Journal of Applied Microbiology ISSN 1364-5072

ORIGINAL ARTICLE

Packaging gas selects lactic acid bacterial communities on raw pork € rkroth1 T.T. Nieminen1,2, M. Nummela1 and J. Bjo 1 Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland 2 Ruralia institute, Faculty of Agriculture and Forestry, University of Helsinki, Sein€ ajoki, Finland

Keywords lactic acid bacteria, Lactobacillus, Lactococcus, Leuconostoc, meat, modified atmosphere, pork, spoilage. Correspondence Timo T. Nieminen, Ruralia institute, Kampusranta 9 C, FI-60320 Sein€ajoki, Finland. E-mail: [email protected] 2015/0506: received 10 March 2015, revised 29 May 2015 and accepted 20 June 2015 doi:10.1111/jam.12890

Abstract Aims: To study the effect of different CO2-rich packaging atmospheres on the composition of lactic acid bacterial communities proliferating on raw pork. Methods and Results: Raw pork loin was inoculated with a mixture of 14 lactic acid bacteria (LAB) strains previously associated with meat and packaged with four gas atmospheres: (i) 100% CO2; (ii) 80% N2, 20% CO2; (iii) 80% N2, 20% CO2, 04% CO and (iv) 80% O2, 20% CO2. The colony counts of LAB, pH and composition of packaging gas were monitored every other day during the storage of 14 days at +6°C. The compositions of lactic acid bacterial communities on pork were evaluated after 7 days of storage with cultureindependent, terminal restriction fragment length polymorphism analysis of 16S rRNA gene fragments. After 14 days of storage, the compositions of lactic acid bacterial communities were evaluated using identification of plate-grown LAB isolates by numerical ribopattern analysis. The results showed that (i) high concentration of CO2 in packaging atmosphere favoured Lactobacillus sp. (ii) high concentration of O2 favoured Leuconostoc spp. (iii) atmosphere with 80% N2, 20% CO2 favoured Lactococcus sp. Conclusions: The composition of modified packaging atmosphere is a major factor selecting lactic acid bacterial communities proliferating on raw meat. Significance and Impact of the Study: The study provides an explanation for the compositions of lactic bacterial communities on modified atmosphere packaged raw meat observed in other studies. The results should be considered when attempting to manipulate LAB communities in raw meat, e.g. by protective cultures.

Introduction According to McMillin (2008), ‘modified atmosphere packaging (MAP) is the removal and/or replacement of the atmosphere surrounding the product before sealing in vapour-barrier materials’. MAP for meat involves elevated concentrations of CO2 that extends the shelf-life by decreasing growth rate of spoilage bacteria. Different types MAP are used for different purposes. Vacuum packaging is the oldest form of MAP and is still widely used today to pack raw meat and meat products for consumers. Vacuum packaging relies on CO2 that is generated by product and/or active microbiota after the package has been sealed. 1310

Raw pork and beef are often packaged in modified atmosphere (MA) containing high concentration of O2 to maintain oxymyoglobin and red colour of meat. Because oxygen in MA shortens the shelf-life of meat (McMillin 2008; Lagerstedt et al. 2011), low concentrations (e.g. 04%) of carbon monoxide can be added instead of oxygen to maintain colour. Meat products and raw broiler meat do not require maintenance of red colour and are typically packaged in MAs containing only CO2 and N2. Several studies have been conducted to elucidate how MA composition affects meat spoilage, e.g. (Kakouri and Nychas 1994; Sørheim et al. 1999; Skandamis and Nychas 2002; Viana et al. 2005; Balamatsia et al. 2006). Many of these have also studied the effect of MA on bacterial

