Microorganisms of food importance Classification of food bacteria Classification of fungi in food Classification of yeasts in food Dangerous Telephone number list living organisms in food Habitat of microorganisms microbial development Water activity (aw) Water activity is the amount of free water present in a food that can be used by microorganisms . Microorganisms use water for their growth in two different ways: As a solvent for nutrients , allowing their transport and availability in the cytoplasm. As a chemical agent that takes part in hydrolytic reactions that give rise to Telephone number list monomers (amino acids, sugars and fatty acids) necessary for microbial synthesis and for energy reactions. The water activity (hereinafter aw) indicates the availability of water in a given medium for chemical and biochemical reactions and for transfers through semi-permeable membranes. Its value ranges between 0 and 1.
The aw is defined as the ratio between the vapor telephone number list pressure of water in solution (P) and the vapor pressure of pure water (P0) at the same temperature: a w = P / P0 In a closed environment, the relative humidity (RH) of the environment is related to the aw of a product through the following relationship: aw = HR/l00 In foods with low aw (0.61 - 0.85), the most Telephone number list frequent microbial alterations are caused by molds . Bacteria are inhibited at these values. Telephone number list Yeasts and xerophilic molds can grow in the lower part of this range. Any decrease in aw affects bacterial growth; most bacteria have optimal growth around 0.990 to 0.995 . For lower values, the growth decreases. Most fresh foods, such as fruits, vegetables, meat, milk, and fish, have an aw of 0.970 to 0.996, so all these foods are favorable for bacterial growth. Cakes and sliced breads are sensitive to mold growth . aw-values Oxidation-reduction potential (REDOX) A medium is oxidizing when it captures electrons and Telephone number list reducing when it gives them up . The oxidation-reduction potential (REDOX), measures the ease with which a medium loses (if it is reducing) or gains (if it is oxidizing) electrons. Its measurement is made in volts.
An oxidation-reduction reaction (REDOX) occurs as a consequence of a transfer of electrons between atoms or between molecules. A medium containing strongly hydrogenated substances, such as ascorbic acid, will be reductive. This is the case for many food products. The presence of atmospheric oxygen, either on the surface or inside the mass, makes Telephone number list these products have a positive redox potential. Microorganisms based on their oxygen requirements are classified as: Strict aerobes . Pseudomonas, Micrococcus, Bacillus; They need oxygen as the final electron acceptor. facultative aerobes . Enterobacteriaceae, Staphylococcus; They can grow in the presence or absence of oxygen. However, in anaerobic situations there is less growth (particularly in yeasts). strict anaerobes . Clostridium, Propionibacterium, etc.; They grow in the absence of oxygen. Certain Clostridia are slightly aerotolerant. Temperature This is one of the most important Telephone number list factors acting on the growth of microorganisms . It determines the physical state of the water in a given medium and, therefore, its greater or lesser availability for the growth of microorganisms.
