Wednesday, April 7, 2010

Enlightening vegetables

For the best retention of nutrients in vegetables, the common view is that they should be eaten as soon as possible after harvesting. Certainly, they don’t want to spend too long in the supermarket. That view may have to change, for spinach at least.

Photosynthesis continues under light

After harvesting, fresh produce is not necessarily “dead” or “dying”. A recent study by the US Department of Agriculture found there was a benefit to leaving spinach under supermarket lights.

Plants have two forms of chlorophyll, helpfully called A and B, one absorbing the blue/violet light and the other absorbing the red/yellow, while the plant reflects green light so vegetables like spinach look like spinach. The fluorescent lights used in supermarkets mimic the spectrum of natural sunlight. The light exposure, particularly in the blue and red range of the spectrum, allows the process of photosynthesis to continue, encouraging the production of vitamins, especially B vitamins.

Folate & vitamin C benefit

In the study, spinach was kept in clear plastic containers at 4ÂșC and exposed to light continuously for up to nine days. In that time the vitamin C levels rose over three days then returned to the original level over the next six days. When spinach is kept in the dark, folate levels decline by 30% in a week. This loss was prevented when stored under light.

All bio-active compounds benefit

Overall, spinach stored under continuous light had higher levels of all bio-active compounds compared to spinach kept in the dark. Senior research Gene Lester suggests that consumers should consider grabbing produce from the front of supermarket display cases that are kept under light.

I don’t think this research will make any practical difference to how you choose or store vegetables, except that you might now no-longer assume that supermarket fluorescent lighting, or even sunlight, causes nutrient loss. You should still be eating your veggies in the days soon after purchase. It is still wise to keep veggies in the fridge as the cool temperature slows nutrient loss and keeps them fresher for longer. Maybe the future will see the veggie crisper have a fluoro light.

What does it all mean?

There is am assumption that nutrient levels start declining once fresh produce leaves the farm. I have worked for three different fresh produce growers in the last five years. We know that fruit like bananas and avocadoes ripen after harvest without a significant drop in nutrition. Expose mushrooms to sunlight post-harvest and their vitamin D levels dramatically increase. And now we know that leafy veggies, like the spinach, continue to manufacture vitamins under fluorescent light.

Excuse the clichĂ© – nature is full of surprises, or, put another way, nature can make a mockery of your assumptions.

Reference: Journal of Agricultural & Food Chemistry 2010; 58: 2980-2987

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