Post-processing Contamination Research Articles

Microbiota mesophilic aerobic contaminant UHT milk

In 2011 the national production of ultra-high temperature milk (UHT) was 5.81 billion liters, corresponding to 78% of fluid milk consumed in Brazil. The present work aimed to study UHT milk contamination by mesophilic aerobes (MA), verifying the accordance with microbiological standards, classifying the groups found according to its morpho-tinctorial characteristics and discussing the methodology determined by Normative Instruction (NI) 62 from the Brazilian Ministry of Agriculture, Animal Husbandry and Supply. From 60 studied samples, 23 (38.3%) presented results above the 100 CFU/mL standard established by NI 370 for (MA). When B. sporothermodurans was considered, maximum counts raised 71.2% in whole milk samples, and 31.0% in skimmed milk samples. Regarding the higher dilutions inoculated that have shown growth, it was possible to isolate 462 colonies of (MA) that, in Gram coloration corresponded to 64.3% Gram positive bacteria and 9.5% Gram negative. Molds and yeasts added up to 26.2%. Among Gram positive, there was a prevalence of cocci, B. sporothermodurans , and other Gram positive bacilli. Among Gram negative, the coccobacilli and bacilli prevailed. Considering that the samples represent UHT milk from important industries of southern Brazil, the results demonstrate that 11 out of the 15 studied brands showed high counts of (MA) when compared to the established standards. Furthermore, among the groups of microorganisms found in the samples, especially heat sensitive Gram negative bacteria, indicates possible failures in milk processing and/or post-processing contamination.

Prevalence of Veterinary Drug Residues and Heavy Metals in Catfish Nuggets

Seafood such as catfish can sometimes become contaminated with chemicals and heavy metals at levels which would harm human health. There has been renewed interest by the USDA Food Safety Inspection Service (FSIS) in determining the incidence and prevalence of potentially harmful contaminants in catfish products. Many studies of retail catfish have focused on the fillet portion of the fish. Catfish nuggets are the fatty belly flap of the fish which is removed during processing and are sold as a separate product. Retail catfish nuggets from domestically raised catfish were collected in New Jersey, Pennsylvania, New York and Delaware and then tested for the presence of chemical contaminants including the heavy metals arsenic, lead, mercury, and cadmium. Of the 24 nugget samples tested none tested positive for the presence of arsenic or lead. Cadmium was detected in nine samples, but the levels were well below the regulatory action levels indicated for seafood. Mercury was detected in one catfish sample, but again the concentration was well below the U.S. FDA action limit for methyl mercury in fish. In addition, the presence of veterinary drug residues including malachite green, gentian violet and chloramphenicol in domestic catfish nuggets was also determined. One sample tested positive for the presence of gentian violet, however, given the low level detected (1.1 ppb) it is theorized to have occurred due to post-process contamination.

INCIDENCE OF AEROBIC SPOILAGE- AND PSYCHROTROPHIC BACTERIA IN NON-PASTEURISED AND PASTEURISED BOVINE MILK FROM MASERU

The presence of pathogenic bacteria in milk is a possible source of food-borne diseases. One hundred and sixty non-pasteurised and forty pasteurised milk samples from the Maseru area were analysed for the presence of bacteria. It is recommended by legislation that milk be free from pathogenic bacteria, and microbial counts must be within the ranges as stipulated in Regulation 1555 of 21 November 1997. Eighty seven of the non-pasteurised milk samples had high total aerobic bacterial counts that were not within the stipulated range for microbial counts as outlined in Regulation 1555, whereas twenty seven pasteurised milk samples had unacceptably high aerobic bacterial counts. Unacceptably high counts of E. coli were detected in thirty five of the non-pasteurised samples. Bacterial phosphatase was detected in seven of the pasteurised samples, indicating possible post-processing contamination. Listeria monocytogenes was isolated from five non-pasteurised milk samples and Listeria innocua was isolated from one sample. The presence of psychrotrophic Listeria could contaminate the milk processing plant rendering pasteurised milk unsafe for human consumption. Community members should be informed regarding the dangers of consuming non-pasteurised milk. Small-scale farmers should be educated regarding the dangers of Listeria infection in the herds.

