## 3 Results and Discussion
### Effect of Pulsed-Light Treatment on Spoilage Microorganisms and Campylobacter  
#### 3.2.1 Spoilage Microorganisms  
Poutlry meat samples presented counts of 3.1 \(\pm\) 0.3 log cfu/g and 2.5 \(\pm\) 0.3 log cfu/g for total psychotropic and Enterobacteriaceae, respectively (see Appendix A Table A1). As described by other authors [28; 29], this initial level of contamination was typical on poultry meat for these microbial groups. In fact, and according to [PERSON] et al. [29], the microbiota of poultry meat is composed 54.1% by sequences assigned mainly to Gram-negative bacteria families, with 17.4% belonging to the _Enterobacteriaceae_ family, while the majority 32.9% was represented by _Vibrionaceae_ with references to _Shevanella_ and _Aeromonas_. _Pseudomonas_ spp., _Acinetobacter_ spp., and _Flavobacterium_ spp. were also common in aerobically packaged poultry meat. Gram-positive bacteria, _Brochotrix_, _Carobacterium_, _Lactobacillus_, _Lactococcus_, and _Leuconostoc_ genera, can grow under refrigeration temperatures and have an important role in the spoilage of poultry meat under modified atmosphere package.  
In this study, the application of PL on samples did not promote any significant difference on total psychotropic counts independently of the increased energy dose applied (Figure 3). This could be related to the presence of psychotropic Gram-negative and positive bacteria, as described by [28; 29], with different resistances to the PL treatments. PL inactivation of microorganisms was attributed to photothermal (thermal effect due to the increase of temperature) and/or photochemical (inhibiting formation of new DNA chains in the process of DNA replication due to the formation of dimers) and/or photophysical (damage of cell membrane and elution of protein) mechanisms that can affect more Gram-negative than Gram-positive bacteria [15; 30; 31]. In addition, the roughness of the matrix food could produce different shadows, which contribute to differences in bacteria inactivation [13; 16; 19]. After all, PL was more effective regarding Gram-negative bacteria since the samples treated by PL had a decrease of _Enterobacteriaceae_ counts when compared to samples not treated, approximately 1-1.3 log cfu/g (Figure 4a).  
This data was interesting since with low fluence (lower than 5 J/cm\({}^{2}\)) there was a count reduction induced by a photochemical action. This reduction of Enterobacteriaceae aureus counts, a hygiene indicator, can be indirectly related to the control and reduction of spoilage bacteria and potential pathogens. [PERSON] et al. [32] in their studies in vitro, observed reductions of _E. coli_ under pulsed UV light with a range of 2.4-9.6 J/cm\({}^{2}\). Additionally, other authors [19; 33] reported a reduction of _Salmonella_ and _E. coli_ on poultry meat but not more than 2 log cfu/g when pulsed UV light was applied at 8 cm with exposure  
Figure 2: Effect of the PL energy dose on samples temperature (°C).  
time of 45 s or at 5 cm during 15 s for unpackaged samples and 5 cm-30 s for vacuum-packaged samples.  
However, and surprisingly, increased doses of fluence (J/cm\({}^{2}\)) among treated samples (treatments 1 and 3) did not decrease the _Enterobacteriaceae_ counts (Figure 4b) significantly. The photothermal action with a temperature increase to 10 \({}^{\circ}\)C induced by higher energy doses (fluence, J/cm\({}^{2}\); Figure 2) did not promote a higher bactericidal effect. This _Enterobacteriaceae_ family that includes mesophilic bacteria was not significantly affected under higher energy doses and temperature.