Saturday, December 22, 2012

Telecom turtle might bring more than increased sales

A recent series of adverts for Telecom in New Zealand features a young boy and his pet turtle.  The adverts are quite funny and obviously are appealing to adults and children alike.  They may even result in more sales of cellphones.  Apparently, a side effect of this advertising is greatly increased sales of turtles, which are now practically unobtainable, according to the 3-News this evening.

If you have bought a baby turtle, or are given one for Christmas, make sure that you wash your hands carefully after handling it and that children are instructed on hygiene - touching or kissing turtles (why would you?) might result in a Salmonella infection.  Don't forget that the infecting dose for Salmonella may be quite small and the bacteria are easily transferred from hands to mouth.  I'm not sure of the incidence of Salmonella in turtles in New Zealand, but in America, there is a high frequency of carriage in baby turtles, with a concomitant infection rate in children.

Be careful out there, folks.

Tuesday, December 18, 2012

Toxic kai moana. Summer warnings

In what has been termed the worst toxic shellfish poisoning in the region's history, twenty people have become ill after eating shellfish collected in New Zealand's Bay of Plenty.  Ten of these victims have been hospitalised and two are in intensive care.

The symptoms of this type of paralytic shellfish poisoning (PSP) range from numbness of the lips, through to vascular collapse and respiratory failure.  The toxins are actually a group of chemicals called saxitoxins and gonyautoxins and are produced by certain species of algae and released into the shellfish after ingestion.

Kai Moana means seafood in the Maori language and at this time of year, when families gather at beaches for barbecues and picnics, many people will collect shellfish to eat.  Unfortunately, cooking will not destroy the toxin, which is produced by dinoflagellates ingested by the shellfish.  Though it is difficult to measure precisely, it appears that mussels filter between 8 and 10 litres of water per day, so they are able to concentrate the dinoflagellates to high levels in their gills and gut.  The dinoflagellates themselves grow more rapidly in warm water containing high levels of nutrients.  They may be responsible for 'red tides'.

The only way to be safe is to heed warnings not to collect shellfish from the affected waters.  Signs are usually erected by the Ministry of Primary Industries warning of the risk and indicating the extent of affected waters.

And while you are planning your summer picnics and barbecues, think about how you will keep your family safe from other forms of food poisoning.  Make sure that meats and fish are kept cool, and handle only with washed hands.  If you are barbecuing, make sure that food is cooked thoroughly and remember to use clean plates and utensils for serving cooked food, as raw meat may contain pathogens.

Above all, have a safe and happy Christmas holiday.  Thanks for reading Safe Food in 2012.


Tuesday, December 4, 2012

Antibiotic Resistance in the Environment

Recently I wrote a post about excessive use of antibiotics in animal rearing and the potential for spread of antibiotic resistant bacteria.

One of my research students is studying the presence of antibiotic resistance genes in bacteria in stream and river muds, comparing pristine waters with polluted along a stretch of a river in the Waikato region of New Zealand.

She sampled mud from the river and isolated bacteria.  Her next step was to test the bacteria for resistance to a set of antibiotics drawn from two classes of antibiotics used in animal rearing and human therapy.

The results are surprising:  of 40 isolates, only one was sensitive to any of the antibiotics tested.  At this stage, there is no smoking gun, but it is certainly of concern to see such  antibiotic resistance in so many different bacteria in the environment.

Monday, November 26, 2012

Unwanted passenger on cruise liner

Recently, the cruise liner Voyager of the Seas was struck with what appears to have been a Norovirus outbreak.   'Norovirus' is not a unique organism; there are many different strains, so you can become infected several times during your life.   Norovirus causes diarrhoea and vomiting, which in turn result in contamination of surfaces and generation of aerosols.  If you get virus particles in your mouth, you are highly likely to contract the disease, which appears to have a very high hit rate in exposed people.  (Now do you understand why I never get invitations to be an after-dinner speaker?)

 The virus may be present in the intestines before the onset of symptoms, and may remain in faeces for more than two weeks after recovery.  During all of this time, the virus can be spread. The problem is compounded when a population is effectively captive, such as in hostels or on a cruise liner.  The virus lives for quite a long time on surfaces, so door knobs, bathroom surfaces, lift buttons, soiled bed linen and clothes can be sources of virus particles.  If someone throws up in the dining room, other diners are immediately at risk from the aerosol.  Obviously, if the ill person is working in the kitchens, this is even more serious, as all exposed food and utensils may become contaminated.

The cruise line might be criticised for not promptly informing passengers waiting to board in Sydney about the problem, but the necessary disinfection of a whole ship is a major undertaking, and it appears that the line has made strenuous efforts to protect new passengers from infection.

What can you do to protect yourself?  Rigorous hand washing with soap and hot water (sing Happy Birthday to yourself twice while washing, to ensure that you spend enough time working the soap into hands and under nails) particularly after visiting the toilet or changing baby's nappy and before eating or preparing food.  Do not prepare food for others if you have diarrhoea.  Use of alcohol hand sanitisers may be beneficial, but these are not a substitute for washing.

Wash raw fruits and vegetables before eating them and be sure to cook seafoods thoroughly - Norovirus can survive temperatures of around 60 C.

If you are caring for someone who has symptoms of vomiting and diarrhoea,  handle soiled clothing carefully to avoid generating aerosols; wear rubber or disposable plastic gloves.  Use strong bleach solution to disinfect surfaces in bathrooms etc.  

Odd spot:

In the case of chlorine solutions, more is not necessarily better.  If the solution is made from bleaching powder (sodium or potassium hypochlorite), the more powder we add, the more alkaline the solution becomes.  The active component in a solution of bleach is actually hypochlorous acid.  This acid is unstable and breaks down in alkaline solution.  At pH 10, almost no hypochlorous acid is present in the solution.  Thus, a solution of hypochlorite containing 1000 ppm has a pH of 11.0 - 12.00 and has no active hypochlorous acid, while a solution with only 25 ppm has a pH of 8.0 - 9.0 and so is actually more germicidal than the higher concentration.

Wednesday, October 31, 2012

Mould, the consumer and the retailer

Many searchers of this blog have asked "Will spoiled food make you sick?"  I have commented on this before.

Over the last few weeks, I have purchased two blocks of cheddar cheese from a large supermarket chain in New Zealand.  When they were opened, both blocks were found to have a few mould colonies growing along the edges and at the corners.  This became apparent when the plastic film was peeled back.

Do these mould colonies represent a health hazard?  According to Dr. John Pitt, Aspergillus flavus is unable to produce aflatoxin at refrigerator conditions, so it is unlikely that there is a health hazard if the cheese is eaten.  I just cut the mould off, together with a bit extra to avoid eating cheese with changed flavour resulting from the mould growth. 

My wife, who is obsessed with "food going out of it's date stamp" suggested that the cheese might be old,  ("Well, that's why you buy mature cheese, dear"), but the best-before date stamp was mid-2013.

I wrote, complaining to the supermarket chain and pointing out that there were probably only two reasons  that these blocks of cheese could have had mould growth inside the pack - the cheese was packed under poor hygiene conditions in which mould spores were able to contaminate the block, and maybe the film had been pulled too tightly at the edges and corners, increasing the gas permeability and allowing air to penetrate the pack to allow the strictly aerobic moulds to grow.

No harm, no foul you might say.  But the consumer is entitled to buy safe, wholesome food and to have mouldy cheese only when mould is part of the normally accepted description of the cheese, such as Brie, Camembert and Roquefort.  Cheddar is not mould-ripened.

What I found interesting about this, besides the technical issue, was that the supermarket chain completely ignored my complaint, not even sending some sort of "We are looking into it" brush-off.  Do they not care about consumer perceptions of their stores, or does this happen so often that they feel it is 'normal'?

Saturday, October 6, 2012

Eat at your own risk?

I just spent a week in Miami attending the 6th American Society for Microbiology Biofilms Conference.  Over 400 biofilm microbiologists met to discuss all aspects of biofilm research.

Of course, nobody can sit in a darkened room and listen to heavy duty research papers all day for a week, and food microbiologists always have to investigate the local food and beverage outlets!

A couple of menus caught my eye.  One was on the waterfront in Downtown, where raw food seemed to be the major offering.  Another was in one of the glorious sidewalk restaurants on Ocean Drive.  Both had almost identical wording:
"Consuming raw or undercooked hamburgers, meats, poultry, seafood, shellfish or eggs may increase your risk of foodborne illness, especially if you have certain medical conditions".

All good, and if you want to eat such delicacies, you need to be informed of the risks.  Consumption of any of these foods can potentially lead to illness.  Consumers are totally dependent on the purity of the raw materials and the water from which they are sourced, as well as the hygiene of preparation; a range of bacteria and viruses can be found in raw foods.

I wonder what Bill Marler would have to say about such a disclaimer - is the restaurant owner absolved of responsibility, assuming they take reasonable care in preparation, if a customer can show that they became ill as a result of eating the raw or rare-cooked food?

Wednesday, September 19, 2012

Odd Spot - cause of my heartburn?

Sometimes the life of a food safety researcher can be fun.  (Well, actually it's nearly always fun).

