Effects of Water Activity in Model Systems on High-Pressure Inactivation of Escherichia coli

The objectives of the study were to measure the effect of water activity (a (w)) and to quantitatively evaluate the effect of the selected humectants under high-pressure processing (HPP) in combination with processing parameters such as treatment time, temperature, and pressure on the inactivation of Escherichia coli K12 in solid and liquid model systems. Glycerol was used in liquid and solid models to vary a (w) at 0.90, 0.95, and 0.99 levels. The model systems samples and transmitting media were preconditioned to initial temperatures of 4 and 20 A degrees C to compensate for adiabatic heating upon compression to ensure that HPP treatments at 400 and 600 MPa were performed at final temperatures not higher than 40 A degrees C. Decrease of a (w) from 0.99 to 0.90 in glycerol-based models caused considerably less inactivation of E. coli K12 at tested pressures and temperatures. Effect of different humectants at a (w) 0.95 and 0.99 on the inactivation of E. coli K12 was studied comparing glycerol, fructose, sodium chloride, and sorbitol. Among four types of solutes tested in the study, sodium chloride appeared the least protective, with glycerol and fructose being approximately equal, and sorbitol showed the most protective effects on inactivation of E. coli K12. The obtained data of E. coli K12 inactivation by HPP at varied a (w) levels in different solutes demonstrated similar effects of a (w) on microbial inactivation by thermal treatments. The results must be taken into account when HP preservation process and foods are developed.