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The flour produced from the cassava plant, which on account of its low content of noncarbohydrate constituents might well be called a starch, is known in world trade as tapioca flour. It is used directly, made into a group of baked or gelatinized products or manufactured into glucose, dextrins and other products.
Starchy foods have always been one of the staples of the human diet. They are mostly consumed in starch-bearing plants or in foods to which commercial starch or its derivatives have been added. The first starch was probably obtained from wheat by the Egyptians for food and for binding fibres to make papyrus paper as early as 4000-3500 B.C.
Starches are now made in many countries from many different starchy raw materials, such as wheat, barley, maize, rice, white or sweet potatoes, cassava, sago palm and waxy xaize. Althbugh they have similar chemical reactions and are usually interchangeable, starches from different sources have different granular structures which affect their physical properties.
Starch and starch products are used in many food and nonfood industries and as chemical raw materials for many other purposes, as in plastics and the tanning of leather. Nonfood use of starches - such as coating, sizings and adhesives - accounts for about 75 percent of the output of the commercial starch industry.
In many industrial applications, there is competition not only among starches from various sources but also between starches and many other products. Resin glue has largely replaced starch in plywood because of its greater resistance to moisture; resin finishes are used in the textile industry and natural gums compete with starches in paper making. Nevertheless, the continuous development of new products has enabled the starch industry to continue its expansion. The growth of the starch industry in the future appears to be very promising, providing the quality of products and the development of new products permit them to compete with the various substitutes.
FOOD INDUSTRIES
The food industries are one of the largest consumers of starch and starch products. In addition, large quantities of starch are sold in the form of products sold in small packages for household cooking. Cassava, sago and other tropical starches were extensively used for food prior to the Second World War, but their volume declined owing to the disruption of world trade caused by the war. Attempts were made to develop waxy maize as a replacement for normal noncereal starches; but the production of cassava starch has increased considerably in recent years.
Unmodified starch, modified starch and glucose are used in the food industry for one or more of the following purposes:
(a) directly as cooked starch food, custard and other forms;
(b) thickener using the paste properties of starch (soups, baby foods, sauces and gravies, etc.);
(c) filler contributing to the solid content of soups, pills and tablets and other pharmaceutical products, fee cream, etc.;
(d) binder, to consolidate the mass and prevent it from drying out during cooking (sausages and processed meats);
(e) stabilizer, owing to the high water-holding capacity of starch (e.g., in fee cream).
Bakery products
Although starch is the major constituent of flours, the art of' bread baking depends to a large extent on the selection of flour with the proper gluten characteristics. Starch is used in biscuit making, to increase volume and crispness. In Malaysia, cassava starch is used in sweetened and unsweetened biscuits and in cream sandwiches at the rate of 5-10 percent in order to soften zyestexture. add taste and render the biscuit nonstickv. The use of dextrose in some kinds of yeast-raised bread and bakery products has certain advantages as it is readily available lo the yeast and the resulting fermentation is quick and complete. It also imparts a golden brown colour to the crust and permits longer conservation.
Confectioneries
In addition to the widespread use of dextrose and glucose syrup as sweetening agents in confectioneries. starch and modified starches are also used in the manufacture of many types of candies such as jellybeans. toffee. hard and soft gums, boiled sweets (hard candy). fondants and Turkish delight. In confectioneries. starch is used principally in the manufacture of gums. pastes and other types of sweets as an ingredient, in the making of moulds or for dusting sweets to prevent them from sticking together. Dextrose prevents crystallization in boiled sweets and reduces hvdroscopicity in the finished product.
Canned fruits, jams and prederves
Recent advances in these industries include the partial replacement of sucrose by dextrose or sulfur-dioxide-free glucose syrup. This helps to maintain the desired percentage of solids in the products without giving excessive sweetness, thereby emphasizing the natural flavour of the fruit. The tendency toward crystallization of sugars is also decreased.
