Evaluation of the on-chain refrigeration of broiler carcasses on Campylobacter contamination

Thermophilic Campylobacters are the first cause of foodborne illness in the European Union (about 230,000 cases in 2015) [1]; it is estimated that about 20-30% of human Campylobacteriosis cases are linked to the consumption of broiler meat [2]. The prevalence of Campylobacters on broiler carcasses after slaughtering is very high [3], due to their wide distribution in the chicken population and to the cross contamination during slaughtering. Campylobacter is not able to grow on the meat surfaces and is gradually inactivated by refrigeration [4], especially when low temperatures are combined with a drying of meat surface, as can be achieved with air-chilling.This study aimed to evaluate the effect of on-chain air chilling on Campylobacter contamination of broiler carcasses in an industrial slaughterhouse. During three sampling sessions (form March to July), a total of 14 slaughtered broiler batches were analyzed as follows: - Detection of Campylobacter spp. in the caecal content (one pooled sample from 5 caeca for each batch); - Detection and count of Campylobacter spp. in neck/breast skin samples (3 pools from 10 broiler carcasses for each batch), taken before and after the air refrigeration (4°C for 45 min). For the analyses, ISO methods were applied, and isolates were identified by PCR. The temperature of the carcasses during the refrigeration (on the surface and under the skin) was also registered. The refrigeration process led to a mean temperature decay of the carcasses of 14.7°C (surface) and 9.1°C (under the skin). All the broiler batches showed the presence of Campylobacters both in caecal content and on carcass surfaces, with about half of the pooled carcass samples having counts >3 Log CFU/g. The refrigeration of the carcasses resulted in a mean decrease of 0.27 Log CFU/g in Campylobacter counts, a slight but statistically significant effect. The main frequency class of counts was higher for pre-refrigeration samples (3-4 Log CFU/g vs 2-3 Log CFU/g). A high correlation was shown between counts pre and post refrigeration, stressing the importance of the previous phases to achieve a low contamination level. Due to the extremely high diffusion of Campylobacters, no differences were detected considering the slaughtering order of the batches or the sampling season. All the isolates belonged to the species C. jejuni or C. coli, with the prevalence of C. jejuni (71%) and of C. coli (86%) in pre and post refrigeration samples, respectively. The application of this chilling step could be useful, in combination with further refrigeration phases (during marketing and storage), in order to achieve constant low counts on broiler meats.