Microbial shelf life of chub-packaged ground beef from four large Microbial shelf life of chub-packaged ground beef from four large U.S. processing plants U.

Ten pound chubs of coarsely ground beef quality of ground beef becomes an important of two different lean:fat specifications (73:27 issue. The nutrients in meat that are essential and 81:19) were stored at three temperatures for humans also are essential for microorgan(34, 38 or 45EF) to monitor the effects of isms, resulting in an extremely perishable storage temperature on microbial condition of product. the product. Ground beef from four U.S. plants was tested (2 trials each), and microIncreased bacterial growth reduces shelf bial analyses were conducted on storage days life by initiating spoilage characteristics such 0, 6, 10, 14, and 18 using seven different as off odor, off color, and gas formation in media to estimate counts of total aerobic and vacuum bags. Contamination during processanaerobic, lactic acid bacteria (LAB), and ing limits shelf life of the already fragile Gram-negative bacteria. Bacterial counts for ground beef product. a given culture medium were similar among plants and meat types. At day 10, total miGroups of microorganisms interact to crobial counts from chubs stored at 38 or inhibit each other, depending especially on 45EF were approximately 8 log CFU/g, storage temperature. A small number of 10 whereas total counts from chubs stored at initial carcass microflora are psychrotropic 34EF were approximately 4.5 log CFU/g (4 (grow best in the cold). They increase as the 10 log=10,000, CFU is colony forming units). initial predominant mesophilic organisms Regardless of storage temperature and meat (grow best at body temperature) decrease type, LAB predominated. Growth of gramunder cold conditions. negative enteric bacteria was delayed in chubs stored at 34EF throughout the 18 day Organisms associated with meat spoilage study, whereas counts increased in chubs include Pseudomonas, Acinetobacter, Morstored at 38 or 45EF. axella, Serratia, Altermonas, Brochrothrix,


Summary
Ten pound chubs of coarsely ground beef quality of ground beef becomes an important of two different lean:fat specifications (73:27 issue.The nutrients in meat that are essential and 81:19) were stored at three temperatures for humans also are essential for microorgan-(34, 38 or 45EF) to monitor the effects of isms, resulting in an extremely perishable storage temperature on microbial condition of product.the product.Ground beef from four U.S. plants was tested (2 trials each), and micro-Increased bacterial growth reduces shelf bial analyses were conducted on storage days life by initiating spoilage characteristics such 0, 6, 10, 14, and 18 using seven different as off odor, off color, and gas formation in media to estimate counts of total aerobic and vacuum bags.

Introduction
In 1994, the average American consumed 64 pounds of ground beef.Therefore, the Lactobacillus, and Hafnia.Packaging can alent in aerobically packaged fresh beef, whereas Hafnia alvei has been implicated in the spoilage (gassy packages, hydrogen were transported on ice to either Kansas sulfide odor) of vacuum-packaged strip loin State University (KSU) steaks.Because the initial microflora on Manhattan, KS or the Food Research Instimeat is primarily mesophilic, shelf life is tute (FRI) Madison, WI for microbiological prolonged by the combined use of refrigera-analysis.The chubs to be sampled on days 6, tion and vacuum packaging.A greater in-10, 14, and 18 were transported to correcrease in microbial counts in chub-packed sponding laboratories by commercial refrigerground beef during storage was reported at ated truck.45EF than at 36EF.Total aerobic plate counts have been reported to increase during Kansas State University stored ground storage, as well as the proportion of gram beef from two plants at 38 and 45EF, and the negative to gram positive organisms.Severe FRI stored product from two other plants at or even slight temperature abuse contributes 34 and 45EF.Immediately upon arrival at the to premature product deterioration, resulting laboratories, chubs were separated randomly in financial loss and negative response from into two equal groups and stored at the two consumers.
different temperatures.
This study was conducted to determine Microbial analyses were performed on the changes in microflora of three formula-two chubs from each temperature on days 0, tions of chub packaged ground beef over an 6, 10, 14, and 18.A 50 g sample of ground 18 day storage at three temperatures using beef was removed aseptically from the chub total aerobic and anaerobic plate counts in and placed into a stomacher bag along with conjunction with selective and differential 150 ml of 0.1% peptone (Difco), resulting in agars.Four individual meat packing facilities an initial 1:4 dilution.Serial 1:10 dilutions in four separate locations throughout the (0.1% peptone) were spiral-(KSU), spread-United States were sources of beef.

Experimental Procedures
Ten pound ground beef chubs were sam-Tryptic Soy Agar (Difco, Detroit, MI) pled from four U.S. meat processing facili-with 5% defibrinated sheep blood added was ties.Samples were collected twice from each used to determine both the total aerobic and facility between August, 1996 and January, anaerobic plate counts.Anaerobic incubation 1997.Three product types with different fat conditions were achieved using an anaerobe and lean concentrations were examined from jar in conjunction with a BBL GasPak Plus each facility [73/27 (73%) ground beef, 81/19 anaerobic atmosphere generators (4 to 10% (81%) ground beef, and 81/19 (GC) ground carbon dioxide).APT Agar (APT) was used chuck].All ground beef samples were by KSU, whereas the FRI used MRS Agar coarsely ground.During product collection (MRS) to enumerate LAB.Pseudomonas from each facility, chubs from each product Isolation Agar (PIA) was used to determine type were collected randomly and boxed.All the presence of Pseudomonas spp., especially chubs used for one trial at one plant were P. aeruginosa.Violet Red Bile Agar produced on the same day during the same (VRBA) was used in the pour plate method shift.The chubs used for day 0 sampling to determine coliform and gram negative seven different commercially available agars and incubated at 68EF for 5 days.
counts.Desoxycholate Lactose Agar (DL) was used to enumerate gram negative enteric reached 7 to 8 log CFU/g.Because counts bacilli.All plates were incubated at 68EF. of 8 log CFU/g also were recovered on

Results and Discussion
Because the bacterial plate counts were similar for all three meat types, data are Initial gram negative enteric bacteria were presented only for 73% lean ground beef.
present at about 2 to 3.5 log CFU/g in Initial total aerobic plate counts were approx-samples from all plants and increased to imately 4 to 5 log CFU/g for samples from approximately 5.0 and 5.

Food
Research Institute, University of Wisconsin, Madison, MI 53706.
4EF increase in storage temperature other plants, KSU) increased approximately resulted in more rapid microbial growth and 1 log CFU/g by day 10 and reached 7 log faster product spoilage.