Effect of caliber size and fat level on the inactivation of E. coli O157:H7 in dry fermented sausages

Dry fermented sausages (DFS) have been subject to numerous validation studies, as pathogen reduction heavily relies on both ingredients and processing. In this study the effect of product caliber size (32, 55, 80 mm), and fat level (low, 9.67%; high, 18.46% wt/wt) on the inactivation of E. coli O157:H7 during DFS production was examined. Sausages containing a five-strain cocktail of E. coli O157:H7 at 107 CFU/g were manufactured and monitored for changes in physicochemical properties and inoculated E. coli O157:H7 numbers were enumerated during the DFS production stages and log reduction rates were calculated. Significant (P < 0.01) reduction in pH from 5.9 to 4.9 was observed in all sausages within 72 h of fermentation; however, the observed pH reduction was not significantly (P > 0.05) different among sausages of different caliber size or fat levels. No significant (P > 0.05) reduction in aw was observed during fermentation of the sausages. However, during the drying phase, sausages with larger caliber sizes required a significantly longer duration of drying to achieve the same aw of smaller caliber size sausages. For instance, to achieve an aw of ≤ 0.9, following 5 days of fermentation/curing, 80 mm caliber sausages required up to 27 days of drying compared with 13 and 6 days for 55 and 32 mm caliber size sausages, respectively. Fat levels on the other hand did not significantly (P > 0.05) effect the reduction of aw during drying of the sausages. During the fermentation stage there was a significant and rapid reduction in E. coli O157:H7 counts by about 1.1- to 1.4-log units, but was not significantly different among sausages of different caliber size and fat levels. Considering the whole process, only caliber size had a significant effect on log reduction of E. coli O157:H7. ANOVA of log reduction rates of E. coli O157:H7 among sausages of different caliber size and fat levels revealed no significant differences during the fermentation, however, during the drying of the sausages, log reduction rate of E. coli O157:H7 was significantly (P < 0.01) lower in sausages with larger caliber sizes and higher fat levels. For instance, log reduction rates for E. coli O157:H7 in high fat large caliber sausages was the lowest at − 0.082 ± 0.004 log CFU/g/day compared to all other fat and caliber size combinations. These results suggest that DFS manufacturers producing higher fat and large caliber size products need to consider longer drying periods to achieve the required 5-log inactivation of E. coli O157:H7.