Between harvest and plate… where do the vitamins and minerals go?

[12 March 2010 - 09h55]

Tomatoes, courgettes, leeks, turnips… the vegetables we eat are picked, then stored, chopped up and finally cooked before they eventually land on our plates. Yet these stages are often fatal to the vitamins and minerals they are bursting with… at the time of picking!

Micronutrients are fragile. Air and light, for example, are enough to destroy a percentage of minerals and vitamins. In the case of fresh vegetables, it is best to consume these within 72 hours of purchase to avoid oxidation. This, though ideal, is often unachievable as everyday life means that we have to “stock up” during our one weekly shopping trip.

To avoid such damage, don’t cut up cucumbers and tomatoes until the last minute. Then use them straight away, all in one go, because once they have been cut, oxygen gets into vegetables and all their vitamins are lost in a matter of hours. When you wash vegetables, don’t leave them soaking in water. This will cause them to lose their hydrosoluble vitamins – group B vitamins and vitamin C in particular.

For the same reason, cooking in water is not really recommended as a large percentage of their vitamins and minerals dissolves in the water! Of course, there’s no reason why you shouldn’t drink this cooking liquid or use it to make gravy and sauces. Liposoluble vitamins – vitamin A, D, E and K – are more heat resistant. This means that carrots lose only 10% of their beta carotene (or provitamin A) when they are cooked in water.

Steaming is the best way of preserving vitamins and minerals. As for pressure cooking… cooking “under pressure” at over 100°C speeds up oxidation. Very few vitamins can withstand such a temperature. Microwaves, like steaming, have hardly any detrimental effect on minerals. And if you don’t have fresh vegetables to hand, frozen ones are a good alternative: rapidly processed after harvesting, frozen vegetables lose “only” 20% of their vitamins. By comparison, tinned and bottled vegetables lose between 30% and 40% of their vitamins. However, they retain all their fibre and other nutrients!

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