Due to different purposes and basis, corn can be divided into different categories. The most common ones are based on kernel morphology and structure, growth period, and kernel composition and use.

(1) Classification according to particle morphology and structure.

Based on the presence or absence of lemma husk in the kernel, the shape of the kernel and the properties of the endosperm, corn can be divided into 9 types.

① Durum type: Also known as flint type, it has strong adaptability, resistance to barrenness and early maturity. The ears are mostly cone-shaped and the top of the kernel is rounded because the periphery of the endosperm is made of horny starch. Therefore, the appearance of the seeds is transparent, the outer skin is shiny, hard, and mostly yellow. The food quality is good and the yield is low.

② Dent-tooth type: tall plants, resistant to fertilizer and water, high yield, late maturity. The ear is cylindrical, and the kernels grow and become flat. The two sides of the kernel are horny starch, and the center and top are powdery starch. When mature, the top powdery starch loses water and dries quickly, and the top of the kernel is sunken and has a dent shape, hence the name. The degree of depression depends on the starch content. The food quality is not as good as the hard grain type.

③Powdery type: Also known as soft-grained type, the shape of the ear and kernels is similar to that of the hard-grained type, but the endosperm is entirely composed of powdery starch, and the kernels are milky white and dull. It is excellent for manufacturing starch and brewing. raw material.

④Sweet type: Also known as sweet corn, it has short plants and small ears. The endosperm contains more sugar and water. When mature, the seeds shrink due to evaporation of water. Most of them are horny endosperm, which is hard and translucent. It is mostly made into vegetables or canned.

⑤Sweet powder type: The upper part of the kernel is sweet horny endosperm, and the lower part is powdery endosperm. It is relatively rare in the world.

⑥ Bursting type: Also known as corn wheat, each plant has more ears, but the ears and grains are small, the grains are round, the top is protruding, and the starch type is almost all horny. When exposed to heat, the moisture in the starch forms steam and bursts.

⑦Waxy type: also known as waxy type. Originating from my country, the ears are small and the endosperm in the kernel is almost entirely composed of amylopectin, which is opaque, matte and waxy. Amylopectin reacts red when exposed to iodine solution. It is very sticky when eaten, so it is also called sticky corn.

⑧League type: The seeds are covered by a longer lemma shell, hence the name. There are sometimes awns on the top of the lemma shell. It has strong autoflowering sterility, well-developed male inflorescences, hard seeds, and difficulty in threshing.

⑨Semi-dental type: It is between the hard kernel type and the dent type. The depth of the depression at the top of the kernel is shallower than that of the dent type, and there is more horny endosperm. The seed coat is thicker and the yield is higher.

(2) Classification by growth period.

Mainly due to genetic differences, different corn types have different growth periods from sowing to maturity. According to the length of the growth period, they can be divided into early, medium and late maturing types. Due to the vast territory of our country, the standards for classifying early, medium and late maturity are not completely consistent in various places. It is generally believed that:

① Early maturing varieties: 80 to 100 days for spring sowing, 2000 to 2200°C accumulated temperature, 70 to 85 days for summer sowing , the accumulated temperature is 1800~2100℃. Early-maturing varieties generally have short plants and a small number of leaves, ranging from 14 to 17. Due to the restriction of growth period, the yield potential is small.

② Medium-ripening varieties: Spring sowing takes 100 to 120 days and requires an accumulated temperature of 2300 to 2500°C. Sowing in summer takes 85 to 95 days, and the accumulated temperature is 2100 to 2200°C. The number of leaves is greater in early-maturing varieties and less in later-sowing varieties.

③ Late maturing varieties: 120 to 150 days after spring sowing, with an accumulated temperature of 2500 to 2800°C. Summer sowing lasts for more than 96 days, and the accumulated temperature is above 2300°C. Generally, the plants are tall and have many leaves, mostly 21 to 25. Due to the long growth period, the yield potential is large.

Due to differences in temperature and light hours, the growth period of corn varieties will change when they are introduced in the north-south direction. The general rule is: when northern varieties are introduced to the south, the growth period is often shortened due to short days and high temperatures; conversely, when varieties are introduced to the north, the growth period will be lengthened. The size of the change in the growth period depends on the sensitivity of the variety to light and temperature. The more sensitive it is to light and temperature, the greater the change in the growth period.

