Control of Fusarium moulds and fumonisin B1 in seeds by gamma-irradiation

The distribution of naturally occurring Fusarium moulds producing fumonisin B₁ in seeds was determined. Fusarium infection of seed samples ranged from 10% to 60%, Fusarium moniliforme was the predominant species. Fusarium counts in wheat seeds were 8.1 × 10⁴ CFU/g, 6.3 × 10⁶ CFU/g in maize and 4.8 × 10³ CFU/g in barley. Wheat, maize and barley seeds naturally contaminated with varying levels of fumonisin B₁ 1.4–5.8, 8.0–13.8 and 0.1–0.5 μg/g, respectively. F. moniliforme and Fusarium proliferatum were major Fusarium contaminants producing fumonisin B₁. The effect of gamma irradiation on Fusarium moulds and levels of fumonisin B₁ was also determined. The viable counts of Fusarium in seeds decreased by increasing the radiation dose levels and the growth of Fusarium spp. was inhibited at 4.0 kGy for barley and 6.0 kGy for wheat and maize. Application of radiation dose at 5 kGy inactivated fumonisin B₁ by 96.6%, 87.1% and 100% for wheat, maize and barley, respectively, and a dose of 7 kGy was sufficient for complete destruction of fumonisin B₁ in wheat and maize.     

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.     

The microbiological quality of ready-to-eat food in Siu Mei and Lo Mei shops in Hong Kong

The safety of ready-to-eat food is an important issue. Improper handling of ready-to-eat food items may result in foodborne outbreaks. In this study, Chinese barbecued pork (Char Siu in Chinese) was selected as the target ready-to-eat food item for a microbial survey. The aim of this study was to evaluate the microbiological quality of Chinese barbecued pork sold in licensed Siu Mei and Lo Mei shops in Hong Kong. A total of 115 samples were collected from supermarkets or wet markets in the 18 districts. They were tested for aerobic plate counts (APC), Escherichia coli and Staphylococcus aureus counts, and the presence of Salmonella spp. for assessing their safety level. Results showed APC ranging from 1.97 to 6.84 log CFU/g, with a mean of 5.05 log CFU/g; E. coli counts ranging from none detected to 3.10 log CFU/g, with a mean of 1.78 log CFU/g; and S. aureus counts ranging from none detected to 1.42 log CFU/g, with a mean of 0.15 log CFU/g. The mean APC and E. coli counts of samples from supermarkets were found to be significantly lower than those from wet markets (p < 0.05) indicating that supermarkets had better microbiological quality than wet markets. Salmonella spp. were isolated from 39% of the samples analyzed, indicating that cross-contamination was quite a serious problem in Siu Mei and Lo Mei shops in Hong Kong. Based on these results, recommendations such as routine inspections and training of vendors were suggested to improve the microbiological quality of products sold in licensed Siu Mei and Lo Mei shops in Hong Kong so as to minimize risks of foodborne outbreaks.     

Microbiological evaluation of fresh-cut organic vegetables produced in Zambia

This study was undertaken to assess the microbiological quality of fresh-cut organic vegetables produced in Zambia. Fresh-cut organic mixed vegetables and green beans produced in Zambia were analysed for aerobic plate counts, coliforms, Enterobacteriaceae, Escherichia coli, Bacillus cereus, Clostridium perfringens, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus, and yeast and mould counts. The study included 160 samples for most of the parameters. The vegetables were grown on farms meant primarily for the export market. The vegetables were treated/washed with 150 μg ml⁻¹ chlorine solution at the processing plant prior to sampling. The aerobic plate count ranged between 3 log₁₀ and 9.7 log₁₀ CFU/g, with the highest count recorded for green beans. The largest grouping (26.1%) of vegetable samples fell between 3 and 4 log₁₀ CFU/g. Coliform counts were between 1.0 log₁₀ and 7.7 log₁₀ CFU/g. The highest incidence level was 31.4% for total coliform counts between 3 log₁₀ and 4 log₁₀ CFU/g. E. coli was only detected on mixed vegetables in the range of 0.6 log₁₀ to 3 log₁₀ CFU/g, while Enterobacteriaceae counts ranged between 1.6 log₁₀ and 9.8 log₁₀ CFU/g with the highest counts being found on green beans. The highest incidence level was of 25.8% for counts within the same range as the aerobic plate counts. Yeast and mould counts showed the highest incidence level between 5 log₁₀ and 6 log₁₀ CFU/g with an overall range between 1.5 log₁₀ and 5.6 log₁₀ CFU/g. L. monocytogenes, Salmonella spp. and S. aureus were detected in 20%, 23.1% and 83.9% of samples, respectively . C. perfringens and B. cereus were not detected in any of the samples analysed.     

