Two studies were undertaken to determine the microbiological of beef carcass meat and frozen boneless bulk packed beef produced in Australia. Samples were collected from 1,063 beef carcasses and from 929 cartons of frozen boneless bulk packed beef over a period of approximately 12 months. Samples were collected from works processing beef carcasses for the Australian domestic market and from works targeting export markets. On carcasses processed for export markets, where bacterial counts were obtained, the log10 mean of the APC (aerobic plate count) was 3.13 CFU/cm2, the geometric mean of the coliform count was 19 MPN/cm2, and the geometric mean of Escherichia coli was 13 MPN/cm2. A small percentage (0.59%) of export samples were found positive for Listeria monocytogenes, 0.16% were positive of r coagulase-positive for Campylobacter jejuni/coli, 0.22% were positive for Salmonella spp., and 29% were positive for coagulase-positive Staphylococcus spp. Bacterial numbers were lower on carcasses processed for export markets and higher carcasses chilled for more than 24 h. Escherichia coli O157 was recovered from 4 of 893 export carcasses tested (0.45%). Of the export frozen boneless bulk packed beef samples that tested positive, the log10 mean of the APC was 2.5 CFU/g, the geometric mean of the coliform count was 15 MPN/g, and the geometric mean number of e. coli was 15 MPN/g. Three of 787 export frozen samples (0.38%) tested positive for Salmonella spp., E. coli O157 was not isolated from any of the 685 export frozen samples tested for this bacteria. Export samples tested for this bacteria. Export samples on average had lower APCs than domestic samples. Results from both surveys are compared with data from similar studies in other countries.
The spoilage of vacuum-packaged fresh beef during storage at 5°C was studied using analytical taste panels. In the absence of contaminating micro-organisms, meat spoiled due to the development of an "off" flavor described as "liver-like." This occurred even when the meat was packaged in bags made of film of very low oxygen permeability, but the rate of spoilage increased as the film permeability increased. Thus, vacuum-packaged beef has a limited shelf life even in the absence of a significant population of contaminating microorganisms. Pure cultures of lactic acid bacteria increased the rate of spoilage, which was then due largely to the development of flavor defects described as sour, acid and bitter. Depending upon the strain of bacteria chosen, off flavor became significant 13-28 days after the population reached 1 08/cm2.
The spoilage of vacuum‐packaged sliced luncheon meats at 5°C by Microbacterium thermosphactum and lactobacilli was studied using analytical taste panels. M. thermosphactum caused rapid spoilage. “Off” aroma was significant at about the time the bacterial population reached 108/g and “off” flavor 2–3 days later. In contrast homofermentative lactobacilli caused spoilage much more slowly. No “off” aroma was detected with products which had carried a population of 108/e. for 21 days the time at which “off” flavor first became significant. Heterofermentative lactobacilli were intermediate in their effect. Thus shelf life is dependent upon the types of bacteria present. Under such circumstances a “total count” microbiological standard is of little value.
Lactobacillus sake L13 produced hydrogen sulphide during growth at 0°C on vacuum‐packaged beef of normal pH (5·6–5·8) when the packaging films used had oxygen permeabilities as high as 200 ml/m2/24 h/atm (measured at 25°C and 98% relative humidity. No hydrogen sulphide was detected when the film permeability was 300 ml/m2/24 h/atm. Sulphmyoglobin was formed whenever hydrogen sulphide was present except when the film permeability was very low (1 ml of oxygen/m2/24 h/atm). Lactobacillus sake L13 also produced hydrogen sulphide when grown on beef under anaerobic conditions at 5°C. When meat pH was high (6·4–6·6) hydrogen sulphide was first detected after incubation for 9 d. When 250 μg of glucose was added to each g of high pH meat, or when meat pH was normal (5·6–5·8), hydrogen sulphide was first detected after incubation for 18 d. The spoilage of beef by hydrogen sulphide‐producing lactobacilli is more rapid when the pH of the meat is high because high‐pH meat contains less glucose. Sulphmyoglobin formation and greening can be prevented by the use of packaging films of very low oxygen permeability.
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