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communities in detail, by identifying bacterial isolates (Samelis and Georgiadou 2000; Doulgeraki et al. 2010) and/or with culture-independent, DNA-based methods (Ercolini et al. 2006, 2011a,b; Chaillou et al. 2015). These studies have well established, among other findings, that lactic acid bacteria (LAB) are typically predominating in meat after extended chilled storage under MA with elevated CO2 concentration. It is not clear, however, whether specific composition of MA has a role in selecting which LAB become predominant during the storage. LAB have varying spoilage potential (Korkeala et al. 1988; Vermeiren et al. 2005; Vihavainen and Bj€ orkroth 2007) and it is of interest to elucidate the factors that determine the composition of LAB communities in commercial meat packages. Here, we studied how four MAs with elevated CO2 concentration selected meat-associated LAB inoculated to raw pork loin. Materials and methods Inoculation of pork LAB strains originally isolated from meat or other types of food (Table 1) were selected for the experiment because of their ability to predominate in food stored chilled for extended periods and/or because they belonged to species associated with spoilage of raw meat. The strains were cultivated overnight at 25°C in Man– Rogosa–Sharpe (MRS)-broth (Difco, Detroit, MI) or tryptic soy broth (Oxoid, Basingstoke, UK). Optical densities (600 nm) of the cultures were measured and a defined volume of each culture, calculated using the formula V(ll) = OD600/15, was mixed together. The volume of the strain mixture was adjusted to 400 ml with 09% NaCl solution. Fresh pork loin (Longissimus dorsi) was purchased from the local wholesaler and cut aseptically to 5–10 g blocks. The blocks were mixed with 400 ml of bacterial suspension on metal tray. Extra liquid was poured off and the inoculated blocks were weighed to 2 dl food-grade plastic trays, 180 g per tray and mixed with 15 ml of sterile water. The dimensions of the trays were such that added liquid formed 2 mm liquid layer on an empty tray suggesting that liquid did not form a major obstacle to diffusion of gases in the packages. The trays were put in 4 l bag with oxygen barrier (Amilen Ox 90, Finnvacum, Helsinki, Finland). Septums (ø 15 mm; PBI Dansensor, Ringstedt, Denmark) were attached inside and outside each bag to create four double septa per bag for sampling purposes. The bags were filled with four different packaging gases (Table 2), four packages per gas mixture and thermally sealed. Gas mixtures were as follows: C 100% CO2; N 80% N2, 20% CO2; O 80% O2, 20% CO2; X 80%

Lactic acid bacteria on raw pork

Table 1 Bacterial strains used in this study Strain

Originally isolated from

Leuconostoc gelidum subsp. gasicomitatum LMG 18811T Leuc. gelidum subsp. gelidum NCFB 2775T Leuc. gelidum subsp. gasicomitatum KG16-1 Leuc. carnosum NCFB 2776T Lactobacillus oligofermentas DSM 15707T* Lactobacillus sp. MKJ35* Lactobacillus sp. ITSL2c* Lactococcus piscium MKFS47 Lc. piscium LTM33-6 Lc. piscium JL3-4

Marinated broiler meat

Carnobacterium Carnobacterium ATCC 35586T Carnobacterium Carnobacterium

divergens ATCC 35677T maltaromaticum

Beef Beef Vegetable sausage Broiler meat Broiler meat Broiler meat Broiler meat Pork Minced meat (beef and pork) Minced beef Diseased rainbow trout

maltaromaticum N12-7 divergens Ma8-6

Broiler meat Broiler meat

*Precultures in Tryptic Soy Broth.

N2 and 20% CO2, 04% of CO. Gas mixes C, O and N were mixed with our laboratory equipment (Witt KM 100-2 MEM gas mixer). Gas mixture X was purchased from AGA (Espoo, Finland). The packages were stored at +6  1°C. Sampling Samples were collected from each package eight times during the storage period of 14 days. First, concentrations of O2 and CO2 in the package gas were measured (Checkpoint, PBI Dansensor) through a double septum described above. Then, 7 ml of sterile distilled water was injected on pork blocks in the package through a double septum using a syringe and needle. Package was gently mixed by hand on the table plane and 7 ml of liquid was drawn from the tray with a syringe and needle. One ml of sample was used for colony counting. Two 1 ml portions were collected to two 15 ml Table 2 Measured concentrations of CO2 and O2 and calculated concentration of N2 in pork loin packages. Gas composition was measured on every other day during the 14 day monitoring period from each of the four parallel packages resulting in 32 measurements per gas mixture Concentration in packaging gas (%) Gas mixture

C N O X*

O2

CO2

Mean

SD

Mean

SD

N2 Mean

16 046 75 042

26 039 54 054

92 20 18 19

15 19 11 046

64 80 70 80

*Contained 04% of CO according to the manufacturer.

