Incidence of microorganisms from fresh orange juice processed by squeezing machines

This study was carried out to evaluate the microbiological quality of orange juice obtained from squeezing machines in foodservice establishments. The samples included fresh squeezed orange juice and juice which is maintained in metal jugs until consumption. According to the European Commission Regulation (No. 2073/2005 and No. 1441/2007) and Spanish microbiological criteria (No. 3484/2000), 12% and 43% of the total examined lots exceed the adopted limits of mesophilic aerobic counts and Enterobacteriaceae, respectively. Possibly, this contamination is caused by incorrect handling of oranges and juices and also by inadequate cleaning and sanitization of squeezing machine and metal jugs. Furthermore, 0.5 and 1% of all the examined lots were positive for the presence of Salmonella spp. and Staphylococcus aureus, respectively. However all lots were negative for Escherichia coli and Listeria monocytogenes. These results emphasize the need for applying and maintaining good hygienic practices in the restaurants.     

Inactivation of Escherichia coli O157:H7 and spoilage yeasts in germicidal UV-C-irradiated and heat-treated clear apple juice

The decimal reduction times (D) of individual and composited Escherichia coli O157:H7 or spoilage yeasts in UV-C irradiated and heated (55 °C) clear apple juices (pH 3.68, 12.5 °Brix) were determined. Spoilage yeasts (D = 6.38-11.04 min) were found to be generally more UV-C resistant than E. coli O157:H7 (D = 0.5-2.76 min), while the opposite was observed in terms of thermal resistance (E. coli D=0.9-4.43 min; yeast D = 0.03-6.10 min). All spoilage yeast proliferated in the untreated juice (25 °C) while all E. coli strains were inactivated. Except for E. coli O157:H7 in UV-C irradiated apple juice, the composited inocula of both pathogenic and spoilage test organisms were less tolerant than the identified most resistant strain or species. The results of this study may be used in identifying appropriate target organisms, as well as the modes of inoculation, in challenge studies and eventually in the establishment and validation of process lethalities for apple juices and similar commodities.     

Suboptimal growth conditions induce heterologous ultraviolet-C adaptation in Salmonella enterica in orange juice

This study was conducted to determine the effects of single and simultaneous physicochemical stress exposures on the subsequent resistance of Salmonella spp. to ultraviolet-C (UV–C) in orange juice (pH 3.1, 11.5 °Brix, 0.63% citric acid). Seven strains of the test bacterium were individually subjected to suboptimal growth conditions (24 h), including gradual acidification (final pH 4.5), abrupt desiccation (a_w 0.96), heat stress by incubation at high temperature (40 °C), and combinations of acid + desiccation (pH 4.5, a_w 0.96), acid + heat (pH 4.5, 40 °C), and desiccation + heat (a_w 0.96, 40 °C). Cocktail of the different strains previously exposed to specific stress were then subjected to UV–C inactivation. The UV–C resistance of Salmonella enterica was expressed in terms of D and D_UV–C values, which correspond to the unit time of exposure and UV–C energy necessary to reduce the population by 1 log cycle (90%), respectively. Results showed that in all treatments, S. enterica exhibited logarithmic linear or first-order UV inactivation kinetics, indicating that the cells had homogenous responses towards the environmental stresses and the eventual kill step. Except for heat, all prior stress exposures resulted in cells more resistant to UV–C than the control (D = 12.7 s, D_UV–C = 63.56 mJ/cm²). Cells previously exposed to desiccation were most resistant to UV–C with a D and D_UV–C values of 16.6 s and 83.20 mJ/cm², respectively. Combining desiccation with acid (D = 16.2 s, D_UV–C = 80.88 mJ/cm²) and heat (D = 15.0 s, D_UV–C = 75.16 mJ/cm²) also resulted in relatively more resistant cells, with D and D_UV–C values greater than those exposed to acid (D = 14.9 s, D_UV–C = 74.56 mJ/cm²), acid + heat (D = 14.4 s, D_UV–C = 72.00 mJ/cm²), and heat stresses (D = 11.9 s, D_UV–C = 59.67 mJ/cm²). All (D ratio = D stress/D control >1.0) but those previously exposed to heat stress (D ratio <1.0) exhibited heterologous adaptation against UV–C in orange juice. These results provide additional evidences of the induction of heterologous UV–C tolerance response in S. enterica from environmental stresses commonly encountered by cells in food and food processing ecologies.     

