Psychrophilic Growth Research Articles

Biomolecular Analysis of Arctic Microorganisms Capable of Psychrophilic Growth on Biodegradable and Compostable Plastic

Biomolecular Analysis of Arctic Microorganisms Capable of Psychrophilic Growth on Biodegradable and Compostable Plastic

Aeromonas salmonicida intraspecies divergence revealed by the various strategies displayed when grazed by Tetrahymena pyriformis.

Worldwide, Aeromonas salmonicida is a major bacterial pathogen of fish in both marine and freshwater environments. Despite psychrophilic growth being common for this species, the number of characterized mesophilic strains is increasing. Thus, this species may serve as a model for the study of intraspecies lifestyle diversity. Although bacteria are preyed upon by protozoan predators, their interaction inside or outside the phagocytic pathway of the predator can provide several advantages to the bacteria. To correlate intraspecies diversity with predation outcome, we studied the fate of psychrophilic and mesophilic strains of A. salmonicida cocultured with the ciliate Tetrahymena pyriformis. A total of three types of outcome were observed: digestion, resistance to phagocytosis, and pathogenicity. The psychrophilic strains are fully digested by the ciliate. In contrast, the mesophilic A. salmonicida subsp. pectinolytica strain is pathogenic to the ciliate. All the other mesophilic strains display mechanisms to resist phagocytosis and/or digestion, which allow them to survive ciliate predation. In some cases, passage through the phagocytic pathway resulted in a few mesophilic A. salmonicida being packaged inside fecal pellets. This study sheds light on the great phenotypic diversity observed in the complex range of mechanisms used by A. salmonicida to confront a predator.

Optimization of in-package cold plasma treatment conditions for raw chicken breast meat with response surface methodology

Response surface methodology (RSM) was used to optimize in-package cold plasma (IPCP) treatment for raw chicken breast meat. Non-inoculated and inoculated samples with Campylobacter (5.06 log10 CFU/mL) and Salmonella (5.40 log10 CFU/mL) were packaged in 35% O2/60% CO2, 65% O2/30% CO2, or 95% O2/0% CO2 and treated at 60, 70, or 80 kV for 60, 180, or 300 s. Microbial counts, color, pH, and drip loss were measured. There were no differences in Campylobacter, Salmonella, drip loss, or pH between treatments. IPCP could reduce psychrophiles by >1.0 log, depending on O2 and voltage interaction. Treatment effects on meat color varied by CIE L*a*b*. RSM analysis suggested that packaging atmosphere with 35% O2 and 60% CO2 and IPCP at 60 kV for 60 s were the optimal condition for maximizing microbiological shelf-life and minimizing appearance changes in raw chicken meat packaged in a barrier film and stored at 4 °C for 5 days. The current study used response surface methodology to determine the optimal condition in the combination of voltage and time of an in-package cold plasma (IPCP) treatment and modified atmosphere (MA) packaging for extending shelf life and reducing food safety risk of pre-packaged raw chicken breast meat during refrigerated storage. Our data provided evidence that the optimal IPCP-treatment parameters and packaging atmosphere varied with targeted microorganisms and CIEL*a*b* color indicators. In MA packaging, changes in IPCP treatment voltage and time did not affect populations of Campylobacter and Salmonella, drip loss and pH; however, low IPCP treatment voltage (60 kV) for short exposure time (60 s) was as effective as the high voltage (80 kV) for longer treatment time (300 s) against psychrophiles and could reduce the changes in raw meat appearance (indicated with CIEL* measurements) due to IPCP treatment. Reducing O2 in packages from 95 to 35% resulted in better inhibition of psychrophilic growth on raw meat and changes in raw meat appearance or meat color lightness. It is recommended to use MA of 35% O2 and 60% CO2 and IPCP treatment at 60 kV for 60 s to extend microbiological shelf life, improve food safety, and retain quality of raw chicken breast meat packaged with a barrier film and stored at refrigerated temperature.

