Efficacy of integrated treatment of UV light and low-dose gamma irradiation on inactivation of Escherichia coli O157:H7 and Salmonella enterica on grape tomatoes.

The study evaluated the efficacy of integrated ultraviolet-C light (UVC) and low-dose gamma irradiation treatments to inactivate mixed strains of Escherichia coli O157:H7 and Salmonella enterica on inoculated whole grape tomatoes. A mixed bacterial cocktail composed of a 3 strain mixture of E. coli O157:H7 (C9490, E02128, and F00475) and a 3 serotype mixture of S. enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) was used based on their association with produce-related outbreaks. Spot inoculation (50 to 100 µmL) on tomato surfaces was performed to achieve a population of appropriately 10(7-8) CFU/tomato. Inoculated tomatoes were subjected to UVC (253.7 nm) dose of 0.6 kJ/m(2) followed by 4 different low doses of gamma irradiations (0.1 kGy, 0.25 kGy, 0.5 kGy, 0.75 kGy). The fate of background microflora (mesophilic aerobic) including mold and yeast counts were also determined during storage at 5 °C over 21 d. Integrated treatment significantly (P < 0.05) reduced the population of target pathogens. Results indicate about 3.4 ± 0.3 and 3.0 ± 0.1 log CFU reduction of E. coli O157:H7 and S. enterica, respectively, per tomato with UVC (0.6 kJ/m(2) ) and 0.25 kGy irradiation. More than a 4 log and higher reduction (>5 log) per fruit was accomplished by combined UVC treatment with 0.5 kGy and 0.75 kGy irradiation, respectively, for all tested pathogens. Furthermore, the combined treatment significantly (P < 0.05) reduced the native microflora compared to the control during storage. The data suggest efficacious treatment strategy for produce indicating 5 or higher log reduction which is consistent with the recommendations of the Natl. Advisory Committee on Microbiological Criteria for Foods.

Inhibitory effects of organic acid salts on growth of Clostridium perfringens from spore inocula during chilling of marinated ground turkey breast.

Inhibition of Clostridium perfringens germination and outgrowth by salts of organic acids such as sodium lactate, sodium acetate, buffered sodium citrate and buffered sodium citrate supplemented with sodium diacetate was evaluated during continuous chilling of ground turkey. Turkey breast meat was injected with a brine-containing NaCl, potato starch and potassium tetra pyrophosphate to yield final in-product concentrations of 0.85%, 0.25% and 0.20%, respectively. The meat was ground, mixed with either sodium lactate (1%, 2%, 3% or 4%), sodium acetate (1% or 2%), buffered sodium citrate (Ional, 1%) or buffered sodium citrate supplemented with sodium diacetate (Ional Plus trade mark, 1%), in addition to a control that did not contain added antimicrobials. Each product was mixed with a three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.8 log10 spores/g. Inoculated products (10 g) were packaged into cook-in-bags (2 x 3 in.), vacuum sealed, cooked at 60 degrees C for 1 h, and subsequently chilled from 54.4 to 7.2 degrees C in 15, 18 and 21 h following exponential chilling rates. Products were sampled immediately after cooking and then after chilling. Chilling of cooked turkey following 15, 18 and 21 h chill rates resulted in germination and outgrowth of C. perfringens spores to 6.6, 7.58 and 7.95 log10 CFU/g populations, respectively, from initial spore populations of ca. 2.80 log10 CFU/g. Incorporation of sodium lactate (1%), sodium acetate (1%), Ional or Ional Plus (1%) substantially inhibited germination and outgrowth of C. perfringens spores compared to controls. Final C. perfringens total populations of 3.12, 3.10, 2.38 and 2.92 log10 CFU/g, respectively, were observed following a 15-h exponential chill rate. Similar inhibitory effects were observed for 18 and 21 chill rates with the antimicrobials at 1% concentrations. While sodium lactate and sodium acetate concentrations of 1% were sufficient to control C. perfringens germination and outgrowth (<1.0 log10 CFU/g growth) following 15 h chill rates, higher concentrations were required for 18 and 21 h chill rates. Ional at 1% concentration was effective in inhibiting germination and outgrowth to <1.0 log10 CFU/g of C. perfringens for all three chill rates (15, 18 and 21 h) tested. Use of sodium salts of organic acids in formulation of ready-to-eat meat products can reduce the risk of C. perfringens spore germination and outgrowth during chilling.

