Would you like your Salmonella over easy or sunny side up, sir?

550,000,000 eggs have now been withdrawn from the market in two recalls in USA.

380m eggs were recalled early last week by Wright County Egg and now 170m eggs have been recalled by Hillandale Farms of Iowa.  Eggs from both companies have been linked with salmonellosis affecting at least 1700 people.

Salmonella is a bacterium found in the gut of man, animals and birds.  It causes nausea, vomiting, abdominal pain and diarrhoea that may last for several days and can be fatal in the very young or elderly.  It is usually contracted by ingestion of faecally contaminated food, though this is not the only route of infection.  The disease is described as a “food borne infection”, because after ingestion of infected food, the bacteria grow in the gut, causing the symptoms, which appear 12 to 14 hours after ingestion. 

Why have so many eggs been withdrawn?  I think it’s probably because of the way the regulations governing poultry farming in the US are written.  As I understand it, testing is conducted under the FDA “Egg Rule” -Environmental Testing for Salmonella Enteritidis (21 CFR 118.5).  Samples are taken from the environment to determine if S. Enteritidis is present, because this is an indicator of the effectiveness of the SE control plan.  The pullet environment is tested when the pullets are 14 – 16 weeks old and in addition, the environment in each poultry house is tested when any group of laying hens reaches 40 – 45 weeks of age.  

If rodents, birds or insects introduce Salmonella to the poultry house, between testing times, the infection could spread rapidly throughout the flock and eggs could be produced from infected hens. Hens can become infected internally and eggs can be infected before the shell is formed.  There is no way to tell if an egg is infected with Salmonella, other than cracking it and culturing the contents. Eggs are required to be tested only when an environmental sample is shown to be positive.  So the huge recall is to ensure that all potentially contaminated eggs are removed from the market place and homes.

How can consumers protect themselves from contracting salmonellosis?  The most obvious precautions are the proper refrigerated storage and cooking of eggs, washing hands after handling eggs and avoidance of products containing raw eggs, such as home made ice cream and mayonnaise, or coddled eggs.  If you have eggs subject to the recall, dispose of them or return them to the retailer for a refund.

Eggs in New Zealand are unlikely to contain Salmonella.  In the next posting, I’ll discuss this and the latest on Campylobacter in New Zealand.

Just a thought:  How are they going to dispose of 550m eggs?  At 60g (about 2 ounces) each, that is about 33,000 tonnes (36,376 US tons) of eggs.

More on Salt in Foods

It’s generally accepted that we eat too much salt in New Zealand – up to 150% of the maximum recommended intake (see Sodium in Food, 13 July 2010). Excessive consumption of sodium raises blood pressure and may increase the risk of cardiovascular disease. Bread is the greatest contributor to our sodium intake, followed by sausages and processed meats.

One of the concerns of manufacturers of foods that contain added salt is that the consumer will detect the change if salt content is reduced and refuse to buy that brand.

In 2003, I took part in a trial in which we tested three commercially baked breads with varying levels of salt, from the standard content at that time of 550 mg/100g, 5% reduction (530 mg/100g) and 10% reduction (490mg/100g). We performed controlled trials in which 60 consumers were given three samples - two identical and one different - and asked to pick the odd one out. This is called a triangle test. Twenty eight percent of the panellists correctly identified the 5% reduced sample and 37% identified the 10% reduced salt bread. This relatively small trial showed that these differences in perception of salt content were not statistically different i.e. that the consumers could not detect the lowered salt breads. Recent figures show that some breads now have 20% less salt than equivalent products in 2003.

As I wrote in “Sodium in Food”, July 2010, sodium chloride has many functions in foods besides flavouring. What are the alternatives to salt? We can replace some sodium with other ions, such as potassium, magnesium and calcium. We can purchase reduced sodium table salt, though the UK Food Standards Agency does not recommend the use of salt substitutes, as they don’t reduce consumers’ taste for salt. Replacement of 40% of sodium by potassium in manufactured foods may result in detectable flavour changes and there may be problems for people with kidney conditions. We could use other preservatives, but consumers have been fed the line that preservatives are bad for them, so there is likely to be resistance to this approach. We could target other sources of sodium in the diet, such as monosodium glutamate (MSG, a flavour enhancer), or water binding agents, such as sodium tripolyphosphate.