Evaluation of a post-lethality treatment against Listeria monocytogenes on Ricotta salata cheese

As a control measure for Listeria monocytogenes contamination a post-lethality heat treatment was applied in vacuum packaged Ricotta salata, a traditional whey cheese obtained from sheep’s milk. In Ricotta salata L. monocytogenes usually occurs as post-process contamination and its concentration can increase during storage at refrigeration temperature. Ricotta salata wheels were challenged spraying the rind with a L. monocytogenes suspension, obtaining a contamination level of ca. 106 cfu g−1. In order to take into account strains differences in growth, the inoculum contained a mixture of the reference strain NCTC 10887 (serovar 1/2b) and two wild type (serovar 1/2a) strains. 87 artificially contaminated Ricotta wheels were randomly selected and subjected to water bath heat treatment at 85 °C for 90 min, while 21 served as negative controls. Samples were stored at refrigeration temperatures until analysis. L. monocytogenes, background microflora and physico-chemical properties were assessed 6 h, 2, 4, 6 and 12 months after the artificial contamination. Pulsed filed gel electrophoresis was conducted to distinguish between the inoculated and recovered strains. L. monocytogenes cells were below the limit for the enumeration method in samples submitted to the lethal treatment. Heat treatment was effective to achieve a 6 log10 reduction of L. monocytogenes cells.

Research on Staphylococcus aureus in four varieties of cheese produced in a dairy from the northwest of Paraná

<p>Cheese is frequently pointed as a potential vehicle of diseases transmitted by food, due to its rich composition, humidity and the excess of manipulation. <em>Staphylococcus aureus</em> is one of the main microorganisms responsible for outbreaks of food poisoning by ingestion of milk and cheese contaminated with preformed enterotoxins. In this context, this paper aims to evaluate the occurrence of <em>Staphylococcus aureus</em> in 46 cheese samples of four varieties, which are: frescal, mozzarella, danbo and ricotta, produced by the same dairy from the northwest of Paraná from August 2009 to July 2010. According to the obtained results, 95.65% of the analyzed samples followed the RDC nº 12/01 established standards by the National Health Surveillance Agency (ANVISA). It is believed that the unsatisfactory results obtained in two of the studied samples, frescal and ricotta, were due to poor hygiene of equipment and of the handlers, contaminated raw material or post-processing contamination.</p><p> </p><p> </p><p>DOI: http://dx.doi.org/10.14685/rebrapa.v2i1.36</p>

Inactivation of Listeria innocua on Frankfurters by Flash Pasteurization and Lauric Arginate Ester

Listeria monocytogenes , a psychrotrophic food-borne pathogen, is a recurring post-process contaminant on ready-to-eat meat (RTE) products including frankfurters. Flash Pasteurization (FP) uses short pulses of steam to decontaminate the surface of precooked sausages such as frankfurters. The antimicrobial lauric-arginate-ester (LAE) has been shown to reduce levels of L. monocytogenes and its nonpathogenic surrogate L. innocua on frankfurters. In this study the use of FP to inactivate L. innocua on frankfurters followed by application of LAE immediately prior to vacuum-packaging in a pilot plant setting was investigated. Use of FP (1.5 s, 120°C steam), LAE (3.33 ml of a 5% volume/volume solution per pack of four frankfurters), or FP followed by application of LAE, resulted in a 2.5, 1.6, and 3.3 of log reductions of L. innocua that was surface-inoculated onto frankfurters, respectively. Although FP alone reduced L. innocua levels by 2.5 log, the bacterium recovered and grew to a density of >10 6 CFU/g within 2 weeks during refrigerated storage (10°C). LAE inhibited L. innocua growth for 8 weeks, but the bacterium was able to recover and grow to a density of >10 6 CFU/g by week 12. The use of FP in combination with LAE effectively inhibited the growth of L. innocua for 12 weeks. The use of FP in combination with LAE had little effect on frankfurter color and texture, and was found to be an effective hurdle process for decontamination of frankfurter surfaces.

