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Although the air temperature was high in summer (29.46 ± 3.85 °C), the temperature and humidity in the refrigerated vehicles remained relatively constant during the pig carcass transportation to 200, 300, 400 and 500 km (Fig. 2a & b). The values at the end points of transportation were significantly different with the temperature being the greatest for the 500 km group but the smallest for the 400 km group (3.62 ± 0.21 °C vs. 3.34 ± 0.21 °C, P < 0.05, Table 1), while the humidity was the greatest for the 200 km group and the smallest for the 400 km group (91.10 ± 9.87% vs. 83.73 ± 5.26%, P < 0.05, Table 1).
Figure 2.
Changes in vehicle temperature and humidity and carcass temperature during transportation. (a) Vehicle temperature, (b) vehicle humidity, (c) carcass temperature.
Table 1. Temperature and humidity values in refrigerated vehicles.
Transportation distance /km Vehicle temperature/ºC Vehicle humidity/ºC Carcass temperature/ºC 200 3.49 ± 0.21ab 91.10 ± 9.87a 2.87 ± 0.54ab 300 3.42 ± 0.19ab 88.83 ± 5.70ab 3.04 ± 0.51ab 400 3.34 ± 0.21b 83.73 ± 5.26b 2.70 ± 0.43b 500 3.62 ± 0.21a 88.16 ± 5.81ab 3.25 ± 0.35a a,b Different letters in the same column indicate significant differences among distance groups (P < 0.05). The carcass temperature showed similar changes to the air temperature in refrigerated vehicles (Fig. 2c). At the end points, the carcass temperature was the greatest for the 500 km group but the smallest for the 400 km group (3.25 ± 0.35 °C vs. 2.70 ± 0.43 °C, P < 0.05, Table 1).
Changes of microbial colony counts on the surface of pig carcasses
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At the starting point of transportation, the average colony forming count per square millimeters (CFU/cm2) on the surface of pig carcasses was 1.48 ± 0.19. The values were the greatest on the outside of the shoulder of pig carcasses and the smallest on the inside of the belly (P < 0.05, Fig. 3a), but there was no significant difference in microbial colony count among other sampling sites (P > 0.05, Fig. 3a).
Figure 3.
Microbial colony counts on the surface of pig carcasses. (a) Before transportation, (b) at the end point of transportation, (c−f) at the different market points. a,b Different letters indicate significant differences among groups (P < 0.05).
At the end points of transportation, the sampling sites showed significant difference between the inside of the belly and the outside of the shoulder when the carcasses were transported to 200 and 400 km (P < 0.05, Fig. 3c & e). The values of the 200 km group were similar to those of the starting point of transportation (P > 0.05), while the other groups were higher than the 200 km group (P < 0.05, Fig. 3d, e & f). These results indicate that short-time refrigerated transportation did not affect the microbial growth on the surface of pig carcasses.
At the market points, the microbial colony counts on the surface of cuts were not significantly different (P > 0.05, Fig. 3b). The values were 1.96 ± 0.27, 2.38 ± 0.20, 2.35 ± 0.19 and 2.27 ± 0.36 log10(CFU/cm2) for the 200, 300, 400 and 500 km, respectively.
Changes of microbiota composition on the surface of pig carcasses
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A total of 3,982,386 reliable reads were obtained. The PCA scores plot showed that the first two principle components accounted for 58.45% of the total variance among the samples. The first principal component reflected the variation of transportation distance, and the second principal component indicated the variation of samples within the same distance group (Fig. 4). The samples in the starting point group (T0km) were well separated from other samples, indicating that the microbiota composition on the surface of pig carcasses underwent a significant change during refrigerated transportation and subsequent handling. The samples in the end point of transportation groups (T200km-a, T300km-a, T400km-a, and T500km-a) remain similar within the group but show a good separation from the samples of the market point groups (T200km-b, T300km-b, T400km-b, and T500km-b). For the samples in the market point groups, the 200 km and 400 km groups (T200km-b, T400km-b) are well separated from the 300 km and 500 km groups (T300km-b, T500km-b). This indicates that carcasses could be contaminated during transfer at the end points of transportation and the market points.
Figure 4.
PCA scores plot of samples. T0km, the start point of transportation; T200km-a, T300km-a, T400km-a, T500km-a, the end points of 200, 300, 400 and 500 km transportation; T200km-b, T300km-b, T400km-b, T500km-b, the market points after 200, 300, 400, and 500 km transportation.