How will we know if reducing salt in our food will result in safe food? We can conduct computer-based modelling experiments, using the vast resources of microbial growth models stored in databases. Some of these databases are freely available and allow us to predict such things as “time to spoil” or “time to toxicity” or simply “how long will it take this initial level of contamination to grow to an unacceptable population?” We can vary the formulation of the food and run the model again to see how it performs. In a matter of minutes, we can do extensive trials of alternative formulations.

Unfortunately, these models are not real foods. Once we have modelled the likely shelf life etc. we have to make samples and test them under normal storage and abuse conditions. This is not straightforward and can be very costly. The likelihood therefore is that we will not see rapid reductions in salt content of our manufactured foods, but rather a progressive reduction, as was the case with bread. We can, however, make a start on personal salt intake reduction by using other seasonings and spices in our homes.

The joy of cleaning (yeah, right)

I was recently interviewed for a forthcoming television programme dealing with mould in the bathroom. I decided to brush up on my knowledge of cleaning chemicals to try to avoid getting caught flat-footed by the interviewer. When you really get into it, the science behind modern cleaning technologies is quite fascinating and more complex than you might expect.

My research team specialises in the study of biofilms. These accumulations of microorganisms and their sticky products on surfaces are extremely hard to clean. Since I have mentioned biofilms in earlier posts, I thought that it might be time to examine them in more detail here.

Pasteur and Koch laid the foundations of modern microbiology by culturing bacteria on solid media in pure culture. This development enabled microbiologists to study individual strains of bacteria without the interference of other types and we have continued to use their techniques. However, it is now generally accepted that bacteria grow preferentially as biofilms – complex communities growing on a surface and surrounded by polysaccharide slime known as glycocalyx. Among other things, this glycocalyx gives the bacteria protection from cleaning agents. Failure to take account of this when formulating cleaners and disinfectants can result in incomplete removal of the film. This is particularly important when the surface is a piece of food processing equipment.

Go and have a look at your beautiful stainless steel kitchen sink or the shower tray. They look perfectly smooth and should be easy to clean. However, when we use a scanning electron microscope to see the surface on the same scale as bacteria, it is clear that the surface is anything but smooth (see first figure). Bacteria can get down into the troughs between the grain boundaries and it’s obvious that getting them out of there is going to be difficult. The difficulty of cleaning is made worse if the bacteria are left to grow long enough to form a proper biofilm. The bacteria produce a sticky mixture of polysaccharides, which glues them to the surface and attracts other bacteria and traps food particles (see image at right).

When we buy a cleaning product from the supermarket, we are buying a carefully formulated mixture of chemicals that has a number of functions: it must bring the chemicals into close contact with the biofilm; proteins, carbohydrates and fats must be solubilised or suspended so that they can be rinsed away; for domestic cleaning it is also desirable that the cleaning product should kill bacteria. (In industrial cleaning, a separate sanitiser is usually applied after cleaning).

To satisfy these requirements, most cleaning products contain a surfactant to break down the surface tension of water (to make it “wetter”) and an alkali to solubilise proteins and fats. Sometimes an acid is used to remove scale deposits. Industrial cleaners for food processing equipment often also contain hypochlorite, which releases hypochlorous acid and ultimately an oxygen radical, both of which are strong oxidising agents that can break down dirt. Because of the potential danger to consumers, domestic cleaning products are usually much less alkaline and generally weaker than industrial cleaners.

I am often asked whether there is an alternative to the “harsh chemicals” used in cleaning products. Well, there are so-called “green cleaners” derived from plant materials, but the principles behind the formulations are the same – combination of surfactant such as an alkyl polyglucoside from palm and coconut, with citric acid and a solvent, D-limonene, from citrus skins. I have heard of white vinegar being used to remove bathroom mould instead of the chlorine-based cleaners. However, even the proponents of such substitutions admit that a lot more effort is required to remove the mould and that it soon comes back. This is partly because vinegar has no surfactant properties.

Successful cleaning requires four things: the right concentration of cleaning product, suitable temperature, mechanical energy (“elbow grease”) and sufficient time for the chemicals to penetrate the dirt and destroy bacteria. The best way to ensure that cleaning is successful is to follow the instructions on the label – the manufacturer has formulated and tested the product to be used in a certain way.


If done correctly, cleaning will remove biofilms from stainless steel. The two images at left show a piece of stainless steel before and after cleaning. The bacteria were stained with a fluorescent dye and observed under UV light in a fluorescence microscope.











However, a successful cleaning operation is only a temporary fix and regular cleaning is essential to prevent biofilms from forming. Like death and taxes, it’s not much fun and there’s really no getting away from having to clean.




Credits for photographs provided by my research group:
First image by Steve Flint and Doug Hopcroft; Second image by Shanthi Parkar and Doug Hopcroft; Third and Fourth images by Shanthi Parkar.

(The description given above is still a simplification of cleaning technology. I have tried to capture just the essentials of the process and the cleaning products).

Sodium in food

Most people like to have salt on their food. In mediaeval England, salt was expensive and only the nobility could afford it, as it was made by evaporating salt water over a fire. The salt was placed in the middle of the high table; the commoners sat at lower trestle tables and did not have access to the salt. Thus they were "below the salt" and this came to be an indication of rank.

Around 1650, rock salt was mined in Cheshire and salt became more readily available. The connotation of the value of salt remains, however, in expressions like "He's worthy of his salt".

These days, we probably have too much salt in our diets. In New Zealand, for instance, we consume around 150% of the recommended upper intake level. Much of this intake is involuntary - manufacturers add it to foods including bread, sausages and pies. The recent television series "Master Chef" had the judges saying repeatedly "Don't forget the seasonings", meaning not just herbs and spices, but also salt.

So, should we just ban salt in food and let individuals add salt to taste?

The answer may surprise some readers. Salt (sodium chloride) contributes to the safety of food and is essential for developing texture and flavour in processed meats. It helps to bind proteins, improving texture; it increases water binding capacity of proteins, also contributing to texture and assists in stabilising meat batters by improving fat binding. It also decreases fluid loss in vacuum-packed, thermally processed products.

Not only that - salt improves safety and shelf life by inhibiting the growth of bacteria, though relatively high levels are required if salt is used alone. It helps to reduce the water activity^* of the food, making it more difficult for bacteria to grow. That's why salted beef and pork were carried on long sea voyages - the meat was preserved.

Stringer and Pin (Institute of Food Research, Norwich, UK) have noted that "There is scope to reduce salt in foods. However, as salt influences bacterial growth, survival and recovery after adverse treatments, reducing salt in foods will have consequences for food safety that must be considered". These researchers used predictive models to show that reducing sodium content from 1.5g/100g to 0.76g/100g food allowed a much greater growth rate of certain foodborne pathogens. This could be acceptable, but other preservative mechanisms would need to be put in place. For example, other preservatives might be added at low levels and refrigeration might be necessary. Above all, reducing salt content would require even stricter adherence to good manufacturing practices, particularly with respect to plant and operator hygiene.

I'll write more on sodium in food in a follow-up posting.

* See the end of "Free Choice or Safety of the Population" in this blog for an explanation of water activity.

Old lessons not learned - Re-post

I have just returned from a meeting of food experts in Wageningen, Holland. One evening, we were taken to the Zoo in Arnhem. This fantastic place has a number of indoor environments, such as a jungle, ocean, desert and a restaurant.

After the visit, we had a meal in the somewhat inappropriately named Burgers Zoo Restaurant. A feature of this is the do-it-yourself barbeque. This ingenious device is like the continuous toasters you see in some hotel dining rooms – the food is placed on a continuous belt grill and passes over heated briquettes. Diners select their meats and salads from the large range set out on side tables.

Not having completely switched out of professional mode, I watched my fellow foodies to see how they would cope. I guess I should not have been surprised to see several of them take their raw meats and salads onto a single plate. They cooked the meats and then put them back onto the same plate! Nobody took fresh tongs or heated the ones used to put the meat on the grill.

Clearly, not all the participants were experts in food safety, but I had hoped that they would know about basic food safety rules – cooked food should NEVER be put on a plate that has held uncooked meat and cross contamination of salads from raw meats must be avoided. When I pointed out their mistake to a couple of my colleagues, they understood, but still didn’t know what to do about it.

At the other end of the scale, one young lady expressed concern as to whether she had cooked her steak sufficiently and was she at risk of food poisoning? In my opinion, her meat was over-cooked, but it would certainly have been safe to eat. Raw steaks from a healthy animal are essentially sterile on the inside, so they can be made safe by cooking the outside properly. (Minced or ground meat has had the outside mixed into the inside, so cannot safely be eaten rare). She expressed the view that barbequing was a bloke’s job, but I wonder if it should be left to food microbiologists?

Safe Food has a following!

I noticed today that someone has become a Follower of Safe Food. Thanks, Kim.

You can keep track of new posts if you click the "Follow" tag next to the search box at the top of Safe Food. Your picture, contact details and other followings will appear in my Blogger Dashboard, but currently will not appear on the page. If you have a Blogger Dashboard, you can set up a reading list and new postings will appear there.

