As the economy continues to improve, people's focus on food is becoming more and more nutritious and healthy, so plant and animal proteins that benefit human health stand out from the crowd. Due to the unsustainable nature of animal agriculture, animal protein production has yet to keep up with the growing demand for protein. The consumption of plant proteins relieves the pressure on the supply of livestock products and is also environmentally and socially sustainable. This paper summarizes the main applications of plant proteins and their processing techniques. It discusses the problems in developing plant protein products to promote the further development of plant protein applications. Proteins are multifunctional components in food, and in addition to their nutritional value, their physicochemical and functional properties during processing play an important role in determining the final quality of food. The structural diversity and amphiphilicity of proteins allow them to interact with other components of food (carbohydrates, fats, water, vitamins, minerals, and other proteins) through a series of interactions and chemical bonds. Among plant proteins, soy protein is the most widely used. In addition, other high-quality proteins such as wheat protein, pea protein, and peanut protein are also emerging.
(1) Soy protein
Soybeans are native to China and have become the most crucial legume crop since they have been widely planted worldwide. Soybean is rich in protein (about 35% ~ 40%) and contains fat, calcium, phosphorus, iron, vitamins, and other essential nutrients. According to the protein content, soy protein can be divided into soy protein powder, soy protein concentrate, and soy protein isolate. Regarding protein digestibility, soy protein is comparable to milk, meat, and eggs. In addition, soy protein also contains the decomposition of carcinogenic substances that promote intestinal peristalsis of oligosaccharides, which can play a role in improving resistance and preventing constipation.
(2) Wheat protein
Wheat is China's third largest staple food; its annual output can reach 13 million t. Its dry matter, crude protein, crude fat, crude fiber, crude ash, calcium, and total phosphorus content of 88%, 13.4%, 1.7%, 1.9%, 1.9%, 1.17% and 0.41%. Wheat protein, also known as gluten, is a natural protein separated from wheat flour; according to its solubility characteristics, it can be divided into clear protein, globulin, alcohol-soluble protein, and gluten.
(3) Pea protein
Peas are also one of the essential edible legumes, and their global annual production is about 13.5 million tons. Peas are rich in carbohydrates, proteins, vitamins, minerals, etc. The content of protein is about 20% to 30%, and the proportion of amino acids is balanced, does not contain allergenic substances, and has the effect of lowering blood pressure and blood lipids. Pea protein can be divided into clear protein, globulin, alcohol-soluble protein, and gluten. According to its solubility characteristics, it is mainly composed of salt-soluble globulin and water-soluble clear protein. Among them, the content of globulin is about 70%~80%. Pea protein has strong gel-forming ability, surface hydrophobicity, foaming and dispersing ability, and good emulsification stability. Part of the pea protein in the taste can not only replace the fat intake, adding a silky feeling but can also improve chewiness-rich taste.
The digestibility of plant proteins is also generally lower than that of animal proteins. Some animal proteins, such as whey proteins, are rapidly digested after supplementation, and their amino acids appear in the bloodstream quickly, providing nutrients to the body faster and stimulating muscle metabolism and synthesis. Vegetable proteins have a lower digestibility due to the presence of antinutrient factors. Antinutritional factors are food components or compounds in the food matrix that interfere with the absorption of certain nutrients, such as phytates, tannins, trypsin inhibitors, lectins, etc. They may also lead to increased urea production and reduced stimulation of muscle protein synthesis when ingested.
There are several ways to improve the nutritional quality of plant proteins. Blending different sources of plant proteins can improve the structure of essential amino acids. To ensure amino acid balance, legume proteins can be combined with grain proteins rich in sulfur-containing amino acids, a combination that balances the amino acid profile of plant proteins and improves their quality. In addition, the concentration of antinutritional factors in plant proteins can be reduced through food processing techniques such as soaking, steaming, autoclaving, sprouting, microwaving, irradiation, spraying and freeze-drying, fermentation, and extrusion, which can improve the digestibility of plant proteins and reduce the risk of consumption.
