Fresh Meats and Poultry
87
Table 4–13 pH and Concentrations in 10 Fresh Livers of Glycogen,
Glucose, Lactic Acid, and Ammonia
Component
Average Concentration and Range
Glucose
2.73 (0.68–6.33) mg/g
Glycogen
2.98 (0.70–5.43) mg/g
Lactic acid
4.14 (3.42–5.87) mg/g
Ammonia
7.52 (6.44–8.30) µmol/g
pH
6.41 (6.26–6.63)
Source: Gill and DeLacy, 72 copyright c
1982, American Society for Microbiology.
sarcoplasmics. Aeromonas spp. were active on both myofibrillar and sarcoplasmic proteins. With pure
cultures, protein changes were not detected until counts were above 3.2 × 10
9 /cm
2 . Earlier, Borton
et al.
15 showed that P. fragi effected the loss of protein bands from inoculated pork muscle, but no
indication was given as to the minimum numbers that were necessary. For more on the microbial
spoilage of muscle foods, see the review by Ellis and Goodacre.
49
SPOILAGE OF FRESH LIVERS
The events that occur in the spoilage of beef, pork, and lamb livers are not as well defined as for
meats. The mean content of carbohydrate, NH 3 , and pH of 10 fresh lamb livers is presented in Table
4–13.
72 Based on the relatively high content of carbohydrates and mean pH of 6.41, these may be
expected to undergo a fermentative spoilage, with the pH decreasing below 6.0. This would undoubtedly occur if livers were comminuted or finely diced and stored at refrigerator temperatures, but most
studies have been conducted on whole livers, where growth was assessed at the surface, from drip, or
from deep tissue. In a study of the spoilage of diced beef livers the initial pH of 6.3 decreased to about
5.9 after 7–10 days at 5
◦ C and the predominant biota at spoilage consisted of lactic acid bacteria.
158
In most other studies, the predominant biota at spoilage was found to consist essentially of the same
types of organisms that are dominant in the spoilage of muscle meats. In pork livers held at 5
◦ C for
7 days, the predominant organisms found in one study were Pseudomonas, Alcaligenes, Escherichia,
lactic streptococci, and B. thermosphacta.
64 In five beef livers stored at 2
◦ C for 14 days, Pseudomonas
constituted from 7% to 100% of the spoilage biota, while the mean initial pH of 6.49 decreased to 5.93
over the 14-day period.
82 In another study of beef, pork, and lamb livers, the predominant biota after
5 days at 2
◦ C differed for the three products, with beef livers being dominated by streptococci, yeasts,
coryneforms, and pseudomonads; lamb by coryneforms, micrococci, and “streptococci”; and pork
livers by staphylococci, Moraxella-Acinetobacter, and “streptococci”.
80 The mean initial pH of each
of the three livers declined upon storage, although only slightly. In a study of spoilage of lamb livers
by Gill and DeLacy,
72 the spoiled surface biota was dominated by Pseudomonas, Acinetobacter, and
Enterobacter; drip from the whole livers was dominated by Pseudomonas and Enterobacter; whereas
Enterobacter and lactobacilli were dominant in the deep tissues. It was shown in this study that the
initial pH of around 6.4 decreased to around 5.7 in antibiotic-treated samples, indicating that liver
glycolytic events can lead to a decrease in pH in the absence of organisms even though these samples did contain <10
4 organisms/cm
2 . The high glucose level was sufficient to allow visible surface
87
Table 4–13 pH and Concentrations in 10 Fresh Livers of Glycogen,
Glucose, Lactic Acid, and Ammonia
Component
Average Concentration and Range
Glucose
2.73 (0.68–6.33) mg/g
Glycogen
2.98 (0.70–5.43) mg/g
Lactic acid
4.14 (3.42–5.87) mg/g
Ammonia
7.52 (6.44–8.30) µmol/g
pH
6.41 (6.26–6.63)
Source: Gill and DeLacy, 72 copyright c
1982, American Society for Microbiology.
sarcoplasmics. Aeromonas spp. were active on both myofibrillar and sarcoplasmic proteins. With pure
cultures, protein changes were not detected until counts were above 3.2 × 10
9 /cm
2 . Earlier, Borton
et al.
15 showed that P. fragi effected the loss of protein bands from inoculated pork muscle, but no
indication was given as to the minimum numbers that were necessary. For more on the microbial
spoilage of muscle foods, see the review by Ellis and Goodacre.
49
SPOILAGE OF FRESH LIVERS
The events that occur in the spoilage of beef, pork, and lamb livers are not as well defined as for
meats. The mean content of carbohydrate, NH 3 , and pH of 10 fresh lamb livers is presented in Table
4–13.
72 Based on the relatively high content of carbohydrates and mean pH of 6.41, these may be
expected to undergo a fermentative spoilage, with the pH decreasing below 6.0. This would undoubtedly occur if livers were comminuted or finely diced and stored at refrigerator temperatures, but most
studies have been conducted on whole livers, where growth was assessed at the surface, from drip, or
from deep tissue. In a study of the spoilage of diced beef livers the initial pH of 6.3 decreased to about
5.9 after 7–10 days at 5
◦ C and the predominant biota at spoilage consisted of lactic acid bacteria.
158
In most other studies, the predominant biota at spoilage was found to consist essentially of the same
types of organisms that are dominant in the spoilage of muscle meats. In pork livers held at 5
◦ C for
7 days, the predominant organisms found in one study were Pseudomonas, Alcaligenes, Escherichia,
lactic streptococci, and B. thermosphacta.
64 In five beef livers stored at 2
◦ C for 14 days, Pseudomonas
constituted from 7% to 100% of the spoilage biota, while the mean initial pH of 6.49 decreased to 5.93
over the 14-day period.
82 In another study of beef, pork, and lamb livers, the predominant biota after
5 days at 2
◦ C differed for the three products, with beef livers being dominated by streptococci, yeasts,
coryneforms, and pseudomonads; lamb by coryneforms, micrococci, and “streptococci”; and pork
livers by staphylococci, Moraxella-Acinetobacter, and “streptococci”.
80 The mean initial pH of each
of the three livers declined upon storage, although only slightly. In a study of spoilage of lamb livers
by Gill and DeLacy,
72 the spoiled surface biota was dominated by Pseudomonas, Acinetobacter, and
Enterobacter; drip from the whole livers was dominated by Pseudomonas and Enterobacter; whereas
Enterobacter and lactobacilli were dominant in the deep tissues. It was shown in this study that the
initial pH of around 6.4 decreased to around 5.7 in antibiotic-treated samples, indicating that liver
glycolytic events can lead to a decrease in pH in the absence of organisms even though these samples did contain <10
4 organisms/cm
2 . The high glucose level was sufficient to allow visible surface