Monosodium glutamate (MSG)
This product is used extensively in many parts of the world in powder or crystal form as a flavouring agent in foods such as meats, vegetables, sauces and gravies. Cassava starch and molasses are the major raw materials used in the manufacture of MSG in the Far East and Latin American countries. The starch is usually hydrolyzed into glucose by boiling with hydrochloric or sulfuric acid solutions in closed converters under pressure. The glucose is filtered and converted into glutamic acid by bacterial fermentation. The resulting glutamic acid is refined, filtered and treated with caustic soda to produce monosodium glutamate, which is then centrifuged and dried in drum driers. The finished product is usually at least 99 percent pure.
The production of commercial caramel
Caramel as a colouring agent for food, confectionery and liquor is extensively made of glucose rather than sucrose because of its lower cost. If invert sugar, dextrose or glucose is heated alone, a material is formed that is used for flavouring purposes; but if heated in the presence of certain catalysts, the coloration is greatly heightened, and the darker brown products formed can be used to colour many foodstuffs and beverages.
Uniform and controlled heating with uniform agitation is necessary to carry the caramellization to the point where all the sugar has been destroyed without liberating the carbon.
THE GLUCOSE INDUSTRY
According to Whistler and Paschell, Abu Mansur, an Arabian teacher and pharmacologist, about 975 A.D. described the conversion of starch with saliva into an artificial honey. In 1811 Kirchoff discovered that sugar could be produced by the acid hydrolysis of starch. Glucose, or dextrose sugar, is found in nature in sweet fruits such as grapes and in honey. It is less sweet than sucrose (cane or beet sugar) and also less soluble in water; however, when used in combination with sucrose, the resulting sweetness is often greater than expected.
The commercial manufacture of glucose sugars from starch began during the Napoleonic Wars with England, when suppliers of sucrose sugar were cut off from France by sea blockade. Rapid progress was made in its production in the United States about the middle of the nineteenth century.
At present, glucose is usually produced as a syrup or as a solid. The physical properties of the syrup vary with the dextrose equivalent (DE) and the method of manufacture. Dextrose equivalent is the total reducing sugars expressed as dextrose and calculated as a percentage of the total dry substance. Glucose is the common name for the syrup and dextrose for the solid sugar. Dextrose, sometimes called grape sugar, is the D-glucose produced by the complete hydrolysis of starch.
Starch hydrolysis
Two methods for starch hydrolysis are used today for the commercial production of glucose: acid hydrolysis and partial acid hydrolysis followed by an enzyme conversion.
Acidification is the conversion of starch into glucose sugar by acid hydrolysis. This operation is carried out in batches or a continuous process. In the first process, the starch slurry, 20-21ºBe, is mixed with hydrochloric acid (sulfuric acid is sometimes used) to bring the pH to around 1.8-2.0 in a steam converter and heated to about 160ºC until the desired DE is reached. The continuous process, which is replacing the batch process, involves feeding the mixture of starch slurry and hydrochloric acid into a tubular heat-exchanger. The time and temperature of the process are adjusted to the desired DE in the end product.
In the next step, neutralization, the acidified mixture is neutralized with sodium carbonate or soda ash to remove the free acid and bring the pH value to 5.0 7.0. Sodium chloride is formed in the syrup in small quantities as a result of the neutralization of the hydrochloric acid by the sodium carbonate and remains in solution.
Refining follows. Some solids - impurities, precipitated protein and coagulated fat - can be removed by centrifugal separation. Impurities will depend largely on the starch used and its purity. The solution is then passed through filters (filter presses or candle-type ceramic filters).
The clear brown filtrate is decolourized by passing it through tanks of activated carbon, which removes colours and other impurities from the solution by surface adsorption but has no effect on the sugar.
Refining can be done by ion-change resins instead of activated carbon or combined with it. A recent development is to refine the converted liquor by electrodialysis, and the final glucose syrup is very superior.
Concentration is the final step. The refined syrup is concentrated under vacuum in batch converters or continuous heat exchangers until the concentrated syrup reaches 80-85 percent solids or 43 45ºBé. Commercial glucose syrups are sold according to the Beaumé standard, which is a measure of the dry substance content and specific gravity.
