Influence of the packaging atmosphere and presence of co-contaminants on the growth of photobacteria on chicken meat

Fresh meat is commonly packaged in modified atmosphere to decelerate spoilage processes. The applied gas mixture affects the growth of spoilage organisms and selectively shapes the spoilage community. In this study, we investigated the impact of O2 and CO2 on the growth of Photobacterium (P.) phosphoreum and P. carnosum strains in situ on chicken meat by packaging under different modified atmospheres (air, 70% O2/30% CO2, 70% N2/30% CO2, 100% N2). Combination of 70% O2 and 30% CO2 resulted in significant growth reduction of the analyzed strains, suggesting inhibitory effects of both gases in combination. In contrast, 30% CO2 alone had only a minor effect and photobacteria are supposed to have a growth advantage over other meat spoilers in this atmosphere. Additionally, single growth of the strains in the different atmospheres was compared when challenged with the presence of Pseudomonas (Ps.) fragi or Brochothrix (B.) thermosphacta as prominent co-contaminants in different ratios (10:1, 1:1, 1:10). Presence of co-contaminants resulted in increased cell numbers of P. carnosum TMW2.2149 but reduced or unchanged cell numbers of P. phosphoreum TMW2.2103 in most packaging atmospheres. The initial ratio of photobacteria and co-contaminants defined the relative abundance during storage but did not change the type of the interaction. Our results suggest either a commensalistic (P. carnosum) or competitive interaction (P. phosphoreum) of photobacteria and co-contaminants on modified atmosphere packaged chicken, respectively. Furthermore, in a mix comprising seven prominent spoilers, strains of both Photobacterium species prevailed as a constant part of the spoilage microbiome during 7 days of refrigerated storage on chicken meat packaged under O2/CO2 atmosphere.