As the world's population continues to grow, per capita protein demand and global protein consumption are increasing year by year, due to the shortage of traditional protein, the search for sustainable, environmentally friendly and high-quality protein is the focus of the global scramble to overcome. Yeast protein is regarded as a new protein star because of its comprehensive nutrition, efficient production and environmental friendliness. In November 2023, yeast protein was approved as a new food ingredient in China (Announcement No. 10 of 2023). Based on the review article "Yeast Protein: A New Sustainable Alternative Protein for Food Applications" in Trends in Food Science Technology, the composition of yeast protein and its separation and extraction methods, its functional properties and applications in the food field, and the application prospects of environment-friendly proteins are shared as follows.
Yeast protein is characterized by high quality and safe microbial proteins.
1. Complete protein rich in a variety of micronutrients
Yeast is the highest-protein microorganism in the world with the highest annual yield. In yeast cells, the protein content accounts for 40%-60% of the dry weight. By removing non-protein parts such as the cell wall of yeast cells, high-purity yeast protein can be obtained that can be used in the food industry.
Yeast protein (ANPRO) contains 18 amino acids, including 2 semi-essential amino acids and 8 essential amino acids. Lysine is the first limiting amino acid in vegetable protein (wheat grains), but is abundant in yeast proteins. In addition, glutamate, glutamine, alanine, and branched-chain amino acids (isoleucine, leucine, and valine) are also high in yeast proteins. Early studies suggested that yeast protein was slightly lower in sulfur amino acids (methionine and cysteine). However, the latest diaas protein evaluation method has studied the amino acid score and ileal digestibility of yeast protein, and the results have proved that the sulfur amino acid content of yeast protein is second only to whey protein and higher than that of other plant proteins (Table 1). In addition, yeast protein contains more than 16 biobound minerals and vitamins, including 8 B vitamins. With a complete and well-proportioned amino acid composition and abundant micronutrients, yeast protein is expected to be a new alternative protein source with better quality than plant protein.
Table 1 Amino acid scores (AAS) and digestible essential amino acid scores (DIAS) for different proteins
Note: WPC, whey protein; WPI, whey protein isolate; soy, soy protein; anpro, yeast protein; WHE, wheat protein; PEA, pea protein.
2. "Slow protein" with high digestion and absorption rate and good persistence
Digestibility is a criterion for judging the nutritional quality of protein. The data in the review article show that the in vitro digestibility of yeast protein is about 8106%, higher than sorghum protein (42%-64%) and soybean protein (75%-80%); It is also higher than some animal proteins, such as fish protein (74%-81%). It should be particularly pointed out that the research of Angel Yeast Co., Ltd. *** Research Institute [1] shows that the in vitro digestibility of yeast protein in the stomach is 121%, which is significantly lower than whey protein (339%）；But in the small intestine, the terminal digestibility is 925%, which is close to whey protein (95.).9%), and there was no significant difference in absorption rate between the two (Figure 1). Yeast proteins have low digestibility in the stomach or are related to the combination of proteins and yeast-dextran to form complexes, and this effect has a greater effect on gastric absorption than in the small intestine. As a protein with a relatively slow stomach digestibility, yeast protein can be absorbed at a rate comparable to whey protein, and may provide a longer feeling of fullness.
Fig.1 Percentage of protein digestion and absorption at different times in the in vitro simulated digestion assay[1].
YPC, yeast protein; WPC, whey protein; SPI, soy protein isolate.
3. Environmentally friendly alternative protein
By reusing multiple carbon sources, including the high ability to make "waste" such as sugar sugarcane by-product molasses, yeast protein production not only improves production efficiency, but also reduces carbon emissions, saves arable land and freshwater resources, and has significant advantages in terms of sustainability and environmental friendliness. The current industrial production line has formed a closed-loop ecological industrial chain of "molasses, hydrolyzed sugar-yeast-yeast protein-yeast fermentation broth-fertilizer-crops". (Figure 2).
Fig.2 The whole process of yeast protein production.
Functional properties of yeast proteins.
1. Solubility and water retention.
Yeast proteins have good solubility and water retention in most non-extreme environments. Vegan meat products with added yeast protein lose less moisture during cooking, improving tenderness and juiciness. This characteristic shows that yeast alone has advantages in food processing such as vegetarian meat burgers, vegetarian meat sausages, and vegetarian meat fried dumplings, which can improve the flavor of food and bring a similar bite and fiber sensation to the product.
2. Ability to bind to metal ions.
Proteins themselves can bind to positively charged metal ions. Taking calcium ions as an example, yeast proteins combine with them to form calcium-containing proteins, which can be transported and absorbed by the human body, and are expected to become a new calcium supplement.
3. Biological activity of yeast protein peptides.
Yeast proteolyzed peptides have shown many health benefits, such as antioxidant, cholesterol-lowering, antihypertensive, anti-diabetic, immunomodulatory, and antibacterial. At present, antimicrobial peptides hydrolyzed from yeast proteins have been used as substitutes for chemical preservatives in the food industry.
Yeast protein applications and future prospects.
Compared with animal protein, yeast protein has attracted much attention for its hypoallergenicity (almost allergen-free) and lactose-free characteristics. Compared with plant protein, plant protein is under pressure on agricultural inputs and the environment, as well as the incomplete composition and low content of most essential amino acids in plant protein, accompanied by the presence of anti-nutritional factors such as phytic acid, tannins, and alkaloids. Studies have shown [2] that yeast protein has been consumed in 19-month-old rats [1.].0 g (kg d) for 3 months significantly improved the ultrastructure of the mouse muscle and increased the thickness of its muscle fibers (Figure 3). The reason may be that yeast proteins improve the function of aging muscle fibers by regulating the gut microbiota. A similar study showed that a daily supplement of 16g of yeast protein or whey protein for 6 months in healthy elderly over 60 years old could significantly improve the skeletal muscle index of limbs and shorten the walking time by 6 meters, and there was no significant difference between the two. The above studies partly suggest that the use of yeast protein as a protein supplement to improve sarcopenia in specific groups is promising.
Figure 3 Supplement 1Changes in muscle fibers of 0 g (kg d) yeast protein in 3-month-old mice.
As global impacts such as climate, environment and population intensify, the synergy between sustainable development, resource security and human health is gaining global attention. As an essential part of the food system, protein production systems are being reshaped. The approval of yeast protein as a new food raw material in China marks a breakthrough in science and technology in China's big food concept of "asking for calories and protein from microorganisms".