CHAPTER 2 Review of Related Literature and Studies 2.1
ELATED LITERATURE R ELATED
2.1.1 Cassava
Cassava(Manihot esculenta), esculenta), sometimes also called manioc, is the third largest source source of carbohy carbohydra drates tes for human consum consumpti ption on in the world, world, with with an estima estimated ted annual annual world world produc productio tion n of 208 millio million n tonnes tonnes.. In the Phili Philippi ppines nes,, it is common commonly ly called as kamoteng kahoy or balinghoy. Cassava is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, root, a major source of carbohydrates of carbohydrates.. Cassava's starchy roots produce more food energy per unit of land than any other staple crop. It is a major source of low cost carbohydrates and a staple food for 500 million people in the humid tropics. On infertile land where the cultivation of other crops is difficult, unless considerable inputs are applied, cassava still has a reasonable yield. (Kuiper et. al, 2007) Cassava Cassava thrives better in poor soils than in any other major food plant. As a result, result, fertilizati fertilization on is rarely necessary. necessary. However, However, yields yields can be increased increased by planting cuttings on well drained soil with adequate organic matter. Cassava is a heat-loving plant that requires a minimum temperature of 80oF to grow. Since many cultivars are drought drought resistan resistant, t, cassav cassavaa can surviv survivee even even during during the dry season season when when the soil soil moisture is low, but humidity is high. The plant grows tall, some reaching 15 feet, with leaves varying in shape and size. The edible parts are the tuberous root and leaves. The tuber (root) is somewhat dark brown in color and grows up to 2 feet long. (Sugino and Mayrowani, 2009) The crop is highly efficient efficient in producing producing starch, is available all year round, is tolerant to extreme stress conditions, and fits nicely within traditional farming systems. Fresh roots contain about 30% starch. Cassava starch is one of the best fermentable substances for the production of ethanol. At the moment, sugarcane is the most widely used crop for bio-ethanol in the tropics, but sugarcane requires a lot of water (Ado et.
8
al, 2009). Therefore, cassava is the best option as a feedstock for bio-ethanol production since it can be grown easily and with low maintenance. Aside from that, a much larger area in the tropics is available and suitable for growing cassava. In each locality in the Philippines where the crop is grown, numerous cassava cultivars exist, with different leaf sizes, plant heights, colors, tuber shapes, timings of maturity, overall yields, dry matter contents, starch contents and cyanogenic glycoside contents of the roots. Roots with irregular shapes are more difficult to harvest and to peel, resulting in greater losses of usable root material. (Apea-Bah et. al, 2009) Traditionally, cassava roots are processed by various methods into numerous products, which are utilized in various ways according to local preferences. 2.1.2 Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. It is a natural organic polymer manufactured by green plants through photosynthesis to serve as metabolic reserve. It is the most important carbohydrate in the human diet and is contained in such staple foods as potatoes, wheat, maize (corn), rice, and cassava. In grains, starch is contained in a husk of cellulose. Precisely speaking, starch is basically a complex carbohydrate called polysaccharide and is composed of several thousand glucose elements. Starch also contains amylose and amylopectin and is the most important resource for food for humans (Dean, 2000). Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin (Mcmurry, 2003). Glycogen, the glucose store of animals, is a more branched version of amylopectin. Amylose is a linear polymer made up of D-glucose units. This polysaccharide
is one of the two components of starch, making up approximately 20-30% of the structure. Because of its tightly packed structure, amylose is more resistant to digestion than other starch molecules and is therefore an important form of resistant starch which has been found to be an effective prebiotic. (Dean, 2000)
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Figure 2.1: The molecular structure of amylose
Amylopectin
polysaccharide
and
is
a
highly
soluble branched
polymer of glucose found in plants (Mcmurry, 2003). Starch is made of about 70% amylopectin by weight, though it varies depending on the source (higher in medium-grain rice till 100% in waxy rice, waxy potato starch and waxy corn and lower in long-grain rice, amylomaize and russet potato, for example). Amylopectin is highly branched, being formed of 2,000 to 200,000 glucose units. (Dean, 2000).
