Microorganisms need an amount of water to live, grow and multiply.
The water activity (Aw) is the equilibrium humidity of a product, determined by the partial pressure of water vapor at its surface.
The water activity value depends on the composition, temperature and water content of the product. Thus, it can be defined as the amount of free water that is available in food for microbial growth.
Microorganisms need an amount of water to live, grow and multiply, which is why many conservation methods are based on reducing this amount of water and therefore the activity of water through dehydration, lyophilization, addition of sugars or salts, evaporation or freezing.
WATER ACTIVITY VALUES
The water activity takes values between 0 and 1 . The lower the water activity value (closer to 0), the less water is available to microorganisms and the food will be less perishable.
The higher the water activity value (closer to 1), the greater the amount of water available to microorganisms and the shorter the shelf life of the food .
Therefore, water activity is one of the most critical factors to ensure food quality and safety, since it has an impact on quality characteristics, such as: texture, flavor, color, taste, nutritional value of the product and its storage time.
ANALYSIS OF WATER ACTIVITY IN FOODS
It is convenient to determine the water activity with precision for each one of the products, in order to characterize the risk of each of them:
- Aw = 0.98: almost all pathogenic microorganisms can grow and give rise to food spoilage and poisoning.
The most susceptible foods are fresh meat or fish and fresh fruits or vegetables. - Aw = Between 0.93 and 0.98: a large number of pathogenic microorganisms can be formed.
The most susceptible foods are fermented or cooked sausages, short-ripened cheeses, canned cured meats, lightly salted meat or fish products, and bread. - Aw = Between 0.85 and 0.93: In this case, as a bacterium, only S. aureus grows, which can lead to food poisoning. However, the fungi can still grow.
The most outstanding foods include cured and matured sausages, Serrano ham or condensed milk. - Aw = Between 0.60 and 0.85: bacteria can no longer grow in this interval , if there is contamination it is due to microorganisms that are very resistant to low water activity, the so-called osmophiles or halophiles. It can be the case in foods such as nuts, cereals, jams or cured cheeses.
- aww< 0.60: there is no microbial growth , but there may be microorganisms due to contamination during production that survive long periods of time.
This is the case of chocolate, honey, cookies or sweets.
Convet has the necessary instrumentation to measure the water activity by means of the dew point accurately and quickly, as well as the interpretation of the results obtained to define the microorganisms to be studied in each type of product.