Ethanol production from henequen (Agave fourcroydes Lem.) juice and molasses by a mixture of two yeasts

Isolation, Identification, Optimization of Baker’s Yeast from Natural Sources, Scale-Up Production Using Molasses as a Cheap Carbohydrate Source, and Evaluation for Bread Production

(1) Background: Bangladesh must has to spend a large amount of foreign currency to import commercial baker’s yeast every year. We could save money by finding a potential Saccharomyces cerevisiae from natural sources compatible with commercial baker’s yeast production. (2) Methods: Grapes, rice, pineapples were collected, processed, and inoculated on YMA plates and incubated at 30 °C for 48 h. Then 11 single morphologically well-formed colonies were isolated, purified, and identified, three as S. cerevisiae, three as S. rouxii, three as S. bisporus, and two as S. exigus based on standard cultural, morphological, and biochemical characteristics. Identified S. cerevisiae (designated as G2, P5 and R3) were then assessed for CO2 production as a measure of their baking potential during bread production and compared with two commercial strains (designated as C1 and C2). (3) Results: Isolate-G2 produced the maximum of 1830 mm3 of gas, whereas C1, C2, R3, and P5 produced 1520, 1680, 770, and 610 mm3 gas, respectively. No strain produced H2S which is associated with an off-flavor and unpleasant taste. These isolates showed maximum cell density at a pH range of 4–5.5 in 4–16% molasses broth at 30 °C after 4 days of incubation and maximum 4.75 × 109, 7.9 × 108, 1.472 × 1010, 2.08 × 1010 and 5.24 × 109 CFU mL−1 were produced by C1, C2, G2, P5 and R3, respectively. Isolate-G2 was found to have the most potential, whereas isolate-R3 and P5 have satisfactory potential. (4) Conclusions: G2 could be a good candidate for commercial trials.

The complete chloroplast genome of Agave fourcroydes

Agave fourcroydes (henequen) is the only cultivated Agave species in the Yucatan Peninsula, which is mainly used for fiber production. In the present study, we have successfully assembled the chloroplast (cp) genome of A. fourcroydes. The full length of the cp genome is 157,291 bp with a GC content at 37.8%. The cp genome is constructed with an inverted repeat region a (IRa) of 26,573 bp, a small single copy region (SSC) of 18,230 bp, an inverted repeat region b (IRb) of 26,573 bp and a large single copy region (LSC) of 85,915 bp. The annotation result reveals 132 genes on the cp genome, including 86 protein-coding genes, 38 tRNAs and 8 rRNAs. Phylogenetic tree reveals that A. fourcroydes is closely related with A. sisalana.

Kluyveromyces marxianus: Current State of Omics Studies, Strain Improvement Strategy and Potential Industrial Implementation

Bioethanol is considered an excellent alternative to fossil fuels, since it importantly contributes to the reduced consumption of crude oil, and to the alleviation of environmental pollution. Up to now, the baker yeast Saccharomyces cerevisiae is the most common eukaryotic microorganism used in ethanol production. The inability of S. cerevisiae to grow on pentoses, however, hinders its effective growth on plant biomass hydrolysates, which contain large amounts of C5 and C12 sugars. The industrial-scale bioprocessing requires high temperature bioreactors, diverse carbon sources, and the high titer production of volatile compounds. These criteria indicate that the search for alternative microbes possessing useful traits that meet the required standards of bioethanol production is necessary. Compared to other yeasts, Kluyveromyces marxianus has several advantages over others, e.g., it could grow on a broad spectrum of substrates (C5, C6 and C12 sugars); tolerate high temperature, toxins, and a wide range of pH values; and produce volatile short-chain ester. K. marxianus also shows a high ethanol production rate at high temperature and is a Crabtree-negative species. These attributes make K. marxianus promising as an industrial host for the biosynthesis of biofuels and other valuable chemicals.

Effect of Myclobutanil Pesticide on the Physiological Behavior of Two Newly Isolated Saccharomyces cerevisiae Strains during Very-High-Gravity Alcoholic Fermentation