Aflatoxin contamination of dried red chilies: Contrasts between the United States and Nigeria,two markets differing in regulation enforcement

Dried red chilies are among the world’s most consumed spices. From farm to fork, chilies go through cropping, harvest, drying, processing and storage. Chilies are susceptible to infection by aflatoxin producing fungi and subsequent contamination by aflatoxins at every stage. Aflatoxins are highly regulated, hepatotoxic carcinogens produced by fungi in Aspergillus section Flavi. The current study examined prevalence of aflatoxin B₁ (AFB₁) in chilies from markets across the United States (US) and Nigeria, and determined predisposition of chilies to aflatoxins post-harvest. Aflatoxin B₁ was detected in 64% chilies from US markets (n = 169), and 93% of Nigerian chilies (n = 55) with a commercial lateral flow assay (Limit of Detection = 2 μg/kg). Two percent of US samples exceeded the aflatoxin regulatory limit of 20 μg/kg, while the highest concentration detected was 94.9 μg/kg. Aspergillus spp. could be recovered only from 40% of samples from the US, and aflatoxin levels did not correlate with quantities of Aspergillus section Flavi (Colony Forming Units g⁻¹), suggesting fungi associated with chilies in US markets were killed during processing. Both average AFB₁ concentrations and fungal quantities were significantly higher (p < 0.01) in Nigerian chilies. The most contaminated sample contained 156 μg/kg AFB₁. Aflatoxin concentrations in Nigerian chilies increased as an exponential function of the quantities of Aspergillus section Flavi (r² = 0.76). Results indicate that high rates of chili consumption may be associated with unacceptable aflatoxin exposure.     

Occurrence and diversity of Bacillus cereus and moulds in spices and herbs

Spices and herbs can contain toxin-producing bacteria and moulds, which can cause health problems for consumers and contribute to food spoilage and shelf-life reduction. The aims of the present work were (i) to determine the occurence and levels of B. cereus and moulds; (ii) to charactize the incidence and diversity of B. cereus emetic toxin (ces, CER), and diarrhoeal toxin-encoding genes (entFM, nheA, hblC, cytK) and toxigenic potential of Hbl toxin-producing B. cereus strains. Black ground pepper samples showed the most contamination with the highest concentration of B. cereus 2.49 log₁₀ CFU/g. Moreover, cumin contained the most prominent mould concentration level of 3.6 log₁₀ CFU/g. The most common moulds were Aspergillus and Penicillium spp. Compared to packaging type, all products acquired from the local market, except curry for B. cereus, exchibited high concentrations of B. cereus and moulds. Four genes were identified – 96% of B. cereus strains contained entFM, 94% nheA, 56% hblC, 42% cytK. None of the samples contained emetic toxin-encoding genes (ces, CER). Toxigenic potential of Hbl toxin was found in 72% of B. cereus strains. Different temperature, moisture levels and hygiene practices were observed at places of sale in local markets thus facilitating contamination and development of moulds. Moreover, the presence of B. cereus and its ability to produce toxins in spices and herbs, may suggest the need to establish microbiological criteria for mould and spore-forming bacteria in spices and herbs.     

Microbial quality and safety of fresh and dried Rastrineobola argentea from Lake Victoria,Tanzania