In-package Pasteurization of Ready to Eat (RTE) Meat Products-an Effective Way to Control Post-processing Contamination

In-package Pasteurization of Ready to Eat (RTE) Meat Products-an Effective Way to Control Post-processing Contamination

A Risk Assessment Model for Enterotoxigenic Staphylococcus aureus in Pasteurized Milk: A Potential Route to Source‐Level Inference

This article describes a probabilistic model that quantifies hazards that arise from Staphylococcus aureus in milk that is sold as pasteurized in the United Kingdom. The model is centered on coupled dynamics for S. aureus populations, staphylococcal enterotoxins, and the concentration of alkaline phosphatase throughout the milk chain. The chain includes farm collection and storage of pooled milk, further pooling for off-farm processing, high temperature short time thermal processing, and possible postprocess contamination. The model is implemented as a Bayesian belief network. The results indicate that milk sold as pasteurized is relatively safe with respect to the hazards associated with S. aureus and that most risk is associated with small scale on-farm processing. An additional analysis of likelihood ratios shows that alkaline phosphatase concentrations in filler tank milk are a good indicator of potential hazards and that these concentrations, in conjunction with other measurements, can be used effectively to discriminate over possible failure modes. The ability to discriminate over potential failure modes can support preemptive actions, such as maintenance or hygiene, which assist with milk chain management and, over extended periods, accumulate to drive improved safety, efficiency, and security.

Aerobic bacterial, coliform, Escherichia coli and Staphylococcus aureus counts of raw and processed milk from selected smallholder dairy farms of Zimbabwe

A cross sectional study was conducted to enumerate total viable bacteria (TBC), coliforms, Escherichia coli and Staphylococcus aureus in raw (n=120) and processed (n=20) milk from individual farms from three smallholder dairy schemes of Zimbabwe between October, 2009 and February, 2010. Data on management factors were collected using a structured questionnaire. A standard pour plate technique was used to enumerate total viable bacteria, while for coliforms, E. coli and S. aureus, counts were assessed by the spread plate technique. The association of total viable bacterial counts and management factors was assessed using univariable and a linear regression model. The log₁₀ TBC for raw milk differed significantly (P<0.05) amongst the schemes with the lowest (5.6±4.7 log₁₀ cfu/ml) and highest (6.7±5.8 log₁₀ cfu/ml) recorded from Marirangwe and Nharira respectively. The mean log₁₀ of TBC of processed milk (6.6±6.0 log₁₀ cfu/ml) were marginally higher than those of raw milk (6.4±5.6 log₁₀ cfu/ml) but not significant (P>0.05). The coliform, E. coli and S. aureus counts for raw milk significantly differed (P<0.05) amongst the study areas. The variation in TBC, coliforms, E. coli and S. aureus counts amongst the schemes could be attributed to differences in milking hygiene where farms with more access to training and monitoring of microbiological quality of milk had lower counts. Linear regression analysis revealed dairy scheme, delivery time and season of milking as independently associated with increased TBC of raw milk. The high TBC of raw and processed milk generally indicated low levels of milking hygienic practices, and high level of post-processing contamination, respectively. The high TBC, coliform, E. coli and S. aureus counts of both raw and processed milk may present a public health hazard. Thus, educating the farmers on general hygienic practices, quickening the delivery of milk to collection centres, or availing cooling facilities on-farm will improve the microbiological quality and safety of milk.

Isolation of Psychrotrophic multiple drug resistant Pseudomonas from Pasteurised milk

The present study was taken up with the objective of assessing the microbiological quality of milk processed in an organized dairy plant. The standard plate count and coliform count of all the samples tested were within the limits specified by Prevention of Food Adulteration standards. However microbiological analysis of pasteurized milk revealed a unique bacterial profile characterized by the predominance of Pseudomonas aeruginosa. Assessment of potential of the isolate to multiply at 7oC confirmed its psychrotrophic nature. Antibiogram of the isolate revealed that, of the seven antibiotics tested, the isolate was sensitive only to enrofloxacin. Results are suggestive of the trait of multiple drug resistance in the isolate. Such multiple drug resistant (MDR) bacteria in processed foods are potent biological hazards as there are possibilities for resistance genes to be spread to human beings via food. Isolation of such Multiple drug resistant (MDR) bacteria in pasteurised milk, an essential component of human diet is highly significant from the public health point of view. Presence of Pseudomonas species in processed products implies that post processing contamination can hinder even the quality of properly processed products. The result signifies the importance of appropriate handling practices of processed food to assure safe products at consumer level.

