Extension of shelf-life of chilled sliced roast beef by carbon dioxide packaging

Microbiota encompassing putative spoilage bacteria in retail packaged broiler meat and commercial broiler abattoir

It is well established, that certain bacteria within the Brochothrix, Carnobacterium, Lactobacillus, Lactococcus, and Leuconostoc genera have an important role in the spoilage of chill stored poultry meat packaged in modified atmosphere. However, little is known about the role of microorganisms that are difficult to culture and the microbiota during poultry spoilage. We combined traditional cultivation and culture-independent 16S rRNA amplicon sequencing to investigate the microbiota encompassing putative bacteria of whole broiler meat, packaged in modified atmosphere, during and exceeding shelf-life. Samples were taken from 6 flocks during independent slaughter days. Additional samples were analysed from the production line. There was a significant difference in the microbial community structure of 80%O₂/20%CO₂ retail packaged broiler meat during different times of shelf-life, mainly due to an increase of species within the Brochothrix, Carnobacterium, Vagococcus, and Janthinobacterium genera. These genera were already detected four to eight days after slaughter. However, no significant difference between flocks with respect to the microbiota encompassing putative spoilage bacteria was observed when examined in retail packaged broilers, slaughtered at the same abattoir on different days. Our study also showed that lactic acid bacteria within the Vagococcus genus can constitute a dominating part of the later shelf-life microbiota in fresh whole broiler meat packaged in 80%O₂/20%CO₂ modified atmosphere. A single operational taxonomic unit (OTU) assigned as Janthinobacterium lividum, an occasional spoiler of meat products, was identified as a major part of the microbiota in late shelf life broiler meat and swab samples in the cooling facility at the slaughter house production line. The combination of traditional cultivation and culture-independent methods provided a great insight into the microbiota of broiler meat during shelf-life and identified a potential point of contamination in the production line for cold tolerant Janthinobacterium.

Shelf-life of a chilled precooked chicken product stored in air and under modified atmospheres: microbiological, chemical, sensory attributes

This study evaluated the effect of modified atmosphere packaging on shelf-life extension of a precooked chicken meat product stored at 4 degrees C using microbiological, physico-chemical and sensory analyses. The following gas mixtures were used: M1: 30%/70% (CO2/N2), M2: 60%/40% (CO2/N2) and M3: 90%/10% (CO2/N2). Identical chicken samples were aerobically packaged and used as control samples. Sampling was carried out at predetermined time intervals namely: 0, 4, 8, 12, 16 and 20 days. Total viable counts (TVC), Lactic acid bacteria (LAB), Brochothrix thermosphacta, pseudomonads, yeasts and molds, and Enterobacteriaceae were monitored. TVC of precooked chicken product reached 7 log cfu/g, after days 12 and 16 of storage (air and M1 samples), respectively. The M2 and M3 gas mixture packaged samples did not reach this value throughout the 20 days storage period under refrigeration. LAB and to a lesser degree B. thermosphacta, constituted part of the natural microflora of precooked chicken samples stored in air and under MAP reaching 7.0-8.1 log cfu/g at the end of storage period. Of the remaining bacterial species monitored, both pseudomonads and yeasts/molds were significantly higher (P<0.05) for chicken samples stored in air than under MAP (M1, M2, M3) throughout the entire storage period under refrigeration. Finally, counts of Enterobacteriaceae were low (<2 log cfu/g) in all chicken samples irrespective of the packaging conditions throughout the entire storage period. Of the chemical indices determined, thiobarbituric (TBA) values in all cases remained low, equal or lower than 3.0 mg malonaldehyde (MA)/kg during the entire storage period. Results of the present work show that the limit of sensory acceptability was only reached for the aerobically stored and M1 gas mixture chicken samples somewhat before days 16 and 20 of storage, respectively. This limit coincided with high TVC and LAB populations (>6.8 log cfu/g), increased lipid oxidation (aerobic storage only) and apparent growth of yeasts/moulds on the surface of chicken samples. The use of MAP as shown in the present study, resulted in an extension of shelf-life of precooked chicken by ca. 4 days (M1 gas mixture), and by more than 6 days (M2 and M3 gas mixtures), respectively. Precooked chicken meat was better preserved under M2 and M3 mixtures maintaining desirable odor/taste attributes even on final day of storage tested.

Cresol red thallium acetate sucrose inulin (CTSI) agar for the selective recovery of Carnobacterium spp

Carnobacterium spp. are commonly isolated from a variety of foods, especially from meats stored under anaerobic atmospheres at refrigeration temperatures, but the role of these organisms in the spoilage of meat and meat products is yet to be determined. Cresol Red Thallium Acetate Sucrose (CTAS) agar was developed as a selective medium for enumeration of carnobacteria, however problems such as poor recovery of Carnobacterium spp. and interference by other microorganisms have precluded its general use. The aim of this study was to improve CTAS agar by broadening its spectrum of selective recovery for carnobacteria while restricting the ability of interfering species to grow. Ten Carnobacterium spp. (five ATCC cultures and five isolates from fresh pork) and 20 other genera were used in testing the agar. A wider range of Carnobacterium spp. recovery was obtained by modifying concentrations of sucrose, manganese sulphate and thallium acetate. Additions of inulin and thiamine hydrochloride also improved growth response. The additions of vancomycin and Chrisin (nisin) eliminated interference from other microorganisms. A two-temperature incubation procedure was included to improve the characteristic growth of Carnobacterium spp. on the modified medium, identified as Cresol Red Thallium Sucrose Inulin (CTSI) agar. Lactic acid bacteria and Enterobacteriaceae were unable to grow on CTSI incubated aerobically. Growth of Carnobacterium spp. on CTSI yielded pink colonies, except for Cb. mobile, which formed gray colonies. In some instances, a red precipitate formed in the center of the colony. Yellowing and clearing of the growth medium was also frequently observed. Recovery of carnobacteria using CTSI was identical to that obtained with All Purpose Tween (APT) agar.

Effects of modified atmosphere and vacuum packaging on the growth of spoilage and inoculated pathogenic bacteria on fresh poultry

Fresh chicken breast meats inoculated with Yersinia enterocolitica and Aeromonas hydrophila were packaged in glass jars either containing different compositions of modified atmospheres (MA) (100% CO2; 80% CO2/20% N2), or in vacuo or containing air, and were stored at 3 +/- 1 degrees C and 8 +/- 1 degrees C. The changes in gas composition as well as Y. enterocolitica, A. hydrophila, total aerobic bacterial, total psychotropic, Lactobacilli and Enterobacteriaceae counts were determined after 0, 1, 3, 7, 9, 11 and 14 days of storage. The results show that while the growth of Y. enterocolitica and A. hydrophila were retarded following MA storage, the pathogens were capable of growth in MA and vacuum storage at both temperatures, for the inoculation levels studied. For total aerobic bacterial counts, there were no differences between the values for chicken breast meats kept in different atmospheres. Being packaged in CO2 had the greatest inhibitory effect on the growth of psychotropic aerobic bacteria during the first 3 days. Lactic acid bacteria levels of samples stored in MA conditions and in vacuo increased rapidly when compared to those levels of samples stored in air. It was also found that the effect of MA storage increased at 3 +/- 1 degrees C.