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.

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.

Is there such a thing as totally safe food?

The short answer is "No!".  Even if we eat only sterilised food, such as canned meat, we are reliant on the proper delivery of the sterilisation process and prevention of post-process contamination.  Low acid canned foods are essentially sterile - the food is hermetically sealed in a can, which is then processed under pressure to destroy bacterial spores, specifically, the process is designed to reduce the chance of survival of a Clostridium botulinum spore to less than 1 in 10^12.  On that basis, you have a better chance of winning the PowerBall lottery than getting botulism.

But nobody wants to live exclusively on canned food.  Are there any other ways that we can make food safe, or at least reduce the risks of food poisoning to acceptable levels?

Yes!  Food microbiologists and food processors study the bacteria that can cause food poisoning - pH range for growth, water activity range for growth, requirement for oxygen, growth temperature range, response to preservatives etc. - and they also look at the intrinsic parameters of the food - pH, water activity - and then consider the storage conditions, such as relative humidity, temperature and atmosphere in the pack etc.

Taking all these factors into account, foods can be designed to be safe under proper conditions of handling and storage.  A significant part of the training of  food technologists centres around study of these conditions and manipulation of the conditions in the food to achieve the manufacture of safe foods.

As an example, look at a tank of raw milk on the farm.  Immediately after it is drawn from the cow, the milk is chilled.  This reduces the growth rate of bacteria, which come either from the cow or the equipment.  When the milk arrives at the processing factory, it is pasteurised - the temperature is raised to 72C and held for 15 seconds.  This kills all the vegetative pathogens, that is, the bacteria that are not in the spore form.  The milk is now safe, but will not keep indefinitely, because heat resistant spoilage bacteria are still present.  We can make the milk keep for a much longer time by ultra high temperature processing (UHT).  In this process, the milk is heated to around 140C and held for a few seconds.  This sterilises the milk, so there are no viable bacteria to cause food poisoning or spoilage.

The milk can be dried to powder.  This lowers its water activity below the threshold for bacterial or mould growth.  Alternatively, the milk can be fermented to yoghurt or cheese by addition of starter cultures.  The starters convert lactose to lactic acid and reduce the pH of the milk until it curdles and sets.  pH is a measure of the acidity of the food; the scale runs from 0 to 14.  Numbers below 7 are acid, those above are alkaline.  As the pH falls, fewer and fewer bacteria are able to grow.  Below pH 4.0 no pathogens are able to grow.  Typical pH of yoghurt is 3.65 to 4.40

Other foods may be made safer by the application of hurdle technology, where several preservation mechanisms are brought together to prevent growth of pathogens in the food.  There is a number of new technologies appearing, such as high pressure processing, electron beam irradiation and ohmic heating.  None of these processes can guarantee safe food, but each has its advantages.  I'll look at some of these techniques in future postings.

Safety management systems, like HACCP can be used to control food processing operations to ensure that safe food is produced.  However, some foods are inherently less safe, such as raw vegetable sprouts, raw shellfish, or very unusual foods that require highly skilled preparation, such as fugu.
 
Consumers must take some responsibility in their choice of food and eating habits.  If you are doing the traditional turkey for Christmas dinner, ensure that it is properly cooked - use a meat thermometer - and consider cooking the stuffing separately.

If you are going to barbecue this Christmas, don't cook chicken legs on the BBQ without first microwaving them - they are an irregular shape and ensuring that they are properly cooked is difficult.  Don't use the same plate or utensils for cooked meat as for raw.   Don't keep foods beyond their use-by date and ensure that all raw foods are refrigerated during storage. 

Have a wonderful holiday and keep safe this Christmas.