In-Package Air Cold Plasma Treatment of Chicken Breast Meat: Treatment Time Effect

The objective of this study was to investigate the effects of in-package dielectric barrier discharge (DBD) atmospheric cold plasma (CP) on meat color, microbiological quality and safety of chicken breast meat (pectoralis major). Raw broiler breast meat was collected from a local commercial plant. Noninoculated meat samples and meat samples inoculated with Campylobacter and Salmonella were packed in polymeric trays with air. The packaged samples were CP-treated at 70 kV for different times (0, 60, 180, or 300 sec) and stored at 4°C for 5 days. Microbial counts (psychrophiles, Campylobacter, Salmonella) and meat color (International Commission on Illumination (CIE) L∗a∗b∗) were measured before CP treatments and after 5 days of posttreatment storage. Psychrophile growth was inhibited (P<0.05), and both food-borne pathogens were reduced (P<0.05) by more than 90% with CP treatments regardless of treatment time. No differences in pathogenic bacterial counts were observed between the three treatment times; however, increasing treatment time beyond 60 sec resulted in additional inhibition of psychrophilic growth. There were no differences (P>0.05) in a∗ and b∗ values between pretreatment and posttreatment plus storage; however, all CP treatments resulted in increased L∗ value (P<0.05). Results indicate that in-package CP treatments can be used to reduce both microbial spoilage and food-borne pathogen risks, which could increase microbial food safety, although it may result in an overall paler breast meat, and the reduction (about 1 log) in pathogenic and spoilage microbes are limited.

Monitoring of spoilage-associated microbiota on modified atmosphere packaged beef and differentiation of psychrophilic and psychrotrophic strains.

This study aimed to explore the discriminatory power of MALDI-TOF MS as a high-throughput method to monitor growth dynamics of meat-spoiling bacteria on modified atmosphere packaged (MAP) beef and to differentiate psychrophilic and psychrotrophic spoilage-associated strains. MAP beef steaks were incubated for 21days at constant 4 and 10°C. Development of headspace gas composition, pH, CFU and spoilage-associated microbial composition were monitored. MALDI-TOF MS exhibited high discriminatory power for reliable, high-throughput identification of spoilage-associated, psychrotrophic microbiota. Microbiota development was highly dependent on initial abundance of specific species. Organoleptic onset of spoilage was concomitant with an alteration of headspace atmosphere and pH. Screening for psychrophiles at 4°C on beef revealed the abundance of Leuconostoc gelidum subsp. gelidum TMW2·1998 with characteristic psychrophilic growth behaviour. We suggest that control of initial contaminants is crucial to predict the onset of spoilage and that headspace atmosphere and pH are important parameters with spoilage-indicative potential. MALDI-TOF MS proved suitable for high-resolution monitoring of psychrotrophic and psychrophilic spoilage-associated microbiota and enables improved insights in the spoilage progress. The presence of psychrophilic strains on beef is the likely causative for unexplained spoilage events.

Temperature-Dependence of Lipid A Acyl Structure in Psychrobacter cryohalolentis and Arctic Isolates of Colwellia hornerae and Colwellia piezophila.

Lipid A is a fundamental Gram-negative outer membrane component and the essential element of lipopolysaccharide (endotoxin), a potent immunostimulatory molecule. This work describes the metabolic adaptation of the lipid A acyl structure by Psychrobacter cryohalolentis at various temperatures in its facultative psychrophilic growth range, as characterized by MALDI-TOF MS and FAME GC-MS. It also presents the first elucidation of lipid A structure from the Colwellia genus, describing lipid A from strains of Colwellia hornerae and Colwellia piezophila, which were isolated as primary cultures from Arctic fast sea ice and identified by 16S rDNA sequencing. The Colwellia strains are obligate psychrophiles, with a growth range restricted to 15 °C or less. As such, these organisms have less need for fluidity adaptation in the acyl moiety of the outer membrane, and they do not display alterations in lipid A based on growth temperature. Both Psychrobacter and Colwellia make use of extensive single-methylene variation in the size of their lipid A molecules. Such single-carbon variations in acyl size were thought to be restricted to psychrotolerant (facultative) species, but its presence in these Colwellia species shows that odd-chain acyl units and a single-carbon variation in lipid A structure are present in obligate psychrophiles, as well.

The ecology of pelagic freshwater methylotrophs assessed by a high-resolution monitoring and isolation campaign.

