Effect of water activity and temperature on the growth of Aspergillus flavus,the expression of aflatoxin biosynthetic genes and aflatoxin production in shelled peanuts

The contamination of peanuts with Aspergillus flavus and subsequent aflatoxins is considered to be one of the most serious safety problems in the world. Water activity (a_w) and temperature are limiting factors for fungal growth and aflatoxins production during storage. To optimize the practical storage parameter, the effect of a_w (0.85–0.99) and temperature (15–42 °C) on fungal growth, aflatoxin production and the expression of aflatoxin biosynthetic and regulatory genes in shelled peanuts was investigated. A. flavus grew at a lower rate when temperature ≤20 °C or a_w ≤ 0.85. For the growth of A. flavus in shelled peanuts, the optimum conditions were a_w was 0.98, and the optimum temperature was 37 °C. The maximum amount of AFB₁ in peanuts was obtained at 28 °C and a_w 0.96. Real-time analysis showed that 16 of 25 genes had highest expression levels at 28 °C under a_w 0.92, while 9 genes had highest expression levels at 37 °C under a_w 0.92. Compared with 37 °C, all aflatoxin biosynthetic pathway genes were down-regulated at 42 °C. All the pathway genes and laeA were up-expressed at a_w of 0.96 under 28 °C, compared to a_w 0.99. Furthermore, there was a good positive correlation between the ratio of aflS/aflR and AFB₁ production. The expression of laeA was also positively correlated with AFB₁ production while the expression of brlA was correlated with the A. flavus growth. The results of this study suggest that AFB₁ production in peanut kernels can occur over a wider range of a_w × temperatures levels compared to formula media and peanut media. Previous studies have showed that AFB₁ could not be produced on formula media at 37 °C without the expression of most aflatoxin structural genes. But, in the un-autoclaved shelled peanuts, high concentration of AFB₁ was produced at 37 °C with up-regulation of some aflatoxin biosynthetic genes. From a food safety point of view, the results can be used to optimize certain food technological processes and develop prevention strategies to control such carcinogenic natural metabolites in grains (such as peanuts, maize and rice) and derived products.     

Modelling the interaction of storage temperature,pH, and water activity on the growth behaviour of Listeria monocytogenes in raw and pasteurised semi-soft rind washed milk cheese during storage following ripening

The objective of this study was to investigate the growth of Listeria monocytogenes in semi-soft rind washed cheese made from raw and pasteurised milk at different storage temperatures (4, 10 and 15 °C) over a 28 day period simulating storage following ripening. Changes in water activity (a_w) and pH in cheeses were also monitored during storage. Response surface models were used to model the interaction of storage temperature and time on a_w, pH and L. monocytogenes population. Growth curves were fitted using Baranyi, modified Gompertz and Logistic models at all storage temperatures for both cheeses, and model parameters were statistically analysed. In raw and pasteurised milk cheeses, all models showed a significant (P < 0.05) increase in the specific growth rate (SGR, Day⁻¹) of L. monocytogenes with an increase in storage temperature. A higher SGR was observed for L. monocytogenes in pasteurised milk cheese (0.18–0.85 Day⁻¹) compared to raw milk cheese (0.05–0.37 Day⁻¹) at all storage temperatures studied. Response surface models indicated an increase in the L. monocytogenes population and pH with an increase in storage temperature. However, a decreasing trend in a_w for both cheese types was observed. The predicted regression model parameters for both the raw and pasteurised milk cheese showed a high correlation coefficient R² > 0.87. Overall, the L. monocytogenes population increased up to 3 log₁₀ cfu⁻g⁻¹ for both cheeses during storage following ripening. The fitted models confirmed different L. monocytogenes growth behaviour between raw and pasteurised milk cheeses, which could support the Food Business Operator in predicting growth during storage following ripening.     

