Chapter: Corn PDF

Chapter: Corn Tip cap Types of Corn Corn, Zea Mays, is grown in most countries throughout the world and it require Warmer-Climate. Following are different kinds of corn, 1) DENT CORN 2) FLINT CORN 3) WAXY CORN 4) SWEET CORN 5) POP CORN 6) INDIAN CORN 7) FLOUR CORN Dent Corn It...

Chapter: Corn Tip cap Types of Corn Corn, Zea Mays, is grown in most countries throughout the world and it require Warmer-Climate. Following are different kinds of corn, 1) DENT CORN 2) FLINT CORN 3) WAXY CORN 4) SWEET CORN 5) POP CORN 6) INDIAN CORN 7) FLOUR CORN Dent Corn It contains both hard and soft starch and become indented at maturity, a major crop used to make food, animal feed, and industrial products and starch production Flint Corn It has hard, horny, rounded, or short and flat kernels with the Soft and starchy endosperm. It is similar to Dent and is used for the Same Purposes. Most of it is grown in South America. Waxy Corn WAXY corn is a corn variety with grains that have a waxy appearance when cut, and that contains only branched-chain starch. It is grown to make special starches for thickening foods.  Sweet Corn It is grown in many horticultural varieties, and is considered specific mutation of dent corn, it contain high sugar level at Milk- Stage when suitable for Table use.  Indian Corn This corn has white, red, purple, brown, or multi-colored kernels. It was the original corn grown by the Indians. And it is known by the scientific name Zea Mays.  Pop Corn It has small ears and rounded kernels which on exposure to dry heat, are popped or everted by the expulsion of the contained moisture, and form a white starchy mass many times the size of the original kernel.  Flour Corn It is composed almost entirely of soft starch. The USA grows small amounts of blue flour corn to make tortillas, chips, and baked goods. DRY AND WET MILLING OF CORN Milling of Corn The basis of the maize milling process is the separation of the maize kernel into its different parts. Starch has been produced from corn for many years by two general procedures, namely 1. Dry milling 2. Wetmilling Both dry and wet milling procedures accomplish separation of the germ from which corn oil is obtained and removal of the hull which constitutes the majority of the high fiber portion.  CORN DRY MILLING Dry milling process consists of the following steps: Cleaning Conditioning Degerming Drying Cooling Grading Grinding Cleaning When corn is received at the mill, it is cleaned by both dry and wet process. Cleaning steps are sieving, separating particles by shape and density and removing ferromagnetic metals by permanent magnets. Conditioning The cleaned corn is conditioned, which basically means that water is added and the moisture allowed to equilibrate within the kernels. A moisture content of 21% is considered optimal. Degermination The purpose of degerming is to remove hull, tip cap and germ and leave the endosprum into large grits. Drying The degermer product are to be dried to 15-18% moisture content for proper grinding and sifting. Drying is performed by conventional rotary steam tube dryers. Cooling Counter-flow or cross flow rotary cooler can be used for cooling the dried products. Grading Recovery of various primary products is the next step. The through-stock is sifted or classified by particle size and enters into a conventional long reduction system having the function of removing bran and germ while releasing a maximum amount of clean large grits. Milling The milling operation consists of the steps of grinding, sifting, classifying, purifying, aspirating and in some case, final drying. The normal flow is through break rolls and then to sifters. The break rolls are followed by reduction roll which grind the endosperm to the desired particle size. Wet milling of corn  Impact Mill Receipt corn Degermination Storage Fiber Starches Slurry & Gluten Hydro cyclones Centrifugation Cleaning Steeping Fiber, Germ starch, Gluten Starch gluten Oil Extraction Steeped water Ethanol Animal Feed Production Residues Evaporation Corn steep liquo r Corn Gluten Meal Cleaning Clean the shelled corn to ensure that they are free from dust and foreign bodies. Steeping The corn is soaked in water, called steepwater, at 50˚C for between 20 and 30 hours, during which time it doubles in size.  Sulphur dioxide is added to the water to prevent excessive bacterial growth. As the corn swells and softens, the mildly acidic steepwater starts to loosen the gluten bonds with the corn, and to release the starch. The corn goes on to be milled.  