Transfer of salmonellae from a desiccated existence in dry food ingredients or processing environments to food products having higher water... Show moreTransfer of salmonellae from a desiccated existence in dry food ingredients or processing environments to food products having higher water activities (e.g., peanut butter used in pie, chocolate in cake) leads to partial or full re-hydration of the bacteria. This study characterized the thermal behavior of Salmonella in response to desiccation and the subsequent rehydration. The thermal resistance of the desiccated S. enterica ser Tennessee was inversely correlated to aw: for example, desiccation at 11 to 97% equilibrated relative humidity (ERH) resulted in 0.5 to 3.3 log reduction, respectively, after 60ºC treatment for 10 min. Cells stored at lower ERH showed a lower survival rate, but higher thermal resistance. Once cells established their initial physiological response to desiccation, continual storage at 11% ERH up to three weeks did not further change the thermal resistance of Salmonella. Rehydration of the desiccated cells (11% ERH) to higher ERH conditions (84 to 97%) led to greater than 5 log reduction after heating cells at 60ºC for 10 min, in contrast, the same heat treatment resulted in approximate 3 log reduction for cells stored constantly at 84-97% ERH. There was no significant difference in regard to thermal sensitivity between cells rehydrated from 11% ERH to 33-55% ERH and that stored constantly at each ERH, only about 0.3-0.5 log CFU reduction in both cases. The study showed that rehydration moderately reduced cell viability, but greatly increased thermal sensitivity when a drastic aw shift occurred. M.S. in Food Safety and Technology, December 2011 Show less
