Agriculture is the foundation of the national economy. Food is the foundation of the foundation. It is a necessary condition for human survival, reproduction, and development. It is also the foundation of the food industry and the source of basic raw materials for all food industries. Rice (Oryza sativa) is one of the important food types for humans, especially in Asia. Statistics from the International Rice Research Institute in 2007 showed that in recent years, the total annual output of rice in the world was about 533 million tons, and China’s total rice output reached 186.5 million tons, accounting for 35%, ranking first in the world. Rice production and consumption are concentrated in Asia, especially China, Indonesia, Bangladesh, Vietnam, and Thailand. As the country with the largest rice producer in the world, China has been developing vigorously as its rice planting industry, while deep processing and comprehensive utilization of rice have provided new growth points for my country’s agricultural economy.
When rice is processed, only starch is often used. By-products such as broken rice, rice germ, rice bran, rice husk, and other processing by-products contain a large amount of high-quality rice protein, which has not been effectively developed and utilized, resulting in a great waste of protein resources. The quality of rice protein is better than wheat protein and zein, and the allergy is low. At the same time, the amino acid composition pattern of rice protein is better than casein and soy protein isolate, which can meet the amino acid requirements of children aged 2 to 5 years, which makes it very suitable for development. Baby food. In addition, rice protein can be processed into soy sauce, high-protein powder, protein beverage, peptone, and protein foaming powder, etc. If it is degraded into short peptides or amino acids, it can be made into an amino acid nutrient solution with high nutritional value for health care. Beverages, condiments, food additives, etc. For a long time, the deep processing of rice production and rice processing products and by-products has been highly concerned by food scientists. The research on the development and utilization of rice protein is based on the research and comprehensive utilization of enriching rice processing products and rationally using rice processing by-products. Therefore, the extraction and rational use of protein in rice have important social and economic significance.
Four kinds of proteins are prepared from rice by Osborne fractionation. The main components are gluten and gliadin, which are storage proteins, and albumin and globulin, which are low in content, are physiologically active components. Among them, albumin, which accounts for 2% to 5% of the total, is soluble in water, dilute acid and dilute alkali solutions, and is spread throughout the organism; In neutral dilute salt solution, it is commonly found in organisms; gluten, which accounts for more than 80% of the total, is easily soluble in dilute alkali, dilute acid, and insoluble in water, alcohol and neutral salt solutions; it accounts for 1% of the total ~5% of gliadin, it is soluble in 70%~80% of ethanol, insoluble in water, and mostly exists in plant seeds.
Rice protein mainly exists in the form of two protein bodies (PB), namely PB-I and PB-II. Electron microscope observations showed that the PB-I protein body has a lamellar structure, and the diameter of dense particles is 0.5-2μm. Gliadin is present in PB-I; while PB-II has an ellipsoidal shape with no stratification and uniform texture. The diameter is about 4μm, the peripheral membrane is not obvious, and gluten and globulin are present in PB-II. Two kinds of protein bodies often coexist.
The solubility of rice protein is not very good, mainly because rice protein contains more than 80% alkali-soluble gluten. This gluten is formed by many macromolecular fragments through disulfide bonds, cross-linked and agglomerated with each other, while albumin which is soluble in water It only accounts for 2% to 5% of rice protein. In the study of the effect of pH on the solubility of rice protein, it was found that the solubility of gluten in rice protein increased slowly when the pH value was 4 to 7, and the protein solubility increased rapidly when the pH value was close to 9. At the same time, the modification will also have a certain impact on the solubility of rice protein. Studies have shown that the degree of deamidation is between 19.6% and 64.5%. As the degree of deamidation increases, the solubility of rice protein increases, and the maximum solubility can reach 96.6%. Through the comparative analysis of various proteases, it is known that the hydrolysis effect of alkaline protease is better than other proteases, but the orthogonal test results show that even under optimized conditions, the solubility of rice protein hydrolyzed by a single alkaline enzyme reaches 43.12%. . If first hydrolyzed with alkaline protease and then hydrolyzed with complex protease, the protein solubility is as high as 71.46%, while the combined application effect of alkaline protease and other enzymes is slightly worse; if the complex protease is used first and then the alkaline enzyme is used, the protein solubility is only 54.73%. Therefore, different enzymes have different hydrolysis characteristics for rice protein molecules.