Glucose syrup is transported in drums or in bulk road or rail tanks. It should not be stored in large quantities for long periods of time because its colour may deteriorate.
In the acid-enzyme process the starch slurry is treated by acidification, neutralization and filtration as in the acid hydrolysis process and then is fed into the enzyme converter. The temperature and pH are adjusted to the optimum conditions and the enzyme is added with slow agitation. The time of conversion depends on the initial dextrose equivalent obtained by acid hydrolysis, the type and strength of the enzyme and the final DE required. After the conversion has been completed, the enzyme is rendered inactive by raising the temperature and adjusting the pH, and the converted syrup is then refeed and concentrated in the same manner as in the acid-converted glucose syrup.
The use of certain enzymes results in DE values as high as 98-99 which means a higher yield of dextrose from starch, or nearly complete conversion of starch into dextrose. When acid is used as the hydrolyzing agent, the DE of the conversion liquor, however, reaches only about 92 because a certain degree of polycondensation takes place and some of the yield of dextrose is lost owing to the acidity and high temperatures required for the conversion.
The production of dextrose
At present most of the dextrose in commerce is prepared in the form of pure dextrose monohydrate by a combined acid-enzyme process. The hot, thick glucose syrup with a concentration of 70-80 percent dextrose is run from the evaporator into crystallizing pans. Crystal formation is largely controlled by the quantity of dextrins left with the glucose. The separation of crystals from the syrup is carried out in centrifugal separators and the impurities are left in the mother liquor. Crystalline dextrose is then dried in rotary hot-air driers under vacuum and bagged in moisture-proof materials.
Recrystallization of dextrose will yield practically 100 percent pure dextrose crystals which are used as a pharmaceutical-grade sugar.
The starch used in the manufacture of glucose syrup must be as pure as possible with a low protein content (particularly soluble protein). In this respect, cassava starch can be preferable to other starches.
There is an increasing interest in manufacturing glucose syrup directly from starchy roots or grains rather than from the separated starch in order to save on capital investments for the production and purification of starch from such raw materials.
The starch conversion industry (glucose and dextrose) is the largest single consumer of starch, utilizing about 60 percent of total starch production. Glucose syrup and crystalline dextrose compete with sucrose sugar and are used in large quantities in fruit canning, confectioneries, jams, jellies, preserves, ice cream, bakery products, pharmaceuticals, beverages and alcoholic fermentation.
The functional purpose of glucose and dextrose in the confectionery industry is to prevent crystallization of the sucrose; in the bakery products industry it is to supply fermentable carbohydrates; and in the ice-cream, fruit-preserves and similar industries it is to increase the solids without causing an undue increase in the total sweetness, thus emphasizing the natural flavour of the fruit, and also to prevent the formation of large ice crystals which mar the smooth texture.
In general, glucose and dextrose are used in the food industry as a partial or complete substitute for sucrose. The use of dextrose has increased in recent years in the food-processing industries.
In many developing countries bread consumption is continually expanding and there is increasing dependence on imported wheat. Most of these countries, however, grow staples other than wheat that can be used for bread. Some grow various starchy tubers such as cassava, yam or sweet potatoes and some others grow cereals such as maize, millet or sorghum. It would therefore be economically advantageous for those countries if imports of wheat could be reduced or even eliminated and the demand for bread could be met by the use of domestically grown products instead of wheat.
The Composite Flour Programme initiated by the Food and Agriculture Organization of the United Nations in 1964 was conceived primarily to develop bakery products from locally available raw materials, particularly in those countries which could not meet their wheat requirements. Although the bakery products obtained were of good quality, similar in some of their main characteristics to wheat-flour bread, the texture and palatability of the composite-flour bakery products were different from those made from wheat flour. Bread made of nonglutenous flour has the crust and crumb structure of cake rather than bread and may not be considered acceptable by people who are accustomed to conventional bread.
