Yeast extracts (YE) are concentrated and purified preparations derived from raw yeast sources, primarily Saccharomyces cerevisiae (Baker's or Brewer’s yeast) and Candida utilis (Torula yeast).

YE production process : cultivating the yeast cells, harvesting them, performing a disruption of the cells through an autolysis or an enzymatic hydrolysis, and extracting the desired contents.  After the extraction process, the YE is concentrated and optionally purified, with purification aiming to reduce endotoxin levels. If desired, the extract can be further processed to form a dry, powdered product or left in the form of a liquid or paste.

YE composition: Abundant quantity of amino acids, polypeptides, vitamins and minerals. They can be customized to meet the specific needs and requirements of different cell lines and bioprocesses. The composition of YE is influenced by process production factors such as the fermentation medium, yeast strain, and extraction methods. Manufacturers can for example change the parameters of their treatment process (such as the pH, temperature, and time), to obtain YE with different concentrations of components. [1]

Yeast Extracts play a crucial role in the formulation of biologics, particularly in the upstream process for the development of cell culture media. YE support cell growth, metabolism, and protein expression.

• B Vitamins: thiamine (B1), riboflavin (B2), niacin (B3), and pyridoxine (B6) are essential cofactors for energy production
• Growth factors: IGFs (insulin-like growth factors) and EGFs (epidermal growth factors), activate surface receptors to promote cell proliferation.
• Cytokines: CSFs (Colony-Stimulating Factors) and ILs (Interleukins), enhance the differentiation and maturation of specific cell types
• Minerals: magnesium, potassium, iron, zinc, calcium, support cell growth and can act as enzyme cofactors
• Peptides: glutathione, oligopeptides, glutamine peptides play a role in cellular defense and can have antioxidant properties
• Amino acids: glycine, tyrosine, and serine serve as precursors for the synthesis of nucleic acids or proteins.

A study showed that in the absence of these three key amino acids, the activity of Polyvinyl Alcohol-Degrading enzymes decreased drastically ( respectively by 78.7%, 66.9%, and 83.1%). [2]

Yeast extracts also dispose of a buffering capacity which allows to maintain optimal pH range between 6.8 and 7.4 for cell growth.

To boost furthermore the cells of interest and therefore increase production yields, it is possible to either enrich our YE by adding minerals, amino acids, growth factors, nucleotides, lipids or peptones.

As mentioned previously, every microorganism has its own specific needs and requirements regarding its growth and production efficiency. It is therefore important to select the most appropriate YE depending on the type of molecule of interest/biologics you want to produce.

Examples:

• Fungi: require yeast extracts rich in polypeptides
• Spore-forming bacteria (Bacillus): yeast extracts with high content of free amino acids and iron