Figure 2.2: The molecular structure of amylopectin
Starch, which is mainly composed of amylopectin and amylase, can be converted to alcohol by means of fermentation. Since certain organisms like yeast cannot directly ferment the starch into alcohol, the starch must be broken down first into simple sugars in the process call hydrolysis. The acid or enzyme hydrolysis of starch produces two simple sugars of glucose which is consumed by yeast to produce a by-product which is ethanol and carbon dioxide. This conversion of starch to alcohol can be utilized as a renewable source of bioethanol since a huge variety of crops contains a high percentage of starch. The development of this kind of technology helps sustain the increasing demand for energy in this world.
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2.1.3 Alcohols
Alcohol is commonly thought of as either rubbing alcohol, the active ingredient in an alcoholic drink, or the additive that makes gasoline into gasohol. Chemists generalize its meaning to include almost any carbon-hydrogen compound with at least one hydroxyl group (symbolized as -OH) in its molecular structure (Brewster et. al., 1997). Categorized by the number and placement of the -OH groups, and the size and shape of the attached carbon molecule, alcohols are fundamental to organic chemical synthesis. There are different kinds of alcohols depending on how the –OH group is positioned on the chain of carbon atoms. There are some chemical differences between the various types such as its solubility and boiling p oints. Alcohols are produced industrially from petroleum, coal, or other natural products. Both ethanol and methanol can be obtained from petroleum or natural gas, ethanol may be the most interesting because it can be obtained from a renewable resource, particularly from organic material such as grain or cellulosic materials (Azmi et.al, 2010). The "cracking" of crude petroleum yields many lower-molecule-weight chemical compounds, including some starting materials for alcohols such as ethylene and propylene. Ethylene reacts with hot steam over a catalyst to yield ethanol directly. A process known as hydration produces isopropyl alcohol when water is chemically added to propylene (Shreve, 1984). Alcohol can also obtain synthetically, via ethene or acetylene, from calcium carbide, coal, oil gas, and other sources. In addition, fuel alcohols can be produced from a variety of crops, such as sugarcane, sugar beets, maize, barley, potatoes, cassava, sunflower, eucalyptus through the process of fermentation (Cortes-Camidero, 2010). Fermentation, one of the oldest chemical process known to man, is used to make a variety of products, including foods, flavorings, beverages, pharmaceuticals, and chemicals. At present, however, many of the simpler products such as ethanol are synthesized from petroleum feedstock at lower costs. Alcohol fermentation is done by yeast and some kinds of bacteria. These microorganisms convert sugars in ethyl alcohol and carbon dioxide. Alcoholic fermentation begins after glucose enters the cell. The glucose is broken down into pyruvic acid. This pyruvic acid is then converted to CO2, ethanol, and energy for the cell. Fermentation process from any material that 11
contains sugars can derive ethanol. The many and varied raw materials used in the manufacture of ethanol via fermentation are conveniently classified under three types of agricultural raw materials: sugars, starches, and cellulose materials. Sugars (from sugar cane, sugar beets, molasses and fruits) can be converted to ethanol directly. Starches (from grains, potatoes, root crops) must first be hydrolyzed to fermentable sugars by the action of enzymes from malt or molds. Cellulose (from wood, agricultural residues, waste sulfite liquor from pulp and paper mills) must likewise be converted to sugars, generally by the action of mineral acids. Once simple sugars are formed, enzymes from yeast can readily ferment them to ethanol (Lim et.al, 2002). Alcohols have applications in industry and science as reagents or solvents. One of the examples of alcohols is ethanol which is widely used as solvent. Ethanol, because of its low toxicity and ability to dissolved non-polar substance, can be used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In addition to its presence in alcoholic beverages, ethanol also is used as a solvent for food extracts such as vanilla, perfumes, cosmetics, and some types of paints and lacquers. It is relatively safe, and can be used to dissolve many organic compounds which are insoluble in water. Isopropyl alcohol is widely used in industry as a solvent for paints and chemical processes. Most alcohols, including ethanol, burn in air and are frequently used as fuel. Methanol can sometimes be used as a fuel, though it evaporates too quickly for regular use in cars (Zhang and Feng, 2010). Agricultural alcohol for fuel requires substantial amounts of cultivable land with fertile soils and water. However, if the fuel alcohol is made of the stalks, wastes, clippings, straw, corn cobs, and other crop field trash, then no additional land is needed. Using these sources for this purpose, however, would require additional replacement in animal feedstock, fertilizers and electric power plant fuels (Eggeman, 2010). Using alcohol as a renewable source of energy has a great impact not only in our economy but also to our environment. It helps sustain energy for our combustion engines and preserve the natural habitats in our environment. 2.1.4 Tests for Alcohols Lucas Test