MILLING AND SEPARATION  The corn is coarsely milled in the cracking mills to separate the germ from the rest of the components (including starch, fibre and gluten).  The corn flows to the germ separators to separate out the corn germ.  The corn germ, which contains about 85% of the corn’s oil, is removed from the slurry and washed. It is then dried and sold for further processing to recover the oil.  FINE GRINDING AND SCREENING  After the fine grinding, which releases the starch and gluten from the fibre, the slurry flows over fixed concave screens which catch the fibre but allow the starch and gluten to pass through. The starch-gluten suspension is sent to the starch separators.  The collected fibre is dried for use in animal feed.  SEPARATING THE STARCH AND GLUTEN  The starch-gluten suspension passes through a centrifuge where the gluten, which is less dense than starch, is easily spun out.  The gluten is dried and used in animal feed.  The starch, which still has a small percentage of protein remaining, is washed to remove the last traces of protein and leave a 99.5% pure starch.  The starch can either be dried and sold as corn starch, or it can be modified to turn into other products, such as corn sweeteners, corn syrups, dextrose and fructose.  Starch Industry Overview Corn Wet Milling Separation Starch Wheat Dry Milling Value Added Conversion Starches Glucose Syrup Hydrogenation Fermentation Refining Sorbitol 42 & 55 HFCS Crystalline Dextrose Citric Acid Crystalline Fructose Ethanol Maltodextrin Xanthan Gum 8 HIGH FRUCTOSE CORN SYRUP What is High Fructose Corn Syrup? High fructose corn syrup (HFCS) is a sweetener made from corn and can be found in numerous foods and beverages Known by name glucose/fructose in Canada Glucose – Fructose Syrup (GFS) in the EU High-fructose maize syrup in other countries— comprises any of a group of corn syrups that has undergone enzymatic processing to convert some of its glucose into fructose to produce a desired sweetness. DIFFERENCE B/W SUCROSE AND HFCS  Cornstarch made from the inner germ layer and outer husk of the corn or maize is the key ingredient for Corn Syrup. Natural enzymes alpha-amylase is first added to the mixture to break it down into oligosaccharides Next, enzyme glucoamylase is added to break oligosaccharides into glucose Glucose is added directly to the glucose-isomerase or xylose isomerase and the slurry liquid is further heated. It gets converted to a mixture comprising 50–52% glucose, 42% fructose and traces of other sugar Production and Chemical reaction of HFCS A.K.A: also known as  Easy to transport. Fructose is sweetest of all naturally occurring carbohydrate. High solubility lead to softer product and ability to retain moisture and better texture and baked goods. Free monosaccharides in HFCS provide better flavor enhancement, stability, freshness, texture, color, pourability, and consistency in foods in comparison to sucrose.  Breads Condiments(like yogurts, ketchups etc) Soft drinks Beverages Fast foods Increased Appetite Pancreatic cancer  Barley Classification Barley is a grass belonging to the family Poaceae, the tribe Triticeae. The chief taxonomic characteristic of Hordeum is its one–flowed spikelet. Three spikelets alternate on opposite sides at each node of the flat rachis of the spike or head. The Chemical Composition of Barley and Malt  Processing of Barley It is milled to obtain blocked barley, pearled barley, barley groats, barley flakes and barley flour for human consumption. The sequence of operations in barley milling may be as follows: ❖ preliminary cleaning, ❖ conditioning or tempering, ❖ bleaching (blue aleurone barley), ❖ blocking or shelling, aspiration, size grading by sifting, ❖ groat cutting, ❖ pearling of blocked barley or large barley groats, ❖ grading and ❖ sifting and ❖ polishing i. Pot and pearled barley are prepared by gradual removal of hull, bran and germ by abrasive action in a stone mill. Production of pot barley is the first stage of pearling, which may remove 7 – 14% of the weight of the grain. Further abrasion results in the removal of seed coat (testa and pericarp), aleurone, subaleurone layers and the germ leaving behind a central endosperm rich in carbohydrates and proteins. ii. Barley flour is made by roller–milling of pearled or blocked barley. iii. Barley flakes are made by pre-damping of barley groat, steam cooking of groats or pearledbarley, flaking and hot air drying of flakes. iv. Barley bran (excluding the hulls) consists of testa and pericarp, germ, the tricellular aleurone and subaleurone layers. Barley bran is obtained as a by–product during barley milling process Flow Diagram of barley processing Germination of barley grain  Malting of Barley In the production of malt based beverages and malted milk food, barley grain is first converted into malt. The malting process commence with the steeping of barley in water at a temperature of about 12°C for 36 hours with frequent aeration, to achieve a moisture level sufficient to activate metabolism in the embryonic and aleurone tissues, leading in turn to the development of hydrolytic enzymes.  