1. 1 evaluation of nutritional index of peanut protein
Peanut kernel contains 24% ~ 36% protein, which is second only to soybean and higher than sesame and rape compared with several important oil crops. Peanut protein contains about 10% albumin, and the remaining 90% is alkaline protein. It consists of peanut globulin and arachidonic acid, of which about 63% is globulin and 33% is arachidonic acid. It is a highly nutritious plant protein resource, with a biological titer (BV) of 58 and a protein titer (PER) of 1: 7.
1.2 nutritional components of peanut protein
The nutritional value of peanut protein is similar to that of animal protein, and the content of protein is higher than that of crucian carp, lean meat and eggs, without cholesterol.
Amino acid composition of 1.3 peanut protein
Peanut protein contains a lot of essential amino acids, the content of aspartic acid is higher than that of rice, flour and corn, and the effective utilization rate is as high as 98.4%, but the content of methionine and tryptophan is less.
2 Functional characteristics of peanut protein
Peanut protein can be dissolved in dilute alkali solution or 10% NaCl or KCL solution. As a plant protein resource, it is widely used in food industry. Besides being used as a food additive, it is more important to make use of its functional characteristics. The functional characteristics of plant protein refer to some physical and chemical properties that can affect the quality of food. It mainly includes water absorption, wettability, expansibility, adhesion, dispersibility, solubility, viscosity, gelation, emulsification, foaming and so on. These functional characteristics are not only related to the inherent properties of protein, such as amino acid composition, molecular size, structural morphology, etc., but also related to other food components that interact with protein, such as water, ions, fat, and the environment such as temperature, pH value, ionization intensity, etc. At the isoelectric point of pH=4.5, its solubility, foamability and water holding capacity are the lowest. When the temperature reaches 55℃, the solubility begins to decrease, but with the increase of temperature, the foaming property increases and the water holding capacity decreases. When the concentration of protein is about 3%, its foaming performance is the best.
3 Extraction of Peanut Protein Powder
At present, there are many methods to extract peanut protein, such as pressing, leaching, acid precipitation, alkali dissolution and acid precipitation, aqueous solution, membrane separation technology and so on.
3. 1 pressing method
The pressing methods are divided into cold pressing and hot pressing. According to the product requirements, 50% ~ 60% of oil can be removed by cold pressing with hydraulic press, and its soluble protein content is high (PDI retention rate is above 98%), while 80% ~ 90% of oil can be removed by hot pressing with screw oil press, but the protein denaturation rate is high. Because the water solubility of denatured protein becomes lower, some amino acids combine with sugar, which reduces the content of amino acids, and because of the decomposition and change of amino acids, the nutritional value of peanut protein is greatly reduced, so it is often used as feed.
3.2 Leaching method
Leaching method can be divided into direct leaching method and preloading leaching method. If the low-temperature leaching and desolventizing processes are adopted, the protein denaturation in the produced peanut cake is small, and the water-soluble protein content of the obtained peanut powder is high.
3.3 Acid precipitation method
Acid precipitation is often used to prepare concentrated protein. It uses dilute acid solution with pH close to the isoelectric point of protein to remove a small amount of soluble components such as water-soluble sugar and ash, while starch and cellulose are concentrated with concentrated protein.
3.4 Alkali dissolution and acid precipitation method
Alkali dissolution and acid precipitation are used to prepare isolated protein. Not only water-soluble sugar, but also starch, cellulose and other components are removed, and the obtained product has high protein content.
3.5 water method
Extraction of peanut oil and peanut protein by aqueous solution method is a new technology developed in 1980s. Oil, protein and carbohydrate are separated by aqueous solution. Compared with the traditional process, it has incomparable advantages: ① it does not need flammable and explosive solvents, which improves production safety and reduces air pollution; ② Protein powder, oil and other products can be produced at the same time, which shortens the production process. The oil yield is generally 92% ~ 94%, and the protein recovery rate can reach over 70%. ③ The peanut oil produced has high purity, low phospholipid content, light color and low acid value and peroxide value.
3.6 Membrane separation technology
Membrane separation technology is often combined with the process of preparing isolated protein by aqueous solution method or alkali dissolution and acid precipitation method. The protein slurry is treated by ultrafiltration membrane, and the treated liquid is dried as a by-product; Because the filtrate contains few solids, it can be returned to the leaching process to reduce the amount of wastewater.
4 Application of peanut protein in food
Because peanut protein has high nutritional value, contains a lot of amino acids that can be easily absorbed and utilized by human body, and has attractive fragrance, peanut protein powder can be widely used as the main component and auxiliary material of food.
4. 1 peanut protein bread and biscuits
Adding 5% peanut protein powder rich in amino acids to bread raw materials and 10% peanut protein powder to biscuits can produce bread and biscuits with good taste, good flavor and rich nutrition.
4.2 Peanut protein beverage
The liquid beverage made of peanut protein as the main raw material is a health beverage because it contains no cholesterol, is rich in protein, essential amino acids, vitamins and unsaturated fatty acids, and is more easily absorbed by human body.
4.3 Peanut protein dipping meat manufacturing
Take 400 grams of defatted peanut protein, add 2 liters of water, decompose it in an autoclave for 4 hours, then filter, dilute the filtrate, introduce sulfur dioxide to make the pH value of the filtrate reach 4.8, and decolorize and bleach. Under these conditions, polymer protein also precipitated. After filtration, the filtrate was placed in a vacuum evaporation kettle, concentrated, sprayed and dried at 65438 00℃ to form powdered meat peptone.
5 development prospects
Peanut is one of the six major oil crops in China. In China, peanuts are not only eaten directly, but also used to extract oil. Every year, about 65.438+0.25 billion Jin of peanut cake can be obtained after peanut oil is pressed, and if it contains 50% protein, it will be 625 million Jin, 78g per person per day, which can supply 654.38+0.4 billion people in the country for 6 days. Therefore, the development and utilization of peanut protein resources is of great significance to meet people's material living standards, promote social and political stability and national economic development, and has broad development prospects.