whereas one strain Meyerozyma caribbica MJTm3 tolerated 20%. These strains also showed tolerance to 45°C, 50% of sugar, and pH 2–10. Meyerozyma caribbica MJTm3 produced 12.7% (v/v) of alcohol with an actual ethanol concentration of 26 g L−1, an ethanol yield of 47%, 78% of theoretical yield, and a productivity of 0.54 g L−1 h−1 from 30 °Brix of molasses at 48 h incubation under laboratory scale. Based on the one variable at a time optimization (OVAT), the optimal parameters for maximum bioethanol production were at initial pH 5.5, 35 °Brix, 30°C, 15% inoculum size, 150 rpm, 4 g L−1 di-ammonium phosphate supplement, and 48 h incubation. Under these optimum conditions, 14% (v/v) alcohol, 42 g L−1 actual ethanol concentration, 69% ethanol yield, 89% of theoretical yield, and productivity of 0.88 g L−1 h−1 were obtained.

Conclusion

These results indicated that M. caribbica MJTm3 should further be evaluated, optimized, and improved for industrial bioethanol production due to its fermentation potential.

Novel microencapsulated yeast for the primary fermentation of green beer: kinetic behavior, volatiles and sensory profile

The development of innovative and more cost-effective approaches of making beer throughout continuous fermentation process remains a challenging problem, which is worthy of serious exploration. The current work focuses on the application of a commercial brewing yeast (S. cerevisiae Nottingham Ale), entrapped into chitosan-calcium alginate double layer microcapsules, for the production of a Pale Ale beer. During the primary alcoholic fermentation, the consumption rate of fermentable brewing sugars and dissolved O₂, estimated by the Gompertz equation, was halved in the beer obtained by encapsulated yeast in comparison with the free cell. The physical-chemical parameters of beer (i.e. pH, alcohol content, color and bitterness) were not remarkably affected by the different yeast-inoculating form. However, the volatile profiles identified by means of HS-SPME-GC-MS analysis, significantly differed in terms of terpenes, esters and alcohols content, thus proving that the yeast-inoculating form may typify the odor and flavor descriptors of the green beer.

Comparative study on two commercial strains of Saccharomyces cerevisiae for optimum ethanol production on industrial scale

Two commercial strains of Saccharomyces cerevisiae, Saf-Instant (Baker's yeast) and Ethanol red (Mutant) were compared for ethanol production during hot summer season, using molasses diluted up to 6-7^° Brix containing 4%-5% sugars. The yeasts were propagated in fermentation vessels to study the effects of yeast cell count and varying concentrations of Urea, DAP, inoculum size and Lactrol (Antibiotic). Continuous circulation of mash was maintained for 24 hours and after this fermenter was allowed to stay for a period of 16 hours to give time for maximum conversion of sugars into ethanol. Saccharomyces cerevisiae strain (Saf-instant) with cell concentration of 400 millions/mL at molasses sugar level of 13%–15% (pH 4.6 ± 0.2, Temp. 32°C ± 1), inoculum size of 25% (v/v), urea concentration, 150 ppm, DAP, 53.4 ppm and Lactrol,150 ppm supported maximum ethanol production (8.8%) with YP/S = 250 L ethanol per tone molasses (96.5% yield), and had significantly lower concentrations of byproducts. By selecting higher ethanol yielding yeast strain and optimizing the fermentation parameters both yield and economics of the fermentation process can be improved.