The wet barley is germinated around 14°C for a period of about 144 hours. During germination, enzymes migrate through the starchy endosperm, progressing from the embryo end of the kernel to the distal end. In this mobilization phase, generally referred as “modification”, the cell wall and protein matrix of the starchy endosperm are degraded, exposing the starch granules.  After a period of germination, the “green malt” is kilned at a temperature not exceeding 85°C, to arrest germination and stabilize the malt by lowering the moisture levels, typically to less than 5%. In the process, undesirable raw flavours are removed and pleasant “malty” notes are introduced. The kilning process is also responsible for developing the colour of the malt.  Biochemistry and chemistry of malting Malting allows the optimal development of hydrolytic enzymes by the aleurone cells of barley and controlled action of these enzymes to eliminate structural impediments to subsequent easy and complete extraction during mashing. Elucidation of the part played by gibberilic acid in stimulating secretion of –amylase, endopeptidase, endo– –glucanases and inorganic ions from the aleurone to the central endosperm has encouraged the development of malting modifications. Steeping The steeping operation is the most critical stage in malting. To produce homogeneous malt, it is necessary to achieve even moisture content across the grain bed. Most barley requires a steeping regime that takes them to 42 – 46% moisture.  At the commencement of steeping, the embryo and husk absorb water far more rapidly than does the starchy endosperm. Besides water, barley requires a supply of oxygen to support respiration. Oxygen access is inhibited if the grain is submerged in water for prolonged periods, a phenomenon that dictates use in modern malting regime of steeps interrupted by air rest periods.  The steep water may be aerated or oxygenated. Air rests serve the added role of removing carbon dioxide and ethanol, which are the products of respiratory metabolism and may inhibit germination. A typical steeping regime may involve an initial steep to 32 – 38% moisture, an air rest of 10 – 20 h, followed by a second steep to raise moisture to 40 – 42%. The entire steeping operation in the modern malting plants is likely to cover 48–52 h. Germination Germination is generally targeted to generate the maximum available extractable material by promoting endosperm modification through the development, distribution and action of enzymes. Enzyme synthesis occurs during germination in the aleurone and subsequently migrates into the endosperm to effect hydrolysis.  During hydrolysis enzyme development follow the sequence: cell wall degrading enzymes, proteases, and then amylases. The process is controlled by maintaining moisture levels within the grain, supplying oxygen, removing carbon dioxide, and eliminating excess heat formed by respiration. Temperature is controlled throughout the germination period, typically in the range of 16 – 20°C.  Modification of the barley commences at the proximal end of the grain, adjacent to the scutellum. The rate of modification depends on: (1) the rate at which moisture distributes through the starchy endosperm, (2) the rate of synthesis of hydrolytic enzymes, (3) the extent of release of these enzymes into the starchy endosperm, and (4) structural features of the starchy endosperm that determine its resistance to digestion. Kilning Through the controlled drying of green malt, the maltster is able to: (1) arrest modification and render malt stable for storage, (2) ensure survival of enzymes, where appropriate, for subsequent employment in processing, and (3) introduce desire colour and flavour characteristics.  Kiln drying is divided into four major phases: (1) free drying down to approximately 23% moisture, (2) an intermediate stage, to 12% moisture, (3) the bound water stage, from 12 to 6% moisture, and (4) curing, in which the moisture is typically taken to 2– 3%.  