Today I saw this interesting ingredient listed on a meat pie:

Look at the fourth line down.  Perhaps this is why I get heartburn when I eat meat pies.

Monday, September 17, 2012

Thank you!

I note that over the weekend, the cumulative number of page views topped 100,000.

It's very gratifying to see that Safe Food is read around the world and that there is such interest in food safety.

Thank you all for reading my blog; I'll try to keep it interesting and to provide comment on current food safety issues.  I guess the next target is the quarter million views mark.


Friday, August 31, 2012

Economic downturn no excuse for sloppy hygiene

Reporter Katie Chapman writes in the Dominion Post this week that some restaurants in Wellington are blaming their lapses in hygiene on the economic downturn.  The number of restaurants temporarily closed has more than doubled in the last six months compared with the average over the last five years.  In addition, one in five restaurants managed to achieve only the minimum standard.

Rodent and cleaning failures were the reasons given for temporary closures of all eight restaurants between February and July this year.  In most cases, the restaurants reopened within a day.  This suggests that the effort required to keep them clean and hygienic would not be very great if cleaning and self inspection were done on a daily basis.

Hard times are no excuse for sloppy hygiene, even if staff numbers have been reduced.  It's essentially the same argument sometimes presented against a requirement for food companies to have risk based food safety plans - "We can't be expected to have a food safety plan, we are only a small operation and we can't afford it".

My suggestion is "If you can't afford to keep your premises clean and rodent free, you can't afford to be in business;  if you cause a food poisoning outbreak, you'll pretty soon be out of business and looking for work somewhere else".

Wednesday, July 18, 2012

Listeria strikes in Hawke's Bay, NZ

The news service Stuff has reported that Listeria has caused one death and contributed to another between May and June this year in Hawke's Bay, New Zealand .  At this stage, two other people have been infected, but have recovered.  It is not clear where the infection came from, though there is circumstantial evidence that pre-packaged ready-to-eat meat may have been involved.

Investigation of this type of food poisoning is very difficult.  The great majority of the population will not become ill from exposure to Listera.  In the two deaths, the women were 60+ and 80+ respectively and both were apparently immunocompromised, putting them in a more susceptible group.  The infection can take up to a few weeks for symptoms to show, making it unlikely that patients can remember what they ate and even more unlikely that samples remain for testing.

Listeria is capable of growing at refrigeration temperatures, so cooked and ready-to-eat foods should be stored for only one or two days.  Of course, this poses a problem with salad vegetables, which are not going to be cooked before consumption.

The only real way to combat food borne listeriosis is to be very careful in handling foods, prevent cross contamination between raw and cooked foods, wash fruits and vegetables thoroughly and keep utensils, chopping boards and hands clean.

If you are at risk - pregnant, already unwell, immunocompromised, elderly etc. it is better to eat freshly cooked foods, pasteurised dairy products, canned foods, bread and baked goods without cream, cereals and beverages such as tea, coffee or beer, which have all been heated during production.

You can find more articles on Listeria in this blog by typing "Listeria" in the search box at the top left of this page.

Friday, June 8, 2012

Don't be an Alice

In Lewis Caroll's Alice in Wonderland, Alice found that taking a bite out of a mushroom would make her grow very tall; the other side made her shrink.  At one level, this is a childrens' tale, or at another it could be argued to be about taking hallucinogenic drugs.

Unfortunately, if you don't know what you are doing when it comes to eating mushrooms, you can wind up taking a different kind of trip - to the hospital or the mortuary.

There are many mushrooms (fruiting bodies of fungi) that can be eaten.  At this time of year in New Zealand, the mornings are often damp and we see mushrooms and toadstools popping up all over the place.  In my opinion, field mushrooms, Agaricus campestris, have a much better, stronger flavour than cultivated mushrooms bought from the supermarket.  They are a delight to collect and eat and I have spent many hours walking around our small farm searching for these delicacies.

But how can you tell if a mushroom is safe to eat?  My grandfather told me that you should cook them in cream and eat them on toast for supper.  If you woke up in the morning, they were edible!  This is NOT the way.  Neither is peeling and cooking a way of making mushrooms safe - the toxins of many poisonous fungi, such as the Amanitas are not destroyed by heating. 

The only safe way to know if a mushroom is edible is to have a good knowledge of their appearance and where they are found.  There are guides to help you identify mushrooms and toadstools, but to the untrained eye, many different species look the same.  If you aren't sure, don't eat!

Even the terminology is open to interpretation.  Strictly, the word ‘mushroom’ refers only to the genus Agaricus.  The cultivated mushrooms sold in the supermarkets are usually the white buttons of Agaricus bisporus, though we do see other varieties, such as the large browns. The word 'toadstool' is then used to describe any other fruiting body with a cap and stem that appears different from Agaricus, often implying that it is poisonous.