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The Lucas test is a test in alcohols that is conducted to test and differentiate between the types of primary, secondary or tertiary alcohol. It uses the differences in reactivity of hydrogen halides and the three classes or types of alcohol. In the reaction the hydroxyl group is replaced by chlorine. The time it takes in the appearance of turbidity is used as a measure for determining the class of alcohol. (Grolier, 2010)
Hence, the time taken for turbidity to appear is a measure of the reactivity of the class of alcohol with Lucas reagent, and this is used to differentiate between the three classes of alcohols: •
no visible reaction: primary, such as normal amyl alcohol
•
solution turns cloudy in 3-5 minutes: secondary, such as sec-amyl alcohol
•
solution turns cloudy immediately, and/or phases separate: tertiary, such
as tert-
amyl alcohol (2-Methyl-2-butanol) The test is usually conducted at room temperature.
Chromic Acid Test
Chromic acid is capable of oxidizing many kinds of organic compounds and many variations on this reagent have been developed. Chromic acid in aqueous sulfuric acid and acetone is known as the Jones reagent, which will oxidize primary and secondary alcohols to carboxylic acids and ketones respectively, while rarely affecting unsaturated bonds. Tertiary alcohol groups are unaffected. Because of the oxidation is signaled by a color change from orange to a blue-green, chromic acid is used as a qualitative analytical test for the presence of primary or secondary alcohols. (Acid test, 2010) Iodoform Test
Compounds with a methyl group next to a carbonyl group give a positive result with the iodoform (tri-iodomethane) test. Ethanol and secondary alcohols with a
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methyl group attached to the same carbon as the –OH group will also give a positive iodoform test. This is because the iodine oxidizes the alcohols to a carbonyl compound with a methyl group next to the carbonyl group. When iodine and sodium hydroxide are used as the reagents, a positive reaction gives iodoform. Iodoform (CHI3) is a pale yellow substance. Due to its high molar mass due to the three iodine atoms, it is solid at room. It is insoluble in water and has an antiseptic smell. A visible precipitate of this compound will form from a sample only when either a methyl ketone, ethanal, a methyl secondary alcohol or ethanol are present. (Brewster et.al, 1977) 2.1.5 Fermentation
In a general sense, fermentation is the conversion of a carbohydrate such as sugar into an acid or an alcohol. More specifically, fermentation can refer to the use of yeast to change sugar into alcohol or the use of bacteria to create lactic acid in certain foods. Fermentation occurs naturally in many different foods given the right conditions, and humans have intentionally made use of it for many thousands of years. Fermentation is a chemical process and produces heat. In concentrated or particularly large mashes, the temperature can actually rise to levels dangerous to yeast. Since the ideal temperature for yeast is around 85oF, it’s best to maintain the temperature by either utilizing cooling coils. (Yah et.al, 2010) Fermentation process produces valuable products like ethanol which is used in alcoholic beverages, as a solvent, and as a fuel. When certain species of yeast (Saccharomyces cerevisiae) metabolize sugar, they produce ethanol and carbon dioxide. The chemical equation below summarizes the conversion (Ocloo et. al, 2010): C6H12O6
2 CH3CH2OH + 2 CO2
Conversion of sugars to alcohol and CO2 will complete in three to five days, depending on the temperature of the mixture and the type of yeast used. You can tell when the mash is done by watching the “cap” of soils on top of the solution. During fermentation, the rising of CO2 keeps the solids in constant motion, but when the
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bubbling stops, the solids fall to the bottom. At this time, you’re ready to separate the solids from the liquids and distillation is employed to separate the alcohols from other liquids and increase the purity of the ethanol. 2.1.6 Yeast
Yeast is a group of single celled fungi, a few species of which are commonly used to leaven bread and ferment alcoholic beverages. More than one thousand species of yeasts have been described. The most well known and commercially significant yeast are the related species and strains of Saccharomyces Cervisiae. These organisms have long been used to ferment the sugars of rice, wheat, barley, and corn to produce alcoholic beverages and in baking to expand, or raise, dough. (Grolier, 2000) In the absence of oxygen, fermentative yeasts produce their energy by converting sugars into carbon dioxide and ethanol. This energy is necessary to sustain life, from the oxidation of organic substances by molecular oxygen, in the process of respiration. Under anaerobic conditions (low oxygen concentrations), many organisms, including yeast, obtain the energy from the process of fermentation (Bailey, 1986). In alcoholic fermentation, characteristic of many yeast species, the fermentation process starts with one molecule of the six carbon sugar - glucose, and terminates with two molecules of the two carbon alcohol - ethanol, and two molecules of CO2. Yeast plants can propagate in a solution with or without air so agitated only enough to saturate the wort with air and then let it stand still. If the mash is continually agitated, the yeast will reproduce faster and make less waste: carbon dioxide and alcohol. But if the solution becomes anaerobic (without air) the yeast slows down reproduction and makes more alcohol and carbon dioxide. (Shuler et.al, 2002) Yeast also produces enzymes of its own to convert complex sugars. Since sugar conversion and alcohol conversion takes place simultaneously, the amylase enzymes and the yeast work in cooperation to convert dextrins to glucose and fructose and then to alcohol and carbon dioxide. 2.1.7 Co-product Yields
