Fresh Meats and Poultry Microbiology

Fresh Meats and Poultry Microbiology

Fresh Meats and Poultry Microbiology

It is generally agreed that the internal tissues
of healthy slaughter animals are free of bacteria
at the time of slaughter, assuming that the animals are not in a state of exhaustion. When one
examines fresh meat and poultry at the retail
level, varying numbers and types of microorganisms are found. The following are the primary
sources and routes of microorganisms to fresh
meats with particular emphasis on red meats

• The stick knife. After being stunned and
hoisted up by the hind legs, animals such as
steers are exsanguinated by slitting the jugular vein with what is referred to as a "stick
knife." If the knife is not sterile, organisms
are swept into the bloodstream, where they
may be deposited throughout the carcass.
• Animal hide. Organisms from the hide are
among those that enter the carcass via the
stick knife. Others from the hide may be
deposited onto the dehaired carcass or onto
freshly cut surfaces

• Gastrointestinal tract. By way of punctures,
intestinal contents along with the usual
heavy load of microorganisms may be deposited onto the surface of freshly dressed
carcasses. Especially important in this regard is the paunch or rumen of ruminant

THE BIOTA OF MEATS AND
POULTRY
The major genera of bacteria, yeasts, and
molds that are found in these products before
spoilage are listed inTables 4-1 and 4-2. In general, the biota is reflective of the slaughtering
and processing environments as noted above,
with gram-negative bacteria being predominant.
Among gram positives, the enterococci are the
biota most often found along with lactobacilli.
Because of their ubiquity in meat-processing
environments, a rather large number of mold
genera may be expected, including Penicillium,
Mucor, and Cladosporium. The most ubiquitous
yeasts found in meats and poultry are members of the genera Candida and Rhodotorula

Genus	Gram Reaction	Fresh Meats	Fresh Livers
Acinetobacter	XX
Aeromonas	XX
Alcaligenes
Arcobacter
Bacillus

Genera of Fungi Most Often Found
on Meats and Poultry
Fresh and

Refrigerated

Genus	Meats	Poultry
Molds
Alternaria	X	X
Aspergillus	X	X
Aureobasidium	X
Cladosporium	XX	X
Eurotium	X
Fusarium	X
Geotrichum	XX	X
Monascus	X
Monilia	X
Mucor	XX	X
Neurospora	X
Penicillium	X	X
Rhizopus	XX	X
Sporotrichum	XX
Thamnidium

INCIDENCE/PREVALENCE OF
MICROORGANISMS IN FRESH
RED MEATS

The incidence and prevalence of microorganisms in some red meats are presented in
The aerobic plate counts (APCs) of
the fresh ground beef in this table are considerably

trending-down of bacteria in fresh ground beef
or of laboratory methodology is unclear. For
many decades, comminuted meats have been
shown to contain higher numbers of microorganisms than noncomminuted meats such as steaks,
and there are several reasons for this:

• Commercial ground meats consisting of
trimmings from various cuts that are handled
excessively generally contain high levels of
microbial contamination. Ground meats that
are produced from large cuts tend to have
lower microbial numbers.

• Ground meat provides a greater surface area,
which itself accounts in part for the increased flora. It should be recalled that as
particle size is reduced, the total surface area
increases with a consequent increase in surface energy.

• This greater surface area of ground meat
favors the growth of aerobic bacteria, the
usual low-temperature spoilage flora.

• In some commercial establishments, the
meat grinders, cutting knives, and storage
utensils are rarely cleaned as often and as
thoroughly as is necessary to prevent the
successive buildup of microbial numbers.
This may be illustrated by data obtained
from a study of the bacteriology of several
areas in the meat department of a large grocery store. The blade of the meat saw and
the cutting block were swabbed immediately
after they were cleaned on three different
occasions with the following mean results:
the saw blade had a total log10 per square
inch count of 5.28, with 2.3 coliforms, 3.64
enterococci, 1.60 staphylococci, and 3.69
micrococci; the cutting block had a mean
log per square inch count of 5.69, with 2.04
coliforms, 3.77 enterococci, <1.00 staphylococci, and 3.79 micrococci. These are
among the sources of the high total bacterial count to comminuted meats.

• One heavily contaminated piece of meat is
sufficient to contaminate others, as well as
the entire lot, as they pass through the
grinder. This heavily contaminated portion

 

Mechanically Deboned Meat, Poultry,
and Fish

When meat animals are slaughtered for human consumption, meat from the carcasses is
removed by meat cutters. However, the most economical way to salvage the small bits and pieces
of lean meat left on carcass bones is by mechanical means (mechanical deboning). Mechanically
deboned meat (MDM) is removed from bones
by machines. The production of MDM began in
the 1970s, preceded by chicken meat in the late
1950s and fish in the late 1940s.3336 During the
deboning process, small quantities of bone powder become part of the finished product, and the
1978 U.S. Department of Agriculture (USDA)
regulation limits the amount of bone (based on
calcium content) to no more than 0.75% (the
calcium content of meat is 0.01%). MDM must
contain a minimum of 14% protein and no more
than 30% fat. The most significant parametrical
difference between MDM and conventionally
processed meat relative to microbial growth is
the higher pH of the former, typically 6.0-7.0.3334
The increased pH is due to the incorporation of
marrow in MDM.
Although most studies on the microbiology
of MDM have shown these products to be not
unlike those produced by conventional methods,
some have found higher counts. The microbiological quality of deboned poultry was compared
to other raw poultry products, and although the
counts were comparable, MPN coliform counts
of the commercial MDM products ranged from
460 to >l,100/g. Six of 54 samples contained
salmonellae, four contained C. perfringens, but
none contained S. aureus.