On the phylum level, Proteobacteria, Firmicutes, Bacteroides, and Actinomycetes are the predominant bacteria in all samples (Fig. 5a). At the start point, the T0 km samples had high relative abundance of Proteobacteria, Bacteriodes, Firmicutes and Actinomycetes. In addition, three samples had a high relative abundance of Fusobacteria. At the end point of transportation, the relative abundance of Proteobacteria and Firmicutes increased compared with T0km samples, and Proteobacteria was dominant. The relative abundance of Actinobacteria decreased slightly in the 200, 300 and 400 km samples. Compared with the samples at the end points of transportation of each distance, the samples at the marketing points had lower relative abundance of Actinobacteria. On the other hand, the relative abundance of Proteobacteria increased significantly (Fig. 5a).
Figure 5.
Microbial composition in samples. (a) Phyla; (b) genera. T0km, the start point of transportation; T200km-a, T300km-a, T400km-a, T500km-a, the end points of 200, 300, 400 and 500 km transportation; T200km-b,T300km-b, T400km-b, T500km-b, the market points after 200, 300, 400, and 500 km transportation.
On the genus level, Acinetobacter, Pseudomonas, Psychrobacter, Chryseobacterium, Staphylococcus, Brochothrix, Moraxella, and Flavobacterium were the predominant bacteria (Fig. 5b). Acinetobacter, Psychrobacter, Chryseobacterium, Staphylococcus, Brochothrix, Morexella, and Flavobacterium were dominant in the T0km samples. The relative abundance of Acinetobacter increased significantly and Psychrobacter was also highly abundant in T200km-a and T300km-a samples. At the market points, the diversity of microbiota decreased significantly, but the relative abundance of Acinetobacter and Pseudomonas increased substantially. In the T200km-b and T400km-b groups, Acinetobacter and Pseudomonas account for 75% of the total abundance of microbiota. In the T300km-b samples, the relative abundance of Acinetobacter, Pseudomonas, and Psychrobacter was higher. In the T500km-b samples, Acinetobacter and Psychrobacter were highly abundant. Notably, Pseudomonas is the main environmental polluting bacterium. During carcass transportation, meat handling and storage, the microbiota dynamically changes. This phenomenon is consistent with the findings of Zhao et al.[25].
LDA analysis showed that the relative abundance of Proteobacteria was high at the starting point and significantly decreased at the end points of transportation (Supplemental Fig. 1a). Compared with the samples at the end points of transportation, the samples at the market points had different relative abundance of Proteobacteria and Firmicutes (Supplemental Fig. 1b). The microbiota composition in T200km-a and T400km-a samples was quite different from that in the T0km samples.
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The air temperature and humidity of vehicles, and the carcass temperature was relatively constant during cold-chain transportation. The total colony counts showed significant differences among samples sites on the surface of pig carcasses at the start and end points of cold-chain transportation, and increased with the transportation distance from 200 km to 400 km. During transportation, microbial diversity on the carcass surface decreased. Acinetobacter, Pseudomonas, Brochothrix, and Moraxella were dominant microorganisms.
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About this article
Cite this article
Wu J, Li R, Zhang M, Shan K, Jia X, et al. 2021. Microbiota changes on the surface of pig carcasses during refrigerated transportation and marketing. Food Materials Research 1: 4 doi: 10.48130/FMR-2021-0004
Microbiota changes on the surface of pig carcasses during refrigerated transportation and marketing
- Received: 30 November 2021
- Accepted: 23 December 2021
- Published online: 30 December 2021
Abstract: We investigated changes in the microbiota composition on the surface of pig carcasses during refrigerated transportation of different distances (200, 300, 400, 500 km) and further transferring to the market place. Microbial samples were obtained by sterile swabs at the starting point, the end points of transportation and the market points. Core temperature of pig carcasses, temperature and air humidity in refrigerated vehicles were also tracked. The air temperature and humidity in the refrigerated vehicles remained relatively constant during transportation. However, the air temperature and carcass temperature at the end points of transportation were the highest for the 500 km group and the lowest for the 400 km group (P < 0.05), while the air humidity was the highest for the 200 km group and the lowest for the 400 km group (P < 0.05). Microbial colony counts showed a slight increase during transportation and differed among five sampling points on the surface of pork carcasses with the highest for the outside of the shoulder and the lowest for the inside of the belly (P < 0.05). Microbiota composition changed greatly and Acinetobacter, Pseudomonas, Psychrobacter, Chryseobacterium, Staphylococcus, Brochothrix, Morexella, and Flavobacterium were the predominant genera. Pseudomonas was the most predominant during transportation.
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Key words:
- Pork carcass /
- Microbiota /
- Transportation /
- Pseudomonas /
- Temperature