Use of gamma radiation for inactivating Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in tahini halva.

Tahini halva is a traditional sweet product that is consumed with bread in different countries. It is a low water activity (aw) product basically made by mixing and cooking tahini, sugar, citric acid and Saponaria officinalis root extract together. Tahini halva maybe contaminated with foodborne pathogens during any stage of production from tahini and other raw ingredients, workers, environment or contact surfaces. The objectives of the study were to i) investigate the efficacy of gamma radiation to inactivate Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in tahini halva, ii) evaluate the effect of pre-irradiation storage (0, 7 and 30 days at 21 °C) of tahini halva on the sensitivity of these microorganisms toward gamma radiation, and iii) evaluate the effect of post-irradiation storage of tahini halva for up to 6 months on the their survival characteristics. Tahini halva samples were inoculated with Salmonella spp., E. coli O157:H7 and L. monocytogenes separately then stored at 21 °C for 0, 7 and 30 days prior to irradiation at 0-4 KGy and for up to 6 months after irradiation at 4 KGy. Salmonella spp. were the most irradiation resistance among the tested microorganisms. Irradiation (0.8-4.0 KGy) reduced the bacteria in samples stored for 0, 7 and 30 days pre-irradiation in the range of 0.43-2.11, 0.45-2.68 and 0.52-2.7 log10 CFU/g for Salmonella spp., 0.55-3.08, 0.66-3.00 and 0.60-2.80 log10 CFU/g for E. coli O157:H7, and 0.69-2.96, 0.86-4.30, 0.62-3.29 log10 CFU/g for L. monocytogenes, respectively. The D10-value, the irradiation dose needed to inactivate 1 log10 of pathogen, was 1.83, 1.47 and 1.50 KGy for Salmonella spp., 1.28, 1.32 and 1.48 KGy for E. coli O157:H7, and 1.33, 0.94 and 1.27 KGy for L. monocytogenes in pre-irradiation stored samples for 0, 7 and 30 days, respectively. Post-irradiation storage was efficient in decreasing the levels of the microorganisms ca. ≥2 log10 CFU/g in the first month and to undetected level after the second month of storage but enrichment results showed that Salmonella spp. and L. monocytogenes were detected in the samples until of the end of storage period. The study demonstrates that gamma radiation can be applied to inactivate of foodborne pathogens in tahini halva. Irradiation dose at 4 KGy can reduce Salmonella spp., E. coli O157:H7 and L. monocytogenes in tahini halva by 2-3 log10 CFU/g. Storage of tahini halva before or after irradiation may reduce the risk of foodborne pathogens in the product.

Osaili TM ，Al-Nabulsi AA ，Aljaafreh TF 《-》

Inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in ready-to-bake cookie dough by gamma and electron beam irradiation.

This study was conducted to investigate the efficacy of gamma and electron beam irradiation to inactivate foodborne pathogens in ready-to-bake cookie dough and to determine the effect on quality by measuring color and texture changes. Cookie dough inoculated with Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes was subjected to gamma and electron beam irradiation, with doses ranging from 0 to 3 kGy. As the radiation dose increased, the inactivation effect increased among all tested pathogens. After 3.0 kGy of gamma and electron beam irradiation, numbers of inoculated pathogens were reduced to below the detection limit (1 log CFU/g). The D10-values of E. coli O157:H7, S. Typhimurium, and L. monocytogenes in cookie dough treated with gamma rays were 0.53, 0.51, and 0.71 kGy, respectively, which were similar to those treated by electron beam with the same dose. Based on the D10-value of pathogens in cookie dough, L. monocytogenes showed more resistance to both treatments than did E. coli O157:H7 and S. Typhimurium. Color values and textural characteristics of irradiated cookie dough were not significantly (P > 0.05) different from the control. These results suggest that irradiation can be applied to control pathogens in ready-to-bake cookie dough products without affecting quality.

Jeong SG ，Kang DH 《-》

Effect of gamma irradiation on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes on pistachios.

This study evaluated the efficacy of gamma irradiation to inactivate food-borne pathogens on pistachios (Pistacia vera L.). Pistachios inoculated with Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes were subjected to gamma irradiation in the range of 0, 0·5, 1, 3 and 5 kGy, and colour change was evaluated after treatment and during storage at room temperature. Pathogen populations decreased with increasing treatment doses. A gamma irradiation dose of 5 kGy decreased the three pathogens on pistachios to under the detection limit (1·0 log CFU per g) without effecting colour change. During storage following treatment, pathogens were reduced due to the postirradiation effect. D-values of pathogens on pistachios showed that L. monocytogenes was more resistant to gamma irradiation than was E. coli O157:H7 or S. Typhimurium. During gamma irradiation treatment, L, a and b values of pistachios did not significantly change but these values changed during storage. These results show that gamma irradiation has potential as a nonthermal process for inactivating food-borne pathogens in pistachios without inducing colour changes. SIGNIFICANCE AND IMPACT OF THE STUDY: Generally, nuts have lower water activity which precludes the growth of food-borne pathogens. But, food-borne outbreaks due to pathogen-contaminated nuts have been reported in the last few decades. Pistachios are one of the most popular nuts and have many health beneficial effects. However, many pasteurization interventions have been used to reduce pathogens on pistachios, but most of them are not effective. This study confirms the effectiveness of gamma irradiation on pasteurization of pistachios. This may be helpful in nut processing industries to ensure the microbial safety of nuts.

