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.     

Determination of biogenic amines in sucuk

The biogenic amines content of sucuk (Turkish dry fermented sausage) were determined on 30 samples obtained from retail markets and butchers in Turkey. Also, pH and a_w values, microbiological properties, and NPN levels of these samples were analyzed. The most important biogenic amines were tyramine (range 2.4–676 mg/kg), followed by putrescine varied from not detected to 364 mg/kg. Histamine content was under 50 mg/kg in 80% of the samples while it was over 100 mg/kg in only one sample. Tryptamine was detected in 16 of 30 samples in the range of 1.2–82.3 mg/kg.

Lactic acid bacteria, Micrococcus/Staphylococcus and Enterobacteriaceae counts of samples varied from 2.84 to 8.85 log cfu/g, <2.00 to 6.74 log cfu/g, and <2.00 to 5.04 log cfu/g, respectively. pH values were varied between 4.53 and 6.29 while water activity (a_w) were measured to be between 0.761 and 0.960. NPN values were determined to be between 1.47% and 4.10%. Generally, total amine content was high in samples that had high NPN levels.     

Application of electrolyzed oxidizing water on the reduction of bacterial contamination for seafood

For reducing bacterial contamination, electrolyzed oxidizing water (EO water) has been used to reduce microbial population on seafood and platform of fish retailer. The specimens of tilapia were inoculated with Escherichia coli and Vibrio parahaemolyticus, and then soaked into EO water for up to 10 min. EO water achieved additional 0.7 log CFU/cm² reduction than tap water on E. coli after 1 min treatment and additional treatment time did not achieved additional reduction. EO water treatment also reduced V. parahaemolyticus, by 1.5 log CFU/cm² after 5 min treatment and achieved 2.6 log CFU/cm² reduction after 10 min. The pathogenic bacteria were not detected in EO water after soaking treatment. In addition, EO water could effectively disinfect the platform of fish retailer in traditional markets and fish markets.     

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.     

Analysis of 140 pesticides from conventional farming foodstuff samples after extraction with the modified QuECheRS method

Pesticides in foodstuff are becoming a major issue due to their intensive use in agriculture. Thus an appropriate control of their residues in food samples has to be operated. In this study we analysed 105 pesticides with GC/SQ-MS and 46 pesticides with HPLC/IT-MS after extraction with the QuECheRS method in four matrices (grape, lemon, onion and tomatoes). For GC-amenable substances, the LOD and LOQ ranged from 0.4 to 48.2 μg/kg and from 1.2 to161 μg/kg, respectively. For HPLC-amenable substances, they varied from 1.0 to 115 μg/kg and from 3.3 to 382 μg/kg, respectively. With GC/MS, 61–82% of the substances showed a recovery in the range of 70–110% and 6–30 % presented a recovery higher than 110% at the 500 μg/kg fortification level. With HPLC/MS, 87–93% of the substances presented recoveries in the range of 70–110% at the 500 μg/kg fortification level compared to 78–85% at the 50 μg/kg fortification level. Lemon and onion showed poor recoveries but are known to be difficult matrices (high acidic and high sulfur content, respectively). The method was proved to be repeatable with RSD lower than 20% at 500 μg/kg and lower than 15% at 50 μg/kg with both devices.     

An evaluation of the effect of storage and processing temperatures on the microbiological status of sous vide extended shelf-life products

The microbiological and organoleptic quality of selected sous vide products was monitored over a storage period of up to five weeks at 3°C and 8°C, respectively. Sous vide products stored at the recommended temperature of 3°C showed negligible microbial growth and were found to be organoleptically acceptable throughout the storage period. Total plate counts at the end of the fourth week of storage were in the range <10–7×10³ CFU/g for all 19 products under study. Listeria monocytogenes, Salmonella, Clostridium perfringens, Bacillus cereus and Enterobacteriaceae were not detected in any of the processed samples. At 8°C, under temperature abuse conditions, while some products had acceptable microbial levels of 10²–10⁴ CFU/g after three weeks, others such as chicken chasseur had counts above 10⁶ CFU/g by the second week of storage. Lactic acid bacteria and Pseudomonas species were dominant in the microbial flora of spoilt samples and B. cereus (>3×10⁴ CFU/g) was isolated from spoilt chicken chasseur samples in the fourth week of storage at 8°C. Critical factors affecting sous vide product safety are discussed.     

The in vitro antimicrobial and antioxidant activities of the essential oils and methanol extracts of endemic Thymus spathulifolius

The present study was conducted to evaluate the in vitro antimicrobial and antioxidant properties of essential oil and methanol extracts from a unique and endemic plant, Thymus spathulifolius (Hausskn. and Velen.). The antimicrobial test results showed that the essential oil of T. spathulifolius strongly inhibited the growth of test microorganisms studied, except for 4 fungi species while polar and non-polar subfractions of the methanol extract had moderate antibacterial, but not antifungal and anticandidal activity. The antioxidative potential of the samples was evaluated using two separate methods, inhibition of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and β-carotene–linoleic acid systems. The polar subfraction of the methanol extract was able to reduce the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ of 16.15 ± 0.5 μg/ml, which was lower than that of synthetic antioxidant, BHT, (19.8 ± 0.5 μg/ml). Inhibition values of linoleic acid oxidation were calculated as 92% and 89% for the oil and the polar subfraction, respectively. Gallic acid equivalent total phenolic constituent of the polar subfraction was 141.00 ± 0.90 μg/mg (14.1%, w/w). The chemical composition of a hydrodistilled essential oil of T. spathulifolius was analyzed by a GC and GC/MS system. A total of 28 constituents representing 99.2% of the oil were identified; thymol (36.5%), carvacrol (29.8%), p-cymene (10.0%) and γ-terpinene (6.3%) were the main components comprising 82.6% of the oil. Results presented here may suggest that the essential oil and extracts of T. spathulifolius possess antimicrobial and antioxidant properties, and therefore, they can be used as a natural preservative ingredient in food and/or pharmaceutical industry.     

Assessment of estimated daily intake of nitrite by average consumption of processed foods in Korea

This study has been performed to estimate the average daily intake of nitrite used in Korea as a color fixative. The crude estimation of daily intake was calculated based on maximum permitted levels (MPL) and national food disappearance data in 1998. In order to refine estimated daily intake (EDI), daily food consumption nationwide National Health and Nutrition Survey in 1998 and the concentration of nitrite in their permitted foods were applied. The crude EDI of nitrite was 17.85 μg/kg bw/day, representing 25.5% of acceptable daily intake (ADI) assigned by JECFA. The refined average EDI for nitrite was 0.87 μg/kg bw/day, representing 1.25% of ADI. For average consumers of age–sex groups ranged from 0.2 to 4.8 μg/kg bw/day, representing 0.3%–6.9% of the ADI.     

The dissipation rates of cyprodinil, fludioxonil, procymidone and vinclozoline during storage of grape juice

The disappearance of the fungicides cyprodinil, fludioxonil, procymidone and vinclozoline, which are widely used to control grey mold in vineyards, from commercially sterilized white grape juice was studied. Fungicide losses from white grape juice stored at 40 °C were monitored for about 2 months in order to simulate in a fast way the shelf-life of the product at room temperature (about 1 year). The fungicides were determined by using a simple method based on a liquid–liquid extraction (LLE) and gas chromatographic separation, followed by mass spectrometric detection (GC–MSD). Fortified white grape juice subsamples were taken three times a week from the oven and the degradation of the fungicides monitored for 56 days. The half-lives at 40 °C for vinclozoline and procymidone were found to be 11 and 20 days, respectively. Those for the more recently introduced fungicides fludioxonil and cyprodinil were somewhat longer (33 and 44 days, respectively). Based on the first-order rate constants obtained, the fungicides dissipated in the following sequence: vinclozoline (0.062 d⁻¹) > procymidone (0.035 d⁻¹) > fludioxonil (0.021 d⁻¹) > cyprodinil (0.016 d⁻¹).     

