Yeasts and Molds Testing

Yeasts and molds are fungi that include several hundred species. Molds exist in the form of multicellular filaments. Yeasts typically grow as single cells with no spores. The majority of yeasts and molds are obligate aerobic, and they have relatively broad temperature and pH range for growth.

Figure 1. Morphological characteristics of molds and related contaminated foods

Yeasts and molds are usually considered as significant organisms causing food spoilage in low water activity or high acid food products. Unlike most bacteria, yeasts and molds require relatively low moisture levels to grow. They can cause different degrees of decomposition and deterioration of foods. Most yeasts have the ability to break down carbohydrates in foods, resulting in fermentation. Foods with low pH and high sugar have more risk to be contaminated by yeasts. They can grow virtually on any type of foods including crops and fruits in fields during pre-harvest and storage. They also grow on food mixtures and processed foods. The methods that commonly used to reduce or destroy yeasts and molds are the application of heat process, low temperature, and the removal of water during storage.

The spoilage caused by yeasts shows odors and abnormal flavors through gas production. Molds can cause the change in appearance in foods such as rot spots of various colors and sizes and highly colored sporulating mold. It is important to consider the pH and water activity of food products as well as packaging materials and production equipment during food processing in order to prevent yeast and mold spoilage issues. Several foodborne molds and yeasts can form mycotoxins which are toxic metabolites and harmful to the health of human and animals. Spoilage of food products caused by yeasts and molds results in great economic losses in food industry.

Currently there is no established contamination limit available for yeasts and molds in foods. It is critical to ensure the safety of raw material, the final food products, and the production environment by testing for potential spoilage yeasts and molds. Food companies usually monitor the total counts of yeasts and molds on raw materials and final products in order to determine a suitable shelf life for each product.

Yeasts and Molds Testing of Food at Alfa Chemistry

The standard methods (EN/ISO and FDA BAM) that have been widely used to enumerate yeasts and molds are culture-based methods using general microbiological testing supplies. Selective mediums or Petrifilm dry rehydratable film are used to incubate yeasts and molds at room temperature for five days followed by the plate counting technique to determine the level of yeasts and molds in the sample. Plating method for yeasts and molds uses solid medium of Dichloran rose bengal chloramphenicol (DRBC) agar. For low water activity foods, they are tested using medium such as Dichloran 18% glycerol (DG18) agar. We also have expertise in the sample preparation of different types of food matrices.

Alfa Chemistry offer accurate and validated testing platforms for the enumeration of yeasts and molds in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting technique

Limit of detection: 10 CFU/g

Sample type: Solid and liquid food samples

Sample size: 25 g