Principle changes occurring during kilning is the browning or Maillard reaction. The interaction of reducing sugar and amino acids produces reductones, which in turn can be converted by polymerization to the colourful melanoidins or, by alternative routes, to the heterocyclic pyrazines, thiophenes, pyrrolles, and furans. The oxygen heterocyclics are responsible for toffee or caramel flavours. The pyrazines impart the roasted, coffee like flavours.  BREAKFAST CEREALS: CLASSIFICATION & TECHNOLOGIES  Introduction Cereal grains have found a significant use as breakfast foods. Breakfast cereal technology has evolved from the simple procedure of milling grains for cereal products that require cooking to the manufacturing of highly sophisticated ready-to-eat products that are convenient and quickly prepared. Breakfast cereals are generally eaten cold and mixed with milk as opposed to hot cereals like oatmeal, grits, etc.  Definition of Breakfast Cereals Breakfast cereals have been defined as “processed grains for human consumption”. One or more of the cereal grains or milled fractions therefore are indeed major constituents of all breakfast cereals, approaching 100% in the case of cereals for cooking. The proportion drops well below this in many ready-to- eat cereals, and to less than 50% in pre-sweetened products. Classification  Ready-to-eat (RTE) cereals are made primarily from corn, wheat, oats or rice usually with added flavour and fortifying ingredients. Breakfast cereals are classified into two major categories: hot cereals and RTE cereals. Hot cereals are made primarily from oats or wheat nevertheless; hot cereals from corn or rice are produced in relatively small quantities.  Hot cereals require cooking at home before they are ready for consumption with the addition of either hot water or milk. The processing of RTE cereals involves first cooking the grains with flavouring material and sweeteners. Sometimes more heat stable nutritional fortifying agents are added before cooking. Most RTE cereals are grouped into eight general categories 1. Flaked cereals 2. Gun-puffed cereals 3. Extruded gun puffed cereals 4. Shredded whole grains 5. Extruded and other shredded cereals 6.Oven puffed cereals 7. Granola cereals 8. Extruded expanded cereals  Manufacturing Processes for Breakfast Cereals The proprietary nature of the breakfast cereal industry limits the information base to patent records and publications by individuals not directly associated with industry. In broad terms, breakfast cereal ingredients may be classified as grains or grain products, sweeteners, flavouring, texturizing ingredients, and micro- ingredients for nutritional fortification and preservation.  The processing of ready-to-eat cereals typically involves first cooking the grains with flavouring material and sweeteners, followed by forming operation. Sometimes the heat stable nutritional fortifying agents are added before cooking. Two cooking methods are employed in the industry - direct steam injection into the grain mass and continuous extrusion cooking.  Various unit operations are involved in the manufacturing of the breakfast cereals such as tempering, puffing, flaking, shredding, baking and drying, etc. These unit operations yield breakfast cereals with certain forms such as puffed, cracked, flaked, cakes, pellets or definite shapes such as circular, cylindrical, rectangular, nuggets, oval, triangle; and irregular shapes such as chunks.  Processing Steps Cooking Flaked breakfast cereals can be made by cooking whole kernel cereals or legumes by pressure cooking followed by pressing through rollers. Alternatively it can be made by extrusion cooking of flour. Cooking helps in development of desirable flavour and nutritional benefits. It also assists in creation of desirable physical properties necessary for the development of desire texture – primarily by starch gelatinization.  Batch cooking Corn flakes, wheat or bran flakes and shredded wheat are processed in batch pressure cook processes, where steam is injected into the pressure cooker. Atmospheric cooking with steam injection especially in case of shredded wheat in steam jacketed mixing vessel is also used. Product from the batch pressure cooker forms lumps or individual grits, which are subsequently deplumed before the next processing step, which is drying. Extrusion cooking  The starting material for extrusion cooking is dough from which intermediates or half products are anticipated prior to puffing or flaking. Different types of extruders are employed in manufacture of breakfast cereals such as single screw, twin screw or kneading or forming – type extruder  Tempering Tempering is a physico-chemical effect that influences the quality of finished product. Tempering follows a drying or cooling step and is the period during which the cooked grain mass or cereal pellets are held to allow the equilibration of moisture within and among the particles. It assist in the development of desired flakability or shredability. During tempering the retro gradation of starch (firmness of grain due to starch crystallization) allows moisture equilibration.  