Bioethanol

Bioethanol, beer and wine originate from very efficient fermentation processes, and they account for a global market that exceeds 700 USD billion per annum.

From: Advances in Applied Microbiology , 2019

An Overview of the Potential Uses for Coffee Husks

Leandro S. Oliveira , Adriana S. Franca , in Coffee in Health and Disease Prevention, 2015

31.4.5.2 Ethanol Production

Bioethanol is a biofuel regarded as a promising substitute for gasoline in the transportation sector. To make it competitive with fossil fuels, however, it is necessary to reduce production costs by using alternative biomass feedstock. Current industrial processes for bioethanol production use either sugarcane or cereal grains as feedstock, directly competing with the food sector. Also, projected fuel demands indicate that alternative, low-priced feedstocks are needed to reduce ethanol production costs. Furthermore, it is estimated that ethanol production from agricultural residues could increase to 16 times the current production. 20 Given the high concentration of carbohydrates in CHs, this residue can be viewed as potential raw material for bioethanol production. Furthermore, the produced ethanol could be used for biodiesel production based on coffee oil obtained from defective coffee beans, thus further contributing to the implementation of sustainable development in the coffee production chain. 8,20 However, the production of ethanol from CHs has not yet been adopted on a practical scale.

Early studies indicated that biofuel fermented just from CP contained only 2.5–3.0% ethanol (w/v), which would require high energy costs during the distillation stage. 6 A preliminary feasibility study by Gouvea et al. 5 however, demonstrated that fermentation of sticky CHs led to a product containing 14% ethanol (w/v). Ethanol production was comparable to other agricultural residues that were being studied for bioethanol production, 5 and most of the residues were either supplemented with sugar or underwent hydrolysis.

Kefale et al. 21 studied a suitable condition for bioethanol production from CP using commercial baker's yeast; the pulp was hydrolyzed using dilute sulfuric acid and distilled water at boiling temperature. A 90% maximum total sugar concentration was obtained at 4   h acid-free hydrolysis. Based on the hydrolysis results, fermentation was performed, and it was observed that ethanol concentration decreased with increases in acid concentration, hydrolysis time, and fermentation time. The maximum ethanol concentration of 7.4   g/l was obtained with distilled water hydrolysis for 4 and 24   h of fermentation. Results indicated that CP could be a potential feedstock for bioethanol production in Ethiopia. The production of ethanol by fermentation of CP extracts was studied by Menezes et al. 22 The effects of heat treatment and comminution on the yield and composition of CP extracts were evaluated, and the extraction process deemed most efficient was that using grinding followed by pressing at room temperature. Five different fermentation media were tested for ethanol production: sugarcane juice or molasses diluted with water or with CP extract and a medium with only CP extract. The addition of CP extract to sugarcane juice or molasses did not influence the fermentation or yeast viability, and thus it was concluded that the mixture can be used for the production of bioethanol, with a yield of approximately 70   g/l.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095175000310

Whey and Whey Powders: Fermentation of Whey

T. Tavares , F.X. Malcata , in Encyclopedia of Food and Health, 2016

Bioethanol

Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or starch crops such as corn, sugarcane, cereal, sugar beet, or sweet sorghum. It has a number of advantages over conventional fuels, being biodegradable and far less toxic than fossil fuels. It is generally CO 2 neutral, and it can help reduce the amount of CO2 as well as other poisonous gases produced during fuel combustion. Bioethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. Nowadays, the bioethanol market continues to grow rapidly.

Whey could be a suitable and less expensive substrate for bioethanol production. All over the world, there are several industrial-scale whey-ethanol plants. Fermentation could be done in batch cultures or in a semicontinuous process, for which a kinetic model was developed.

