In modified-atmospheres containing elevated levels of both CO 2 and
O 2 growth of pseudomonads is restricted by the CO 2 while the high levels
of O 2 maintain the bright red colour of oxygenated myoglobin in the
meat. Here the microflora depends on the type of meat, its storage
temperature, and whether it was vacuum packed or aerobically stored
previously. In general terms though, the microflora and spoilage tend to
follow a similar pattern to that of vacuum packed meat. Hetero-
fermentative lactic acid bacteria can be more numerous due to the
stimulatory effect of oxygen on their growth and, under some circum-
stances, Brochothrix thermosphacta, Enterobacteriaceae and pseudo-
monads can be more important.
Meat can be processed in a number of different ways which affect
its characteristics, shelf-life and microbiology. The variety of these is
illustrated by Figure 5.5; they will not be discussed further here but
are treated in greater detail under the generic technologies in Chapters 4
and 9.
5.4 Fish
Here we are mainly concerned with what most people think of as fish;
principally the free swimming teleosts and elasmobranchs. The same
term can also encompass all seafoods including crustaceans with a
chitinous exoskeleton such as lobsters, crabs and shrimp, and molluscs
such as mussels, cockles, clams and oysters. Microbiologically these
share many common features with free swimming fish but some specific
aspects are discussed in Section 5.4.3.
Historically the extreme perishability of fish has restricted its con-
sumption in a reasonably fresh state to the immediate vicinity of where
Figure 5.5 Meat and meat products.Tindicates elevated temperature;Eh, low redox
potential; pH, reduced pH;aw, reducedaw; and * stored at chill temperatures
Chapter 5 139