I took the following from an ABC report that followed the death this week of a Chinese visitor to Australia who appears to have eaten Death Cap (Amanita phalloides) toadstools:


  • Death cap mushrooms are considered the most poisonous in the world and one is enough to kill an adult human.
  • At least six people have died and at least 12 made sick from eating death cap mushrooms in Australia in the past decade.
  • Death caps have been involved in the majority of deaths around the world from mushroom poisoning, including that of Roman emperor Claudius.


  • Death cap mushrooms are similar in appearance to several species of edible mushrooms commonly used in cooking, such as paddy straw mushrooms and Caesar's mushroom.
  • Death caps may be white but are usually pale green to yellow in colour, with white gills and a white or pale green stalk up to 15cm long. (See image below from Wikipedia)
  • The entire mushroom is poisonous and cooking or peeling the mushroom does not remove toxicity.


  • Death caps are said to taste pleasant and symptoms can occur six to 24 hours after consumption.
  • Initial symptoms can include abdominal pain, diarrhoea, vomiting, hypotension and jaundice, followed by seizures, coma, renal failure and cardiac arrest.


  • Death cap mushrooms can be found in parts of south eastern Australia, particularly ACT and parts of Victoria.
  • They are commonly found near established oak trees and some other hardwood trees and are most common during later summer to early winter after heavy rain or irrigation.
  • It is thought death caps were introduced to Australia with the importation of different hardwoods.


  • Death caps are extremely poisonous and if consumed it is a medical emergency.
  • Anyone who suspects they have eaten a death cap should seek immediate medical attention and where possible take a mushroom sample for identification.  
There are approximately eight toxins in A. phalloides, the major ones being α-amanitin and β-amanitin, which inhibit RNA polymerase.  This prevents protein synthesis, resulting in the death of cells.  The liver is usually the first organ to be damaged, often irreparably, and later the kidneys.
Picture of Amanita phalloides from Wikipedia:

Have a look at Peter Valda's comments on mushrooms and toadstools:,_books,_techniques_and_tools/mushrooms_and_toadstools

Monday, June 4, 2012

Safe Food in Troubled Times

On 4th September, 2010, Christchurch was violently shaken by a Magnitude 7.1 earthquake.  On 22nd February 2011, an M 6.1 shock destroyed much of the city centre and since that time, there have been about 3400 shocks of greater than M 3.

After the February earthquake, I expected to read of food and water related diseases spreading through the population - the water supplies were seriously damaged and sewer pipes were destroyed, while liquefaction of the ground allowed mixing of ground water and sewage to occur.  Contamination of water supplies by faecal bacteria and viruses was therefore a serious consideration.  People handling food for themselves and others would have to take great care with personal hygiene and cleaning of food preparation areas.

Amazingly, there were no major disease outbreaks.

New Zealand sits on the Pacific Ring of Fire and is sometimes called The Shaky Isles.  We are taught to look after ourselves during a shake and to make preparations to look after ourselves in the aftermath.  In my rumpus room out back, I have a cache of canned food and bottled water.  But how many of us expected the Christchurch earthquakes to go on for so long?  My cache would last for only a couple of days.  Some people in badly damaged areas had to cook in their gardens on barbeques and open fires for many days.

This set me thinking about security of food supplies after such disasters.  I guess that natural disasters are one thing; what must it be like when those waging civil war deliberately set out to destroy infrastructure?

We can expect that help might take a few days to arrive.  Local emergency services will be overwhelmed by the number of people requiring assistance and their own degraded response capabilities - roads will be damaged and may be impassable for emergency vehicles.  Stores and warehouses may be destroyed, power supplies will be interrupted and food may therefore be scarce, spoiled and possibly contaminated.

The first few days are therefore critical for the population to survive and begin rebuilding their lives.  A secure and safe supply of food and water is essential.  How does the average family prepare for their own and their neighbours' welfare?  Dried and canned foods provide a safe and stable basis for the emergency supply.

There are many websites that will help you plan.  Civil Defence in New Zealand provides lots of valuable information, such as lists of things you need in a survival kit; commercial organisations offer ready-made kits and meals that can be prepared with minimal resources. 

I don't endorse the following sites or products, but you may find them useful.

A quick search on one of the major search engines will provide you with many more links to valuable information.

If you want more information on the Christchurch earthquakes, see the following:

Wednesday, April 18, 2012

How much does Joe Sixpack know about food safety?

