Friday, December 17, 2010
The probable reason we continue to pay is that it gives us peace of mind, knowing that if we do smash the car into a BMW or Rolls Royce, we won't be bankrupted by the repair bills for the other car. We can drive, secure in the knowledge that we have that one covered.
Pasteurisation of milk is insurance and free. A mild heat treatment kills all the pathogens that might have got into the milk during milking and transport, leaving the nutritional value essentially unchanged. Why would you even consider drinking raw milk or eating raw cheese, knowing that there is a small chance that it could result in illness that would change your life or that of your family for ever? There has been plenty written about the dangers of Escherichia coli O157:H7 and other STECs, so I'm not going to go over it again here. (See other posts on E. coli by clicking the E. coli label at the RHS of this blog).
Please, this Christmas season, if you really want to eat and drink raw milk products, you can make an informed choice. But don't give these products to children - they don't have that choice and a dose of E. coli O157:H7 can lead to HUS, which will probably ruin the rest of their lives.
Thursday, December 16, 2010
Perhaps it's a good thing he used the abbreviation E. coli
That set me thinking. Does the general public find the names of bacteria so difficult to pronounce that they put all thoughts of them to the back of their minds? Or do they regard all bacteria as "germs"?
The difficulty is that there are literally thousands of different bacteria, so microbiologists have to give them names that mean something and so that they can be grouped for study. Sometimes the genus is named after its discoverer, or in honour of a famous microbiologist. Salmonella was named after D.E. Salmon, an American bacteriologist; Bacillus is named from the Latin noun meaning "a small rod", while Acetobacter is so named because it oxydises ethanol to acetic acid (vinegar).
When microbiology students start out, they often have difficulty in remembering, or even pronouncing, names like Vibrio parahaemolyticus and Pediococcus pentosaceus. Small wonder that the rest of the population has problems.
In fact, in terms of food poisoning, Joe Sixpack doesn't need to know these names. Basically, if you mistreat food by contaminating it, or by holding it at temperatures that permit growth, there is a possibility that numbers of pathogenic bacteria will increase to what is termed an "infecting dose" or that toxins will be secreted into the food. The latter cause food poisoning when ingested. So what is our favourite bloke going to do to keep himself and his family safe?
Easy - clean, cook, cover and chill. This little mnemonic includes it all: Clean-handle all foods with clean hands and utensils; Cook frozen foods after proper defrosting and use a thermometer to ensure that poultry or meat patties are properly heated through. If foods are to be reheated, ensure that the temperature reaches at least 75C right through to the centre; Cover cooked foods during cooling and place in the refrigerator within 30 minutes; Chill foods to 4C and hold at that temperature until served (remember that some bacteria grow readily at refrigerator temperatures, so even chilled food will not remain safe forever) or hold above 60C. You can find more extensive guidelines for these important concepts on the MAF website in New Zealand, or the FDA sites in America.
In the Southern Hemisphere, we are at the start of the barbecuing season. It's important to be really careful - never put cooked meat on the same plate as raw meat and pre-cook chicken legs etc. making sure that patties are heated right through.
I was once at a company barbecue, standing in line to collect my meal. I heard someone behind me whisper "See what he takes, he's a microbiologist". I didn't need to name the bacteria that might have survived on my meats, choosing only steak and thoroughly cooked burger patties.
Saturday, December 11, 2010
This principle is applied to modern food preservation. "Hurdle Technology" is a term coined by Lothar Leistner in about 1985. The concept is simple. Set up a series of "fences" and force bacteria to jump over them; if they don't fall at the first one, a later fence may trip them. In food, the fences are low levels of preservatives, modified atmospheres, special packaging, low temperatures, acid pH and so on. Some bacteria will be able to grow at refrigerator temperatures, but not in acid, or without oxygen etc.
There is a tendency among consumers to regard food processing as something sinister thought up by food technologists and done by manufacturers; fresh food is somehow better. In fact, by use of multiple hurdles, food can be kept for longer and the amounts of preservatives in the food are reduced without compromising safety.
Monday, November 15, 2010
For example, most of us know that smoking is hazardous and that the risk of lung cancer and heart disease associated with smoking is high. Ask someone about the risk of flying in an airliner. If there has been a crash in the recent past, they may respond that flying is a high risk activity. The truth is that flying on a scheduled commercial flight is very safe. It's just that if an airliner crashes, it makes the news headlines all around the world, which influences our thinking.
Quite a long time ago, so long that I can't find the original reference, a few simple questions were put to food consumers. Food scientists assessed the actual risks. These people were asked "What is the food safety risk posed by the following?" What would your responses be?
Risk factor Perceived risk Actual risk
Microbial contamination Low High
Packaging failure Low High
Pesticide residues Medium Low
Irradiation High Very low
Recent events in the USA may have changed your perception, at least with respect to microbial contamination.
Monday, November 8, 2010
Proponents of raw milk consumption have long claimed health benefits of raw milk and products made from it. One of those claims is that lactose intolerant individuals, who don't produce sufficient lactase in the small intestine, suffer reduced symptoms if they consume raw milk, rather than pasteurised.
Stanford School of Medicine recently conducted a study of self-reported lactose intolerant individuals, who were given raw milk, pasteurised milk and soy milk in a randomized, double-blind, three-way crossover trial. This classic experimental design removes bias in experimenters and subjects. If lactose intolerant individuals consume lactose (the sugar found in milk) they cannot break it down to glucose and galactose. Anaerobic bacteria in the colon grow on the lactose and produce hydrogen, some of which enters the bloodstream and appears in exhaled breath.
The participants were tested for exhaled hydrogen on the first and last days of each 8-day exposure period. There was no statistically significant difference between consumption of raw or pasteurised milk, but soy milk resulted in much smaller amounts of breath hydrogen. Similarly, the symptoms reported - flatulence, abdominal cramping and diarrhoea - were the same for both raw and pasteurised milk.
The researchers reported that the results from their work, collected under standardised, controlled conditions, did not support the claim that, with respect to lactose intolerance, raw milk has benefits over pasteurised milk.
Meanwhile, raw milk and raw milk products continue to be linked with outbreaks of Escherichia coli and Listeria diseases
Sunday, October 17, 2010
Though the subject is not really on the topic of safe food, I thought it would be good to provide readers with a link to a new website from the Marler Clark stable. The website is just about to go live, but here is an introductory link:
Sunday, September 26, 2010
Of course, this doesn't prove that the restaurant was responsible. Indeed, her description of the symptoms and time of onset make me wonder if another common source was involved.
However, a TVNZ One News investigation shows that on average, one Auckland food establishment per week has been shut down this year because of safety or cleanliness violations.
An Auckland City Council Environmental Health spokesperson said that the increase in closures was a result of tougher action by health inspectors in response to unsatisfactory performance and suggested that this was partly because of the economic recession - companies were selling food that would previously have been thrown out.
A disturbing statistic given in the TVNZ report is that over 100 restaurants and cafes are still operating, despite poor hygiene ratings, though to be fair, businesses are given the opportunity to clean up their act before being closed down if they don't improve.
This report begs the question "If inspectors had previously found unsatisfactory conditions in food outlets, why didn't they close them down at the time? What has changed in the requirements to serve wholesome, safe food in clean premises?"
Wednesday, September 22, 2010
I don’t think there is an easy solution, but until the cowboys have all gone, I see no alternative to better legislation, more truly independent inspection, more frequent testing of product and full traceability of raw materials and finished products.
Friday, August 20, 2010
Thursday, August 12, 2010
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.
Saturday, August 7, 2010
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).
Tuesday, July 13, 2010
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.
Sunday, June 27, 2010
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?
Friday, May 28, 2010
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Friday, May 21, 2010
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