Effect of selected antimicrobial compounds on the radiosensitization of Salmonella Typhi in ground beef.

AIMS: In this study, we extended our previous work to determine the efficiency of antimicrobial compounds in increase of relative radiosensitivity of Salmonella Typhi in medium fat ground beef (23% fat) by testing 41 different essential oils (EOs), oleoresins and food sauces. METHODS AND RESULTS: Ground beef samples inoculated with Salmonella Typhi (10(6) CFU g(-1)) were treated with each antimicrobial compound at a concentration of 0.5% (w/w). Then, the samples (25 g each) were packaged under air and irradiated in a (60)Co irradiator at doses from 0 to 1.75 kGy. Radiosensitivity was evaluated by calculating relative radiation sensitivity, defined as the ratio of radiation D(10) value in the absence/presence of antimicrobial compound. CONCLUSIONS: Depending on the compound tested, the addition of antimicrobial compound decreased the D(10) value of Salmonella Typhi, resulting in an increase of the radiation sensitivity up to more than four times. Among these antimicrobial compounds, Chinese cinnamon EO, clove EO and trans-cinnamaldehyde were most effective to increase the radiosensitivity of Salmonella Typhi in ground beef. SIGNIFICANCE AND IMPACT OF THE STUDY: These observations demonstrate that some active compounds can function as radiosensitizers of Salmonella Typhi.

Combined effect of natural essential oils, modified atmosphere packaging, and gamma radiation on the microbial growth on ground beef.

Selected Chinese cinnamon, Spanish oregano, and mustard essential oils (EOs) were used in combination with irradiation to evaluate their ability to eliminate pathogenic bacteria and extend the shelf life of medium-fat-content ground beef (23% fat). Shelf life was defined as the time when the total bacterial count reached 10(7) CFU/g. The shelf life of ground beef was determined for 28 days at 4 degrees C after treatment with EOs. The concentrations of EOs were predetermined such that sensory properties of cooked meat were maintained: 0.025% Spanish oregano, 0.025% Chinese cinnamon, and 0.075% mustard. Ground beef samples containing EOs were then packaged under air or a modified atmosphere and irradiated at 1.5 kGy. Ground beef samples (10 g) were taken during the storage period for enumeration of total mesophilic aerobic bacteria, Escherichia coli, Salmonella, total coliforms, lactic acid bacteria, and Pseudomonas. Mustard EO was the most efficient for reducing the total mesophilic aerobic bacteria and eliminating pathogenic bacteria. Irradiation alone completely inhibited the growth of total mesophilic aerobic and pathogenic bacteria. The combination of irradiation and EOs was better for reducing lactic acid bacteria (mustard and cinnamon EOs) and Pseudomonas (oregano and mustard EOs). The best combined treatment for extending the shelf life of ground beef for up to 28 days was EO plus irradiation (1.5 kGy) and modified atmosphere packaging.

Effect of selected plant essential oils or their constituents and modified atmosphere packaging on the radiosensitivity of Escherichia coli O157:H7 and Salmonella typhi in ground beef.

Twenty-six different essential oils were tested for their efficiency to increase the relative radiosensitivity of Escherichia coli and Salmonella Typhi in medium-fat ground beef (23% fat). Ground beef was inoculated with E. coli O157:H7 or Salmonella (10(6) CFU/g), and each essential oil or one of their main constituents was added separately at a concentration of 0.5% (wt/wt). Meat samples (10 g) were packed under air or under modified atmosphere and irradiated at doses from 0 to 1 kGy for the determination of the D10-value of E. coli O157:H7, and from 0 to 1.75 kGy for the determination of the D10-value of Salmonella Typhi. Depending on the compound tested, the relative radiation sensitivity increased from 1 to 3.57 for E. coli O157:H7 and from 1 to 3.26 for Salmonella Typhi. Addition of essential oils or their constituents before irradiation also reduced the irradiation dose needed to eliminate both pathogens. In the presence of Chinese cinnamon or Spanish oregano essential oils, the minimum doses required to eliminate the bacteria were reduced from 1.2 to 0.35 and from 1.4 to 0.5 for E. coli O157:H7 and Salmonella Typhi, respectively. Cinnamon, oregano, and mustard essential oils were the most effective radiosensitizers.

Influence of antimicrobial compounds and modified atmosphere packaging on radiation sensitivity of Listeria monocytogenes present in ready-to-use carrots (Daucus carota).

Radiosensitization of Listeria monocytogenes was determined in the presence of trans-cinnamaldehyde, Spanish oregano, winter savory, and Chinese cinnamon on peeled minicarrots packed under air or under a modified atmosphere (60% O2, 30% CO2, and 10% N2). Samples were inoculated with L. monocytogenes HPB 2812 serovar 1/2a (106 CFU/g) and were coated separately with each active compound (0.5%, wt/wt) before being packaged under air or the modified atmosphere and irradiated at doses from 0.07 to 2.4 kGy. Results indicated that the bacterium was more resistant to irradiation under air in the absence of active compound. The dose required to reduce L. monocytogenes population by 1 log CFU (D10) was 0.36 kGy for samples packed under air and 0.17 kGy for those packed under the modified atmosphere. The active compounds evaluated in this study had an effect on the radiation sensitivity of L. monocytogenes on carrots. The most efficient compound was trans-cinnamaldehyde, where a mean 3.8-fold increase in relative radiation sensitivity was observed for both atmospheres compared with the control. The addition of winter savory and Chinese cinnamon produced a similar increase in relative radiation sensitivity but only when samples where packed under modified atmosphere conditions.