Saturday, June 11, 2016

Putting the squeeze on raw milk

Many of you will know that I have written several articles on the dangers of consuming raw milk.  In my opinion, any perceived benefits are greatly outweighed by the real risks.

However, if you will permit me to mix metaphors, you can now have your cake and eat it.

An Australian company, Made by Cow, is offering raw milk processed by "cold pressure".  There are few details available, but it appears that the company is using an established process (High Pressure Processing, HPP) to make the milk as safe as pasteurised milk.  The process has been approved by the New South Wales Food Authority, and the product can be sold in stores.

The concept of killing bacteria by applying high pressure has been known for many years, (Hite studied the effects of pressure on bacteria in 1899), but practical machines to process food have been difficult to build and the processes have all been slow.  

Pressures of up to 6800 Bar (about 100,000 psi) held for several minutes are required to kill bacteria. Of course, there are many possible combinations of pressure, temperature and time, and whether the pressure is applied in a single treatment or is cycled several times.  However, the degree of inactivation appears to depend on the duration of the high pressure, and not the number of cycles.

The primary site of damage to the bacterial cell appears to be the cell membrane.  If this membrane is damaged, its permeability may be greatly changed, resulting in failure of respiration and transport functions, and hence death of the cell.  Spores are very much more resistant, so milk processed by pressure alone is unlikely to be sterile.  There are some changes in foods resulting from HPP - some enzymes may be inactivated, while others have their activity enhanced.  Other effects seen in foods are the gelling of some non-enzyme proteins and enhanced browning reactions at high pressure.  One assumes that the Made by Cow patented process has overcome these undesirable changes in the milk.

The major problem with current HPP is that the machines are batch processes, so throughput is low and the products are likely to be expensive.  However, if you are adamant that thermal pasteurisation damages the nutritional and functional properties of the milk, HPP milk may be the way to go.

Monday, January 11, 2016

Do antibacterial soaps and wipes have any effect on antibiotic resistance? Should we use them in the home?

Over the Christmas holiday, our kitchen has fed more people than normal and cleaning has therefore increased.  I have been giving a lot of thought to the possible benefits and risks of using antimicrobial cleaners and soaps.  When you get into this subject, you find it is actually quite complex.

I have written about something similar before, but there is now a lot of published work that suggests that in most cases, there is no benefit to using antibacterial soaps in the home - there is no statistically significant reduction in infectious disease if antibacterial preparations are used in preference to soap and water*.  Nevertheless, in the US alone, nearly $1 billion per year is spent on antibacterial soaps**.

Of course, many infectious diseases are caused by viruses; they are probably not affected by antibacterial compounds, which have a definite target in the bacterial cell.  Thus, an antibacterial soap or wipe will be no better at preventing transmission of cold viruses than a thorough cleaning with soap or detergent and water.

I have recently been asked to review a couple of scientific papers in which evidence is presented that suggests cleaning agents commonly used in the food industry may induce antibiotic resistance in bacteria.  Antibiotic resistance results when bacteria develop enzymes capable of breaking down the active component of the antibiotic.  One of the first instances of antibiotic resistance occurred very soon after the introduction of penicillin.  Bacteria developed the ability to break the beta-lactam ring of penicillin with an enzyme called beta-lactamase.  (Antibiotic resistance genes can often be transferred from one bacterium to another, so in time, many bacterial strains become resistant.)

We already know that many of our antibiotics are no longer effective because of resistance.  Overuse of antibiotics is blamed.  It is ironic that our cleaning agents may also be causing resistance.

But there is another potential driver for antibiotic resistance: sub-lethal exposure of bacteria to certain herbicides have been shown to change antibiotic susceptibility of Escherichia coli and Salmonella enterica serovar Typhimurium***.  This is not a straightforward relationship, but it is clear that there is the potential to select for antibiotic resistance in these bacteria, which, if transferred to humans by contact with animals and food, can potentially reduce the effectiveness of antibiotic therapy.

Well, that's fairly heavy for the first post of 2016, but it should cause us to think when purchasing home cleaning agents and soaps, or chemicals for use in agriculture and domestic gardens.

* Effect of Antibacterial Home Cleaning and Handwashing Products on Infectious Disease Symptoms.  Larson, Elaine L;Lin, Susan X;Gomez-Pichardo, Cabilia;Della-Latta, Phyllis.  Annals of Internal Medicine; Mar 2, 2004; 140, 5


*** Kurenbach B, Marjoshi D, Amábile-Cuevas CF, Ferguson GC, Godsoe W, Gibson P, Heinemann JA. 2015. Sublethal exposure to commercial formulations of the herbicides dicamba, 2,4-dichlorophenoxyacetic acid, and glyphosate cause changes in antibiotic susceptibility in Escherichia coli and Salmonella enterica serovar Typhimurium.  
mBio 6(2):e00009-15. doi:10.1128/mBio.00009-15.

Saturday, January 2, 2016

Lies, damned lies, and misinterpretation of the data.

I am constantly amazed by the apparent ignorance and credulity of the general public on matters of food safety and nutrition.  But should I be surprised?   Few people are lucky enough to have studied food technology, food science or nutrition.  Their main sources of information are then the popular press, magazines, television cooking shows and the all-pervasive Internet. 

