The main purpose of poultry immersion chillers is to submerge carcasses in water that has been chilled to a temperature low enough to inhibit pathogen growth. As an extra precaution, processors add chemical disinfectants to the water to eliminate any microbes that may pose a food safety risk.
Researchers with the Georgia Tech Research Institute’s (GTRI) Agricultural Technology Research Program have been investigating the use of ice slurry (a mixture of micro-sized ice crystals and water) as an alternative chilling medium that may also have antimicrobial properties.
“We began the project operating on the assumption that the ice slurry’s increased cooling capacity per unit mass of water would likely reduce water consumption while also providing a faster chill compared with conventional chilled water,” says Dr. Comas Haynes, GTRI principal research engineer and project director.
In fact, initial scaled experiments using an auger chiller demonstrated the ice slurry’s superior cooling capacity as compared with conventional chilled water. Results showed carcass core temperatures decreased on average an additional 25 percent in 45 minutes within the ice slurry at an initial temperature of minus 1°C compared with 45 minutes within the chilled (liquid) water at an initial temperature of 4°C. The corollary, explains Haynes, is that a target temperature could be reached in the same processing time but with less water if the slurry form is used.
Having shown that the ice slurry does, in fact, allow for significantly greater cooling per unit mass of water, researchers began to wonder if the slurry’s texture could act as a scrubber along the carcasses’ skin. The idea is that the scrubbing motion would be like an abrasive force that could help to loosen or weaken potential microbial colonies or biofilms adhering to the carcasses, thus creating an opportunity for the slurry to aid antimicrobial activity.
“We began to wonder if this perceived scrubbing phenomenon could possibly improve the effectiveness of chemical disinfectants,” says Haynes. He also likens the plausible effect to “scrubbing while sanitizing” common household surfaces using the popular two-sided kitchen cleaning sponges.
To test the hypothesis, experiments were conducted using whole-bird carcasses inoculated with a specialized strain of Salmonella and chilled by either water or ice slurry that contained various levels of the antimicrobial agent peracetic acid (PAA). The carcasses were then compared with a control set of carcasses that were not chilled or treated.
Using a 50 ppm PAA concentration and 20 minutes of immersion, the results showed an average of 0.6-log reduction in pathogen presence versus the control set when using water chilling, while the ice slurry chilling showed an average 1.2-log reduction versus the control set. This was an instance of twice the log-scale reduction when slurry was used as the intervention medium instead of chilled water.
“Aside from these log reduction numbers, we believe ice slurry amplifies the effect of the antimicrobial agent,” says Haynes. “We think that ultimately greater pathogen reduction may be possible through an extensive investigation of processing conditions.”
To this end, researchers have built several 15-gallon micro-testers that are alternatives to the 250-gallon scaled auger chiller previously used. The micro-testers allow them to conduct more experiments on the impacts of ice slurry conditions within a shorter period of time.
“These micro-testers afford more operational control and degrees-of-freedom to explore optimal settings such as fluidic routing of chiller media to maximize benefits,” explains Haynes.
Experiments with chicken parts, specifically wings, are underway. These tests of chicken parts as opposed to whole-birds will provide insight for processors who are interested in chilling or applying antimicrobial interventions to individual parts only.
Researchers are also using the micro-testers to further explore the ice slurry’s observed antimicrobial benefits. Haynes says the team is hoping to determine if these benefits are due to the scrubbing effect or if there are other physical phenomena at play.
“Ice slurry is emerging as a more potent form of water for cooling and antimicrobial chiller efficacy in poultry processing, and we are excited that our research efforts are helping to optimize these benefits,” says Haynes.
This research is conducted with support from several industrial and government partners: IceSynergy and Highland Refrigeration have loaned ice slurry machines; whole-bird carcasses have been donated by a local poultry company; the USDA’s Russell Research Center has provided a laboratory-scale auger chiller; Enviro Tech Chemical Services has provided the peracetic acid (PAA) for antimicrobial tests; and representatives from Southern Company Services have provided sponsorship and technical advice in regard to electricity/energy savings.