The P-word

The European Commission set new limits for the use of nitrites and nitrates as food additives in 2008.  These chemicals are intended to protect against the growth of pathogenic bacteria such as Listeria, Salmonella, and Clostridium botulinum, while the EU limits are aimed at reducing exposure to nitrosamines.  We have long used nitrate and nitrite as preservatives in curing meat.  Nitrate and nitrite are permitted for use in foods in many countries such as Mainland China, the United States, the European Union, Canada, Australia and New Zealand.  The concern is that nitrate can be converted into nitrite in the gut and then form N-nitroso compounds such as nitrosamines, which may cause cancer in humans, though evidence as to whether nitrate or nitrite per se in food can cause cancer in humans is inadequate or limited.  We need to be very careful before branding food additives as causing human disease - we can find naturally occurring nitrates and nitrates in water and vegetables, especially in leafy and root vegetables such as lettuce, beets, celery, carrots, and more.  
There is a group of people who regard preservatives as being unhealthy and added by unscrupulous manufacturers.  They want their food to be “all-natural, with minimal processing and no chemicals”.  Apart from the fact that this description is meaningless, it got me thinking about additives and specifically preservatives.

As a first step in preparing this post, I followed standard research principles and surveyed the packaged foods in our kitchen cupboard and read all the ingredient labels - a challenge in itself for anyone with less than 20:20 vision.  It came as something of a surprise to find that few of the foods contained anything that I would regard as unnecessary in the food type.  Sure, there were acidity regulators and anti-caking agents, salt and the occasional antioxidant, natural colours and flavours, while some of the wines declared sulphur dioxide, but very few specific mentions of the dreaded preservatives.  A list of permitted additives can be found on the New Zealand Government food safety website.  [1]

From the microbiologist’s point of view, preservatives are added to prevent the growth of pathogens or spoilage organisms during the shelf life, reducing loss and increasing food safety.  Acidulants, organic acids and parabens have all been used, but ‘natural alternatives’ are being increasingly used.  Many leafy and root vegetables contain nitrate and nitrite and it is estimated that around 80% of the nitrates and nitrites we consume are naturally occurring from the plants we eat.  Nitrite may be formed by reduction of nitrate by bacteria in the food.

While I was at Hong Kong University, I co-supervised a PhD student who was studying the use of extracts of traditional Chinese herbs as food preservatives.  Several of the papers that came out of that work have been my most heavily cited, and it is clear that there is great interest in these natural chemicals in the preservation of meats and dairy products.  However, the potential for reliance on extracts may be limited because of source availability, and synthetic nature-identical versions of the active components may be necessary if natural preservatives are to be used extensively. 

Of course, manufacturers will often use chemical additives in conjunction with other preservation processes, such as refrigeration, freeze-drying or UV irradiation.  Boiling and addition of sugar, followed by sealing in airtight jars and packages, kills bacteria and prevents their regrowth and recontamination.  Canned foods are processed for long-term shelf stability and if the food is “low acid” i.e. with a pH greater than 4.5 and thus able to support the germination and growth of Clostridium botulinum spores, the heat process is designed to reduce the spore count by a factor of 10^12, resulting in a sterile product that will keep for years, provided that the can remains sealed.

[1]  Identifying Food Additives.  ISBN No.: 978-1-99-004303-1 Online). https://www.mpi.govt.nz/dmsdocument/3433/direct



 

Is the food still safe to eat?

 For the past few days, New Zealand has suffered from high winds and extensive flooding as a result of Cyclone Gabrielle, which in some coastal areas has coincided with high tides.  Many areas have been without power for extended periods and thousands of people have had to leave their homes, in some cases being rescued from the roofs of their houses.

I was interviewed by a radio journalist who wanted to ask questions about the safety of food and water. Any food that has been contaminated by the flood waters is, of course, not fit to eat.  But what of foods that were in refrigerators and freezers?

This is a difficult question to answer.  If the power has been off for a few hours and the refrigerator has not been opened, the food will probably be safe to eat, however, some areas are not likely to have power restored for several days.  Some foods, such as yoghurt are naturally preserved by their acid content and will be shelf-stable even at room temperature for a few days.  Hard cheeses will also be safe.  Similarly, milk in sealed bottles will be OK for a couple of days.  Vegetables are also shelf-stable for several days at room temperature, provided that they have not been in the water.  Eggs have their shells to protect the contents, but it would be worth washing the shells to prevent contamination of the contents when they are cracked open.  Perhaps a good guide is to think of supermarket displays - if the food such as fruit, potatoes, tomatoes and cabbages is sold from open counters, it can reasonably be expected to last for several days.

