Postprocess contamination of flexible pouches challenged by in situ immersion biotest.

Packages were evaluated for leaks by determining microbial penetration through microchannels as a function of test organism concentration, location in a retort, and microchannel diameter and length. A flexible pouch was used in an in situ immersion biotest coupled with a state-of-the-art retort. Microchannel diameters of 10 to 661 microm with 3- and 6-mm lengths were created by placing tungsten wires in vacuum heat-sealed flexible pouches. After removing the wires, these pouches were subsequently heat processed under pressure. They were then biotested in cooling water containing 10(3) and 10(6) CFU of motile Enterobacter aerogenes per ml for 30 min and were dried immediately after manual unloading. After incubation at 37 degrees C for 3 days, they were visually examined for contamination. The high-temperature retorting process was shown to decrease microchannel diameters by an average of 20%. Generally, the smaller the microchannel diameter, the greater the percent shrinkage. Statistical analysis of the biotesting data showed that microchannel diameter and length had strong effects on microbial penetration (P < 0.01). Microbial concentration had a borderline significant effect (P < 0.05), but the effect of package location in the retort was not significant. At conservative conditions, such as a 3-mm microchannel length and a cooling water contamination level of 10(6) CFU/ml, the selected microorganism can penetrate microchannels with diameters as small as 7 microm. However, the minimum microchannel diameter for penetration could be as large as 46 microm at practical conditions of 6-mm microchannel length and contamination levels of 10(3) CFU/ml.