A little history of smoked foods

This story actually began many years ago when I had noticed a personal and definitive link between ingesting smoky BBQ sauces and crippling stomach pains. The remedy was simple as it just meant avoiding such BBQ sauces but an indiscreet dinner of smoked pork knuckle in Porto, Portugal, recently brought back the fury of stomach cramps again.

A little history of smoked foods

Let us start by recounting the long history of smoked foods, in particular meat and fish. It would appear that Paleolithic humans had been eating smoked flesh since the discovery of cooking with fire, perhaps some 400,000 years ago - the smoking of meats was initially accidental while they grilled food over wood fires but they could not have failed to notice that smoked meats decay slower than cooked meats.

This is primarily due to the compounds and aldehydes in smoke which confer a degree of antibacterial and antifungal protection to the meats. This reduced rate of decay allowed meats to be stored, conveniently transported and even traded.

As a result, for many thousands of years, early humans associated smoky flavours with good, edible food - and this association during a significant period of our evolution has never really left us. Smoking flesh was so prevalent that many communities in medieval Europe (5th to 15th century AD) had private or public smokehouses to smoke and store fish and meat.

Today, a stroll through any large supermarket will lead you past sections of smoke-flavoured foods such as salmon and trout, bacon and ham, kippers, sausages and salamis, cheeses, sauces, vegetables (eg. smoked garlic), crisps and even wines. Many modern grills have hoods to retain the smoke when grilling food over wood-based flames - simply because humans really enjoy the flavour of smoke in foods.

PAH!

The compounds that flavour smoked meats and smoky sauces are usually derived from the thermal decomposition of wood in a low oxygen environment (a process known as pyrolysis) - it is how charcoal is made from wood and the vapours arising from pyrolysis of certain woods are used to smoke food. The actual smoke compounds found in these vapours are called Polycyclic Aromatic Hydrocarbons (PAHs) and it is painfully clear that I have a negative reaction to one or more of the PAHs in certain smoked foods.

PAHs are a diverse group of several hundred organic (carbon-based) compounds - and they are interesting in that they are also studied by astronomers as PAHs constitute a significant proportion of the carbon out there in the universe.

This space study is done by analysing the characteristic infrared spectra emitted from individual PAHs after being battered by cosmic ultraviolet radiation.

Closer to earth, PAHs found in soot have been linked to cancers since the 18th century - and more recent research confirms that many PAHs can induce tumours and other mutagenic (damaged DNA) diseases in test mammals.

In fact, I cannot find a single PAH that can be deemed wholly safe for mammalian consumption in quantities exceeding the maximum recommended amounts - this is of course also true for almost all food additives, but there is an extra twist regarding PAHs which will be explained later.

However, to be clear, the amounts of PAHs permitted in smoked foods sold in the shops should always remain below the thresholds where they get problematic - so eating commercial smoked foods should not present any significant danger for most people.

Chemically, PAHs are compounds that consist of only carbon and hydrogen atoms, bonded as 2 to 7 "aromatic" rings in three types of molecular arrangements: angular, linear and clustered.

Although they are called "aromatic", it is not because they smell nice or have any smell at all - in chemistry, aromatic molecules are cyclic, planar (or flat) structures which exhibit a property called resonance which allows them to link up in stable configurations. Examples of 4-ring PAHs are chrysene (which is angular), naphthacene (linear) and pyrene (clustered).

The most carcinogenic PAHs appear to be those with 4 to 7 ring arrangements but it is likely that all PAHs have some negative health aspects, depending on dosage.

Although this article deals primarily with PAHs in foods, it should be noted that most PAHs are formed due to the incomplete oxidation of organic materials - this is not just wood in smokers or barbecues but also from other human-related activities such as burning fossil fuels, industrial processes, rubbish disposal, forest fires, tobacco smoking, et cetera.

Some of the seriously toxic elements of smog in certain major cities are PAHs, and the pollutants of large swaths of land, plants, rivers, lakes and seas are also PAHs - it is impossible to avoid PAH contamination in some form or another in the modern world.

In case you are wondering how come PAHs are so dangerous, it is because of their ability to bind (via other reactive molecules) to cellular macromolecules such as DNA, and therefore disrupting or damaging the cell structure. This damage is replicated and exacerbated when the cells subsequently reproduce, potentially causing tumours and mutagenic diseases.

As confirmation, recent experiments have detected enhanced levels of the P53 protein in the blood of people who have just ingested PAHs - P53 is also known as the tumour suppressor gene and indicates that the body is trying to limit DNA damage caused by eating PAHs by spurring an increase of P53 proteins.

Smoking via smoke

Coming back to the subject, it would be reasonable to assume that smoke compounds get into meats and food by the simple process of allowing food substances to comingle with and absorb the smoke vapours arising from heated woods in a smoker or covered BBQ.

To some extent, this is correct though it has to be mentioned that not all woods are suitable for smoking food. Harder woods like oak and hickory are best for meats and lighter woods such as those from fruit trees such as apple or cherry are better for fish and poultry - it is also possible to mix different woods for smoking, which is what some specialist restaurants do for their unique flavours.

Some woods, such as pine, cedar, sycamore, eucalyptus, and et cetera, should never be used for smoking food due to their high resin content or toxic compounds in the sap which render the smoke poisonous.

