Evaluation of a novel commercial ground beef production system using a chlorinated nanobubble antimicrobial technology to control Shiga toxin-producing Escherichia coli and Salmonella spp. surrogates

Abstract

A variety of antimicrobial processes are used to reduce pathogen risks on commercially processed raw beef. Little research has evaluated chlorinated water on beef tissues, especially in a processing water dip scenario. Interest in nanobubble technology has increased due to its proposed surfactant properties, but it is undetermined whether this improves antimicrobial effectiveness of chlorine-based solutions in food applications. Benchtop studies were conducted to evaluate chlorinated nanobubble waters (0 to 11.94 ppm) against Shiga toxin-producing Escherichia coli O26, O45, O103, O111, O121, O145, and O157:H7 (STEC-7), Salmonella spp., and USDA-approved non-pathogenic STEC surrogates 1) in pure culture with the goal of characterizing the lethality contributions of pH (5 or 7), temperature, free available chlorine level (FAC), inclusion of nanobubbles, or a combination thereof; 2) in select chlorinated nanobubble “red water” (water containing 0.1% beef purge) solutions; and 3) on the surface of lean and fat beef tissue. In pure culture solutions, surrogates demonstrated greater resistance (P ≤ 0.05) to chlorinated solutions (3.4-5.5 log CFU/mL reductions) with increased reductions at the higher (11.94 ppm) FAC levels. STEC-7 and Salmonella population reductions were also notably reduced (3.3-7.1 log CFU/mL) by the higher FAC concentrations. No definitive impacts of temperature, nanobubble inclusion, or acidic pH were observed. At an average 5.23 ppm FAC in red water, all microbial populations were reduced by > 6 log CFU/mL after 60 minutes. Reductions of target organisms on inoculated lean and fat tissues were ≤ 1 log CFU/g in red water; likely due to the inability to maintain FAC levels above 0.7 ppm in the presence of organic loading. An in-plant antimicrobial validation study of a proprietary raw beef manufacturing process was conducted to determine the effectiveness of a recirculating acidic nanobubble water system, chlorinated to 5 ppm FAC using EO water generated concentrate, against the USDA-approved STEC surrogates. Preliminarily, inoculated beef trim was introduced into the system targeting 5 ppm FAC; chlorine concentrate reinfusion rates were determined to establish applicable operational parameters and sampling strategies for the system. An optimized in-plant study was conducted. Meat inoculated at ~ 7 log CFU/g was introduced into the recirculating chlorinated nanobubble system every other day over 6 days, achieving an average 1.6 log CFU/g surrogate reduction on inoculated meat throughout the manufacturing process. Approximately 2.7 log CFU/g of residual surrogates were recovered on non-inoculated meat ~35 minutes after inoculated meat entered the system, indicating that harborage of microbial contamination on processing equipment can lead to subsequent contamination carry-over that must be controlled during processing. Surrogate organisms were recovered by enrichment only from non-inoculated meat 24 h after inoculated meat processing on alternate days, likely stemming from inadequately sanitized processing equipment after inoculated batch processing. Control of the residual surrogate population in the system following inoculation was accomplished through daily equipment sanitation and boosting recirculated processing water to 50 ppm during a 4-h sanitation period (no beef entering system). The optimized study will be used as an antimicrobial process validation against STEC and Salmonella spp. in beef manufacturing.