Tuesday, September 22, 2015

When art meets science

This post is the first for some time - as a retired microbiologist, I now have a lot of work on my hands, though it is much more varied than when I was working full-time.  Indeed, I wonder how I ever found time to go to work!

I thought I would give readers a little present as thanks for continuing to follow Safe Food.  The post is only indirectly about safe food, but I hope you will allow me a little whimsy.

Modern culture media contain various indicators that change the colour of the agar or stain bacterial colonies in ways that allow the microbiologist to presumptively identify the bacteria.  This has led the more artistic microbiologists to use bacteria to draw on the agars.  Recently, this art form has blossomed, to the extent that the American Society for Microbiology runs a competition for the best image.  I posted a more primitive image at Christmas time last year http://foodsafetywithjaybee.blogspot.co.nz/2014/12/fungi-for-christmas.html

I particularly liked this beautiful drawing done on Hektoen Agar, which is used for isolating Gram-negative enteric pathogens.  I reproduce the image and description from the ASM website, unchanged, below: 


Flowering Sunshine
A moderately selective differential medium, Hektoen is used in the isolation Gram negative enteric pathogens, particularly Salmonella and Shigella.  Bile salts inhibit Gram positive and some non-pathogenic Gram negative organisms, making the medium partially selective. Lactose, sucrose and salicin aid in the colour differentiation of colonies.  Being non-fermenters of these compounds, Salmonella and Shigella don't change the color of the pH indicator system, whereas some organisms like Escherichia coli change the colour to yellow or orange, fermenting one or more of these compounds to acids. Ferric ammonium citrate in this medium enables the detection of H2S production by Salmonella. This picture exhibits its differentiating characteristic with Salmonella grown into a Black butterfly and E.coli, a yellow flower and few stripes in the butterfly.

Of course, Salmonella, Shigella and some strains of E. coli can all cause enteric disease, and it is important to be able to isolate them and identify them if they occur in foods.

I don't know the artist's name, but I have the feeling that some post-graduates have too much time on their hands!

Friday, April 24, 2015

Would you eat transgenic food?

Many readers will immediately respond to the title of this post with a resounding "NO".

Don't be so hasty!

Looking close to home, we find that our own bodies contain many foreign genes.  It is estimated that around 8% of the human genome consists of fragments of endogenous retroviruses - about 100,000 of them.  Not all of these fragments are "junk" (a term the popular press is rather keen on).  A number of viral genes have been co-opted for our own purposes, in gene regulation, production of transfer RNA and ribosomal RNA.  One viral gene is critical to the formation of the placenta.  

On this basis, I'm not too surprised to read a piece of recent research* that shows that some of our vegetable crops are naturally transgenic.  Cultivated sweet potatoes contain the transfer DNA sequences from a bacterium called Agrobacterium.  This genus naturally infects the roots of certain plants, causing a nodule or hairy roots.  This T-DNA is not present in the wild type sweet potatoes, implying that one or more traits carried on this piece of DNA were selected for during the domestication of the sweet potato.The authors of the paper point out that sweet potatoes have been consumed for millennia, and that this "may change the paradigm governing the "unnatural" status of transgenic crops". 

In my opinion, if we look further, it is almost certain that we will find other bacterial or viral genes in our fruits and vegetables.

* The article is technical, but you can find it online

The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop


Thursday, April 23, 2015

Dangers of the Google degree

With the explosion of information on the Internet, we all use Google or Yahoo, or perhaps other search engines, to find just about anything, from a second hand multi rotor to nutritional information. I only have to look at the behaviour of my own family to see how important the search engine has become.  I freely admit that when I write a blog or a scientific article, I consult various websites to collect information or links to other websites.

My favourite website is Web of Science; this gives me access to abstracts of scientific papers on just about any subject.  Of course, if you search for a topic such as "Antioxidants", you will get a huge number of hits.  Indeed, I just searched "Antioxidant" and got 35,600,000 hits in 0.27 seconds.  Wikipedia was the lead reference, but many others were from government, university and medical sites.  Others were from commercial sites promoting health foods and bodybuilding aids, and from less easily identified sites, including blogs.

There is a temptation to believe that all sites are of equal standing.  Unfortunately, this is not the case.  With the exception of government-sponsored blogs and websites, almost all blogs, including this one, are published without peer review.  For example, if I read about food borne disease on the Centres for Disease Control website, I can be reasonably confident that the information is correct.

This is not the case for all blogs and websites.  Some authors write authoritatively on the subject, but if you go deeper, you find that the authors have no qualification other than that they "have done the research".

Most times, this is not a big deal; if someone wants to push a point of view, then that's fine.  However, in the case of health and nutrition information, there is the potential to cause great harm.  One could almost label some of the writings as "misinformation".

An area that has been exercising the minds of New Zealand food technologists recently is the exaggerated and misleading claims for coconut oil.  There are regulations in place in New Zealand about making unsubstantiated claims for food products.

The Food Babe has also been hitting the headlines recently.  Her website is a mixture of fact and fantasy.  She writes well, looks happy and healthy, and is convincing in her enthusiasm for the subject.  However, her writings are shot through with errors too many to mention.  The problem is that those with appropriate scientific qualifications can recognise the errors, but the general public does not.  She plays upon the fears of the "worried well".  I'm not going to criticise Food Babe further here.  If you are interested in a more detailed analysis, visit Sciblogs.com and search for "From the mouth of Food Babe".  See also "What to take away from the Food Babe's meltdown" on Makeuseof.com

Oh, I nearly forgot.  Food Babe does have a qualification - it's in the field of computer science.

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"