Due to different purposes and bases, corn can be divided into different categories, the most common are classified according to kernel morphology and structure, classified according to fertility period, and classified according to kernel composition and use.
(1) Classification according to kernel morphology and structure.
Based on the presence or absence of lemma husk, shape of kernel and nature of endosperm, corn can be divided into nine types.
①Hard grain type: also known as flint type, adaptable, barren, early maturity. The cob is mostly conical, and the top of the kernel is rounded, due to the periphery of the endosperm is horny starch. Therefore, the kernel appearance is transparent, the outer skin is glossy, and hard, mostly yellow. Excellent flavor quality, low yield.
② Horse-tooth type: tall plants, fertilizer resistance, high yield, late maturity. Fruit spikes are cylindrical, the kernel grows flat, the sides of the kernel for the angular starch, the center and the top of the powdery starch, the top of the maturity of the powdery starch loss of water drying faster, the kernel apical depression in the shape of a horse's teeth, hence the name. The degree of depression depends on the starch content. The flavor quality is not as good as the hard grain type.
3 Powdery type: also known as soft type, the shape of the cob and kernel is similar to the hard type, but the endosperm consists of powdery starch, the kernel is milky white, no luster, it is an excellent raw material for making starch and brewing.
4 sweet quality type: also known as sweet corn, the plant is short, small ears. The endosperm contains more sugar and water, the seeds crumpled due to evaporation of water at maturity, mostly horny endosperm, hard translucent, more vegetables or canned food.
5 sweet powder type: the upper part of the seed is sweet type horny endosperm, the lower part is powder endosperm, it is rare in the world.
6 burst type: also known as corn wheat, more ears per plant, but the ears and kernels are small, rounded kernels, the tip protrudes, starch type is almost entirely horny. When exposed to heat, the water within the starch forms a vapor and bursts.
7 wax type: also known as glutinous type. Native to China, the spike is small, the endosperm in the kernel is almost entirely composed of branched-chain starch, opaque, lusterless as wax. Branched-chain starch meets iodine solution is red reaction. Sticky when eaten, so also known as sticky corn.
8 lemma type: the kernel is covered by a longer lemma shell, hence the name. The tip of the lemma shell sometimes has an awn. It has strong autoflowering sterility, well-developed male inflorescences, hard kernels, and threshing difficulties.
9 Semi-horse-toothed type: between hard-grained type and horse-toothed type, the depth of apical depression of the kernel is shallower than horse-toothed type, and the horny endosperm is more. The seed coat is thicker and the yield is higher.
(2) Classification according to fertility period.
Mainly due to genetic differences, different types of corn from sowing to maturity, that is, the fertility period is not the same, according to the length of the fertility period, can be divided into early, medium and late maturity types. Due to the vastness of our country, the division of early, medium and late maturity standards are not entirely consistent, it is generally believed that:
①Early maturing varieties: spring sowing 80 to 100 days, cumulative temperature of 2000 to 2200 ℃, summer sowing 70 to 85 days, cumulative temperature of 1800 to 2100 ℃. Early-maturing varieties are generally short plants, the number of leaves is small, 14 to 17 pieces. Due to the limitation of fertility, yield potential is small.
② medium-ripening varieties: spring sowing 100 to 120 days, the need for cumulative temperature 2300 to 2500 ℃. Summer sowing 85 to 95 days, cumulative temperature 2100 to 2200 ℃. The number of leaves is more than early varieties and less than late sown varieties.
3 late-maturing varieties: spring sowing 120 to 150 days, cumulative temperature 2500 to 2800 ℃. Summer sowing more than 96 days, cumulative temperature of more than 2300 ℃. Generally tall plants, the number of leaves, mostly 21 to 25. Yield potential is high due to the long fertility period.
Due to the differences in temperature and light hours, corn varieties in the north-south introduction, the fertility period will change. The general rule is: northern varieties to the south, often due to short sunshine, high temperatures and shorten the fertility period; conversely, to the north of the introduction of seed fertility will be extended. The size of the change in fertility, depending on the variety itself to the degree of sensitivity to light and temperature, the more sensitive to light and temperature, the greater the change in fertility.
