Inactivation of Escherichia coli in orange juice using ozone

This research investigated the efficacy of gaseous ozone for the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in orange juice. Orange juice inoculated with E. coli (10⁶ CFU mL^− 1) as a challenge microorganism was treated with ozone at 75–78 µg mL^− 1 for different time periods (0–18 min). The efficacy of ozone for inactivation of both strains of E. coli was evaluated as a function of different juice types: model orange juice, fresh unfiltered juice, juice without pulp, and juice filtered through 500 µm or 1 mm sieves. Fast inactivation rates for total reduction of E. coli were achieved in model orange juice (60 s) and in juice with low pulp content (6 min). However, in unfiltered juice inactivation was achieved after 15–18 min. This indicated that juice organic matter interferes with antibacterial activity of gaseous ozone. The effect of prior acid (pH 5.0) exposure of E. coli strains on the inactivation efficacy of ozone treatment was also investigated. There was a strain effect observed, where prior acid exposure resulted in higher inactivation times in some cases by comparison with the control cells. However, the overarching influence on inactivation efficacy of ozone was related to the pulp content. Generally, the applied gaseous ozone treatment of orange juice resulted in a population reduction of 5 log cycles.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. This study demonstrates that the use of ozone as a non-thermal technology is effective for inactivation of E. coli and acid exposed E. coli in orange juice. Information on the design of the ozone treatment for inactivation of E. coli which results into safe juice products is also among the main outputs of this work. Ozone auto-decomposition makes this technology safe for fruit juice processing.     

The effects of acid adaptation on Escherichia coli inactivation using power ultrasound

Inactivation of Escherichia coli in liquids was carried out using power ultrasound. Parameters examined included amplitude levels (0.4 µm, 7.5 µm, 37.5 µm), treatment time, cell condition (non-adapted cells, acid adapted cells), liquid media (TSB, model orange juice and model apple juice) and E. coli strain (ATCC 25922, NCTC 12900). The efficacy of ultrasound treatment was found to be a function of amplitude level, treatment time and media (p < 0.05). The kinetics of inactivation followed zero order kinetics (R > 0.95), with the highest inactivation achieved using an amplitude of 37.5 µm. The D-values of E. coli 25922 at all amplitudes in model orange juice were not significantly different than in TSB media. However, at 0.4 µm and 37.5 µm amplitude D-values of E. coli 12900 were significantly different in model orange juice compared to TSB media. When efficacy of ultrasound was assessed in model apple juice and phosphate buffered saline treatment times were significantly reduced by comparison with TSB. Inactivation of E. coli was found to be influenced by strain, prior acid adaptation and suspension liquid, but the effect was negated at the higher amplitude levels.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. This rule comes after a rise in the number of food borne illness outbreaks and consumer illnesses associated with consumption of untreated juice products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. Ultrasound has been identified as one possible non-thermal technology to meet the required microbial log reduction. However it is important to determine if conditions such as acid adaptation and pathogen strain influence ultrasound efficacy, if the technology is to be adopted by industry.     

A feasibility study of Lactobacillus plantarum in fruit powders after processing and storage

The aim of this study was to develop fruit powders (apple, banana and strawberry) enriched with a probiotic strain (Lactobacillus plantarum 299v). Two methodologies were proposed: (i) drying of the fruit with probiotic culture incorporated (by convection) or (ii) drying of fruit (by convection) and addition of spray‐dried probiotic culture. In the first methodology, processing caused a notable reduction in probiotic viable counts in apple, but this reduction was lower during drying of banana and strawberry. A large reduction in viable cells was also recorded during storage. In the second methodology, the survival of L. plantarum 299v was considerably higher during spray‐drying, and fruit powders with a microbial content suitable for a probiotic food (10⁸–10⁹ cfu g^?1) were obtained. The fruit powders incorporating L. plantarum 299v can be stored at 4 °C or at room temperature, for at least 3 months. This preliminary study demonstrated that fruit powders are good carriers of probiotic cultures, but the techniques used to produce them should be carefully considered.     

