Physical-chemical properties and qualities of biological products

Physical-chemical properties of biological media (pH, aw and Eh) are crucial for the preservation of food products, for their nutritional qualities to be maintained and for the development of their organoleptic properties. Physical-chemical properties are related to the composition of the food (salt concentration, water, organic acid amounts, etc.) any modification in food composition or in the process causes a change of the physical-chemical properties, and therefore of the final product. 

Water activity is a property of equilibrium, it is constantly used to evaluate the diffusion of water during processing. The relationship between the amount adsorbed (equivalent to the water content) of various gases such as oxygen, nitrogen and water vapor depending on their activity coefficient (equivalent to 

In the case of meat products such as dried ham, salt plays an important role in the development of flavors as well as in the texture of the product. As a matter of fact, the pH, the concentration of NaCl and the temperature are the factors that most influence proteolysis during ham curing. An ultimate low pH ( 5.7) promotes the release of proteases, whereas a strong concentration in NaCl is an inhibitor for the activity of proteases. As a result, the decrease in NaCl in dry ham not only causes problems of health safety but also texture defects (flabby and doughy) [HAR 14]. 

The role of redox potential (Eh) is much less known, particularly due to the difficulty of measuring it. However, it intervenes in the oxidation reactions of lipids and proteins, in the selection of microorganisms aerobic microorganisms that grow when Eh is positive or anaerobic when Eh is negative. 

---