Thursday, November 12, 2020

Hello Fresh fish causes food poisoning in New Zealand

 At least three people have been treated in hospital for scombroid poisoning after eating Trevally from a meal kit supplied by Hello Fresh.

Histidine in the fish tissue can be converted to histamine by histidine decarboxylase, found in Escherichia coli, Morganella morganii, Proteus, Pseudomonas and Klebsiella species, which may occur naturally in the gills, skin and gut.  If the fish is not properly handled after being caught and during transport and distribution, allowing the temperature to rise for an extended period, these bacteria can grow and produce sufficient histamine to cause an allergic reaction in the consumer.  

Scombroid poisoning was originally named because Scombridae fish naturally contain higher levels of histidine.  The range of symptoms varies, but includes nausea, headaches, vomiting and diarrhoea and possibly itching and a burning sensation in the lips.

Unfortunately, the fish may not appear to be spoiled and the enzyme remains active even after the bacteria have been killed,  continuing to produce histamine under cold storage.  Activity can  resume when frozen fish is thawed.  Histamine cannot be destroyed by cooking, so control of storage temperature is essential throughout the food chain.

Friday, September 4, 2020

Nothing new under the Sun

 Sorry!  That was a click bait title.  However, as far as food poisoning goes, there really is very little that is new - the same old suspects keep turning up.

I've written about Clostridium botulinum before (and you can find those posts by searching the labels).  It has now caused food poisoning in Vietnam, this time in Minh Chay pate products, which have all been recalled.  The outbreak is reported in Food Safety News.  The article includes a photograph of the product, which is packed in screw capped jars and possibly cans.

The Department of Food Safety, Ministry of Health, inspected the premises and found 'sanitary issues' with cleaning and drainage.  The factory was instructed to cease production until the problems were fixed.

There is insufficient information in the article to make definitive pronouncements on the causes of the contamination, but some reasonable arguments can be made.  C. botulinum releases a toxin when it sporulates, and for this it must grow.  Since the bacterium is anaerobic, it requires the absence of oxygen.  It appears, therefore, that the pate was contaminated during manufacture, possibly from the unclean factory environment, and the organism then grew in the sealed containers.  The article doesn't state whether the product was hot-filled, or heat processed in the containers.  In the former scenario, the spores of C. botulinum could germinate and grow in the product, eventually leading to toxin production.  If the containers were heat processed after filling, it is possible that contaminated cooling water leaked into the containers through faulty seams or seals.

The toxin binds in the nerve synapses and prevents the secretion of acetyl choline, thus preventing nerve impulse transmission.  This usually causes respiratory paralysis, so patients need support to breathe.

Interestingly, if you search for 'Botulin toxin' on-line, the first five hits refer to Botox, the cosmetic treatment to reduce frown lines and crows' feet.  Food poisoning is mentioned almost as an afterthought.

Thursday, August 27, 2020

Infection transmission

 The COVID-19 pandemic should have got us all thinking about infection transmission and control.  Yet, the virus continues to spread.

I remember the pretty much the first laboratory class we did in Microbiology 101 was a demonstration of how infection transfers within a community.  There were 24 students in the class.

First, everyone wiped their hands with a paper tissue, one of which had been contaminated with a bacterial culture.  This organism was Serratia marcescens, which produces a bright red pigment when grown under the right conditions.  A sequence grid was set up, so that everyone shook hands with one other class member and then plated their hand onto an agar plate.

The second round of hand shakes was then undertaken with different class members, without first washing our hands, and, again, hands were plated.  This sequence continued until, by the end, everyone had shaken hands with about 10 classmates and plated their hands.

The plates were incubated, and a couple of days later were examined for the presence of the bright red colonies.  Scoring the positives against the sequence grid, it was very obvious how the infection had spread throughout the class.  Not everyone became infected initially, but the infection spread exponentially and after six rounds, everyone in the class was positive.

How is this relevant to COVID-19 spread?  This virus is supposedly spread predominantly by droplet inhalation.  However, an individual may become infected by touching their face with infected hands or perhaps by rubbing their eyes.  The virus, like the Serratia, might be picked up on the hands from surfaces like door handles, wash basin surrounds, pens, or from shaking hands with a carrier etc.  "OK, I don't touch my face and eyes".  Are you sure?  I used to lecture to classes of up to 130 students and occasionally counted how many were touching their face at any one time.  (Yes, I know, I had put half of them to sleep and their heads were in their hands).  Up to 60% of the class touched their faces and noses and eyes.  A similar surreptitious survey found that up to 30% of students left the toilets without washing their hands!

The take-home message here is - "Wash and sanitise your hands regularly - many times a day; avoid hand shaking and kissing 😞 and if you are sick, STAY HOME.  In fact, if you don't have to mix with people, stay away from them."  Like in our first year experiment, there was no indication that any particular person was carrying the infection until two days later when the test results were available.

Saturday, July 25, 2020

Should we switch to plant-based proteins?

While New Zealand was in lockdown, I had ample opportunity to think about life, the universe and everything.  Specifically, I was thinking about plant-based protein as human food.  Recently, meals at home have exposed me a variety of new dishes and some of these were plant-based.  I’m setting out these thoughts in the hope that they will stimulate conversation between readers.

First, there is a strong drive from some members of the community to change from eating animal proteins to eating plant-based protein meals.  Some of this is a concern for the welfare of animals and some is ideological.  Probably the primary driver is health, but the second driver is sustainability and environmental concerns around our planet and its long term health.  Is it really more healthy to eat only plant proteins?  Is it truly better for the environment?  There is concern that rivers and waterways are being polluted by our raising of animals for meat and milk, but will the production of plant proteins result in greater use of fertiliser and hence increase runoff?  Methane emissions will decrease, but growth of legumes may ultimately result in increased nitrate leeching. Of course, traditional farming mixed plants and animals - the vegetables etc. were grown on land fertilised by animal manure, but if we no longer raise animals, that cycle will be eliminated. 

What is the point of trying to reproduce the taste, appearance and texture of products such as burgers, but using plant proteins?  Really, that is just a sop to confirmed meat eaters.  As I understand it, The Impossible Burger is more expensive to produce than the meal it is trying to emulate.  Is there going to be resistance to the use of colours and flavours to simulate animal products?  The key ingredient that gives the Impossible Burger its meaty taste and makes it bleed like meat when cut is soy leghemoglobin, derived from genetically engineered yeast.  Production of the yeast by fermentation requires inputs of industrially manufactured, chemically synthesised ingredients.  The safety of these inputs will be subject to regulatory approval and their use will not be universally accepted.  Ikea is introducing a non-meat version of its traditional Swedish meatball  and claims that conversion of about 20 per cent of its meatball sales to plant balls would mean around 8 per cent reduction of the climate footprint for the food business at Ikea.  Meanwhile, KFC has announced that it is collaborating with 3-D Bioprinting Solutions to develop chicken nuggets made with cultured chicken cells and plant material.  The thinking of food technologists and new product developers is way ahead of the general population.

We all require iron in our diets, young or pregnant women particularly.  The recommended daily allowance for vegetarians is 1.8 times higher than for people who eat meat. This is because heme iron from meat is more bioavailable than non-heme iron from plant-based foods, and meat, poultry, and seafood increase the absorption of non-heme iron. This is just one aspect of changing from eating animal protein to exclusively plant-based protein.  There is any amount of information on the Internet regarding iron requirements and sources, but caution is required before believing everything!

I really have no answers for these questions, but I think that the proponents of moving to an exclusive plant protein diet haven’t thought it through.  Here are some questions that I’d like answered:

Does New Zealand have sufficient agricultural land to produce all the plant protein we need to feed the population, assuming that we all move to consuming it?  Much of our farming is on hill country.  This is not suitable for crop production.

Will the energy inputs for food production increase or decrease?  We will need diesel to harvest the crops and energy to dry some of the products.  With the shutdown of the Tiwai Point Aluminium smelter, there may be an opportunity to divert some of the surplus electricity to processing of plant proteins, but will that be enough or even practical?

What of our exports?  In 2019, dairy, eggs and honey earned NZ$16.3 billion and accounted for 27.9% of total exports, while meat earned NZ$8.03 billion - 13.9% of total exports.  If meat and dairy were no longer produced here, that would be a loss of nearly 42% of our exports.  In the current post COVID-19 era, it would be hard to replace those contributions.