Recently, we ran a small competition for attendees at a public food expo.  They had to enter answers to questions on food safety knowledge set by a computer.  The machine stored the answers and we drew a prize from those who got them all right.  Incidentally, we used this as an educational opportunity by giving immediate feedback on the answers entered.

Though the survey was not statistically valid, I analysed the responses.  The results were largely unsurprising - approximately 65 to 75 percent of responses were correct for most questions.

However, a third of respondents didn't know which food poisoning bacterium (Campylobacter) causes the most food poisoning in New Zealand, despite extensive coverage in the news media over the past two years.  A third also incorrectly identified pesticide residues as more important than packaging failure in causing human foodborne disease, and again, a third thought that it was illegal to sell food past its "best before" date.  Only a quarter of respondents knew that it is legal to sell raw milk in New Zealand.

It was pleasing to see that 97 percent of respondents knew that refrigeration would not stop the growth of all bacteria in food, and 80 percent understood that irradiation is not a means for unscrupulous manufacturers to make spoiled food appear fresh.

Of more concern was the belief by 80 percent of respondents that chicken can be regarded as cooked if the juice runs clear when the thigh meat is pricked, and 28 percent of respondents thought that if it were safe to eat a rare steak, it was also safe to eat hamburger rare.

It seems that we still have some way to go in educating our population about safe food handling and consumption.

Saturday, March 31, 2012

Bacteria in canned food

Looking through the search terms that produced hits on Safe Food this month, I came across "Listeria in canned food".

Is canned food hazardous from the point of view of Listeria?  In my opinion, the answer is "No" with just one small caveat:  "unless the food has been grossly underprocessed, or post- processing contamination has occurred".

Canned foods are divided into two main categories: Low Acid (LACF) and Acid Canned foods (ACF).  The dividing line is pH 4.6, low acid foods having a pH greater than this, and acid food having a pH lower than 4.6.

The significance of this pH value is that Clostridium botulinum can grow at pH above 4.6. 
C. botulinum is able to form very heat resistant spores and can grow in the anaerobic conditions in canned food.  Since C. botulinum also produces a lethal toxin, it is essential to destroy the spores.  So we heat the food in the cans to temperatures above boiling point (in fact we heat to the equivalent of 121.1C for 2.52 minutes and this is called a 12D process).  Properly processed LACF is safe.

When we look at acid foods, we find that C. botulinum is incapable of growth under these acid conditions and so no toxin can be produced.  Since we don't need to deliver a 12D process, we can heat for a shorter time or at lower temperature.  This has the advantage that the food is changed less and it costs less to deliver the process.  Depending on the food and the degree of acidity, we really need only destroy vegetative (i.e. non-sporulating) pathogens and spoilage microorganisms.  This will then destroy Listeria.

What about my conditional clause above?  If the food canner doesn't properly control the process, it might be possible for cans to be underprocessed.  This might occur if the steam supply to the retort (pressure cooker) is lacking or turned off too soon.  Another possibility is that cans might by-pass the retort altogether.

Post-processing contamination could occur if the cooling water is contaminated.  The can seals are not 100% watertight while they are still hot, so using contaminated water may allow a few bacteria to enter the can during cooling.  This resulted in a typhoid outbreak in Aberdeen in 1964, when people consumed imported Argentinian canned  corned beef that was cooled in untreated, sewage-contaminated river water.

Damage to the can seams caused by rough handling can also allow contamination, as there is a partial vacuum in the can.  Momentary opening of the seam caused by a blow can permit bacteria to be drawn into the can.

In summary, providing cans are properly processed and handled with reasonable care, LACF are essentially sterile, so all bacteria, including Listeria will have been killed; ACF are pasteurised and this process will also kill Listeria.

Tuesday, March 20, 2012

Giving bacteria a cold

I hope that title got your attention. I could equally have used "Fight fire with fire" or "Biological warfare".

Food Standards Australia New Zealand is calling for submissions on an application to use viruses to aid in the control of Listeria monocytogenes.  L. monocytogenes is a bacterium found in the environment that can infect food and may cause listeriosis.  The majority of the population is unaffected by Listeria, but it is a hazard for pregnant women, young children and the elderly, in addition to those who are immunocompromised.  Note that you don't have to have had an organ transplant to be immunocompromised - you might just have another infection stressing your immune system.

You might think that deliberately putting viruses into foods is crazy.  However, these viruses are special.  They exclusively target bacteria and are called bacteriophages.  Bacteriophages (or "phages") are extremely common; they occur at levels up to 9×108 per mL in bacterial mats at the surface of the sea.  They were first identified in 1915 by Frederick Twort in England and, independently, in 1917 by Felix d'Herelle in France.

