The quality of the grain

Source: Inta Balcarce

The quality of the grain of corn is associated so much with its physical constitution that determines the texture and hardness, like with its chemical composition that defines the nutritional value and the technological properties. The relative importance of these characteristics will be of the destination of the production. The markets are more and more demanding and they are interested in the content of proteins, amino acids, starch, oils and other components, and gradually it decreases the tolerance to polluting substances. For the industries that use grain of corn, their quality and technological properties are a fundamental concern. Healthy, clean grains are required, standardize of size, texture and color. On the other hand, the seed companies  carry out, in a mark of high competitiveness, big investments to put within reach of the hybrid new producer that cover the requirements of the market and of the industry. In this context, when they taking the sow decision, the producer will decide about the possibility of carrying out specific productions of agreement with the demand of the industry, being able to make direct contracts with the companies of the sector with superior prices to those of the market to bulk.

Items to consider:

Composition

Hardness

Relationship between protein and hardness

Due variations to the genotype

Incidence of the atmosphere and of the handling of the cultivation in the quality

Quality of the corn for the trade to bulk

Quality of the corn for the industry

Composition

The mature grain of corn is integrated by different fabrics that conform: the germ or embryo (12%), responsible for forming a future new plant; the endosperma (82%), structure of storage of the grain that constitutes their main reservation energetics; and the pericarp or covered with the grain (5%) that protects the seed of the entrance of mushrooms and bacterias before and after the siembra. The remaining 1% corresponds to the remains of the pedicelo in the base of the grain.

Hardness

The hardness of the grain is the resistance that possesses to the mechanical action or the one broken during the crop and the harvest. That resistance  determines the quality that possesses the grain for its use and conservation, is related in direct form with the hardness of the endosperma that in turn,  is due to the relationship between the horny endospermas and harionso, and in smaller measure, to the compactación of the cellular components, to the thick of the main proteic that surrounds to the granules of starch, and to the thick of the pericarp. So much adult will be the hardness of the grain, as much as adult is the proportion of horny endosperma that composes it.

Relationship between protein and hardness

The increases in the percentage of proteins of the grains, in general, associate with increases in the quality of the same ones. The main reservation proteins that it possesses the grain of corn they are the zeínas. These present four different structural types: alpha, beta, delta and range.

They group in structures calls "proteical bodies", in which stand out for their abundance the alpha and the range zeínas. The different types can group in two you proteic fraction: zeína 1 and zeína 2.

The first one is integrated in their biggest part by alpha zeínas, and in a small proportion, for delta zeínas. The second are the result of the sum of the beta and range zeínas. The primary structure of the range zeínas, their capacity to unite by means of connections disulfuro, their localization in the bodies proteicos, its homology with structural proteins and its biggest deposition in the vitreous endospermas suggests that this protein participates in to determination of the physical properties or hardness of the grain of corn.

The hardness is determined by the ligament between the starch and the proteins of the endosperma. In the horny fraction of the endosperma, the starch and the protein they are very strongly bound, while in the floury fraction they are only weakly bound.

Due variations to the genotype

The genetic improvement in corn has been successful in modifying the hardness of the endosperma and the percentages of oil, protein and starch of the grain, as well as the quality of its protein and the type of its starch.

Corn of high percentage of oil

The percentage of oil in the common corns is usually between 2.5 and 5.5%, with more frequent values of the 4 to 5%.

The corns with high content of oil and smaller proportion of carbohydrates make a bigger energy contribution to the diet of animals. Their employment in bovine and swinish that require a high caloric content in their diet, the attaché of oil avoids in the portion and it allows a bigger efficiency in the use of hormones of growth.

Corn with modified starch

The alteration of some enzymes gives place to mutants with its modified starch. This procedure throws two types of corn as a result: the waxen corn or "waxy", and the corn with high amilosa.

Waxen corn or "waxy": A gene affects the synthesis of the starch in a such way that amilopectina chains are only formed, with complete exclusion of the amilosa chains. This originates the corns waxy or waxen that are particularly appropriate for the industries that use that type of starch.

Corn with high amilosa: Due to the action of another recessive mutant, this type of corn possesses until 80 amilosa% in its composition - when the normal corn possesses between the 25 and 30% -. The amilosa is a molecule that can become a fine movie and reveal as the cellophane, allowing its use for plastics, it photographs and other products, having the great advantage of being biodegradable.

