a further and more probable hypothesis is that the
nonselective counts allowed a better recovery of the
microbiota from the stress associated with the storage
conditions (1uC), while a full recovery was not possible in
the presence of selective supplements or low pH. Pseudomonas
populations were able to grow in spite of the use of
vacuum packaging, as previously reported (11). The ability
of Pseudomonas bacteria to grow at low levels of oxygen
was recently proved (9, 11, 19). The permeability of the film
used could have allowed traces of oxygen to enter the
package, causing the development of the aerobes. The
presence of residual oxygen in the beef muscle could be
another possible reason for the development of aerobic
bacteria. The pH did not show significant changes during
storage (P , 0.05), probably as a result of the balance
between the acidifying activity of LAB and protein
breakdown by other spoilage populations with consequent
release of alkaline substances.