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Alcoholic fermentation begins after glucose enters the cell. The glucose is broken down into pyruvic acid. This pyruvic acid is then converted to CO2, ethanol, and energy for the cell. The by-product, CO2, bubbles through the liquid and dissipates into the air. The other by-product alcohol, remains in the liquid which is great for brewers but not for the yeast because yeast dies and fermentation stops when the yeast becomes poisoned by its own waste the alcohol. 2.1.7-1 Ethanol
Ethanol is a chemical compound having the formula C2H6O. Ethanol is flammable with a boiling point of approximately 78° C. It is completely miscible with water. It is a volatile, colorless liquid with a strong odor, and it tends to burn with a smokeless blue flame which is not always visible in normal light. Ethanol has a characteristic azeotrope with water. When mixtures of ethanol and water are distilled at atmospheric pressure, the maximum concentration of ethanol in the overhead distillate is approximately 96% by volume, with the remaining 4% by volume of the overhead distillate being water. Ethanol has a specific gravity of approximately 0.789 grams per cubic centimeter. (Grolier, 2001) Ethanol is frequently produced industrially by fermentation processes. For example, a source of organic material, such as a food source, can be inoculated with yeast. The yeast will then begin to consume the organic material, and give off ethanol as a metabolic waste product. Ethanol produced by micro-organisms tends to be toxic to the micro-organisms, so when ethanol is produced above certain levels it inhibits the micro-organisms and stops the fermentation process (Brad Cort, 2010). Micro-organisms are more efficient at converting some sorts of organic compounds than others. The commonly used baker's yeast tends to be more efficient at converting sugars in such things as sugar cane or corn than in converting cellulosic materials into ethanol. Most ethanol production in the world now is based on organic materials with high sugar content, such as corn or sugar cane. (Yah et. al, 2010) After the fermentation process, the ethanol is typically recovered from the fermentation mash. This is frequently done through distillation, and the ethanol is
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recovered with water as an azeotrope. There are also ways to recover pure ethanol from an azeotropic mixture of water and ethanol. For example, the collected overhead ethanol and water can be run through a carbon absorption system to absorb the water, leaving essentially pure ethanol. The fermentation of an organic material with microorganisms is typically done anaerobically, or not in the presence of oxygen. When little or no oxygen is present, the micro-organisms find energy from the food source and not from available free oxygen. Some yeast will preferentially produce water instead of ethanol as a by-product of metabolism when oxygen is present. (Flickinger, 1999) The yield of ethanol from agricultural crops can be estimated if the amount of fermentable components – sugar, starch, and cellulose – is known prior to fermentation. If the yield is predicted based on percentages at the time of harvest, then the loss of fermentable solids during storage must be taken to account. (Dawson and Boopathy, 2009) Ethanol has a variety of uses in different industries. This chemical ranks second to water as the most widely used solvent in chemical industry and as these industries have expanded, so the demand for industrial alcohol has increased. Alcohol acts as a solvent for an immense range of industrial products, including paints, lacquers, dyes and oils. In addition, some are used as a raw material in chemical synthesis and a little in the form of fuel (Ocloo and Ayernor, 2010). Fuels available in the Philippines include ethanol to improve the efficiency of the engine because of its anti-knock properties. (Eggeman, 2010) 2.1.7-2 Carbon Dioxide
In the fermentation process, carbon dioxide is generated as a by-product, and this carbon dioxide typically bubbles out of the fermentation mash. Carbon dioxide is the harmless gas given off during fermentation and that responsible for the bubbles in all fizzy drinks, including sparkling and slightly gassy wine. During fermentation, pure carbon dioxide is given off for a considerable period of time. The fermentation of six-carbon sugars by yeast results in the formation of carbon
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dioxide as well as ethanol. For every 1 gallon of ethanol produced, 6.33 pounds of carbon dioxide are formed. This ratio is fixed; it is derived from the chemical equation: C6H12O6