Pop Corn

The pop corn it is cultivated for human consumption. The main characteristic that differentiates it of the other types of corn is its capacity to form big flakes when it explodes in answer to the heat. This characteristic is controlled by genes of quantitative inheritance and it has allowed the development of specially capable cultivares. The genetic improvement has achieved hybrid with high capacity of expansion of its endosperma, pericarp that fragments in small portions, great terneza of the flake and good flavor. Looking for to assure a good humidity for maximum expansion (between 13,5 and 14,8%) the pericarp should conserve its integrity, of there the necessity to carry to an extreme the cares during the crop and post harvest

Sweet corn

In the sweet corn the synthesis of starch in the grain is inhibited. The mutant recessive sugary-l (their l) it stops the conversion on behalf of the sugar in starch, determining sucrose levels in the grain of twice as much or triple of the common corn. Their production demands special cares since the period in that it remains sweet the grain is very short. Its refrigeration requirement in the commercialization is reduced, since the conversion of sugars in starch is slow to ambient temperature. The fresh of the pericarp, their sweetness and flavor, their flavor and appearance, they were objective of improvement of this sweet corn.

Incidence of the atmosphere and of the cultivation handling

Physical damages or mechanics: The quality of the corn grain can be affected so much in the field cultivation, like in the crop and post harvest. The physical damages or mechanics can be external and/or internal. The external damages consist on courts and abrasions of the pericarp of the grain, while the internal damages are manifested in form of fissures in the horny endosperma.

Biological damages: They are responsible for the damage, heating and burned of the grains of corn during the storage, several species of mushrooms of the goods Penicillium and Aspergillus. The mushrooms that attack to the grain of corn in the field require high content of humidity in the grain and they rarely survive in the storage. The mushrooms responsible for such attacks generally correspond to the goods Fusarium and Giberella.

Percentages of proteins in the grain: The climatic variations and the cultivation conditions determine modifications in the grain percentage of proteins. Several authors found that with a good nitrogen nutrition in corn the density of the grain increases, reducing the susceptibility to the one broken. It takes place as consequence of the biggest protein content, especially of present zeína in the horny endosperma, and of the increment of the proportion of this endosperma type.

Quality of the corn for the trade to bulk

For the trade to bulk, the resistance of the grain to the one broken in the manipulation post harvest determines the quality for the conservation and the later uses. The hardness of the endosperma is directly associated with this resistance.

Hardness of the grain

The hardness is an intrinsic property of the grain that is generally expressed in its resistance to the mechanical action. It is an inheritable characteristic, modified by the cultivation conditions and the handling post harvest. The grains of more hardness are those that present a bigger proportion of horny endosperma.

The hardness of the grain in the Argentinean corn

The corn traditional Argentinean is the "Silver", of red hard type with horny endosperma of flat crown and orange reddish color. It is appreciated in the export markets by their biggest grade of hardness that makes it less susceptible to leave or to be broken by effect of the mechanical crop and of the later movements of load and it discharges in storing plants, shipment and transport.

Tipificación of the corn in the Argentina

The commercial types of corn that govern in the current Argentinean standard are:

Hard type: corns with grains of horny, mainly vitreous nature

Jagged type: corns with grains of floury nature, presenting or don't unite fissure in the crown.

Characterization of the hardness

The most appropriate methods to measure the hardness use special mills to determine the time of process or the required power. Also, diverse authors established equations that estimate the texture grade or hardness of the grain starting from parameters of easy mensuration correlated with this character (I eat for example, starting from the protein percentage and oil of the grain, and of their weight hectolítico).

Quality of the corn for the industry

The industry in the developed countries uses the corn in almost a thousand of different applications based in the chemical composition of the grain. For example, we can find it so much in the corn flour, like in biodegradable plastics. The technological quality of a grain varies according to the destination of the production, and it is related with the transformation technique and industrial production. For the industry of the dry mill of they need grains of hard corns, since in this industry they care the hardness of the endosperma and the relationship of particle sizes that it is of the mill.

The quality demanded fundamentally in the yield in big proportions of thick fractions, leaning for the hard red type. The industry of the humid mill has demands of quality something different from those of the dry mill, leaning for the types of jagged corn, since they demand smaller maceration time in the extraction processes. They are required, then, corns with high content of starch, caring their purity and their recovery efficiency, and grains especially with high content of oil or of protein.