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Bread is a common medium for mold growth.

Mold


What is Mold?

Molds are multicellular fungi that grow on plant and animal materials in the form of a tangled mass. This mass is referred to as mycelium. As a complex group of microscopic fungi, the number of mold species is largely unknown. However, upwards of 300,000 species are thought to exist.

Food Spoilage

Losses of bakery products due to mold spoilage in the industry is as high as 5%, depending on seasons, type of products and methods of processing.1

The appearance of mold is considered food spoilage, and indicates the end of its shelf life. A few examples of common mold spoilage include gray fur on processed meats, fuzzy green dots and black spots on breads, and white dust on cheese.

On food surfaces, molds generally consist of three parts. Root threads penetrate the surface of the food, allowing the microorganisms to anchor to the food. From these root threads, a stalk is generally the second part of the mold fungi. Finally, spores can be found at the end of the stalk, allowing the mold to spread to other food surfaces as well as the environment at large.

Since molds are commonly found on grains, they are very prevalent in flour products, making them the main cause of microbial spoilage in the bakery industry. While most molds are harmless, a few species can be quite dangerous. For this reason, molds which produce mycotoxins are of particular concern in the baking industry.

Origin

Molds are considered a living fossil, influencing life on Earth for hundreds of millions of years. While their exact origins are not known, molds are thought to be one of the first great leaps in evolutionary biology.

Requirements for Mold Growth

The removal of any one of these 4 critical items requirements will delay mold growth4:

  1. Mold spores – lack of sanitation practices and the recycling of unfiltered air in the bakery increases the changes of mold spores.
  2. Food – animal and plant matter are both sources of food for mold.
  3. Temperature – cooler temperatures reduces mold growth.
  4. Water – lower water activity levels reduces mold growth.

Optimum growth of all isolates over water activity (aw) and temperature ranged tested showed optimization at 0.90 aw and 30⁰C, with an interval of growth rate of 3.8mm – 5.1mm d-1 . At 0.75 aw, growth was less than 0.15mm d-1.1

Mold Inhibition

The prevention of mold spoilage of foods can only be carried out successfully, if the species, which are actually spoiling the food, the associated funga, are known.2 With this said, a number of theories can be used to inhibit the overall growth of mold. These methods include lower pH (more acidic), lower water activity, spore control, fungicides and modified atmospheres.

Since molds are strictly aerobic, for the attainment of long shelf lives the levels of residual oxygen levels must be kept below 1%.3

The presence of lactic acid bacteria (LAB) in sourdough bread cultures increases the shelf life of the sourdough bread and other sweet baked goods made with these cultures, due to the inhibitory effect of organic acids on spoilage molds. In addition, it has been found that when sourdough LAB are cultivated, they produce antifungal substances, such as organic acids (in particular, lactic acid and acetic acid), carbon dioxide, ethanol, and hydrogen peroxide, and others, as yet unidentified inhibitory substances, that prevent mold growth.5

Essential oils represent an alternative to synthetic preservatives in the food industry against spoilage yeasts and molds. It seems that the main target of essential oils is the cell membrane also in fungi, causing increased permeability and disruption of membrane integrity. Both monoterpenes and phenolics are involved in the action against the cell membrane and key enzymes important for energy regulation or synthetic pathways; and mycotoxin production of molds is also affected by the essential oils.6

References

  1. Saranraj, P Geetha, M. “Microbial Spoilage of Bakery Products and Its Control by Preservatives.” International Journal of Pharmaceutical and Biological Archives. 2012;3(1):38-48
  2. Filtenborg O, Frisvad JC, Thrane U. “Moulds in Food Spoilage.” International Journal of Food Microbiology. 33(1996) 85-102
  3. Ortola, C., and C. Santacreu. 1998. “Principios de aplicacion del envasado en atmosfera modificada a los productos de panificacion y bolleria.” Aliment. Eqiup. Tecnol.  1998. 17:111-117.
  4. http://www.fsec.ucf.edu/en/consumer/buildings/basics/moldgrowth.htm
  5. Ven Kam P, Bianchini A, Bullerman L. “Inhibition of Mold Growth by Sourdough Bread Cultures.” RURALS: Review of Undergraduate Research in Agricultural and Life Sciences. 2007 Volume 2 Issue 1. 
  6. Krisch J, Tserennadmid R, Vágvölgyi C. “Science Against Microbial Pathogens: Communicating Current Research and technological Advances.” FORMATEX. 2011. http://www.formatex.info/microbiology3/book/1135-1142.pdf