2C2H5OH + 2CO2 + heat
2.1.7-3 Other Co-products
The conversion and fermentation of agricultural crops yield products in addition to ethanol and carbon dioxide. For example, even if pure glucose is fermented, some yeast will be grown, and they would represent a co-product. These co-products have considerable economic value, but, since they are excellent cultures for microbial contaminants, they may represent a pollutant if dumped onto land. Therefore, it becomes doubly important that these co-products be put to good use. 2.1.8 Statistical Tests 2.1.8-1 Confidence Interval
The range that shows within which the true treatment effect is likely to lie is called the confidence interval. These confidence intervals provide different pieces of information from that of hypothesis tests which produces decision about any observed difference either statistically significant or statistically not significant. Confidence intervals provide a range about the observed effect size constructed in such a way that how likely it is that the true value is captured is known. It is a range of values for a variable of interest constructed to include the true value of the variable at a specified probability which is called the confidence level. It is conventional to create confidence intervals at the 95% level which means 95% of the time properly constructed confidence intervals should contain the true value of the variable of interest. The upper and lower bounds of the confidence interval which is called confidence limits gives information on how big or small the true effect might plausibly be. If it is narrow, any effects far from this range have been ruled out by
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the study and if it is wide it must have captured a diverse range of effect sizes and any estimates of effect size will be quite imprecise.(Davies et al. 2009) If t α/2 is the t value with degrees of freedom n-1 leaving an area of α/2 to the right; x and s are the mean and standard deviation of a random sample from a normal population with unknown variance σ2 Confidence Interval for μ (mean) and σ (standard deviation for whole population) unknown are computed as: x-tα/2sn<μ
2.1.8-2 Analysis of Variance (ANOVA)
Analysis of variance (ANOVA) is a very common procedure used to deal with testing population means for experiments involving one factor with more than two levels. An ANOVA estimates group means, assess magnitude of variation attributable to specific sources, partitions the variation according to source, extension of 2-sample t-test to multiple groups, population model and sample model. One-way ANOVA is of one type which is characterized by selecting random samples of size n from each k (level) populations. The k different populations are classified on the basis of a single criterion like treatment or groups. In the analysis of variance, it is assumed that the k populations are independent and normally distributed with means μ1, μ2... μk and common variance of σ2. ANOVA determines statistically whether or not a significant difference in means across groups exists. The hypotheses to be tested are the null hypothesis which states that all means are equal and the alternative hypothesis is that at least one of the means is different from the others. A significant result (null hypothesis is rejected) is obtained if the Fvalue is ≥ Fα;k-1;N-1 and not to reject null hypothesis if otherwise. The formulas that are used are: Sample Variance
SS (sum of squares)
SST(sum of the squared deviations between each observation and the overall mean:
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SSW(sum of squared deviations between each observation the mean of the group to which it belongs)
SSB(sum of the squared deviations between each group mean and the overall mean, weighted by the sample size of each group ngroup)
MSW(within groups mean square or variation within group)
MSB(between groups mean square or variation between group)
The ANOVA Table for k groups and N populations
Source of Variation
Sum of Squares
Df
Mean Square
F
Between Groups
SSB
k-1
MSB
MSBM SW
Within Groups Total 2.1.8-3 Tukey’s Test
SSW
N-k N-1
MSW
To determine where among the individual means of the factors differ significantly from the other, multiple comparison test such as Tukey test with equal sample sizes of the different fermentation time and varying amount of yeast. Tukey test tests the two tailed null hypothesis, H 0: μ a = μ b where “a” and “b” represent all
8
possible combinations of the sample means in the factor. The first step in doing the Tukey test is to calculate for the standard error which is given by the formula: sE= MSwithinnobservation
for equal sample sizes
The next step is to rank the sample means from lowest to highest for fermentation time and another for the amount of yeast then obtain the difference of the paired means within the factors. Pairing starts from the highest of the sample means against the next smallest mean to the smallest. The difference is then compared to Tukeys critical value multiplied by the standard error (CD). There is a significant difference if the difference of the means is larger than the CD value, if not the two means are declared to have no significant difference. If any non-significant differences are detected between two means, then no comparisons are made for other means within this interval.
