Follow-up on canned food production.

In the last posting, I was writing about canned foods and the consequences of their going out of their “best before” date.

I was confident that the young man in question was not at risk. Here’s why (sorry for the lecture).

Canned foods have been made commercially in significant amounts since about 1874, when Schriver invented the closed kettle – a device that allowed processing at temperatures above that of boiling water. Before that, commercial production was carried out, but the products sometimes spoiled. (We tend to forget that up until 1860 it was not known that bacteria cause food spoilage. The spoilage was almost certainly the result of failing to deliver a harsh enough heat process to destroy bacterial spores. Some spores can survive more than 4 hours in boiling water).

In all that time, manufacturers have developed reliable processes by experience. Scientists have been able to explain why the heat treatments work and thus design new processes with confidence. In the case of low acid canned foods (LACF) we have to rely totally on the process. We cannot test for safety.

You might ask “Why would it be difficult?” The problem is that we demand a high level of security i.e. we set the acceptable risk of food poisoning from LACF as around 1 in a billion (I mean a million million) i.e. only one can in a billion would contain a vibale spore. There is no testing regime that could detect the presence of viable spores even ten times that limit.

The LACF process is designed, using a combination of knowledge of the type of microorganisms likely to be found in the food (and able to grow under those conditions) and the measured death rate of these bacteria, to calculate a process that will guarantee to destroy them. In the case of LACF, we are interested in a process that will destroy the heat resistant spores of Clostridium botulinum, leaving only one survivor in a billion. We call this a "12D" or 12 decimal reduction process. (See also the previous posting).

So when my reader contacted me and asked me to test the food for her, I knew that it was pretty much pointless. If the food had been processed properly and the seal remained unbroken, then she could rely on the food being safe for her son.

Do consumers understand “Use-by” and “Best-before” dates?

I think that many consumers don't understand these package marks.

I recently received a message from a very distressed reader. She'll recognise herself, but I'm sure she won't mind my writing this.

The reader had a 16-month-old son and had fed him a jar of organic apple, pear, blueberry and blackberry with vitamin C. The young man had eaten it all and was apparently bouncing around, as 16-month-olds tend to do. The jar and contents appeared normal, with a suitable vacuum in the headspace.

After the meal was over, the mother looked at the jar and found the “best before date was 29th July 2008!” (her exclamation mark). She went on: “I am very concerned that he could get Botulism from this - is there a way that I could get the remains of the food in the jar tested to make sure that he is not in any danger? Please, I am happy to pay for this and your time.

“I have spoken to a few people and they have all said that we will have to wait the 10 days to be on the safe side. Is there anything else I can do to protect my son? or help to prevent anything really nasty making him sick from this?”

This mother was obviously very frightened. Her concern was triggered by the best before date, which is an advisory to the consumer about quality. Chemical changes can occur slowly in cans or jars of food during storage. These changes may be accelerated if the food is exposed to sunlight or high temperatures. These changes may make the food less appetising, such as giving a "cardboardy" or flat, oxidized taste. The changes are not harmful. If the food is outside the Best Before date, it does not necessarily indicate that it is unsafe to eat, though that might be the case with something like ham or egg salad, which are much more perishable.

I didn’t have any further information on the product, but would expect that it would have been processed either as an acid food (pH less than 4.6) and pasteurised, perhaps hot-filled, or processed as a low acid food (pH above 4.6) and thus be given a 12D process (sterilised). In either case, Clostridium botulinum toxin would not be produced. Any changes occurring after the best before date would be quality deterioration only, not safety issues. There are several other points to come out of this discussion, but I'll cover them in a future posting.

Extrapolating from this, it is probable that consumers and perhaps retailers don’t fully understand the significance of “use-by” dates. I have certainly seen products in supermarket display cabinets with the original “use-by” date covered with a second label bearing a later date. The latter is illegal in New Zealand.*

And the boy? I had a message from his Mum today - this is the 11th day since he ate the food, which had actually been made in 2006. He didn't get sick and is now toddling around the home at high speed. Well, some food stories have happy endings!


* You can find an article "Date Marking - Standard 1.2.5" on the NZFSA website at www.nzfsa.govt.nz/

Don’t read this if you have a weak stomach

The reason for the title will become apparent later on!

People who have an opportunity to influence the public have a duty to make sure they know what they are talking about and to think about the consequences of their comments.

Last week, popular TVNZ breakfast show host Paul Henry was talking about the state of cleanliness in public toilets. The breakfast show is a mixture of news, views and entertainment and Paul made a meal (if you’ll pardon the pun) of the issue, drawing out as much toilet humour as possible. Unfortunately, he also claimed that washing your hands in a public convenience would result in your hands being more contaminated than if you had not bothered.

This is hard to stomach. Certainly, taps and door handles may be contaminated, often with faecal bacteria and it may be that soap and soap dispensers are also contaminated. However, I find it difficult to accept that not washing hands is better than washing.

If you didn’t take the earlier warning, now is the time to quit reading.