Microbial inactivation by pulsed electric fields in a batch treatment chamber: effects of some electrical parameters and food constituents

The inactivation of Escherichia coli by high voltage pulsed electric fields in a batch treatment chamber was studied in liquid, solid and semisolid foods or model systems. Treatment heterogeneity was demonstrated and found to be due to the presence of an air bubble trapped inside the chamber. Agitation of the inoculated liquid samples (16 mM sodium phosphate buffer, pH 7, ρ=460 Ωcm) during pulse processing resulted in efficient microbial inactivation (five log cycles at 33 kV/cm and 25°C after 261 μs of cumulated pulses). A slower inactivation rate was observed in inoculated solid agar gels of the same pH and resistivity, under the same pulse processing conditions. The inactivation of E. coli in inoculated dairy cream (33% fat, pH 6.8, ρ=370 Ωcm), ovalbumin solution (10% protein w/v, pH 6.7, ρ=370 Ωcm) or fish egg suspension (pH 6.8, ρ=400 Ωcm) was almost identical to that in 16 mM phosphate buffer, pH 7. Thus emulsified lipids, soluble proteins or conductive food particulates do not appear to protect against microbial inactivation by electric pulses.     

Identification and characterization of Dekkera bruxellensis, Candida pararugosa, and Pichia guilliermondii isolated from commercial red wines

Yeast isolates from commercial red wines were characterized with regards to tolerances to molecular SO₂, ethanol, and temperature as well as synthesis of 4-ethyl-phenol/4-ethyl-guaiacol in grape juice or wine. Based on rDNA sequencing, nine of the 11 isolates belonged to Dekkera bruxellensis (B1a, B1b, B2a, E1, F1a, F3, I1a, N2, and P2) while the other two were Candida pararugosa (Q2) and Pichia guilliermondii (Q3). Strains B1b, Q2, and Q3 were much more resistant to molecular SO₂ in comparison to the other strains of Dekkera. These strains were inoculated (10³–10⁴ cfu/ml) along with lower populations of Saccharomyces (<500 cfu/ml) into red grape juice and red wine incubated at two temperatures, 15 °C and 21 °C. Although Saccharomyces quickly dominated fermentations in grape juice, B1b and Q2 grew and eventually reached populations >10⁵ cfu/ml. In wine, Q3 never entered logarithmic growth and quickly died in contrast to Q2 which survived >40 days after inoculation. B1b grew well in wine incubated at 21 °C while slower growth was observed at 15 °C. Neither Q2 nor Q3 produced 4-ethyl-phenol or 4-ethyl-guaiacol, unlike B1b. However, lower concentrations of volatile phenols were present in wine incubated at 15 °C compared to 21 °C.     

Effects of rapid chilling of carcasses and time of deboning on weight loss and technological quality of pork semimembranosus muscle

The effect of rapid air chilling of carcasses in the first 3 h of chilling at −31 °C (then at 2–4 °C, till 24 h post-mortem) and the possibility of earlier deboning (8 h post-mortem) after rapid air chilling, compared to conventional air chilling (at 2–4 °C, till 24 h post-mortem) on weight loss and technological quality (pH value, tenderness, drip loss, cooking loss and colour - L^*a^*b^* values) of pork M. semimembranosus was investigated. Under the rapid chilling conditions, weight loss was 0.8% at 8 h post-mortem and increased to 1.4% at 24 h post-mortem when weight loss was 2.0% under conventional chilling. Carcasses that were rapid chilled had significantly lower (P < 0.001) internal temperature in the deep leg at 4 (25.7 °C), 6 (13.0 °C), 8 (6.2 °C) and 24 h (3.8 °C) post-mortem compared to conventional chill treatment (32.7, 24.2, 19.1 and 5.1 °C, respectively). Rapid chilling reduced significantly (P < 0.05) the rate of pH value decline at 8 h (6.02) post-mortem in M. semimembranosus compared to conventional chill treatment (5.88). Compared to conventional chilling, in M. semimembranosus deboned in different time post-mortem, rapid chilling had a positive significant effect on drip loss (P < 0.05, muscles deboned 8 h post-mortem), cooking loss (P < 0.001) and incidence of pale colour (L^* value). Rapid chilling i.e. rapid chilling and earlier deboning had neither positive nor negative significant effects (P > 0.05) on other investigated technological quality parameters of M. semimembranosus (tenderness, a^* value and b^* value) compared to conventional chilling.     

