Category Archives: Technology

Research – Prevalence of Listeria species and Listeria monocytogenes on Raw Produce Arriving at Frozen Food Manufacturing Facilities

Journal of Food Protection

Ubiquity of Listeria monocytogenes in the environment impacts the food industry and presents concerns for frozen food facilities. This study determined the prevalence and numbers of Listeria species and L. monocytogenes on raw produce arriving at frozen food facilities. Raw produce was collected using multi-level blinding protocols to ensure anonymity of participants and avoid traceback. Five raw vegetables were selected: corn, carrots, green beans, peas, and spinach. Raw products were collected after arrival at the facilities but before any cleaning or other pre-processing steps that are typically performed inside the facility. The FDA BAM method for detection of Listeria spp. and L. monocytogenes was followed, with PCR screening followed by selective plating methods. Listeria numbers were estimated from positive samples using MPN methodology. A total of 290 samples were collected, with 96 and 17 samples positive for Listeria spp. (33.1%) and L. monocytogenes (5.9%), respectively. Enumeration data for the 96 Listeria spp. samples indicated 82 samples had greater than 100 MPN Listeria spp./g and 14 samples less than 100 MPN Listeria spp./g. The prevalence of Listeria spp. varied by commodity: spinach (66.7%), peas (50%), corn (32.2%), green beans (22.2%), and carrots (13%). L. monocytogenes prevalence was determined in corn (13.6%), peas (6.3%), and green beans (4.2%) arriving at processing facilities. Such data was previously unavailable to frozen vegetable processors and is valuable in implementing process control standards. The prevalence and pathogen concentration data from raw commodities found in this study can provide the industry information to conduct more accurate quantitative risk assessments and provide a baseline to model and target appropriate pathogen reduction steps during processing.

Research – “Aquaponics offers solutions to foodborne illness outbreaks”

Horti Daily

Soilless growing offers a viable alternative to growing crops in a low-risk environment for many microbial sources. Aquaponics, which is often greenhouse-grown, is an innovative way of growing fish and plants in rural or urban settings. For years, commercial aquaponic farms have obtained food safety certifications from Global GAP, USDA Harmonized GAP, Primus GFS, and the SWF Food Safety Program, in addition to being certified USDA organic (Aquaponic Association, 2019) and sold commercially across North America.

In an aquaponic system, the healthy microbes actually serve as biological control agents against pathogenic bacteria making their survival minimal (Fox, 2012). While aquaponics produce is not immune to all pathogenic contamination, it is one of the safest agriculture methods against pathogenic risk.

NEW FOOD SAFETY GUIDE – Ensuring Food Safety in the Cold Chain

Cold Chain Federation

The Cold Chain Federation has published the first ever handbook on managing food safety specifically for temperature-controlled storage and distribution.

The handbook, Ensuring Food Safety in the Cold Chain, brings together the latest information on compliance, best practice and recommendations for managing the key food safety risks in the cold chain and insights into likely future considerations, the new guide meets the industry’s need for a holistic, comprehensive and up-to-date cold chain food safety reference guide.

For a copy of the guide e-mail:

Research – High Hydrostatic Pressure Treatment Ensures the Microbiological Safety of Human Milk Including Bacillus cereus and Preservation of Bioactive Proteins Including Lipase and Immuno-Proteins: A Narrative Review


Breast milk is the nutritional reference for the child and especially for the preterm infant. Breast milk is better than donated breast milk (DHM), but if breast milk is not available, DHM is distributed by the Human Milk Bank (HMB). Raw Human Milk is better than HMB milk, but it may contain dangerous germs, so it is usually milk pasteurized by a Holder treatment (62.5 °C 30 min). However, Holder does not destroy all germs, and in particular, in 7% to 14%, the spores of Bacillus cereus are found, and it also destroys the microbiota, lipase BSSL and immune proteins. Another technique, High-Temperature Short Time (HTST 72 °C, 5–15 s), has been tried, which is imperfect, does not destroy Bacillus cereus, but degrades the lipase and partially the immune proteins. Therefore, techniques that do not treat by temperature have been proposed. For more than 25 years, high hydrostatic pressure has been tried with pressures from 100 to 800 MPa. Pressures above 400 MPa can alter the immune proteins without destroying the Bacillus cereus. We propose a High Hydrostatic Pressure (HHP) with four pressure cycles ranging from 50–150 MPa to promote Bacillus cereus germination and a 350 MPa Pressure that destroys 106 Bacillus cereus and retains 80–100% of lipase, lysozyme, lactoferrin and 64% of IgAs. Other HHP techniques are being tested. We propose a literature review of these techniques. View Full-Text

Research – Effect of UVC light-emitting diodes on pathogenic bacteria and quality attributes of chicken breast

Journal of Food Protection

This study aimed to investigate the inactivation of foodborne pathogens and the quality characteristics of fresh chicken breasts after Ultraviolet-C light-emitting diode (UVC-LED) treatment. Fresh chicken breasts were separately inoculated with Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes at an initia population of 6.01, 5.80, and 6.22 log 10 CFU/cm 2 , respectively, then were treated by UVC-LED at 1000 to 4000 mJ/cm 2 . UVC-LED irradiation could inactivate the tested bacteria in a dose-dependent manner. After UVC-LED treatment at 4000 mJ/cm 2 , the populations of S . Typhimurium, E . coli O157:H7, and L . monocytogenes on chicken breasts were decreased by 1.90, 2.25, and 2.18 log 10 CFU/cm 2 , respectively. No significant ( P > 0.05) changes were found in the color, pH value, texture properties, and thiobarbituric acid reactive substances (TBARS) values of chicken breasts following the UVC-LED radiation at doses up to 4000 mJ/cm 2 . Overall, this study indicates that UVC-LED is a promising technology to reduce the number of microorganisms while maintaining the physico-chemical characteristics of poultry meat.

Research – Microbial Inactivation and Quality Preservation of Chicken Breast Salad Using Atmospheric Dielectric Barrier Discharge Cold Plasma Treatment


Microbiological safety of ready-to-eat foods is paramount for consumer acceptability. The effects of in-package atmospheric dielectric barrier discharge cold plasma (ADCP) treatment on the microbiological safety and quality of model chicken salad (CS) were investigated in this study. CS, packaged in a commercial polyethylene terephthalate container, was treated with ADCP at 24 kV for 2 min. The inactivation of indigenous mesophilic bacteria, Salmonella, and Tulane virus in CS; growth of indigenous mesophilic bacteria and Salmonella in CS; and quality of CS during storage at 4 °C were then investigated. ADCP inactivated indigenous mesophilic bacteria, Salmonella, and Tulane virus by 1.2 ± 0.3 log CFU/g, 1.0–1.5 ± 0.2 log CFU/g, and 1.0 ± 0.1 log PFU/g, respectively. Furthermore, it effectively retarded the growth of the microorganisms, while not significantly affecting the color of chicken, romaine lettuce, and carrot, and the antioxidant capacity of all vegetables throughout storage at the tested temperatures (p > 0.05). The color, smell, and appearance of all vegetables evaluated on day 0 were not significantly different in the sensory test, regardless of the treatment (p > 0.05). Collectively, ADCP treatment effectively decontaminates packaged CS without altering its quality-related properties. View Full-Text

Research – Comparison of peracetic acid and chlorine effectiveness during fresh-cut vegetables processing at industrial scale

Journal of Food Protection

This study was conducted to compare the efficacy of two sanitizing agents (chlorine and PAA) in reducing (both spoilage and pathogenic) microorganisms and in reducing disinfection by-products ( DBPs) in the washing stage of three types of minimally processed vegetables: Iceberg lettuce, carrots and baby leaves. These fresh-cut products are consumed uncooked and, hence, a proper sanitation is essential in preventing food-borne illness outbreaks. The comparison was done at industrial scale, using equipment already present in the fresh-cut industry and washers designed and manufatured for this purpose. Results showed that, regarding washing water hygiene and final product microbial quality, the use of PAA had a similar efficacy than chlorine. Different scenarios (SCN) combining PAA, chlorine and water have been tested simulating the current industrial processes for each one of the tested vegetables. Overall, results confirmed that the use of a sanitizer, PAA or chlorine, in the washing water of the three tested vegetables is effective for the prevention of cross-contamination during the washing process and hence, to guarantee produce food safety. Regarding final product microbiological quality and shelf life, the use of chlorine or PAA showed no significant differences in lettuces neither in baby leaves. Regarging the potential formation of chlorinated DBPs in processing water, they were found not in significant amounts when washing water was treated with PAA in all scenarios and vegetables tested. Washing with 80 mg/L chlorine generated important amounts of THMs, chlorates and chlorites. While chlorates and chlorites were always below the recommended levels or legal limits established for drinking water, THMs exceeded these legal limits . With respect to perchlorates, values were below the quantification limit in all SCNs. Results obtained in the present study show that PAA is a reliable alternative to chlorine disinfection strategies in the fresh-cut industry.

Research – Effect of UV-C Irradiation and Lactic Acid Application on the Inactivation of Listeria monocytogenes and Lactic Acid Bacteria in Vacuum-Packaged Beef


The objective of this study was to test the effect of the combined application of lactic acid (0–5%) (LA) and UV-C light (0–330 mJ/cm2) to reduce Listeria monocytogenes and lactic acid bacteria (LAB) on beef without major meat color (L *, a *, b *) change and its impact over time. A two-factor central composite design with five central points and response surface methodology (RSM) were used to optimize LA concentration and UV-C dose using 21 meat pieces (10 g) inoculated with L. monocytogenes (LM100A1). The optimal conditions were analyzed over 8 weeks. A quadratic model was obtained that predicted the L. monocytogenes log reduction in vacuum-packed beef treated with LA and UV-C. The maximum log reduction for L. monocytogenes (1.55 ± 0.41 log CFU/g) and LAB (1.55 ± 1.15 log CFU/g) with minimal impact on meat color was achieved with 2.6% LA and 330 mJ/cm2 UV-C. These conditions impaired L. monocytogenes growth and delayed LAB growth by 2 weeks in vacuum-packed meat samples throughout 8 weeks at 4 °C. This strategy might contribute to improving the safety and shelf life of vacuum-packed beef with a low impact on meat color. View Full-Text

Research – Listeria monocytogenes Cold Shock Proteins: Small Proteins with A Huge Impact


Listeria monocytogenes has evolved an extensive array of mechanisms for coping with stress and adapting to changing environmental conditions, ensuring its virulence phenotype expression. For this reason, L. monocytogenes has been identified as a significant food safety and public health concern. Among these adaptation systems are cold shock proteins (Csps), which facilitate rapid response to stress exposure. L. monocytogenes has three highly conserved csp genes, namely, cspAcspB, and cspD. Using a series of csp deletion mutants, it has been shown that L. monocytogenes Csps are important for biofilm formation, motility, cold, osmotic, desiccation, and oxidative stress tolerance. Moreover, they are involved in overall virulence by impacting the expression of virulence-associated phenotypes, such as hemolysis and cell invasion. It is postulated that during stress exposure, Csps function to counteract harmful effects of stress, thereby preserving cell functions, such as DNA replication, transcription and translation, ensuring survival and growth of the cell. Interestingly, it seems that Csps might suppress tolerance to some stresses as their removal resulted in increased tolerance to stresses, such as desiccation for some strains. Differences in csp roles among strains from different genetic backgrounds are apparent for desiccation tolerance and biofilm production. Additionally, hierarchical trends for the different Csps and functional redundancies were observed on their influences on stress tolerance and virulence. Overall current data suggest that Csps have a wider role in bacteria physiology than previously assumed. View Full-Text

Hong Kong – Listeria monocytogenes in Cheese Products


Food Safety Focus (94th Issue, May 2014) – Incident in Focus

Listeria monocytogenes in Cheese Products

Reported by Ms. Janny MA, Scientific Officer,
Risk Assessment Section,
Centre for Food Safety

On 18 April 2014, the US Centers for Disease Control and Prevention (CDC) announced its final investigation on a listeriosis outbreak which involved eight persons, including two mother-newborn pairs and a newborn, with one death in the US. Results of the investigation, with food (fresh cheese curd) and environmental samples tested positive for Listeria monocytogenes, indicated that cheese products made by Roos Foods were the likely source of the outbreak. This article discusses the risk of L. monocytogenes in cheese products.


Cheeses can generally be obtained by coagulating the protein of milk and by partially draining the whey resulting from the coagulation. Nowadays, over 500 types of cheeses are available worldwide, with variations deriving from different cheese manufacturing processes, e.g. type of milk, coagulation method, starting culture, addition of salt and ripening etc.

Various types of cheeses are available on the local market
Various types of cheeses are available on the local market

In fact, there are various ways to categorise cheeses. Traditionally, cheeses have been classified principally by their moisture content-

Soft cheese – Has a higher moisture content, e.g. Feta, Brie, Camembert

Semi-hard cheese – Moisture content sits between soft and hard cheeses, e.g. Edam, Gouda

Hard cheese – Has a lower moisture content, e.g. Cheddar, Emmental

Extra hard cheese – Dry, slightly brittle, suitable for grating, e.g. Parmesan

Cheeses may also be grouped according to their principal ripening –

Unripened/ Fresh cheese – Ready for consumption soon after manufacture, e.g. Cottage cheese, Ricotta

Ripened cheese – Not ready for consumption shortly after manufacture; must be held for such time, temperature and other conditions that results in the necessary biochemical and physical changes characterising the cheese, including –

  • Mould ripened cheese – ripening has been accomplished primarily by the development of characteristic mould growth
  • Internal mould ripened: c haracterised by the growth of Penicillium roquefortii resulting a network of blue and green veins throughout the cheese (blue cheese), e.g. Danish blue, Roquefort, Stilton
  • Surface mould ripened: characterised by the growth of Penicillium camemberti on the cheese surface, e.g. Brie, Camembert
  • Cheese in brine – has no actual rind and preserved in brine e.g. Feta

Listeria monocytogenes in Cheeses

Cheeses, particularly soft cheeses, have been implicated in listeriosis outbreaks worldwide. Foodborne listeriosis is a relatively uncommon but serious disease caused by L. monocytogenes, a pathogen that can be killed under normal cooking temperature but is able to grow slowly at refrigerated temperature as low as 0°C. Asymptomatic infection of listeriosis probably occurs in most healthy people, but it can pose serious health risks for the susceptible population including pregnant women, elderly and immunocompromised individuals such as patients with AIDS and diabetes mellitus.

The presence of L. monocytogenes in cheeses may be originated from the ingredients particularly raw milk or can come from the processing plant environment, including the equipment, personnel or cross-contamination between finished products and raw materials. If the temperature as well as other conditions especially acidity and water content permit, L. monocytogenes can grow to high levels upon prolonged storage.

Cheeses of Higher or Lower Risk

Since pasteurisation, by heating milk to a specific temperature for a set period of time, kills L. monocytogenes effectively, cheeses made with pasteurised milk are generally considered of lower risk unless post-process contamination occurs.

For cheeses made with unpasteurised milk, their safety relies on a range of factors that influence the presence, growth, survival and inactivation of pathogenic microorganisms including L. monocytogenes.

In general, soft cheeses made with unpasteurised milk are of much higher L. monocytogenes risk than hard/ extra hard cheeses made with unpasteurised milk as the formers are likely to be less acidic and contain more moisture, which provide a favourable environment for the growth of L. monocytogenes, than the latter. A recent risk assessment study conducted by Food Standards Australia New Zealand also pointed out that the estimated L. monocytogenes risk from the consumption of certain raw milk soft cheeses i.e. feta and camembert is low in the general population but is high in the susceptible population. However, the L. monocytogenes risk upon the consumption of raw milk cheddar cheese (a type of hard cheese) and extra hard cheese in the general and susceptible populations is negligible and low/ very low respectively.

Key Points to Note:

  1. Cheeses, particularly soft cheeses, have been implicated in outbreaks of listeriosis worldwide.
  2. Cheeses made with pasteurised milk are generally considered of lower risk.
  3. Soft cheeses made from unpasteurised milk are the most risky.

Advice to susceptible populations

  • Read food labels and choose cheeses carefully before consumption.
    • Hard and extra hard cheeses are generally safe.
    • Avoid soft cheeses (e.g. Feta, Brie, Camembert) and blue cheeses (e.g. Danish blue, Gorgonzola and Roquefort).
    • For other types of cheeses, choose only those made from pasteurised milk.
    • Do not eat if in doubt.
  • Store cheese products strictly in accordance with the instructions on the labels.

Advice to the trade

  • Maintain good food and personal hygiene and avoid cross-contamination.
  • Provide sufficient information on food label for the consumers to make informed food choices.
    • Properly label whether the cheese products are made from raw/ unpasteurised or pasteurised milk.
    • Consider providing more information e.g. description on firmness of the cheese products.