Rastrineobola argentea (silver cyprinid/sardines) is an important commercial fish species found in Lake Victoria. It is an important protein source for consumers in several African countries including Tanzania. A cross-sectional study was conducted using standard methods to assess the bacteriological quality of fresh and dried sardines from Lake Victoria. Sardine samples were randomly collected from main landing sites and retail markets in the city of Mwanza. Total viable counts (TVC) in fresh sardines were in the range of 5.18–7.90 log₁₀ cfu/g while those dried on racks contained 3.13–4.85 log₁₀ cfu/g which were 0.75% of those dried on sand with 4.80–7.13 log₁₀ cfu/g (p < 0.001, 95% CL: 0.40%–1.42%). Thus, rack dried sardines had mean TVC below the national acceptable food standard of 5 log₁₀ cfu/g. Faecal contamination with E. coli in fresh sardines ranged from 2.38 to 5.38 log₁₀ mpn/g and those dried on sand contained 1.18–3.32 log₁₀ mpn/g, however, sardines dried on racks, did not contain any E. coli. Similar findings were found in the two types of dried sardines from the retail markets. Prevalence of Salmonella spp. in fresh R. argentea was 25% (n = 40), sand dried sardines at landing sites contained 30% (n = 20) and those from the markets contained 15% (n = 20) Salmonella spp. Salmonella spp. were not detected in sardines dried on racks. To conclude, sun drying of sardines on racks is an effective drying method providing a safe product for human consumption.     

Potential of Escherichia coli as a surrogate indicator for postchill broiler carcasses with high Campylobacter counts

Surrogating Campylobacter contamination level in broiler carcasses with other bacterial indicators, used to evaluate the hygienic status of the slaughterline operations, might be stimulation to the broiler meat industry to improve control of Campylobacter during slaughter. Theoretically, Escherichia coli might have some practical merits as a potential indicator for carcasses contaminated with Campylobacter. This study investigates the correlation between the counts of E. coli and Campylobacter in 231 postchill broiler carcasses. The impact of setting a process hygiene target based on E. coli counts on reducing the frequency of carcasses contaminated with Campylobacter at level of ≥3 log₁₀ CFU/g was also investigated. Almost half (48.9% (46/94)) of the carcasses with enumerable Campylobacter (≥1 log₁₀ CFU/g) had E. coli counts between 3 and 4 log₁₀ CFU/g. In addition, 54.8% (17/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g were correlated with E. coli count range of ≥3 & <4 log₁₀ CFU/g. A theoretical scenario assuming that hygiene and processing measures could allow achieving a target for E. coli that not exceeding 3 log₁₀ CFU/g showed a parallel impact on Campylobacter contamination in broiler carcasses. In such scenario, the overall number of Campylobacter-positive carcasses could be dropped from 40.6% to 12.5%; in addition, 80.6% (25/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g could be eliminated. Findings from this study reveal that a hygiene target based on E. coli count could be used as an indirect sanitary tool for reducing the level of Campylobacter contamination in postchill broiler carcasses.     

Reduction of Campylobacter jejuni counts on chicken meat treated with different seasonings

To analyze the potential of various seasoning combinations in reducing Campylobacter jejuni counts on fresh chicken meat, fresh chicken drumstick samples were inoculated with a mixture of two C. jejuni strains at log 4–5 CFU/g and subsequently treated with six different seasonings. After addition as a dry powder to the meat’s surface, all seasoning combinations adsorbed water from the meat and formed a gel on the meat’s surface. The samples were placed in individual packages containing a modified gas atmosphere (N₂ 80% and CO₂ 20%) and stored at 4 °C for seven days and C. jejuni counts in CFU/g were determined at the beginning, after 15 min, 1 h, 1 day and 7 days. The most effective seasoning combination contained, among other ingredients and food additives, sodium lactate and potato protein fractions; it reduced counts by mean 1.52 to 1.66 log CFU/g in seven days. The other seasoning combinations without potato protein fractions decreased counts in the range of mean 1.05 to 1.16 log CFU/g; simultaneously, the counts in control meat samples decreased by mean 0.21 log CFU/g. The death rate estimates after 1 h storage was in the range of ?0.25 log CFU/g/h to ?0.34 log CFU/g/h.In conclusion, various combinations of seasonings decreased the counts of C. jejuni, with the highest C. jejuni death rate during the first hour and further minor reductions in C. jejuni counts with additional storage time. These types of treatments may decrease human exposure to Campylobacter from fresh poultry meat.     

Mycoflora and absence of aflatoxin contamination of commercialized cassava chips in Benin, West Africa

Studies conducted in Benin, in which the main staple foods are maize, cassava, groundnuts and yams, showed high levels of aflatoxin residues in blood of the exposed population. The natural contamination with fungi and aflatoxins in cassava chips sold at markets in Benin, West Africa was investigated. A total of sixty samples were sampled from open markets in 11 districts of 3 agroecological zones and analyzed for the presence of mycoflora and aflatoxin B₁, B₂, G₁ and G₂. Fourteen genera of fungi were associated with marketed dried cassava chips. Within these, twenty- two isolates were identified to species level, whereas four were identified only to genus. The dominating fungal species isolated were Rhizopus oryzae, Nigrospora oryzae, Chrysonilia sitophila, Cladosporium resinae, Cladosporium herbarum, Apergillus niger and Aspergillus flavus. Fifty-four out of sixty samples were contaminated with A. flavus. The rate of occurrence in CFU/g of A. flavus fungi was lower than for all other fungal species together. Aflatoxin was not detected in any of the samples analyzed using HPLC with post-column photochemical derivatization and fluorescence detection. The limit of detection (LOD) was 0.1 μg/kg. Results from this study suggest cassava chips are unlikely to be a source of aflatoxin in Benin, and that other staples such as maize and groundnuts are more important in aflatoxin exposure. Therefore it can be speculated that staples like maize and groundnut are more important in aflatoxin exposure.     

Antimicrobial efficacy of vacuum impregnation washing with malic acid applied to whole paprika,carrots, king oyster mushrooms and muskmelons

Antimicrobial effect of vacuum impregnation (VI) applied to organic acid washing against Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on paprika fruit, carrots, king oyster mushrooms and muskmelons was investigated. Samples were treated with intermittent VI with 21.3 kPa and compared with dipping washing in 2% malic acid. The initial sample pathogen levels were approximately 10⁵–10⁷ CFU/cm². Enumerations of the three pathogens on paprika and carrots treated with VI washing were reduced to below the detection limit (= 1 log₁₀ CFU/cm²) after 3–5 min and 15–20 min, respectively. For each time point where populations of the three pathogens were reduced to below the detection limit by VI treatment, populations of 1.2–1.9 log CFU/cm² and 2.5 to 2.8 log CFU/cm² survived on paprika and carrots, respectively, when subjected to dipping treatment. After 20 min of dipping treatment, surviving populations of the three pathogens ranged from 3.5 to 4.1 and 3.3 to 4.4 log CFU/cm² on king oyster mushrooms and muskmelons, respectively. After 20 min of VI treatment, surviving populations of the three pathogens ranged from 3.0 to 3.6 log and 3.1 to 4.1 log CFU/cm², respectively, on king oyster mushrooms and muskmelons. Additionally, there were no significant (P ≥ 0.05) differences in pathogen reductions between dipping and VI treatment for both king oyster mushrooms and muskmelons. King oyster mushrooms (R_a = 6.02 ± 1.65 μm) and muskmelons (R_a = 11.43 ± 1.68 μm) had relatively large roughness values compared to those of paprika (R_a = 0.60 ± 0.10 μm) and carrots (R_a = 2.51 ± 0.50 μm). Scanning electron photomicrographs showed many deep protected sites in king oyster mushrooms and muskmelons with many microbes located deep in these sites following VI treatment. Instrumental color, texture and titratable acidity values of paprika and carrots subjected to VI washing treatment with 2% malic acid for 5 and 20 min were not significantly (P ≥ 0.05) different from those of untreated control samples during 7 day storage.     

Inactivation of aflatoxigenic fungi and the reduction of aflatoxin B1 in vitro and in situ using gamma irradiation

Detailed investigation on the effect of gamma (γ) irradiation on germination, sporulation, and growth of aflatoxigenic moulds (Aspergillus parasiticus 2999, Aspergillus flavus 305, and Aspergillus niger 388), as well as on the reduction of aflatoxin B₁ (AFB₁) level in artificially and naturally contaminated maize/feed samples was performed. The results of in vitro and in situ experiments with aflatoxigenic moulds demonstrated that 5 kGy-γ irradiation manages to prevent sporulation, germination and growth of the tested moulds both when in form of a pure and when in form of a mixed culture. In the feed samples artificially contaminated with AFB₁ (50 μg kg⁻¹) 5 kGy-γ irradiation reduced AFB₁ level by around 60%, while 10 kGy-dose reduce it for around 85%. Similarly, in feed samples spiked with AFB₁ in the concentrations of 100 μg kg⁻¹ 5 kGy-dose reduced the AFB₁ level by approximately 70%, while the dose of 10 kGy reduced it by approximately 90%. The experiments on naturally contaminated maize samples (n = 30) confirmed these observations; following a 5 kGy-irradiation, the overall mean AFB₁ reduction equalled to 69.8%, while the irradiation with a 10 kGy-dose achieved the overall mean toxin reduction of 94.5%. The obtained results indicate that γ irradiation can be used to prevent the growth of aflatoxigenic moulds and to reduce the AFB₁ levels in various goods intended for animal and human consumption, thus minimizing the animal and human exposure to this carcinogenic mycotoxin.     