Yeasts are usually the microorganisms used in the fermentation of lactose from ultrafiltered whey permeate to bioethanol production. The potential applications of yeast strains are focussed on Kluyveromyces sp. Though it has a great advantage because of the use of lactose as a direct substrate, it is very sensitive to ethanol concentration (inhibiting the process at very low concentrations). In addition, it presents a low conversion yield (~   40%). Thus, Saccharomyces cerevisiae can be used, presenting a fermentation yield of 50% and a fourfold ethanol tolerance. Notwithstanding, the fermentation performed by this yeast is an indirect one, not having the ability to hydrolyze lactose directly. Although the yeasts that assimilate lactose aerobically are widespread, those that ferment lactose are rare. In the last decades, researchers have been studying ways to overcome this problem. Genetic engineering is used in order to achieve the optimal yeast strain. Other efforts have been made, aiming to facilitate the process with a simultaneous lactose hydrolysis, for example by coimmobilization of yeast cells with the enzyme.

The development of yeasts' biotechnology processes and engineering techniques leads to the application of different stimulation processes that improve the biological activity of yeasts, achieving new ways to produce higher ethanol amounts. It has been seen that proper ultrasonic stimulation has the function of promoting the activity of enzymes, cell growth, and cell membrane permeability.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123849472007492

Molecular Breeding of Sorghum bicolor, A Novel Energy Crop

Reynante Ordonio , ... Makoto Matsuoka , in International Review of Cell and Molecular Biology, 2016

3.4 Low Kafirin Mutants

Sorghum is not only important for bioethanol production but also for human and animal consumption. Like some cereals, sorghum has poor protein quality because of a lack in essential amino acids such as lysine and tryptophan. Compounding this problem is the fact that sorghum proteins have very poor digestibility. The predominant seed proteins in sorghum are alcohol-soluble prolamins called kafirins, which comprise over 80% of the endosperm protein component of the grain ( Hamaker et al., 1995). Kafirins are categorized into α, β, and γ groups, and assembled into discrete protein bodies, whereby α-kafirins compose the core and the β and γ-kafirins decorate the periphery of the protein bodies. It has been considered that such protein body structure is a major cause of poor protein digestibility in sorghum (Hicks et al., 2001). A highly digestible high-lysine (hdhl) mutant with a single-point mutation was found to produce opaque/floury endosperm with reduced accumulation of kafirin (Weaver et al., 1998; Wu et al., 2013). The reduction in kafirin content in the mutant increased its nutritional value due to better digestibility and higher lysine content. A similar case was observed by Mehlo et al. (2013) in another mutant in which not only lysine but also other essential amino acids in the endosperm were increased at the expense of kafirin, which was being redirected to the germ instead.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S193764481500091X

Lipid production by oleaginous yeasts

Atrayee Chattopadhyay , Mrinal K. Maiti , in Advances in Applied Microbiology, 2021

2.3 Biofuel

The most common liquid biofuels are bioethanol and biodiesel, which are presently used as supplements with gasoline/petrol and diesel, respectively. These are greener alternatives to fossil fuels and are hugely preferred nowadays for reduced emission of sulfur and particulate matters as opposed to the conventional fossil fuels. Presently, biofuels are mainly obtained either from unprocessed organic materials that are used directly and comprise the primary sources, or processed biomasses that are considered to be the secondary sources ( Nigam & Singh, 2011). These processed biomasses usually come from various types of food crops (such as corn, sugarcane, etc.) and edible oilseed crops (e.g., palm, soybean, sunflower, etc.) that give rise to first generation biofuel. However, in order to mitigate the explosive demand of fuel globally, extensive cultivation of these crops has led to shortage of cultivable land and a persistent competition between food crops and fuel crops. Additionally, their cultivation requires regular irrigation and suitable climate. To address these issues, second generation biofuel has been developed, which utilizes nonfood and nonedible oil feedstock mainly lignocellulosic biomass, agricultural waste, and nonedible oil-bearing crop plants like Jatropa (Cherubini, 2010; Lam & Lee, 2012). Unfortunately, low conversion rates and lack of appropriate sources have reduced the feasibility of such fuel production and led to exploring the prospects for third generation biofuel. With respect to biodiesel, it refers to the oil obtained from oleaginous microorganisms, which include bacteria, yeasts, molds and algae. Although it is still under development, many promising studies conducted in the past few decades have indicated the potential of this biodiesel to supplement, if not to replace the conventional petroleum in future.

