Prevalence of Listeria monocytogenes in delicatessen food products in China

This study was to investigate the prevalence of Listeria monocytogenes in delicatessen food, raw materials and environmental samples in food processing chain. Two hundred and forty-five samples of delicatessen foods in markets, 98 samples of cooked foods from restaurants and hotels, 154 samples of food product contact surfaces such as counters, iceboxes and chopping blocks etc. from processing and selling sites, 51 environmental samples from the food-cooking rooms of restaurants and hotels were collected and detected for the prevalence of L. monocytogenes. The results showed that there were 32 strains isolated from delicatessen foods in the market and the average prevalence was 13.06% which is significantly higher (p < 0.01) than those isolated from cooked foods in hotels and restaurants (1.02%) suggesting that the delicatessen food products may be contaminated during the delivery from hotels and restaurants to the markets. Ten strains were isolated from 335 raw materials and 21 strains were isolated from 154 processing equipments in selling and processing sites. No strains were isolated from 51 samples of equipments in cooked food rooms of hotels and restaurants. The study shows that the prevalence of L. monocytogenes in delicatessen foods in the market was significantly higher than those in the cooked foods of hotels and restaurants, and therefore, the critical control points were: (1) to establish relative closed selling rooms; (2) to establish the sterilizing measures to keep the delicatessens from being contaminated with L. monocytogenes during the delivery from restaurants or hotels to the retail markets.     

Survival and growth of Listeria monocytogenes on sausage formulated with inoculated and stored rework product

To assess the effect of including contaminated rework on survival and growth of Listeria monocytogenes, two sausage formulations (one American, Bologna sausage; and one Bulgarian, Stranja sausage) were inoculated with the pathogen and stored for 4 days at 10 °C plus 15 h at 30 °C. After storage, both rework types were included (at 20% and 40%) in corresponding fresh sausage emulsions and heated to 68, 70 and 71.7 °C; fresh Bologna and Stranja emulsions served as controls and were inoculated with 24 h broth cultures of the same 10-strain mixture of L. monocytogenes and thermally treated to the same temperatures. The results showed that heating to 68 and 70 °C inactivated 3–4 log CFU/g of the initial concentration of L. monocytogenes cells (>7 log CFU/g), while heat treatment to 71.7 °C in the center of experimental samples reduced counts by 6 log CFU/g. Survival of L. monocytogenes in samples heated to 68 and 70 °C was higher in controls. Control samples of Stranja emulsion heated to 71.7 °C allowed higher growth (P < 0.05) during storage (5 days at 10 °C) as compared to other control and experimental rework samples. The Stranja emulsion had a higher fat content (20.2%) compared to the Bologna emulsion (11%). This study provides evidence about the possible danger when potentially contaminated rework is stored and then introduced into fresh product formulations.     

Comparison of Oxford Agar, PALCAM and Listeria monocytogenes Blood Agar for the recovery of L. monocytogenes from foods and environmental samples

This work had as the main objective a comparison between Listeria monocytogenes Blood Agar (LMBA) and the conventional selective agar media, Oxford and PALCAM, relative to its efficacy in the detection of L. monocytogenes in naturally contaminated food and environmental samples. 173 environmental samples and 272 samples of foods were analysed. A higher sensitivity for detection of L. monocytogenes was verified for LMBA than for PALCAM and Oxford. In LMBA L. monocytogenes could be distinguished from other Listeria spp. by detection of hemolysis. In Oxford and PALCAM this distinction was not possible. The higher growth rate of L. innocua cf. L. monocytogenes in selective liquid media could result in a high number of false negatives (non-detection of the target organism on plates, although its presence was observed by other tests, eg. mini-VIDAS LMO). The need for specific media for the detection of L. monocytogenes in food was confirmed. LMBA could be an alternative medium to use together with PALCAM or Oxford.     

Antibacterial activities of the surface microflora of Kefalograviera cheese

The microflora developed on the surface of Kefalograviera, a hard cheese, during ripening in the warm room was studied. The microbial total counts and yeasts decreased (P < 0.05) and the same was observed with the pH on ripening for 15 days. Bacilli dominated at day 4 while at 15 days Micrococcaceae and enterococci occurred frequently. A great number (38 out of 56) of the isolates exhibited narrow spectrum of antibacterial activities against Gram-positive indicator strains, while ten of the Bacillus isolates (Bacillus pumilus) inhibited the growth of Listeria monocytogenes. The extracellular antilisterial substances were sensitive to proteinase K and heat labile (at 100 °C).     