The light, evenly structured bread made of wheat flour and the characteristic soft crumb are due to the swelling properties of wheat-flour gluten in water. If pure starch from another cereal or tuber is used, the product is considerably more rigid and its texture is irregular because gases are insufficiently retained in the dough. Therefore, when starches that do not contain gluten-forming proteins are used, a swelling or binding agent must be added during the preparation of the dough to bind the starch granules (i.e., egg white, gums, glyceryl monostearate).
Efforts have been made in many countries to produce bread by conventional methods from wheat flour to which other flours such as cassava flour were added. It was generally found that the upper limit of such an addition was about 10 percent as the quality of the resultant bread was rapidly impaired beyond this limit of nonwheat flour content. However, recent experiments have shown that it is possible to increase the level of the nonwheat flour considerably without too great a change in the bread characteristics, provided certain bread improvers such as calcium stearyl lactylate are added or a relatively high percentage of fat and sugar is used. Bread of acceptable quality was obtained by the use of 30 percent of either cassava or corn (maize) starch and 70 percent wheat noun
Experiments made by the Institute of Food Technology in Rio de Janeiro show that 10 percent flour and 5 percent cassava or corn (maize) starch can be added to wheat flour of only medium strength (9-11 percent gluten) and made into a dough containing only I percent shortening which can be baked into loaves of as good quality and appearance as those of the respective wheat-flour samples.
Other experiments in some countries have been undertaken to make bread from nonwheat flours alone or mixed with wheat flour. Flours included cassava flour and cassava starch and sources of proteins included full-fat and defatted oilseed flours such as cottonseed, soybean and groundnut, as well as fish meal. In addition, binding agents, water, salt and sugar were used. The proportion of the protein source to starch was varied so as to ensure a protein content of 1820 percent in the composite flour. Results of using nonwheat flours alone suggested that the combination of cassava flour and cassava starch could be used in bread-making and that bread made from cassava flour and defatted soybean flour was of good quality. From the nutritional point of view, the protein quality of both the cassava-soya and the cassava-groundnut breads was higher than that of common wheat bread. In general, as in normal bread-making, the results depend on different factors operating in the bread-making procedure and the quality of the raw materials.
In India, a new product called tapioca macaroni was developed by adding a small percentage of specially prepared groundnut meal and wheat semolina to cassava flour. The mixture is processed, cooked and consumed in the same way as foodgrains. The protein content is comparable to that of wheat (about 10 percent) and the macaroni is nearly twice as nutritious as rice.
The Food and Agriculture Organization has lately considered it desirable to investigate the possibility of making bread and similar bakery products of raw materials derived from starchy tubers and defatted oilseeds. An agreement was made between the Organization and some well-known research institutions to study this possibility. The following experiments have been realized:
(a) Development of a bread made from nonwheat materials at the Institute of Grain, Flour and Bread (TNO), Wageningen, the Netherlands.
(b) Development of a bread with partial replacement of wheat flour at the Tropical Products Institute, London.
MECHANICAL LEAVENING
Mechanical leavening of bread doughs is fast replacing conventional fermentation systems. This process offers the advantages of simplification, elimination of bulk fermentation and better uniformity of dough consistency besides the possibility of utilizing weaker flours and starches with wheat flour. The Chorleywood Bread Process, adopted in 1961, is used to produce the highest proportion of all the bread consumed in the United Kingdom.
Experiments carried out by the British Arkady Co. Ltd., using mechanical leavening rather than bulk fermentation for the ripening of the dough and a blend of 60 percent wheat flour, 30 percent cassava starch and 10 percent soybean flour, produced a bread of good quality almost equal to the normal wheat-flour bread in volume, appearance and eating quality.
Several FAO-operated UNDP/SF projects concerned with the use of composite flours in bread-making have been realized. Bakery products made from composite flours of wheat (at least 75 percent) and potato, maize and cassava have been developed by an experimental bakery in Campinas, State of São Paulo, Brazil. (Other projects involving the use of flours other than cassava flour in bakery products have been carried out in Niger, Senegal and Sudan.) The report of a joint FAO/UNDP mission in Colombia recommended the establishment of an experimental bakery to determine the suitability of locally available raw materials for the production of bakery products from composite flours (e.g., cassava/soybean). The project was executed with FAO participation under a bilateral agreement between Colombia and the Netherlands.
NUTRITIONAL VALUE OF COMPOSITE FLOURS
The nutritional value of bakery products made from composite flours was assessed in 1965 by the Central Institute for Nutrition and Food Research, (Utrecht, Zeist), where the nutritional value of cassava/soya bread and cassava/groundnut bread was compared with the protein quality of common wheat bread. It was concluded that the protein quality of both breads was higher than that of common wheat bread. The cassava/soya bread topped the other two breads in protein quality, while the cassava/groundnut bread was slightly superior to common wheat bread.
In 1969 at the Queen Elizabeth College, London, breads produced at the British Arkady Co. Ltd. were assessed. They were made from various composite flour mixtures consisting of wheat flour, cassava starch, soya flour, millet and sorghum flour and fish-protein concentrate in various proportions with mechanical leavening. Results indicated that the protein value of the original bread had not been impaired by supplementation, but showed improvement.
Prospects for commercial production and widespread consumption of bread made of composite flours in different countries will depend upon local acceptance (taste and characteristics of the bread) and the price at which the bread will be available to the public.
Food habits are primarily based on socioeconomic and other conditions rather than on scientific considerations. Changes in established habits can take place gradually through public education and the spread of knowledge.
Cassava is widely used in most tropical areas for feeding pigs, cattle, sheep and poultry. Dried peels of cassava roots are fed to sheep and goats, and raw or boiled roots are mixed into a mash with protein concentrates such as maize, sorghum, groundnut or oil-palm kernel meals and mineral salts for livestock feeding.
In many tropical regions, the leaves and stems of the cassava plant are considered a waste product. However, analytical tests have proved that the leaves have a protein content equivalent to that of alfalfa (about 17-20 percent). Feeding experiments also showed that dehydrated cassava leaves are equivalent in feed value to alfalfa. Imports of dehydrated alfalfa in the Far East, mainly in Japan, have reached about 240 000 tons a year. Therefore, a large potential exists for the exportation of dehydrated stems and leaves of cassava.
In Brazil and many parts of southeast Asia, large quantities of cassava roots, stems and leaves are chopped and mixed into a silage for the feeding of cattle and pigs. This use of cassava is increasing.
Cassava, similar to feedgrains, consists almost entirely of starch and is easy to digest. The roots are, therefore, especially suited to feeding young animals and fattening pigs. Many feeding experiments have shown that cassava provides a good quality carbohydrate which may be substituted for maize or barley and that cassava rations are especially suitable for swine, dairy cattle and poultry. However, cassava cannot be used as the sole feedstuff because of its deficiency in protein and vitamins, but must be supplemented by other feeds that are rich in these elements.
The amount of cassava and its products fed to animals as scraps in the tropical regions must be fairly large, but there is no way of estimating it. Barnyard fowls, goats and pigs probably consume cassava roots and leaves regularly in many parts of the tropics, but a true livestock feeding industry based on cassava has been developed only in very few areas.
In the European Economic Community the highly developed compound animal-feed industry uses dried cassava roots as an ingredient, and large quantities of cassava chips, pellets and meal are imported into these countries for this purpose. The composition of a compound animal feed varies according to the animal (cattle, pigs or poultry) as well as to the kind of production (dairy, meat or eggs).
There are many constituents which can be used to supply the main elements in compound feed, such as starch, protein, fat, minerals and vitamins. In general, oil cakes are the main ingredients in the feedstuffs for cattle, while feedgrains are the most important for pigs and poultry. Cassava products were long used as a raw material for compound feedstuffs until their use declined after the Second World War, when grains became cheaper than cassava products in Europe. When grain prices rose again, cassava products were once more used extensively. The maximum content of cassava products in compound feedstuffs is officially set in many countries. In the Federal Republic of Germany, it varies according to the type, but is generally as follows: 10-40 percent for pigs, 20-25 percent for cattle and 10-20 percent for poultry; in the Netherlands and Belgium, however, the figures are much lower.
At present many large manufacturers are equipped with electronic computers to determine the composition of compounds in terms of feed values and price.
Starch makes a good natural adhesive. There are two types of adhesives made of starches, modified starches and dextrins: roll-dried adhesives and liquid adhesives.
The application of cassava in adhesives continues to be one of the most important end uses of the product. In the manufacture of glue the starch is simply gelatinized in hot water or with the help of chemicals. For conversion into dextrin it is subjected separately or simultaneously to the disintegrative action of chemicals, heat and enzymes.
In gelatinized starch adhesives, quality requirements are such that the medium-quality flours can be used. In dextrin manufacture, the demands are much more exacting: only the purest flours with a low acid factor are acceptable. Cassava dextrin is preferred in remoistening gums for stamps, envelope flaps and so on because of its adhesive properties and its agreeable taste and odour.
Dextrins were accidentally discovered in 1821 when during a fire in a Dublin (Ireland) textile mill one of the workmen noticed that some of the starch had turned brown with the heat and dissolved easily in water to form a thick adhesive paste.
Three primary groups of dextrins are now known: British gums, white dextrins and yellow dextrins.
British gums are formed by heating the starch alone or in the presence of small amounts of alkaline buffer salts to a temperature range of about 180°220°C. The final products range in colour from light to very dark brown. They give aqueous solutions with lower viscosities than starch.
White dextrins are prepared by mild heating of the starch with a relatively large amount of added catalyst, such as hydrochloric acid, at a low temperature of 80º-120°C for short periods of time. The final product is almost white, has very limited solubility in water and retains to varying degrees the set-back tendency of the original starch paste.
Yellow dextrins are formed when lower acid or catalyst levels are used with higher temperatures of conversion (150°-220°C) for longer conversion times. They are soluble in water, form solutions of low viscosity and are light yellow to brown in colour.
The following are some of the major uses of dextrins in nonfood industries.
Corrugated cardboard manufacture. One of the large users of dextrins is the corrugated cardboard industry for the manufacture of cartons. boxes and other packing materials. The layers of board are glued together with a suspension of raw starch in a solution of the gelatinized form. The board is pressed between hot rollers, which effects a gelatinization of the raw starch and results in a very strong bonding. Medium-quality flours are suitable for this purpose provided the pulp content is not too high.
Remoistening gums. These adhesives are coated and dried on surfaces, such as postage stamps and envelope flaps, for moistening by the user before application to another surface. Cassava dextrins in aqueous solution are well suited for this purpose as they give a high solids solution with clean machining properties.
Wallpaper and other home uses. Various types of starch-based products are used as adhesives for wallpaper and other domestic uses.
Foundry. Starch is used as an adhesive for coating the sand grains and binding them together in making cores which are placed in moulds in the manufacture of castings for metals.
Well drilling. Starches and modified starches mixed with clay are used to give the correct viscosity and water-holding capacity in bores for the exploratory drilling of oil wells or water wells. These starch products are replacing other commercial products for making the muddy materials which are indispensable for drilling wells. For this purpose a coldwater-soluble pregelatinized starch which can be made up to a paste of the required concentration on the spot is desired.
Paper industry. In the paper and board industries, starch is used in large quantities at three points during the process:
(i) at the end of the wet treatment, when the basic cellulose fibre is beaten to the desired pulp in order to increase the strength of the finished paper and to impart body and resistance to scuffing and folding;
(ii) at the size press, when the paper sheet or board has been formed and partially dried, starch (generally oxidized or modified) is usually added to one or both sides of the paper sheet or board to improve the finish, appearance, strength and printing properties;
(iii) in the coating operation, when a pigment coating is required for the paper, starch acts as a coating agent and as an adhesive.
Cassava starch has been widely used as a tub size and beater size in the manufacture of paper, in the past mainly on account of its low price. A high colour (whiteness), low dirt and fibre content, and, above all, uniformity of lots are needed in this instance.
An important new application of starch is in the machine-coating of magazine paper, formerly done exclusively with caseins. There are indications that cassava is particularly well suited to the purpose; however, definite specifications for the starch still have to be worked out.
Textile industry. In the textile industry, starches occupy an important place in such operations as warp sizing, cloth finishing and printing. Warp sizing is the application of a protective coating to prevent the single yarns from disintegrating during weaving. The size consists of an adhesive and a lubricant and is generally removed after weaving. Cloth finishing alters the "feel" of the fabric by making it firmer, stiffer and heavier. Cassava starch is also used for cloth printing or producing certain designs in various colours on the smooth surface of a finished fabric. While cassava accounted for about 20 percent of all starch for these purposes in 1937, it has been largely replaced by other starches after the Second World War.
An exception is the manufacture of felt, where cassava continues to be used exclusively in the finishing process.
Wood furniture. Before the Second World War the manufacture of plywood and veneer relied mainly on cassava as a glue. The basic material in this case is gelatinized at room temperature with about double the amount of a solution of sodium hydroxide. After prolonged kneading of the very stiff paste in order to give it the required stringy consistency, the glue is applied to the wood with rollers. As the presence of a certain amount of the pulp is useful, medium- to low-quality flours are acceptable or even preferable, although the presence of sand is objectionable.
Since 1945, however, the use of cassava as a glue has declined to second place owing to the increasing success of water-resistant plastics.
As cassava cultivation increases, more stalks will become available for disposal. The Tropical Products Institute, London, has been working on the utilization of the cassava plant. Particle boards could be made from cassava stalks by cutting them into small sections and mixing them with certain resins. The strength of the board can be varied by altering the resin content or the density.
CASSAVA ALCOHOL
Cassava is one of the richest fermentable substances for the production of alcohol. The fresh roots contain about 30 percent starch and 5 percent sugars, and the dried roots contain about 80 percent fermentable substances which are equivalent to rice as a source of alcohol.
Ethyl alcohol is produced from many carbohydrate materials. In Malaysia and some other countries, many factories are equipped to use cassava roots, starch or molasses (by-product of the sugar industry), the type of product depending on the costs of the raw materials. When cassava is used, the roots are washed, crushed into a thin pulp and then screened. Saccharification is carried out by adding sulfuric acid to the pulp in pressure cookers until total sugars reach 15-17 percent of the contents. The pH value is adjusted by using sodium carbonate, and then yeast fermentation is allowed for three to four days at a suitable temperature for the production of alcohol, carbon dioxide and small amounts of other substances from sugar. Alcohol is then separated by heat distillation. The yield of conversion is about 70-110 litres of absolute alcohol per ton of cassava roots depending on the variety and method of manufacture. The crude alcohol of cassava is described as average in quality. It has a disagreeable odour, but can be improved if the first and last fractions in the distillation process are discarded. It is usually utilized for industrial purposes, as in cosmetics, solvents and pharmaceutical products. If the production is required for human consumption, special care should be taken in handling the roots to rid them of hydrocyanic acid.
DRIED YEAST
Microbial protein is attracting growing interest owing to the enormous protein requirements of the world. Among the microorganisms which are considered possible food sources, yeast has perhaps stirred the greatest interest. Candida and saccharomyces yeasts have had a well-established place for many years as feed, and the technology of production, the composition and the nutritive value of yeast are well known.
Most of the production of yeast is based on such low-cost raw materials as waste liquids, wood hydrolyzates and molasses. Starch-rich plant materials from wastes or surplus production are also utilized as substrata for yeast production. Cassava starch and cassava roots are being used in Malaysia and some other countries for the production of yeasts for animal feed' the human diet and for bakery yeast. The starch is hydrolyzed into simple sugars (predominantly glucose) by means of mineral acid or by enzymes. Certain yeasts are then propagated which assimilate the simple sugars and produce microbial cellular substances. The dry, inactive yeast contains about 7 percent moisture and the raw protein content can vary between 40 and 50 percent depending on the raw material.
The yield of yeast production also depends on the raw material. In some applications of cassava starch conversion into substances obtained from yeasts, a 38-42 percent yield of yeast product containing 50 percent raw protein has been obtained.