Impact of Poultry Processing Operating Parameters on Bacterial Transmission and Persistence on Chicken Carcasses and Their Shelf Life

Abstract

It is important for the poultry industry to maximize product safety and quality by understanding the connection between bacterial diversity on chicken carcasses throughout poultry processing to the end of shelf life and the impact of the local processing environment. Enumeration of total aerobic bacteria, Campylobacter and Pseudomonas, and 16S rRNA gene amplicon sequencing were used to evaluate the processing line by collecting 10 carcasses from five processing steps: prescald, postplucker, pre- and post-immersion chill, and post-air chill. The diversity throughout a 12-day shelf life was also determined by examining 30 packaged carcasses. To identify the sources of possible contamination, scald water tank, immersion chilling water tank, air samples, and wall surfaces in the air-chill room were analyzed. Despite bacterial reductions on carcasses (>5 log₁₀ CFU/ml) throughout the process, each step altered the bacterial diversity. Campylobacter was a minor but persistent component in the bacterial community on carcasses. The combination of scalding, defeathering, and plucking distributed thermophilic spore-forming Anoxybacillus to carcasses, which remained at a high abundance on carcasses throughout subsequent processes. Pseudomonas was not isolated from carcasses after air chilling but was abundant on the wall of the air-chill room and became the predominant taxon at the end of shelf life, suggesting possible contamination through air movement. The results suggest that attention is needed at each processing step, regardless of bacterial reductions on carcasses. Changing scalding water regularly, maintaining good hygiene practices during processing, and thorough disinfection at the end of each processing day are important to minimize bacterial transmission.IMPORTANCE Culture-based and culture-independent approaches were utilized to reveal bacterial community changes on chicken carcasses at different processing steps and potential routes from the local processing environment. Current commercial processing effectively reduced bacterial loads on carcasses. Poultry processes have similar processes across facilities, but various processing arrangements and operating parameters could impact the bacterial transmission and persistence on carcasses differently. This study showed the use of a single tunnel incorporating scalding, defeathering and plucking may undesirably distribute the thermoduric bacteria, e.g., Campylobacter and Anoxybacillus, between the local environment and carcasses, whereas this does not occur when these steps are separated. The length of immersion and air chilling also impacted bacterial diversity on carcasses. Air chilling can transfer Pseudomonas from wall surfaces onto carcasses; this may subsequently influence chicken product shelf life. This study helps poultry processors understand the impact of current commercial processing and improve the chicken product quality and safety.

Keywords: 16S rRNA; Anoxybacillus; Campylobacter; Pseudomonas; bacterial diversity; environment; food safety; microbiome; poultry processing; shelf life.

FIG 1

Diagram illustrating the Australian poultry processing line investigated and the stages (highlighted in gray boxes) at which samples were collected. Ten birds were collected from the prescald, postplucker, pre- and post-immersion chill, and post-air chill processing steps each, as well as 30 birds after packaging for the shelf life study. There were various environmental samples collected throughout the processing, including the scalding water, the immersion chilling water, the air, and the wall surface in the air chilling room.

FIG 2

Bacterial counts of total aerobic plate counts, Campylobacter, and Pseudomonas on chicken carcasses through the processing plant (A, log₁₀ CFU/ml) and from the environmental samples (B, the scald water and immersion chill water in log₁₀ CFU/ml, the air sample in the air chill room in log₁₀ CFU/m³, the air chill room wall in log₁₀ CFU/m², and the shackles through the air chill room in log₁₀ CFU/sponge). *, P < 0.05; **, P < 0.01; ***, P < 0.001; NS, not significant.

FIG 3

Prevalence of Campylobacter across all sampling points.

FIG 4

Relative abundances of the four most abundant taxa at the phylum level across all sampling points.

FIG 5

Relative abundances of 46 taxa pooled from the 10 most abundant taxa at each sampling point in a bar plot (A) and a shade map (B). The order of the 46 taxa is descending according to their respective relative abundance in the prescald step.

FIG 6

Distribution and correlations between sampling points. The circular shape (•) represents the processing sample group, the square shape (☐) represents the shelf life sample group, and the cross shape (+) represents the environmental sample group. Dark blue represents samples from the prescald step, light red represents samples from the postplucker point, light green represents samples from the pre-immersion chill point, purple represents samples from the post-immersion chill point, light blue represents samples from the post-air chill point, medium green represents the start of shelf life point, dark red represents the end of shelf life point, gray represents samples from the scald water point, dark green represents the immersion chill water point, black represents the air in the air chill room point, orange represents the air chill room wall point, and dark yellow represents the shackles through the air chill room point. (A) PCoA of all the 92 samples based on all identified taxa at genus level using the Bray-Curtis coefficient. Each shape with a different color represents one sample at its respective sampling point. (B) Metric MDS of sampling points after they were determined by bootstrapping samples at 95% confidence intervals on a weighted spearman rank correlation. (C) PCoA of all the sampling points based on the 46 taxa pooled from the 10 most abundant taxa in each sampling point to identify the similarity level between sampling points. Each shape with a different color represents a sampling point in its respective sample group. The dotted and solid circles indicate the sampling points were clustered at 80 and 60% similarity levels based on their bacterial diversity, respectively.