Quality improvement of non-sulphited mango slices by drying at high temperatures

An optimum drying routine for producing non-sulphited mango slices has been developed. The interaction of essential drying parameters (air temperature, air velocity, dew point, slice thickness and drying time) on water activity (a_W) and browning was determined. Microbiological stability of the dried product was achieved at a moisture content of 17% wet base (w.b.) corresponding to a_W = 0.6. Browning was monitored by the red colour shade of the product (CIE-Lab chromaticity coordinate a*). Drying air temperature and drying time were shown to be the primary factors influencing product colour and a_W. In contrast to common practice, drying for about 6 h at elevated air temperature (80 °C), instead of 50 or 60 °C for a longer time, was optimal, since significant colour changes of the mango slices were not observed even without the use of any chemical or thermal pre-treatment. Moreover, at increased temperature, drying time was considerably shortened from about 9 h to 6 h, resulting in significant extension of the drying capacity.

Industrial Relevance

The suggested process concept for dried mango slices based on high-temperature drying is of utmost significance for the international marketing of dried fruit products. Chemical pre-treatments such as sulphitation often used to minimise quality deficiencies could be avoided. Sulphitation has been recently under critical consideration with respect to allergen labelling of foodstuffs implemented by EU-Member States in November 2004 (Directive 2003/89/EC) [Directive 2003/89/EC. Official Journal of the European Union, 25.11.2003, pp. L308/15–18 (http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_308/l_30820031125en00150018.pdf)]. Export quality was improved and the drying process simplified, improving the utilisation of drying capacities. Particularly referring to an application of the technology in small- and medium-sized enterprises with limited investment possibilities, the suggested novel drying procedure in mango processing aimed at the optimisation of well-established simple drying methods instead of choosing technically more sophisticated technologies.     

A Feasibility Study on the Drying of Lime Juice: The Relationship between the Key Operating Parameters of a Small Laboratory Spray Dryer and Product Quality

Concentrated lime juice with 20% total soluble solids was dried using three levels of maltodextrin (40%, 50%, and 60% solid base) and a BüCHI B-190 spray dryer. The drying air temperature and flow rate were 140 °C, 155 °C, and 170 °C and 47.1, 53.5, and 57.8 m³/h, respectively. A total of 27 experiments were conducted (in triplicate) with the feed rate, temperature, and compressed air flow for the atomizer kept constant. Analysis of the data revealed that product recovery increased when the maltodextrin in the feed and drying air flow rate were increased, but the inlet air temperature had no significant (P < 0.05) effect on powder recovery. The moisture content of the powder varied with the maltodextrin level, inlet air temperature, and air flow rate. Using scanning electron microscope images, larger particle size was observed with the increase of maltodextrin concentration. Powder bulk density also increased from 0.41 to 0.68 g/cm³, depending on the level of maltodextrin, whereas the drying air temperature and flow rate were not as effective. The results of this study are beneficial for scaling up the spray drying of lime juice to the food industry.     