Growth potential of Listeria monocytogenes in traditional Austrian cooked-cured meat products

European Union legislation limits for Listeria monocytogenes in ready-to-eat foods are based on whether or not foods favour the multiplication of this bacterium. The latter is defined by criteria for water activity (a_w), pH and shelf-life. We studied a peculiar group of traditional Austrian meats implicated in foodborne listeriosis made from cured cooked comminuted meat with gelatin/aspic (Presswurst), blood (Blutwurst) or fat as a binder (Leberpaté, Streichwurst, Zwiebelstreichwurst). Average pH values were 5.74 ± 0.45; 6.62 ± 0.31; 6.18 ± 0.36; 6.19 ± 0.15; 6.28 ± 0.04 for Presswurst (n = 15), Blutwurst (n = 15), Leberpaté (n = 10), Streichwurst (n = 18) and Zwiebelstreichwurst (n = 3), respectively. Corresponding a_w values were: 0.968 ± 0.004; 0.965 ± 0.004; 0.961 ± 0.005; 0.963 ± 0.003 and 0.957 ± 0.005. There were no statistically significant differences of pH among spreadable meat products. Presswurst had significantly lower pH values, but a significantly higher level of lactic acid bacteria. With the exception of one low pH Presswurst sample, all foods under study would favour the growth of L. monocytogenes. In a 9 days challenge test, Blutwurst showed a strong potential for supporting L. monocytogenes growth (2.4–4.6 log). In contrast, Presswurst was not able to support growth in all temperatures tested. A pH vs. a_w chart was designed delineating the growth/no-growth border (defined as 0.43 log increase over 216 h) at 2, 4 and 8 °C. For a given sample (i.e. a pH/a_w data pair), it could be easily assessed if the product would likely be “safe” for 9 days at temperatures of <2 °C, 2–4 °C etc. by simply plotting the data point in the chart. Agreement of predicted bacterial growth and multiplication in food samples was studied in one Presswurst and three Blutwurst products. In our conservative approach, additional anti-listerial effects of lactic acid bacteria and food additives were not considered, but could be integrated, if desired. The usefulness of such a pH vs. a_w chart for small businesses, the competent authority and for didactic purposes is discussed.     

The occurrence of the selected fusarium mycotoxins in Czech malting barley

In 2008–2011, the occurrence of deoxynivalenol (DON), zearalenone (ZON), T-2 toxin (T-2), and HT-2 toxin (HT-2) was studied in 325 malting barley samples collected from various regions of the Czech Republic. The highest occurrence of fusarium mycotoxins was recorded in crop 2009 (2213.5, 59.4 and 145.0 μg/kg for DON, ZON and ∑T-2, HT-2, respectively). Only one measured value exceeded the maximum allowable limit for DON set by the European Union.The validated method of high-performance liquid chromatography coupled with mass spectrometry was used for the analysis of the above mentioned toxins. Limits of detection were 1.5 μg/kg for DON, ZON and HT-2 and 0.3 μg/kg for T-2, the limits of quantification were 5.0 μg/kg for DON, ZON and HT-2 and 1.0 μg/kg for T-2.     

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.     

Responses of E. coli O157:H7, L. monocytogenes 1/2 c and Salmonella enteritidis to pH,aw and temperature stress combinations

This study compared the responses of Escherichia coli O157:H7, Listeria monocytogenes 1/2 c and Salmonella enteritidis toward different combinations of physicochemical stresses (pH: 3–8; a_w: 0.93–0.99; temperature: 3–62 °C). Results showed that L. monocytogenes generally had lower inactivation rates and was able to exhibit growth in most number of tested combinations, including those with very high and very low factor settings. Temperature introduced the greatest variation in the measured growth and death parameters but the contributions of both pH and a_w in all temperature ranges were also noted. The results of this study may be applied in the selection of appropriate pathogens in the evaluation of safety of foods that are preserved using individual or combined physicochemical factor control.     