If you have wiped your backside with toilet tissue, then the chances are that your fingers are contaminated with faecal bacteria and viruses. Way back when I started teaching food microbiology, I used to run an exercise with my students. They took various numbers of sheets of toilet tissue and placed them over a finger end, which they then gently wiped across a Petri dish of indicator bacteria. These, as it happens, were Escherichia coli, the bacteria always present in the gut. These bacteria have the ability to produce a green metallic sheen when they grow on an agar called Eosine Methylene Blue. Since they occur only in the gut, we should not normally expect to find them on our hands, except for the obvious reason. After the wiping phase of the experiment, the tissue was discarded and the same finger pressed onto the EMB agar, which was then incubated overnight. The students then washed their hands and dried them before making a further agar impression.

The students were usually horrified to discover that even when using 6 sheets of 2-ply toilet tissue, their finger impressions often grew bacterial colonies with a green metallic sheen. Now, not to put too fine a point on it, 6 sheets is an almost unmanageable wad of paper! Washing usually removed all the bacteria, but only if soap and warm water were used.

There are several messages here.
• No matter how much tissue you use, you can’t be sure that you won’t have faecal bacteria and viruses on your fingers.
• Washing your hands with soap and then drying them will remove most of the bacteria

Unfortunately, when you turn on the tap with contaminated hands, they will transfer bacteria and viruses to the tap. After you have washed, you recontaminate your hands when you turn the tap off. That’s why in hospitals and laboratories the taps have long handles that can be operated with wrists or forearms, or are operated by foot pedals or infra-red sensors. These days, many washroom taps have press buttons that allow the water to run for only 30 seconds or so and don’t need to be turned off.

So what can you do?
• Turn the tap on with your wrist
• Wash your hands thoroughly with soap (sing “Happy birthday" to yourself twice to ensure you wash for long enough)
• Thoroughly dry your hands on a paper towel and then use it to turn the tap off
• If the washroom has blower hand dryers, be careful not to touch the machine (if it has an on button, push it with your knuckle)

Watch a microbiologist in a washroom. When I go in there, I do all the above and then open the door with the crook of my little finger. It’s not foolproof, but a lot better than not washing. If you are still paranoid, buy a small spray bottle of hand sanitizer and carry it in your bag for use after you have left the washroom and before you eat.

I hope you read this far, Paul.

Can legislation control Salmonella?

Obviously, some very intelligent people think so. Unfortunately many of them misunderstand the control of food safety.

Food safety legislation is similar to the laws governing road traffic. There are lots of requirements for the design and maintenance of vehicles and prescribed behaviours for their operation. Maximum speeds for each piece of road are set by traffic authorities and advised by signs on the roads. If you exceed the speed limit, you might get away with it most of the time, but speed cameras may catch you. Then you get a ticket and a fine. That’s just money and perhaps demerit points on your licence. Do the speed signs and threat of punishment make us better or more responsible drivers?

Suppose we have an accident and injure or kill another motorist or pedestrian. If we are shown to be at fault, perhaps because of ignoring the speed limit, does the fact that we receive a stiff fine make it any better for the injured party or their family? No way.

The recent outbreak of salmonellosis in the US, carried in peanuts, was almost certainly the result of the flouting of many food safety regulations – the factory was dirty and infested and in-process peanuts were not protected from recontamination. Yet the factory had been inspected and the overall level of food safety was pronounced “superior”. It must be pointed out that the inspector was given only one day to inspect a factory processing several million pounds of peanuts each month and was not an expert in this type of operation. A federal investigation team later discovered that company testing records showed that Salmonella had been found in its products on at least 12 occasions since June 2007. Those products were apparently retested until negative results were obtained and then released to the market.

At least nine people have died from salmonellosis associated with the peanut products and 22,500 were sickened. The existing legislation clearly did not protect them. Some products containing the affected peanuts are apparently still on retail outlet shelves.

In a radio and television address to the American people on 14th March*, President Obama offered his “top ten” ideas for improving food safety. He noted that only about 5% of the 150,000 food production premises were inspected last year, so one billion dollars would be invested in the FDA to increase its ability to inspect premises. Penalties for selling unsafe food would be increased. Unfortunately, he then went on to state that only government can ensure that foods are safe to eat. Wrong, Mr. President!

Food safety is a partnership of trust between government, food producers and suppliers and the consumer. Sure, regulations are required and must be enforced, but no inspection force can guarantee the production and supply of safe food; the manufacturers must be committed to doing so on every day of the year, whether the inspector is due or not.



* http://www.youtube.com/watch?v=lkKp02lluq8

Black-balled peas

If Talleys of New Zealand have been correctly reported, it seems to me that they have placed the wrong priority on their response to the complaint by Humphrey Elton about his finding Black Nightshade berries in a pack of frozen peas last August. A number of other contaminated packs of peas and beans have turned up since then, the latest being frozen peas and corn last week. One complainant has claimed that almost half of the peas were actually Black Nightshade. If that really is the case, then there is a serious problem in the factory or on the farms.

According to Mr. Elton, Talleys informed him that this is a common agricultural weed and nothing to worry about. He received a cheque for five dollars as compensation.