You can also subscribe to Safe Food by clicking on the RSS symbol at the right hand end of your browser address bar.  You will receive an e-mail notification each time I add a new post.

You can search Safe Food by entering Label terms into the search box in the page header. You will find an alphabetical list of all the Labels I have used under the Blog Archive.

You will also find under the Labels list a few links to other food safety sites that I read.

I hope that these enhancements will help you to benefit from reading Safe Food.

Guest Editorial - Additives in New Zealand Foods

This blog has not been updated for some time, mainly because we have been hard at work studying the growth of Cronobacter sakazakii. This work has now been submitted for publication and I have time to write more articles. Some of our work on C. sakazakii will appear in a later post.

To get us off to a good start, here is a guest article, written by one of my colleagues, Associate Professor Owen Young of Auckland University of Technology:

Food Additives in New Zealand

I recently had AUT University students systematically survey packaged food labels in Auckland supermarkets for health claims. These could be real (e.g. ‘if you eat this food your cholesterol will be lower’), or implied (e.g. ‘contains no additives’, ‘all natural ingredients’ etc.).

Over 30% of products surveyed had a ‘fat’ claim such as ‘lo fat’, ‘low in saturated fat’, or ‘98% fat-free’. Arguably these claims could be useful to a buyer seeking to control their weight, but overlooks the fact that total energy intake is really what matters for obesity. Fat is not the only beast with calories.

But of more interest to me were the claims for avoiding Public Enemy Numbers 1, 2 and 3: artificial colours (28% with claims), preservatives and artificial flavours (both 24%). Anyone would think these things were dangerous. But are they dangerous in the way they are used in foods?

Take the yellow food colouring tartrazine for example. Googling ‘tartrazine allergy’ will score you thousands of hits. On the face of it you would have to wonder why Food Standards Australia New Zealand (FSANZ) allows artificial food colouring to be used at all. The reason is because the evidence for adverse effects from these colours is so flimsy as to be laughable. Colours have been used in foods for decades with no adverse effects. So why are some colours banned in certain countries? The reason is that pressure groups have been so strident that it becomes politically expedient to roll over and appease the activists.

Preservatives are sometimes put in prepared foods to minimise the growth of bacteria. These bacteria can either degrade the food, but be otherwise harmless, or they can be pathogens. At best the latter can make you sick and at worst can kill you. The maximum quantity of preservative added is typically hundreds of times lower that the amounts required to show any kind of response in humans. Preservatives have excellent safety records, and that is why FSANZ allows their use. You would have to wonder about a food manufacturer who neglected to add a preservative to a susceptible food. Such action should be viewed as callous indifference to your health.

The so-called artificial flavour that gets most bad press is MSG, monosodium glutamate. Ostensibly MSG is responsible for the Chinese restaurant syndrome with its claimed headache, flushing, and tingling symptoms. But MSG has been used extensively in Asian cooking for donkey’s years. If it’s so bad, why doesn’t everyone in Asia have a headache? The truth is that it is not bad for you.

Very many common foods have high concentrations of MSG, but no one complains about MSG in cheese, soy sauce, walnuts and broccoli, and a host of other foods. Chinese restaurant syndrome is nothing but an enduring urban myth. So why does MSG have to be declared on labels? One reason is that regulators are simply responding to activist demands. Any hint of a potential problem is dealt with by a label declaration that presumably implies that the additive is a risk and so feeds the myth.

What can or cannot be added to food in New Zealand is governed by FSANZ’s Food Code, which is online for all to read. One guiding principle is you can put additives into foods only where allowed and where needed – up to a specified limit – and crucially, only enough to achieve the required result. You cannot add stuff just for the hell of it, and indeed why would you? Additives cost money and there is often no need for them.

Take beer for example. Current advertisements frequently have an ‘all natural ingredients’ claim ­– whatever ‘natural’ means – and a ‘no preservatives added’ claim. The Food Code allows only one preservative in beer, sulphur dioxide, but it is seldom added because beer, by its very nature, keeps well without preservatives. Similarly, preservatives are not added to breakfast cereals because they are not needed in these dried foods.

The Food Code is thus a very conservative document, making New Zealand food supplies among the safest in the world.

So feel free to ignore the implied health claims that are built on the flimsiest of evidence, and are used to part you and your money through a fear of chemicals – chemophobia (n): an irrational fear of chemicals, particularly those man-made.

Associate Professor Owen Young is Academic Leader, Food Science, AUT University, Auckland