The Microbiology of Cereals and Cereal Products

Editor’s Note: This article is excerpted from a longer article that appeared in “Microbiologically Safe Foods,” edited by Norma Heredia, Irene Wesley, and Santos Garcia. The book was published in 2009 by John Wiley & Sons, which also publishes Food Quality. To access a PDF of the full article, go to our website at A PDF of another chapter from the book, “Foodborne Pathogens and Toxins: An Overview,” is also available on our website.

Cereals and cereal products are significant and important human food resources and livestock feeds worldwide. Cereal grains and legumes are food staples in many, if not most, countries and cultures and are the raw materials of many of our foods and certain beverages. The main cereal grains used for foods include corn (maize), wheat, barley, rice, oats, rye, millet, and sorghum. Soybeans are not a cereal product, but rather, are legumes or a pulse, but are often considered with cereals because of their importance as a food source.

Examples of cereal products derived from cereal grains include wheat, rye, and oat flours and semolina, cornmeal, corn grits, doughs, breads, breakfast cereals, pasta, snack foods, dry mixes, cakes, pastries, and tortillas. In addition, cereal products are used as ingredients in numerous products, such as batters and coatings, thickeners and sweeteners, processed meats, infant foods, confectionary products, and beverages such as beer.

Table 1. Major Storage Fungi and the Moisture Contents of Commodities at Which Mold Invasion May Occur

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Table 1. Major Storage Fungi and the Moisture Contents of Commodities at Which Mold Invasion May Occur

Because of their extensive use as human foods and livestock feeds, the microbiology and safety of cereal grains and cereal products is a very important area. The sources of microbial contamination of cereals are many, but all are traceable to the environment in which grains are grown, handled, and processed. Microorganisms that contaminate cereal grains may come from air, dust, soil, water, insects, rodents, birds, animals, humans, storage and shipping containers, and handling and processing equipment. Many factors that are a part of the environment influence microbial contamination of cereals, including rainfall, drought, humidity, temperature, sunlight, frost, soil conditions, wind, insect, bird and rodent activity, harvesting equipment, use of chemicals in production versus organic production, storage and handling, and moisture control.

The microflora of cereals and cereal products is varied and includes molds, yeasts, bacteria (psychrotrophic, mesophilic, and thermophilic/thermoduric), lactic acid bacteria, rope-forming bacteria (Bacillus spp.), bacterial pathogens, coliforms, and Enterococci. Bacterial pathogens that contaminate cereal grains and cereal products and cause problems include Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Escherichia coli, Salmonella, and Staphylococcus aureus. Coliforms and enterococci also occur as indicators of unsanitary handling and processing conditions and possible fecal contamination.

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