Microbiological quality and safety of minimally processed vegetables marketed in Campinas,SP – Brazil,as assessed by traditional and alternative methods

In this study, a total of 172 samples of minimally processed vegetables (MPV) were collected from supermarkets in the city of Campinas, Brazil. The MPV were analyzed using traditional and/or alternative methods for total aerobic mesophilic bacteria, total coliforms, Escherichia coli, coagulase positive staphylococci, Salmonella and Listeria monocytogenes. All the MPV analyzed presented populations of aerobic mesophilic microorganisms and total coliforms were >4 log₁₀ CFU/g and 1.0–3.4 log₁₀ CFU/g, respectively. E. coli was enumerated in only 10 samples out of 172 collected, while none of the 172 samples of MPV presented contamination by coagulase positive Staphylococcus (<10¹ CFU/g). Among the four methods used for detection of Salmonella in MPV (Vidas, 1,2 Test, Reveal, and Traditional), when Reveal was used a total of 29 positive samples were reported. For L. monocytogenes, the four methods tested (Vidas, Vip, Reveal, and traditional) performed similarly. The presence of Salmonella and L. monocytogenes in MPV was confirmed in one (watercress) and two samples (watercress and escarole), respectively. In conclusion, it has been observed that the microbiological quality of MPV commercialized in Campinas is generally satisfactory. Besides, the choice of microbiological method should be based not only on resource and time issues, but also on parameters such as sensitivity and specificity for the specific foods under analysis.     

Use of gamma irradiation for inactivation of pathogens inoculated into Kimbab,steamed rice rolled by dried laver

The effect of gamma irradiation for inactivating the pathogens inoculated into the ready-to-eat Kimbab, steamed rice rolled by dried laver, was investigated. The pathogens used were Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus and Listeria ivanovii which are important for public health. The growth of four test organisms inoculated (about 10⁶–10⁷ CFU/g) into the Kimbab were sustained by an irradiation treatment during 24 h of storage regardless of the temperature at 10, 20 and 30 °C. Four pathogen inoculated into Kimbab decreased 2–3 log CFU/g by 1 kGy treatment and was not detected after 3 kGy. The D₁₀ value of pathogens inoculated into the Kimbab were 0.31–0.44 kGy among the four organisms. This study indicated that a low dose irradiation can maintain microbial safety for ready-to-eat Kimbab, steamed rice rolled by dried laver.     

Behavior of Listeria monocytogenes type1 355/98 (85) in meat emulsions as affected by temperature,pH, water activity,fat and microbial preservatives

The aim of this work was to analyze the effect of temperature (10–30 °C), fat content (20–50%), sodium chloride (2.5–5.0%) and preservative concentrations: sodium nitrite (0–150 ppm), lactic acid (50–500 mM) and nisin (0–100 IU/g (international units per gram)) on the growth of Listeria monocytogenes in a meat emulsion system.Individual and simultaneous effects of the parameters were tested and the results were mathematical modeled; inhibition indexes were calculated in each case. The addition of 7.5% NaCI inhibited the growth of L. monocytogenes at 20 and 30 °C, however, at 10 °C, microbial counts reached approximately 10⁶ CFU/g. The addition of 50 mM of lactic acid to obtain a pH ≤ 5 inhibited the growth of L. monocytogenes. The combinations of lactic acid with sodium nitrite or with nisin showed an enhancement of the inhibitory effect. However, considering the low toxicity of nisin, the combination of lactic acid (50 mM) and nisin (20 IU/g) would be more acceptable in the prevention of the growth of Listeria monocytogenes.     