Methylotrophic planktonic bacteria fulfill a particular role in the carbon cycle of lakes via the turnover of single-carbon compounds. We studied two planktonic freshwater lineages (LD28 and PRD01a001B) affiliated with Methylophilaceae (Betaproteobacteria) in Lake Zurich, Switzerland, by a combination of molecular and cultivation-based approaches. Their spatio-temporal distribution was monitored at high resolution (n=992 samples) for 4 consecutive years. LD28 methylotrophs constituted up to 11 × 10(7) cells l(-1) with pronounced peaks in spring and autumn-winter, concomitant with blooms of primary producers. They were rare in the warm water layers during summer but abundant in the cold hypolimnion, hinting at psychrophilic growth. Members of the PRD01a001B lineage were generally less abundant but also had maxima in spring. More than 120 axenic strains from these so far uncultivated lineages were isolated from the pelagic zone by dilution to extinction. Phylogenetic analysis separated isolates into two distinct genotypes. Isolates grew slowly (μmax=0.4 d(-1)), were of conspicuously small size, and were indeed psychrophilic, with higher growth yield at low temperatures. Growth was enhanced upon addition of methanol and methylamine to sterile lake water. Genomic analyses of two strains confirmed a methylotrophic lifestyle with a reduced set of genes involved in C1 metabolism. The very small and streamlined genomes (1.36 and 1.75 Mb) shared several pathways with the marine OM43 lineage. As the closest described taxa (Methylotenera sp.) are only distantly related to either set of isolates, we propose a new genus with two species, that is, 'Candidatus Methylopumilus planktonicus' (LD28) and 'Candidatus Methylopumilus turicensis' (PRD01a001B).

Occurrence of trans monounsaturated and polyunsaturated fatty acids in Colwellia psychrerythraea strain 34H.

Colwellia psychrerythraea strain 34H is an obligately psychrophilic bacterium that has been used as a model cold-adapted microorganism because of its psychrophilic growth profile, significant production of cold-active enzymes, and cryoprotectant extracellular polysaccharide substances. However, its fatty acid components, particularly trans unsaturated fatty acids and long-chain polyunsaturated fatty acids (LC-PUFAs), have not been fully investigated. In this study, we biochemically identified Δ9-trans hexadecenoic acid [16:1(9t)] and LC-PUFAs such as docosahexaenoic acid. These results are comparable with the fact that the strain 34H genome sequence includes pfa and cti genes that are responsible for the biosynthesis of LC-PUFAs and trans unsaturated fatty acids, respectively. Strain 34H cells grown under static conditions at 5 °C had higher levels of 16:1(9t) than those grown under shaken conditions, and this change was accompanied by an antiparallel decrease in the levels of Δ9-cis hexadecenoic acid [16:1(9c)], suggesting that the cis-to-trans isomerization reaction of 16:1(9c) is activated under static (microanaerobic) culture conditions, that is, the enzyme could be activated by the decreased dissolved oxygen concentration of cultures. On the other hand, the levels of LC-PUFAs were too low (less than 3% of the total), even for cells grown at 5 °C, to evaluate their cold-adaptive function in this bacterium.

Triacylglyceride composition and fatty acyl saturation profile of a psychrophilic and psychrotolerant fungal species grown at different temperatures

Pseudogymnoascus destructans is a psychrophilic fungus that infects cutaneous tissues in cave dwelling bats, and it is the causal agent for white nose syndrome (WNS) in North American (NA) bat populations. Geomyces pannorum is a related psychrotolerant keratinolytic species that is rarely a pathogen of mammals. In this study, we grew P. destructans and G. pannorum in static liquid cultures at favourable and suboptimal temperatures to: 1) determine if triacylglyceride profiles are species-specific, and 2) determine if there are differences in fatty acyl (FA) saturation levels with respect to temperature. Total lipids isolated from both fungal spp. were separated by thin-layer chromatography and determined to be primarily sterols (∼15%), free fatty acids (FFAs) (∼45%), and triacylglycerides (TAGs) (∼50%), with minor amounts of mono-/diacylglycerides and sterol esters. TAG compositions were profiled by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF). Total fatty acid methyl esters (FAMEs) and acyl lipid unsaturation levels were determined by gas chromatography-mass spectrometry (GC-MS). Pseudogymnoascus destructans produced higher proportions of unsaturated 18C fatty acids and TAGs than G. pannorum. Pseudogymnoascus destructans and G. pannorum produced up to a two-fold increase in 18:3 fatty acids at 5°C than at higher temperatures. TAG proportion for P. destructans at upper and lower temperature growth limits was greater than 50% of total dried mycelia mass. These results indicate fungal spp. alter acyl lipid unsaturation as a strategy to adapt to cold temperatures. Differences between their glycerolipid profiles also provide evidence for a different metabolic strategy to support psychrophilic growth, which may influence P. destructans' pathogenicity to bats.

