Wednesday, April 5, 2017

Fermented foods - tasty, safe and good for you.

Recently, one of my regular readers watched a BBC television programme on 

"Which foods can improve your gut bacteria?" narrated by Dr. Michael Mosley.  She wrote and asked me  to comment on the safety of such foods, how they should be stored, plus potential risks of manufacturing them at home.

Traditional, naturally fermented foods have been around for hundreds, if not thousands, of years.  These days, we tend to relate the term "Fermented food" to sauerkraut, kimchi, tempeh, or perhaps yoghurt and cheese.  However, the Egyptians knew about wine production 5,000 years ago (though they didn't know that yeasts were involved).

Fermentation is a natural process, carried out by bacteria, yeasts and occasionally moulds, that actually preserves raw foods, often by production of acid or alcohol, which prevent spoilage.  Of course, the preserved food sometimes bears little resemblance to the original.  We enjoy these foods because the fermentation changes the flavour and texture of the raw material, often increasing the complexity.

We now know that our gut microflora, now called the gut biome, can be influenced for the better by consumption of some fermented foods.  The microorganisms that carry out the fermentation can sometimes pass through the very acid conditions of the stomach and may be able to colonise the gut wall, perhaps displacing undesirable bacteria, though some just pass through, having a transitory effect on the gut biome.  They can help with traveller's diarrhoea or lactose intolerance.

Dr. Mosley and his team investigated the claims for such benefits by setting up three groups to consume various fermented products for four weeks and looked for changes in their gut bacteria.  You can read about it in the link above.

The team also tested the products to determine the range of bacteria in them.  Home-made fermented foods tended to contain a diverse range of bacteria, while commercial products, which may have been pasteurised, often contained very few.  Thus the flavours and textures would be similar, but the potential health benefits of the microbial populations had been removed.

Over many years of teaching food microbiology, I made sauerkraut with my students.  It's an easy fermentation to carry out, requiring only finely shredded cabbage and about 2 - 2.5% salt packed in a suitable container.  Air must be excluded to prevent the growth of moulds on the surface of the kraut. We followed the fermentation daily, counting and identifying the bacteria taking part, and measuring the titratable acidity and pH.  

We always found a succession of bacteria.  The undesirables, like Escherichia coli and other coliforms disappeared within the first couple of days as lactic acid bacteria produced lactic acid and reduced the pH.  Leuconostoc  species, found on the inside leaves of the cabbage, would begin the acid production, giving way to Lactobacillu plantarum and eventually L. brevis.  The final pH of the sauerkraut is around 3, which is plenty low enough to prevent the growth of pathogens.

The kraut can be stored in the refrigerator for a short time, but must be protected from oxygen to prevent spoilage.  If you would like to make some at home, download the original recipe, written by Carl S. Pederson in 1939.  He studied the fermentation extensively over many years.  There are many other, more recent recipes available on-line and much has been published in the scientific literature on the microbiological changes that occur during fermentation.  You can also find many recipes for kimchi on-line.

Are home-made fermented vegetables safe to consume?  Yes, provided that the fermentation has produced sufficient acid to lower the pH to around 3 to 3.5, which will prevent the growth of pathogenic bacteria.  The finished product must not be allowed to go mouldy, since moulds can metabolise the acid and raise the pH to levels at which pathogens could grow.  My son, who is an electronics engineer, has successfully made sauerkraut and kimchi at home.  You don't need to be a microbiologist or food technologist to make safe, tasty fermented foods!

Saturday, March 18, 2017

Food Trash Writing

Once again, an article about fast food has been posted on several “healthy living” websites and reposted on FaceBook.  On this occasion, HealthZone.Tips writes about McDonald’s french fries under the title:
When You Find Out What is in McDonald’s French Fries, You Will Be Disgusted!

Whatever you think about fast foods, you would expect the article to be accurate and not merely sensational.  The article claims that McDonald’s puts more than ten ingredients into its fries, and quotes Grant Imahara (Myth Busters), suggesting that the fries are not really potatoes!  This article is just plain scaremongering, and I wonder what is the author’s motivation.