Potential of nisin-incorporated sodium caseinate films to control Listeria in artificially contaminated cheese

A sodium caseinate film containing nisin (1000 IU/cm 2) was produced and used to control Listeria innocua in an artificially contaminated cheese. Mini red Babybel ® cheese was chosen as a model semi-soft cheese. L. innocua was both surface- and in-depth inoculated to investigate the effectiveness of the antimicrobial film as a function of the distance from the surface in contact with the film. The presence of the active film resulted in a 1.1 log CFU/g reduction in L. innocua counts in surface-inoculated cheese samples after one week of storage at 4 °C as compared to control samples. With regard to in-depth inoculated cheese samples, antimicrobial efficiency was found to be dependent on the distance from the surface in contact with the active films to the cheese matrix. The inactivation rates obtained were 1.1, 0.9 and 0.25 log CFU/g for distances from the contact surface of 1 mm, 2 mm and 3 mm, respectively. Our study demonstrates the potential application of sodium caseinate films containing nisin as a promising method to overcome problems associated with post-process contamination, thereby extending the shelf life and possibly enhancing the microbial safety of cheeses.

Loss of viability of Listeria monocytogenes in contaminated processed cheese during storage at 4, 12 and 22 °C

The behaviour of Listeria monocytogenes in a processed cheese product was evaluated over time by inoculating the product with three different L. monocytogenes strains (Scott A, CA and a strain isolated from processed cheese) at three different inoculation levels (ca. 6 × 10 5, ca. 6 × 10 3 and 10 2 CFU/g of cheese or less) and after storage of the contaminated products at 4, 12 or 22 °C. Growth of L. monocytogenes was not observed in any of the experimental trials (experiments involving different combinations of strain, inoculum level and storage temperature) throughout the storage period. L. monocytogenes populations decreased over time with a rate that was strain- and storage temperature-dependent. Nonetheless, for cheeses that had been inoculated with the higher inoculum and stored at 4 °C viable populations of L. monocytogenes could be detected for up to nine months post-inoculation. The L. monocytogenes survival curves obtained from the different trials were characterised by a post-inoculation phase during which the populations remained essentially unchanged (lag phase) followed by a phase of logarithmic decline. The duration of the lag phase and the rate of inactivation of L. monocytogenes in the different trials were estimated based on data from the linear descending portions of the survival curves. In addition, a non-linear Weibull-type equation was fitted to the data from each survival curve with satisfactory results. The results of the present study emphasize that, according to the definition laid down in the European Union Regulation 1441/2007, the processed cheese product tested in this work should be considered and classified as one that does not support the growth of L. monocytogenes under reasonable foreseeable conditions of distribution and storage. However, post-processing contamination of the product should be austerely avoided as the pathogen can survive in the product for extended periods of time, particularly under refrigerated storage (4 °C).

Reduction of Listeria monocytogenes on frankfurters treated with lactic acid solutions of various temperatures

United States regulations require ready-to-eat meat and poultry processors to control Listeria monocytogenes using interventions which may include antimicrobials that reduce post-processing contamination by at least 1 log-cycle; if the treatment achieves ≥2 log reductions, the plant is subject to less frequent microbial testing. Lactic acid (LA) may be useful as a post-lethality intervention and its antimicrobial properties may increase with temperature of application. The aim of this study was to evaluate the effect of LA solution concentration and temperature on L. monocytogenes counts of inoculated frankfurters and to identify parameters (concentration, temperature, and time) that achieve 1 and 2 log-unit immediate reductions. Frankfurters were surface-inoculated with a 10-strain mixture of L. monocytogenes (4.4 ± 0.1 log CFU/cm 2) and then immersed in distilled water or LA solutions (0–3%) of 4, 25, 40, or 55 °C for 0–120 s. A regression equation for L. monocytogenes reduction included significant ( P < 0.05) effects by the terms of concentration, time, temperature, and the interaction of concentration and temperature; other tested parameters (other interactions, quadratic and cubic terms), within the experimental range examined, did not affect ( P ≥ 0.05) the extent of reduction. Results indicated that the effectiveness of LA against L. monocytogenes, in addition to concentration, increased with solution temperature (in the range of 0.6–2.8 log CFU/cm 2). The developed equation may allow processors to vary conditions of treatment with LA to achieve a 1 or 2 log-unit reduction of the pathogen and comply with United States regulations.

