88
Modern Food Microbiology
colony growth before off-odors developed, and herein may lie the explanation for the dominance of
the spoilage biota of livers by nonlactic types.
Because most psychrotrophic oxidative, Gram-negative bacteria grow at a faster rate and are more
favored by the higher surface O/R than the lactic fermentative Gram positives, their dominance in
whole liver spoilage may not be unexpected. The higher concentration of carbohydrates would delay
the onset of amino acid utilizers and explain in part why pH does not increase with whole liver spoilage
as it does for meats. In this regard, comminuted livers would be expected to support the growth of lactic
acid bacteria because of the redistribution of the surface biota throughout the sample where the lactics
would be favored by the high carbohydrate content and reduced O/R away from the surface. This would
be somewhat analogous to the surface spoilage of meat carcasses, where the slower-growing yeasts
and molds develop when conditions are not favorable for bacterial growth. Fungi never dominate the
spoilage of fresh comminuted meats unless special steps are taken to inhibit bacteria. By this analogy,
lactic acid bacteria are inconspicuous in the spoilage of whole livers because conditions favor the
faster-growing, psychrotrophic Gram-negative bacteria.
INCIDENCE/PREVALENCE OF MICROORGANISMS IN FRESH POULTRY
Whole poultry tends to have a lower microbial count than cut-up poultry. Most of the organisms on
such products are at the surface, so surface counts/cm
2 are generally more valid than counts on surface
and deep tissues. May
120 showed how the surface counts of chickens build up through successive
stages of processing. In a study of whole chickens from six commercial processing plants, the initial
mean total surface count was log 10 3.30/cm
2 . After the chickens were cut up, the mean total count
increased to log 10 3.81 and further increased to log 10 4.08 after packaging. The conveyor over which
these birds moved showed a count of log 10 4.76/cm
2 . When the procedures were repeated for five
retail grocery stores, May found that the mean count before cutting was log 10 3.18, which increased
to log 10 4.06 after cutting and packaging. The cutting block was shown to have a total count of
log 10 4.68/cm
2 .
Campylobacter jejuni is found less often on turkey products than salmonellae. Fertile turkey eggs
and newly hatched turkey poults were free of this organism in one study.
2 However, fecal samples
were positive about 2 weeks after hatching in up to 76% of those in one brooder house. The organism
could not be recovered from either the surface or the drip of frozen, thawed turkey carcasses at the
wholesale or retail level, and the scalding and carcass washing steps appear to have been responsible.
1
Of the various cooked poultry products, precooked turkey rolls have been found to have considerably
lower microbial numbers of all types (Table 4–14). In an examination of 118 samples of cooked
broiler products, C. perfringens was found in 2.6%.
112 In a study of chicken carcasses in Argentina,
7 of 70 contained Yersinia spp. including Y. enterocolitica and Y. frederiksenii (4.3% for each); and Y.
intermedia (1.4%). All Y. enterocolitica isolates belonged to biogroup 1A, serotype 0:5, and phagotype
X 2 .
56 Enterococci are common on poultry products. Of 227 turkey samples examined in the state of
Iowa in 2001–2002, 226 were positive for these organisms with 60% of isolates identified as E. faecium
and 31% of E. faecalis.
84 Of 234 chicken samples, 236 were positive with 79% of isolates being E.
faecium and 16% E. faecalis.
The changes in enteric bacteria during various stages of poultry chilling were studied by Cox et al.
29
who found that carcass counts before chilling were 3.17 log 10 cfu/cm
2 for APC and 2.27 log 10 cfu/cm
2
for Enterobacteriaceae. After chilling, the latter organisms were reduced more than the APC. On day
0, E. coli constituted 85% of enterics but after 10 days at 4
◦ C, they were reduced to 14% whereas
Enterobacter spp. increased from 6 to 88% during the same time. In another study, Micrococcus
Modern Food Microbiology
colony growth before off-odors developed, and herein may lie the explanation for the dominance of
the spoilage biota of livers by nonlactic types.
Because most psychrotrophic oxidative, Gram-negative bacteria grow at a faster rate and are more
favored by the higher surface O/R than the lactic fermentative Gram positives, their dominance in
whole liver spoilage may not be unexpected. The higher concentration of carbohydrates would delay
the onset of amino acid utilizers and explain in part why pH does not increase with whole liver spoilage
as it does for meats. In this regard, comminuted livers would be expected to support the growth of lactic
acid bacteria because of the redistribution of the surface biota throughout the sample where the lactics
would be favored by the high carbohydrate content and reduced O/R away from the surface. This would
be somewhat analogous to the surface spoilage of meat carcasses, where the slower-growing yeasts
and molds develop when conditions are not favorable for bacterial growth. Fungi never dominate the
spoilage of fresh comminuted meats unless special steps are taken to inhibit bacteria. By this analogy,
lactic acid bacteria are inconspicuous in the spoilage of whole livers because conditions favor the
faster-growing, psychrotrophic Gram-negative bacteria.
INCIDENCE/PREVALENCE OF MICROORGANISMS IN FRESH POULTRY
Whole poultry tends to have a lower microbial count than cut-up poultry. Most of the organisms on
such products are at the surface, so surface counts/cm
2 are generally more valid than counts on surface
and deep tissues. May
120 showed how the surface counts of chickens build up through successive
stages of processing. In a study of whole chickens from six commercial processing plants, the initial
mean total surface count was log 10 3.30/cm
2 . After the chickens were cut up, the mean total count
increased to log 10 3.81 and further increased to log 10 4.08 after packaging. The conveyor over which
these birds moved showed a count of log 10 4.76/cm
2 . When the procedures were repeated for five
retail grocery stores, May found that the mean count before cutting was log 10 3.18, which increased
to log 10 4.06 after cutting and packaging. The cutting block was shown to have a total count of
log 10 4.68/cm
2 .
Campylobacter jejuni is found less often on turkey products than salmonellae. Fertile turkey eggs
and newly hatched turkey poults were free of this organism in one study.
2 However, fecal samples
were positive about 2 weeks after hatching in up to 76% of those in one brooder house. The organism
could not be recovered from either the surface or the drip of frozen, thawed turkey carcasses at the
wholesale or retail level, and the scalding and carcass washing steps appear to have been responsible.
1
Of the various cooked poultry products, precooked turkey rolls have been found to have considerably
lower microbial numbers of all types (Table 4–14). In an examination of 118 samples of cooked
broiler products, C. perfringens was found in 2.6%.
112 In a study of chicken carcasses in Argentina,
7 of 70 contained Yersinia spp. including Y. enterocolitica and Y. frederiksenii (4.3% for each); and Y.
intermedia (1.4%). All Y. enterocolitica isolates belonged to biogroup 1A, serotype 0:5, and phagotype
X 2 .
56 Enterococci are common on poultry products. Of 227 turkey samples examined in the state of
Iowa in 2001–2002, 226 were positive for these organisms with 60% of isolates identified as E. faecium
and 31% of E. faecalis.
84 Of 234 chicken samples, 236 were positive with 79% of isolates being E.
faecium and 16% E. faecalis.
The changes in enteric bacteria during various stages of poultry chilling were studied by Cox et al.
29
who found that carcass counts before chilling were 3.17 log 10 cfu/cm
2 for APC and 2.27 log 10 cfu/cm
2
for Enterobacteriaceae. After chilling, the latter organisms were reduced more than the APC. On day
0, E. coli constituted 85% of enterics but after 10 days at 4
◦ C, they were reduced to 14% whereas
Enterobacter spp. increased from 6 to 88% during the same time. In another study, Micrococcus