Combination of electrolysed water, UV-C and superatmospheric O2 packaging for improving fresh-cut broccoli quality

The effects of neutral electrolysed water (NEW), ultraviolet light C (UV-C) and superatmospheric O2 packaging (HO), single or combined, on the quality of fresh-cut kailan-hybrid broccoli for 19 days at 5 °C were studied. As controls, washing with water and sanitation with NaClO were both used. Electrolyte leakage, sensory, microbial and nutritional quality changes throughout shelf-life were studied. At day 15, the combined treatments achieved lower mesophilic and psychrophilic growth compared to the single ones. Single treatments produced higher ascorbate peroxidase (APX) reductions just after its application, while superoxide dismutase (SOD) showed the opposite behaviour. After 5 days at 5 °C, a great increase of APX and guaiacol peroxidase (GPX) activity was observed, NEW + UV-C + HO and HO-including treatments achieving the highest and the lowest APX increases, respectively. UV-C-including treatments produced the highest α-linolenic acid (ALA) decreases ranging 35–38% over control contents on the processing day. NEW-including treatments greatly reduced, throughout shelf-life, ALA and stearic acid (SA) content by 27–44% and 31–61%, respectively. Total phenolic content and antioxidant capacity (1415 mg ChAE kg−1 fw and 287 mg AAE kg−1 fw, respectively) remained quite constant during shelf-life. In general, the treatments and their possible combinations seem to be promising techniques to preserve, or even enhance, the quality of fresh-cut kailan-hybrid broccoli and, probably, other vegetables.

Effect of selected modified atmosphere packaging on Campylobacter survival in raw poultry

Most current research on Campylobacter has focused on preharvest or processing plant cross-contamination. Little is known about the effect of storage environment on the survival of Campylobacter on raw poultry. We evaluated the effects of modified storage atmosphere and freezing on the survival of naturally occurring Campylobacter on raw poultry. Broiler carcasses (n = 560) were collected as they exited the chiller in 2 commercial processing plants and were sampled for the detection of Campylobacter, Escherichia coli, psychrophiles, and total aerobes at 0 and 14 d of refrigerated (2°C) storage. Gases evaluated were air, 100% O(2), 100% CO(2), and a standard poultry modified atmosphere packaging mixture (5% O(2) + 10% CO(2) + 85% N). Freezing was included as a control group. All carcasses were sampled by the whole-carcass rinse method. The rinse fluid was recovered and pooled from 5 individual rinses, and serial dilutions were made for examination of Campylobacter (42°C, 48 h), E. coli (37°C, 24 h), psychrophiles (plate count agar, 4°C, 7 d), and total aerobic bacterial populations (plate count agar, 37°C, 24 h). Campylobacter counts for all treatments were reduced during the 14-d storage period but the 100% O(2) treatment caused a significantly (P < 0.05) greater reduction than the other gas treatments. For the psychrophiles, storage in air resulted in the greatest growth after 14 d, with reduced psychrophilic growth allowed by either O(2) or the modified atmosphere packaging mixture (not different from each other). Of the treatments evaluated, CO(2) allowed the least growth of psychrophiles. Proliferation of E. coli and aerobes was the greatest when packaged in air after 14 d, whereas CO(2) packaging resulted in the least growth. These data suggest that storage under O(2) may reduce Campylobacter recovery and slow psychrophile and aerobe recovery following storage.

The protein folding challenge in psychrophiles: facts and current issues

The protein folding process in psychrophiles is impaired by low temperature, which exerts several physicochemical constraints, such as a decrease in the folding rate, reduced molecular diffusion rates and increased solvent viscosity, which interfere with conformational sampling. Furthermore, folding assistance is required at various folding steps according to the protein size. Recent studies in the field have provided contrasting and sometimes contradictory results, although protein folding generally appears as a rate-limiting step for the growth of psychrophiles. It is proposed here that these discrepancies reflect the diverse adaptive strategies adopted by psychrophiles in order to allow efficient protein folding at low temperature. Cold adaptations apparently superimpose on pre-existing cellular organization, resulting in different adaptive strategies. In addition, microbial lifestyle further modulates the properties of the chaperone machinery, which possibly explains the occurrence of cold-adapted and non-cold-adapted protein chaperones in psychrophiles.