Survival of Listeria monocytogenes inoculated in retail soymilk products

The consumption of soymilk products has been growing; because these foods contain proteins and isoflavone, and lack of lactose and cholesterol. The survival and growth of Listeria monocytogenes in the soymilk products were investigated by inoculating Listeria monocytogenes into various retail soymilk products which claimed to improve or fortify the functional properties. The results show that the refrigeration cannot successfully prevent the growth of Listeria monocytogenes in soymilk products. The addition of fiber content and higher viscosity in soymilk may significantly inhibit the growth of L. monocytogenes at 4–7 °C; however, this phenomenon was not observed when the incubation temperature was elevated to 22 °C. The change of pH value and TTS (total soluble solids) in soymilk products owing to L. monocytogenes, especially those with rich fiber content, might be negligible for the public. Thus the possible contamination of L. monocytogenes to soymilk products should be of crucial concern.     

Control of biological hazards in cold smoked salmon production

An outline of the common processing technology for cold smoked salmon in Denmark is presented. The safety hazards related to pathogenic bacteria, parasites and biogenic amines are discussed with special emphasis on hazards related to Clostridium botulinum and Listeria monocytogenes. Critical control points are identified for all hazards except growth of L. monocytogenes. For this reason a limitation of shelf life to three weeks at + 5 °C for cold smoked vacuum-packed salmon having ≥3% water phase salt is recommended.     

Microbiological quality of tomatoes and peppers produced under the good agricultural practices protocol AGRO 2-1 & 2-2 in Crete, Greece

The efficiency of the good agricultural practices (GAP) protocol AGRO 2-1 & 2-2, in advancing microbiological-quality of tomatoes and peppers, was studied in greenhouses at Ierapetra, Crete, Greece. The 240 tested vegetables-samples, produced under AGRO 2-1 & 2-2, showed satisfactory quality: Listeria monocytogenes absent per 25 g; Escherichia coli < 20 Colony Forming Units per gram (CFU/g); total coliforms 4.37–4.68 log CFU/g; aerobic plate counts 5.78–5.92 log CFU/g. Based on actual results and practices evaluation, we conclude that AGRO 2-1 & 2-2 can reduce microbial hazards for consumers and furthermore can establish practices in compliance to basic Euro-Retailer-Produce GAP (EUREPGAP) requirements.     

Characteristics of Bacillus cereus isolates from legume-based Indian fermented foods

An antibiogram of 48 strains of Bacillus cereus isolated from 6 different kinds of legume-based Indian fermented foods (amriti, dhokla, dosa, idli, papad and wadi) was generated against 18 different antibiotics that are commonly used against foodborne diseases, mainly gastroenteritis. Each of the isolates was found to be resistant against at least nine different antibiotics. Production of extracellular enzymes, namely protease, lipase and amylase by 33%, 27% and 46%, respectively, of the isolates indicates their potentiality for food spoilage. In brain–heart infusion broth supplemented with glucose, the D_100 °C-values for the tested 12 strains ranged from 3.0 to 9.2 min. In nutrient broth, the minimum and maximum pHs permitting growth of B. cereus were 5.3 and 11.6, respectively. The minimum inhibitory concentrations of sodium chloride, benzoic acid and sorbic acid for the growth of the isolates were 65–85 mg ml⁻¹, 400–700 μg ml⁻¹ (pH 5.0–4.2) and 500–600 μg ml⁻¹ (pH 5.0–4.8), respectively. Of the tested 10 strains, eight were resistant to 300 μg nisin ml⁻¹ (pH 5.0). While studying the combined effect of selected hurdles on the growth of an isolate, the judicious combination considered was 20 mg sodium chloride, 300 μg benzoic acid and 25 μg nisin ml⁻¹ at pH 5.6. The whole-cell protein fingerprinting (WCPF) analysis using SDS–PAGE revealed a high level of diversity among the isolates. At 60% similarity level, the WCPF profiles could be grouped into four major clusters which were divided into 34 subclusters. Most of the subclusters were source-wise homogeneous.     