Saturday, April 11, 2020

Safe Food in Lockdown

Are you tired of reading and hearing about COVID-19 yet?  Are you totally confined to your home, or are you an essential service worker?  How have things changed for you?

My on-line news service provides the ten top items each day as links.  For the last two weeks, nine out of the ten have been about COVID-19 and mostly they provide depressing reading.  I'm not going to rehash all that.

New Zealand, where I live, has closed its borders. 

The majority of shops are closed, so our food shopping is mostly confined to visits to the supermarket, which may involve long queues and limited numbers of people in the building at any time, so the on-line ordering and collection option is popular. The 2-metre separation rule is now being followed by most people.

How does this affect our eating habits?  Well, restaurants and fast food joints are closed, so we are all preparing many more meals at home from what we have on hand.  This may involve substitution of ingredients, or complete change of menu at short notice.  Not everyone is used to cooking meals at home and there may be a few disasters! 

Do we need to worry about contracting the virus from our food?  The best information I have is that this is a respiratory infection and you can't pick it up from food.  Since it is a virus, it can't replicate in stored food, so the only concern is with contamination of the packaging.  Survival time on surfaces seems to vary, but studies by CDC, researchers at various universities and FDA indicate that the survival time varies from a few hours to about three days, but it is important to remember that the AMOUNT of virus remaining may be as low as 0.01% of the original contamination.  It is unlikely that you can contract the virus from food packaging, but it's a good idea to wipe the packaging down with a 1:48 dilution of household 6% bleach, (5mL 6% bleach into 240mL water) or just leave the packages unopened for a few days.

So, do we need to change our cooking and eating habits?  Essentially, I think the answer is "No" but we do need to be very careful.  Nobody wants to waste food, so it's likely that leftovers will be stored for future use.  We don't want to burden our hospitals with food poisoning cases.  Here are a few tips:

Keep leftovers refrigerated and reheat to at least 75C - use a thermometer
Wash your hands thoroughly and frequently
Don't touch your face
Ensure that food is cooked properly (as you would normally) 
Be very wary of cross contamination of raw and cooked food
Stay home; don't pop down to the corner store just to pick up a bottle of milk - plan your shopping.

Just a couple of final points:
The experts now think that the wearing of masks available to the general public is not going to protect you from infection.  Don't forget that the virus is tiny and if you get it in your eyes, it will run down your tear ducts into your nasal passages and can initiate an infection

I am now washing my hands more thoroughly and frequently than when I was working with green lipped mussels deliberately infected with high levels of Salmonella!

Saturday, August 17, 2019

Can this be real?

It's amazing how a throwaway line can be picked up and takes on a life of its own.  A New Zealand botanist referred to a lichen, Xanthoparmelia scabrosa, as "Sexy Pavement Lichen" because it contains a PDE5 inhibitor.  See

It appears that powdered X. scabrosa is being sold on-line as a Viagra alternative.  It has even been reported that people are actually licking sidewalks!  This is probably not a smart way to obtain a potential erectile disfuntion medication, as the inhibitor is not the same thing as Viagra and is also somewhat toxic, not to mention the contamination of the lichen from vehicle exhaust, dust and grit etc.

According to Tom Hale, writing for IFLScience, the US FDA analysed a sample of the powder bought on-line and found it consisted of 80% Viagra and 20% grass clippings (really?)

Thursday, July 25, 2019

Listeria in smoked salmon - again.

The Department of Health in Australia is investigating three separate cases of Listeriosis apparently associated with smoked salmon.  There have been two deaths and one

This is not a reason to stop eating smoked salmon, or even cause for a massive recall.  There is a couple of things we all need to know.

Firstly, no specific smoked salmon product has been recalled.

Secondly, the three cases were in three different states and occurred over the period 22nd February to 7th June.  i.e. they were well separated both in location and time.

Thirdly, and probably most importantly, all three patients were over 70 years old and had other health conditions that may have predisposed them to infection by Listeria.

This is a reminder that people who may be susceptible to listeriosis should avoid foods that are known to carry higher risk of infection.

See:  and search the blog using keyword Listeria.