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microcentrifuge tubes and mixed with 400 ll of sterile water. The tubes were centrifuged at 200 g for 2 min and 1 ml of supernatant was collected to a 2 ml microcentrifuge tube. This tube was centrifuged at 10 000 g for 3 min, supernatant was removed and tubes containing the pellets were stored at 20°C. From the remaining portion of the original 7 ml sample, pH was measured by an inoLab pH 720 (WTW GmbH, Weilheim, Germany) instrument. LAB counts A decimal dilution series was prepared from suspension collected from pork package. Portions (01 ml) of dilutions were spread on Man–Rogosa–Sharpe agar (MRS, pH 62, Oxoid CM0361, Basingstoke, UK) and cultivated in jars made anaerobic by commercial atmosphere generation system (Oxoid AN0035) at 25°C for 5 days. Identification of LAB isolates To identify the LAB prevailing in pork, 10 colonies were randomly picked from the MRS plates containing the highest dilutions of each sample homogenate. Altogether 160 isolates were picked. To obtain pure cultures, the isolates were cultivated in MRS broth and on MRS agar. Some of the isolates were lost during isolation resulting in 111 meat isolates which were stored in MRS broth at 70°C for identification. The identified isolates were collected from the four parallel plates obtained from gas mixtures C, O and N and three parallel plates for gas mixture X (isolates from one plate were lost). The isolates were identified based on numerical analysis of 16 and 23S rRNA gene HindIII restriction fragment length polymorphism patterns (ribopatterns) as described by Vihavainen et al. (2007). In short, genomic DNA was isolated and cleaved with HindIII restriction endonuclease. The restriction fragments were separated in gel and transferred onto a nylon membrane. A mixture of labelled oligonucleotide probes was hybridized to the fragments. The resulting banding pattern was visualized, scanned and imported to BIONUMERICS software (ver. 5.1.0.; Applied Maths, Sint-Martens-Latem, Belgium). A dendrogram depicting the similarities of all the ribopatterns obtained in this study and those of inoculated strains and those of 300 type strains included in the library was generated. The isolates were identified based on their location in clusters which contain ribopatterns of type and reference strains. Species specificities of the clusters have been described earlier in several polyphasic taxonomy studies (Bj€ orkroth et al. 2002; Koort et al. 2005 and references therein) and compared with phylogenetic analysis of 16S rRNA gene sequences (Vihavainen et al. 2007). 1312

Culture-independent characterization of LAB communities by T-RFLP Bacterial DNA was extracted from the frozen pellets (see ‘Sampling’) as describe before (Nieminen et al. 2012a) to characterize the bacterial communities. Two parallel extracts were collected from each package and analysed separately. The DNA extracts were used as a template for PCR amplification of approximately 940-bp 16S rRNA gene fragment with forward primer Bact-8F (50 -AGA GTT TGA TCC TGG CTC AG) and reverse primer 926r (50 -CCG TCA ATT CMT TTG AGT TT). The primers were targeted against all bacteria. PCR, restriction digestion with enzymes Hpy8I, HinP1I and NlaIV and capillary electrophoresis was performed as described earlier (Nieminen et al. 2011). T-RFLP data matrices were created for each restriction enzyme and combined to a single data matrix for calculation of distance matrix based on Jaccard inder as described before (Nieminen et al., 2012b). The distance matrix was used for nonmetric multidimensional scaling (NMDS) that was performed in R software environment (v. 2.12.1) using the functions in the library vegan (Oksanen et al. 2011). NMDS was performed using the functions metaMDSiter and postMDS. To assign the terminal restriction fragments (T-RFs) to bacterial groups, we compared the T-RF lengths obtained with the three restriction enzymes to those measured from 130 known meat-associated strains, including Brochothrix thermosphacta, 92 LAB and 30 Gram-negative strains (Nieminen et al. 2011). Results The concentrations of O2 and CO2 were monitored in the pork loin packages throughout the experiment. Measured gas compositions remained close to the initial, planned values (Table 2). CO in gas mixture X was not measured but the red colour of meat was enhanced by CO as expected. Plate counts of LAB in pork loin drip (Fig. 1) show that the LAB growth rates were similar in gas mixtures N, O and X. The higher CO2 concentration in mixture C seemed to slow LAB growth in comparison to the other gas mixtures. The maximum mean (measured from the four parallel pork packages) LAB plate counts were in the range of 86–90 log CFU g1 in all four gas mixtures. The pH measurements of pork loin drip (Fig. 2) show that pH decreased under gas mixtures C and O from initial value of 55–56 to minimum value of 51. Under gas mixtures N and X loin drip was acidified more during the experiment and decreased to minimum of 49. The bacterial communities were characterized cultureindependently after 7 days of storage by T-RFLP using

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109

108

107

Na7a Xd7a Xc7b Xd7b Nc7b Nc7a Nd7a Xb7a Nd7b Xb7bXa7a Nb7b Xc7a Na7b Cb7b Ob7a

105

Cd7bCc7a

2

4

6

8

10

12

14

16

Time (days) Figure 1 Plate counts of lactic acid bacteria in pork loin packaged under different gas mixtures and stored at +6°C. Gas mixtures C (□), N (M), O (■), X (▲) Error bars indicate standard deviation of four parallel meat packages.

5·7 5·6 5·5

pH

5·4 5·3 5·2 5·1 5·0 4·9 0

2

4

6

8 10 Time (days)

Cd7a Cc7b Ca7a Ca7b

–0·4

0

4·8

Nb7a

–0·2

106

Od7b Cb7a Oa7a

Oc7a

0·0

0·2

Od7a Ob7b Oa7b

NMDS2

Lactic acid bacteria (log CFU g–1)

T.T. Nieminen et al.

12

14

16

Figure 2 pH development in pork loin packaged under different gas mixtures and stored at +6°C. Gas mixtures C (□), N (M), O (■), X (▲) Error bars indicate standard deviation of four parallel meat packages.

three restriction enzymes. The resulting terminal restriction fragment lengths and relative abundances were tabularized and distance matrix was calculated. NMDS was performed on these distances. The results (Fig 3.) show that the bacterial communities in pork loin packaged in gas mixtures N and X were indistinguishable from each other indicating that CO added to mixture X did not affect the bacterial communities. The bacterial communities in pork packaged in gas mixture C (with high CO2 content) and O (with oxygen) were, however, distinguishable from each other and from the communities in gas mixtures X and N. The two outlying results from gas mixture C (Fig 3.) were measured from the parallel package that had leaked resulting in CO2 concentration of 59% and O2 concentration of 83% at the time of sam-

–0·4

–0·2

0·0

0·2

NMDS1 Figure 3 Nonmetric multidimensional scaling plot based on terminal restriction fragment length polymorphism of bacterial communities in pork loin packaged in gas mixtures C, O, N, X and stored for 7 days at +6°C. First letter in the sample code indicates gas mixture, second parallel pork package, 7 indicates sampling time and last letter (a or b) technical repeats of T-RFLP.

pling. The corresponding CO2 and O2 concentrations in the three other packages originally filled with mixture C were ≥98 and ≤05% respectively. The position of the leaked package in the NMDS plot in between gas mixtures C and O was thus in concordance with the measured gas composition. The LAB predominating in pork after 14 days of storage were identified by identifying LAB colonies on MRS plates by ribopattern analysis. The results (Table 3) show that of the LAB strains inoculated to pork, Lactobacillus strains prevailed in pork packaged in gas mixture C, Lactococcus piscium in mixtures N and X and Leuconostoc gelidum subsp. gasicomitatum in O. There was some indication that CO mixed with nitrogen in gas mixture X favoured the growth of Lc. piscium in comparison to the gas mixture N (without CO) after 14 days of storage. The LAB associations in pork were also characterized culture-independently after 7 days of storage by comparing the lengths of the T-RFs obtained by the three restriction enzymes to the fragment lengths of known LAB strains. The fragmentograms obtained by HinP1I (Fig. 4) show that the T-RFs 204 and 581 bp, associated with Leuconostoc sp. and Lactococcus sp., respectively, predominate in the fragmentograms obtained from pork packaged in gas mixtures N and X. Similarly, fragments 603, 606 and 938 bp, associated with Lactobacillus spp., predominated in pork packaged in gas mixture C, whereas fragment 204 bp, associated with Leuconostoc gelidum subsp.

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Table 3 Number of LAB isolates from meat with ribopatterns identical to those of the inoculated strains Number of LAB isolates with a ribopattern identical to that of

Gas mixture

Lactobacillus sakei subsp. carnosus CCUG 31331

Lactobacillus oligofermentas DSM 15707T

Leuconostoc gelidum subsp. gasicomitatum KG 16-1

Leuc. gelidum subsp. gasicomitatum LMG 18811

Lactococcus piscium JL3-4

Leuc. gelidum NCFB 2775

Sum

C N O X

11 3 1 0

10 2 1 0

4 7 21 1

0 0 3 0

5 13 0 23

2 1 3 0

32 26 29 24

LAB, lactic acid bacteria.