Yeasts are able to act as biosorbents, as their cell wall includes several components capable of binding organic xenobiotic compounds that can potentially be removed during various fermentation processes. In the present investigation, two novel Saccharomyces cerevisiae strains (LMBF-Y 16 and LMBF-Y-18), previously isolated from grapes, were studied regarding their physiological behavior (dry cell weight-DCW production, substrate uptake, and ethanol and glycerol biosynthesis) during fermentations of grape must, in some cases enriched with commercial glucose and fructose (initial total sugar concentration approximately 150 and 250 g/L, respectively). Myclobutanil (a chiral triazole fungicide broadly used as a protective agent of vine) was also added to the culture media at various concentrations in order to assess the ability of the yeasts to simultaneously perform alcoholic fermentations and detoxify the medium (i.e., to remove the fungicide). In the first set of experiments and for both tested strains, trials were carried out in either 250 mL or 2.0 L agitated shake flasks in either synthetic glucose-based experiments or grape musts. Since the results obtained in the trials where the cultures were placed in 2.0 L flasks with grape musts as substrates were superior in terms of both DCW and ethanol production, these experimental conditions were selected for the subsequent studies. Both strains showed high fermentative efficiency, producing high amounts of DCW (9.5-10.5 g/L) in parallel with high ethanol production, which in some cases achieved values very close to the maximum theoretical ethanol production yield (≈0.49 g of ethanol per g of sugar). When using grape must with initial total sugars at approximately 250 g/L (very high gravity fermentation media, close to winemaking conditions), significantly high ethanol quantities (i.e., ranging between 105 and 123 g/L) were produced. Myclobutanil addition slightly negatively affected sugar conversion into ethanol; however, in all cases, ethanol production was very satisfactory. A non-negligible myclobutanil removal during fermentation, which ranged between 5%-27%, as a result of the adsorptive or degradative capacity of the yeast was also reported. The presence of myclobutanil had no effect on DCW production and resulted in no significant differences in the biosynthesis of glycerol. Therefore, these newly isolated yeast strains could be excellent candidates for simultaneous high ethanol production and parallel pesticide removal in a general biorefinery concept demonstrating many environmental benefits.

Exploitation of olive oil mill wastewaters and molasses for ethanol production using immobilized cells of Saccharomyces cerevisiae

An alcoholic fermentation process is described, involving molasses, the main by-product of the sugar industry, blended with crude olive oil mill wastewaters (OOMWs) and immobilized Saccharomyces cerevisiae cells on delignified cellulosic material (DCM). For comparison, fermentations with free cells were also carried out. Initially, the optimum blending mixture for molasses dilution was sought after, while at a second step repeated batch fermentations at a temperature range 5-30 °C were performed to monitor the operational stability of the system. A 1/1 ratio of OOMWs/tap water blending mixture and cell immobilization resulted in higher fermentation parameters. Ethanol concentration and daily productivity values recorded at temperatures ≥ 20 °C (up to 67.8 g L^-1 and 67.6 g L^-1 d^-1, respectively) could be adopted by the industrial sector, although the decline in fermentation efficiency observed, probably due to the toxicity effects of OOMWs. Finally, the potential of OOMWs treatment for ethanol production is highlighted and assessed.

Agave as a model CAM crop system for a warming and drying world

As climate change leads to drier and warmer conditions in semi-arid regions, growing resource-intensive C3 and C4 crops will become more challenging. Such crops will be subjected to increased frequency and intensity of drought and heat stress. However, agaves, even more than pineapple (Ananas comosus) and prickly pear (Opuntia ficus-indica and related species), typify highly productive plants that will respond favorably to global warming, both in natural and cultivated settings. With nearly 200 species spread throughout the U.S., Mexico, and Central America, agaves have evolved traits, including crassulacean acid metabolism (CAM), that allow them to survive extreme heat and drought. Agaves have been used as sources of food, beverage, and fiber by societies for hundreds of years. The varied uses of Agave, combined with its unique adaptations to environmental stress, warrant its consideration as a model CAM crop. Besides the damaging cycles of surplus and shortage that have long beset the tequila industry, the relatively long maturation cycle of Agave, its monocarpic flowering habit, and unique morphology comprise the biggest barriers to its widespread use as a crop suitable for mechanized production. Despite these challenges, agaves exhibit potential as crops since they can be grown on marginal lands, but with more resource input than is widely assumed. If these constraints can be reconciled, Agave shows considerable promise as an alternative source for food, alternative sweeteners, and even bioenergy. And despite the many unknowns regarding agaves, they provide a means to resolve disparities in resource availability and needs between natural and human systems in semi-arid regions.

Hydrolysis of Agave fourcroydes Lemaire (henequen) leaf juice and fermentation with Kluyveromyces marxianus for ethanol production

BACKGROUND

Carbon sources for biofuel production are wide-ranging and their availability depends on the climate and soil conditions of the land where the production chain is located. Henequen (Agave fourcroydes Lem.) is cultivated in Yucatán, Mexico to produce natural fibers from the leaves, and a juice containing fructans is produced during this process. Fructans can be hydrolyzed to fructose and glucose and metabolized into ethanol by appropriate yeasts. In Mexico, different Agave species provide the carbon source for (distilled and non-distilled) alcoholic beverage production using the stem of the plant, whilst the leaves are discarded. In this work, we investigated the effect of thermal acid and enzymatic hydrolysis of the juice on the amount of reducing sugars released. Growth curves were generated with the yeasts Saccharomyces cerevisiae and Kluyveromyces marxianus and fermentations were then carried out with Kluyveromyces marxianus to determine alcohol yields.

