Survival of Bacteria in Food Cooked by Microwave Oven, Conventional Oven and Slow Cookers 1.

To assess the destructive effect of different cookery methods on bacteria, strains of Escherichia coli , Clostridium perfringens , Streptococcus faecalis and Staphylococcus aureus were used to inoculate a meatloaf preparation. After inoculation, a sample was withdrawn for bacterial analysis and the remainder of the meatloaf was divided and cooked by microwave oven, conventional oven and slow cooker. The temperature of the meatloaf was recorded at various locations immediately after cooking to obtain minimum, maximum and mean temperatures for each loaf. Also, just after cooking, representative samples were taken and analyzed by conventional means for the specific bacteria and for total bacterial content. Survival percentages were calculated and plotted against temperature for each cooking method. Temperature variation within the loaf was greatest for those cooked with microwaves and smallest for those cooked by the slow method. For each bacterial strain and the total count, the destructive effect of cooking method was not different at the 0.05 level of significance.

Mutagenicity of Tenebrionid Flour Beetle Secretions Using Drosophila melanogaster Sex-Linked Recessive Lethal Test.

The Tribolium spp. beetles are the most common tenebrionids infesting flour and other stored foods. 2-Ethyl-1, 4-benzoquinone (EBQ) and 2-methyl-1, 4-benzoquinone (MBQ) are the major secretory products of these insects. Benzoquinones are highly reactive compounds which have been reported to be acutely toxic and carcinogenic to laboratory animals. Using the Drosophila melanogaster sex-linked recessive lethal test, we examined the mutagenicity of EBQ and MBQ. Feeding concentrations of 1 mM EBQ and 2 mM MBQ in 1% sucrose resulted in 72-h mortalities of 25% for EBQ and 39% for MBQ in adult Canton-S male flies. A comparable mortality rate for negative control insects fed 1% sucrose was 2.5%, while positive control flies fed 1 mM ethyl methanesulfonate (EMS) in 1% sucrose resulted in a 2.3% mortality rate. Mutation rates resulting from these exposure levels are as follows: negative control, 0.03%; positive control, 16.05%; 1 mM EBQ, 0.16%; and 2 mM MBQ, 0.13%. The mutation rates for flies fed EBQ and MBQ were significantly higher (p<0.005 for EBQ and p<0.016 for MBQ) than those of concurrently tested negative control insects when analyzed by both the Fisher's exact and Kastenbaum-Bowman tests. These results show EBQ and MBQ to be mutagenic when tested using the sex-linked recessive lethal Drosophila melanogaster system. Analysis of brood mutation rates indicate that both EBQ and MBQ act as indirect mutagens. The presence of benzoquinone-secreting Tribolium spp. flour beetles in food products could represent a toxicologic hazard to the consumer. Presently no distinction is made between benzoquinone-secreting insects and other arthropods infesting stored products when establishing rejection standards for infested foods.

Mutagenic Potential of Chemicals Associated with Tenebrionid Flour Beetle Secretions as Determined by the Ames Assay.

Infestation of flour and other stored products by the tenebrionid (flour beetles) has been proven a health hazard to the public. Secretions from these insects have been found to be harmful toxicologically. These secretions also possess characteristics typical of mutagens. Therefore the mutagenic potential of 2-methyl-1, 4-benzoquinone (MBQ), 2-ethyl-1, 4 benzoquinone (EBQ) and 1-pentadecene (P-dec) was assessed by using the Ames Salmonella/Mammalian Microsome Mutagenicity Assay, a screening test for detection of mutagens. Tester strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538 were exposed to doses of 10-1 mg/plate to 3.2 × 10-5 mg of MBQ/plate, 10-2 mg/plate to 3.2 × 10-6 mg of EBQ/plate and 1 mg/plate to 3.2 × 10-4 mg of P-dec/plate. No evidence of mutagenic potential was observed at the levels tested.

Colony Count Accuracy Using Selective Media: Analysts Versus Automatic Colony Counters 1, 2.

Using two different methods of counting, a comparison was made of the ability of five analysts to enumerate colonies on selective bacteriologic media. First, analysts manually counted the colonies aided by a Quebec colony counter and a hand tally. This was followed by the counting of colonies on each of three automated colony counters. In this pilot study, the media used included violet red bile agar. KF streptococcal agar, sulfite-polymyxin-sulfadiazine agar, and Standard Methods agar with 2,3,5 triphenyltetrazolium chloride added. The analysts' ability to count colonies on selective media by the manual method was superior to results obtained with the automatic colony counters.

Survey of the Bacterial Populations of Bologna Products 1, 2.

Bologna products most frequently are stored and consumed as refrigerated products. Thus bacteria that survive processing or those that contaminate the product subsequent to processing are not destroyed. Ten types of presliced, vacuum-packaged bologna products were purchased from a high-volume retail market and analyzed for total aerobic plate count (APC) and common foodborne pathogens. No Salmonella were isolated. Less than 1% of the 419 samples analyzed contained either Clostridium perfringens or Escherichia coli , Staphylococcus aureus was isolated from 4% of the samples, but only one sample contained more than 1000/g. Just over 5% of the samples contained coliform organisms. The manufacturer appeared to play an important role in bacterial quality of the finished items. An APC < 5 × 106/g is a realistic criterion for bologna products at the time of delivery to retail markets.

