![]() Sampling can be very difficult because pockets of mold growth, and therefore mycotoxin formation, can occur during storage and transport. Testing of raw materials can help to limit the amount of toxins in food. Processing temperatures can kill the mold but will not remove toxins that are already formed. Mycotoxins can be formed on cereal grains such as corn and wheat. Penicillium, Eurotium and Aspergillus were the main genera of mold present on higher moisture samples of the food. Ochratoxins were found in 10% of the samples at low levels. (1997) for the presence of aflatoxin and ochratoxin found that 84% of these foods contained amounts that were below detectable limits. A test of dry cereal-based pet foods and wild bird seed by Scudamore et al. Formation of mycotoxins depends on the type of mold, substrate and storage conditions, which include pH, temperature and water activity. Toxins, notably mycotoxins in the case of feedstuffs, may be formed during the course of microbial growth, but not below 0.80 A w (Lowe and Kershaw, 1995). These fungi all grew faster under acidic rather than neutral pH conditions (Gock et al., 2003). ![]() Eurotium repens germinated at 0.70 A w at 30☌, but at 25 and 37☌, the minimum water activity for germination was 0.74. For example, Penicillium roqueforti germinated at 0.82 A w at 25☌, 0.86 A w at 30☌ and was unable to germinate at 37☌. Types of mold, temperature and water activity play a role in determining growth characteristics. Mold can grow at water activity levels as low as 0.61. Microorganisms and the water activities at which they are typically inhibited. ![]() It often becomes a formulation tradeoff between maintaining a moist, chewy food and the added costs of preservatives and/or processing. Supplementary processing such as pasteurization, pH control or addition of preservatives is necessary for protection of these foods. Soft pet foods and kibbles typically fall in this intermediate range (0.60-0.85 A w). Growth of these microorganisms can cause spoilage and physical deterioration. Water activities of less than 0.85, while considered non-hazardous from the standpoint of pathogenic bacterial growth, will still support the growth of many yeasts and molds. Canned foods, however, are typically higher than 0.85 A w and must be treated as acidified foods. At this low level of available water (<0.60 A w), microbial stability is not an issue. Dry pet food and hard treats typically are in the 0.40-0.45 A w range. Water activities of many common ingredients and categories of pet foods are shown in Table 2. At a water activity of less than 0.85, a food is considered non-hazardous because there is not enough available water to support pathogen growth. A water activity of less than 0.85 is needed in food in order to avoid regulatory attention. Table 1 details the level of water activity needed to inhibit different types of microorganisms (Fontana, 2000). Bacteria, molds and yeast require water for growth and every microorganism has a minimum water activity below which it will not grow. Water activity plays a role in the microbial stability of ingredients and final pet foods. Characteristics of individual ingredients can be very important and will be discussed in this paper. Silicon dioxide, for example, could absorb 50% moisture and maintain a very low water activity while crystalline sucrose absorbs little water until it reaches an A w of 0.80. The relationship between moisture and water activity depends on the specific material. Moisture content is the combination of free and bound moisture. Water activity is not to be confused with moisture content. Free moisture can be explained as water that is available to participate in physical, chemical and biological reactions. It is also defined as the quotient of the water vapor pressure of the substance divided by the vapor pressure of pure water at the same temperature (US FDA, 2005). Water activity is a measure of the free moisture in a foodstuff. Water activity (A w) is one of several important parameters that affect stability of foods. ![]() ![]() Changes in physical, chemical or microbiological properties of food can be considered loss of stability. One important aspect of food quality is the stability of the final product. The Federal Food, Drug, and Cosmetic Act requires that pet foods, like human foods, be pure and wholesome, containing no harmful or deleterious substances.Ĭonsumers are becoming increasingly aware of the quality aspects of what they eat, as well as the quality of what they feed their beloved pets. As 2006 rolls forward, we can see that the attention focused on the safety of food is here to stay. ‘Food safety’ was one of many buzz phrases for 2005. ![]()
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