Puffing Puffing is a thermal process in which rapid heat transfer takes place in order to phase shift the water to a vapor. Two things are important for grain to puff – the grain must be steeped or cooked, and a large, sudden pressure drop must occur in atmosphere surrounding the grain. Rice and wheat are most widely used cereals for puffing. They are puffed as whole kernel grains.  In gun puffing, high temperatures are attained (600 – 800°F) followed by a pressure drop of 100 – 200 psi. A rotating gun is heated by means of gas burners with very hot flames; the moisture in the grain is converted into steam. When the lid is opened to fire the gun, the internal pressure is released, and the puffed grain is caught in a continuously vented bin.  Flaking Flaked products are produced by passing tempered grits or pellets through two large counter rotating metal rolls, one of which is adjustable so that the distance between them or roll gap can be set to produce a flake of the desired thickness. These rolls are hollow and are internally cooled by passing water through the interior of the roll. A scraper knife on each roll removes the flakes, which are then conveyed to toasting oven.  Shredding The grain used in whole kernel form for shredding is primarily wheat. Shredded wheat is made by cooking soft white wheat in an excess of water at atmospheric pressure. The drained wheat is cooled to ambient temperature and contains approximately 50% moisture. The next step is tempering for 24 hours to allow for moisture equilibration and firming of the kernel.  Next, the wheat is squeezed between two Counter rotating metal shredding rolls – one with a smooth surface, the other grooved. Shredding rolls are water cooled to control the roll surface temperature. The shreds are laid down on a conveyor under the rolls running parallel to the shredding grooves and subsequently conveyed to dryer for drying to a final moisture content of around 3 – 4%.  Baking Cerealgranules or granola cereals are usually produced using a modified bread baking process. A stiff dough is prepared from wheat flour, malted barley flour/rolled oats, salt, yeast and water. Other raw materials such as nut pieces, coconut, honey, malt extract, dried milk, dried fruits, vegetable oil, spices can also be added.  The dough is mixed and allowed to ferment for 4 – 5 hours at 80°F and 80% relative humidity (RH). After fermentation the dough is baked at 300 - 425°F until the material is uniformly toasted to a light brown and moisture reduced to about 3%. The dried pieces are ground into small pieces and screened to obtain desired particle size. The final product has a notable crunchy texture.  Drying Most ready-to-eat breakfast cereals require drying as an intermediate processing step. This drying is the controlled removal of water from the cooked grain and other ingredients to obtain appropriate physical properties for further processing such as flaking, puffing, forming, toasting or packaging. Cereals are dried at various stages of processing.  Pellets for flake products have a moisture content of 30 – 33% prior to the drying and are dried down to 16 – 22% moisture. Pellets for gun puffing are dried from 30 – 32% to 10 –12% moisture. This pre-drying prevents agglomeration of cooked cereals. Multi pass dryer design for better control over residence time and humidity are widely used for drying of cereals.  Additives in breakfast cereals Breakfast cereals available in market are manufactured from variety of cereals such as corn, wheat, oats, barley, rice, rye singly or in combination. Breakfast cereals are usually eaten/mixed with milk, certain breakfast cereals contain milk solids as one of the ingredients. Breakfast cereal ingredients may be classified as (1) grain or grain products, (2) sweeteners, (3) other flavouring or texturizing ingredients, (4) minor ingredients for flavour and colour and (5) minor ingredients for nutritional fortification and self- life preservation. Additives in Breakfast Cereals