Bacteriophages are deceptively simple - essentially a piece of nucleic acid contained within a protein coat called a capsid.  They can't reproduce independently and have to have a means of infecting a living cell.  Perhaps the most famous phage is the T4 phage that infects Escherichia coli and always reminds me of the lunar lander(I sometimes wonder how something like this could have evolved by chance).  See image from Wikipedia below.  

 When a phage infects a bacterial cell, it injects its DNA into the cell.  The viral nucleic acid then takes over the bacterial synthetic machinery and makes copies of itself, and synthesises new phage coat and other components.  The components are then assembled into new phage particles, whereupon the bacterial cell is lysed and releases the phage.  Burst sizes may be around 100 viruses per bacterial cell.  Since these are all infective, the infection of the population proceeds rapidly, resulting in the death of the majority of the bacterial cells.  Phages cause the cheese-making industry a lot of trouble, because they kill the starter bacteria.

The application currently under consideration is for the use of a mixed bacteriophage preparation, sold commercially as LISTEX™ P100, as a processing aid.  This preparation was the first phage product to be classified as Generally Recognized as Safe (GRAS) by the FDA  and USDA.

A number of scientific papers have been published on the efficacy of the P100 preparation, showing that the phage significantly reduces the population of L. monocytogenes on foods, such as salmon fillets or surface-ripened cheeses*.

The use of bacteriophage to control pathogens, such as Listeria and Salmonella, can reduce the risk of food poisoning, though it is unlikly that it can be a total solution, as the pathogen population may not be totally destroyed.  However, when used in an integrated food safety programme, the processing aid can be a valuable tool, reducing the reliance on chemicals to inhibit the bacteria.

*  See:  doi:10.1016/j.yrtph.2005.08.005

Electron micrograph of T4 phage adsorbed to a bacterial cell.
Image by Elizabeth Kutter, Bacteriophage Ecology Group

Odd Spot:  When I was researching this post, I searched on "Listeria virus".  I got many hits, predominantly in popular press and websites, where the Listeria bacteria were described as "viruses".  In modern microbiology terms, this is totally wrong.  However, "virus" is derived from the Latin word for poison and this apparently appeared in the English lexicon in 1392. "Virus" was also used in 1728 to describe an "agent that causes infectious diseases".  I'm sure that most of those press writers didn't know this, but, strictly, they were correct.

Friday, March 2, 2012

Toxic salt in Poland?

Anonymous sent me a comment after I posted "Is Vinegar just for Fish and Chips?".

In fact, the comment was not relevant to the original post, but I followed up on the quote Anonymous sent me.  It appears that an investigation has been broadcast by an independent Polish television station, TVN.  In the report, the reporter presented evidence of industrial salt - obtained as a waste by-product of calcium chloride production and claimed to contain dangerous carcinogens - being sold wholesale to the food industry as edible salt.

I have been unable to verify this report, because the commentary is, presumably, in Polish, but it has also been reported on CNN iReport, labelled as "Not vetted by CNN".

The programme claimed that up to 1000 tons per month of the waste product, labelled as being intended only for de-icing of roads or as a chemical industry raw material, has been purchased over the last 10 years.  The salt was made as a by-product by a fertiliser company in Poland.  Three Polish businesses have repackaged and on-sold the salt to numerous food processing plants as edible. 

The Polish government has made some arrests of those thought to be responsible, but has not published the identities of any food processors who received the salt.

The concern is that toxins and potential carcinogens have been incorporated into the Polish food supply and, by implication, to some exported foodstuffs.

Food fraud is by no means a new thing and knows no national bounds.  Where there's a fast buck to be made, you can bet that someone will try it.  Unfortunately, this is not a victimless crime - those who suffer are often the unwitting consumers or their children, as we saw in the melamine milk scandal.  Only the vigilance of regulatory authorities and investigative reporters can hope to reduce our exposure to food fraud.

Can I build a business around Mum's secret recipe?

I am often asked this question.

On the face of it, this is a simple question.  Mum has for years made a special dish or sauce and the whole family enjoys it.  Perhaps it is a traditional dish made back in "the old country" and an enterprising emigrant wants to make it commercially in the adopted country.  All that is necessary is to scale up production, right?

In some cases, this might be so.  However, there may be hidden pitfalls.

Perhaps the most important difference between Mum's cooking and a commercial operation is the timing - Mum cooked the dish or sauce and served it straight from the kitchen, whereas commercial manufacture involves packaging, storage, transport, retail display and purchase.  The shelf life must also leave time for the consumer to store it at home before consumption.

How about putting the sauce into a glass jar or a plastic pouch?  This introduces a new variable not present in the original.  This is exactly the scenario presented to me recently and I want answers to some additional questions before I'll agree that the product is safe.

