Fig. 5 shows the microbial growth in vacuum-packed HHP-treated
meat (at 300 and 600 MPa) and fresh meat samples (FM) during
refrigerated storage at 4 °C for a) mesophilic bacteria and b) lactic acid
bacteria. According to Articles 255 bis hese values can be considered as a reference for our chemical
pre-treated and HHP beef product.
In the case of fresh meat counts of mesophilic and lactic acid bacteria
were higher than the legally permitted levels at the third week of
refrigerated storage and Enterobacteriaceae counts were higher than
100 CFU/g after the second week.
The lactic acid bacteria and the mesophilic bacteria were the main
constituents of non-treated fresh meat's flora during the refrigerated
storage at 4 °C.
After a pressure of 300 MPa was applied, both the mesophilic bacteria
and the lactic acid bacteria counts were under 2 log CFU/g until the
fourth week of storage increasing to around 4 log CFU/g at the fifth
week, and traversed two logarithmic cycles over the following week.
The samples treated at 600 MPa showed a slight increase in the
mesophilic bacteria counts throughout the seven weeks of storage,
while the lactic acid bacteria increased at the fifth week.
There was an increase of Enterobacteriaceae (ABRV) in HHP nontreated
vacuum-packed fresh meat during the first week of storage
(3.83 ± 0.13 log CFU/g), with a relatively high concentration in the second
week (4.39 ± 0.25 log CFU/g), while in the HHP-treated samples
(at both pressure levels) the Enterobacteriaceae concentration was
below the detection limit of the Most Probable Number (MPN) method
throughout the storage period.
No fungi or yeasts were detected, and there was no increase of the
psychrotrophic bacteria in the fresh meat or in the HHP-treated samples.
An Escherichia coli detection test was also conducted in MacConkey
broth using the Most Probable Number method, with negative results
across all samples.
The high hydrostatic pressure treatment applied guaranteed the
microbiological innocuity of the products. Based on these findings, it
can be concluded that at 300 MPa the samples were microbiologically
stable during 4 weeks and at 600 MPa during 6 weeks.
In order to ensure that the legally permitted concentration limits for
preservatives were not exceeded, the sodium nitrite and sodium chloride
concentrations of the HHP-treated meat samples stored at 4 °C
were analysed. The values obtained at the beginning of the storage
period – which remained stable until the end – were as follows:
0.048 ± 0.004 g NaNO2/kg meat tissue and 33.4 ± 1.80 g NaCl/kg
meat tissue, which complies with the regulations of the Codex
Alimentarius for NaNO2