Billions of tons of food are lost in the United States each year to fungal contamination, most notably mold damage. Often working in combination with yeast and bacteria, molds are essential in the production of numerous indigenous fermented foods and are heavily used in industrial processes to produce organic acids and enzymes. At the same time, molds are a leading concern in the food plant environment. Under certain conditions, some molds may produce mycotoxins which are toxic to man and animals.
Under the Lens
Molds can invade and grow on virtually any type of food. Field crops, such as grains, nuts, vegetables, and fruits, are susceptible to mold contamination prior to harvesting and during storage, and this contamination can spread throughout the food processing chain. Foodborne molds include several hundred genera and there is virtually a mold for almost all occasions and environments.
The survival and growth of molds are affected by the same physical and chemical factors that affect bacteria: water activity (aw); pH;, temperature; oxygen or gas tension; salt and inhibitors; or preservatives. Molds normally do not outgrow bacteria under conditions that suit bacteria best, such as in non-acid and moist foods. Mold spores can survive harsh environmental conditions, such as dry conditions, that do not support normal mold growth.
Molds have the ability to grow over a wide range of temperatures, usually between 5oC- 35oC, but some species can grow above or below this range. Aspergillus, Cladosporium and Thamnidum can grow at refrigeration temperatures. Cladosporium herbarum can even develop at temperatures as low as -8oC. Thermotolerant molds, such as Aspergillus flavus and A. niger, can grow between 8oC – 45oC and are among the most destructive molds known. Some heat-resistant molds, such as Byssochlamys fulva and Neosartorya fisheri, can sometimes survive the juice pasteurization process.
A wide assortment of adverse health effects, including liver damage and nervous system impairment, have been reported following the ingestion of moldy foods.
Carbon dioxide levels of 5%-50% have been shown to inhibit mold growth in various food systems. Levels of about 10% have been shown to retard the rotting of refrigerated fruits and vegetables by molds. True to their diversity, however, there are molds that are oxygen scavengers and will grow at very low levels and even under vacuum conditions; other molds will grow slowly in atmospheres of 80% carbon dioxide.
Molds can enter a plant and the processing chain on anything that goes into the plant, including the air, but their primary means of entrance is on raw materials and ingredients. If a plant has a mold problem, it usually indicates the contamination of raw materials; that favorable growth conditions exist somewhere in the facility; or both.
Like other microorganisms, molds are opportunistic and their growth is not always restricted to specific foods. Thus, the identification of problematic molds is not likely to provide the positive information as to where they came from or how to eliminate them from the facility. However, It will give the plant some insight into possible sources of the molds and their characteristics. This information will be helpful in developing plans to eliminate them from the plant.
A wide variety of molds are known to produce mycotoxins. The Aspergillus, Fusarium, and Penicillium generas are of primary significance because they produce the most common mycotoxins, aflatoxins, fumonisins and vomitoxins.
Cool and damp conditions during harvest periods are highly favorable for the production of mycotoxins. They are usually quite stable and survive processing. Because they can contaminate a wide variety of products, the presence of mycotoxins in raw materials or ingredients is of great concern to manufacturers.
Hard to Eliminate
Since molds are ubiquitous in the environment, it is highly difficult to eliminate them from freshly-harvested raw materials. To reduce mold levels during growing, harvesting and transport of raw materials, suppliers should follow good manufacturing practices (GMPs) and undertake a number of measures, including:
- Thoroughly washing materials
- Discarding materials which appear damaged, bruised or exhibit signs of decomposition
- Expediting shipments to processors
- Controlling moisture in grains and utilizing sanitary trucks
Cleaning and sanitizing practices must be stringently enforced to ensure that products are being produced in a clean environment. Routine sampling of the plant environment for molds, yeast, and aerobic bacteria should be conducted to verify that the cleaning and sanitizing program is meeting its goals. Employing air exposure plates to identify potential spores in open product zones is another consideration. Periodic testing of the finished product to verify the success of the controls is also strongly recommended.
Testing & Analysis
The standard detection method for fungi requires a five-day incubation period. Silliker will soon offer a new rapid testing solution from 3M that provides testing results for yeast and mold in 60 hours, depending on product matrix and matrix validation. 3M’s Petrifilm Rapid Yeast and Mold Count Plates utilizes a new indicator technology that makes colonies easier to read than standard plate counts. Click here for more information, on the availability of this upcoming new technology.