Whey protein is a kind of protein obtained from whey through special concentration, refining and extraction process. Whey protein compared to other proteins, not only has a high biological price, high protein efficacy ratio and high utilization rate, but also has emulsification, water retention, gel and other excellent processing characteristics, with the continuous progress of the dairy production industry technology and in-depth research on the composition of the whey protein and its function, whey protein has gradually become an important raw material and additive ingredients for functional, nutritional health food and food for special medical purposes. The application of whey protein in aerospace food

The application of whey protein in aerospace food can significantly improve the protein digestion and absorption rate of aerospace food, replenish calcium, prevent muscle atrophy, enhance antioxidant effect, and improve immunity, so as to satisfy the needs of aerospace food in terms of nutrition and absorption characteristics.

Classification of whey protein and its products

Whey is a product of casein in cow’s milk that is discharged after coagulation by acid or rennet. According to the different cheese processing techniques, whey protein can be divided into sour whey and sweet whey; according to the degree of tolerance to temperature, whey protein is divided into heat-stable whey protein and heat-unstable whey protein.

At present, whey protein products mainly include whey protein concentrate (WPC), whey protein isolate (WPI) and hydrolyzed whey protein.

According to the different protein content, whey protein concentrate is divided into WPC-34, WPC-50, WPC-75 and WPC-80. WPI is a high-purity whey protein with protein content greater than 90%. Hydrolyzed whey protein has many physiological functions due to the presence of various bioactive peptides.

Nutrition of Whey Protein

1. Whey protein composition and function
Whey protein contains all 20 amino acids that make up proteins, as well as a variety of proteins and peptides with unique biological activities; at the same time, whey protein is low in sodium and cholesterol and high in minerals, especially calcium, making it one of the most nutritionally complete natural protein supplements available.

In addition to the compositional advantages, some of the protein fragments and peptides produced by whey protein after digestion and absorption are also biologically active and functional, which makes the application research of whey protein has a broader space.

2.Amino acid composition and function of whey protein
Whey protein contains 8 essential amino acids required by the human body, and the amino acid composition pattern is very similar to that of the human body, which is easier to be digested and absorbed, and the bioavailability is very high.

The amino acid composition of whey protein has the following characteristics.
① leucine, isoleucine, valine and other branched-chain amino acids in abundance, they are not only one of the precursors for the synthesis of glutamate, but also as an energy source to provide energy.

② Rich in sulfur-containing amino acids such as cysteine and methionine, which can well maintain the level of glutathione (GSH) in the body and play an antioxidant role.

③ It is an excellent source of threonine, which can promote the synthesis of intestinal mucin and play a protective role for intestinal cells and intestinal barrier.

④ Containing a large amount of lysine and arginine, it can stimulate the secretion and release of metabolic hormones or muscle growth factors to promote muscle growth and maintain muscle health.

2.1 Threonine and intestinal health
Threonine accounts for more than 30% of the amino acid composition of human intestinal mucin, and has an important role in human intestinal health.

More than 60% of dietary threonine can be absorbed by human intestines to synthesize intestinal mucins, thus protecting intestinal cells and enhancing the coherence of intestinal barriers; the lack of threonine affects the synthesis of intestinal mucins and reduces the barrier function of the intestines.

2.2 Sulfur-containing amino acids, branched-chain amino acids and the body’s antioxidant system
Whey protein is a good food source of sulfur-containing amino acids (cysteine, methionine). First of all, sulfur-containing amino acids are important precursors for the synthesis of GSH and taurine.

GSH plays a key role in the body’s free radical scavenging and immune response, and is an important part of the body’s antioxidant system; GSH and taurine, as important antioxidant substances, have antioxidant effects such as inhibiting lipid peroxidation.

Secondly, cysteine is an effective supplement of GSH in the organism, and whey protein hydrolysis products can substantially increase the level of GSH in prostate epithelial cells, and through the antioxidant and anti-inflammatory activities of GSH, avoid or reduce the occurrence of diseases closely related to the oxidative state of the organism.

2.3 Branched-chain amino acids (leucine) and muscle tissue health
Whey protein is also a good food source of branched-chain amino acids (leucine, isoleucine, valine). Branched-chain amino acids are one of the precursors for the synthesis of glutamate, which is essential for the synthesis of GSH.

Branched-chain amino acids, especially leucine, make up about 26% of the total whey protein. Leucine is both an important raw material for skeletal muscle protein synthesis and a stimulus that regulates the anabolic pathway of skeletal muscle protein.

At the same time, leucine and its oxidized metabolites can inhibit the activity of protein hydrolases and reduce the rate of myosin breakdown. Supplementation with whey protein resulted in a significant reduction in the probability of skeletal muscle reduction.