A preliminary study of T-2 and HT-2 toxins in cereals sold in traditional market in South Korea

Fusarium species are responsible for the production of harmful trichothecenes mycotoxins in cereals. These mycotoxins are cytotoxic, potentially immunosuppressive and potent fast-acting inhibitors of protein and nucleic acid synthesis. This study validated a HPLC method for simultaneous detection of T-2 and HT-2 toxins. The method was then used for the detection of T-2 and HT-2 toxins in cereals sold in traditional markets in Gyeongnam Province, South Korea. Seventy five samples analyzed, out of which 13 and 25 samples were found to be contaminated with T-2 (35.2–431.0 ng g^?1) and HT-2 (21.1–442.7 ng g^?1) toxins, respectively and 4 samples were found to be contaminated with both toxins. This study provides data on the contamination level of T-2 and HT-2 toxins in cereals in traditional market in Gyeongnam province, South Korea.     

Efficacy of chlorine dioxide gas and freezing rate on the microbiological quality of frozen blueberries

Blueberries are prone to microbial contamination, with growth of bacteria, yeasts and molds during bulk freezing negatively impacting quality and marketability. As a follow-up to our previous work, the combined impact of ClO₂ gassing and freezing rate on the microbiological quality of frozen blueberries was examined. Sixteen lugs of blueberries (∼9.1 kg/lug) were stacked inside a large plastic container at a commercial blueberry processing facility. In each of four trials, one container was exposed to ClO₂ gas (4 ppm) using three 3-kg sachets while one ungassed container remained untarped. Before and after commercial processing, 50-g samples of gassed and ungassed blueberries were quantitatively examined for mesophilic aerobic bacteria (MAB), yeasts, and molds. After processing, additional 50-g samples were placed in a −20 °C freezer under different conditions where the berries reached a temperature of −3 °C after 3 h (quick-frozen), 2 days (intermediate-frozen) and 5 days (slow-frozen). Fruit was sampled periodically during 6 months of frozen storage at −20 °C. MAB yeast and mold populations decreased ∼2 and 1 log CFU/g, respectively, in ClO₂-gassed and ungassed fruit, with MAB, yeast and mold populations increasing ∼1 log CFU/g during quick freezing to −3 °C and ∼2 log CFU/g during intermediate and slow freezing to −3 °C. Based on these findings, ClO₂ gassing followed by quick freezing provides an effective means for meeting the current microbiological standards being imposed by buyers of frozen blueberries.     

Effect of packaging and storage conditions on quality of shelled walnuts

The present study investigated the effect of packaging and storage conditions on quality of raw shelled walnuts. Walnut kernels were packaged in: (a) low density polyethylene (LDPE), 55 μm in thickness in air, (b) polyethylene terephthalate||polyethylene (PET||PE), 70 μm in thickness under N₂, and (c) PET-SiO_x||PE pouches, 62 μm in thickness under N₂. Samples were stored either under fluorescent light or in the dark at 4 or 20 °C for a period of 12 months. Quality parameters monitored were peroxide value (PV), hexanal, 2-thiobarbituric acid (TBA), odor, and taste of product. PV ranged between 0.3 for fresh walnut kernels and 31.4 meq O₂/kg oil for walnuts packaged in PE pouches exposed to light after 12 months of storage. Respective values for hexanal were <28.5 μg/kg and 36.0 mg/kg and for TBA ca. 0.2 and 11 mg MDA/kg. Values for odor ranged between 0.2 for fresh walnut kernels and 5.7 for walnut kernels packaged in PE exposed to light after 12 months of storage at 20 °C. Respective values for taste were 0.7 and 6.8. Taste proved to be a more sensitive attribute than odor. Based on shelf life (taste) values and PV data it is proposed that the upper limit value for PV is close to 10.0 meq O₂/kg walnut oil. Respective limit values for hexanal are 1–2 mg hexanal/kg walnut and for TBA is 1–2 mg malondialdehyde/kg walnut. Walnuts retained acceptable quality for ca. 2 months in PE-air, 4–5 months in PET||PE-N₂ and at least 12 months in PET-SiO_x||PE-N₂ pouches at 20 °C, with samples stored in the dark retaining slightly higher quality than those exposed to light. The effect of parameters investigated followed the sequence: temperature > degree of O₂ barrier > lighting conditions.     

Simultaneous determination of mycotoxin in commercial coffee

Mycotoxins are secondary metabolites produced by filamentous fungi that usually contaminate food products. Coffee is a natural product susceptible to mycotoxin contamination. The present study evaluates the presence of nivalenol, deoxynivalenol, T-2 and HT-2 Toxin, diacetoxyscirpenol, aflatoxin B₁, aflatoxin B₂, aflatoxin G₁, aflatoxin G₂, fumonisin B₁, fumonisin B₂, ochratoxin A, zearalenone, enniatin A, enniatin A₁, enniatin B, enniatin B₁, and beauvericin in coffee samples, using liquid chromatography tandem mass spectrometry (LC-MS/MS). The results show that zearalenone was not present in any sample. In the positive samples the contents of fumonisins ranged from 58.62 to 537.45 μg/kg, emerging mycotoxins ranged from 0.10 to 3569.92 μg/kg, aflatoxins ranged from 0.25 to 13.12 μg/kg, and trichothecenes, excepting nivalenol, ranged from 5.70 to 325.68 μg/kg. Nivalenol presented the highest concentrations, from 0.40 to 25.86 mg/kg. Ochratoxin A ranged from 1.56 to 32.40 μg/kg, and five samples exceeded the maximum limit established by the European Commission.     

Behavior of Salmonella Rubislaw on ground black pepper (Piper nigrum L.)

Among spices, black pepper is highly appreciated and Brazil is one of the largest producers of it in the world. However, spices may reach consumers presenting poor quality, due to the loss of volatile compounds, microbial contamination or even due to insect infestation. Salmonella spp. frequently contaminate ground black pepper and may be recovered from products with low levels of free water, even after they have been submitted to high temperatures. The objective of this trial was to evaluate the behavior of a Salmonella Rubislaw strain on ground black pepper (Piper Nigrum L.), as well as to study the effects of water activity (A_w) and storage temperature (5, 25 and 35 °C) for 2 and 15 days. The most probable number technique was used for the quantification of the S. Rubislaw. Data obtained in the present trial indicate that differences in the reduction in counts were observed in relation to A_w (P = 0.006) and storage temperature (P = 0.000). Nevertheless, there was no significance as to the interaction of the two factors (P’s > 0.05). Bonferroni multiple comparisons tests have shown significant differences only when related to the A_w: 0.663, 0.815 and 0.887 (P’s < 0.05). When the product is stored at 5 °C, the number of surviving cells is even greater (P = 0.000). Considering the data obtained, we may conclude that, after contamination, S. Rubislaw remains viable in pepper for up to 15 days.     

Modelling the recovery of Listeria monocytogenes in high pressure processed simulated cured meat

Current EC regulations require that ready-to-eat products should not exceed the limit of 100 CFU/g for Listeria monocytogenes throughout their shelf-life. On that basis a quantitative analysis for high hydrostatic pressure to produce safe (regarding L. monocytogenes levels) cured meat products with low salt concentration has been developed. An extended Doehlert design for a range of pressures (450–800 MPa), sodium chloride (0–34.9 g/L) and sodium nitrite (mg/L) concentrations, as well as the resulting a_w (0.955–0.987) levels, was generated. Based on the logistic regression analysis, it appears that the recovery of L. monocytogenes is influenced by the applied pressure, the storage time and the synergistic effect of pressure and a_w on inhibiting microbial recovery. This means that the sodium chloride and sodium nitrite concentrations tested indirectly affected the recovery of Listeria and consequently the shelf-life of the product by regulating the a_w levels. The lower the water activity, the less the inactivation and recovery induced by pressure immediately and during storage, respectively.     

Presence of Fusarium toxins in maize from Autonomous Province of Vojvodina,Serbia

Fusarium toxins are recognized as worldwide concern since those contaminants may potentially affect human and animal health and could also be a cause of great economical losses. The aim of this study was to determine the presence of the following Fusarium toxins: fumonisins (FUMs), deoxynivalenol (DON), zearalenone (ZEA) and sum of T-2/HT-2 toxins in maize. A total of 90 samples were collected during the harvest 2012 from four different maize growing areas in Autonomous Province of Vojvodina, Serbia. Analysis showed that 100%, 53.3% and 2.22% of examined maize samples were contaminated with FUMs, T-2/HT-2 and DON with median values of 1606, 35.3 and 650 μg/kg, respectively. None of the maize samples was contaminated with ZEA. Differences in the occurrence of investigated Fusarium toxins could be explained by different conditions required for their growth and synthesis of the toxins. Maize growing season 2012 was characterized by drought conditions. Hot and dry weather conditions were particularly favorable for FUMs production. This is the first report of the natural co-occurrence of FUMs, T-2/HT-2, ZEA and DON in maize from Serbia.     

Patulin accumulation in apples during postharvest: Effect of controlled atmosphere storage and fungicide treatments

The aim of this study was to assess the opportunities of Penicillium expansum to develop and produce patulin in apples under two different CA storage methods (LOW and U-LOW) at 1 °C. Differences in lesion diameter and patulin accumulation depending on CO₂ and O₂ partial pressure were studied. Further apple rot and patulin production during a three days post-storing stage at 20 °C was also monitored so that effect of further storage at room temperature could be assesed.Two lots of apples of Golden variety with different ripeness degrees were used. Half of each lot was fungicide treated. Apples were inoculated with patulin producer P. expansum strains and stored at 1 °C for either two month or 2.5 months at both LOW and U-LOW conditions. The extent of lesions and patulin accumulation both at the end of CA cold storage and after three days at 20 °C were assessed. CA storage conditions had strong significance in P. expansum growth on apples and factors such as fruit ripeness, fungicide treatment and time at the storage room had significant influence. In general, bigger lesions were observed under U-LOW than under LOW conditions, lesions being similar or bigger when increasing the storage time from 2 to 2.5 months. P. expansum grew faster in riper apples, although fungicide application was clearly more effective for ripe rather than for underripe apples. Although lesions were evident after both storage conditions, no patulin was detected. Increase of lesion when fruits were subsequently stored at 20 °C was evident in all cases and patulin was detected at this moment. No differences in patulin content were found at this stage between LOW and U-LOW stored apples.     

Mycological quality and mycotoxin contamination of Sri Lankan peppers (Piper nigrum L.) and subsequent exposure assessment

The aim of the study was to characterize the toxigenic moulds and to screen different mycotoxins in peppers (Piper nigrum L.) of Sri Lankan origin. Aspergillus flavus, Aspergillus parasiticus, Aspergillus niger and Penicillium spp. were found to be the most dominant fungi. Characterization of the moulds was carried out in A. flavus and parasiticus agar (AFPA) and malt extract agar (MEA) in 77 black pepper (BP) and 11 white pepper (WP) samples. In total, 73% of the BP and 64% of the WP samples were contaminated with A. flavus and/or A. parasiticus (AfAp). A BP sample with water activity (a_w) 0.70 recorded the highest count of AfAp (4.3*10⁴ CFU/g). Moreover, 75% of the BP samples exceeded the safe a_w limit (0.65) set by the European Spice Association (ESA). The frequency of occurrence of A. niger in BP was 62% with counts up to 1.3*10³ CFU/g. Penicillium spp. were found in 61% and 55% of the BP and WP samples, respectively. In BP 94% of the samples had a Penicillium contamination below 10³ CFU/g. Other Aspergillus spp, found in peppers included, Aspergillus terrus, Aspergillus tamarii, Aspergillus candidus, Aspergillus penicilloides, Aspergillus sydowii and Aspergillus fumigatus. Mould counts in BP (10²–10⁴ CFU/g) were significantly higher than that of WP (<10² CFU/g). Apart from the occurrence of “classical mycotoxins” of spices, aflatoxins (<LOQ-18 μg/kg) and ochratoxin A (<LOQ-79 μg/kg), other toxins including fumonisin B1 (<LOQ-135 μg/kg), sterigmatocystin (<LOQ-49 μg/kg) and citrinin (<LOQ-112 μg/kg) were detected in peppers. In total, 63% of the BP samples were contaminated with at least one mycotoxin. Mycotoxin contamination in WP was significantly less compared to BP. The exposure to aflatoxins and ochratoxin A by consuming pepper remains harmless considering the existing pepper dietary intake data of the Sri Lankan population.     

