Water activity in food preservation2/29/2024 Many food components may be present in several states: crystalline solids, amorphous solids either rubbery or glassy, aqueous solution, or bound to other components.Protein and starch adsorb much more water at low aw than do fatty or crystalline substances (ex.Yeast and mould are more tolerant at < 0.80, but no growth below the aw < 0.6. Pathogenic bacteria inhibited < 0.85 – 0.86. Minimum aw values for growth and toxin production by microorganisms of public health concern. The ERH of a food product is defined as the relative humidity of the air surrounding the food at which the product neither gains nor loses its natural moisture and is in equilibrium with the environment. A relationship therefore exists between ERH and aw since both are based on vapour pressure. This same NaCl solution in a closed container will develop an equilibrium relative humidity (ERH) in a head space of 75.5%. A saturated solution of sodium chloride has a water activity of 0.755. Pure water has an aw of 1, one molal solution of sugar - 0.98, and one molal solution of sodium chloride - 0.9669. Comparing this vapour pressure with that of pure water (at the same temperature) results in a ratio called water activity (aw). These water-binding effects reduce the vapour pressure of the food substrate according to Raoult’s Law. The water activity of a food is the amount of unbound water available. (osmotic binding), and by the surface effect of the substrate (matrix binding). Salt is effective as a preservative because it reduces the water activity of foods. In the bound state, water is not available to participate in these reactions as it is bound by water soluble compounds such as sugar, salt, gums, etc. Free water in fruit or vegetables is the water available for chemical reactions, to support microbial growth, and to act as a transporting medium for compounds. Water has been called the universal solvent as it is a requirement for growth, metabolism, and support of many chemical reactions occurring in food products. The concept of aw has been very useful in food preservation and on that basis many processes could be successfully adapted and new products designed.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |