Studies to determine the critical control points in pork slaughter hazard analysis and critical control point systems

Aerobic mesophilic counts (AMC), coliform (CC) and coliform resuscitation counts (CRCs) were obtained by swabbing 50 cm² areas at three sites (ham, belly and neck) on pig carcasses, after each of seven stages of the slaughter/dressing process (bleeding, scalding, dehairing, singeing, polishing, evisceration and chilling). In most cases, there were no statistical differences (P>0.05) among the counts derived by these three methods. Reductions in counts at individual sites were observed after scalding (3.5 log₁₀ cfu cm⁻²), and singeing (2.5 log₁₀ cfu cm⁻²). Increases in counts at individual sites were observed after dehairing (2.0 log₁₀ cfu cm⁻²) and polishing (1.5 log₁₀ cfu cm⁻²). The incidence of Salmonella on pig carcasses was also obtained by swabbing the outside surfaces of 100 half carcasses. Information on the incidence of Salmonella in scald tank water (108 samples) was also investigated. Carcass swabs and scald tank water were examined for the presence of Salmonella using standard enrichment methods. Salmonella were detected on 31% of carcasses immediately after bleeding, 7% of carcasses immediately after dehairing and evisceration, and 1% of carcasses immediately after scalding. Serovars included Salmonella Typhimurium, Salmonella Hadar, Salmonella Infantis and Salmonella Derby. No Salmonella were recovered from samples of scald tank water. The impact of pig slaughter/dressing processes on carcass microbiology and their potential use as critical control points (CCPs) during pork production are discussed.     

Microbiological quality of ayib, a traditional Ethiopian cottage cheese

One-hundred samples of ayib, a traditional Ethiopian cottage cheese, were purchased from Awassa market and analysed for their aerobic mesophilic counts, psychrotropic counts, yeasts and molds, coliforms, spore-formers, enterococci, lactic acid bacteria, Listeria monocytogenes, staphylococci and Bacillus cereus. The majority of the samples showed counts of mesophilic aerobic bacteria, yeasts and enterococci of 10⁸, 10⁷ and 10⁷ cfu/g. About 55% of the samples were positive for coliforms and faecal coliforms. Listeria spp. were not detected in any of the samples. B. cereus and S. aureus were isolated at varying frequencies but at low numbers (10²–10³). The pH value of the samples varied between 3.3 and 4.6 with about 40% having pH lower than 3.7.     

Microbiological quality of 18 degrees C ready-to-eat food products sold in Taiwan

A total of 164 samples of 18 °C ready-to-eat (RTE) food products, purchased in 1999–2000 from convenience stores and supermarkets in central Taiwan, were examined to determine the microbiological quality of these products. The 18 °C RTE food products, manufactured by 16 factories, were divided into groups based on the type of food and their major ingredients. Aerobic plate count, coliforms, Escherichia coli, Bacillus cereus, Staphylococcus aureus and psychrotrophic Pseudomonas spp. were evaluated. The incidence of E. coli and coliforms in these 18 °C RTE food products was 7.9% and 75.0%, respectively, while 49.8% and 17.9% of the samples were found to contain B. cereus and S. aureus, respectively. Among the samples tested, 1.3% of the food products contained more than 10⁵ CFU g⁻¹ of B. cereus and 0.7% contained more than 10⁵ CFU g⁻¹ of S. aureus. The pH values of the samples were all below 7.0, except for cold noodles, which had pH values ranging from 5.18 to 8.20. Among the five types of 18 °C food products tested, the highest incidence of E. coli (16%) and Pseudomonas spp. (64.0%) were detected in hand-rolled sushi in a cone shape. On the other hand, the highest incidence rate of coliforms, B. cereus, and S. aureus were found in sandwiches (88%), cold noodles (66.7%) and rice balls rolled in seaweed (25.0%), respectively. Food products made of ham contained the highest incidence of coliforms (88.0%) and E. coli (16.0%), while food products containing meat and ham as the major ingredients had the highest incidence rates of B. cereus (62.5%) and S. aureus (26.1%), respectively. For coliforms, E. coli, B. cereus and S. aureus, the percentage of 18 °C RTE food products exceeding the microbiological standards for RTE food accepted by Republic of China was 75.0%, 7.9%, 49.8% and 17.9%, respectively.     

Behaviour of Listeria monocytogenes in raw sausages (merguez) in presence of a bacteriocin-producing lactococcal strain as a protective culture

The effectiveness of a bacteriocin produced by Lactococcus lactis subsp. lactis M in reducing population level and growth of Listeria monocytogenes ATCC 7644 in fermented merguez sausage was examined. Two different formulas (with or without added nitrites) were assayed and predetermined numbers of Listeria (ca 10⁶ cfu g⁻¹) were added to sausage mixture. The effect of in situ production of the bacteriocin by Lactococcus lactis M on Listeria monocytogenes ATCC 7644 during fermentation and storage of merguez sausages at room (ca 22 °C) or at refrigeration (ca 7 °C) temperature was tested. Results indicated that counts of Listeria monocytogenes were decreased during fermentation of merguez samples fermented with either the bacteriocin-producing Lactococcus lactis M (Bac⁺) or a nonbacteriocin-producing Lactococcus lactis J (Bac⁻). However, reduction in Listeria cfu's was greater in samples fermented with the Bac⁺ than in those fermented with the Bac⁻ starter. In merguez sausage made without nitrites addition, the Bac⁺ starter induced further decrease in Listeria counts by 1.5 log cycles compared with that induced by the Bac⁻ starter. While in merguez samples with added nitrites (0.4%), the effect of the bacteriocin produced in situ was less important than in those made without nitrites addition.     

Survival of pathogenic microorganisms in an egg-nog-like product containing 7% ethanol

A liquor consisting of whole egg, saccharose (25% w/v) and ethanol (7.0% w/v) was artificially contaminated with Salmonella enteritidis, S. typhimurium, Staphylococcus aureus (three different strains), Bacillus cereus and Listeria monocytogenes. After 3 weeks of incubation at 22°C the numbers of Salmonella, S. aureus and L. monocytogenes decreased more than 3 log₁₀ units. Under such conditions, however, the total number of microorganisms increased 3 log₁₀ units. At 4°C the decrease of pathogenic microorganisms was much slower and a decrease of 3 log₁₀ units was observed only after 7 weeks of incubation. Egg-nog, without ethanol, incubated at 22°C allowed growth of Salmonella and S. aureus, while the numbers of B. cereus spores remained unchanged. Vegetative cells of B. cereus as well as L. monocytogenes decreased in numbers. However, after prolonged incubation the numbers of L. monocytogenes increased significantly.     

Influence of various preservatives on the quality of minced beef under modified atmosphere at chilled storage

The effect of preservatives on microbial quality, pH, drip-loss, roasting-loss, colour, and sensorial properties of modified atmosphere packaged (70% O₂ and 30% CO₂) minced beef (M. semimembranosus) stored at (2 ± 0.5 °C) for 12 days was investigated. Beef cubes (approx. 20 × 20 × 20 mm size) were immersed in solutions of 2% and 5% lactic acid, 2% lactic acid combined with 0.5% sodium ascorbate, 20% potassium lactate and 20% potassium sorbate before mincing. Addition of lactic acid was associated with pH drop, which increased drip-loss and roasting-loss. Application of all additives inhibited aerobic micro-organisms (10³–10⁴ CFU g⁻¹ on day 12) compared to reference sample (9 × 10⁵ CFU g⁻¹ on day 12). Lactic acid discoloured samples, while sodium ascorbate seemed to improve colour stability. Despite good visual colour characteristics, potassium sorbate treated samples were organoleptically unacceptable with massive off-flavour.     

Pre-selection of protective colloids for enhanced viability of Bifidobacterium bifidum following spray-drying and storage, and evaluation of aguamiel as thermoprotective prebiotic

The objective of this work was to demonstrate that Bifidobacterium bifidum viability to spray-drying and with storage time could be substantially enhanced by pre-selecting protective colloids offering resistance to oxygen diffusion (high activation energy) and adding aguamiel as a thermoprotector prebiotic. Three different protective colloids blends exhibiting relatively high, medium and low activation energies were mixed with B. bifidum harvested in the late log phase, with or without aguamiel, spray-dried at 130, 140 and 155 °C, and stored at 4 °C at a water activity of 0.32. Viability was determined by cell total count in MRS agar. Best viability was achieved when microencapsulating the microorganism in the protective colloids blend exhibiting highest activation energy (40.7 kJ mol⁻¹), with aguamiel, and dried at 140 °C. Viability ranged from 1.26 × 10⁸ cfu g⁻¹ immediately after drying to 6.0 × 10⁶ cfu g⁻¹ after 5 weeks storage time at 4 °C.     

The occurrence of Staphylococcus aureus in fermented milk products (fura and manshanu) in Nigeria

Ninety-three samples of fermented milk cereal (Fura) and 79 of local butter (Manshanu) were collected from four different markets around Zaria. For Fura the mean content of Staphylococci for each of the four markets ranged from 4.5 × 10³ to 4.3 × 10⁴ cfu/ml and the mean aerobic mesophilic plate count from 5.6 × 10⁵ to 2.7 × 10⁶ cfu/ml. For Manshanu the mean staphylococcal count and aerobic mesophilic plate count ranged from 3.4 × 10² to 2.2 × 10³ cfu/ml and 6.7 × 10⁴ to 1.1 × 10⁶ cfu/ml respectively. Significant differences were seen between the different markets.     

Thermal inactivation of lectins (PHA) isolated from Phaseolus vulgaris

The influence of the thermal process on the loss of ability to bind a carbohydrate target was studied on lectins (PHA) purified from Phaseolus vulgaris seeds. Thermal inactivation of aqueous solutions of pure PHA occurred according to a biphasic first-order mechanism, the thermodynamic parameters, at pH 7·3, being as follows: ΔH*₁ = ΔH*₂ = 86·2 kcal mole⁻¹, ΔS*₁ = − 54·04 cal deg⁻¹ and ΔS*₂ = − 56·71 cal deg⁻¹. The first-order rate constants appeared to be dependent on pH (minimal around 7) and divalent cations. All different subunits constituting the whole PHA were inactivated at the same rate. The biphasic nature of this process is independent of the presence of 10 m Ca⁺⁺ or Mg⁺⁺ and appeared to indicate a discrete aggregation of PHA molecules.     

Selective enumeration and survival of bifidobacteria in fresh cheese

Five species of bifidobacteria (15 strains), two strains of Lactococcus lactis ssp. lactis, two strains of L. lactis ssp. cremoris, and one strain of L. lactis ssp. lactis var diacetylactis were included in a study to develop a selective medium for enumeration of bifidobacteria from fresh cheese. Viable counts of bifidobacteria or lactococci on modified Columbia agar base (CAB with 0.05% cysteine-HCl) plus raffinose (0.5%) containing various selective agents were compared with non-selective media. The mCAB plus raffinose with lithium chloride (2 g L⁻¹) and sodium propionate (3 g L⁻¹) with pH adjusted to 5.1 was used successfully as a selective medium for the enumeration of bifidobacteria from fresh cheese. Using this medium, it was determined that bifidobacteria could survive up to 15 days at a level higher than 10⁶ cfu g⁻¹ in a fresh cheese stored at 4 or 12°C. The decrease in the viable counts of bifidobacteria was faster during storage at 4°C than at 12°C.     

Comparison of the microflora isolated from spoiled cold-smoked salmon from three smokehouses

The microflora on spoiled, sliced and vacuum packed, cold-smoked salmon from three smokehouses was quantified and characterized in two independent experiments. Large variations in the microflora were observed both within (i.e. among vacuum packs from the same batch) and among the smokehouses. Lactic acid bacteria dominated the microflora, which reached 10⁷ cfu g⁻¹. Total viable counts of microorganisms alone were not related to quality, though spoilage characteristics were typical for microbiological spoilage. Among the lactic acid bacteria, Lactobacillus curvatus (ca 52–55%) was the most common species in both experiments with Lactobacillus saké, Lactobacillus plantarum, Carnobacterium spp. and Leuconostoc spp. present in smaller numbers. In some cases, large numbers of Enterobacteriaceae were also present and identified species were Serratia liquefaciens, Enterobacter agglomerans and Hafnia alvei. The microflora on cold-smoked salmon appeared to be related to the source of contamination i.e. the raw material and/or the smokehouse rather than being specific for the product, thus rendering the identification of the specific spoilage organisms difficult.     

Listeria innocua and aerobic mesophiles during chill storage of inoculated mechanically recovered poultry meat treated with high hydrostatic pressure

Mechanically recovered poultry meat (MRPM) was inoculated with Listeria innocua 910 CECT at a level of approximately 10⁸ CFU g⁻¹. Vacuum-packaged samples were treated by combinations of pressure (350, 400, 450 and 500 MPa), time (5, 10, 15 and 30 min) and temperature (2, 10 and 20°C) and later stored at 2°C for 2 months. Counts of L. innocua and aerobic mesophilic bacteria were determined 1, 4, 7, 15, 30 and 60 days after pressurisation. For mesophiles, in most treatments, pressurization at 2°C gave the significantly best results. High pressure caused a marked bactericidal effect on L. innocua: reductions higher than 7.5 log units were achieved in several cases. Some cells were just sublethally injured by pressure. Samples treated at 500 MPa for 30 min at 2°C had counts of only 2.3 log units after 60 days of chill storage. Noninoculated pressurised MRPM did not show Listeria growth throughout storage. These results suggest that high pressure processing can enhance the microbiological quality of MRPM.     

Effect of modified atmospheres on microbiological, color and sensory properties of refrigerated pork

Pork loin samples were stored (4 °C) in nylon polyethylene plastic bags using different modified atmospheres packaging (MAP): vacuum, 100% CO₂ 99% CO₂ + 1% CO, 100% O₂ or 100% CO followed by vacuum. Throughout the storage period Pseudomonas growth was limited in loins packaged in all MAPs evaluated, except for 100% O₂. Psychrotrophs reached 10⁷ CFU g⁻¹ after 20 days of storage except for the loin samples in 100% O₂ MAP that present count above 10⁸ CFU g⁻¹. The 1% CO/99% CO₂ atmosphere was best for preserving the desirable pork loin color and the L* and a* values remained similar to the fresh meat values using this MAP. Pork loins in 99% CO₂/1% CO MAP obtained the highest consumer acceptance scores after 24 h of storage. These samples and those treated with CO and then vacuum packaged received the greatest acceptance scores even after 20 days of storage.     

Microbiological quality and shelf-life of vacuum-packaged ‘gravad’ rainbow trout stored at 3 and 8 °C

Microbiological and sensory changes of vacuum-packaged ‘gravad’ rainbow trout slices were studied during storage at 3 and 8 °C. At the time of spoilage, after 27 and 20 days of storage at 3 and 8 °C, respectively, both mesophilic viable counts (MVC) and psychrotrophic viable counts (PVC) reached 10⁶–10⁷cfu/g at 3 °C and 10⁷–10⁸ cfu/g at 8 °C. H₂S-producing bacteria constituted a high proportion of the PVCs and lactic acid bacteria (LAB) counts were lower than the other determined bacterial counts. Sensory scores decreased with increasing MVC and PVC. The judges considered samples unfit for human consumption at MVC and PVC levels exceeding 10⁶ and 10⁷ cfu/g for samples stored at 3 and 8 °C, respectively. At respective levels of 10⁷ and 10⁸ cfu/g, most of the samples were deemed unfit. The main reasons for sensory rejection at both storage temperatures were the lack of the typical product odour or an ammonia off-odour and colour change to dark violet. The shelf-lives of the rainbow trout slices based on microbiological and sensory analyses were 20 days and 18 days at 3 and 8 °C, respectively.     

Microbiological quality of freshly shot game in Germany

In the framework of a project on the hygiene status of freshly shot game 289 samples were microbiologically analysed: 127 samples from wild boars, 95 from roe deer and 67 from red deer. The microbiological parameters evaluated were the mesophilic aerobic count (APC), which showed mean log10-counts of 2.6 cfu/cm² for roe deer, 2.9 cfu/cm² for red deer and 3.2 cfu/cm² for wild boars and the numbers of Enterobacteriaceae, which gave mean log10-values of 2.1 cfu/cm² for all three species with differing ranges. The concentrations of coagulase positive staphylococci were >2.0 log10 cfu/cm² between 3.2 and 6.3%, according to species. Listeria was found in 14 samples and three samples gave a positive result for Campylobacter. Salmonella was not found in any of the samples analysed.     

The effects of spray and blast-chilling on carcass shrinkage and pork muscle quality

Combinations of blast- and spray-chilling of pork carcasses were compared to spray-chilling at conventional chilling temperatures with regard to carcass shrinkage during chilling and pork muscle quality. In experiment 1, pork sides were spray-chilled at 1°C for the first 10 h (40 spray cycles of 60-s duration every 15 min) of cooling or blast-chilled at −20°C for 1, 2 or 3 h followed by spray-chilling for 9, 8 or 7 h duration, respectively. All pork sides were then chilled to 24 h post mortem at 1°C. Experiment 2 followed the same procedures as experiment 1, except that −40°C was used as the blast-chill temperature.

Carcass shrinkage was similar for all treatments in experiment 1 at 24 h ranging from 0·5–0·7 g 100 g⁻¹. Blast/spray-chilling increased the rate of chilling and reduced the rate of post-mortem pH decline in two muscles (longissimus thoracis, LT and semimembranosus, SM) compared to the combined conventional/spray-chill treatment. Carcasses that were blast-chilled for 3 h had LT muscles that were darker with a higher protein solubility, less drip loss, shorter lengths and higher shear values compared to those from carcasses in the conventional/spray-chill treatment. In experiment 2, carcasses blast-chilled for 3 h at −40°C recorded a weight gain at 24 h of 0·4 g 100 g⁻¹, compared to a weight loss in all other treatments (0·2–0·4 g 100 g⁻¹). Muscle colour was darker in both the LT and SM of carcasses blast-chilled for 3 h at −40°C compared to carcasses from the conventional/spray-chill treatment, but most other measurements of muscle quality showed an inconsistent response to chilling treatment.     

Modeling transfer of Escherichia coli O157:H7 and Staphylococcus aureus during slicing of a cooked meat product

Cross contamination is one of the most important contributing factors in foodborne illnesses originating in household environments. The objective of this research was to determine the transfer coefficients between a contaminated domestic slicing machine and a cooked meat product, during slicing. The microorganisms tested were Staphylococcus aureus (Gram positive) and Escherichia coli O157:H7 (Gram negative). The results showed that both microorganisms were able to transfer to all slices examined (20 successively sliced) and at different inoculum levels on the blade (10⁸, 10⁶ and 10⁴ cfu/blade). The results also showed that the number of log cfu transferred per slice, during slicing, decreased logarithmically for both microorganisms at inoculum levels of 8 and 6 log cfu/blade. The type of microorganism significantly influenced transfer coefficients (p < 0.05) and there was an interaction between inoculum level and transfer coefficient for S. aureus (p < 0.05), but not E. coli O157:H7. Finally, to describe bacterial transfer during slicing, two models (log-linear and Weibull) were fitted to concentration on slice data for both microorganisms (at 6 and 8 log cfu/blade), obtaining a good fit to data (R²  0.73).     

A new measure of uptake: desorption of unreacted phosphine from susceptible and resistant strains of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Previous studies of phosphine (PH₃) uptake by insects have concentrated on the process as a whole (“gross uptake”), without distinguishing between absorption of the gas and oxidation to non-volatile products. The lower gross uptake by phosphine-resistant (R) strains of stored product pests has given some insights into resistance mechanism(s). In this study, a recently described method of fumigant residue analysis in grains (microwave irradiation followed by headspace gas chromatography) was adapted to measure absorbed unreacted PH₃ (“reversible uptake”) in a susceptible (S) and an R strain of the rust red flour beetle Tribolium castaneum. At a concentration of 0.9 mg l⁻¹, S insects contained 20 ng g⁻¹ after 15 min exposure, rising slowly to 50 ng g⁻¹ after 5 h. The R strain yielded 190 ng g⁻¹ after 15 min, falling to 50 ng g⁻¹ over 5 h. Falling PH₃ content corresponded with increasing mortality in the R strain, while all except the shortest exposure killed 97% or more of the S strain. Insects of either strain, killed prior to PH₃ exposure by freezing in liquid nitrogen, contained 130–140 ng g⁻¹ after 30 min, rising to 190–200 ng g⁻¹ after 5 h. Gross uptake under the same conditions was 50 μg g⁻¹ (S) and 8 μg g⁻¹ (R) after 5 h, which accords with the literature. Reversible uptake by living insects of either strain under anoxia was 40–50 ng g⁻¹ over 30 min to 2 h. By examining the time-course of reversible PH₃ uptake, a new hypothesis of phosphine action and uptake, in which PH₃ oxidation in vivo is a consequence of reactive oxygen species generation, rather than a direct cause of toxicity, is discussed.     

Effects of supercritical carbon dioxide extraction conditions on yields and antioxidant activity of Chlorella pyrenoidosa extracts

Yields and antioxidant activity of Chlorella pyrenoidosa extracts obtained by supercritical carbon dioxide extraction through an orthogonal experiment (L₁₆(4⁵)) were investigated to get the best extraction conditions. The results showed that extraction pressure, temperature and modifier were the main three variables that influenced the yields of extracts. The highest yield was obtained at 32 °C, 40 MPa, 20 L h⁻¹ with dosage of modifier 1 mL ethanol g⁻¹ sample for 3 h. Moreover, increasing pressure and concentrations of modifier led to the increase of extraction yields and antioxidant activity. DPPH radical scavenging method showed that almost all the extracts had significantly higher antiradical activities varying from 29.67 ± 0.29% to 54.16 ± 4.49% comparing to -tocopherol, Trolox, and BHT as references except extracts at 32 °C, 35 MPa and 15 L h⁻¹ without modifier for 1.5 h. These results indicate that supercritical extraction is a promising alternative process for recovering compounds of high antioxidant activity from C. pyrenoidosa.     

Growth of Listeria monocytogenes on vacuum-packaged horsemeat for human consumption

In order to investigate the likelihood of Listeria monocytogenes (serotype 4b, ATCC 19115) growth on vacuum-packaged horsemeat at refrigeration temperature, fourteen horsemeat surface/volume homogeneous 150 g weight pieces were superficially inoculated with serotype 4b L. monocytogenes and vacuum packaged. The samples were stored at 4 ± 1 °C. Two pieces (one for pH determination and one for L. monocytogenes counts) were examined at days 0, 7, 14, 21, 28, 35 and 42. Surface pH did not show significant variations during the experiment. The average L. monocytogenes initial contamination level was 1.77log₁₀ CFU/g. A lag phase of 7 days was recorded. The exponential growth rate between day 7 to day 35 was 0.125log₁₀ CFU/day, corresponding to 3.51log₁₀ CFU/g in 28 days. At the end of the experiment the mean L. monocytogenes log₁₀ CFU/g was 5.78.