The French, who know a thing or two about food (not to mention the Can-Can), are happy to proclaim the nutritional virtues of canned food, writes Peter Crosskey
Two hundred years ago, Nicolas Appert invented time travel for food. A case of his bottled garden peas, picked and bottled on his Brittany smallholding at the turn of the eighteenth century, came to light in Paris a few years ago. At the time, French breakfast television presenter William Leymergie sampled one live on his show.
Last Tuesday Leymergie hosted a national event dedicated to this French national hero. Appert's contribution to food preservation gave us the bottled food that sustained Napoleon's armies as they marched across Europe, as well as the canned food that fed explorers tramping to and from the poles, and will sustain us for years to come in many new guises, such as pouches and retortable cartons.
A former quartermaster to Napoleon, Appert discovered that if he packed raw ingredients into glass jars, sealed them hermetically and boiled them, the cooked contents would last for years. Freed from the seasonal constraints of finding fresh food wherever his troops went, Napoleon gratefully awarded Appert a prize of 12,000 gold francs in January 1810.
Today's canning processes bear little outward resemblance to Appert's kitchen table techniques, although these are still practised in rural households across Europe to this day. But the discoveries that are being made in appertised food go further than many of us would credit.
Thanks to the research director at the French national health and medical research institute INSERM, Dr Jean-Marie Bourre, much more is being discovered about the real nutritional value of canned foods. "We know more about the structure of DNA than we do about what we eat," he said at the 11th national appertised food day conference.
For the past few years he has been double-checking the work of a research team building a nutritional database, covering the core French canned food repertoire. Their findings show that cans bring healthier foods to our tables than we might have thought.
"We now know that there are nutritionally valuable compounds in products like canned tomatoes which you won't read about in the ingredient listing. We are filling in those gaps," says Dr Bourre.
The cooking process used while canning tomato products helps to release an antioxidant called lycopene. This was first identified just over five years ago, by researchers in the US working on ketchup.
Antioxidants can help the body by neutralising the harmful effects of chemicals that might otherwise build up and cause a range of conditions, including cancers and circulation disorders.
When our bodies come under attack from infection, part of our natural response is to generate free radicals, molecules in which an oxygen atom is looking for something to react with.
At high concentrations these free radicals can damage cell walls and cause the kind of DNA alterations associated with cancer cells. By bonding with the available oxygen, antioxidants can help to defuse the situation.
Many of the antioxidants we need to protect ourselves come from what we eat and cannot be made by our bodies. Lycopene is one of these and is probably one of the keys to the success of the Mediterranean diet.
Much of this locked-in nutritional value is already reaching Irish shores. Five years ago, Ireland imported just 60 tonnes of canned tomatoes, while last year the figure climbed to 1,169 tonnes.
A study cited by the World Processing Tomato Council found that lycopene can be absorbed 2.5 times more effectively from tomato paste than it can from fresh tomatoes. Although it can also be found in water melons, papaya, pink grapefruit and rosehips, tomatoes account for 95 per cent of our dietary lycopene intake.
Because lycopene dissolves in oil, but not water, we can absorb more from eating cooked dishes like ratatouille than we would from eating the equivalent quantity of fresh tomatoes. A can also protects lycopene from the harmful effects of light and air until we are ready to eat it.
In the case of the humble tomato, few of those sold fresh by retailers have had a chance to finish ripening on the vine. The result is that they have not finished laying down their full lycopene potential: the lack of colour can be quite marked.
When tomatoes are picked for canning, they need to be fully ripened on the plant for the peeling process to work properly. They are also canned within hours of leaving the fields. Dr Bourre's results show that there is 70 per cent more available lycopene in canned tomatoes than fresh. "Our bodies just can't extract it as efficiently from fresh tomatoes," he explains.
Although a high proportion of the heat-sensitive vitamin C is lost during cooking, this is readily available elsewhere. Dr Bourre also argues fervently that we need greater diversity in our diets.
Our hunter gatherer digestive systems have not evolved as rapidly as our lifestyles: where once we would have eaten hundreds of different foods, the breadth of our intake has shrunk radically. This lack of dietary diversity is a major threat to health in the industrialised world, on a level with smoking. "There are tens of thousands of cases of cancer and all sorts of heart conditions which could be avoided with a more diversified diet," urges Dr Bourre.
Even the French health ministry is starting to recommend canned fruit and vegetables as an additional source of fibre. In Britain, under pressure from a less well-informed Food Standards Agency, Heinz has withdrawn the Five-a-Day logo from its products in the UK. The French image of canned food is a very positive one and they eat a kilo per person per week. The hotel and restaurant trade in France is happy to use canned ingredients where appropriate, because of the consistency achievable when cooking a recipe. This is not a national foible: it is because appertised food does rather more than it says on the can.