The Sources, Preparation and Peptides Found In Yeast Extracts

Yeast extracts are rich, nutrient-dense substances derived from the cell contents of yeast cells. They are widely used in food, pharmaceutical, and biotechnology industries as flavor enhancers, nutritional supplements, and sources of bioactive compounds. Yeast extracts contain a wide range of proteins, peptides, amino acids, vitamins, and minerals, making them versatile and valuable ingredients.

In this guide, we will explore the sources of yeast used to produce extracts, the preparation process, and the types of peptides formed, including the important Type I and Type II peptides.

Yeast Sources for Yeast Extracts

Yeast extracts can be derived from various species of yeast, with two primary sources being:

1. Saccharomyces cerevisiae: This is the most common species of yeast used in the production of yeast extracts. It is also the yeast used in baking and brewing. Saccharomyces cerevisiae is rich in proteins, vitamins (especially B-complex vitamins), and minerals.
2. Candida utilis: Also known as “torula yeast,” Candida utilis is another popular source of yeast extract. It is often used because it can grow on a variety of substrates, including those derived from agricultural waste. Candida utilis is especially known for its high nucleic acid content, which can be broken down into flavor-enhancing compounds.

Other yeast species, such as Kluyveromyces marxianus and Pichia pastoris, can also be used in specific applications, but Saccharomyces cerevisiae remains the most widespread.

How Yeast Extracts are Prepared

The preparation of yeast extracts involves breaking down yeast cells to release their internal components, particularly proteins and peptides. The process generally follows these steps:

1. Fermentation of Yeast:

• Yeast cells are grown in controlled fermentation conditions, typically in a nutrient-rich medium containing sugars or other carbon sources. This step allows the yeast to grow and multiply, increasing the biomass.

2. Autolysis (Self-Degradation):

• In this step, yeast cells undergo autolysis, a self-degradation process where the yeast cells break down their own cell walls and membranes. This is often achieved by heating the yeast to a temperature (around 45–60°C) that activates enzymes within the yeast cells but does not kill them immediately.
• During autolysis, the yeast’s own enzymes break down cellular components, especially proteins, into smaller peptides and amino acids.

3. Enzymatic Hydrolysis (Optional):

• To speed up or control the breakdown of proteins, additional enzymes (like proteases) may be added to the autolyzed yeast. This is known as enzymatic hydrolysis, where specific enzymes further break down the proteins into a mix of peptides and amino acids.
• This process enhances the yield of peptides and allows for a more controlled production of specific types of peptides with desired properties.

4. Separation and Filtration:

• Once the yeast cells have been broken down, the cell walls and other insoluble components are removed via filtration or centrifugation. What remains is a liquid rich in soluble compounds, including peptides, amino acids, vitamins, and minerals.

5. Concentration and Drying:

• The filtered yeast extract can be concentrated through evaporation to reduce its water content. Depending on the final product’s application, the yeast extract may be dried into a powder or retained as a paste or liquid.

Yeast extracts can be tailored to have varying flavors and functionalities depending on the fermentation conditions, autolysis time, and additional enzymatic treatments used.

Highly sophisticated techniques for isolation and purification of bioactive peptides are available. We can exploit ultrafiltration (UF), gel filtration chromatography (GFC), preparative HPLC and even UPLC -ESI-Q-TOF MS/MS have all been used successfully as was the case in identifying salt-enhancing peptides (Shen et al., 2022).

Types of Peptides Produced in Yeast Extracts

Peptides are short chains of amino acids linked by peptide bonds. During the preparation of yeast extracts, proteins are broken down into a variety of peptides that can exhibit biological activity or functional properties, such as enhancing flavor or contributing to the nutritional value of the extract.

There are two primary classes of peptides produced in yeast extracts: Type I and Type II peptides.

