Abstract:

Changes in dominant bacterial populations (DBP) on the surface of grass carp meat packaged under three
different atmospheric conditions (air, vacuum and modified atmosphere packaging environment) and then irradiated by Co-
60 gamma ray at six different doses (0, 2, 4, 6, 8, and 10 kGy) after subsequent storage at 4 ℃ for 18 days were investigated
by polymerase chain reaction-denaturing gradient gel electrophoresis analysis (PCR-DGGE). The bacteria on the surface
of fish meat samples were washed and collected, and their DNA was then extracted. The V3 variable region of 16S rDNA
was amplified with PCR. Identification of DBP was performed with DGGE. The amounts and species composition of
DBP varied with the type of packaging. Pseudomonas sp. was dominant on all fish samples. Lactic acid bacteria and Serratia sp.
were also dominant on air-packaged samples, and Serratia sp. was inhibited when the irradiation rose was more than
8 kGy. Pseudomonas sp., Serratia sp., Brochothrix thermosphact, and Yersinia sp. were identified as the dominant bacteria
on vacuum-packaged samples; Serratia sp. was inhibited when the irradiation dose was above 6 kGy, Yersinia sp. could
be inhibited even when the irradiation dose exceeded 2 kGy, and B. thermosphact exhibited high irradiation resistance for
its occurrence even at doses of 6 and 8 kGy. For modified atmosphere packaged fish, the DPB were Pseudomonas sp. and
Lactobacillus sp.; however, lactic aci bacteria were dominant only when the irradiation dose was 2 or 8 kGy. In conclusion,
PCR-DGGE provides a good way to analyze dominant bacterial populations on the surface of grass carp meat.

Key words: grass carp, polymerase chain reaction-deformation gradient gel electrophoresis analysis (PCR-DGGE), microorganisms, dominant bacterial population, modified atmosphere package, irradiation