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Cultivation of Yeast & Molds

 
Industrial Microbiology
 

Cultivation of Yeast & Molds

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Unique Granulated Culture Media

Yeasts and molds, both eukaryotic fungi, play a significant role in spoilage of foodstuffs and beverages, and Merck provides a wide range of media for the enrichment, isolation and enumeration of these organisms. These high quality, consistent culture media are available in a variety of formulations as dehydrated culture media in the form of granules.

Merck’s uniquely granulated culture media are not only convenient but also safe, meeting the highest industry performance standards as described in ISO 11133. Granulation causes significantly less dust than powdered media, leading to less inhalation of hazardous media components that cause allergic responses. In addition, it minimizes contamination of the work environment.

All Merck media are quality controlled according to stringent standards. This guarantees the consistent high quality of our products.

Detection of Yeasts & Molds



Detection of Yeast & Molds

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Molds in Food & Beverages

Molds are a large and taxonomically diverse group. They grow as multicellular filaments called hyphae. The network of a mold’s hyphae is considered a single organism and called a mycelium. There are thousands of known species with a wide range of lifestyles but all requiring moisture for growth. They include saprotrophs, mesophiles, psychrophiles and thermophiles.

A Universal Spoilage Organism

About a quarter of the world's food is believed to be contaminated by the mycotoxins of molds. Such toxins are produced by most molds under certain conditions an can infest food anywhere: in the field, in storage silos, in manufacturing facilities, on supermarket shelves and in the kitchen.

Molds as Pathogens

High levels of airborne mold spores can cause allergic reactions, asthma episodes, irritations of the nose, eye and throat, sinus congestion, as well as other respiratory problems. When mold spores are inhaled by an immunocompromised person, some of these spores may start to grow on living tissue, attach to cells along the respiratory tract and cause further problems.

Yeasts in Food & Beverages

Approximately 1,500 species of yeasts are currently known. They are unicellular, although some species may become multicellular through the formation of so-called pseudohyphae, or false hyphae. Yeast cell sizes can vary greatly depending on the species, though they typically measure 3 to 4 µm in diameter. Most yeast species reproduce asexually by mitosis, and many do so by an asymmetric process called budding.

The Contribution of Yeast to Our Food & Beverages

The yeast Saccharomyces cerevisiae converts carbohydrates to carbon dioxide and alcohols. For thousands of years mankind has made use of this species’s metabolic abilities: its carbon dioxide has been used in baking and its alcohol in alcoholic beverages.

Yeast as Spoilage Organism

Yeasts can grow in foods with a low pH using sugars, organic acids, or other easily metabolized carbon sources. During growth, they metabolize compounds and produce metabolites. These can cause the look and taste of a food product to change and spoil. Beverages and foods affected include cheeses, meats, fruit juices and semi-liquid products, such as syrups and jams.

Yeast as Pathogens

Some yeast species are opportunistic pathogens that can cause infections in humans whose immune systems are compromised. Cryptococcus neoformans is a noteworthy such pathogen, causing the disease called cryptococcosis. Yeast cells are surrounded by a rigid capsule of polysaccharides, which helps to prevent them from being recognized by the immune system. Yeasts of the genus Candida, another group of opportunistic pathogens, cause oral and vaginal infections in humans, a condition known as candidiasis. Candida occurs as a commensal yeast in the mucus membranes of humans. The same strains, however, can become pathogenic under certain circumstances.

Cultivation of Yeast in the Laboratory

Yeasts can be grown in the laboratory on solid culture media or in liquid broths. Typical media used for the cultivation of yeasts include potato dextrose agar or broth, Wallerstein nutrient agar, yeast peptone dextrose agar, and yeast mold agar or broth.

 
 
Granulated Dehydrated Culture Media Video

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Granulated Dehydrated Culture Media

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