Thursday, February 26, 2015

At what point do we start to trust scientific opinion?

I have spent quite a bit of time recently trying to sort out the difference between demonstrable scientific fact and informed scientific opinion.  An example of the former is the measurement of 'g', the acceleration due to gravity; the latter might be the opinion of medical practitioners and nutritionists that consumption of large amounts of saturated fat can lead to heart disease.  Few people would argue about 'g', but there is much discussion, even amongst the experts, about the effects of saturated fat in the diet.  An opinion gains validity when, if challenged, it can be supported by peer-reviewed research.

Of course, it is impossible to prove a negative, but at what point do we say "The overwhelming evidence indicates that ..."

At what point do we trust the opinions?

I found the following graphic on-line.  Click on the image to see it full size if it doesn't display properly in your browser.   I was surprised at how many learned groups had made these opinions known.  I am not going to state my own opinions here - I don't consider myself an expert in the field, but my training as a scientist does allow me to evaluate evidence provided to me in peer-reviewed literature.  It would be a very long stretch to claim that all of these individuals and groups were either supported by, or influenced by the companies producing GM foods.

Wednesday, January 28, 2015

How much or how little salt is good for you?

The Food Police keep changing their minds - "Should you eat eggs; how many eggs per week are OK; should you avoid saturated fat; does poly-unsaturated fat bring other problems; does sodium affect heart disease..."

I'm not going to get into those arguments, but I will suggest that the best way to avoid diet-related diseases is to eat a whole range of foods - fruits, vegetables, meats, dairy products, nuts and grains, and wash them down with plenty of water and moderate amounts of wine and beer.  Note: this is my personal view and I have no scientific evidence to support it.

I have a policy for this blog that I will not publish comments or articles that are thinly disguised advertising for commercial services.  However, I have made the occasional exception where I think the benefit to readers outweighs the downside.  Today is one of those exceptions.

The FDA recommends a maximum intake of 2,300 mg sodium per day.  In principle, it should be possible to limit our intake.  However, salt is used in many foods and, in some cases, is a critical part of the preservation process, while in others, it's primarily about sensory characteristics of the food.

I was approached by Maggie from Healthline in San Francisco, offering a link to a visualisation of sodium intake, illustrated as the amount found in various foods.

I am not familiar with some of the food products, but it allows readers to evaluate their own sodium intake in more easily digested (sorry) terms than milligrams of sodium.  I think that this link is worth a look.  I was surprised to see how much sodium there is in my favourite smoked salmon and chicken breast, but not at all surprised to see the levels in bread and snacks.  By remembering the high salt foods, consumers can at least moderate their involuntary sodium intake.

A few years ago, my colleagues and I did some formal sensory evaluation on breads baked with various levels of salt.  The results suggest that the average consumer cannot detect a small but significant reduction in salt level in white bread.  The baking industry, and several other sectors in New Zealand have taken steps to reduce sodium in their products to help protect the health of their consumers.

Wednesday, January 14, 2015

More GM foods to be permitted in Europe?

It looks as though individual countries within Europe will be able to permit the growing of genetically modified crops.  This is an unusual departure from the usual European policy, where all member countries have to abide by the rulings.

There are possibly some anomalies: it may be possible to import GM foods, but not to grow them at home.

Not everyone will be happy about this.  However, there is no doubt that GM foods have been more closely studied than most other foods and the insertion of particular genes can be closely controlled.  Other growers, who don't want to have GM crops on their land may face difficulties if pollen spreads from GM to non-GM crops.  And there is the potential for the originators of GM seeds to claim that those growers whose land has been invaded are growing the GM crops without paying royalties etc.

This decision will be well worth watching.

Wednesday, December 31, 2014

Raw cookie dough and Salmonella

A recent post on FaceBook caused me some concern, amusement and despair.  The argument centred on whether you can get salmonellosis from eating raw cookie dough.  Comments ranged from serious through flippant to borderline insane.

What concerned me was the level of ignorance on basic food safety and the authoritative, but incorrect, advice given.  For example, one writer said that there was no problem with cookie dough containing raw egg, because Salmonella is found only on the outside of the shell; washing the outside of the egg would remove faecal material, rendering the eggs safe.  Both of these comments are wrong.

The egg shell is not an hermetic seal; if eggs are washed and then they cool, moisture can be drawn into the egg and bacteria on the outside may also pass through.  There is a defence mechanism in the egg white.  Lysozyme is an enzyme that can attack the cell wall of Gram positive bacteria.  Unfortunately, Salmonellae are Gram negative, so may survive.  In addition, the hen may be infected with Salmonella, so the egg may be contaminated even before the shell is formed.

Laying flocks in New Zealand are unlikely to be infected with Salmonella because of the biosecurity measures employed on New Zealand poultry farms.  The situation may be different in other countries.

Commercial cookie dough may be made with pasteurised egg, in which case any Salmonellae will have been destroyed.  But unpasteurised eggs may contain Salmonella.

Statements that athletes drink raw egg drinks for breakfast and suffer no consequences are without scientific support.  Arguments that real mayonnaise is made with raw egg are also misleading, as mayonnaise also contains vinegar, which not only loosens the emulsion, but also reduces the pH.

