Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-.6% yeast extract (TSBYE) or sterile, whole milk and heated at 62.8°C in sealed thermal death time tubes. Severely heat-injured cells were recovered in TSBYE within sealed thermal death time tubes because of the formation of reduced conditions in the depths of the TSBYE. Also, the use of strictly anaerobic Hungate techniques significantly increased recovery in TSBYE containing 1.5% agar compared with aerobically incubated controls. The exogenous addition of catalase, but not superoxide dismutase, slightly increased the recovery of heat-injured cells in TSBYE containing 1.5% agar incubated aerobically. Growth of cells at 43°C caused a greater increase in heat resistance as compared with cells heat shocked at 43°C or cells grown at lower temperatures. Growth of L. monocytogenes at 43°C and enumeration by the use of strictly anaerobic Hungate techniques resulted in D62.8°C values that were at least sixfold greater than those previously obtained by using cells grown at 37°C and aerobic plating. Results indicate that, under the conditions of the present study, high levels of L. monocytogenes would survive the minimum low-temperature, long-time treatment required by the U.S. Food and Drug Administration for pasteurizing milk. The possible survival of low levels of L. monocytogenes during high-temperature, short-time pasteurization and enumeration of injured cells by recovery on selective media under strictly anaerobic conditions are discussed.

Effect of temperature, pH, water activity, and nine antifungal agents on growth of Aspergihs flavus and A. parasiticus was determined on Sabouraud-Dextrose Agar and on corn. Maximal growth of the two molds occurred at 33"C, the highest temperature used, pH of 5.0 and a, of 0.99. At 15'C, growth was observed at a, of 0.95 but not 0.90. Slight growth was observed at an a, of 0.85 at 27°C and 33°C. Nine antifungal agents (Botran, Orthocide, Polyram 80, Topsin-M, Thiram, Imazalil, sodium propionate, sodium sulfite and DDVP) were tested for inhibition of growth. Activity of the antifungals increased as the a, was decreased. All antifungals showed inhibitory activity, but Imazalil and DDVP were the most effective agents at the lowest concentrations.

A simple well-plate technique was utilized to determine the effect of various metals on the growth of microorganisms in media containing different polyphosphates. Aspergillus flavus and four gram-positive bacteria were completely inhibited by media containing 1% of various alkaline polyphosphates, whereas four gram-negative bacteria were not. Significant differences were observed between the type of polyphosphate added, the type of metal added, and the species of gram-positive bacterium inhibited. The addition of Mg2+ stimulated growth of A. flavus and Bacillus cereus in the presence of tetrasodium pyrophosphate, whereas Mn2+ permitted growth of A. flavus and Staphylococcus aureus in the presence of sodium hexametaphosphate. Iron supplementation allowed the growth of S. aureus and Listeria monocytogenes on media containing 1 % tetrasodium pyrophosphate. A method for determining the amount of calcium and magnesium in water was modified to detect free Mg2+ by replacing EDTA with phosphate. The addition of free Mg2+, but not Mg2+ chelated by tetrasodium pyrophosphate, permitted the growth of B. cereus on a medium containing tetrasodium pyrophosphate. It is speculated that polyphosphates specifically inhibited A. flavus and gram-positive bacteria by removing essential metals from cation-binding sites located within their cell walls.

The effects of selected organic acids and salts on microbial numbers, pH, exudate, and color were studied for vacuum-packaged, fresh pork chops. Pork chops were dipped for 2 min in (vhr) 1% acetic acid, 1% acetic/l% lactic acid, 1.5% acetic/l.5% sodium acetate, 3% acetic/ 3% sodium ascorbate, 3% acetic/2% NaCl or sterile, distilled water before being vacuum-packaged and stored at 2" -4°C for 6 weeks. Treatments containing 3% acetic acid resulted in lower aerobic microbial numbers (PcO.05) and effectively inhibited Enrerobacferiaceae. Treatments containing 1% acetic acid, with or without 1% lactic acid, were ineffective.All acid treatments increased exudate and were detrimental to meat color (PcO.05) although sodium ascorbate reduced color damage. Chops treated with 3% acetic acid/3% sodiuti ascorbate had the highest Hunter a and L color scores.

No abstract

The effects of low dose (100 krad) irradiation on microflora, sensory characteristics, and development of oxidative rancidity of vacuum packaged pork loins was investigated after irradiation and during low temperature (4°C) storage up to 2 1 days. Irradiation reduced numbers of mesophiles, psychrotrophs, anaerobic bacteria (P

Survival and growth of naturally occurring or inoculated bacteria were studied in refrigerated (5"C), vacuum-packaged ground pork irradiated at 100 krad (1kGy). Numbers of naturally occurring mesophiles, psycbrotrophs and anaerobes or facultative anaerobes were reduced (PCO.01) by irradiation, whereas lactic acid bacteria were least affected. Partial bacterial recovery during subsequent storage at 5°C suggested sublethal bacterial injury due to irradiation. Irradiation prolonged shelf-life 2.5-3.5 days (3@44%) in uninoculated and l&1.5 days in inoculated (lo5 CFU/g) meat. Added sodium acid pyrophosphate (SAPP) (0.4%) contributed two additional days to inoculated, irradiated pork shelf-life but had no effect on the naturally occurring micrbflora. Lipid oxidation did not increase (P>O.O5) due to irradiation and was unaffected by phosphates.

Microbiological and some physical and chemical effects of treating pork chop surfaces with sodium acid pyrophosphate, a commercial phosphate blend, potassium sorbate and phosphate/sorbate/sodium acetate solutions, with or without sodium chloride, before packaging were studied in pork chops vacuum-packaged and stored at 2A"C for 10 weeks. All treatments containing potassium sorbate reduced (P