Exploration of the application of whey protein in aerospace foods

1. Characteristics of aerospace food
Aerospace food is a kind of food developed for the special environment of spaceflight. First of all, it should strictly meet the requirements of safety and edibility. In the space environment, the astronauts and all the objects in the cabin are in the state of low pressure and weightlessness, the movable space is narrow, and most of the food on the land has lost its significance.

Therefore, spaceflight food should be able to pass the strict flight simulation test, not only to ensure the safety of astronauts’ consumption, but also to overcome the influence of vibration, radiation, low air pressure and other undesirable environmental factors, and have the characteristics of small volume, light weight, easy to carry and simple consumption method, so as to fully guarantee the carrying out of spaceflight tasks; secondly, spaceflight food should have good nutritional protection. Spaceflight environment will cause many irreversible damages to human body, and from the perspective of nutrition, spaceflight food should have higher nutritional value.

2. Effects of aerospace environment on human body
2.1 Bone loss and osteoporosis.
Bone loss is one of the symptoms that astronauts are very prone to in space and after return, and astronauts are earlier or more prone to osteoporosis. Therefore, dietary supplementation with sufficient high-quality calcium and vitamin D is particularly important for astronauts’ bone health.

2.2 Muscle atrophy.
Spaceflight environment will lead to changes in the structure and function of human skeletal muscle, such as reduced muscle quality, easy to fatigue, and reduced voluntary movement ability, etc. Therefore, timely supplementation of high quality protein and vitamin D for astronauts is very important. Therefore, timely supplementation of astronauts with high-quality protein is important for the prevention and treatment of muscle wasting in astronauts.

2.3 Weight loss.
Weight loss is mainly due to insufficient energy intake of astronauts, at the same time, insufficient energy intake is not conducive to the adaptation process after astronauts return to the ground, and even cause permanent damage to the organism.

④ Spaceflight metabolic disease.
The spaceflight environment affects the metabolism of energy, protein, lipid, sugar and vitamins, leading to cardiovascular dysfunction, water and electrolyte balance disorders, a decrease in the number of red blood cells and iron deficiency anemia.

⑤ Dysbiosis of intestinal flora and microecological disorders.
Under the space environment, the intestinal flora of astronauts changes, the number of their own beneficial bacteria decreases, harmful bacteria proliferate greatly, and the gastrointestinal function changes accordingly.

Extremely harsh environments such as spaceflight weightlessness, high vacuum, large temperature fluctuations and high-energy radiation will have different degrees of influence on astronauts’ immune function and the regulation of the nervous system, and may even cause permanent injuries that are difficult to recover from.

3. Types of spaceflight food
According to the different processing and storage methods, space food can be divided into: rehydrated food, fresh food, canned food, bite-sized food and functional food.

Rehydrated food can be rehydrated quickly, with less loss of nutrients, and the weight can be preserved easily. However, the operation of rehydration is complicated, the food residue is large, and the taste and flavor are not good after rehydration;

Fresh food has normal water content, which can provide the vitamins and water needed by the human body at the right time and allow astronauts to better adapt to the space environment, and has a good taste. However, fresh food usually weighs a lot and is not easy to store;

Canned food is resistant to storage and easy to carry, but the viscosity of the product is large and the sugar and salt content is high;
Bite-sized food is square pressed food with the volume of only one bite size, with a clear calorie of a single portion, and is more commonly found in bread and cookies, etc. It is simple to consume, small in size and light in weight, space-saving, and easy to carry, but it has a low water content and a less-than-ideal flavor.

Functional food is a product developed for the special spaceflight environment. By adding health care functional factors, it improves the immunity of astronauts and reduces and prevents foreseeable and unpredictable injuries and diseases caused by radiation, weightlessness and other special environments.

4.The significance of whey protein applied to spaceflight foods
Steamed bread is one of the most important traditional staple food of Chinese people, its texture is fluffy, easy to digest and absorb, widely accepted by the public.

But the traditional staple food steamed bread is mainly processed by wheat flour, the composition is relatively single, in order to improve the astronauts’ adaptability to the spaceflight environment, reduce the negative impact of the spaceflight environment on the human body, and to ensure the nutritional health of the astronauts, can be added to the steamed bread with a certain amount of whey protein powder, supplemented with a certain proportion of cheese and buckwheat flour, to make a fermented flavor and should not be off the dregs of the “one mouthful of food”! “Nutritional fortification of steamed bread products, not only can provide a wealth of easily absorbed protein, high-quality calcium, the appropriate ratio of calcium and phosphorus and vitamin D, but also through a specific base powder, significantly improve the product’s protein digestibility, enhance the effect of antioxidants and lowering the effect of glucose to meet the aerospace food for the nutritional and absorption characteristics of the needs of the demand.