Morphological and Molecular Characterizations of Psychrophilic Fungus Geomyces destructans from New York Bats with White Nose Syndrome (WNS)

BackgroundMassive die-offs of little brown bats (Myotis lucifugus) have been occurring since 2006 in hibernation sites around Albany, New York, and this problem has spread to other States in the Northeastern United States. White cottony fungal growth is seen on the snouts of affected animals, a prominent sign of White Nose Syndrome (WNS). A previous report described the involvement of the fungus Geomyces destructans in WNS, but an identical fungus was recently isolated in France from a bat that was evidently healthy. The fungus has been recovered sparsely despite plentiful availability of afflicted animals.Methodology/Principal FindingsWe have investigated 100 bat and environmental samples from eight affected sites in 2008. Our findings provide strong evidence for an etiologic role of G. destructans in bat WNS. (i) Direct smears from bat snouts, Periodic Acid Schiff-stained tissue sections from infected tissues, and scanning electron micrographs of bat tissues all showed fungal structures similar to those of G. destructans. (ii) G. destructans DNA was directly amplified from infected bat tissues, (iii) Isolations of G. destructans in cultures from infected bat tissues showed 100% DNA match with the fungus present in positive tissue samples. (iv) RAPD patterns for all G. destructans cultures isolated from two sites were indistinguishable. (v) The fungal isolates showed psychrophilic growth. (vi) We identified in vitro proteolytic activities suggestive of known fungal pathogenic traits in G. destructans.Conclusions/SignificanceFurther studies are needed to understand whether G. destructans WNS is a symptom or a trigger for bat mass mortality. The availability of well-characterized G. destructans strains should promote an understanding of bat–fungus relationships, and should aid in the screening of biological and chemical control agents.

Characterization and recombinant expression of a divergent ice nucleation protein from ‘Pseudomonas borealis’

Isolates of 'Pseudomonas borealis' were recovered after ice-affinity selection of summer-collected soils. 'P. borealis' DL7 was further characterized and shown to have ice nucleation activity (INA), a property that allows the crystallization of ice at temperatures close to the melting point, effectively preventing the supercooling of water. INA was optimally detected after culturing at temperatures consistent with psychrophilic growth. The sequence encoding the 'P. borealis' ice nucleation protein (INP) was obtained using both PCR and chromosome walking. When expressed in Escherichia coli, the resulting inaPb recombinants had INA. The 'P. borealis' sequence, dubbed inaPb, is clearly related to previously cloned INP genes, but it shows greater divergence. Sequence analysis suggests that there are two opposite flat surfaces, one relatively hydrophobic that likely serves as an ice template, and the other that could function as a complementary face to facilitate interprotein interaction for ice-step formation.

Two onygenalean fungi from Russian Far East soil

Two onygenalean fungi isolated from forest soil in the Sikhote-Alin reserve, Russian Far East (east Siberia), are described and illustrated:Gymnostellatospora parvula as a new species andAphanoascus canadensis as a new record.Gymnostellatospora parvula is characterized by psychrophilic growth, pale yellow to pale cinnamon ascomata with a hyphal peridium, small, hyaline discoid ascospores with an equatorial rim and more or less longitudinally ridged wall.

Microbiological Evaluation of Navy Bean Protein Concentrate and Its Blend With Retail Ground Beef

ABSTRACTA protein concentrate (NPC), obtained by alkali extraction of navy beans, was used as a model medium for microbial growth. Only three among eight bacterial cultures (Pediococcus spp, Pseudomonas spp and Streptococcus spp) grew better on mediums with NPC than on the control nutrient broth. Retail ground beef with and without 5%, 10%, and 15% NPC was wrapped with plastic film and stored up to 6 days at 4°C. Aerobic plate count, psychrophiles, coliforms, yeasts and molds were determined at 0, 3, and 6 days. All levels of NPC added to ground beef had a significant influence on aerobic plate count and coliforms. Growth of psychrophiles and yeasts and molds was not affected by NPC. Lactobacillus spp was a dominant part of the microflora of all samples.

Microbiological evaluation of navy bean flour and its blend with retail ground beef

Sterile water suspensions of navy bean flour (NF) were used as a model medium on which the growth of eight microorganisms important for food hygiene and technology was evaluated. Almost all microorganisms grew better on model mediums with 10 and 15% of NF than on the nutrient broth (control). Retail ground beef with and without 5, 10 and 15% addition of NF was wrapped with plastic film and stored at 4°C. Aerobic plate count, psychrophiles, coliforms and yeasts and molds were assessed after 0, 3 and 6 days. Navy bean flour added to ground beef had a significant effect only on aerobic plate count. Growth of psychrophiles, coliforms, yeasts and molds was not affected by addition of NF. Microflora of retail ground beef-NF blends mainly consisted of Lactobacillus spp., while other genera of bacteria were found in smaller numbers. The pH of blends increased in proportion to the level of NF added and was significantly higher in comparison with retail ground beef alone, but decreased during storage due to the large amount of lactic acid bacteria.