Effect of Zataria multiflora Boiss. essential oil and nisin on Salmonella typhimurium and Staphylococcus aureus in a food model system and on the bacterial cell membranes

The effects of different concentrations of Zataria multiflora Boiss. essential oil (EO: 0, 5, 15 and 30 μl 100 ml⁻¹) and nisin (N: 0, 0.25 and 0.5 μg ml⁻¹), temperatures (T: 25 and 8 °C), and storage times (up to 21 days) on growth of Salmonella typhimurium and Staphylococcus aureus in a commercial barley soup were evaluated in a factorial design study. The growth of S. typhimurium was significantly (P < 0.05) decreased by EO concentrations and their combinations with N concentrations at 8 °C. For S. aureus, the viable count was significantly (P < 0.05) inhibited by EO and N concentrations and their combinations, incubated at both storage temperatures. The mechanism of the antimicrobial action of EO, N, and their combinations against cell membranes of the tested organisms were also studied by measurement of the release of cell constituents and by the electronic microscopy observations of the cells. The significant increase of the cell constituents’ release of both organisms was observed as a result of treatments with EO and EO in combination with N. Electronic microscopy observations revealed that the cell membranes of S. typhimurium treated by EO and EO in combination with N were significantly damaged, while cells treated with only N looked similar to untreated cells. The electron micrographs of treated cells of S. aureus with EO, N, and their combination also showed important morphological damages and disrupted membranes.     

Spray drying conditions for orange juice incorporated with lactic acid bacteria

This work aimed to develop an orange juice powder by spray drying with lactic acid bacteria (Lactobacillus plantarum 299v and Pediococcus acidilactici HA‐6111‐2), testing their survival both during drying and storage (room temperature and 4 °C). Initially, the best conditions for spray drying were chosen to allow the best survival of each LAB: (i) inlet air temperature of 120 °C and (ii) 0.5:2 ratio of the orange juice soluble solids and drying agent added (prebiotics: 10 DE maltodextrin or gum Arabic). Survival of LAB was not affected by drying process, and it was higher when cultures were stored at 4 °C. A slightly higher protection was conferred by 10 DE maltodextrin, in the case of L. plantarum and at 4 °C. Pediococcus acidilactici was more resistant during storage at 4 °C, with logarithmic reductions lower than 1 log‐unit. It was demonstrated that it is possible to produce a functional nondairy product, orange juice powder supplemented with prebiotic compounds, containing viable LAB for at least 7 months, when stored at 4 °C.     

Viability of multi-strain mixtures of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage

The fate of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on soudjouk. Fermentation and drying alone reduced numbers of L. monocytogenes by 0.07 and 0.74 log₁₀ CFU/g for sausages fermented to pH 5.3 and 4.8, respectively, whereas numbers of S. typhimurium and E. coli O157:H7 were reduced by 1.52 and 3.51 log₁₀ CFU/g and 0.03 and 1.11 log₁₀ CFU/g, respectively. When sausages fermented to pH 5.3 or 4.8 were stored at 4, 10, or 21 °C, numbers of L. monocytogenes, S. typhimurium, and E. coli O157:H7 decreased by an additional 0.08–1.80, 0.88–3.74, and 0.68–3.17 log₁₀ CFU/g, respectively, within 30 days. Storage for 90 days of commercially manufactured soudjouk that was sliced and then surface inoculated with L. monocytogenes, S. typhimurium, and E. coli O157:H7 generated average D-values of ca. 10.1, 7.6, and 5.9 days at 4 °C; 6.4, 4.3, and 2.9 days at 10 °C; 1.4, 0.9, and 1.6 days at 21 °C; and 0.9, 1.4, and 0.25 days at 30 °C. Overall, fermentation to pH 4.8 and storage at 21 °C was the most effective treatment for reducing numbers of L. monocytogenes (2.54 log₁₀ CFU/g reduction), S. typhimurium (5.23 log₁₀ CFU/g reduction), and E. coli O157:H7 (3.48 log₁₀ CFU/g reduction). In summary, soudjouk-style sausage does not provide a favorable environment for outgrowth/survival of these three pathogens.     