(3) Classification according to use and particle composition.

Based on the composition and special uses of the kernels, corn can be divided into two categories: special corn and ordinary corn.

Specialty corn refers to corn with high economic value, nutritional value or processing and utilization value. These corn types have their own internal genetic composition and show unique characteristics such as kernel structure, nutritional content, processing quality and edible flavor. , therefore have their own special uses and processing requirements. Corn types other than special corn are ordinary corn. Special corn generally refers to high-lysine corn, waxy corn, sweet corn, popcorn, high-oil corn, etc. The United States is the most advanced in the world in the cultivation and development of special corn, with an annual output value of billions of dollars. It has formed an important industry and is developing rapidly. The research and development of special-purpose corn in my country started relatively late. Except for waxy corn, which is native to China, there is a lack of other types of resources. Coupled with insufficient financial resources, there is still a big gap compared with the United States. In recent years, my country's corn breeders have conducted a large number of research experiments and have made great progress in the breeding of high-lysine corn and high-oil corn, laying a foundation for the development of my country's special corn.

①Sweet corn: Also known as vegetable corn, it can be eaten directly after being cooked, or can be made into canned, processed and frozen foods with various flavors. Sweet corn is sweet because of its high sugar content. The sugar content of its grains also changes with different periods. During the suitable 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 three categories: regular sweet corn, enhanced sweet corn and super sweet corn. Sweet corn sells more in developed countries. Sweet corn can be divided into four types: super sweet, enhanced sweet, semi-enhanced sweet and regular sweet.

② Waxy corn: Also known as sticky corn, its endosperm starch is almost entirely composed of amylopectin. The difference between amylopectin and amylose is that the former has a much smaller molecular weight than the latter, and its digestibility is more than 20% higher. Waxy corn has high viscosity and palatability, and can be eaten fresh or canned. In my country, there is also the habit of using waxy corn instead of sticky rice to make pastries. Since waxy corn has high digestibility, its use in feed can improve feeding efficiency. In industry, waxy corn starch is a basic raw material in the food industry and can be used as a thickener. It is also widely used in tapes, adhesives, papermaking and other industries. Actively guiding and encouraging the production of waxy corn will drive the development of the food industry, starch processing industry and related industries, promote the development of animal husbandry, and increase national economic income.

③High-oil corn: refers to the type of corn with an oil content of more than 8. Since corn oil mainly exists in the embryo, intuitively, high-oil corn has larger embryos. The main component of corn oil is fatty acids, especially the high content of oleic acid and linoleic acid, which are necessary for the human body to maintain health. Corn oil is rich in vitamin F, vitamin A, vitamin E and lecithin. Regular consumption can reduce human body cholesterol content, enhance muscle and cardiovascular function, enhance human muscle metabolism, and improve resistance to infectious diseases. Therefore, people call it healthy nutritional oil. Corn oil has become an important source of edible oil in developed countries, and corn oil in the United States accounts for 8% of the edible oil. The oil content of ordinary corn is 4 to 5. Studies have found that as the oil content increases, the protein content of the kernels also increases accordingly. Therefore, high-oil corn also improves the protein quality.

④High-lysine corn: Also known as high-quality protein corn, that is, the lysine content in corn kernels is above 0.4, and the lysine content in ordinary corn is generally around 0.2. Lysine is an essential amino acid type for the human body and other animals. The lack of these amino acids in food or feed will cause serious consequences due to nutritional deficiencies. The nutritional value of high-lysine corn is very high, equivalent to skim milk. When used as feed for raising pigs, the daily weight gain of pigs is 50-110 higher than that of ordinary corn. Feeding chickens also has a similar effect. With the emergence of high-yield and high-quality protein corn varieties, the development prospects of high-lysine corn are extremely broad.

⑤Popping corn: The aforementioned type of popping corn. Its outstanding feature is that the content of horny endosperm is high, and the water in the starch grains explodes when exposed to high temperatures. It is generally popular as a flavor food in large and medium-sized cities.