2.2
R ELATED STUDIES
Countries depended on imported fossils fuels, like the Philippines, feel the pinch caused by the rising cost of crude oil and petroleum excise duties. Add to that, 70% of mineral oil deposits are located in politically unstable areas. In Asia, the UN Food and Agriculture Organization study has found that cassava can be cultivated as an ethanol feedstock, without disrupting food production. The study
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concluded that cassava can be utilized as source of renewable energy. Since the Philippines is a tropical country, which is suitable for cassava production, we can maximize this resource to meet the growing d emand for energy. Many studies have been conducted regarding the production of ethanol from agricultural crops. Sugarcane provides a promising future as a reliable source of biofuel, however certain crops may also be considered since they produce a considerable amount of this renewable energy. Cassava, which contains a high level of starch according to the study conducted by Leen Kuiper from Ecofys Netherlands on 2007, is one of the best fermentable substances for the production of ethanol. He also added that cassava can be grown in any different kind of soils and can be planted in a tropical weather like the Philippines. Ethanol is traditionally produced from feedstock high in sugar and/or starch content by means of fermentation. In 2006, Maria Yuzon conducted a study on the preparation of alcohol from Kamansi seeds using acid hydrolysis process. The alcoholic distillate obtained underwent Iodoform, Lucas, and Chromic Anhydride test. It was proven that starch extracted from Kamansi seeds is a good source of ethyl alcohol. Also, Jimmy Santos described the preparation of alcohol from acacia fruits using a fermenting mixture containing Trichoderma Viride. He employed fermentation using enzymatic process and obtained an average alcohol content of 47.89%. A study conducted by Dawson and Boopathy in 2008 shows that sugarcane bagasse can be a viable source of bioethanol. In their study, they demonstrate that cane processed bagasse could be used to produce fuel grade ethanol without saccharification. A chemical pretreatment process using alkaline peroxide and acid hydrolysis was applied to remove lignin, which acts a physical barrier to cellulolytic enzymes. Yeast Saccharomyces cerevisiae ATCC, strain 765, was used in the experiment. The pretreatment process effectively removed lignin. The results indicate that ethanol can be made from the sugarcane bagasse. In production of bioethanol, certain factors must be considered. Based on the Online Journal of Biological Science released in March 2010, temperature must be optimized for bioethanol production from corn cobs using mixed yeast strain. In this
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study, they employed two methods of sugar extraction, one is through dilute sulfuric acid hydrolysis and the other is enzymatic hydrolysis. As a result, acid hydrolysis of corn cobs gave higher amount of sugars than enzymatic hydrolysis. In their study about the time and temperature of fermentation, the results showed that optimal temperature and time for sugar fermentation were approximately 25oC and 50 h by two yeast strains (S. cerevisiae and P. Stipitis) respectively. At 20 and 40oC, less bioethanol was produced. Varying the temperature of the fermentation process improves the effective utilization of corn cobs sugar for bioethanol production can be achieved. Alcohol produced from cassava flour hydrolysate (CFH) using rice malt as a source of amylase for enzymatic hydrolysis of starch with standard glucose and sucrose used as controls is the focus of the study of Ocloo and Ayernor from Journal of Brewing and Distilling dated last year 2010. The conversion efficiency of sugar to alcohol, rate of fermentation and types of alcohol produced were determined. The effect of yeast concentrations using the combined strain of yeast ( A. niger and Z. mobilis) and fermentation time (24, 36, 48, and 60 h) on the yield of alcohol from CFH were also studied. Results showed that the conversion efficiency of sugars to alcohol was 99.51% and 95.37% for cassava flour hydrolysate (CFH), standard glucose and sucrose solutions respectively. It is therefore concluded that using glucose solution yielded more alcohol than alcohol produced using standard sucrose solution. Alcohol produced was mostly ethanol with traces of methanol. The study suggests that high yield of alcohol could be produced from cassava flour hydrolysate. Generally, bioethanol