Spray‐drying of pomegranate juice with prebiotic dietary fibre

The prebiotic fibres, resistant dextrin and fructooligosaccharides (FOS), were studied for use as drying‐aid agents for the spray‐drying of concentrated pomegranate juice, a low‐caloric juice containing interesting health‐related compounds. Resistant dextrin was the best drying‐aid agent as only 0.5 g g_CPJ^?1 of resistant dextrin was needed to avoid powder stickiness, compared with 1 g g_CPJ^?1 of maltodextrins and 1.5 g g_CPJ^?1 of fructooligosaccharides. The best conditions for spray‐drying a concentrated pomegranate juice (62.6% dry matter) using the resistant dextrin (NUTRIOSE) were 1.25 g_NUTRIOSE g_CPJ^?1 and 0.10 g_CPJ g_solution^?1, a liquid feed rate of 1.08 L h^?1 and an air temperature of 160 °C. Powders were easily solubilised in water, while storage at 25 °C maintained the pomegranate bioactive components, and there were no stickiness problems for at least 2 months. Resistant dextrin could be used with all kind of fruit juices in substitution of maltodextrins, and the resulting prebiotic powders could be employed for formulating novel functional foods.     

Byssochlamys nivea inactivation in pineapple juice and nectar using high pressure cycles

The aim of this work was to assess the inactivation of Byssochlamys nivea ascospores in pineapple juice and nectar by combining pressure sequences involving high pressure cycles with relatively mild thermal processing. The effect of 550 and 600 MPa sustained pressures (holding time of 15 min), combinations of sustained pressures and pressure pulses (holding time of 10 s), and pressure cycles (two, three and five cycles of 550 and 600 MPa for 7.5, 5 and 3 min, respectively), at 20, 40, 60, 70, 80 and 90 °C were compared. B. nivea ascospores were inactivated by applying sustained a pressure of 600 MPa at 90 °C for 5 min (juice) and 15 min (nectar), and three and five cycles of pressure at 600 MPa and 80 °C for nectar with holding time of 5 and 3 min, respectively, and in all pressure cycles for juice. In general, pressure cycles were more effective for inactivating B. nivea ascospores than the application of sustained high pressures.     

Biochemical and thermal characterization of crude exo-polygalacturonase produced by Aspergillus sojae

Crude exo-polygalacturonase enzyme (produced by Aspergillus sojae), significant for industrial processes, was characterized with respect to its biochemical and thermal properties. The optimum pH and temperature for maximum crude exo-polygalacturonase activity were pH 5 and 55 °C, respectively. It retained 60–70% of its activity over a broad pH range and 80% of its initial activity at 65 °C for 1 h. The thermal stability study indicated an inactivation energy of E_d = 152 kJ mol⁻¹. The half lives at 75 and 85 °C were estimated as 3.6 and 1.02 h, respectively. Thermodynamic parameters, ΔH^*, ΔS^* and ΔG^*, were determined as a function of temperature. The kinetic constants K_m and V_max, using polygalacturonic acid as substrate, were determined as 0.424 g l⁻¹ and 80 μmol min⁻¹, respectively. SDS-PAGE profiling revealed three major bands with molecular weights of 36, 53 and 68 kDa. This enzyme can be considered as a potential candidate in various applications of waste treatment, in food, paper and textile industries.     

Clarification of fruit juices by fungal pectinases

This study analyses the efficiency of fungal pectinolytic preparations produced in laboratory and commercial products used in the clarification process of apple, butia palm fruit, blueberry, and grape juices. Two crude enzymatic extracts, produced by Aspergillus niger T0005007-2 (TE1) and Aspergillus oryzae IPT 301 (TE2), were tested in solid-state and submerse cultures, respectively, in comparison to the commercial preparations Pectinex^®Clear and Pectinex^®BE Colour, used for the clarification of clear (apple, butia palm fruit) and dark (blueberry and grape) juices, respectively. With pectinases total activity at 1 U/mL of fruit juice, reactions were conducted at 30 and 50 °C, for 30 and 60 min. Time increase resulted in an improved clarification, whereas temperature increase could not be clearly linked to a greater clarification. When compared to the commercial products, the use of the crude preparation TE1 resulted in similar clarification of apple and blueberry juices. For butia palm and grape juice, however, TE1 presented the highest clarification results, revealing the potential of A. niger T0005007-2 enzymes for commercial application.     