For example: what is the pH of the product - acid or low acid?  This is not just about flavour.  If Mum poured a low acid sauce over your food and you ate it straight away, there was no problem.  But if we now wish to sell it in an hermetically sealed container, it may support the growth of Clostridium botulinumEven if the raw materials are heated during preparation, spores will have survived and can germinate and grow, producing botulin toxin during storage.  There may be no apparent change in the product, but it could be lethal.  In the case of a low acid product, a full 12D process must be applied and this process must be filed with the regulatory authority, must be followed for every batch and under the control of a registered person and full records kept.  Special equipment, capable of heating the product to well over 100C is needed to deliver a 12D process.

What about stability?  Will the sauce separate during storage and transport?  It may need a stabiliser to be added to prevent separation and thus ensure that it looks good to the consumer.  It's not a safety issue, but dissatisfied customers are unlikely to be repeat purchasers.

What shelf life should we put on the label?  Properly conducted storage trials are essential. For that matter, what are the requirements for labelling?  You can't just put a picture of the product onto the label and call it "Mum's special pasta sauce"; in most jurisdictions, there are very specific requirements, including name and address of the manufacturer and a list of ingredients, possibly with warnings about potential allergens like peanuts.  These requirements extend to specifying the size of type required for the nutritional information label.

Not least is the requirement for the product to be manufactured in a suitable premises.  These premises must be inspected and it is unlikely that the home kitchen can be approved for even minor commercial production.

In New Zealand, food manufacturers must have a suitable food safety programme in place.  New legislation will require this programme to be based on an assessment of risk posed by the product and process, and the programme must be documented and detailed records kept, so that premises and process can be audited.

There are many wonderful products on the market today that had their origins in Mum's kitchen in some part of the world.  To avoid tears, the budding entrepreneur should seek the advice of a professional food technologist before putting the product on the market.

Thursday, February 16, 2012

Is vinegar just for fish and chips?

My sister in Australia recently sent me a link to the ABC website "Fact Buster".  The page was entitled "Does vinegar really kill household germs?"


The article concluded that vinegar is an inexpensive, non-toxic, biodegradable antimicrobial, but that it is not as good as commercial cleaners.

Vinegar contains about 5% acetic acid.  The article said that this acid kills bacteria and viruses, and suggested that the effect was probably brought about by denaturing the proteins and fats.  If proteins are denatured (their shape and hence functionality changed) the bacteria may no longer be capable of growth.  I'm not sure that the rate of fat trans-esterification would be very high, but it might contribute to damage of the microorganisms.

The action of vinegar on bacteria is quite interesting.  Strong acids completely dissociate into ions.  For example, hydrochloric acid dissociates into hydrogen and chloride ions.  These particles carry a charge and cannot enter the bacterial cell through the cell membrane.
                            HCl  ⇒  H+  Cl-

Weak acids, such as acetic, citric and ascorbic acids, don't fully dissociate; in solution, a significant proportion of the acid remains undissociated and therefore uncharged.  So for acetic acid:

                        CH3COOH  ⇔  H+  + CH3COO-

This is where it gets interesting; the weak acid solution outside the cell has a moderately low pH, which keeps a proportion of the weak acid in the undissociated form (the equilibrium is driven to the left).  The uncharged molecule can pass through the cell membrane into the cell.  Here it encounters a higher pH (the interior of the cell is closer to neutral pH) and so the equilibrium is driven to the right and more hydrogen ions are produced.  These ions interfere with the cell proteins and hence cell metabolism, since many cell proteins are actually enzymes.  The cells are either slowed or prevented from growing.  A multipurpose cleaner favoured by my wife claims to "kill 99.9% of germs" ***.  The active ingredient is 3.2% citric acid.

However,  the Fact Buster authors also consulted an infectious diseases specialist, Professor Peter Collignon, at the Australian National University.  He made the point that concentration on disinfection is the wrong emphasis.  Thorough cleaning would practically remove the need for disinfection in many cases - remove the dirt and you remove practically all the bacteria.  Disinfectants may not penetrate a layer of dirt or the slime produced by a bacterial biofilm.  The film may actually neutralise the disinfectant by reacting with it.

The priority should therefore be to remove dirt and bacteria and only then apply a disinfectant if it is required.

***  This claim is ambiguous.  Does it mean that 99.9% of all known germs are killed by the product, or does it kill 99.9% of the organisms on the surface?  These are very different statements.  And never forget: 0.1% of a very large number may still be a large number!

Tuesday, January 24, 2012

Want to know more about the origin of Shigatoxin-producing E. coli?