World wide traditional cheeses: Banned for business?

Traditional cheeses are characterized by strong links to their territory of origin and are testimonial of the history and the culture of the community that produces them. Every traditional cheese originates from a complex system which results in unique organoleptic characteristics. The development of these unique characteristics is linked to several biodiverse factors: the environment, the climate, the natural pasture, the breed of the animals, the use of raw milk and its natural microflora, the cheesemaking technology with the unique role of human beings rather than automated technology, historical tools as well as the natural aging conditions. In many countries traditional products are almost banned, even in Europe, despite Article 8 of the Directive 92/46 of the EEC, which grants derogations for the manufacture of cheese with a period of aging or ripening of at least 60 days. Issues relating to “food safety” are frequently given as a “false” argument to explain the banning of traditional products. Reviews of food safety outbreaks have demonstrated that raw-milk cheeses do not pose any greater risk than industrial cheeses made from pasteurized milk. Improper pasteurization, post-processing contamination, storage and cross-contamination are the main contributing factors that are responsible for these outbreaks. Traditional cheeses cannot be identified simply by the use of “raw milk”; there are a “multiplicity of practices” that have the potential to make safe products. The challenge for the research community is to demonstrate the role and the importance of those practices to deliver the maximum safety benefits to the consumer. Eliminating the production of traditional cheeses would make it much easier to market industrial products. However, consumers would lose the opportunity to compare the natural aroma, the health benefits, the cultural background as well as the biodiversity of traditional products.

Spray application of liquid smoke to reduce or eliminate Listeria monocytogenes surface inoculated on frankfurters

In a simulated post process contamination scenario liquid smoke was sprayed on the frankfurters after peeling, and then inoculated with Listeria monocytogenes (Lm). Samples that did not receive a liquid smoke spray remained at approximately 2 log cfu/cm(2) during the 48h of storage while the levels on the liquid smoke treated frankfurters continued to decline until they were below detection level (1 cfu/100 cm(2)). A shelf-life study lasting 140 days indicated that liquid smoke suppressed the growth of Lm for up to 130 days. An application of 2 or 3 ml liquid smoke at packaging resulted in at least a 1 log reduction of Lm within 12h post packaging.

Clostridium botulinum in Cattle and Dairy Products

The use of plastic-wrapped and nonacidified silage as cattle feed has led to an increasing number of botulism outbreaks due to Clostridium botulinum Groups I-III in dairy cattle. The involvement of Groups I and II organisms in cattle botulism has raised concern of human botulism risk associated with the consumption of dairy products. Multiplication of C. botulinum in silage and in the gastrointestinal tract of cattle with botulism has been reported, thus contamination of the farm environment and raw milk, and further transmission through the dairy chain, are possible. The standard milk pasteurization treatment does not eliminate spores, and the intrinsic factors of many dairy products allow botulinal growth and toxin production. Although rare, several large botulism outbreaks due to both commercial and home-prepared dairy products have been reported. Factors explaining these outbreaks include most importantly temperature abuse, but also unsafe formulation, inadequate fermentation, insufficient thermal processing, post-process contamination, and lack of adequate quality control for adjunct ingredients were involved. The small number of outbreaks is probably explained by a low incidence of spores in milk, the presence of competitive bacteria in pasteurized milk and other dairy products, and growth-inhibitory combinations of intrinsic and extrinsic factors in cultured and processed dairy products.

Cellulose derivative based active coatings: Effects of nisin and plasticizer on physico-chemical and antimicrobial properties of hydroxypropyl methylcellulose films

Bioactive composite coatings based on hydroxypropyl methylcellulose (HPMC), broad-spectrum food preservative nisin (Nisaplin®), and hydrophilic plasticizer glycerol were evaluated for mechanical, barrier (O2, H2O), transparency and microbiological effectiveness. Incorporation of Nisaplin® into cellulose derivative, i.e. HPMC-based films strongly increased the film thickness due to salt crystallization while glycerol had normalized it by homogenous dispersibility. The tensile strength of composite films decreased, however ultimate elongation was increased significantly. The dynamic vapour sorption experimental data fitted by different models had shown lesser values of respective energy constants for composite films. The transparency and water permeability of HPMC films were negatively affected by the additives as an effect individual but conversely as combined effect for film transparency. Film bioactivity demonstrated efficacy against Listeria > Enterococcus > Staphylococcus > Bacillus spp. These cellulose derivative based active films may thus be a key approach towards eradicating post-process contamination of healthy foods.

