WATER ACTIVITY, GLASS-TRANSITION AND MICROBIAL STABILITY IN CONCENTRATED/SEMIMOIST FOOD SYSTEMS

This review examines recent published suggestions that ''water dynamics'' may be applied instead of water activity (a(w)) determination to predict microbial stability of concentrated and intermediate moisture food systems. Factors such as the relative effectiveness of additives for antimicrobial stabilization through a(w)-lowering (i.e. glucose vs fructose, glycerol vs propylene glycol) and the importance of glass transition temperature as an indicator of microbial stability were examined, based on available experimental data. Determination of the glass-rubber transition characteristics and/or the use of the ''water-dynamics'' map does not enable prediction of the microbial stability of foods (i.e. inhibition of growth) with confidence. These were no more effective alternatives than the concept of water activity as a basis for predicting microbial growth in foods.