 Bill Marler is a very rare individual: he is a lawyer with an ability to grasp the principles of microbiological food safety and to write about them in a way that is accessible to the general public.  Bill has been closely involved in food borne illness litigation since 1993, when he obtained a $15.6 million settlement for Brianne Kiner, a nine year old girl who suffered HUS and ultimately kidney, liver and pancreas failure after eating Jack-in-the-Box hamburger.  He has become a fiercely active food safety campaigner.

Recently, Bill conducted a literature review on the origins of Shigatoxin-producing Escherichia coli  and has published the first two parts on his food safety blog.  These publications are well worth reading - they are not written in highly technical language, but the reference list allows those readers sufficiently interested and capable to follow up his sources and read the original material.

Links to the first two parts are shown below:

There is just one problem with this review; Bill has taken away my option to set such a study of literature as an assignment for my postgraduate students in my course "Frontiers of Food Microbiology".  The students will still be expected to read and discuss the material, but I can't use their reviews for assessment purposes.  Thanks Bill!

Saturday, January 21, 2012

Who ya gonna call - Ghost Busters?

The title is perhaps a bit over the top for a food safety blog, but there is a link!  Last week I spent a lot of time in my car and listened to many old tapes, including the theme song from Ghost Busters.  According to my stats over the past week, a popular search phrase has been "Polysaccharide slime". It seemed propitious to write a short article on bacterial slime.

Bacterial biofilms produce large amounts of polysaccharide.  Polysaccharides are chains of simple sugar molecules.  Some polysaccharides are tough and fibrous but others can be slimy.

Bacteria growing in suspension, the so-called planktonic phase, generally don't produce large amounts of slime.  However, for most bacteria, the normal mode of growth is as a biofilm - an aggregation of cells attached to and growing at a solid-liquid interface.  It has been estimated that when the cells settle on the surface, up to 30% of the genome is switched on or off;  the biofilm mode of growth is very different from the planktonic mode.

Among the changes is the production of large amounts of extracellular polymeric substance (EPS) much of which is polysaccharide.  The EPS glues the cells to the surface and protects them from materials such as detergents, sanitisers and antibiotics.  It also confers some advantages, such as immobilising extracellular enzymes.

In the food industry, we see EPS helping biofilms to remain in processing plant during cleaning, or bacteria spoiling foods such as meats by producing surface slime.  However, not all slime is involved in food spoilage - dextran, produced by Leuconostoc mesenteroides  and Streptococcus mutans and some other bacteria has laboratory and medical applications and may be used in construction of biosensors.

Monday, January 9, 2012

Moulds and mycotoxins

Pepin Heights Orchards and Minnesota Department of Agriculture have issued advice to consumers not to drink certain batches of Honeycrisp Apple Cider because of the presence of patulin at levels slightly above the 50 microgram per litre maximum level recommended by the World health Organisation. See:

Patulin is one of a host of compounds produced by moulds. These compounds are collectively referred to as "Mycotoxins".

We don't hear a lot about mycotoxins in the popular press - outbreaks of food borne illness are usually caused by Salmonella, Listeria, Campylobacter, or Escherichia coli, with several other bit players.

In fact, many fungi produce mycotoxins. One of my older textbooks devotes 66 pages of its 750 to these chemicals, some of which are very complex molecules. There is considerable discussion as to why moulds produce them, but they are probably just by-products of metabolism, though it has been suggested that in some cases, excretion of these "secondary metabolites" may confer some selective advantage, perhaps by inhibiting competitors in the soil.

Some of these chemicals can be very toxic - I well remember 1960 as the year when it was not possible to buy a turkey for Christmas in the UK, because thousands of young turkeys on poulry farms had died of the mysterious "Turkey X Disease". This was later shown to be caused by Aflatoxin present in peanut meal from Brazil as a result of growth of Aspergillus flavus mould. Intoxication of both humans and animals may be acute, but long term exposure may lead to cancer development.

Patulin in not regarded as particularly toxic to humans, but its presence in apple products is an indication of the quality of the apples used to make the products. There is some inconclusive evidence that patulin is genotoxic, i.e. it can damage the cell's genetic material. Pepin Heights has therefore been very responsible in their actions.

In America, fresh pressed apple juice is called Cider. In Europe, Cider, or Cidre is fermented apple juice. Patulin does not survive the fermentation process, so fermented cider is not likely to be contaminated with patulin.

Odd spot: a numbeer of mycotoxins are beneficial to humans, as they are in fact antibiotics - penicillin is just one example. Many drugs have also been made from mycotoxins.
St Anthony's Fire - ergot poisoning, has been known since about 600 BCE, but the pure ergotamine can be used to treat migraine.

For a much more complete, but readable, description of mycotoxins, go to: