​​​​​Blog

Spring is in the air! 

Which means ambient temperatures will be on the rise. What does this mean in terms of keeping your food safe?

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Most microorganisms which can cause illnesses in humans have optimal growth at temperatures from 25-37°C - the same temperature range of a typical summer's day! This means that consumers need to be extra precautious when handling and transporting perishable foods outside of the fridge or freezer, as the higher outside temperatures can cause food to warm up quicker once taken out of the fridge or freezer.  

Perishable food is food that only lasts a few days in the refrigerator, such as lettuce, grapes and cheese.

Most harmful microorganisms are not able to grow and multiply at refrigerated temperatures (your refrigerator should be below 5°C). This is why it is important to keep perishable foods as cold as possible, so that harmful microorganisms cannot multiply to reach the required 'infective dose', which is the amount of bacteria required to successfully cause illness in the average person. For example, Shigella only require about 10 cells to start an infection, whereas S. aureus can require up to 108 cells.​​

The table gives an estimation of how long perishable food will remain safe to eat when stored at certain temperatures and what temperatures must be reached to kill harmful microorganisms.

>130°C
Death of bacterial spores
75°C and aboveDeath in a few seconds
65°CDeath in a few minutes
55°CDeath after a few hours
±21-50°CDangerous in a few hours
±13-21°CDangerous in several hours
5-13°CDangerous in a few days
1-4°CDangerous in a few weeks
<0°CMicrobial growth slowed


What can you do?

  • ​When grocery shopping, select the frozen and refrigerated food items last. This minimises the time the food spends outside of the fridge or freezer. Take a cooler bag to transport the perishable food in.
  • Minimise the time spent between the grocery shop and your fridge or freezer at home.
  • If you go on a picnic, make sure all perishable food is transported in a cooler bag with ice packs to keep its temperature as low as possible for the duration of the picnic. Keep the cooler bag under the shade!
  • When thawing frozen food, do it in the refrigerator and not at room temperature.

Learn more about keeping your food at the correct temperature:

 

Author: Dr Michaela van den Honert

​​​​Previous ​​Blog​s

Have you ever heard of bacteriophages.pdf

How do you grow bacteria in the lab.pdf



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Is polony safe to eat?

RTE_meat.jpgPolony and other ready-to-eat products such as salads and hams, can be viewed as 'high-risk' products. This is because there is no cooking step required by the consumer, which would kill any potential foodborne pathogens, after the product has been put on the shelves and due to its high water activity, which provides an ideal environment for microbial growth. This means that the ready-to-eat product sitting on the shelves in the supermarket must be of the highest quality possible. This can be achieved by hygienic processing, reaching the required cooking temperatures, and by storing and transporting at refrigerated temperatures (<5°C).

The pathogen most commonly associated with refrigerated ready-to-eat foods is Lis​teria monocytogenes. It is one of the few foodborne pathogens which can grow at refrigerated temperatures.

Listeria is a tricky pathogen to control in food-processing environments due to its ability to form a biofilm, which is a slimy mass that sticks to surfaces and protects the microorganism from being killed by cleaning chemicals. These biofilms like to form in hard-to-reach areas such as cracks, joints and pipes, making them difficult to find and clean.

Through effective cleaning practices, hygienic manufacture and correct heat processing and temperature management during storage and transport, pathogens can be effectively controlled in the production of any food commodity! It is the manufacturer's responsibility to make sure that the proper manufacturing processes are followed correctly. These processes are controlled and monitored through a food safety management system, such as ISO 22000.

Food (including polony) manufactured under the correct conditions will be safe to eat!

What can you do as a consumer?

  • Store all ready-to-eat products in the refrigerator
  • Transport all ready-to-eat products in a cooler bag
  • Clean out your refrigerator regularly to ensure no food is left to become a source of bacterial growth
  • Clean your refrigerator regularly with disinfectant
  • Do not put raw or unwashed food near ready-to-eat food

Listeria facts

  • There are many species of Listeria but Listeria monocytogenes is the one that causes foodborne illnesses.
  • Listeria species can be found everywhere in the environment, such as the soil and in the intestinal tracts of humans and animals
  • Listeria can be associated with unpasteurised milk and milk products and raw fruits and vegetables
  • It's temperature growth range is between 1-45°C, with an optimum growth temperature of 30-37°C
  • L. monocytogenes can cause Listeriosis, a potentially fatal disease which most commonly prevails in immunocompromised individuals, the elderly and pregnant women
  • Only a very small amount of the microorganism is needed to cause an infection in humans
  • After ingestion, symptoms can take anything from 2- 21 days to appear​

Learn more about Listeria and Listeriosis: 

 

Author: Dr Michaela van den Honert
​​The importance of pasteurising raw milk.
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Unpasteurised milk (raw milk), and other diary products which contain raw milk, can contain dangerous microorganisms, such as Salmonella, E. coli, Listeria and Campylobacter, which can cause serious illnesses.

Milk is a highly nutritious food but also provides an ideal environment for microbial growth due to its high nutrient content, near neutral pH and high water activity.

Raw milk has a very short shelf-life due to the presence of bacteria and enzymes. Pasteurisation makes it possible to distribute milk to the public and reduces the risk of consuming pathogenic bacteria.

Raw milk, as secreted by healthy cows, generally contains low numbers of microorganisms (± ≤ 1000 total bacteria per ml). Microorganisms, whether pathogenic or not, can enter the raw milk either from the animal's teat or from other external contaminants including the animal's skin, soil, bedding, manure, milking equipment and during transport and storage. Therefore, collected raw milk can contain levels of a few to several thousands of bacteria per ml, depending on animal health and farm hygiene. 

The process of pasteurising is based on the simple fact that heat kills microorganisms. Pasteurisation is a process that heats a food product to a certain temperature for a certain amount of time. Milk is typically pasteurised at 72°C for 15 seconds, known as 'High Temperature Short Time' (HTST) or at 135°C for 2-5 seconds, known as 'Ultra-High Temperature' (UHT).

This type of processing does not have any significant negative effect on the nutritional quality of milk. The heat treatment during pasteurisation does not affect mineral content, carbohydrates or fats. With regards to proteins, caseins are heat stable and are thus not affected. Whey proteins are not affected by HTST but UHT temperatures have shown to cause some damage to the heat sensitive amino acids of whey proteins but does not have an overall significant effect on protein quality.

There is a small reduction of some vitamins due to their sensitivity to heat during pasteurisation. Vitamin B1 is typically reduced from 0.45 to 0.42 mg/L, vitamin B12 from 3.0 to 2.7 μg/L and vitamin C from 2.0 to 1.8 mg/L. Other vitamins, such as B2, B3, B5, folic acid, A, D, E, K  are not significantly affected.

Pasteurisation also inactivates some enzymes present in milk which are sensitive to heat. This helps to extend the shelf-life of the milk as some enzymes cause degradation of the milk. For example, the enzyme lipase degrades fats, resulting in off odours and flavours. On the other hand, the enzyme lactoperoxidase is heat-stable and is not destroyed during pasteurisation.

The enzymes present in milk do not make a major contribution to the digestion of milk, as they are not the same enzymes used by humans required to digest the major components of milk; which are complex sugars, fats and proteins. These enzymes which digest the components of milk are naturally present in the human stomach and small intestine. Those who are lactose intolerant, do not make enough of the enzyme lactase which is needed to digest lactose and thus the side effects of indigestion occur.​

Learn more about the pasteurisation process:
 

Author: Dr Michaela van den Honert