Sunday, April 11, 2010

Spuds - exactly what was the vitamin C level in last nights nosh?

Potatoes are thought to be a major source of vitamin C in the western diet. The potato promoters state that new cooked potatoes, with skin on, have 15 mg of vitamin C per 100 g. Without the skin this drops to about 4 mg per 100 g. So practical application tip - always leave the skin on potatoes - even for mashing them. 

Nutrient levels in food range widely, thus making a mockery of food tables. An example of this is potatoes grown in Norway (didn't know they did grow them until I read the study). What they found was:
  • That same potato variety varied from 8.4 - 18.7 mg / 100 g depending on location. To put it another way there is 220% variation in vitamin C content due to farming location
  • Different breeds of potatoes had different levels of vitamin C. Breeds had averages of 9 to 19 mg / 100 g. the highest level was more than twice the lower level. (and these are averages, individual samples would add extra variation).
  • Furthermore the breeds were affected differently by different locations. Depending on location this variation was approximately 6, 8 or 10 mg / 100 grams.
  • Vitamin C levels decreased with storage. They compared fresh potatoes to three month old cool store potatoes. They found that the absoulte lose was  approximately 4mg of vitamin C / 100 g. However due to the different starting levels of vitamin C the losses were 36%, 33% and 26%.
So yes the vitamin C level in potatoes are about the 15 mg level quoted at the start of the article. However there are significant effects of growing location, breed and storage. Given that nearly all the vitamin C is in the peel you could make high value hash browns from food scrapes! Nearly all the potato crisp and deep fried potato chips have been peeled. Thus there must be a mountain of peels that go to waste (likely sold as animal feed). Therefore you could purchase these scraps and turn them into a high value nutritional food.

Reference: Nordbotten et al Sampling of potatoes to determine Representative values for nutrient content in a national food composition table. Journal of food composition and analysis vol 13 pg 369, 2000.
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