A UPLC-MS/MS for simultaneous determination of aflatoxins, ochratoxin A, zearalenone, DON, fumonisins, T-2 toxin and HT-2 toxin, in cereals

An ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method is described for simultaneous determination of aflatoxins (AFB₁, AFB₂, AFG₁ and AFG₂), ochratoxin A (OTA), zearalenone (ZEA), deoxynivalenol (DON), fumonisins (FB₁ and FB₂), T-2 and HT-2 toxins in cereals. Mycotoxins were separated by reverse phase liquid chromatography (RP-LC) and detected by tandem mass spectrometry using an electro spray-ionization interface (ESI) in both positive- and negative- ion modes. The mean recoveries of mycotoxins from spiked cereals ranged from 83.5% to 107.3%, whereas the limit of detection (LOD) and limit of quantification (LOQ) ranged from 0.01 to 25 ng/g and 0.02-40 ng/g, respectively. The multi-mycotoxin method developed in this work was applied for the simultaneous determination of mycotoxins in 80 cereal samples collected from Malaysian markets. A total of 60 cereal samples (75%) were contaminated with at least one of these mycotoxins at levels greater than the LOD. Only one maize sample and two rice samples were contaminated at levels exceeding the European regulatory limits for aflatoxins and OTA (4 and 5 ng/g, respectively). The rates of the occurrence of mycotoxins in the commercial cereal samples were 50, 30, 19, 30, 16, 14, 14 and 12% for the aflatoxins (the total amount of AFB₁, AFB₂, AFG₁ and AFG₂), OTA, ZEA, DON, FB₁, FB₂, T-2 and HT-2 toxins, respectively. The results demonstrated that the procedure was suitable for the simultaneous determination of these mycotoxins in cereals and could be performed for their routine analysis in mycotoxin laboratories.     

Co-occurrence and evaluation of mycotoxins in organic and conventional rye grain and products

A study on the co-occurrence of Fusarium toxins in conventional and organic grain and derived products was carried out. A total of 117 samples were collected during the period 2009–2012. Eight mycotoxins were determined using the LC-MS/MS method. Among the investigated mycotoxins, four were of major importance: DON, ZEN, T-2 and HT-2. DON was present at the highest concentration in both the agricultural systems, with its maximum level of 254 ± 23 μg kg⁻¹ being present in conventional rye grain. The co-occurrence of two or more mycotoxins was observed in more than 50% of samples, with the most frequent combination being DON + ZEN. The correlation between the concentrations of T-2 and HT-2, DON and ZEN, as well as T-2 and ZEN was confirmed statistically. The concentration of DON, HT-2 and T-2 was significantly higher in conventional products. Also the higher level of ZEN in organic grain in comparison to derived products was significant. None of the samples contained DAS, while NlV, MAS and 3ADON concentrations were close to the detection limits.     

How safe is European Internet cheese? A purchase and microbiological investigation

The suitability for consumers of a variety of raw milk cheeses purchased over the Internet was investigated in terms of packaging, labelling, physicochemical parameters and microbiological safety. 108 purchases from seven European countries were examined. The prevalences of Salmonella spp., Listeria monocytogenes, Escherichia coli and coagulase positive staphylococci (SA) were determined. All 108 samples were described on websites as raw milk cheeses and thereby qualified for this study. However, after delivery it was noted that 4.6% (5/108) of cheeses were labelled to be manufactured from heat-treated or pasteurized milk. Delivery duration ranged from 24 h to six days. Immediately upon receipt cheese temperatures were observed to range between 5 and 23 °C, whereas in 61.5% of all cases the temperature was higher than 15 °C. Cheese labelling was examined in respect of EC Guideline 2000/13 and Regulation No. 853/2004. Only 17.6% (19/108) of cheeses were properly labelled and fulfilled all European guideline requirements. In 50.9%, 38.8%, 46.3% and 39.8% of all cases (i) specific storage requirements, (ii) name and address of the manufacturer/packer or seller, (iii) net weight and (iv) shelf life (use by date), were missing. Even the labelling information “made from raw milk” was not apparent on 36% of all cheese items delivered. The major foodborne pathogen L. monocytogenes was detected in 1.9% of all samples, one of which had counts of 9.5 × 10³ CFU/g. None of the 108 investigated cheeses showed a pH ≤ 5.0 and a_w value ≤0.94 which are the limiting values for growth of L. monocytogenes. For two samples (0.9%) and 11 samples (10.2%) the pH and the a_w value was ≤4.4 or ≤0.92, respectively at least at one of three stipulated time points (receipt, mid-shelf-life and at expiry). Salmonella spp. could not be detected in any of the samples. E. coli and SA could be detected in a total of 29.6% (≥10 CFU/g; 32/108) and 8.3% (≥100 CFU/g; 9/108) of samples, respectively, indicating poor conditions of hygiene. Results reveal that labelling and hygiene concerns about the safety of Internet purchased cheeses in Europe are justified.     