The big concern will be fish and meat.  If the frozen food has thawed out completely, it may still be safe to eat if it is thoroughly cooked.  if the food still has ice crystals in it, refreezing is possible.  Beef and pork steaks are essentially sterile inside, so it is only necessary to cook the outside, remembering to cook the edges too.  Fish is normally sold in fillets, so again, frying or barbecuing will render it safe, however, the food cannot be stored for another few days before consumption.  I would be more concerned about chicken, which is always difficult to cook throughout because of the uneven thickness of drumsticks etc.  In all cases, the critical thing is to get the temperature of the food above about 75C throughout.  This will kill all vegetative (non-sporulated) bacterial cells.  If a thermometer is used, it must be clean and inserted into the thickest part of the food.  More care is required with minced meat.  During the mincing operation, the outside of the meat is mixed in with the interior portions, so thorough cooking is required - medium-rare hamburgers are out! 

Another, though not infallible guide is to look at the food and smell it - if it smells off, then don't eat it.  Things like bacon sometimes become a bit slimy as a result of bacterial growth on the surface.  If it is fried properly, it will be safe to eat, but may have off-flavours.

Of course, canned foods are safe, provided that there are no holes in the can. Similarly, sealed packages of snack foods, such as 'chippies' will be OK to eat and may make the kids feel a bit happier.  It is a good idea always to have a supply of canned foods in the cupboard so that they are available in emergency situations like ours.

Another major concern is water.  Some water treatment plants have been out of action for a couple of days as a result of power outages and some watersheds may have been swamped by flood waters.  A number of water supply authorities have said that the tap water is safe to drink.  However, if there is any doubt about its safety, it should be boiled.  I was asked about water for making up baby formula.  In that situation, I would always recommend using boiled water.  Rural households often collect water from the house roof and store it in large tanks.  In my opinion, this water will be safe, provided that the roof and tanks have not been inundated, but once again, if there is any doubt and the power is on, it should be boiled.

All of these questions will become more relevant when people are allowed to return to their dwellings. There may be a temptation to try to salvage food from refrigerators and cupboards.  If there is any doubt, the safest thing to do is to dump it, as food poisoning will put even more stress on health services at this time.

Our next concern will be resupply.  Many roads are impassable, leaving some towns completely cut off.  Supermarkets are very short on stock, even if they have power to operate the tills.  Foods may be in short supply for a while, but in addition, orchards and vegetable farms have been severely damaged, so shortages will continue for months.  There may be more reliance on imports.

Odd Spot:  if the cyclone were not enough to challenge the population, we also had a magnitude 6.3 earthquake yesterday.  It was centred about 50km NE of Paraparaumu in the North Island, so it was under the sea.  There have been no reports of injuries or damage, but it's something we could all have done without!

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.

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 botulinum.  Even 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.

Botulism is back

Botulism is back in the news. The US Food and Drug Administration has announced that a canning company in Michigan is recalling certain lots of canned beans. The reason given was that these particular batches of product were not adequately heated during the processing.

As I wrote in “Deadly Poison in the Kitchen” on 5th September last year, the testing of canned foods for Clostridium botulinum is impractical. No sampling plan could detect the very low level of faulty cans that we accept. We are therefore totally reliant on the correct delivery of the thermal process by the manufacturer. Not surprisingly, the regulations covering the processing of Low Acid Canned Foods* are tight and specific.

The cans must be heated in a pressurized vessel called a retort at temperatures greater than 100C (the temperature of boiling water) because the C. botulinum spores are very heat resistant. They can survive for longer than 4 hours in boiling water. Full records must be made of the process, using special controllers and monitoring instruments. The retort operator must sign these records as soon as the cooking process is completed and they must be inspected and signed off by a responsible member of Management within 24 hours.

I don’t know the details of the investigation, other than the information provided in the FDA announcement (http://www.fda.gov/oc/po/firmrecalls/newera01_08.html). However, it does appear that the procedures mentioned above were not followed. The FDA announcement, quoting the company, stated that the recall was made “because a records review identified the possibility that a small number of cans from each lot may not have been adequately cooked”. These cans should not have entered the distribution network until after the processing records had been inspected.

For the benefit of anyone who has concerns about the hazards of handling foods thought to be contaminated with the toxin (botulin) I have quoted the FDA release verbatim below:

“Any food that may be contaminated should be disposed of carefully. Even tiny amounts of toxins ingested, inhaled, or absorbed through the eye or a break in the skin can cause serious illness. Skin contact should be avoided as much as possible, and the hands should be washed immediately after handling the food. Customers who have the product or any foods made with these products should throw them away immediately. Double bag the cans in plastic bags that are tightly closed, then place in a trash receptacle for non-recyclable trash outside of the home. Restaurants and institutions are encouraged to assure that such products are only placed in locked receptacles which are not accessible to the public. Additional instructions for safe disposal can be found at www.cdc.gov/botulism/botulism_faq.htm. Anyone with questions can call FDA at 1-888-SAFEFOOD”.


* A Low Acid Canned Food (LACF) is defined as a food packed in an hermetically sealed container, whose finished equilibrium pH is greater than 4.6 This includes, but is not limited to foods like canned beans, peas, carrots, corn etc. It is not safe to try to make these products at home and industrial production must be conducted in approved premises, using processes approved by thermal processing experts and filed with the authority (in the US this will be either FDA or USDA; in New Zealand it is NZFSA).

Deadly Poison in the Kitchen - updated

February 29, 1984, was an unusual day for New Zealand – it was leap year and the date when the country’s first ever cases of human botulism were confirmed.

Botulism is quite rare in the developed world, (fewer than 200 cases of all forms of botulism are reported each year in the United States) but not a new disease. Emperor Leo VI of Byzantium forbade the eating of blood sausages because the link between their consumption and the disease was recognized. However, it was not until 1895 that it was understood that the disease is caused by the growth of bacteria in the food. Clostridium botulinum can produce one of the most deadly toxins known to man. The toxin is so potent that the lethal dose for humans is approximately 1 μg/Kg body weight.

In the last year there have been several cases of intoxication by foods containing botulin toxin reported around the world – a man in Ireland became ill after eating food sent to him from Poland; bottled carrot juice caused several cases in apparently related incidents; canned chili, stew, hash and other foods were withdrawn from sale after an outbreak, but several days after the recall, the products were still on sale in stores.

In all these cases, the basic rules of food production and distribution had been ignored, or someone had failed to take proper care of the food. The isolated Irish case was probably the result of unsterile food being packaged in an airtight container, resulting in growth of the strict anaerobe C. botulinum and hence production of toxin. In the other cases, the foods were commercially manufactured. The carrot juice may have been pasteurised, but this will not destroy spores of C. botulinum, so the product required refrigeration; the canned products were all low acid foods and should have received a 12D* thermal process, which is sufficient to kill spores and sterilize the product. If this had not been properly delivered, or there had been post-process contamination, spores could have survived and germinated. As for the product remaining on the shelves after the recall, the only comment I can make is that the recall process was flawed, someone was grossly negligent or totally unscrupulous.

One final point: testing of canned foods for C. botulinum is impractical. No sampling plan could detect the one in 10^12 (a 1 followed by 12 zeros) faulty cans, so we are totally reliant on the correct delivery of the thermal process. The fact that the only case we have seen in New Zealand was caused by home-preserved food shows that our canning industry is getting it right.

* A 12D process is one designed to reduce the population by a factor of 10^12. In the case of low acid canned foods, such as canned meats or vegetables, this heating process is based on killing the spores of Clostridium botulinum.

Since I wrote this article, residents of Florida have been advised to throw out products manufactured by Gourmet de Lyon. This company produces food products from a kitchen in a Delray Beach restaurant that has no permit to produce or sell canned products or those sold in jars. It would be fair to say that many of the C. botulinum cases seen in developed countries are caused by consumption of low acid canned foods produced by unlicenced manufacturers or home-canned goods sold illegally. The problem stems from the inability of such producers to control the process sufficiently accurately to ensure the destruction of the C. botulinum spores, which are highly resistant to heat.

For more information on the Florida case, see Bill Marler's website:
http://www.foodpoisonblog.com/2007/12/articles/
food-poisoning-watch/florida-botulism-risk-from-canned-products/index.html

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