No abstract

No abstract

The heat resistance of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes that were in stationary phase, had been exposed to high osmotic pressure, or were acid adapted was evaluated in white grape juice concentrate (58 degrees Brix, pH 3.3). The most heat-resistant cells of all three pathogens were those exposed to high osmotic pressure or in stationary phase. Unlike in single-strength juices, in concentrate the acid-adapted cells for all three pathogens were less heat resistant than were cells in the other physiological states. E. coli O157:H7 had the highest heat resistance for all temperatures tested (e.g., D62 degrees C = 1.8 +/- 0.3 min, with a z-value of 9.9 +/- 0.6 degrees C). L. monocytogenes exposed to high osmotic pressure had the highest z-value (12.3 +/- 1.2 degrees C), although its D-values for all temperatures tested were lower (e.g., D62 degrees C = 0.93 +/- 0.1 min) than those for E. coli O157:H7. Salmonella was the most sensitive of the pathogens under all conditions. Based on the results obtained in this study, one example of a heat treatment that will inactivate 5 log units of all three pathogens in white grape juice concentrate was calculated as 1.5 min at 71.1 degrees C (z = 10.3 degrees C). Validation studies confirmed the predicted D71 degrees C for E. coli O157:H7 exposed to high osmotic pressure.

No abstract

Studies were conducted to investigate the effect of initial container pressure on heat penetration parameters using flexible aluminum containers. A pilot scale liquid nitrogen dispenser, regulated to discharge a fine stream of liquid nitrogen (LN2), provided approximately 10 to 15 psi pressure within the container prior to end‐over‐end processing in a computer‐controlled retort using water immersion with 32 psi over pressure. Thermal process parameters including the heating rate index (fh), lag factor (jh), the cumulative lethality (Fo), cook‐value (Co) and the overall heat transfer coefficient (Uo) were examined in relation to retort temperature (241–261F), rpm (0–15 rpm) and product initial temperature (54–121F) using 5% w/w bentonite suspension with or without liquid nitrogen. Generally, containers with added liquid nitrogen had no impact on evaluated data compared to their counterparts without LN2 under similar experimental conditions. Estimated overall heat transfer coefficient (Uo) compared favorably with published data, while the Co/Fo ratio decreased with increasing temperatures as expected. Product cold spot location migrated in either upward or downward direction depending on the mode of heat transfer. Although added LN2 generally had no limiting effect on both heat transfer and heat penetration data, processing aluminum containers with high initial pressure at high retort temperatures could create excessively high internal pressure that could compromise container seam integrity.