Microbiological quality of organic and conventional vegetables sold in Brazil

While searching for healthier diets, people became more attentive to organic produce. Yet, organic foods may be more susceptible to microbiological contamination because of the use of organic fertilizers, a possible source of pathogenic bacteria. In this study, 130 samples of different organic and conventional vegetable varieties sold in Brazil were analyzed for mesophilic aerobic bacteria, yeasts and molds, total coliforms, Escherichia coli and Salmonella spp. Most of the mesophilic aerobic bacteria counts in organic and conventional vegetables ranged from 6 to 7 log10 CFU/g; most of the yeasts and molds counts ranged from 5 to 6 log10 CFU/g and most of the total coliforms counts ranged from 4 to 5 log10 CFU/g. E. coli was found in 41.5% of the organic and 40.0% of the conventional vegetables, and most samples had counts ranging from 1 to 2 log10 CFU/g. Salmonella spp. was not found in any sample. Comparative analyses of the microbial counts of organic and conventional vegetables showed that some organic varieties have greater counts. However, the global results show that this is not a trend. These results indicate the need of good farming practices, and proper sanitization before consumption, to ensure food quality and safety.     

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.     

Development of a multiplexed PCR assay combined with propidium monoazide treatment for rapid and accurate detection and identification of three viable Salmonella enterica serovars

Salmonella is the leading pathogenic bacteria in food and contaminated water. The aim of this study was to develop a rapid and reliable technique for simultaneous detection of the main three serotypes (Salmonella enterica serovars Typhimurium, Paratyphi B and Typhi) of Salmonella. Primers were designed to amplify the genes specific to each of these three serotypes for simultaneous detection using polymerase chain reaction (PCR). To ensure the detection of only viable cells, propidium monoazide (PMA) was applied to selectively suppress the DNA signal from dead cells. Results showed that the PMA-multiplexed PCR (PMA-mPCR) assay always gave negative results for heat-killed Salmonella at concentrations up to 1 × 10⁶ CFU/ml in pure culture or 1 × 10⁶ CFU/g in spiked food products (tomato, chicken, beef and ham). Results showed that the detection limits of the PMA-mPCR assay were approximately 10² CFU/ml (4.3 × 10² CFU/ml for S. Typhimurium, 3.7 × 10² CFU/ml for S. Paratyphi B, 7.2 × 10² CFU/ml for S. Typhi) in pure culture and 10³ CFU/g (4.3 × 10³ CFU/g for S. Typhimurium, 3.7 × 10³ CFU/g for S. Paratyphi B, 7.2 × 10³ CFU/g for S. Typhi) in food produce. These results demonstrated that the PMA-mPCR assay can simultaneously detect and identify viable S. Typhimurium, Paratyphi B and Typhi in a short period of time, even in food produce.     

Development and validation of an accurate and rapid LC-ESI-MS/MS method for the simultaneous quantification of aflatoxin B1, B2, G1 and G2 in lotus seeds

An accurate and rapid LC-ESI-MS/MS analytical method was developed and validated for the simultaneous determination of aflatoxin B₁, B₂, G₁ and G₂ in lotus seeds. The samples were firstly extracted with methanol-water solution (80:20, v/v), and then cleaned up by immunoaffinity columns. The mass spectrometer was operated in the positive ionization electrospray (ESI+) mode using multiple reaction monitoring (MRM) for analysis of four aflatoxins. The transitions of m/z 313 → 285 (AFB₁, CE 33 eV), m/z 315 → 259 (AFB₂, CE 37 eV), m/z 329 → 243 (AFG₁, CE 37 eV) and m/z 331 → 257 (AFG₂, CE 37 eV) were used to quantify these four aflatoxins, respectively. The limits of detection (LODs) of aflatoxin B₁, B₂, G₁ and G₂ were 0.007, 0.005, 0.003 and 0.005 μg kg^?1 based on a signal-to-noise ratio of 3:1, respectively. The limits of quantification (LOQs) of aflatoxin B₁, B₂, G₁ and G₂ were 0.02, 0.015, 0.01 and 0.015 μg kg^?1 based on a signal-to-noise ratio of 10:1, respectively. Recoveries for samples of spiked lotus seeds were all above 66% with relative standard deviation all below 15% for all compounds. Nineteen out of twenty batches of lotus seeds collected from different drug stores or markets in China were found to be contaminated with aflatoxins at different levels ranging from 0.02 to 688.4 μg kg^?1.