Generally, microbial oils offer some innate advantages over plant oils: with the feedstock available, production is possible round the year, eliminates the need for arable land, microbial production rates are estimated to be 100   × that of plant oils in liters/ha/year (Atabani et al., 2012). Moreover, they mostly produce favorable composition of fatty acids. C18:1 (oleic acid), C16:0 (palmitic acid), and C18:0 (stearic acid) are the principle fatty acids produced by most of the oleaginous yeasts (Meesters et al., 1996) which are also predominant in plant oils used for biodiesel production, such as canola and sunflower oil (Ageitos, Vallejo, Veiga-Crespo, & Villa, 2011; Sitepu et al., 2019). In order for a particular fuel type to comply with the official standards of combustion, it has to possess several suitable properties. Chain length, the degree of unsaturation and branching are the factors influencing fuel properties such as cetane number, melting point, oxidative stability, kinematic viscosity and heat of combustion (Sitepu et al., 2019). Biodiesel production from oleaginous yeasts, therefore, requires correct selection of yeast strain, with desirable lipid production and fatty acid composition, along with selecting suitable culture conditions.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S0065216421000058

Methods in Silkworm Microbiology

Delicia Avilla Barretto , ... Shyam Kumar Vootla , in Methods in Microbiology, 2021

4.4.3 Production of ethanol

Enzymatic approaches using microbes that leads to conversion of mulberry lignocellulosic biomass of waste to bioethanol production maybe one of the most promising eco-friendly alternatives to fossil fuels or petroleum-based products ( Thirupathaiah et al., 2018). Our previous study has reported Blastobotrys bombycis sp. nov. a newly isolated species of yeast belonging to gut microbiota of B. mori (race CSR2xCSR4, Bivoltine hybrid) with ethanol producing properties (Fig. 5). The yeast showed the capability to produce 1.5   g/L ethanol by fermenting 5% d-xylose (Barretto et al., 2018). d-xylose is the second most abundant sugar in lignocellulosic biomass and the utilization of this sugar by yeasts in bioethanol production may be useful in producing second generation ethanol (Cadete & Rosa, 2018). Feng et al. (2011) demonstrated the ethanol producing property of recombinant Proteus mirabilis JV strain. The genes responsible for ethanol fermentation by microbes such as pyruvate decarboxylase (pdc) and alcohol dehydrogenase II (adh II) were cloned from Zymomonas mobilis and transformed into the cellulolytic bacteria P. mirabilis JV that was i isolated from B. mori gut. The recombinant bacteria were able to produce 1% ethanol using the substrates CMC and 4% pretreated sugarcane bagasse (Sobana Piriya et al., 2012).

Fig. 5

Fig. 5. Blastobotrys bombycis sp. nov. obtained from silkworm B. mori gut microflora with potency for ethanol production (Barretto et al., 2018). Blastobotrys bombycis sp. nov was identified as a novel species of Blastobotrys isolated from B. mori gut microflora. This strain has shown the potency for ethanol production by fermenting d-xylose.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S0580951721000039

Advances in yeast alcoholic fermentations for the production of bioethanol, beer and wine

Kevy Pontes Eliodório Gabriel Caetano de Gois e Cunha Caroline Müller Ana Carolina Lucaroni Reinaldo Giudici Graeme Maxwell Walker Sérgio Luiz AlvesJrThiago Olitta Basso , in Advances in Applied Microbiology, 2019

4.3 Bioethanol fermentations

Sugarcane (a grass) and corn (a cereal) are the most used feedstocks for bioethanol production and they have very different compositions. For instance, while the carbon source found in sugarcane is mainly sucrose, that is easily inverted by yeasts, in corn, sugars are present in the form of starch. Thus, the rationale behind the development of representative synthetic media for these two industrial substrates (sugarcane must and corn mash) are quite different.