Control of Clostridium perfringens germination and outgrowth by buffered sodium citrate during chilling of roast beef and injected pork.

Inhibition of the germination and outgrowth of Clostridium perfringens by buffered sodium citrate (Ional) and buffered sodium citrate supplemented with sodium diacetate (Ional Plus) during the abusive chilling of roast beef and injected pork was evaluated. Beef top rounds or pork loins were injected with a brine containing NaCl, potato starch, and potassium tetrapyrophosphate to yield final in-product concentrations of 0.85, 0.25, and 0.20%, respectively. Products were ground and mixed with Ional or Ional Plus at 0, 0.5, 1.0, and 2.0%. Each product was mixed with a three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.5 log10 spores per g. Chilling of roast beef from 54.4 to 7.2 degrees C resulted in C. perfringens population increases of 1.51 and 5.27 log10 CFU/g for 18- and 21-h exponential chill rates, respectively, while chilling of injected pork resulted in increases of 3.70 and 4.41 log10 CFU/g. The incorporation of Ional into the roast beef formulation resulted in C. perfringens population reductions of 0.98, 1.87, and 2.47 log10 CFU/g with 0.5, 1.0, and 2.0% Ional, respectively, over 18 h of chilling, while > or = 1.0% Ional Plus was required to achieve similar reductions (reductions of 0.91 and 2.07 log10 CFU/g were obtained with 1.0 and 2.0% Ional Plus, respectively). An Ional or Ional Plus concentration of > or = 1.0% was required to reduce C. perfringens populations in roast beef or injected pork chilled from 54.4 to 7.2 degrees C in 21 h. Cooling times for roast beef or injected pork products after heat processing can be extended to 21 h through the incorporation of > or = 1.0% Ional or Ional Plus into the formulation to reduce the potential risk of C. perfringens germination and outgrowth.

Heat resistance and fatty acid composition of Listeria monocytogenes: effect of pH, acidulant, and growth temperature.

The objective of this study was to determine the influence of pH, acidulant, and growth temperature history on the heat resistance and fatty acid composition of Listeria monocytogenes Scott A. Cells were grown to late exponential phase (OD600 = 0.6) at 10, 19, or 37 degrees C in brain heart infusion broth acidified to pH 5.4 or 7 with either acetic or lactic acid. Thermal death times at 60 degrees C subsequently were determined by using a submerged-coil heating apparatus. The surviving cell population was enumerated by spiral-plating heated samples onto tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. The thermal resistance of cells cultured at a particular temperature was significantly lower (P < 0.05) when lactic acid was used to acidify the medium of pH 5.4. Regardless of acid identity, D values significantly decreased (P < 0.05) with increased growth temperature when the pH of the growth medium was 5.4, whereas D values significantly increased (P < 0.05) with increased temperature at pH 7. At pH 5.4 adjusted with lactic acid, D values were 1.30, 1.22, and 1.14 min for cells grown at 10, 19, and 37 degrees C, respectively. At pH 5.4 adjusted with acetic acid, L. monocytogenes failed to grow at 10 degrees C; the D values were 1.32 and 1.22 min when the cells were grown at 19 and 37 degrees C, respectively. At pH 7, the D values were 0.95, 1.12, and 1.28 min with lactic acid and 0.83, 0.93, and 1.11 min with acetic acid at 10, 19, and 37 degrees C, respectively. The most abundant fatty acids (44 to 82%) were branched-chain saturated fatty acids (anteiso-and iso-C15:0 and iso-C17:0) regardless of pH, acidulant, or growth temperature. However, there was an increase in C15:0 isomers at the expense of iso-C17:0 when the growth temperature was lowered from 37 to 10 degrees C. While variable changes in longer-chain fatty acids were found, the percentage of longer-chain (C16 and C18) fatty acids was greatest when L. monocytogenes was grown at 37 degrees C regardless of pH or acidulant. This study demonstrates that the heat resistance of L. monocytogenes depends upon its growth conditions.