Smoking via water

What is also true but much less well-known is that the majority of modern smoked foods have never seen the inside of a smoker or barbecue. These smoked foods are given their smoky flavour by the application of liquid smoke - which is very probably the substance I find problematic.

Liquid smoke was originally known as wood vinegar, later as pyroligneous acid, and is derived quite simply by extracting the vaporised compounds from the pyrolysis of certain woods via condensation.

Water is then added to the condensate to separate it out into three distinct sections. The top section is where the lighter waxes and phytosterols (plant oils) are contained, while the bottom section is a dense, often pungent goo known as wood tar. Only the middle section is used for food smoking, being a water-suspension blend of PAHs, carboxylic acid, aldehyde, and phenols.

The reason why liquid smoke is probably the cause of my negative reaction is because unlike actual smoke in a smoker, practically all of the PAHs are collected in the condensate solution - whereas wood smoked foods will accumulate only some of the PAHs, usually mainly on the surface of the food from the lighter compounds in the smoking vapours swirling around.

In short, liquid smoke contains more PAHs and in denser concentrations - and this is exactly what commercial food producers want.

The use of liquid smoke reduces the natural wastage caused by the dry, heated environment in food smokers, where meats and fish can lose a significant degree of moisture - thus reducing the saleable weight of the smoked product.

It also requires more time and labour to load and unload the food items for smoke treatment.

With liquid smoke, there is no loss of moisture or weight and it delivers very little difference in taste to undiscerning consumers - resulting in more profits, simplified processing and time savings for the producers.

A couple of questions

The fact that smoked foods decay slower than ordinary cooked foods indicates additional chemical processes are happening in smoked foods - so a valid question might be: is it a problem if we ingest smoked foods?

The historical evidence suggests that humans tolerate foods smoked with real wood pretty well, otherwise we would not be around enjoying BBQs. So a better question might be: is it a problem if we ingest modern smoked foods which are treated with liquid smoke?

The answer is somewhat complicated and is related to the extra twist mentioned earlier about the maximum recommended quantities of PAHs allowed in food.

But the easy part is that if you ingest an excessive amount of PAHs, then your chances of developing cancers and mutagenic diseases will increase pretty significantly, based on numerous tests on mammals.

Food treated with PAHs, including both real smoke and liquid smoke, are rated as Group 1 carcinogens by the WHO. As you might know from earlier articles, Group 1 carcinogens include mustard gas, asbestos and plutonium though the death rates from PAHs are not nearly as high as for those other agents - mainly because it is usually difficult to eat so much PAHs on a frequently consistent basis.

Statistically, eating commercial smoked foods in "normal" amounts can raise the risk of bowel cancer from 6 per cent to 7 per cent - however, if safety limits are exceeded, then in test mammals, the risks increases rapidly, possibly even exponentially for certain types of PAHs.

How to measure PAHs

And this is the problem. PAHs are a diverse group of several hundred compounds so to derive a standard for measuring PAH food safety, it is impossible to assay individually every PAH in, for example, a piece of smoked salmon. The industry solution was to develop a series of "PAH profiles" to assess the levels of PAHs in food, in the atmosphere, in soils, et cetera.

The technique is rather simplistic. For each PAH analysis situation, a select number of PAHs are picked to indicate the overall level of contamination.

So for air pollution in Western Europe, the PAH most usually measured is benzo[a]pyrene (BaP) along with around 30 other PAHs, usually linked to vehicular and industrial pollution. This makes up the PAH profile for air quality monitoring, even though there are often hundreds of other PAH pollutants in the air.

Breaches in any of the limits assigned to the PAHs in the air profile are reported. It is like having a country represented by a government. The actions of an administration won't always reflect the wishes of the citizens, but other countries will judge the nation by its government.

For smoked food in Western Europe, BaP is also among the 16 PAHs out of hundreds tested for food safety - the rationale for this profile selection is the higher carcinogenic propensity of these 16 PAHs.

As for air monitoring, a breach of any of the monitored PAH levels in the PAH food profile has to be reported - but there is yet another twist to this somewhat general methodology.

Research has shown that some PAHs need to combine and interact with other PAHs and compounds before becoming more severe health issues - and these combinations are not monitored.

For example, PAHs which have passed through the digestive system are turned into PAH metabolites - and certain PAH metabolites such as bay-region diol epoxides have been cited as significant health dangers.

Another downside is that other PAHs are not checked, so a severe spike in an unmonitored PAH can go undetected, even if it reached dangerous levels.

Furthermore, studies in mammals have indicated that individual genetic differences also play a significant role in carcinogenicity and mutagenicity - so there are many varied and complex factors to consider before an authoritative objective assessment of PAH safety is feasible.

But for the moment, what is currently in place is about the best that can be achieved given the level of knowledge and resources.

For my personal situation, gastrointestinal irritation is the main symptom after ingestion of one or more problematic PAHs. And based on current regulations and data, there is no way to find out which PAH or combination of PAHs is the culprit - PAHs are not even listed as food ingredients.

All I am reasonably certain of is that it has something to do with liquid smoke, for wood-smoked foods and BBQs are always fine. It is irritatingly similar to a scatty witness of a car accident - the only recollection is that the cars hit each other at about the same time.