Water Activity Concept and Its Role in Food Preservation

Food preservation involves the action taken to maintain the desired properties or nature of foods, within a time frame, so that it remains safe and pleasant to consume. A stable food product can be developed by applying different processing techniques and by keeping it in appropriate conditions. Food stability determination from a scientific basis rather than empiricism is a challenge to food scientists and engineers. A relatively complete coverage of food preservation is available in the Handbook of Food Preservation and other references [9, 11]. Water is an important basic element in foods. For a long time, the industry has known how important it is to check free water. The water activity (aw) measurement forms the basis of this and provides important information about the quality of a product. Finally it provides information regarding the possibility of microbiological growth on the surface. Only with this conclusions can be made about the stability and durability of a sample [17]. The relative equilibrium humidity of a product, which is ascertained through its partial pressure of water vapor on the surface, depends on the following factors: Chemical compound; Temperature; Water content; Storage environment (T/RH); Absolute pressure; Packing. Free water in products is jointly responsible for the growth of undesirable organism such as bacteria or fungi, which produce “toxins” or other harmful substances. Bat also chemical/biochemical reactions (e.g. the Maillard reaction) increasingly take place and possibly change the following factors of a product: Microbiological stability, Chemical stability, Content of proteins and vitamins, Color, taste and nutritional value, Stability of the compound and durability, Storage and packing, Solubility and texture [5, 15, 26]. The thermodynamic description of these osmotic solutions has been the object of intense reach all along the last century, particularly those involving sugars and/or salts. Most thermodynamic models used to describe vapor-liquid equilibrium of osmotic solutions are based on relations involving Gibbs free energy of the system [24]. In 1994, within the Science and Technology for Development (CYTED) Program, Project’ Development of intermediate moisture foods (IMF) a survey was conducted in eleven countries, collecting information on 260 traditional IM and HM food [7]. The binary combination of aw and pH acts as a relevant hurdle in many of these products preventing proliferation of pathogenic microorganism, while the rest (antimicrobials, thermal treatment, etc.) play a secondary role, mainly against spoilage flora [7]. This paper present recent research nationally and internationally [1-29] regarding the concept of water activity and its role in food preservation. This article presents information related to the processing of fruit and vegetables by combined methods.