Metatranscriptomic analysis of modified atmosphere packaged poultry meat enables prediction of Brochothrix thermosphacta and Carnobacterium divergens in situ metabolism.

In this study, in situ-expressed metabolic routes of Brochothrix (B.) thermosphacta and Carnobacterium (C.) divergens were evaluated based on a metatranscriptomic dataset from bacteria growing on MAP chicken meat (O2/CO2; N2/CO2). Both species exhibited no (C. divergens) or minor transcription regulation (B. thermosphacta) within their main metabolic routes in response to different atmospheres. Both employ pathways related to glucose and ribose. Gluconeogenesis from lipid-borne glycerol is active in the progressing lack of carbohydrates. Pyruvate fates in both species comprise lactate, ethanol, acetate, CO2, formate, C4-compounds and H2O2 (only B. thermosphacta). Both species express genes for a minimal aerobic respiratory chain, but do not possess the genetic setting for a functional citric acid cycle. While products of carbohydrate and glycerol metabolism display mild to medium sensorial off-characteristics, predicted end products of their amino acid metabolism comprise, e.g., isobutyrate and isovalerate (B. thermosphacta) or cadaverine and tyramine (C. divergens) as potent spoilage compounds.

Identification and growth dynamics of meat spoilage microorganisms in modified atmosphere packaged poultry meat by MALDI-TOF MS.

Modified atmosphere packaging (MAP) is widely used in food industry to extend the microbiological shelf-life of meat. Typically, poultry meat has been packaged in a CO2/N2 atmosphere (with residual low O2). Recently, some producers use high O2 MAP for poultry meat to empirically reach comparable shelf lifes. In this work, we compared spoilage microbiota of skinless chicken breast in high (80% O2, 20% CO2) and low O2 MAP (65% N2 and 35% CO2). Two batches of meat were incubated in each atmosphere for 14 days at 4 °C and 10 °C. Atmospheric composition of each pack and colony forming units (25 °C, 48 h, BHI agar) of poultry samples were determined at seven timepoints. Identification of spoilage organisms was carried out by MALDI-TOF MS. Brochothrix thermosphacta, Carnobacterium sp. and Pseudomonas sp. were the main organisms found after eight days at 4 °C and 10 °C in high O2 MAP. In low O2 MAP, the main spoilage microbiota was represented by species Hafnia alvei at 10 °C, and genera Carnobacterium sp., Serratia sp., and Yersinia sp. at 4 °C. High O2 MAP is suggested as preferential gas because were less detrimental and pathogens like Yersinia were not observed.

Prediction of in situ metabolism of photobacteria in modified atmosphere packaged poultry meat using metatranscriptomic data.

Modified atmosphere packaging (MAP) is widely used in food industry to extend the microbiological shelf life of meat. Common CO2-containing gas atmospheres for poultry meat packaging are either nearly O2-free or high O2 MAPs. In this work, we compared spoilage microbiota of skinless chicken breast in CO2/O2 (30/70%) and CO2/N2 (30/70%) MAP, which are culturable with conventional methods and identified isolates by MALDI-TOF MS. These data were compared to metatranscriptome sequencing enabling a culture-independent overview on the composition of microbiota at species level. While typical MAP meat spoilers were confirmed in the transcriptomic approach, we also found high numbers of transcripts mapping to Photobacterium spp. sequences in these samples. As photobacteria were recently shown to occur in different MAP and vacuum packaged meats, we used the respective part of the metatranscriptomic data for prediction of Photobacterium spp. major metabolic routes in situ, upon growth in MAP poultry meat. It is predicted that they employ similar metabolism in both atmospheres: In the lack of carbohydrates upon meat spoilage, the pyruvate pool is filled via glycerol originating from lipolysis and amino acid conversions. From the pyruvate pool, gluconeogenesis is fed enabling cell wall biosynthesis and growth as well as catabolism to lactate and other metabolites, or anaplerosis towards the citric acid cycle. Production is predicted of several biogenic amines including tyramine and cadaverine, enabling generation of proton motive force. Taken together, photobacteria express metabolic pathways upon growth on meat, which should lead to compounds overlapping with those of known potent meat spoilers.