The effect of container size and type on lethality values during production of thermally processed wet pet foods.

Wet pet foods make up 18% of the market. Most studies report thermal inactivation of pathogens, but data reporting the heat penetration in containers other than cans is scarce. Therefore, the objective of this work was to determine if heat penetration in various container types and sizes of pet food. The experiment was conducted as a 2x3 factorial arrangement of treatments with two general container sizes (small; 89-104 mL vs medium; 163 – 207 mL) and three container types (can, pouch, and tray). A model cat formula was produced for all six experimental treatments and each was produced in duplicate over six days in commercial scale equipment. The containers were cooked in a retort (cans: SJ Reid Retort, Bellingham, WA; trays and pouches: FMC retort, Madera, CA) with thermocouples attached to the center of representative cans, pouches, or trays (n=14) in each batch. Software (Calsoft Systems, v. 5.0.5) was used to record the internal temperatures and lethality during processing. Cumulative lethality values were determined for both the cooking and cooling processes. Data were analyzed using the GLM procedure of SAS (v. 9.4), and main effect means and interactions were separated by significant F test. There was an interaction (P<0.05) between container size and type for time to reach the F₀8; wherein, the medium can and tray had the longest time (45.5 and 46.3 min, respectively) the small can and tray, and medium pouch were intermediate (35.4, 36.0, and 32.0 min, respectively), and the small pouch the shortest time (36.0 min). There was no difference for either main effect of container type or size on heating lethality values (each main effect average F_o=10.3). Container size did not affect cooling lethality values (average F_o= 4.6), but pouches and trays had a higher (P<0.05) cooling lethality than cans (F_o=4.5, 5.9 vs 3.3, respectively). Total lethality values were not affected by container size (average F_o= 14.9), but there was a trend (P=0.0569) for pouches and trays to have a higher total lethality than cans. These heating differences may have an impact on the retention of heat labile nutrients like thiamine.