Scientists and engineers know that the best sources of information are peer-reviewed papers published in international journals.  Experts in the field have read the paper and picked it apart, looking for poor experimental design, inconsistencies and faulty interpretation of data.  Believe me, I can say this with certainty from both sides of the fence: it is pretty difficult to get a paper published these days!

The other sources of information mentioned above are generally not peer-reviewed.  Articles can be published by people with no formal qualifications in the subject and are often either highly biased or downright wrong.  See:

Sensationalism and sycophantic following of media celebrities are what sell newspapers and magazines.  We see more food scares and wonder diet advice every month without any reference to the original research.

A few examples spring to mind:

Towards the end of October 2015, the WHO International Agency for Research on Cancer stated that processed meats, including hot dogs and sausages would be added to its list of high risk carcinogens.  Red meats were also declared a probable carcinogen.  Needless to say, this caused a furore in all the media.  A Google search, using the terms “sausages cause cancer” returned 469,000 results!  IARC classifications rank the quality of the evidence that something can cause cancer, but don’t assess the level of risk. The announcement was often quoted out of context.  For example, Discovery News baldly stated “Eating sausages, ham and other processed meats causes colon cancer”.  Other reports mentioned the increase in risk as a percentage, but did not state the base level of risk. This scare is enduring; at a barbecue recently, someone noted that I was cooking “cancer sticks”.

Coconut water appears to have been a major drink commodity this year. I have no sales figures, but the sales in 2013 were around half a billion dollars, see  Claims for coconut water include helping with weight loss, improving skin tone and aiding digestion.   Other claims, now withdrawn, stated that it could fight kidney disease, osteoporosis and viruses.  Coconut water contains potassium, calcium, magnesium and phosphorus, which are required minerals.  As a sports rehydration drink, coconut water is definitely unsuitable - when we sweat, we lose lots of sodium.  The ratio of sodium to potassium in sweat is about 10:1, but the ratio of sodium to potassium in coconut water is around 1:3.  Where are the peer reviewed scientific studies of the value of coconut water? They are never quoted.

Critics of the hypothesis that saturated fat consumption is linked with coronary heart disease use the argument that the correlation between total saturated fatty acids and risk factors is not very good.  Unfortunately, the scientific findings have been misinterpretated by the popular press media, with the result that we are told we can eat as much saturated fat as we wish. This advice is incorrect, unethical and irresponsible, see

Despite all the information on food safety available, in my opinion, a large proportion of the population is still badly educated in this regard.  At an outdoor party this week (it's summer in New Zealand) I sat with a very-soon-to-be mother.  She got stuck into the soft cheese in a big way, but said that she would eat it only during the first half hour of its being unwrapped; thereafter it was to be avoided.  In fact, the cheese had been made with pasteurised milk and she was therefore probably safe in eating it, but where had she got this idea from?  I guess she had read about Listeria in soft cheeses, and believed that the bacteria could multiply as the cheese warmed up.  For reliable information on safe foods to eat during pregnancy, see:

I believe that food scientists and food technologists have a duty to provide unbiased and easily digested (sorry!) information to the public in order to help educate them in food safety.  But how can we compete with big advertising budgets and the pronouncements of media celebrities?

I wish all my readers a happy, successful and safe 2016.

Thursday, October 22, 2015

MPI provides an interactive tool to determine your responsibilities under The Food Act 2014

The New Zealand Food Act 2014 comes into force on 1st March, 2016.  This will not be news to major food manufacturers, but does affect everyone working in the food industry; their responsibility is to produce safe food.

The new Act focusses on the processes of food production, rather than the premises where these activities are carried out. i.e. the old "floors, walls and ceilings" approach is long gone.  The other major difference from earlier legislation is that it takes account of the risk associated with any particular business (and that includes the activities of clubs and societies that raise funds via sales of food, such as pizzas).  The new Act brings in Food Control Plans for high risk food production and supply (in fact, many businesses have been operating under FCPs for some time), and introduces National Programmes for activities with lower risk.  Thus manufacture of ice cream is treated rather differently from the sale of coffee from a mobile operation at shows and open days.

One of the problems currently faced by smaller operations, such as corner dairies, saussage sizzles and community shared meals like club gatherings for members and guests, where food may be sold, but not as the primary purpose of the gathering, is knowing exactly what is required in terms of the regulations.  The New Zealand Ministry of Primary Industries (Te Manatu Ahu Matua) has provided an easy-to-use interactive tool to help all organisations involved in producing, selling and providing food to determine their responsibilities under the new Act.  The tool is called Where do I fit? and poses a series of questions you can answer by clicking responses.  The tool will then tell you your responsibilities and the requirements of the Act, together with links to further information.

I have not tested the tool extensively, but it is very easy to use and provides lots of helpful information.  I specifically tested it from the perspective of my gliding club's putting on a fundraiser and found the output very helpful.

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

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 and search for "From the mouth of Food Babe".  See also "What to take away from the Food Babe's meltdown" on

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