Radiation resistance of lactobacilli isolated from radurized meat relative to growth and environment.

Of 113 lactobacilli isolated from radurized (5 kGy) minced meat, 7 Lactobacillus sake strains, 1 L. curvatus strain, and 1 L. farciminis strain were used for radiation resistance studies in a semisynthetic substrate (i.e., modified MRS broth). Five reference Lactobacillus spp., one Staphylococcus aureus strain, and one Salmonella typhimurium strain were used for comparative purposes. All L. sake isolates exhibited the phenomenon of being more resistant to gamma-irradiation in the exponential (log) phase than in the stationary phase of their growth cycles by a factor of 28%. Four references strains also exhibited this phenomenon, with L. sake (DSM 20017) showing a 68% increase in resistance in the log phase over the stationary phase. This phenomenon was not common to all bacteria tested and is not common to all strains with high radiation resistance. Four L. sake isolates and three reference strains were used in radiation sensitivity testing in a natural food system (i.e., meat). The bacteria were irradiated in minced meat and packaged under four different conditions (air, vacuum, CO2, and N2). Organisms exhibited the highest death rate (lowest D10 values [doses required to reduce the logarithm of the bacterial population by 1] ) under CO2 packaging conditions, but resistance to irradiation was increased under N2. The D10 values of the isolates were generally greater than those of the reference strains. The D10 values were also higher (approximately two times) in meat than in semisynthetic growth medium.

Shelf-Life Extension of Minced Beef Through Combined Treatments Involving Radurization.

The effect of addition of glucose, lactic acid (LA) as well as radurization on several bacterial groups in refrigerated beef was investigated. Glucose added to meat in concentrations of 2 to 10% (w/w) had little influence on the bacteria monitored. Addition of LA to a pH of 5 had a marked effect on several bacteria groups in meat; the effect became more pronounced during storage. An increased shelf life was obtained but the appearance of LA-treated samples was undesirable. Radurization (2.5 kGy) had a far greater effect on shelf life than any of the other treatments, although an overwhelming population of lactic acid bacteria developed toward the end of the storage period. Radurization also caused a significant increase in the shelf life in comparison to control, glucose-treated and LA-treated meat samples. A combiend treatment of radurization and LA had an even greater effect on the bacterial population and the shelf life of meat than that of the two separate treatments.

Radurization of Prime Beef Cuts.

The bacteriology, organoleptic quality and shelf-life extension of radurized beef cuts were investigated. Application of doses of 2 kGy to vacuum-packed meat caused a considerable change in the bacterial population by elimination of the pseudomonads, Enterobacteriaceae and enterococci. The LLP group of lactic acid bacteria was relatively resistant to radiation, and after radurization was mostly comprised of Lactobacillus species. The lactobacilli multiplied rapidly on the meat during storage at 4 C, and reached relatively high numbers toward the end of the storage period. Odor and appearance evaluations were carried out at regular intervals and were used together with organoleptic testing and bacteriological analyses to determine the shelf-life extension of radurized beef cuts. A doubling in the shelf-life of samples irradiated to 2 kGy was attained when compared to non-irradiated (control) samples.