Simple methods for rapid determination of sulfite in food products

Two simple methods for sulfite determination in food products were proposed. The modified para-rosaniline (PRA)-formaldehyde method showed a much broader linear range (0.05–5.0 mg l⁻¹ as SO₂) than the commonly used procedure for the sulfur dioxide detection in the atmosphere (0.05–1.0 mg l⁻¹ as SO₂). By using a standard reference color card, this method only needed 5 min to complete a test. The 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) method was another good alternative for rapid determination of sulfite since it only needed one main reagent and the method was robust and easy to operate with the linear range of 0.10–4.3 mg l⁻¹ as SO₂. When applying to real food samples, the DTNB method had good recoveries for all the tested samples and the results agreed well with those obtained by the official iodometric titration. The modified PRA-formaldehyde method worked well with all the tested dried food products, though matrix effect of sulfite binding was observed for the beer samples. Thus, the modified PRA-formaldehyde method has advantages of sensitivity and rapidity, but the DTNB method offers a wider range of applications. Both methods provided practical ways for in situ determination of sulfite by non-professional operators with the modified PRA-formaldehyde method suited for food samples with less sulfite binding problems.     

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.     

Neural network modelling of the fate of Salmonella enterica serovar Enteritidis PT4 in home-made mayonnaise prepared with citric acid

Fifty-four mayonnaise recipes were generated by the central composite design and tested for microbiological safety at two temperatures (5 and 22 °C). The content of oil: (150–350 ml), egg yolk (10–35 g), citric acid (4.98% w/v) (10–40 g), salt (0–3 g), mustard (0–2 g), sugar (0–1 g) and white pepper (0.25 g) varied among the different recipes. The fate of Salmonella enterica serovar Enteritidis PT4 in mayonnaise products was investigated by both viable count and presence/absence tests and modelled by neural networks. This study demonstrated that feed-forward neural networks were incapable of modelling the survival/growth curves of S. Enteritidis PT4 as a one-step-procedure model, but were capable of modelling the presence/absence of the organism.     

Occurrence of contaminants in foods commonly consumed in Bahrain

The occurrence of mycotoxins (aflatoxins, zearalenone, deoxynivalenol), heavy metals and pesticide residues in 198 susceptible food commodities available in Bahrain was determined. Aflatoxins were found in many of the foods tested and three samples of red chili powder (35.9, 52.6 and 69.2 ng/g), one sample of black pepper powder (27.7 ng/g) and one sample of unshelled pistachio nuts (81.6 ng/g) exceeded the maximum allowable limit of aflatoxins. Zearalenone was present in some samples including cornflakes (3.1 ng/g) and crushed wheat (0.3 ng/g). Although many samples contained heavy metals, one sample of cinnamon powder (13.0 μg/g) and one sample of black pepper powder (11.2 μg/g) exceeded the maximum allowable limit for lead. The average levels of cadmium were highest in cinnamon powder (0.3 μg/g) and ginger powder (0.3 μg/g). Some amount of pesticides was found in cumin powder (0.06 μg/g of lindane), turmeric power (0.04 μg/g heptachlor) and coriander powder (0.4 μg/g permethrin). Almonds, peanuts, cashew nuts infant formulas were free of contaminants. Although the contamination of most foods in Bahrain was within the limit, strengthening of the food control systems is important.     

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.     

Microbiological characteristics of cake prepared from rice flour and sticky rice flour

Microbiological, chemical and sensory changes in MiGao (a traditional Chinese steamed cake) were studied during five days of storage at 25 °C. Microorganisms examined for were: Enterobactericeae, lactic acid bacteria, Gram-positive, catalase-positive cocci, Staphylococcus aureus, Bacillus strains, yeasts and moulds, and pH and moisture content were also analyzed. Total plate counts in the products under study in the third day of storage were in the range <10³ CFU/g and the shelf-life of the product was estimated to be only two or three days by the panelists. During the first two days, Gram-positive bacteria were dominant, mainly represented by Staphylococcus epidermidis. Bacillus strains occurred by the third day, reaching a maximum level of 1 × 10⁶ CFU/g after five days of storage. No Enterobactericeae or Lactic acid bacteria were detected in the processed products throughout the storage period. All the isolated strains from the mannitol salt agar belonged to the genus Staphylococcus. The predominant species were S. epidermidis and S. aureus. Most Bacillus strains, isolated from the tryptone soya agar, belonged to the species Bacillus brevis. The count of yeasts and moulds increased slowly but remained low throughout the storage period.     