The traditional fed-batch fermentation of sugarcane juice and molasses in Brazil is considered a mature technology achieving up to 92% stoichiometric conversion of sucrose to ethanol (Della-Bianca et al., 2013). There are not many reports on media simulating sugarcane-based industrial musts. One of the pioneering works was performed while studying the effects of K, Ca, Mg and Zn on yeast fermentation (Chandrasena et al., 1997). The authors proposed during this investigation a "synthetic molasses medium" based on literature reports on maximum and minimum levels of metals in sugarcane molasses. The results, however, were not representative of a Brazilian molasses sample concerning ethanol yield. In another study, conducted by de Souza, de Menezes, de Souza, Dutra, and de Morais (2015), the effects of mineral composition of different sugarcane juices were investigated. Low ethanol yields were correlated with the excess of minerals in the media (N, P, Ca, Mn and Fe). When the concentrations of such minerals were tested in synthetic media formulated with yeast nitrogen base (YNB) medium supplemented with sucrose (155   g/L), it was also found that ethanol yield was decreased. However, when analyzing the individual effects of the excess of each mineral in this synthetic medium, no significant alteration in ethanol yield was noticed.

Recently, Lino et al. (2018) have proposed a semi-synthetic molasses medium that was adapted from Chandrasena et al. (1997). This medium was developed by adjusting the C/N ratio and the levels of P, K, Mg and Ca based on literature data on molasses composition. In addition, both trans-aconitic acid and malic acid (organic acids present in sugarcane juice) were included, as well as Maillard reaction products via simulation of sugar and amino acid degradation at high temperatures. The proposed medium was benchmarked against Brazilian and Indian industrial molasses samples, in a protocol for bench-scale fermentations simulating the Melle-Boinot process applied in Brazil (Raghavendran et al., 2017). This bench-scale fermentation protocol was proposed considering the size of reactor, inoculum size, anaerobiosis, heat transfer, substrate choice, feeding regime, cell recycling and non-asepsis.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S0065216419300383

Microalgae for biofuel production

D. James Gilmour , in Advances in Applied Microbiology, 2019

2.4 Potential biofuels from microalgae

Third-generation biofuels that can be produced from microalgae biomass include (a) biodiesel from lipids, (b) bioethanol from starch, (c) photosynthetically generated biohydrogen and (d) anaerobic fermentation of algal biomass to produce biogas (mainly methane). The most promising and most widely researched option is the biodiesel production from neutral storage lipids, mainly consisting of triacylglycerol (TAGs) ( Chisti, 2007). The importance of TAG is that it can easily be converted into fatty acid methyl esters (FAMEs) via transesterification in the presence of an alkali metal hydroxide catalyst or an alkoxide catalyst (e.g., sodium methoxide). An excess of methanol is used to drive the reaction in the desired direction (see Eq. 2). Transesterification reaction is a continuous process that takes place in stirred tanks at around 60   °C and the glycerol by-product is removed by continuous centrifugation. Transesterification is a highly efficient process and can reach values of 99% efficiency.

(2)

FAMEs are biodiesel and can be utilized in diesel engines (Knothe, 2005). The original diesel engine dating back to the late 19th century ran on vegetable oil and continued to do so into the 1920s before petroleum-based diesel took over this role (Subramaniam, Dufreche, Zappi, & Bajpai, 2010). The diesel engine is robust and in addition to vegetable oil, a number of different fuel sources were originally proposed including finely powdered coal (Shay, 1993). This historical observation led to the idea of directly using microalgal cells without the need to extract the high-energy lipids and thus save considerably on processing costs. For this to be feasible, the calorific value of the algal cells would need to approach the calorific value of biodiesel (43   kJ   g−   1). For Chlorella species grown on normal Watanabe medium, the calorific value of the biomass is between 18 and 21   kJ   g−   1 (Illman, Scragg, & Shales, 2000). By growing the cells under nitrogen limitation to increase the proportion of lipids, the calorific value increased to 29   kJ   g−   1. This equates to a total lipid content of 63% (w/w) (Illman et al., 2000). A liquid fuel was produced that consisted of an algae (Chlorella) slurry (partly dried algal biomass) mixed with esters of rapeseed oil that worked successfully in a test diesel engine (Scragg, Morrison, & Shales, 2003). This work confirmed the versatility of the diesel engine and but it also demonstrated clearly that extraction of high-energy neutral lipid from algal cells is required to approach the calorific content of petroleum diesel. The calorific value of FAMEs from microalgae is about 38.5   kJ   g−   1, i.e., approximately 80% of the average energy in petroleum oil (Chisti, 2007).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S0065216419300371

Advances in Applied Microbiology

Owen P. Ward , Ajay Singh , in Advances in Applied Microbiology, 2002

I Introduction

Accumulation of CO2 in the atmosphere is long recognized as a major contributor to global warming and climate change (Revelle and Suess, 1957 ). Bioethanol used as a replacement for gasoline reduces vehicle CO 2 emissions by 90% (Tyson et al., 1993). With respect to global warming, ethanol from biomass reduces net CO2 emissions since fermentation CO2, produced during ethanol production, is part of the global carbon cycle (Wyman, 1994). Ethanol has an important impact on automobile tailpipe emissions, producing a significant demand for use of ethanol as an oxygenate (Putsche and Sandor, 1996). With the phase out of the oxygenate methyl tert-butyl ether (MTBE), which reduces CO emissions by improving oxidative combustion, ethanol can replace MTBE as an oxygenate (Blackburn et al., 1999; Unnasch et al., 2001). A disadvantage of ethanol is that it has only 65–69% of the energy density of hydrocarbon fuels (Lynd, 1996).

Brazil produces 12.5 billion liters of ethanol from cane sugar, which is used as a 22% blend with gasoline or as neat ethanol fuel in their Otto cycle engine (Rosillo-Calle and Cortez, 1998). The United States produces 5 billion liters mainly from corn, used mainly as 10% in gasoline, but some as 85% ethanol that can be used in flexible fuel vehicles produced by Ford and Chrysler at no extra cost (Sheehan, 2001).

Because of the problems associated with conversion of lignocellulose to fermentable sugars, ethanol plants have relied on sugar- and starch-based substrates, and have been slow to take on the risks of lignocellulose-based fermentation (Claassen et al., 1999). Nevertheless, several bioethanol production plants, having capacities in the range 1–20 million gal/year, are under construction or are being commissioned. These plants use microbial processes to produce ethanol from lignocellulose, sugar cane waste, and municipal solid waste. It has been estimated that the United States potentially could convert 2.45 billion metric tons of biomass to 270 billion gallons of ethanol each year, which is approximately twice the annual gasoline consumption in the United States (Gong et al., 1999). Shell predicts that fuel from biomass will overtake oil by 2060 (Lynd et al., 1999). The National Science and Technology Council predicts that 50% of organic chemicals will be produced from plant material by 2020 with biobased processes playing a central role (Lynd et al., 1999).

The value of ethanol as an oxygenate and octane booster is $0.80–90   s/gal (Sheehan and Himmel, 1999). The U.S. highway bill includes an extension to the ethanol tax incentive program to 2007, which adds about $0.50/gal to the value of ethanol for the fuel market, allowing ethanol to sell for $1.20–1.40/gal (Sheehan and Himmel, 1999). Ultimately, technological developments must be such as to eliminate the need for the tax incentive.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/S0065216402510017

Vegetable Oils: Types and Properties

A.J. Dijkstra , in Encyclopedia of Food and Health, 2016

Corn germ oil (Zea mays)

Corn germ oil is a by-product of the corn oil milling process. Most corn that is harvested is used as feed but the proportion of the corn that is milled is increasing because of bioethanol production. During the wet milling process, the germ is isolated from the starch using cyclone separators, washed, and dried. The dried germ contains about 50% oil, in which the oil constitutes about 85% of the total amount of oil present in the corn. The oil is produced by first expelling the germ and then extracting the expeller cake with n-hexane. Global annual corn production is 700 million tonnes but corn oil production is only 400   000 tonnes.

Crude corn oil can be dark reddish in color. It is refined either by alkali neutralization followed by bleaching, dewaxing, and deodorization or by degumming the oil to a residual phosphorus content below 5   ppm P, bleaching dewaxing and steam refining. The dewaxing step that comprises cooling the oil to cause the high-melting wax components to crystallize is only necessary when the corn oil is to be sold as salad oil. When the corn oil is to be used as a liquid component in margarine, the dewaxing step can be omitted.

Corn oil contains 13–17% saturated fatty acids and hardly any linolenic acid (18:3). Its main fatty acid is linoleic acid (18:2) at 55–62% followed by oleic acid (18:1) at 22–28%. Its unsaponifiable content is high at 1.3–2.3%, which is in line with its high tocopherol content. This provides the oil with a longer shelf life than would be expected given its high content of polyunsaturated fatty acids.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123849472007066

Lactic Acid Bacteria

F. Mozzi , in Encyclopedia of Food and Health, 2016

High added-value compounds

Recently, the production of high added-value chemicals by LAB has been reported, including lactic acid, 2,3-butanediol (2,3-BDO), 1,3-PDO, bioethanol, and butanol.

Lactic acid has been used in the food industry as a flavor additive and food preservative; however, its main use in the market is in the creation of biodegradable plastics (as a precursor of poly-lactic acid) and pharmaceuticals. Traditionally Lactobacillus casei has been used to produce lactic acid because of its ability to convert more than 95% of the available sugar into this organic acid. However, by means of metabolic engineering processes and the use of renewable resources such as agro-industrial wastes as substrate, other species such as Lactobacillus helveticus and Lactobacillus plantarum have been able to efficiently form lactic acid either by achieving the deletion of the L-ldh (lactate dehydrogenase) gene or by introducing the xylAB operon of Lactobacillus pentosus in the Lactobacillus plantarum genome. By these means, production of pure d-lactic acid with a 0.8   g   g−   1 yield was achieved.

Another important chemical compound is 2,3-BDO which is used as an antifreeze in the plastic, chemical, pharmaceutical, and cosmetic industries. Moreover, acetoin and diacetyl, important buttery flavors in some food products, can be formed by dehydrogenation of 2,3-BDO. Biotechnological processes have produced 2,3-BDO using Klebsiella strains; however, the pathogenic status of this bacterium has encouraged its synthesis by LAB members because many species possess the required biosynthetic pathway. In this respect engineered strains of Lactobacillus plantarum and Lactococcus lactis have been shown to efficiently produce 2,3-BDO from inexpensive substrates such as whey permeate.

1,3-PDO is another compound with multiple applications in the production of polymers, solvents, resins, detergents, and cosmetics. To date, this diol is industrially produced by chemical synthesis; however, its microbial production from glycerol, a byproduct of the biodiesel industry, has been intensively studied. Again, the food-grade status of LAB makes it the preferred option for synthesis of 1,3-PDO, rather than Klebsiella and Clostridium strains, which are considered opportunistic pathogens and thus are not applicable for food and biomedical products. Among the naturally lactobacilli producers of 1,3-PDO, Lactobacillus reuteri has been reported to be the best one so far.

Biotechnological production of ethanol may be one of the most important sources of renewable energy because this compound is used as an alternative biofuel to gasoline. In the past few years, to overcome the natural restrictions of crude oil use, researchers have become interested in using LAB to produce ethanol from renewable biomass such as lignocellulose, given that these microorganisms can metabolize different sugars. So far, the most promising results have been reported for an LDH-negative strain of Lactobacillus plantarum, that expresses pyruvate decarboxylase from a strain of the Gram-positive Sarcina ventriculi.

Also, butanol is a desirable solvent that may be an attractive fuel alternative. While butanol-producing strains cannot tolerate amounts higher than 2%, researchers may apply genetic engineering strategies to certain LAB members to produce butanol in the presence of 3% butanol.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123849472004141