Microbiological safety and quality of commercial sufu – a Chinese fermented soybean food

In this study, the microbiological safety and quality of commercial sufu were investigated. Twenty-three samples of three different types of sufu were obtained, mainly in China and some in The Netherlands. Chemical parameters analysed included moisture, pH, free amino N, NaCl, ethanol, sucrose, glucose, and fructose. Concentrations of NaCl, ethanol, glucose and fructose varied from 6.2%, 0.5%, 0% and 0% to 14.8%, 6.3%, 6.2% and 4.8%, respectively. Microbiological analyses were done for total count of mesophilic aerobic bacteria (TMAB), bacterial endospores, total count of halotolerant bacteria at 10% (THB10) and at 17.5% NaCl (THB17.5), lactic acid bacteria (LAB), fungi, Enterobacteriaceae, and the following pathogens: Bacillus cereus, Clostridium perfringens, Staphylococcus aureus and Listeria monocytogenes. High levels (>10⁵ CFU/g) of TMAB and bacterial endospores were found in most samples, and 85% of TMAB was identified as Gram-positive. Considerable levels (10⁵ and 10⁷ CFU/g) of LAB were detected in two samples of white sufu, and isolates of LAB were identified as most probably Lb. casei. One-third of the samples contained less then 10³ CFU/g B. cereus, but three samples had over 10⁵ CFU/g indicating potential hazard to consumers. All samples had less than 10³ CFU/g C. perfringens, except sample R11 (10⁵ CFU/g). S. aureus could not be detected in any of the samples tested since the competitive microflora (usually bacilli) disturbed typical features on the selective medium used; however S. aureus enterotoxin A was detected in some of the white and grey sufu samples. Fungi, Enterobacteriaceae, and L. monocytogenes were not detected in any of the samples. Based on these results, a microbiological guideline for safe commercial sufu is proposed.     

Antimicrobial activity,safety aspects,and some technological properties of bacteriocinogenic Enterococcus faecium from artisanal Tunisian fermented meat

In an ecological study, a collection of Gram-positive bacteria were isolated from Gueddid, an artisanal Tunisian fermented meat. From these, 24 strains showed antimicrobial activity and identified as Enterococcus faecium using molecular methods. The enterococci strains were further investigated regarding their safety aspects and functional properties. All the isolates produce bacteriocins with inhibitory activity against several food spoilage bacteria and food borne pathogens, including Listeria spp. Enterococcus spp. and Staphylococcus aureus. One isolate was active against Escherichia coli CECT 877. The majority of the isolates tested positive upon PCR amplification of structural genes for enterocins A, B and P. Investigation of virulence factors by PCR amplification revealed the presence of genes encoding for gelatinase (gelE), enterococcal antigen (efaAfm), sex pheromone (cpd and ccf) and expression of cytolysin (the haemolytic component cylB) whereas, other presumed virulence genes encoding for (agg, esp, cylM, cylA, and cob) were not detected. The isolates were mostly resistant to erythromycin, rifampicin, ciprofloxacin, lavofloxacin, and nitrofurantoin. All of them showed sensitivity to several antibiotics (ampicillin, penicillin, vancomycin, chloramphenicol, teicoplanin, gentamicin, streptomycin, and quinupristin/dalfopristin). Tyrosine, lysine, ornithine and histidine were not decarboxylated by any enterococcal isolate. Nine of the antagonistic enterococci tested did not show any virulence traits or produced biogenic amines, and still had important technological properties. The safety aspects of these selected strains should be studied in deeper details in order to evaluate their potential for biotechnological applications.     

Characterization of Mediterranean mussels (Mytilus galloprovincialis) harvested in Adriatic Sea (Italy)

The aim of this work was to analyse some quality parameters of Mytilus galloprovicialis harvested monthly in the period ranging from April 2002 and February 2003 in a longline off-shore mussel farm, located in the Adriatic Sea, near Cattolica (Emilia Romagna Region, Italy). After harvesting, the samples were analysed in order to determine the counts of fecal coliforms (FC) and Escherichia coli, the presence of Salmonella, as prescribed by Italian and European Community regulations, and other pathogens (Vibrio parahaemolyticus, Listeria monocytogenes), as well as the meat yield and its proximate composition, its Fe, Cr, Cd, Zn, Pb and Cu content, the total lipids of the meat and their specific composition. The results obtained evidenced that many of the parameters studied, i.e. the meat proximate composition, the lipid fatty acid composition and the microbiological indices, were subjected to seasonal fluctuations. In particular, the microbiological data showed that 4 mussel samples (June, December, January and February) out of 12 did not match the limit imposed by Italian law and Emilia Romagna protocol concerning the FC and E. coli counts. While L. monocytogenes and Salmonella spp. were never detected in all the samples analysed, three samples (April, January and February) were positive for the presence of V. parahaemolyticus. No seasonal fluctuations were evidenced for Fe, Cr, Cd, Zn, Pb and Cu contents, always under the limits imposed by Italian law.     

Occurrence of virulence factors and antibiotic resistances in Enterococcus faecalis and Enterococcus faecium collected from dairy and human samples in North Italy

The aim of this research was to study the incidence of potential virulence factors and antibiotic resistance in 38 Enterococcus faecalis and 43 Enterococcus faecium strains isolated from dairy products and human samples. The presence of the virulence factors agg, ace, esp, gelE, efaA and of the vanA and vanB genes was evaluated by PCR, while antibiotic resistance was tested by the disk diffusion method. Ent. faecalis displayed more virulence determinants than Ent. faecium, with the presence of multiple virulence traits. Virulence determinants were present in both human and dairy strains, while antibiotic resistance patterns of the two groups of strains were very different with a significant higher diffusion of resistances among human enterococci. Considering the results of our study, dairy enterococci cannot be considered the main potential source for dissemination of antibiotic resistances.     

Reducing nitrite content in hot dogs by hurdle technology

The objective of the present study was to reduce nitrite content in hot dogs using hurdle technology without sacrificing product safety and quality. In the present study, the water activity of the hot dog was adjusted to 0.95 by the addition of humectants. Although the pH at the hot dog was adjusted with Glocono-delta-lacton to 5.4, the product had (p > 0.05) the least acceptance on account of the organoleptic changes (sour taste). Moreover, the temperature of 80 ± 1 °C for an hour with the aim of achieving an internal temperature of 75 °C was applied. Subsequently, the temperature of the hot dog samples reduced to around 5–6 °C within 40–45 min, and afterwards the sausages were kept at chilled temperature (>3 °C but 10 °C) throughout their shelf life. There was a decrease in total aerobic counts in hurdle treated hot dogs (with 50 ppm nitrite), compared to the control (with 120 ppm nitrite), whereas Clostridium perfringens counts and Clostridium botulinum detection were the same (p < 0.05) in both hurdle treated and control samples. The obtained results of present study clearly showed that both hurdle treated sample and control had the same (p < 0.05) overall acceptability and sensory attributes.     

Determination of cadmium and lead in fruit juices by stripping chronopotentiometry and comparison of two sample pretreatment procedures

A method for the determination of cadmium and lead in apple and pear fruit juices by stripping chronopotentiometry (SCP) is described. The results obtained after previous digestion of the sample with concentrated sulphuric acid and dry-ashing (sample pretreatment procedure “A”) and after a treatment with concentrated hydrochloric acid followed by heating in hot water bath (sample pretreatment procedure “B”) were compared. The sample pretreatment procedures were tested on real fruit juice samples and all data confirmed that the efficiency of procedure A was greater than procedure B. In particular, for samples treated with procedure A, good linearity was obtained in the range of examined concentration as is shown by the determination coefficients that were 0.998 (n = 4) for cadmium and 0.996 (n = 4) for lead. Recoveries of 86–104% for cadmium and of 87–102% for lead were obtained from a sample spiked at different levels. The accuracy was also evaluated by means of a matching reference sample of spiked skim milk powder (BCR 150—Community Bureau of Reference) to prove the reliability of the method. The detection limits were 2.0 ng g⁻¹ for cadmium and 4.8 ng g⁻¹ for lead. The relative standard deviations (mean of nine determinations), evaluated on a real sample, were 7.8% and 6.5% respectively. The average content was in the range not detectable–3.0 ng g⁻¹ for cadmium and 8.2–21.3 ng g⁻¹ for lead.     

Use of different methods for detection of thermophilic biosurfactant-producing bacteria from hydrocarbon-contaminated and bioremediated soils

Sixteen bacterial strains were isolated from petroleum hydrocarbons contaminated soils and screened for biosurfactants/bioemulsifiers production in liquid culture containing crude oil under thermophilic conditions. The bacterial strains grew in wide range of temperature, from 37 °C to 100 °C. Six of them were Gram positive. Their biosurfactant-production was evaluated at 45 °C.Blood agar lysis, drop-collapse method, oil spreading and stalagmometric techniques and surface tension (ST) measurements were used to detect biosurfactant production. Emulsification activity for culture broth was also tested using xylene, toluene, petroleum and diesel oils.All isolates reduced surface tension at varying degrees with strains: T/1 resulting in the highest reduction (35 mN/m). The drop-collapse, oil spreading and stalagmometric and reduction techniques all seem to give clear indicative results for biosurfactant production while blood hemolytic activity did not. The use of both the drop-collapse and oil spreading techniques were easy and quick to screen for biosurfactant producers but were not always conclusive.Although surface tension reduction was a good measure of biosurfactant production, it did not correlate well with emulsion ability. Several of our isolates had good emulsifying abilities with all hydrocarbon tested. The simplicity of the above techniques allows effective screening of biosurfactant-producing microorganisms. Although hemolytic activity have been reported as an initial selection criterion for biosurfactant producers, other more conclusive tests such as surface tension measurements should be carried out for confirmation of the obtained results.     