Aflatoxins levels in dried fruits and nuts from Rabat-Salé area, Morocco

The occurrence of aflatoxins (AFs) in dried fruits and nuts available in Rabat-Salé area (Morocco) was surveyed in this study. One hundred samples of dried fruits and nuts, purchased from retail shops and local markets from January to October 2006, were analyzed for AFs content by immunoaffinity (IAC) clean-up with liquid chromatography and fluorescence detection. Results showed that the incidences of total aflatoxins (AFT) and aflatoxin B1 (AFB1) in peanut, dried raisins, dried figs, walnut, and pistachio were 5%, 20%, 30%, 30% and 45% and 5%, 20%, 5%, 30% and 45%, respectively. The highest contamination levels of AFB1 were found in one walnut sample (2500 μg/kg) and one pistachio sample (1430 μg/kg). 5%, 20% and 20% of samples of pistachio, walnut and dried raisins exceeded the maximum tolerable limit (2 μg/kg) set for AFB1 by EU regulations. While 15% of dried figs samples were above the maximum limit (4 μg/kg) set by EU regulations for AFT. The present paper is the first report on the natural occurrence of AFs in dried fruits and nuts available in Rabat-Salé area in Morocco.     

Increasing the microbial inactivation of Staphylococcus aureus in sauces by a combination of enterocin AS-48 and 2-nitropropanol, and mild heat treatments

Staphylococcus aureus was challenged with the cyclic bacteriocin AS-48 in four commercial sauces singly and in combination with sublethal heat treatments (50-60 °C, for 5 min) and with 2-nitro-1-propanol (2NPOH). Heating at 60 °C in combination with AS-48 (25 μg/ml) reduced initial counts (4.1-4.5 log CFU/ml) below detection limit (1.0 log CFU/ml), while a combined treatment at 55 °C inhibited proliferation of staphylococci in sauces for 24 h at 22 °C. In BHI broth, enterocin AS-48 (0-15 μg/ml) acted synergistically with 2NPOH (0-220 mM), reducing the concentrations of both antimicrobials required for inactivation of S. aureus. In sauces, enterocin AS-48 (25 μg/ml) plus 2NPOH (25 mM) reduced initial cell concentrations (4.1-5.0 log CFU/ml) below detectable levels within 8-24 h, depending on the sauce. The combinations of enterocin AS-48 and 2NPOH or sublethal heat are interesting for testing as part of hurdle technology aimed at reducing the risks for proliferation of S. aureus in sauces.     

Microbiological profile of helva sold at retail markets in Izmir city and the survival of Staphylococcus aureus in this product

The objective of this research was to determine the microbiological profile of tahin helva, a low moisture confectionery. A total of 63 tahin helva samples were collected from the retail markets in Izmir, Turkey. These samples were examined by standard procedures for aerobic plate count (APC) and counts of moulds and yeasts, Enterobacteriaceae, Staphylococcus aureus and Salmonella spp. APC of samples ranged from <10 to 1.6 × 10⁵ cfu/g. The counts for moulds, yeasts and Enterobacteriaceae ranged from <10 to 1.8 × 10³, <10 to 7 × 10², <10 to 8.5 × 10² cfu/g, respectively. None of the samples contained S. aureus or Salmonella. The potential for survival of S. aureus in the product stored at refrigeration (4 °C) and room (20 °C) temperatures was evaluated by artificial contamination. S. aureus cells were still recovered after 9 months of storage at both temperatures. The results of this investigation indicate that S. aureus contamination of tahin helva, (a_w of 0.172) may constitute a potential public health hazard, depending on the extent of contamination and mishandled exercise at the sale area and the kitchen.