Inactivation of Salmonella on In-Shell Pecans during Conditioning Treatments Preceding Cracking and Shelling

Abstract

Studies were done to determine the effectiveness of conditioning treatments for killing Salmonella in and on immersion-inoculated and surface-inoculated in-shell pecans. Treatment of immersion-inoculated, dried, stored pecans in chlorinated water (400 μg/ml) reduced Salmonella by not more than 1.6 log CFU/g. Treatment of immersion-inoculated, dried, stored pecans in chlorinated water (200 μg/ml, 1 min) followed by soaking in water for 2 h at 21°C and treating for 10 min in water at 85 to 95°C reduced Salmonella by >5.12 log CFU/g; treatment of nuts containing a low population of Salmonella (<0.60 log CFU/g) for 15 min at 90°C failed to eliminate the pathogen. Reductions of ≥6.42 log CFU/g were achieved by treating surface-inoculated nuts in water at 90 or 95°C for 80 s; treatment of nuts containing 1.78 log CFU/g at 95°C for 10 min did not eliminate the pathogen. Salmonella on surface-inoculated in-shell pecans (kernel moisture, 4.75%; water activity, 0.62) that had been dried and stored at 4°C for 3 to 5 weeks was more resistant to conditioning treatments than was Salmonella on surface-inoculated pecans (kernel moisture, 5.60%; water activity, 0.73) that were not thoroughly dried. Conditioning treatments were less effective for killing Salmonella on immersion-inoculated pecans than on surface-inoculated pecans. Response of Salmonella to conditioning treatments varied, depending on the method of inoculation and whether nuts were dried and stored between the time of inoculation and treatment, which emphasizes the importance of following practices commonly used by commercial pecan shellers when validating the lethality of conditioning treatments.

Evaluation of Sanitizers for Inactivating Salmonella on In-Shell Pecans and Pecan Nutmeats

“…Even on precleaned nuts, however, reductions of pathogens may be minimal. In a previous study, we observed that an initial Salmonella population of 0.63 log CFU/g of precleaned in-shell pecans was not significantly reduced when in-shell pecans were immersed in water containing chlorine at concentrations up to 400 pg/ml (12). When pecans contained a higher Salmonella population (5.62 log CFU/g), decreases of only 0.41 to 0.98 log CFU/g occurred after immersion for 1 h in water containing 100 to 400 pg/ml chlorine.…”

“…Long-term storage temperature has little impact on the resistance of Salmonella to oil roasting (2). Hot water treatment of in-shell pecans during the conditioning step preceding shelling operations has been shown to reduce Salmonella by 5 log CFU/g (12), but temperature and time conditions necessary to dry nutmeats after shelling without compromising sensory quality reduce the pathogen by less than 2 log CFU/g (13). Fumigation with propylene oxide is effective in reducing Salmonella on almonds (23,26) and nonpathogenic E. coli (5) and naturally occurring microbiota (14) on pecan nutmeats.…”

Agricultural practices to reduce microbial contamination of nuts

“…While this rinse water may be treated with antimicrobials to reduce the potential to spread microorganisms, they should not be viewed as a means to reduce pathogens on the surface of the nut (Beuchat and Mann, 2011). From the standpoint of orchard management, the best way to protect consumers from exposure to foodborne pathogens is to avoid usage of non-composted manures.…”

Efficacy of Sanitizers in Reducing Salmonella on Pecan Nutmeats during Cracking and Shelling

“…Immersion treatment of in-shell pecans containing Salmonella at a population of 0.63 log CFU/g with chlorinated water (400 pg/ml) did not cause a significant reduction in counts (5). Reductions of 0.41 to 0.98 log CFU/g resulted from treatment of nuts containing an initially higher population of the pathogen (5.62 log CFU/g).…”

“…Antimicrobial treatments to reduce or eliminate foodborne pathogens on in-shell pecans show promise, but concern still exists that nutmeats may become contaminated during the cracking and shelling process. A potential point of contamination is the vacuum flotation step, in which pieces of nutmeats other than halves are immersed in chlorinated water under vacuum to separate them from inedible in-shell nut components (5). Infiltration of pathogens into subsurface nutmeat tissues may occur during this separation process.…”