Importance and efficiency of in-depth antimicrobial activity for the control of listeria development with nisin-incorporated sodium caseinate films

The effect of antimicrobial sodium caseinate-based films was investigated on inhibition of Listeria innocua in cheese. Nisin was incorporated into sorbitol-plasticized sodium caseinate films at 1000 IU/cm 2 and the films were prepared by casting methods. Mini red Babybel® cheese was chosen as a semi-soft cheese model. The antimicrobial activity was studied based on the contact between antimicrobial films and surface-contaminated as well as in-depth contaminated cheese samples during a 7-day storage at 4 °C. The active films produced resulted in a reduction of 1.1 log CFU/g reduction in L. innocua counts in surface-inoculated cheese samples after 1 week of storage as compared to control samples. Regarding in-depth inoculated cheese samples, antimicrobial effectiveness was found to be dependent on the distance from the contact surface with the films containing nisin to the cheese matrix. The inactivation rates obtained were 1.1, 0.9 and 0.25 log CFU/g with slice 1 (distance from contact surface d = 1 mm), slice 2 ( d = 2 mm) and slice 3 ( d = 3 mm), respectively. Our study demonstrates the potential application of antimicrobial films as a promising method to overcome problems associated with post-process contamination, thus enhancing the safety and extending the shelf life of food products.

Quantitative microbiological risk assessment as a tool to obtain useful information for risk managers — Specific application to Listeria monocytogenes and ready-to-eat meat products

The presence of Listeria monocytogenes in a sliced cooked, cured ham-like meat product was quantitatively assessed. Sliced cooked, cured meat products are considered as high risk products. These ready-to-eat, RTE, products (no special preparation, e.g. thermal treatment, before eating is required), support growth of pathogens (high initial pH = 6.2–6.4 and water activity = 0.98–0.99) and has a relatively long period of storage at chilled temperatures with a shelf life equal to 60 days based on manufacturer's instructions. Therefore, in case of post-process contamination, even with low number of cells, the microorganism is able to reach unacceptable levels at the time of consumption. The aim of this study was to conduct a Quantitative Microbiological Risk Assessment (QMRA) on the risk of L. monocytogenes presence in RTE meat products. This may help risk managers to make decisions and apply control measures with ultimate objective the food safety assurance. Examples are given to illustrate the development of practical risk management strategies based on the results obtained from the QMRA model specifically developed for this pathogen/food product combination.

Control of Listeria Monocytogenes by Lauric Arginate on Frankfurters Formulated with or without Lactate/Diacetate

Listeria monocytogenes (Lm) is a food safety concern that can be associated with ready-to-eat (RTE) meat and poultry products because of its persistence in the processing environment. Listeriosis has a fatality rate of 28% in immuno-compromised individuals. RTE meats receive a lethal heat treatment but may become contaminated by Lm after this treatment. Federal regulators and manufacturers of RTE meats are working to find additional ways to control postprocess contamination by Lm in RTE meats. This research was initiated to validate combinations of antimicrobials that would produce an immediate lethality of at least 1 log of Lm on artificially contaminated frankfurters, and also suppress Lm growth to less than 2 logs throughout the extended shelf life at refrigerated temperatures (4 degrees C). Based on our studies, 22-ppm lauric arginate (LAE, ethyl-N-dodecanoyl-L-arginate hydrochloride) gave more than a 1-log reduction of Lm surface inoculated onto frankfurters within 12 h. The combination of either 1.8%/0.13% or 2.1%/0.15% potassium lactate/sodium diacetate (L/D) in combination with 22 ppm LAE caused more than a 2-log reduction at 12 h. Storage studies revealed that complementary interactions of L/D and LAE also met the 2nd requirement. This combination initially reduced Lm by 2 logs and suppressed growth to less than 2 logs even at the end of the 156-d storage life for frankfurters. These results confirmed that the combination of L/D with LAE as a postprocessing-prepackaging application could be useful in complying with the USDA's Alternative 1 that requires validation for the control of Lm on RTE frankfurters.