190

290

390

490

590

690

790

the T-RFs that associated with LAB covered from 70% to 90% of the total peak area in our fragmentograms, depending on the atmosphere and the restriction enzyme. The results thus suggest that LAB species included in our reference strains for T-RFLP predominated in meat although other bacteria appeared to be present too.

890

C 2 3

1

5 4

O

Discussion

1 2 3

N

1

3

X

1

2

5 4

2

3

5 4

Figure 4 Terminal restriction fragment length polymorphism of HinP1I-digested, partial 16S rRNA gene amplicons obtained from bacterial communities in pork loin packaged in gas mixtures C, O, N and X and stored for 7 days at +6°C. Fragment lengths and the associated bacteria: (i) 204 bp, Leuconostoc spp.; (ii) 581 bp, Lactococcus spp.; (iii) 603 bp, Lactobacillus spp.; (iv) 606 bp, Lactobacillus oligofermentas; (v) 938 bp, Lactobacillus spp.

gasicomitatum, predominated in pork packaged in gas mixture O. The comparison of lengths of T-RFs obtained by Hpy8I and NlaIV (results not shown) to T-RFs obtained from known LAB strains supported the associations of LAB to T-RFs obtained by HinP1I (Fig. 4). The PCR primers used in T-RFLP were targeted against bacteria and were not specific to LAB. However, 1314

Our results confirmed the earlier findings indicating that spoilage LAB Leuc. gelidum subsp. gasicomitatum is favoured by oxygen in packaging gas (Vihavainen and Bj€ orkroth 2007; Johansson et al. 2011). The competitive advantage of leuconostocs in meat packaged in high-oxygen MAP has also been reported in studies that did not identify LAB to species level (Lucquin et al. 2012). J€a€askel€ainen et al. (2012) showed that oxygen favours growth of LAB Leuc. gelidum subsp. gasicomitatum in meat by enabling haeme-dependent respiration. In the present study we showed, using controlled experimental conditions and inoculation with mixture of LAB strains belonging to several genera, that oxygen in the packaging atmosphere indeed selects Leuc. gelidum subsp. gasicomitatum over other psychrotrophic LAB strains communities with meat spoilage. Pork stored in oxygen-rich MA was acidified less during the storage compared to pork stored in gas mixtures with the same CO2 concentration but without oxygen (mixtures N and X, Fig. 2). Also (Venturini et al. 2010) reported that beef steaks stored without oxygen had lower pH values than the samples stored with oxygen. The respirative metabolism of Leuc. gelidum subsp. gasicomitatum (Johansson et al. 2011; J€a€askel€ainen et al. 2012), associated with oxygen-rich MAP in the present study, produces acetoin and diacetyl as the end products and should not acidify growth medium as much as e.g. homofermentative metabolism of LAB. The Leuc. gelidum subsp. gasicomitatum strains inoculated to meat in this study were not the most competitive in all of the gas mixtures tested. Lactococcus piscium predominated in pork loin packaged in 80% of N2 and 20%

