Corn starch is one of the main sources of human starch, and it is also the main raw material of industrial starch and deep processing industry using starch as raw material.
95% of the starch in the US starch processing industry is corn starch, and the main raw material for the production of starch in China is corn.
Generally speaking, corn starch is a mixture of amylose and amylopectin. High amylose corn starch means that the amylose content in corn starch is as high as 55% -85%, while the amylose content in ordinary corn kernels is only 22 % To 27%.
Amylose is a polymer connected by glucose through α-1,4 bonds, with a polymerization degree of 100 to 6000 glucose units and a chain structure. Its aqueous suspension does not generate dextrin when heated, but dissolves with colloids to form an unstable solution with lower viscosity. After standing at 50 ° C to 60 ° C for a long time, crystalline precipitates will be formed, and the reaction is reversible Yes, the reaction is blue with iodine.
1. Application of amylose in biodegradable plastics
Amylose has similar fiber properties and has unique application value compared to ordinary starch. In particular, the amylose function after physical and chemical modification is further strengthened, which provides new raw materials for the application of starch in industrial production.
Films made from amylose have good transparency, flexibility, tensile strength and water insolubility, and are non-toxic and pollution-free. They are widely used in sealing materials, packaging materials and water and pressure resistant materials.
The German BATTELLE Institute has successfully improved the green pea variety and developed a starch with a high linear content, which can be directly formed by ordinary methods. The obtained film is transparent and soft, has similar properties to PVC, and can be completely degraded in water or wet soil. . The United States has applied for a patent for the production of amylose film, which can package both powdered products and frozen foods.
Due to its higher shear resistance and strength, as well as good water resistance, it is also used in the wrinkling and adhesive industries. Amylose can be used in the manufacture of a variety of films and various strips. Films made from amylose have outstanding transparency, elasticity, tensile strength and water resistance.
At present, the world is calling for the treatment of white pollution, that is, plastic pollution in agricultural mulching film and domestic waste has become a major nuisance in the world, especially in China; and photolytic films made from amylose have become The latest scientific and technological achievements in the plastics industry are also the most attractive aspects of high amylose corn. The use of high amylose instead of polystyrene to produce photodegradable plastics. This plastic may be used in the packaging industry and agricultural film processing industry. It is an effective way to solve the increasingly serious white pollution. Its use will bring once Major revolution. The United States has selected high amylose corn to supply raw materials for the production of photolytic plastic films in the United States and Western Europe.
It was reported that 4 kinds of dry corn starch with different linear chains were blended with PLA at 185 ° C. The tensile strength and elongation at break of the blend decreased with increasing starch content, but blended at the same ratio as PLA At the time, the blends of the four starches did not differ significantly. The speed and extent of PLA water absorption in starch increased with increasing starch content. Blends of high amylose content have lower water absorption than blends of ordinary and waxy corn starch.
POM et al. Prepared a blend of PLLA corn starch and PLLA / high amylose corn starch (≤40%). The study found that the tensile strength and elongation of the blend decreased with increasing starch content. At the same starch content, the tensile strength of the blend containing high amylose is greater than that of natural corn starch.
In order to further improve the processing properties of amylose, Qiu Liping et al. Studied the structure and gelatinization properties of high amylose cross-linked modified starch. Studies have shown that the higher the amylose content, the easier the intermolecular binding, the more prone to settling, and the more difficult the gelatinization; however, its strong shearing force and good film-forming properties. After the starch is denatured, its properties will also change. The molecular weight of the cross-linked modified starch formed by high amylose cross-linking is larger than that of high amylose, the shear force is strong, it is more prone to set, difficult to swell, and difficult to gelatinize, but the film forming performance is good; Moreover, the cross-linking effect of 70% high amylose is better than 50% high amylose; the starch with higher amylose content is more difficult to dissolve in water. Due to the above characteristics of amylose, industrially, high amylose cross-linked starch has broad application prospects for further improving the water resistance of degraded materials.
2. Limitations of research and application of high amylose corn
The synthesis of amylose is affected by complex genetic and environmental interactions. Increasing the amylose content may reduce yield and other agronomic traits. The main problems encountered in high amylose corn breeding are:
① The total starch content is reduced; ② The moisture content is increased; ③ The yield is decreased.
At present, the yield of high amylose corn hybrids is only 65% to 75% of ordinary corn. Although the gene can significantly increase the amylose content, it can also cause the poor performance of other agronomic traits. In 2001, Teng Wentao et al. Found that during the process of inbred lines transgenic into high amylose corn with ae gene, the gloss and fullness of the grains changed. Decrease in kernel fullness will inevitably lead to a decrease in the quality of thousand kernels, which may be the main reason for the decline in yield. It is precisely because there are some agronomic traits and processing defects linked to genes. Although the United States has studied high amylose corn for 40 years, currently only the Castum Farm Seed Company produces this corn, only Two large corn wet mills produce corn amylose. Therefore, when breeding high amylose corn, we must not only ensure the efficient expression of ae gene, but also pay attention to the selection of thousand kernel quality.