Comparison of antibiotic resistance patterns in Listeria monocytogenes and Salmonella enterica strains pre-exposed and exposed to poultry decontaminants

Recent opinions expressed by European Union Scientific Committees suggest there is a potential for poultry decontaminants to increase resistance to antibiotics. At this moment there is no scientific information available to estimate this risk accurately. Four strains (Listeria monocytogenes serovar 1/2a, Listeria monocytogenes serovar 4b, Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Enteritidis) were repeatedly exposed to increasing sub-inhibitory concentrations of decontaminants (trisodium phosphate, acidified sodium chlorite, citric acid, chlorine dioxide or peroxyacetic acid) and tested against 15 antibiotics by means of a standard disc-diffusion technique (NCCLS). The antibiotic resistance patterns of strains were compared before and after exposure to decontaminants. Intra-specific differences in antibiotic resistance patterns were found among strains. Increases in resistance to various antibiotics were observed in L. monocytogenes and S. enterica strains after exposure to chemicals (especially ASC). These results raise concerns over the application of certain poultry decontaminants, since they could contribute to the development of microbial resistance mechanisms. However, these are preliminary results derived from laboratory-based experiments. Additional studies under practical field conditions would be needed to substantiate these findings.     

Combined treatment with chlorine dioxide gas,fumaric acid,and ultraviolet-C light for inactivating Escherichia coli O157:H7 and Listeria monocytogenes inoculated on plums

Combined non-thermal treatment with chlorine dioxide (ClO₂) gas, ultraviolet-C (UV-C) light, and fumaric acid was performed to inactivate Listeria monocytogenes and Escherichia coli O157:H7 inoculated on plums. Plums were treated with ClO₂ gas (15 and 30 ppmv), fumaric acid (0.1, 0.3, and 0.5%), and by UV-C irradiation (3, 5, and 10 kJ/m²). The single treatments with 15 or 30 ppmv ClO₂ gas, 0.5% fumaric acid, and 10 kJ/m² UV-C decreased the population of L. monocytogenes by 1.78, 2.00, 1.65, and 1.62 log CFU/g, respectively, and the population of E. coli O157:H7 by 1.73, 1.81, 1.34, and 2.07 log CFU/g, respectively. In addition, combined treatments reduced the populations of the pathogenic bacteria more than each treatment alone. In particular, the combined treatment with ClO₂ gas (30 ppmv) for 20 min, fumaric acid (0.5%), and UV-C (10 kJ/m²) decreased the populations of L. monocytogenes and E. coli O157:H7 by 6.26 and 5.48 log CFU/g, respectively. These results suggest that combined treatment with ClO₂ gas, UV-C light, and fumaric acid may be a useful hurdle technology to enhance the microbiological safety of plums.     

Growth of acid-adapted Listeria monocytogenes in orange juice and in minimally processed orange slices

The aim of this work was to study the growth/survival of acid-adapted cells of Listeria monocytogenes, in orange juice and in minimally processed orange slices. The L. monocytogenes OML 45 behaviour into TSB (Tryptic Soy Broth) medium was evaluated at different pH values (between 3.7 and 6.7). The acid-adapted cells were obtained maintaining L. monocytogenes in TSB at pH 5.7 for 3 h. The obtained cells were then inoculated into a diluted orange juice with a pH of 2.6. Moreover, the acid-adapted cells were inoculated into minimally processed orange slices. The growth was evaluated during storage at different temperatures. The study confirms that orange juice and minimally processed orange slices can support the acid-adapted pathogen growth.     

Shelf life of snow crab clusters (Chionoecetes opilio) stored at 0 and 4 °C

Snow crab (Chionoecetes opilio) presents a commercial and economical important product with attractive sensory attributes. Today, snow crab is captured in the North Pacific, Arctic and Northwest Atlantic and it is mainly exported to the US, Canada, Japan, South-Korea and Europe as live, cooked and refrigerated or frozen. The aim of this work was to estimate shelf life of leg meat in cooked and raw snow crab clusters (one claw plus 4 legs) using sensory, microbial and chemical analysis when stored at 4 and 0 °C. The results revealed a shelf life of 10 and 14 days for cooked clusters stored at 4 and 0 °C, respectively. Corresponding maximum levels of TVC and pseudomonads at 4 °C were log 5.5 and 3.2 CFU/g, respectively, while complementary levels at 0 °C were log 4.9 and 4.2 CFU/g. Shelf life of raw clusters stored at 0 °C was 6 days. This shelf life corresponds to maximum levels of TVC and pseudomonads of approximately log 2.5 CFU/g showing that pseudomonads is the dominant microflora. For cooked clusters, sensory and microbial analyses were the best shelf life indicators, while sensory analysis was the best shelf life indicator in case of raw clusters.     

Survival of Listeria innocua in thermally processed orange juice as affected by vanillin addition

Presence of Listeria monocytogenes could seriously affect the safety of fruit juices. Addition of natural antimicrobials may be an alternative to enhance microbial inactivation in fruit juice thermal preservation. The response of L. innocua, surrogate for L. monocytogenes, to combined treatments involving moderate temperatures (57–61 °C) and addition of different levels of vanillin (0–1100 ppm) was assessed to find the most effective inactivation treatment in orange juice. The presence of vanillin greatly increased the bactericidal effect of the mild heat treatment. This effect considerably depended on the amount of added vanillin when working at the lowest temperature (57 °C), while at higher temperatures (60 or 61 °C) the increase in vanillin concentration did not produce a clear change in the response. Nonlinear semilogarithmic survival curves were successfully fitted using a modified version of Gompertz model and by the Weibullian model.