Growth characteristics of Shiga toxin-producing Escherichia coli (STEC) stressed by chlorine,sodium chloride,acid, and starvation on lettuce and cantaloupe

Shiga toxin-producing Escherichia coli (STEC) is a major foodborne pathogen causing serious illnesses and hospitalizations in the United States. Bacteria that are exposed to environmental stresses during food processing may exhibit different growth patterns in the subsequent growth environment. The purpose of this study was to examine the effect of environmental stresses on the growth of O15H and non-O157 STEC in lettuce or cantaloupe. Strains of O157:H7 and non-O157 STEC (O26:H11, O103:H1, O104:H4, and O145:NM) were subjected to four selected stresses including 2 ppm of chlorine, a_w of 0.97 (osmotic stress), and pH 5 (acid stress) at 22 °C for 24 h, or starvation (lack of nutrients) at 22 °C for 15 d. A cocktail mix of stressed or non-stressed (control) O157 or non-O157 at 3 log CFU/g (control or stressed) was inoculated on lettuce or cantaloupe and incubated at 10 and 22 °C for four weeks. While there were significant differences (p < 0.05) in the growth of stressed and unstressed cells of non-O157 STEC, no difference was observed in the growth of stressed and unstressed O157 STEC cells. Osmotic-stressed non-O157 STEC had significantly higher cell populations than control with 2 log difference (9.0 vs. 6.8 log CFU/g) at 10 °C on lettuce and 1 log difference (9.3 vs. 8.3 log CFU/g) at 22 °C on cantaloupe after 4 weeks. Acid-stressed non-O157 STEC had significantly higher cell populations than control at 10 °C after 4 weeks with >1 log difference (7.7 vs. 6.3 log CFU/ml) on cantaloupe. Starvation-stressed non-O157 STEC showed significantly higher cell populations than control with 1 log difference (8.4 vs. 7.2 log CFU/g) at 22 °C on cantaloupe after 4 weeks. The results indicated that osmotic, acid, or starvation stress may enhance the growth of non-O157 STEC on lettuce or cantaloupe and lead to a greater safety risk.     

Changes in the concentration of aflatoxin M1 during manufacture and storage of White Pickled cheese

In this study White Pickled cheese was produced from cow’s milk contaminated artificially with aflatoxin M₁ (AFM1) at two different levels, 1.5 and 3.5 μg/kg (ppb), and the effects of process stages on the AFM1 contents were investigated. Pasteurization at 72 °C for 2 min caused losses of AFM1 about 12% and 9%, respectively, in milk contaminated with 1.5 μg/kg AFM1, and 3.5 μg/l AFM1. These losses were found to be statistically significant (P < 0.01). After the cheese production, about 56% and 59% of total AFM1 remained in cheese–curd while about 32% of total AFM1 transferred to the whey for both 1.5 μg/kg and 3.5 μg/kg AFM1 contaminated milk. After 3-month storage in brine, AFM1 content of cheeses produced from 1.5 and 3.5 μg/kg AFM1 contaminated milks decreased by 2.9% and 2.8%, respectively. Changes in AFM1 content of cheese samples were found statistically insignificant (P > 0.05 and P > 0.01) for 3-month storage periods.