RESULTS

With thermal acid hydrolysis, the greatest increase in reducing sugars (82.6%) was obtained using 5% H2SO4 at 100°C with a 30 min reaction time. Statistically similar results can be obtained using the same acid concentration at a lower temperature and with a shorter reaction time (60°C, 15 min), or by using 1% H2SO4 at 100°C with a 30 min reaction time. In the case of enzymatic hydrolysis, the use of 5.75, 11.47 and 22.82 U of enzyme did not produce significant differences in the increase in reducing sugars. Although both hydrolysis processes obtained similar results, the difference was observed after fermentation. Ethanol yields were 50.3 ± 4 and 80.04 ± 5.29% of the theoretical yield respectively.

CONCLUSIONS

Final reducing sugars concentrations obtained with both thermal acid and enzymatic hydrolysis were similar. Saccharomyces cerevisiae, a good ethanol producer, did not grow in the hydrolysates. Only Kluyveromyces marxianus was able to grow in them, giving a higher ethanol yield with the enzymatic hydrolysate. The leaves account for a non-negligible weight of the total agave plant biomass, so this work complements the knowledge already developed on agave fermentations by making it possible to produce ethanol from almost the entire plant (stem and leaves).

High-temperature ethanol fermentation by immobilized coculture of Kluyveromyces marxianus and Saccharomyces cerevisiae

Suspended and immobilized cocultures of the thermotolerant yeast, Kluyveromyces marxianus DMKU 3-1042 and the mesophilic flocculent yeast, Saccharomyces cerevisiae M30 were studied for their abilities to improve production and stability of ethanol fermentation. Sugarcane juice and blackstrap molasses, at initial sugar concentrations of 220 g/L, were used as carbon sources. The results indicated that the coculture system could improve ethanol production from both sugarcane juice and blackstrap molasses when the operating temperature ranged between 33 °C and 45 °C. High temperature tolerances were achieved when the coculture was immobilized. The immobilized coculture was more effective in high-temperature ethanol fermentation than the suspended cultures. The coculture immobilized on thin-shell silk cocoon and fermented at 37 °C and 40 °C generated maximal ethanol concentrations of 81.4 and 77.3 g/L, respectively, which were 5.9-8.7% and 16.8-39.0% higher than those of the suspended cultures, respectively.

Optimization of ethanol, citric acid, and α-amylase production from date wastes by strains of Saccharomyces cerevisiae, Aspergillus niger, and Candida guilliermondii

The present study deals with submerged ethanol, citric acid, and α-amylase fermentation by Saccharomyces cerevisiae SDB, Aspergillus niger ANSS-B5, and Candida guilliermondii CGL-A10, using date wastes as the basal fermentation medium. The physical and chemical parameters influencing the production of these metabolites were optimized. As for the ethanol production, the optimum yield obtained was 136.00 ± 0.66 g/l under optimum conditions of an incubation period of 72 h, inoculum content of 4% (w/v), sugars concentration of 180.0 g/l, and ammonium phosphate concentration of 1.0 g/l. Concerning citric acid production, the cumulative effect of temperature (30°C), sugars concentration of 150.0 g/l, methanol concentration of 3.0%, initial pH of 3.5, ammonium nitrate concentration of 2.5 g/l, and potassium phosphate concentration of 2.5 g/l during the fermentation process of date wastes syrup did increase the citric acid production to 98.42 ± 1.41 g/l. For the production of α-amylase, the obtained result shows that the presence of starch strongly induces the production of α-amylase with a maximum at 5.0 g/l. Among the various nitrogen sources tested, urea at 5.0 g/l gave the maximum biomass and α-amylase estimated at 5.76 ± 0.56 g/l and 2,304.19 ± 31.08 μmol/l/min, respectively after 72 h incubation at 30°C, with an initial pH of 6.0 and potassium phosphate concentration of 6.0 g/l.

Solvent extraction of organic acids from stillage for its re-use in ethanol production process

Stillage re-use in the fermentation stage in ethanol production is a technique used for the reduction of water and fermentation nutrients consumption. However, the inhibitory effect on yeast growth of the by-products and feed components that remains in stillage increases with re-use and reduces the number of possible recycles. Several methods such as ultrafiltration, electrodialysis and advanced oxidation processes have been used in stillage treatment prior its re-use in the fermentation stage. Nevertheless, few studies evaluating the effect of solvent extraction as a stillage treatment option have been performed. In this work, the inhibitory effect of serial stillage recycling over ethanol and biomass production was determined, using acetic acid as a monitoring compound during the fermentation and solvent extraction process. Raw palm oil methyl ester showed the highest acetic acid extraction from the aqueous phase, presenting a distribution coefficient of 3.10 for a 1:1 aqueous phase mixture:solvent ratio. Re-using stillage without treatment allowed up to three recycles with an ethanol production of 53.7 +/- 2.0 g L(-1), which was reduced 25% in the fifth recycle. Alternatively, treated stillage allowed up to five recycles with an ethanol final concentration of 54.7 +/- 1.3 g L(- 1). These results show that reduction of acetic acid concentration by an extraction process with raw palm oil methyl ester before re-using stillage improves the number of recycles without a major effect on ethanol production. The proposed process generates a palm oil methyl ester that contains organic acids, among other by-products, that could be used for product recovery and as an alternative fuel.