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CO2 with or without supplementation with 04% carbon monoxide. Lactococcus piscium has been mostly associated with spoilage of raw broiler meat packaged in atmosphere containing 2030% of carbon dioxide and 7090% of nitrogen but no oxygen (Rahkila et al. 2012). The present study suggest that one explanation for the success of Lc. piscium in these types of broiler products is composition of packaging gas: Lc. piscium is not the fastest growing LAB in CO2 concentrations close to 100% found in vacuum packages or in MA with high oxygen content but is highly competitive in modified atmospheres with moderate CO2 concentration (2030%) and only residual oxygen. Lactobacillus sakei and Lactobacillus oligofermentans predominated in gas mixture C with an average CO2 concentration of 92%. Evidence that >80% concentrations of CO2 in meat package atmosphere, found e.g. in vacuum packages, favour Lactobacillus spp. over other LAB has been reported before (Samelis et al. 2000; Ercolini et al. 2011a,b). Lucquin et al. (2012) studied bacterial communities in beef carpaccio and reported that high-oxygen MAP appeared to favour Leuconostoc spp., whereas vacuum package favoured Lactobacillus spp. It is well known that vacuum packaging of meat extends the shelf-life considerably in comparison to high-oxygen MAP (McMillin 2008). The long shelf-live in vacuum can be explained by high CO2 concentration that slows down the growth of all bacteria, spoilage changes introduced by oxygen-dependent metabolism of relevant bacteria (Pin et al. 2002; J€a€askel€ainen et al. 2012) and chemical oxidation of lipids in high-oxygen MAP. Our study and others indicate that vacuum packaging introduces a shift in composition of bacterial communities towards predominance of Lactobacillus spp. which could also contribute to the longer shelf-life in vacuum. Packaging gas composition clearly affected the composition of the bacterial communities (Fig. 3.) presumably because of the effect of gas composition to the growth rates of the individual strains. Interestingly, most of the inoculated strains (or strains with ribopatterns identical to the inoculated strains) were isolated from at least three of the four gas mixtures (Table 3). This suggests that effect of gas composition to the growth rate of a particular strain in relation to the growth rates of the other strains was minor because differences growth rates during the exponential growth quickly result in eradication of the slower growing strain from the predominating part (the part that was covered by colony identification in this study) of the bacterial community. Also earlier when we inoculated Lc. piscium to pork (Rahkila et al. 2012), we saw coexistence of Lc. piscium and Leuc. gelidum subsp. gasicomitatum in the bacterial communities at the stationary phase, although Leuc. gasicomitatum had grown

Lactic acid bacteria on raw pork

much faster than Lc. piscium during the exponential phase. Similar pattern of co-growth of Lc. piscium and Leuc. gelidum subsp. gasicomitatum was seen in unmarinated broiler fillet strips (Nieminen et al. 2012b). The results indicate that the compositions of the psychrotrophic LAB communities in meat are not solely dependent on the maximum growth rates of the individual strains but other factors, such as interaction between the strains, are involved too. In conclusion, this study showed that the composition of modified packaging atmosphere is a major factor selecting LAB communities proliferating on raw meat. Acknowledgements This study was supported by the Finnish Funding Agency for Innovation Tekes (Comeat-project, 2219/31/2010). Erja Merivirta is thanked for the skilful technical assistance. Conflict of Interest No conflict of interest declared. References Balamatsia, C.C., Paleologos, E.K., Kontominas, M.G. and Savvaidis, I.N. (2006) Correlation between microbial flora, sensory changes and biogenic amines formation in fresh chicken meat stored aerobically or under modified atmosphere packaging at 4 degrees C: possible role of biogenic amines as spoilage indicators. Antonie Van Leeuwenhoek 89, 9–17. Bj€ orkroth, K.J., Schillinger, U., Geisen, R., Weiss, N., Hoste, B., Holzapfel, W.H., Korkeala, H.J. and Vandamme, P. (2002) Taxonomic study of Weissella confusa and description of Weissella cibaria sp. nov., detected in food and clinical samples. Int J Syst Evol Microbiol 52, 141–148. Chaillou, S., Chaulot-Talmon, A., Caekebeke, H., Cardinal, M., Christieans, S., Denis, C., Helene Desmonts, M., Dousset, X. et al. (2015) Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage. ISME J 9, 1105–1118. Doulgeraki, A.I., Paramithiotis, S., Kagkli, D.M. and Nychas, G.J. (2010) Lactic acid bacteria population dynamics during minced beef storage under aerobic or modified atmosphere packaging conditions. Food Microbiol 27, 1028–1034. Ercolini, D., Russo, F., Torrieri, E., Masi, P. and Villani, F. (2006) Changes in the spoilage-related microbiota of beef during refrigerated storage under different packaging conditions. Appl Environ Microbiol 72, 4663–4671. Ercolini, D., Ferrocino, I., Nasi, A., Ndagijimana, M., Vernocchi, P., La Storia, A., Laghi, L., Mauriello, G. et al.

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Journal of Applied Microbiology 119, 1310--1316 © 2015 The Society for Applied Microbiology

Packaging gas selects lactic acid bacterial communities on raw pork.

To study the effect of different CO2-rich packaging atmospheres on the composition of lactic acid bacterial communities proliferating on raw pork...
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