from corncobs are
produced
using
simultaneous
saccharification and fermentation with the aid of Aspergillus niger and Saccharomyces cerevisae. This is the center of the study presented by F.S. Johnson in April of 2009. He pointed out that maize is the most abundant cereal grown in many countries and is accompanied by enormous amount of agro wastes of which corncobs form 30%. This agro waste which is currently under utilized was used to produce bio-ethanol. Aspergillus niger isolated from soil sampled was used to hydrolyze the corncobs into simple sugars. Filtrate obtained from corncobs broth fermented by A. niger was used as crude enzyme in optimization tests on corncobs powder suspended in 50 mM citrate buffer pH 5.0. Optimum temperature, pH and substrate concentration for saccharification were 40oC, 4.0
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and 6% respectively. Saccharomyces cerevisae was added to A. niger filtrate to cause fermentation of the corncobs. By applying this method, he concluded that the highest ethanol concentration of 0.64 g/l was recorded over the 24 h fermentation period. Yeast is an important ingredient in fermentation. Zhang and Feng conducted a research regarding the fermentation potential of Zymomonas mobilis in ethanol production from low-cost raw sweet potato. The effects of pH, high concentration of glucose and the initial ethanol content on the fermentation process of ethanol with three strains of Zymomonas mobilis were investigated and the strain of ATCC. It was found that the condition for ethanol production was optimized to be pH 4, substrate concentration of 20%, and time of fermentation of 24 h, resulting in ethanol yield of 66.4 g/L and fermentation efficiency of 93.5%, respectively. This work demonstrates that the low-cost sweet potato is a feasible feedstock for ethanol fermentation with Z. mobilis.
The Department of Agricultural Engineering led by B. A. Adelekan investigates on ethanol productivity of cassava crop as a sustainable source of biofuel in tropical countries. This study found that a total of 6.77 million tonnes or 1338.77 million gallons of ethanol are available from total cassava production from tropical countries. The production and use of ethanol from cassava crop is recommended in the cassava-growing tropical countries of the world like the Philippines. In 2004, the Canadian Firm Iogen brought the first cellulose-based ethanol plant on-stream. The primary consumer thus far has been the Canadian Government, which along with the United States Government particularly the Department of Energy’s National Renewable Energy Laboratory, has invested millions of dollars into assisting the commercialization of cellulosic ethanol. Realization of this technology would turn a number of cellulose-containing agricultural by-products, such as corn cobs, sugarcane and wheat, into renewable energy resources. Philippines has a huge potential of utilizing cassava as a feedstock for the production of ethanol since its climate is suitable for growing a massive volume of this root crop. The Department of Agricultural Economics in UPLB released a paper that discusses the potential of cassava as a source of feedstock for bioethanol and the major
11
policy considerations for developing the industry. The paper provides some recommendations on enhancing the viability of cassava as a source of bioethanol in the Philippines. However as the paper explains, there are certain important concerns that need to be addressed for the project to be viable. These include the market, productivity of cassava production, cost of cassava feedstock with other feedstock sources, potential production areas, production technologies, feedstock supply arrangements between feedstock producers and processing plants, incentives for industry players, and impact on the environment. These related studies proved that ethanol can be obtained from a different variety of agricultural crops with a considerable yield which can be optimized to be the source of renewable energy and help sustain the growing demand for energy.
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