M. O. Hanna

Role of Hafnia alvei and a Lactobacillus Species in the Spoilage of Vacuum-Packaged Strip Loin Steaks

A microbiological examination of vacuum-packaged strip loin steaks that were defective (gassy packages, hydrogen sulfide odor) revealed high total counts (107-108/cm2) with Hafnia alvei , Lactobacillus and Pseudomonas spp. as major isolates. Re-inoculation experiments indicated that H. alvei was the likely cause of the hydrogen sulfide odor. Gas formation resulted from the activity of heterofermentative lactobacilli and H. alvei . Improvements in plant practices and temperature control eliminated the problem.

Microbial Flora of Livers, Kidneys and Hearts from Beef, Pork and Lamb: Effects of Refrigeration, Freezing and Thawing

Aerobic plate counts (APC) of livers, kidneys and hearts obtained from beef, pork and lamb soon after slaughter were nearly always <104 and often <103 per cm2. Differences in APC of different sites of the same liver, kidney or heart, within each species, were not significant (P>0.05). APC of livers, kidneys and hearts from pork and lamb after storage for 1, 3 or 5 days at 2 C were not significantly different (P>0.05) from those at day 0. APC of beef livers, kidneys and hearts after 5 days at 2 C differed significantly (P<0.05) from those at day 0, 1 and 3. Temperature abuse of fresh organs for 6-12 h at 30 C before freezing caused major increases in count. Frozen storage of livers, kidneys and hearts (4 days at -20 C) did not cause significant changes in APC. The initial microbial flora of fresh livers, kidneys and hearts was varied with coryneform bacteria and Micrococcus sp. often constituting a major part (>25%) of the microbial flora. After storage for 5 days at 2 C, Pseudomonas sp. more often became a major part of the microbial flora of liver samples. Frozen storage for 4 days at -20 C did not change the microbial flora of beef samples greatly; in pork and lamb, coryneform bacteria more frequently became a major part of the microbial flora after freezing. Changes in pH of livers, kidneys and hearts during storage for 5 days at 2 C were small.

Effect of Heating, Freezing, and pH on Yersinia enterocolitica-like Organisms From Meat

No survivors of Yersinia enterocolitica were detected in beef roasts inoculated at levels as high as 3.1-3.8 × 106 viable cells per g when the final internal temperature in the center was 60 to 62 C. At 51 C some Y. enterocolitica survived. Extensive destruction of Y. enterocolitica occurred on beef during frozen storage. Counts of surviving organisms were greater on tryptic soy agar than on bismuth sulfite agar plates. Growth of Y. enterocolitica in brain heart infusion was better at pH 7 and 8 than at 6 or 9. Little or no growth occurred at pH 5.

Prevalence of Campylobacter jejuni in Turkey Carcass Processing and Further Processing of Turkey Products

Presence of Campylobacter jejuni was determined at various locations in turkey carcass processing and further processing of turkey products (wieners, ham and boneless breast). Contamination of turkey carcasses with C. jejuni , in most cases, occurred on the surface of the skin or on the surface of the abdominal cavity lining. No contamination of interior muscle tissue was observed. The percentage of turkeys containing C. jejuni upon entering the processing plant varied (50 to 100%). Large numbers of C. jejuni were killed during scalding of carcasses, but extensive recontamination occurred during mechanical defeathering. After scalding, numbers of C. jejuni peaked during evisceration, but dropped to lower levels after washing. Few or no C. jejuni were recovered from the carcasses after leaving the chill tank. No C. jejuni were detected on frozen turkey carcasses, including the drip, at the wholesale or retail level. However, Campylobacter coli was detected in the drip of a few carcasses that had been in frozen storage at the wholesale level for 2 wk and 3 months. Neither C. jejuni nor C. coli was detected on frozen turkeys at the retail level. Although, in some cases, C. jejuni were recovered from turkey meat during initial stages of further processing, no C. jejuni were recovered from heat-treated, further processed products.

Bacteriology of Electrically Stimulated and Unstimulated Rabbit, Pork, Lamb and Beef Carcasses

Electrical stimulation of rabbit muscles caused a reduction in count of Pseudomonas putrefaciens and of a Lactobacillus sp. when inoculated muscles were held for 45 min after electrical stimulation. Little if any change in count was detected on rabbit muscles immediately after electrical stimulation and after 20 min of storage. Electrical stimulation (ES) of pork carcasses did not affect the aerobic plate count (APC) of the skin surface. APC of cutaneous trunci from electrically stimulated sides of beef and lamb carcasses were similar to those of muscles from unstimulated sides or carcasses. APC of ground beef and blade steaks fabricated pre-rigor from electrically stimulated sides were often numerically lower after 3 days of storage than those of corresponding samples from unstimulated sides. Differences in APC between conventional and ES samples of ground beef prepared from vacuum packaged top round were significant (P < 0.05) after 6 days of storage. However, none of the other differences in count were statistically significant (P < 0.05). Electrical stimulation did not cause any consistent substantial changes in microbial types of ground beef, blade steaks, T-bone steaks or rib steaks. When minced, aseptically excised supraspinatus muscle was inoculated with either P. putrefaciens or a Lactobacillus sp., counts of these species in tissues from electrically stimulated beef often were significantly lower than those of corresponding unstimulated samples.

Effects of Packaging Methods on the Microbial Flora of Livers and Kidneys from Beef or Pork

Aerobic plate counts (APC) of vacuum-packaged beef livers, beef kidneys and pork livers during refrigerated storage were nearly always, particularly after 14 days at 2 C, much lower than those of comparable samples packaged in polyvinyl chloride (PVC) film. The pH of vacuum-packaged livers and kidneys decreased during refrigerated storage; the same was true for products stored in PVC film except that the pH of kidneys increased. In refrigerated vacuum-packaged livers and kidneys, lactic acid bacteria (homo- and heterofermentative lactobacilli, streptococci, Leuconostoc sp.) became more predominant, whereas in products packaged in PVC film, gram-negative bacteria frequently became more dominant.

Sensory and Microbial Profile of Steaks Stored in O2-CO2-N2 Atmospheres

The microflora of steaks prepared from 14-day old vacuum-packaged beef strip loins obtained from a commercial packing plant consisted primarily of Leuconostoc sp. with smaller percentages of Pseudomonas sp. and homofermentative lactobacilli. Steaks stored for 10 days at 1 ± 1 C in O2 (65-80%) + CO2 (20-25%) + N2 (0-10%) atmospheres in the dark were rated inferior (surface discoloration, overall acceptability) to steaks prepared from loins which had been stored for an additional 10 days in vacuum packages. Additional storage for 4 days under retail conditions (2 ± 2 C) caused further deterioration of quality. Aerobic plate counts of steaks prepared from loins which had been stored in vacuum packages for an additional 10 days were about 2 logs lower than those of comparable steaks held in O2-CO2-N2 atmospheres.

Development of Yersinia enterocolitica-like Organisms in Pure and Mixed Cultures on Different Bismuth Sulfite Agars

Yersinia enterocolirica -like isolates from meats produced, black colonies on eight of nine lots of bismuth sulfite agar. Differences were observed in size and black metallic sheen of colonies on different lots of this medium. In addition, inhibition of Pseudomonas spp, differed among lots.

Microbial Flora of Vacuum-Packaged Lamb with Special Reference to Psychrotrophic, Gram-Positive, Catalase-Positive Pleomorphic Rods

Wholesale cuts of lamb (loins, legs) were packaged in polyvinyl chloride (PVC) film and in two other types of packages with oxygen transmission rates (cc/100 in2/24 h) of 0.41-0.75 and 2.28 respectively, Psychrotrophic counts were low (2 × 10-1.1 × 103 per in2) intially and after storage for 21 days increased to 103-1.6 × 105 per in2) Initially Corynebacterium species and Microbacterium thermosphactum were dominant. Upon refrigerated storage for 21 days, Lactobacillus , Pseudomonas , and Moraxella-Acinetobacter sp. became more significant. Among the Corynebacterium sp., buff-colored isolates, consisting of long, gram-positive pleomorphic rods in palisades were dominant.

Inoculation of Beef Steaks with Lactobacillus Species Before Vacuum Packaging. I. Microbiological Considerations

Biceps femoris steaks were inoculated with each of four Lactobacillus sp. (atypical streptobacteria and beta bacteria) at a high or low level of cell concentration, vacuum-packaged and stored for up to 35 days at 1-3 C. Total lactobacillus counts of inoculated steaks were numerically higher than those of corresponding control (non-inoculated) steaks at nearly all of the storage intervals tested. Differences in lactobacillus counts between steaks inoculated with a high concentration of Lactobacillus cultures 5, 8 and 642, and those of control steaks usually were significant (P < 0.05) after storage for 0 to 28 days. Differences in lactobacillus counts between steaks inoculated with a low concentration of Lactobacillus cultures and those of control steaks were seldom significant (P < 0.05). After storage for 35 days at 1-3 C, differences in lactobacillus counts of inoculated (high or low levels of inoculum) and control steaks usually were not significant (P > 0.05). The lactobacilli encountered on the inoculated steaks consisted primarily of the type added by inoculation.