It can also meet the needs of spaceflight food for strengthening the flavor of staple food, safe and convenient consumption through the application of mixed fermentation agent, the excavation of anti-melting characteristics of cheese and the improvement of anti-aging performance of steamed bread, which can provide more delicious and nutritious staple food products for astronauts.

4.1 Whey Protein Supplements High Quality Milk Calcium
Every 100g of whey protein can provide 500-800mg of calcium. Calcium is essential for bone health, nerve conduction, muscle contraction and other physiological functions in the human body. Milk-derived calcium is the best known bioavailable calcium, and the high quality, easy-to-absorb, and cost-effective calcium in whey protein makes it an excellent choice for aerospace food calcium source supplements. The addition of whey protein can effectively prevent and accelerate the recovery of osteoporosis caused by weightlessness and bone loss in astronauts.

4.2 Whey protein promotes muscle synthesis
The protein content of whey protein isolate (WPI) is greater than 90%, with a more complete protein structure, fast digestion and absorption, and high utilization rate; WPI contains a high concentration of essential amino acids (45% ~ 55%), especially leucine, which is a key regulator in the transcription initiation pathway of muscle protein synthesis, with a rich content of 14%. Human and animal experiments have confirmed that supplementation of WPI is able to improve the body’s Human and animal tests have confirmed that WPI supplementation can improve body composition, increase muscle weight and promote muscle synthesis, thus effectively preventing muscle atrophy.

WPI contains about 4 times more cystine than other protein products such as casein and soy protein. With sufficient cystine or cysteine in the blood, the production of urinary nitrogen decreases when the liver breaks it down into sulfate and proton, and the nitrogen processing mechanism of the whole body shifts to favor the maintenance of the amino acid pool of the muscles to promote muscle synthesis.

4.3 Antioxidant effects of whey protein
Whey isolate protein is rich in cysteine (Cys), which is the precursor substance of glutathione (GSH), a common antioxidant in the human body, and the rate-limiting amino acid for glutathione synthesis. The antioxidant effect of whey isolate protein is mainly realized by regulating the conversion between cysteine and glutathione within the cell, and the antioxidant effect of the glutathione molecule is realized through its sulfhydryl group (-SH).

Reduced sulfur groups can combine with free radicals in the body and convert them into easily metabolized acids, thus accelerating the removal of free radicals in the body; they can also protect the activity of enzymes containing sulfur groups in the cells and prevent enzyme denaturation due to sulfur oxidation; reduced sulfur groups are also involved in many important redox reactions in the body.

4.4 Whey protein improves the body’s immunity
Whey protein contains a variety of active substances, such as lactoferrin, lactoperoxidase, immunoglobulin, etc. have antibacterial, antiviral and immunomodulatory effects; in addition, there are some proteins in the chemical modification or enzyme digestion, but also play an antiviral role. Whey proteins and their enzymatic products have a regulatory effect on the function of various immune cells.

Glutamine (Gln) is an important substrate for lymphocytes and macrophages in the process of immune response, whey protein contains a large amount of glutamine precursor substances such as glutamic acid, supplementation of whey protein can not only provide energy for the muscle, but also provide raw materials for the synthesis of glutamine to maintain the level of glutamine and protect immune cells.

Lactoferrin has an obvious inhibitory effect on gram-negative and positive bacteria that need iron, and has an obvious regulatory and stimulating effect on bone marrow cell production, complement system, inflammatory response, lysozyme regeneration, enhancement of immunity and improvement of the body’s ability to fight diseases. Lactoperoxidase system (LPS), which is composed of lactoperoxidase and thiocyanate (SCN-), has obvious bactericidal effect and can significantly improve the immunity of the body.

Outlook

Whey protein (WP) is a complex of soluble protein components extracted from cow’s milk, which not only has an amino acid composition similar to that required by the human body and a high digestibility and absorption rate, but also contains a large number of biologically active substances.

Whey protein is one of the most effective nutritional supplements available for spaceflight food, as it improves body components, promotes rapid muscle recovery, strengthens body immunity, reduces and prevents foreseeable and unpredictable injuries and diseases caused by radiation and weightlessness to astronauts, and improves astronauts’ health.

In particular, whey protein isolate (WPI), which has a high quality protein concentration of ≥ 90%, is also very popular in sports nutrition, health food and food for special medical purposes, and has become a universal nutritional and health care ingredient.

Meanwhile, whey proteins possess a variety of excellent processing properties such as gel-forming, heat stability, solubility, water holding – water absorption, adhesion, elasticity, whipping and foaming, and emulsification stability, which are the basis and conditions for the addition of whey proteins to many food products.

Combining whey protein powder with other nutrients to make staple buns is not only beneficial to the nutritional health of astronauts, but also an important direction for whey protein application.