Effects of some Chinese medicinal plant extracts on five different fungi

Chinese medicinal plant extracts were screened against some fungal strains, such as Aspergillus niger, Botrytis cinerea, Fusarium moniliforme, Glomerella cingulata, and Phyllosticta caricae. Plants were extracted with hot water, 80% methanol or acetone. Aliquots of the extracts at variable concentrations were then incubated with different fungal strains, and the minimum inhibitory concentrations (MICs) of each plant extract determined. In this study, the methanol extracts of Cinnamomum cassia had MIC values of 13.3 mg ml⁻¹, when tested against F. moniliforme and P. caricae. The acetone extracts of C. cassia had MIC values of 8.3 mg ml⁻¹ and 10 mg ml⁻¹ respectively, when tested against B. cinerea and G. cingulata. The hot water extracts of C. cassia inhibited significantly the growth of A. niger, B. cinerea, F. moniliforme, and P. caricae with MIC values at 10, 11.7, 5, and 6.7 mg ml⁻¹ respectively. The acetone extracts of Curcuma longa inhibited effectively P. caricae with the MIC value at 6.7 mg ml⁻¹. To determine the stability, various plant extracts were stored at 4 and 25 °C over a period of one month and their effects on fungal growth examined. Results show that the acetone extracts of Cu. longa and Coptidis rhizoma maintained their activity against fungal strains when stored at 4 °C, but not at 25 °C. The methanol extracts of C. cassia lost a great portion of inhibitory activities but not all, after stored at 4 °C and 25 °C for one month. The effect of various combinations of these extracts on antimicrobial activity has also been examined. The combinations of herb extracts showed higher inhibitory effect towards tested fungi than that of individual extract. Results from these findings suggest that these herbal extracts may be used as natural antifungal agents to inhibit growth of foodborne pathogen.     

Virulence factors of Vibrio metschnikovii strains isolated from fish in Brazil

Vibrio metschnikovii is a natural inhabitant of the aquatic environment and has been isolated from seafood, and associated with disease in humans. This study presents results for virulence factors produced by V. metschnikovii strains isolated from fish. Results for virulence factors demonstrated that 38.5%, 92.3% and 100% of the strains were hemolytic on sheep, rabbit, and human blood agar, respectively. Verotoxin was produced by 100% of the strains tested and 76.9% were skin test positive. We concluded that potentially pathogenic Vibrio species, including V. metschnikovii, must be considered when investigating food borne diseases related to consumption of raw or undercooked seafood, mainly fish.     

Inhibition of food poisoning and pathogenic bacteria by Lactobacillus plantarum strain 2.9 isolated from ben saalga, both in a culture medium and in food

The bacteriocinogenic strain Lactobacillus plantarum 2.9 isolated from the traditional pearl millet-based African fermented food ben saalga was tested for inhibition of food poisoning and pathogenic bacteria in MRS broth and in a malted millet flour slurry. In MRS broth, strain 2.9 completely eliminated Bacillus cereus, Escherichia coli O157:H7 and Salmonella enterica cells within 48 h incubation at 22–30 °C. A much lower inhibition was observed at 15 °C. The inhibitory effect of strain 2.9 on the above-mentioned target bacteria was corroborated in the malted millet flour slurry, reducing viable cell counts below detection levels after 8 h storage for B. cereus or after 24 h for S. enterica and 48 h for E. coli. An Enterobacter aerogenes strain was only moderately inhibited in the slurry. Results from the present study suggest that strain 2.9 could be used as starter culture to improve the microbiological safety of fermented ben saalga.     

三氧化钼催化合成季戊四醇四庚酸酯

通过焙烧法直接焙烧钼酸铵((NH4)6Mo7O24·4H2O),制备了一种用于季戊四醇(PER)与正庚酸(HPA)酯化合成季戊四醇四庚酸酯(PETH)反应的三氧化钼(MoO3)催化剂.采用X射线衍射(XRD)、N2吸附-脱附(BET)等手段对催化剂进行了表征.考察了焙烧温度、反应条件(温度、时间、原料配比、催化剂用量)...