Emulsification includes two aspects: emulsification activity and emulsification stability. Emulsification is one of the important functions of the protein. Studies have shown that measures to increase the solubility of rice protein are beneficial to improve the emulsifying properties of rice protein.
Once gluten is dissolved, its emulsifying ability is equivalent to that of soy protein. After RPI and E-RPI are treated with Na2SO3, the emulsification performance is significantly improved, indicating that the physical and chemical functions of rice protein can be improved by removing the polymerization of subunits in the rice protein molecule.
Studies have found that the use of alkaline protease Alcalase to modify rice protein isolate can significantly improve its foaming performance. After extracting rice protein with alkaline enzyme, when the pH is neutral, with the increase of protein concentration, the foaming property increases, and the foaming stability decreases; when the pH value is 6.8, that is, when the rice protein solution is close to neutral, Rice protein has better foaming and foam stability, and the rice protein extracted by alkaline protease has better foam stability than the rice protein extracted by papain; while the rice protein extracted by the two enzymes has better foam stability under different pH conditions. There is little difference in bubble properties. With the increase of the concentration, the foaming property and foaming stability of the rice protein extracted by the two enzymes gradually increased. Generally speaking, rice protein extracted with papain has better foaming and foaming stability than rice protein extracted with alkaline protease.
4.Water and oil retention
Protein water holding capacity is closely related to the preservation and shape retention of food during storage. In addition, it is also related to food viscosity and oil absorption is related to the type of protein, source, processing method, temperature and oil used. The poor solubility of rice protein limits its water and oil retention. However, after deamidation modification, the water retention and oil retention of rice protein are improved. When the deamidation degree is 35.7%, the water retention is the lowest and the oil retention is the highest. When the deamidation degree is 42.4%, the water retention and oil retention are quiet.
The research on rice protein at home and abroad mainly includes food additives that improve the physical and chemical functions of food; as natural thickeners and foaming agents for washing and care products; high-protein nutritional powders for special populations; biologically active peptides that meet specific functions; and promote the body Active ingredients for health care; protein feed for livestock and poultry production; green and environmentally friendly edible film, etc.
- Food additives:
Food additives are additives that can improve the quality and color, aroma, and taste of food. Appropriate molecular size and amino acid composition will give the protein certain physical and chemical properties, such as solubility, foaming, emulsification, etc. Under the hydrophobic, flexible, and disordered structure, rice protein is easier to dissolve in water and concentrate at the gas-liquid interface, showing foaming and emulsifying properties.
- Protein supplements
Due to its low allergenicity and high nutrition, rice protein has become the first choice plant protein to supplement nutrition for special populations. Rice protein formula rice flour can be used for sensitive diarrhea in infants and young children; gluten-free rice protein is more suitable for people with wheat intolerance, allergies or celiac disease; rice protein concentrate can reduce normal protein intake or the digestive function When damaged, it can better supplement the body’s ability and maintain nitrogen balance; and can assist in the treatment of digestive ulcers, trauma, etc.
- Functional peptide development
Modern studies have shown that amino acid residues in small peptides are easier to digest and absorb by the human body than free amino acids. The presence of amino acids in the form of small peptides can not only avoid transport competition but also reduce the toxic and side effects of high concentrations of amino acids. The peptide transport system has low energy consumption and is not easy to saturate, making the research on hydrolyzed protein products to obtain active peptides welcomed by people.
- Protein feed
Rice protein powder, a by-product of rice starch sugar production, is an excellent feed material with high protein content, fast energy conversion, high digestibility, good palatability, good disease resistance, low antigenicity, and balanced amino acid. Adding rice gluten concentrates to aquafeeds can not only improve the digestibility of fish but also control their excretion, so as to keep the water clarified and control water pollution. Rice proteolysis can produce flavor peptides that replace sodium glutamate (MSG), which can effectively mask the bitter taste, enhance the viscosity of feed and improve the palatability of feed, and can chelate trace elements and minerals, which can improve animal feed intake. At the same time, it is safe and harmless.