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MAIZE

Maize (Zea mays), known as ’corn’ in USA, is utilized in more diversified ways than any other cereal. With its high percentage of carbohydrate, lipid and protein, it is nutritious for human consumption. A high percentage of maize grown in developing countries is used for food; in India it is 80-90 per cent. The ready-to-eat breakfast cereal ‘cornflakes’ is a maize product. In developed countries maize is used as an animal feed.

Maize is also used for the manufacture of starch, sugar (corn sugar, dextrin), syrup (corn syrup), industrial alcohol and alcoholic beverages. Corn also finds a number of other uses.

• COMPOSITION
• PROCESSING
• VALUE ADDITION

COMPOSITION

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Maize consist of the outer hull or bran with a high fibre content, embryo (germ) rich in oil and the endosperm rich in starch. Maize is deficient in the vitamin niacin. Maize is a fairly good source of phosphorus, contain an appreciable amount of iron, but is low in calcium.

PROCESSING

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MILLING OF CORN

a. Dry Milling

Corn dry milling system can be divided into two groups: the traditional non degerming system and modern degerming system. In the non degerming system, the whole corn is ground into meal of high fibre as well as high protein contents by a stone grinder without removing germ. After grinding certain amount of germ and hull can be removed from the meal by sifting.

In the degerming system the corn is moistened with a little amount of water and' tempered for moisture equilibration. After degerming the stock is dried, milled and classified into different products. The purpose of all dry degerming corn milling methods is to remove hull, germ and tip cap from the corn kernel as far as practicable and primarily produce corn grits with some meals and flours. The germ is then used for oil extraction and deoiled germ, hull, etc., are used as feed which is known as hominy feed. The yield of endosperm products and horny feed are about 70 per cent and 30 per cent respectively.

TEMPERING-DEGERMING (T.D.) METHOD OF DRY MILLING

The major objectives of this method are:

(a) to remove essentially all germ and hull so that endosperm contains as low as and fibre as possible,
(b) to recover a maximum amount of the endosperm as large clean grits without any dark speck, and
(c) to recover a maximum amount of germ as large and pure particles.   

    
Cleaning of corn

Thorough cleaning of corn is essential for the subsequent milling operations. Pieces of iron, etc., are removed by magnetic separators. Dry cleaners consisting of sieves and aspirators and sometimes a wet cleaner consisting of a washing destoning unit and a mechanical type (dewatering unit, known as whizzer, are used for cleaning of corn.

Hydrothermal treatment/conditioning

Predetermined amount of moisture is added to the corn in the form of cold or hot water or steam in one, two or three stages with appropriate tempering times after each stage. The tempering times (rest periods) vary according to the hydration methods. So also tempering temperatures vary from room temperature to about 50°C accordingly.

Either cold or hot water is used for the addition of moisture. A little heat in the form of open steam is added as and when necessary.

Degerming

The purpose of degerming is to remove hull, tip cap, and germ as far as practicable and leave the endosperm into large grits. However, the products from degermer consists of a mixture of kernel components, freed from each other to varying degrees, with the endosperm particles varying in sizes from grits to flour.

Drying and cooling of degermer stock

The degermer products are to be dried to 15 to 18 per moisture content for proper grinding and sifting.Generally rotary steam tube dryers are used for drying the product. Rotary Louver type dryer can also be employed. The stock is heated to about 50°C. Counter-flow of cross-flow rotary, vertical gravity or fluidised bed types of cooler can be used for cooling the dried products.

Rolling and Grading

Recovery of various primary products is the next step. Further release of germ and husk from the endosperm product occurs during their gradual size reduction roller mills.

The germ, husk and endosperm fragments are then separated by means of sifters, aspirators, specific gravity table separators or purifiers. Sifting is an important operation and is variously referred to as scalping, grading, classifying, or bolting depending upon the means used and purpose. Sifting is actually a size separation ration on sieves. Scalping is the coarse separation made on the product leaving a roller mill or degermer. Grading or classifying is the separation of a single stock (usually endosperm particles into two or more groups according to particle size. Bolting is removal of hull fragments from a corn meal or flour.

b. Wet Milling

The raw corn for wet milling should contain 15-16 per cent moisture and it should be physically sound. Insect and pest infested, cracked and heat damaged corns (treated at temperature around 75° C during drying) are unsuitable for wet milling. The heat damaged corn affects the quality of oil extracted from its germ.

                     
Sufficient amount of moisture is added to the corn during steeping in the wet milling process in order to prepare the corn for subsequent degerming, grinding and separation operations.

The wet milling process consists of the following steps: (a) cleaning, (b) soaking, (c) germ separation and recovery, (d) grinding and hull recovery, and (e) separation of starch and gluten.

Cleaning

All impurities such as dust, chaff, cobs, stones, insect-infested grain and broken grain, and other foreign materials are removed from corn by screening and aspirating. The clean grains are conveyed to the storage bins.

Steeping

The major objectives of steeping are (1) to soften the kernel for grinding, (2) to facilitate separation of germ, (3) to facilitate separation of gluten from the starch granules, and (4) to remove solubles, mainly from the germ.

Water impregnated with SO2 (i.e., acidulated water with H2SO3) is used for stepping; it helps in arresting certain fermentation (luring long sleeping process. The   steeping is carried out at about 50° C   for   a   period varying from 28 to 48 hours in different plants. The steeped corn attains a moisture content of about 45 percent.

BY PRODUCTS OF MAIZE

VALUE ADDITION

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Flaked maize (corn)*           

Maize grits is cooked under pressure and the flavourings are added. The cooked cereal is then dried to 15-20% moisture. The conditioned grain is flaked between heavy flaking rolls and the flakes are then toasted (3% moisture).

Parching of corn *

The traditional method is simply to heat kernels in a heavy skillet over low heat. No oil is used. Stir the kernels with a spatula as they cook. Traditional parching takes about 5 minutes. Hold a lid or grease screen above the pad to keep the kernels from jumping out. Or, instead of using a spatula, cover the pan and stir the corn by shaking the pan on the burner as with pop corn. If the pan is not closed, the kernels will burn. Stop the cooking when the popping mostly.

Pop corn *

A major part of the endosperm of this type of corn comprises hard starch on all sides, with a very small core of soft starch. When the corn is popped the endosperm expands with the formation of a fluffy white irregular mass. The thick outer layers of the corn remain attached to the puffed endosperm in an unexpanded form.

Macaroni*

Ingredients

The flour is kneaded to desired consistency by extruder. The extrudates were dried at 50-55 for 6 hours.

Technologies Available

*    - Post Harvest Technology Centre, TNAU, Coimbatore.

**  - Home Science College and Research Institute, TNAU, Madurai.

Source

1. http://www.thebaitwarehouse.co.uk/images/FRENCH%20MAIZE%201.jpg
2. http://www.thebaitwarehouse.co.uk/images/FLAKED%20MAIZE.jpg
3. eminentlife.blogspot.com/2008/06/vegetable-ch..