Song WJ ，Kim YH ，Kang DH 《-》

Inactivation of stressed Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes in hummus using low dose gamma irradiation.

Hummus is a popular dip in the Middle East region prepared by mixing the boiled chickpeas with tahini and other ingredients, and because its consumption has increased world-wide some notoriety has developed following an increase in the incidence of hummus-related illness outbreaks and recalls. The objectives of the current research were (i) to study the efficiency of low dose gamma irradiation to inhibit Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in hummus, and (ii) to assess the effect of environmental stresses namely cold, heat, and desiccation on the resistance of these pathogens to gamma irradiation. The samples of hummus were prepared and then individually inoculated with approximately 7.0 log CFU/g of unstressed or cold-, heat-, or desiccated-stressed cocktail cultures of each of E. coli O157:H7, S. enterica, and L. monocytogenes. The inoculated samples were then exposed to gamma irradiation at doses of 0.1 to 0.6 kGy. The numbers of unstressed E. coli O157:H7, S. enterica, and L. monocytogenes were decreased by 0.6-3.9, 0.7-2.9, and 1.0-3.0 log CFU/g, respectively, by irradiation treatment. The resistance of E. coli O157:H7 to gamma irradiation was not affected by desiccation, heat, and cold stresses. However, the pre-exposure of S. enterica and L. monocytogenes cells to these stresses reduced their resistance toward gamma irradiation. PRACTICAL APPLICATION: Gamma irradiation is a non-thermal treatment that can be used in food processing to ensure food safety and quality. The current study proved that low levels (≤0.6 kGy) of gamma irradiation can effectively decrease the risk of unstressed and cold-, heat-, or desiccation-stressed Salmonella enterica, Listeria monocytogenes, or Escherichia coli O157:H7 in hummus.

Olaimat AN ，Al-Nabulsi AA ，Osaili TM ，Al-Holy M ，Abu Ghoush M ，Alkhalidy H ，Jaradat ZW ，Ayyash M ，Holley RA ... -  《-》

Evaluation of fermentation, drying, and/or high pressure processing on viability of Listeria monocytogenes, Escherichia coli O157:H7, Salmonella spp., and Trichinella spiralis in raw pork and Genoa salami.

We evaluated the effectiveness of fermentation, drying, and high pressure processing (HPP) to inactivate Listeria monocytogenes, Escherichia coli O157:H7, Salmonella spp., and Trichinella spiralis in Genoa salami produced with trichinae-infected pork. In addition, we evaluated the effectiveness of using HPP to inactivate T. spiralis larvae in pig masseter tissue. In part A, Genoa salami batter (about 2.3 log larvae/g) prepared with trichinae-infected pork was separately spiked with a five-strain cocktail of each microbial pathogen (about 7.0 log CFU/g) and subsequently fermented at 20 degrees C and about 90 to 95% RH for 6h and then at 27 degrees C and about 90 to 95% RH for 26 h before being dried at 20 degrees C and about 65 to 75% RH for 40 h and then at 17 degrees C and about 65 to 75% RH to/for: A) 25 d (65 mm casing), B) a target a(w) of 0.92 (65 mm casing), C) 35 d (105 mm casing), or D) a target a(w) of 0.94 (105 mm casing). Inactivation of L. monocytogenes, E. coli O157:H7, and Salmonella spp. after fermentation and drying ranged from about 1.1 to 1.3, about 1.1 to 2.2, and about 4.2 to 4.8 log CFU/g, respectively. After drying, three replicate salami samples in each of two trials for each treatment were subjected to HPP. Pressurization at 600 MPa or at 483 MPa for 1 to 12 min reduced pathogen numbers by an additional 1.6 to >or=5.0 (L. monocytogenes), 4.7 to >or=5.8 (E. coli O157:H7), and 1.9 to 2.4 (Salmonella)log CFU/g. After storage for 28 d at 4 degrees C, L. monocytogenes levels decreased by up to an additional 3.0 log CFU/g, whereas an additional decrease of up to about 1.1 and 1.7 log CFU/g was observed for E. coli O157:H7 and Salmonella, respectively. In contrast, in each of three trials, T. spiralis was inactivated (about 2.3 log larvae/g) in Genoa salami by all treatments of fermentation and drying as confirmed by both microscopy and mouse bioassays. In part B, in each of two trials, a 10-g portion (2 replicates per treatment) of infected pig masseter muscle (about 3.4 log larvae/g) were pressurized at 483 and 600 MPa for 0.5 to 5 min. T. spiralis was inactivated in pig masseter by all treatments of HPP as confirmed by both microscopy and mouse bioassays. Thus, fermentation and drying and/or HPP of contaminated Genoa salami or pork are effective for inactivating L. monocytogenes, E. coli O157:H7, Salmonella spp., and/or T. spiralis larvae. These data validate that HPP can be used as an alternate to curing for trichinae control and as a post-process intervention to meet performance standards and/or compliance guidelines for the three microbial pathogens evaluated herein.

Porto-Fett AC ，Call JE ，Shoyer BE ，Hill DE ，Pshebniski C ，Cocoma GJ ，Luchansky JB ... -  《-》