Type I Peptides (Free Peptides)

• Structure: Type I peptides are free peptides formed through the enzymatic or autolytic breakdown of yeast proteins. These are smaller chains of amino acids, generally ranging from 2 to 20 amino acids in length.
• Production: Type I peptides result from the partial hydrolysis of yeast proteins during the autolysis or enzymatic hydrolysis process. They are released into the yeast extract as soluble, free-floating peptides.
• Functionality: These peptides are known for their flavor-enhancing properties, particularly their ability to contribute umami taste to food products. The amino acids glutamate and aspartate, common in Type I peptides, are key components in providing savory flavors.
• Nutritional Benefits: Type I peptides can have various health benefits, such as antioxidant activity, immune support, and contributing to the overall amino acid profile of food.

Type II Peptides (Bound Peptides)

• Structure: Type II peptides are bound to larger molecules, such as nucleic acids or other proteins. These peptides are less soluble than Type I peptides and are typically embedded within larger structures in the yeast cell.
• Production: Type II peptides are produced during yeast extract preparation, but they are not fully liberated from their parent proteins or nucleic acids. They may remain attached to other molecules or within cell wall fragments.
• Functionality: While less soluble, Type II peptides play important roles in adding body or mouthfeel to food products. They contribute to the overall texture and viscosity of soups, broths, and sauces where yeast extracts are used.
• Nutritional Benefits: Type II peptides can still provide nutritional benefits when they are eventually broken down during digestion. They can also have prebiotic effects, supporting gut health by serving as substrates for beneficial gut bacteria.

Peptide Bioactivity

In addition to contributing to flavor and texture, many peptides in yeast extracts exhibit bioactive properties that may provide health benefits, such as:

1. Antioxidant Peptides:
   • Some peptides in yeast extracts have been shown to possess antioxidant properties, helping to neutralize free radicals in the body. These antioxidant peptides can help reduce oxidative stress and support overall cellular health.
2. Antimicrobial Peptides:
   • Certain peptides have antimicrobial properties, which can help in preserving foods or inhibiting the growth of harmful microorganisms.
3. Immunomodulatory Peptides:
   • Some peptides from yeast extracts have been found to enhance immune system function. These peptides can stimulate immune cell activity and support the body’s natural defense mechanisms.
4. Blood Pressure Regulation:
   • There is evidence that some peptides in yeast extracts may act as angiotensin-converting enzyme (ACE) inhibitors, potentially helping to regulate blood pressure by reducing the conversion of angiotensin I to angiotensin II, a molecule that narrows blood vessels.
5. Anti-inflammatory Peptides:
   • Certain peptides found in yeast extracts have anti-inflammatory properties, which can help in reducing inflammation and promoting general health.

Applications of Yeast Extracts and Peptides

1. Food Industry:

• Flavour Enhancement: Yeast extracts are used in soups, sauces, snacks, and other savoury foods to enhance flavour, particularly by adding umami. Salt enhancing peptides have also been isolated and extracted. 
• Nutritional Supplements: Due to their high content of essential amino acids, vitamins (especially B vitamins), and minerals, yeast extracts are added to foods to boost their nutritional profile.
• Fermented Foods: Yeast extracts are used to promote fermentation in various food and beverage products.

2. Pharmaceuticals and Nutraceuticals:

• Bioactive Peptides: The health-promoting peptides in yeast extracts can be isolated and used in supplements aimed at improving heart health, immune function, or digestive health.

3. Cosmetics:

• Anti-aging and Antioxidant Formulas: Due to their high antioxidant content, peptides from yeast extracts are used in skincare products to reduce signs of aging and protect the skin from oxidative damage.

Yeast extracts are a valuable source of proteins, peptides, amino acids, vitamins, and minerals. The production process involves fermentation, autolysis, and sometimes enzymatic hydrolysis, resulting in a rich mixture of bioactive peptides and other nutrients. Type I peptides, which are free and soluble, provide flavor-enhancing and nutritional benefits, while Type II peptides contribute to texture and are potentially bioactive after digestion. Both types of peptides make yeast extracts versatile ingredients in food, nutraceutical, and cosmetic industries.

References

Shen, D. Y., Pan, F., Yang, Z. C., Song, H. L., Zou, T. T., Xiong, J., … & Xue, D. D. (2022). Identification of novel saltiness-enhancing peptides from yeast extract and their mechanism of action for transmembrane channel-like 4 (TMC4) protein through experimental and integrated computational modeling. Food Chemistry, 388, 132993.