The post lists the main ingredients, noting that there are other components:

    Canola oil
    Soybean oil
    Hydrogenated soybean oil
    Natural beef flavour
    Hydrolysed wheat
    Hydrolysed milk
    Tertiary butylhydroquinone (TBHQ)

and states that “The three offenders on the list are TBHQ, dimethylpolysiloxane and hydrogenated soybean oil”.

Notice that there is no mention of the amounts of these “offenders” in the fries, as you would find on a food label - usually as grams per 100 grams and grams per serving. 

So let’s look at these three components.

Tertiary butylhydroquinone E319, an anti-oxidant, is used as a preservative for unsaturated vegetable oils and also for many edible animal fats.  Both the FDA and the Scientific Panel on Food Additives, Flavourings, ProcessingAids and Materials in Contact with Food of EFSA  regard TBHQ as safe when used at the permitted levels. The Panel stated that, “Based on the data reviewed, the Panel concluded that TBHQ is not carcinogenic and that further genotoxicity studies were unnecessary.  TBHQ is used in many foods and also in perfumery. In a medium serving of french fries (133 g) there is about 22 g fat and thus about 4.4 mg TBHQ.  Using the EFSA acceptable daily intake (ADI) of 0.7 mg/kg body weight for a 70 kg human, this equates to about 9% of the ADI, which itself has a 100x safety factor built in.

Dimethylpolysiloxane E900  is a polymeric organosilicon compound, used as an antifoamer in cooking oils to prevent foaming and splatter.  FSANZ permits a maximum of 10 mg/kg of the final food.  The WHO summarised a number of studies of the effect of DMPS on humans and animals with “None of these studies has revealed any significant toxicity. The metabolic studies, including those in man, indicate that the orally administered dimethylsiloxanes are mainly excreted unchanged in the faeces.”  It is difficult to obtain data on levels of DMPS in final foods, but using data from Five Guys, I estimate that the level in the frying oil could be around 0.004% and in the fries, the final level could be around 0.9 mg in a medium serving of fries, or 6.8 mg/kg fries.

Hydrogenated soybean oil  is used in the production of margarine, shortening, and salad and cooking oils.  The US FDA Committee on GRAS substances concluded that “There is no evidence in the available information on hydrogenated soybean oil that demonstrates, or suggests reasonable grounds to suspect, a hazard to the public when it is used as a direct or indirect food ingredient at levels that are now current or that might reasonably be expected in the future”.

For those readers who live in New Zealand:  I consulted a fats and oils chemist.  He told me that 
They don’t use hydrogenated soy in Nz and never have done; the oil is now monounsaturated canola/sunflower oil.  TBHQ is no longer used.  As far as he is aware, the oil blend no longer contains DMPS, and even when it was used, the level was around 1ppm.

Tuesday, February 7, 2017

Brexit, Trump and food safety fears

The decision by Britain to leave the EU would not immediately spring to mind as a cause for concern over food safety.  Neither would the election of Donald Trump as President of the USA.

However, decisions made in haste or with little forethought can often have unexpected consequences.

It now appears that a trade agreement between the US and UK might result in food products banned in the EU being imported into the UK.  This might include beef from cattle implanted with growth hormones, chlorine-washed chicken, and unlabelled genetically modified (GM) foods.

This has resulted in a furore on FaceBook, though the concern about chlorine-washed chicken is a little surprising.  Chlorine rinses are used extensively in the food industry to reduce surface contamination on vegetables, during chicken processing and for sanitation of equipment during food processing.

Of course, chlorine is also used in water treatment for decontamination of potable water supplies where UV treatment is not used, perhaps for cost cosiderations.

Over the years, a lot of work has been done on the effects of chlorine in foods.  At the levels used for practical decontamination, there is no risk to human health, though some chemical changes are inevitable. 

If you are keen to follow up on this, The Institute for Environmental and Scientific Research Limited, (ESR) in New Zealand produced a report in 2008 for the New Zealand Food Safety Authority:  

It is available on-line at:

The report stated that "In conclusion, no safety issues were identified due to the use of chlorine dioxide and ASC for poultry carcass disinfection. Chlorination reactions appear to be insignificant for these compounds and oxidation reactions do not appear to result in significant alteration of the fatty acid and amino acid composition of poultry carcasses".   Further, the authors stated " ...we consider that there is insufficient evidence to justify further investigation of the risks to human health from the use of these disinfection chemicals in poultry processing".