I am so caught up with the potentials inherent in Cassava processing, I just had to share more .
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
(Source FAO)
No comments:
Post a Comment