A process for turning pomegranate peels into a valuable food ingredient using ultrasound-assisted extraction and encapsulation

A new method for pomegranate peel application in food industries was developed based on the ultrasound-assisted extraction of phenolic compounds and their subsequent encapsulation by spray drying. The effects of various parameters on extraction yield, on encapsulation efficiency/yield, and on the main physical properties of the microcapsules (moisture content, bulk density, rehydration ability) were studied. Ultrasound was found to increase extraction yield, but mainly to shorten the treatment time by over 20 times. The maximum encapsulation efficiency was 99.80% and the optimum operating conditions were found to be: wall material, maltodextrin/whey protein isolate (50:50); inlet air temperature, 150 °C; drying air flow rate, 17.5 m³/h; ratio of wall to core material, 9/1; feed solid concentration, 30% (w/w). The encapsulated phenolic extract was found efficient in improving the shelf life of hazelnut paste, in spite of the limited solubility of the crude extract in such a high lipid content matrix.Industrial relevancePomegranate peels, a by-product of pomegranate juice and concentrate industries, present a wide range of pharmaceutical and nutraceutical properties. Therefore, the peels could have more beneficial applications in food industries instead of being used as animal feed or in commercial cosmetic products. In this work, a new method for pomegranate peel application was developed based on the ultrasound-assisted extraction of phenolics and their subsequent encapsulation by spray drying.     

Evaluation of the effect of defrosting practices of ground beef on the heat tolerance of Listeria monocytogenes and Salmonella Enteritidis

The effect of common defrosting practices of ground beef, including (i) defrosting in the refrigerator (5 °C for 15 h), (ii) defrosting at room temperature (25 °C for 12 h) and (iii) defrosting in the microwave, on the heat tolerance of artificially inoculated Listeria monocytogenes and Salmonella Enteritidis, was studied. The thermal inactivation of S. Enteritidis was not, overall, affected by defrosting practices. In contrast, defrosting at room temperature resulted, overall, in an increased heat tolerance of L. monocytogenes compared to the rest tested defrosting practices. Inactivation kinetics of the two pathogens for the different defrosting practices were determined by fitting the data to the Weibull model. The δ parameter of the Weibull model (heat challenge time (min) required for the first 1-log reduction) for S. Enteritidis and for defrosting at 25 °C, microwave defrosting, defrosting at 5 °C and for the control (fresh ground beef inoculated with the pathogens just before the heat challenge trials) was 1.13, 1.62, 1.60 and 0.96, respectively, while the corresponding values for L. monocytogenes were 20.13, 10.82, 9.95 and 9.47, respectively. The findings of this study should be useful in risk assessments and in developing food handling guidelines for the consumers.     

Spray drying of red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit juices: physicochemical and antioxidant properties of the powder

This study aims to investigate physical stability and antioxidant properties of spray‐dried red (Hylocereus polyrhizus) and white (Hylocereus undatus) dragon fruit powder upon storage at various relative humidity (RH). Inlet air temperatures of 120 °C (red dragon fruit) and 110 °C (white dragon fruit) as well as maltodextrin concentration of 30% (w/v) were selected as the spray drying conditions as powder was obtained at these minimum conditions. The powder was ranging from 3 to 7 μm in particle size with spherical morphology. The powder had lower antioxidant content and antioxidant activities compared with the control before spray drying. Storage of powder at 43%, 54% or 75% RH at 25 °C for 25 days resulted in structural changes correlating to the depression of glass transition temperatures (T_g) to below storage temperature. At 33% RH, no visible structural changes were observed. Antioxidant properties of the powder remained unchanged after 25 days' storage at the studied RHs.     

