Survival of Salmonella enteric in skim milk powder with different water activity and water mobility

Recently, the safety of low water activity (aw) foods started to become a major concern. It has been observed that microorganisms may not grow in low-aw foods but can survive for rather long periods of time, representing significant risk. Most researchers have been concentrating on the role of water activity. However, little is known about the effect of water mobility on influencing the survival of Salmonella in low-aw foods. In this study, water mobility of skim milk powder was manipulated using ultra-high pressure to change tertiary structure, thus changing water–protein interactions. Skim milk powder with different levels of water mobility at similar aw level were obtained to evaluate how aw and water mobility influenced the survival of Salmonella enteric in low-aw foods. Results showed that aw could influence the survival of S. enteric and the lower the aw, the higher the survival. Water mobility had little influence on the survival of S. enteric when aw was 0.33 and 0.53. However, it influenced its survival when aw was increased to 0.81. The survival population of S. enteric was higher in the sample with low water mobility.