Bacterial Populations of Ground Beef, Textured Soy Protein and Ground Beef Extended With Soy Protein After 3 and 10 Days of Refrigerated Storage 1, 2.

A survey of the microbial populations of 31 samples of ground beef (GB), textured soy protein (TSP), and ground beef extended with TSP (SGB) after 3 and 10 days of storage at 4 C was done. Analyses included aerobic plate count (APC), psychrotrophic plate count (PPC), coliform Most Probable Number (CMPN) and plate determinations (CPC), Escherichia coli MPN (EMPN) and plate determinations (EPC), Staphylococcus aureus MPN, and fecal streptococcus plate count. Statistical analyses of data from the enumeration procedures showed significant increases in the total microbial flora after 10 days of storage. PPCs were significantly higher than APCs. CMPNs were significantly higher than CPCs for GB and SGB. The EMPNs were significantly higher than EPCs in SGB only. These products contained a variety of microorganisms many in large numbers; however if properly handled and cooked before consumption, these products should present no public health problems.

Microbiological Criteria for Food 1, 2.

Microbiological criteria can be separated into standards, guidelines and specifications. These criteria are applied to reduce potential health hazards associated with foods and to evaluate food quality. Microbiological criteria must be realistic, enforceable and consistently applied. In fulfillment of their responsibilities to consumers, both regulators and food purveyors will continue to improve and to establish new microbiological criteria for food.

Types of Clostridium perfringens Isolated from Selected Foods 1, 2.

To determine the proportion of type A Clostridium perfringens occurring among C. perfringens isolates obtained from foods, strains were typed by the mouse serum neutralization method. Of 339 isolates from ground beef, ground pork, ground turkey, live crab, cured sausage, and live clams. 320 (94%) were type A. The remaining 19 isolates produced insufficient exotoxin for typing. The predominance of type A strains from the foods surveyed indicates that definitive typing of strains isolated from these foods, when suspected of causing foodborne disease, is not warranted.

Accuracy and Speed in Counting Agar Plates 1.

To determine the accuracy of colony counts made by analysts, agar plates were photographed. The agar plates and photographs were compared to obtain a true count (photocount) which was used to determine analyst accuracy over selected count ranges. Analyst accuracy was also determined by comparing analyst's counts to the mean of the counts obtained by several analysts ("established standard"). The "established standard" compared favorably with the photocount. Analysts' counts were within 5% of the photocount and "established standard" on 60 and 68% of plates having 30-300 colonies and 60 and 67% on plates having 20-200 colonies, respectively. Average counting time for plates in the 10-100, 20-200, 30-300, and 40-400 colony count ranges was 18, 30, 41, and 52 sec, respectively. Plates having 20-200 colonies were as suitable for counting as plates having 30-300 colonies and were counted with a time-saving of 27%.

Significance of Clostridium perfringens in Processed Foods.

Clostridium perfringens presents a significant public health hazard to consumers of foods which have undergone improper processing or have been improperly handled at some point before consumption. Factors involved in outbreaks of C. perfringens foodborne illness include contamination of food with either spores or vegetative cells of enterotoxigenic strains of C. perfringens , suitable growth temperature. pH, media, oxidation reduction potential, and adequate incubation time. With proper handling of food items, the risk of C. perfringens foodborne illness outbreaks can be eliminated.

Plate Count Accuracy: Analysts and Automatic Colony Counter Versus a True Count 1.

Colony counts obtained by (a) analysts and (b) an automatic colony counter (ACC) were compared to a true count obtained through use of photographs. Factors which caused counting dificulties with the ACC were identified. When plates were properly screened, ACC counts were as accurate as those obtained manually; therefore, it is recommended that further study of ACCs be conducted so that consideration may be given to their use in the forthcoming edition of Standard Methods for the Examination of Dairy Products.

Microbial Flora of Preseasoned Comminuted Turkey Meat.

Preseasoned comminuted turkey meat, prepared at the retail level, was examined and revealed the following levels of microbial contamination per gram: mean standard plate count 2.2 × 108, mean coliform plate count 2.0 × 105, Escherichia coli count 8.7. Gram-positive and gram-negative microbial flora were isolated and identified.

Changes in the Population of Clostridium perfringens Type A Frozen in a Meat Medium 1.

Survival of eight strains of Clostridium perfringens type A frozen in a meat medium at -23 C and held under aerobic conditions for 1,7, and 14 days was 17, 12, and 6.2%, respectively. Holding under anaerobic conditions for 1, 7, and 14 days gave survival percentages of 51, 26, and 10%, respectively. Survival was not affected by cooling rates of 0.5, 1.5, and 20 C per min. Addition of 10% sucrose to the meat medium did not affect survival. The meat medium with glycerol concentrations of 1.0 and 2.0 M gave survival percentages of 13, 63, 144, and 58, respectively, when frozen at -23 C and held for 22 to 24 h.