Control of Listeria monocytogenes growth in a ready-to-eat poultry product using a bacteriophage

A bacteriophage (phage) that infected strains of the species Listeria monocytogenes as well as Listeria ivanovii and Listeria welshimeri, but not Listeria grayi or Listeria innocua, was isolated from sheep faeces. The phage had a contractile tail and an icosohedral head indicating that it was a myovirus, and was morphologically similar to phage A511. At 30 °C, phages added at 5.2 × 10⁷ PFU ml⁻¹ prevented the growth in broth of L. monocytogenes present at approximately twice this concentration for 7 h, but re-growth occurred such that the concentration after 24 h incubation was similar in both control and phage-treated cultures. At the same temperature, but on the surface of vacuum-packed ready-to-eat chicken breast roll, there was an immediate 2.5 log₁₀ CFU cm⁻² reduction in pathogen concentration following addition of phages and then re-growth. However, at a temperature reflecting that at which a chilled food might be held (5°C), this re-growth was prevented over 21 days incubation. The data suggest a dose-dependent rapid reduction in pathogen concentration followed by no continued phage-mediated effect. These results, alongside other published data, indicate that a high concentration of phages per unit area is required to ensure significant inactivation of target pathogens on food surfaces.     

Effect of modified atmosphere and temperature abuse on the growth from spores and cereulide production of Bacillus weihenstephanensis in a cooked chilled meat sausage

The effect of modified atmosphere packaging (MAP) on the germination and growth of toxin producing psychrotolerant Bacillus spp is not well described. A model agar system mimicking a cooked meat product was used in initial experiments. Incubation at refrigeration temperature of 8 °C for 5 weeks of 26 Bacillus weihenstephanensis including two emetic toxin (cereulide) producing strains showed that B. weihenstephanensis is sensitive to MAP containing CO₂. The sensitivity to 20% CO₂ was dependent on strain and oxygen level, being increased when oxygen was excluded from the MAP. Growth from spores was observed at the earliest within 2 weeks when 20% CO₂ was combined with 2% O₂ and in 3 weeks when combined with “0”% O₂ (the remaining atmosphere was made up from N₂). Results were validated in a cooked meat sausage model for two non-emetic and one emetic B. weihenstephanensis strain. The packaging film oxygen transfer rates (OTR) were 1.3 and 40 ml/m²/24 h and the atmospheres were 2% O₂/20% CO₂ and “0”% O₂/20% CO₂. Oxygen availability had a large impact on the growth from spores in the MAP meat sausage, only the most oxygen restricted condition (OTR of 1.3 ml/m²/24 h and “0”% O₂/20 % CO₂) inhibited growth of the three strains during 4 weeks storage at 8 °C. Cereulide production was undetectable during storage at 8 °C irrespective of choice of the MAP (quantified by liquid chromatography mass spectrometry/mass spectrometry). MAP storage at 8 °C for 1 and 3 weeks followed by opening of packages and temperature abuse for 1.5 h daily at 20 °C during 1 week resulted in increased cell counts and variable cereulide production in the meat sausage. A pre-history at 8 °C for 1 week in MAP with OTR of 1.3 or 40 ml/m²/24 h and 2% O₂ resulted in cereulide concentrations of 0.816 – 1.353 µg/g meat sausage, while a pre-history under the most oxygen restricted condition (OTR of 1.3 ml/m²/24 h, “0”% O₂/20 % CO₂) resulted in minimal cereulide production (0.004 µg/g meat sausage) at abuse condition. Extension of MAP storage at 8 °C for 3 weeks followed by abuse resulted in a substantially reduced cereulide production.Data demonstrates that MAP can be used to inhibit growth of a psychrotolerant toxin producing Bacillus spp. during chill storage at 8 °C, and substantially reduce the risk of emetic food poisoning at abuse condition. Results are of relevance for improving safety of ready to eat processed chilled foods of extended durability.