SYMBIOTIC ASSIMILATION OF CO2IN TWO HYDROTHERMAL VENT ANIMALS, THE MUSSELBATHYMODIOLUS THERMOPHILUSAND THE TUBE WORMRIFTIA PACHYPTILA

Shipboard studies showed major differences in the incorporation of CO2 by the specific prokaryotic symbionts of two deep-sea vent invertebrates. The rate of CO2 fixation was optimal at approximately 22°Cin fresh trophosome material from the pogonophoran tube worm R@/1iapachyptila. Sulfide, but not thiosulfate, served as the electron donor. Thirty-five percent ofthe aerobic rate remained in deoxygenated sam pies presumablydue to traces of hemoglobin-bound oxygen. Gill preparationsfrom the mytilid mussel Bathymodiolus thermophilus,however, assimilated CO2 with a maximum rate at 12° to 15°C. Thiosulfate, but not sulfide, served as the electron donor.The activitywascompletelyinhibitedin deoxygenatedsamples.Thesemetabolic dissimilarities between the symbionts ofthe two hosts extend to DNA base ratios and cell sizes. Partialfractionationofthe mussel gill preparationyielded a prokaryoticor “?�bacterial” fraction that showed a CO2 assimilation rate three-fold higher than that of the crude homogenate. This activity was not affected by the in situ hydrostatic pressure of 250 atm (100% barotolerance). The mussel gill symbiont represents the first sulfur-oxidizing vent prokaryote with psychrophilic growth characteristics. The natural distribution ofR. pachyptila and B. thermophilus within the physico-chemical regime ofthe immediate vent vicinity corresponds well with the metabolic differences oftheir symbionts.

Temperature-induced alanine oxidation in a psychrotrophic Pseudomonas.

A psychrotrophic pseudomonad isolated from iced fish oxidized alanine at temperatures close to 0 degrees C and grew over the range 0 degrees C-35 degrees C. The rate of oxidation of alanine, measured manometrically, by cells grown at 2 degrees C was lower than that of cells grown at 22 degrees C. However, the consumption of oxygen after heat treatment at 35 degrees for 35 min was reduced considerably by 2 degrees C grown cells. Alanine oxidase activity was tested in an extract from cells grown at 2 degrees C and 22 degrees C with alanine as the sole carbon, nitrogen, and energy source. Cells grown at 2 degrees C produced an alanine oxidase with a temperature optimum of 35 degrees C and pH optimum of 8, which lost about 80% activity by heat treatment at 40 degrees C for 30 min. There was no change in activity after dialysis at pH 7, 8, or 9. Extracts from cells grown at 22 degrees C contained an alanine oxidase system with an optimum temperature of 45 degrees C, a pH optimum above 8, and only about 30% reduction of activity after heat treatment. This enzyme activity was concentrated in the 0.5 M elution fraction from a Sephadex column, and dialysis reduced the activity at pH 7 and 8. Mesophilic enzyme synthesis apparently started around a growth temperature of 10 degrees C. The crude alanine oxidase systems of Pseudomonas aeruginosa derived from cells grown at 13 degrees C and 37 degrees C had a common optimum temperature of 45 degrees C. These data suggest that one mechanism of psychrophilic growth by psychrotrophic bacteria may be the induction of enzymes with low optimum temperatures in response to low temperature conditions.

Microbial Counts and Rancidity of Fresh Fryer Chickens as Affected by Packaging Materials, Storage Atmosphere, and Temperature

Abstract CARBON dioxide has proved to be beneficial in extending shelf life of chilled poultry. Ogilvy and Ayres (1951) found improved storage life of chicken in up to 25 percent CO2. Wabeck et al. (1968) found that growth of psychrophiles on chicken was inhibited by 10 or 20 percent CO2, but coliforms remained relatively stable. Commercial systems utilizing dry ice as a source of CO2 in shipping boxes were described for unpackaged chicken by Lemmons (1966) and for prepackaged chicken by Burkhart (1966). Effect of packaging material on microbiological condition of chilled unfrozen chicken meat has been studied. Spencer et al. (1956) found that birds packaged in evacuated heat shrinkable polyethylene and polyvinylidene film had longer shelf-life than those in standard cellophane or polyethylene. Wells et al. (1958), using “days to spoilage” as the criterion for shelf-life, found that packaging with either unevacuated cellophane or unevacuated vinylidene chloride copolymer films resulted…