Liquid smoke effects on Escherichia coli O157:H7 in beef Liquid smoke effects on Escherichia coli O157:H7 in beef trimmings and ground beef patties trimmings and ground beef patties

Summary Liquid smoke (LS) reduce d Escherichia coli O157:H7 counts in inoculated beef trim-mings and ground beef patties. The counts were reduced (P<.05) by .5 log


Summary
Liquid smoke (LS) reduce d Escherichia coli O157:H7 counts in inoculated beef trimmings and ground beef patties.The counts were reduced (P<.05) by .5 log cfu/g 10 immediatel y after beef trimmings were treated with 8% LS and by 1.2, 2.0, 1.6, and 2.3 log 10 cfu/g after the trimmings were formed into patties and tested or stored under refrigeration for 1, 2, and 3 days, respectively (2 log reduc-

Introduction
Recently, outbreaks of foodborne illness and deaths associated with ground beef containing E. coli O157:H7 have occurred in the Unite d States.E. coli O157:H7 is the third or fourth most common pathogen recovered from human stool samples and was first recognized as a foodborne pathogen in 1982.Since that time, undercooked groun d beef has been implicated in outbreaks o f E. coli O157:H7 infections.
Smoking of food provides a desirable flavor and color, but also contributes substantially as an antimicrobial agent.As a food additive, it has the advantage of bein g labeled as a natural product.
Preliminar y experiments evaluated the antibacterial properties of liquid smoke (LS) in a model system.The LS inhibite d E. coli O157:H7 growth at all leve l s (6-12%) evaluated in preliminary studies (data not shown).Its bactericida l activity increased with concentration.
Based on those preliminary findings, our objective was to evaluate th e bactericidal effects of adding 8% LS to bee f trimmings inoculated with E. coli O157:H7, which were then used in production of expe rimental ground beef patties.

Experimental Procedures
A low-flavor-profile LS provided by Hickory Specialtie s was used.Fresh beef trimmings (4 days postmortem) were inoculated with a strain of E. coli O157:H7 resistant to the antibiotic Rifamp icin to give a target of 1 × 10 cfu/g 7 and mixed for 4 min usi ng a Hobart mixer.The LS or sterile water (contro l ) was added at 8% to the inoculated trim, and eac h mixed for 4 min.A second unino culated control was mixed for 4 min and used for psychrotrophic counts.Then all treatments were coarsely ground (1.27 cm), followed by a fine grind ( .32 cm), using a sterile grinder.Patties (70-90 g) were made using a manual patty maker, bag ged aerobically in heatsealed bags, and stored in the d ark at 4EC for up to 3 days.Three replications were performed.
Immediately after inoculation, duplicate 25 g surface samples were taken from inoculated beef trimmings, from treated (LS and water) beef trimmings, and from noninoculated beef trimmings to check initia l E. coli O157:H7 population, antibacterial effects of treatment of trimmings , and psychrotrophic counts.The surface samples (approx..7 cm deep) were taken using a sterile scalpel and tongs.Duplicate 25 g samples were taken from the LStreated patties, inoculated control patties, and noninoculated control patties a t days 0, 1, 2 and 3.Each sample was placed i n a filter stomacher bag, 225 ml of .1% of peptone water was added, and the mixture was stomached for 2 min.Serial dilutions were prepared in peptone water (.l%) and spiral plated on MacConkey sorbitol agar containing Rifampicin (inoculated samples) or on plate count agar (noninoculated control samples).The plates for inoculated samples were incubated at 37°C for 24 hr, and the plates for noninoculated samples were incubated at 7°C for 10 days for psychrotrophic counts.A Laser Spiral System Bacterial Colony Counter was used to count colonies growing on or in the culture medium and reported as log 10 cfu/g of sample.
The statistical design was a split-plot design, with meat block was the whole plot and the meat sample each day from the meat block as the subplot.Significance level was set at P<.05.Analysis of variance and least significant difference procedures were used.
E. coli O157:H7 counts were reduced (P<.05) by .5 log 10 cfu/g, after beef trimmings were treated with 8% LS and by 1 .2,2.0, 1.6, and 2.3 log 10 cfu/g in patties made from the trimmings before (0 day) and after 1, 2 and 3 days of refrigerated storage, respectively.The psychrotrophic counts in beef trimmings and ground beef remained constant from day 0 to day 1, but increased rapidly from day 1 to day 3. Psychrotrophic bacterial growth did not impact E. coli O157:H7 growth.E. coli O157:H7 growth was not affected by meat fat content in treated or untreated beef patties (data not shown).Thus, 8% LS was effective in reducing E. coli O157:H7 counts in ground beef patties.
The level of LS we used was higher than normally recommended (1.5-2.0%) for meat products.However, adding 8% LS to beef trimmings could be feasible as a food safety tool for sausage production if the trimmings are only one component of the product formulation.For instance, if beef trimmings were treated with 8% LS, and the sausage contained 25% beef, the LS level would be reduced to a level normal for a meat product.Liquid smoke is used in meat mainly to provide flavor and color.However, because of its antimicrobial characteristics, LS could be added to meat products to make them safer and at the same time to extend product shelf-life.Further research should examine the antimicrobial properties of LS in meat systems.