(3) according to the use and seed composition classification.
Based on the composition of the kernel and special uses, corn can be divided into two categories of special corn and ordinary corn. Special corn refers to the higher economic value, nutritional value or processing value of corn, these corn types have their own inherent genetic composition, showing a distinctive kernel structure, nutritional composition, processing quality and edible flavor and other characteristics, and therefore have their own special use, processing requirements. Corn types other than specialty corn are common corn. Specialty corn generally refers to high lysine corn, glutinous corn, sweet corn, cracked corn, high oil corn and so on. The world's special corn cultivation and development to the United States is the most advanced, the annual output value of billions of dollars, has formed an important industry and rapid development. China's special corn research and development started late, in addition to glutinous corn originating in our country, the lack of other types of resources, coupled with the lack of financial resources, and the United States than there is still a small gap. In recent years, China's corn breeders have conducted a large number of research experiments in high lysine corn, high oil corn and other breeding has made great progress for the development of China's specialty corn has laid the foundation.
①Sweet corn: also known as vegetable corn, can be cooked and eaten directly, but also can be made into a variety of flavors of canned, processed foods and frozen foods. Sweet corn so sweet, because of the high sugar content of corn. The sugar content of its kernels also varies at different times, and during the appropriate harvest period, the sucrose content is 2 to 10 times that of ordinary corn. Due to different genetic factors, sweet corn can be divided into 3 categories: general sweet corn, enhanced sweet corn and super sweet corn. Sweet corn is sold in large quantities in developed countries. Sweet corn can be divided into four types: super-sweet, enhanced sweet, semi-enhanced sweet and general sweet.
② Glutinous corn: also known as sticky corn, its endosperm starch is almost entirely composed of branched-chain starch. The difference between branched-chain starch and straight-chain starch is that the molecular weight of the former is much smaller than that of the latter, and the digestibility of the food is more than 20% higher. Glutinous corn has a high viscosity and palatability, can be eaten fresh or canned, China also used glutinous corn instead of sticky rice to make pastries. Because of the high digestibility of glutinous corn, it can be used for feed to improve feeding efficiency. In industry, glutinous corn starch is the basic raw material of the food industry, can be used as a thickener, but also widely used in tape, adhesives and paper and other industries. Actively guiding and encouraging the production of glutinous corn will lead to the development of the food industry, starch processing industry and related industries, as well as promoting the development of animal husbandry and increasing national economic income.
3 high oil corn: refers to the kernel oil content of more than 8% of the type of corn, because the corn oil is mainly present in the embryo, intuitively high oil corn are larger embryo. The main components of corn oil are fatty acids, especially oleic acid, linoleic acid content is high, is necessary for the human body to maintain health. Corn oil is rich in vitamin F, vitamin A, vitamin E and lecithin content is also high, regular consumption can reduce the body's cholesterol content, enhance muscle and cardiovascular function, enhance the body's muscle metabolism, improve resistance to infectious diseases. Therefore, people call it a healthy and nutritious oil. Corn oil has become an important source of edible oil in developed countries, and corn oil accounts for 8% of edible oil in the United States. Ordinary corn oil content of 4% to 5%, the study found that with the increase in oil content, the kernel protein content also increased accordingly, therefore, high oil corn at the same time also improved protein quality.
4 high lysine corn: also known as high-quality protein corn, that is, corn kernels in the lysine content of 0.4% or more, the lysine content of ordinary corn is generally about 0.2%. Lysine is the human body and other animal body necessary amino acid type, in the food or feed lack of these amino acids will be due to nutritional deficiencies and serious consequences. High lysine corn consumption has a high nutritional value, equivalent to skim milk. Used in feed for hogs, the daily weight gain of hogs is increased by 50% to 110% compared to regular corn, and similar effects are seen in chickens. With the emergence of high-yield high-quality protein corn varieties, high lysine corn development prospects are extremely broad.
⑤ bursting corn: that is, the aforementioned type of bursting corn, its prominent feature is the high content of horny endosperm, starch grains of water in the high temperature and bursting. Generally popular as a flavor food in large and medium-sized cities.