3. Development prospects of high amylose corn
White pollution has brought inestimable losses to the human living environment, which has caused the entire society and even all human beings to attach great importance to environmental protection. In the face of increasingly depleted petroleum resources, the trend-setting biodegradable materials are becoming a research and development hot spot as high-tech environmental protection products. To enter the market, degradable plastics must meet the following requirements:
① Practicality, with application performance similar to similar ordinary plastics;
② Degradability, after completing the use function, it can degrade faster in the natural environment, become fragments that are easily absorbed by the environment, and finally return to nature;
③ Safety, residues during and after degradation are not harmful or potentially harmful to the natural environment;
④ Economical, the price is close to or the same as that of the common ordinary plastic.
However, the price of biodegradable plastics is too high. The price of degradable plastics is more than 50% higher than that of similar current plastic products. Among them, the total degradation can be 4 to 8 times higher, which has become the biggest obstacle to its application. In order to reduce costs and ensure the degradation performance of products, starch biodegradable plastics have become a hot product that the country is paying attention to.
Starch is currently the most widely used class of fully biodegradable polysaccharide natural polymers. It has the advantages of a wide range of raw materials, low prices, and easy biodegradation, and occupies an important position in the field of biodegradable materials. The mechanical properties of various grades of starch plastics published at home and abroad can generally be compared with traditional plastics of similar applications, but their performance is often unsatisfactory. One of the main disadvantages is that starch-containing degradable plastics have poor water resistance. Poor wet strength, its mechanical properties are severely reduced in the presence of water, and water resistance is exactly the advantage of traditional plastics during use. Compared with ordinary starch, high amylose has better water resistance, shear resistance and film-forming ability, so it has great development potential in the plastic industry.
The cost of separating amylose from mixed starch is very high. If it is only imported, the price is very expensive, generally $ 2,000 / t to $ 2500 / t. Until now, China has not conducted a complete and systematic research on high amylose corn, and no hybrid has been bred. China's amylose still mainly relies on imports, and it needs to spend a lot of foreign exchange every year. This requires us to strengthen the cultivation of high amylose corn varieties and select high-quality, high-yield, multi-resistant high amylose corn varieties to be put into production. Grain crops and feed crops are gradually transitioning to cash crops and industrial raw materials.
Nicolas Bogion of the French Agricultural Industry Research and Development Center believes that the manufacture of biodegradable plastics will become an important way to produce cereals in countries around the world. With the acceleration of the global economic integration process, in order to adapt to new needs, the commercial production and utilization of high amylose corn will have important significance for improving the rural industrial structure and the sustainable development of the national economy.
The product has passed ISO14855 compost testing and obtained CNAL international agency certification; FDA certification; SGS certification, BRC certification, ISO9001 international quality management system certification; ISO14001 international environmental management system certification; QS food quality and safety certification.
Corn starch-based biodegradable heterosexual tableware and fully degradable packaging bags are pollution-free green products for human survival and environmental protection. They are advocated internationally and strongly supported by domestic policies.
Disposable degradable tableware, disposable degradation bag advantages:
No harm to human body Because it is refined from corn starch and other environmentally friendly materials, it does not contain harmful substances in the human body, so it can be used safely for a long time.
Zero pollution The product is buried in the soil and can be degraded to form carbon dioxide and water after 180 days at a suitable temperature without causing pollution to soil and air.
Saving resources Corn starch is a renewable resource, inexhaustible and inexhaustible, while paper tableware and plastic tableware require a large amount of wood and petrochemical products. Using corn starch as raw material can save a lot of oil and forest resources.
High quality The product has good tightness, water resistance, oil resistance, and impermeability. At the same time, it has good high temperature and low temperature resistance. It is suitable for refrigerator freezing, refrigerating, fresh food, microwave heating, etc.
Since disposable tableware was first used in China in 1984, foamed plastic tableware made of polystyrene (eps) as the main raw material has quickly spread to every corner of our country, entering people's daily life and forming a huge consumer market. According to statistics, China currently consumes about 10 billion fast food utensils each year, most of which are disposable foam plastic tableware, and the annual growth rate is 25%.
Because polystyrene is non-degradable and difficult to recycle, it brings great inconvenience to the processing. Currently in the streets, tourist attractions, railways, rivers and lakes of cities in China. This kind of discarded disposable tableware can be seen everywhere, it can be described as shocking, causing serious pollution to the environment. This "white pollution" not only increases the labor intensity of sanitation workers and brings visual pollution to people, but also increasingly pollutes the land resources and water resources on which we depend, and also brings a lot of people Inconvenience and harm.
It is gratifying that China has done a lot of work in this area and achieved great results. With the scientific guidance and strong support of the government, various environmental tableware came into being. To good social effects.