The New Zealand Food Safety Authority has noted that the berries are “mildly toxic and should be avoided; the contamination is a food quality issue”. It seems that it has been an issue for at least 8 months, but for some reason has only recently hit the headlines.

The fact is, Mr Elton and other consumers bought frozen vegetables. They did not expect to receive anything else in the pack. Being told that the berries are nothing to worry about is akin to complaining to the waiter about a fly in the soup and then being told not to let other diners hear - it’s extra protein and a bonus.

In a world where consumers are highly aware of food safety and quality, I would have expected a more pro-active response from the company. They could have told the complainants that they were very sorry about the contamination and that they were investigating the occurrence and should not have offered such a miserly compensation. If the problem has been known since last year, they should have been doing something about it long ago. What a difference this would have made to the public perception of the company. The downside is that Paul Henry (TVone Breakfast host) would have been robbed of an opportunity to clown around, testing frozen peas by hitting them with a mallet on the Breakfast table.

How could the contamination have occurred? The most likely causes are excessive growth of Black Nightshade in the fields as a result of favourable weather conditions and failure to control this growth by suitable spraying. When the peas are harvested, a harvesting machine cuts the whole pea vine and separates the peas from the other parts of the plant. The harvester cannot differentiate peas from nightshade berries. Sorting and separation in the processing plant was obviously ineffective.

The temperature's rising (but why?)

I was recently asked to explain some of my comments on detection of faecal coliforms. <See Coliforms and Faecal Contamination Wednesday, July 18, 2007>

I have extracted the essentials of the questions below:

“Since the coliforms when tested… are grown at optimum growth temperature of 37C, why would you need to raise the faecal coliform test temperature to 44.5C to show thermotolerant E. coli are present? Why would food safety people be looking for thermotolerant bacteria in food rather than bacteria that grow at normal temperatures?”


In my article, I provided some background information on "faecal indicator microorganisms", which we use to show that a food or water sample may have been contaminated with faeces. These tests originated in the early days of public health services and safety of public water supply. The coliforms are easier to detect and enumerate than are Salmonella or Shigella or faecal viruses. (Salmonella and Shigella are not coliforms). The reason for incubating at 44.5C to demonstrate the presence of Escherichia coli dates from 1904 when Eijkman suggested it as a means of separating the "B. coli" originating in the faeces of warm blooded animals from the strains characteristic of cold blooded animals and thus providing us with a means to detect faecal contamination of water supplies by warm blooded animals, including humans.

So the answer to the first question is “we are not particularly interested in thermotolerant coliforms; rather we want to show that the water supply may have been contaminated by human wastes and hence potentially contains faecal pathogens”.

Having said that, of course there are other areas of food microbiology where we are very interested in the presence of thermotolerant or thermophilic bacteria. If we pasteurize milk with plate heat exchangers (the standard method) we may find that the cooling stages become colonized by thermotolerant streptococci, which may cause spoilage. In the case of canned foods, we find that some sporeforming bacteria can survive even a very rigorous thermal process. These bacteria are of no public health significance, but they may cause spoilage if the cans are held at high temperatures (greater than about 40C) as might be found in storage facilities in very hot countries or in a restaurant kitchen.

Tha’s gorra eat a peck o’ muck afore tha dies.

For those readers not lucky enough to have been born in Yorkshire, northern England, an approximate translation of this old expression is “You will eat a barrel-full of dirt during your lifetime”.

What brought that on? According to Abby Alford, writing in the Western Mail (1), there may have been some scientific basis to the saying. Bangor University lecturer, Dr Prysor Williams, believes that an obsession with cleanliness reduces contact with dirt and thus with harmful bacteria. Our immune systems become weakened, leaving us susceptible to infection. Unfortunately, the evidence for this view is somewhat lacking, though Dr. Williams is not the only one to have argued this.

Stuart Levy, Director of the Center of Adaptation Genetics and Drug Resistance at Tufts University, provided substantial evidence that the substitution of anti-bacterial agents for good old soap and water increases the ability of bacteria to develop resistance. A few bacterial cells containing genes that confer resistance to the antibiotics can protect neighbouring sensitive cells, rendering the antibacterial agent ineffective. Levy’s group tested the ability of Escherichia coli to mutate to become resistant to triclosan, which inhibits an enzyme involved in fatty acid biosynthesis and thus interferes with membrane biosynthesis. The work was published in the prestigious journal Nature.

In a carefully constructed randomized, double-blind trial, Elaine Larson and her co-workers have also shown that using antibacterial home cleaning and hand-washing products has no significant effect on the incidence of infectious disease symptoms (2).

The take-home message is that while cleanliness may be next to godliness, we do not live in a sterile environment. If we try too hard to protect ourselves and our children from microorganisms, we don’t give our immune systems the chance to develop resistance to bacterial pathogens.

(1) http://www.walesonline.co.uk/news/wales-news/2009/02/16/
how-obsession-with-cleanliness-could-be-making-us-ill-91466-22935582/

(2) Annals of Internal Medicine, 2 March 2004, Volume 140 • Number 5 321