Most of us at some time in our lives have scraped the mixing bowl with no ill effects.  The infecting dose for Salmonella varies with the strain, and we may have been exposed to only low numbers of bacteria.   However, to eat large quantities of raw cookie dough is playing Russian roulette.

My two favourite comments from the many posts:

"I know that if you put Nutella on salmon, you get Salmonella"

"I've eaten it twice, and died both times"

Wednesday, December 24, 2014

Fungi for Christmas!

The image below is my Christmas card to you all.  I didn't create it - the image has been doing the rounds on a science website, but it is truly a microbiologist's Christmas card.

For those who are interested, the Petri dish was seeded with the following:
Top: Talaromyces stipitatus; Tree: Aspergillus nidulans; Ornaments: Penicillium marneffei; Trunk: Aspergillus terreus
Not all of these are likely to be found in food -  T. stipitatus was isolated from rotting wood and can produce some interesting enzymes that may have application in the agri-food industries, P. maneffei can cause human disease, mainly in HIV patients.  A. nidulans was probably one of the first fungi I studied as a microbiology undergraduate, and has been very important in the study of recombination, DNA repair and experimental evolution.

Tuesday, December 23, 2014

Happy and safe Christmas to you all

For us in New Zealand, Christmas Day is only 12 hours away.  It is summer and we will be having BBQs and parties outside.

Don't forget - if you are cooking outside on a fire or a BBQ, steak requires only to be cooked on the outside, as the inside of meat from a healthy animal is essentially sterile.  If the steaks are thick, make sure that the edges are also cooked.  However, meat patties have been made by blending together minced meat and possibly egg as a binder.  The inside of the patty is not sterile and so the patties must be cooked through properly.  Use a meat thermometer to be sure that the inside has reached at least 75C.  You can't judge whether the meat is cooked just by its colour.

I prefer not to cook chicken on the BBQ because it is difficult to ensure even heating.  However, if the BBQ has a hood, it is essentially the same as an indoor oven.  Ensure that the chook is cooked properly, again using a meat thermometer.  I also prefer not to put stuffing into the body cavity - it slows down the cooking process and it's difficult to determine when it's done.  Cook the seasoning separately.

Round our place, there are very rarely any leftovers.  However, make sure that food doesn't stay in the sun any longer than necessary.  Ham that has been handled may well be contaminated with Staphylococcus.  If eaten straight away, this is no problem, but if left at room temperature, the bacteria may grow, since all their competitors have been killed in the preparation process, leaving them free to grow in the salty favourable conditions.

Remember that several food borne pathogens can grow, albeit slowly, in the refrigerator, so use leftovers within a day or so.

Recent changes in legislation in New Zealand mean that driving after more than one alcoholic drink risks being charged with driving under the influence of alcohol.  Better to have a designated driver, or stay off the turps!

To all my readers, I wish a happy Christmas and an enjoyable New Year.

Wednesday, December 17, 2014

Comment on potential hazards of raw milk consumption.

I was recently asked for comment on the tragic death of a youngster in Australia, apparently caused by consumption of raw milk.  I was given only 200 words to get the message across.  Rather than go over all of the arguments again, I have reproduced my comments below:

The recent tragic death of a 3-year old infant and serious illness of four other children in Australia is  yet another example of the risks associated with consumption of raw milk.

Proponents of the consumption of raw milk claim that this is a natural food and has been consumed for hundreds if not thousands of years.  That is true, but ignores the fact that many diseases can be transmitted from animals to humans in the milk.

The hazards of consuming raw milk have been known for a long time. In Ontario around 1900, over 10% of all childhood tuberculosis was thought to be caused by unpasteurised milk. The rate of tuberculosis infection and many other milk-borne diseases in children fell dramatically after enactment of a law in 1938 requiring milk to be pasteurised; this was hailed as a major achievement.

The fact is that between 1998 and 2005, a total of 45 outbreaks resulting in more than 1,000 illnesses, 104 hospitalisations and two deaths due to raw milk or soft raw milk cheese were reported to the US Centres for Disease Control and Prevention. 

There is some evidence that consumption of raw milk early in life can reduce the incidence of allergies.  Bacteria in the raw milk may transiently colonise the intestine, resulting in stimulation of the immune system through infection.  

In addition, when milk is digested, a variety of beneficial ‘bioactive peptides’ are released.  However, it should be noted that pasteurisation does not adversely affect the release of these peptides.

I have said this before and say it again:  Adults who decide for whatever reason to consume raw milk should consider the potential hazards and make an informed decision.  Children, who have no choice in the matter, should not be fed raw milk or soft raw milk cheeses.

The situation is a little different for hard cheeses, such as Parmesan, in which the conditions, or the process, are inhibitory to most pathogens.  Food Standards Australia and New Zealand has made the following determinations:

Extra hard raw milk cheeses pose a low to negligible risk to public health and safety as survival and growth of Campylobactyer jejuni/coli, enterohaemorrhagic Escherichia coli (EHEC), Salmonella spp., Staphylococcus aureus and Listeria monocytogenes is very unlikely.
The selected Swiss-type raw milk cheeses were all assessed as posing a low to negligible risk to public health and safety for the general population as survival and growth of C. jejuni/coli, E. coli (EHEC), Salmonella spp. and S. aureus is very unlikely. 

Note:  The FSANZ document is comprehensive and readers should consult the report for more detail. See: