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We often read in books and Wikipedia that certain fruits or vegetables contain certain amount of vitamins, minerals and other elements.

An example can be seen on Beetroot in the box with nutritional value.

I can imagine that these numbers are only averages and certain minimum ideal conditions must exist for the vitamins to be present. We often hear that supermarket fruit and veg may not in fact contain the nutritional value that is claimed. The soil may be contaminated. When the product is stored and transported part of the vitamins and minerals may be lost. So supposedly healthy food may not in fact be all that healthy. I was little upset when I read that carrot juice may be nitrate concentrate instead of healthy juice.

It's good idea to grow your own fruit and vegetables and have control over your own food.

And now the question: How is nutritional value measured and how are ideal conditions identified? What is the science dealing with these topics?

If I grow my own fruit and veg how can I perform my own measurements? Is there any literature dealing with these topics?

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you ask about literature - i can give you a number of books dealing with the iniquities of commercial food production and questionable supermarket practices - but i'm not sure that would be on topic here. Nor would it answer your question, if your question is how do I analyse my own fruit and veg? –  Tea Drinker Nov 4 '11 at 11:13
    
Beyond just differences in how they're grown, there can be big differences between cultivars as well. I've seen cultivars of broccoli and tomato advertised as having higher than average levels of some nutrient or group of nutrients. –  bstpierre Nov 4 '11 at 11:36
    
The question is about the standard methods and procedures of finding out nutritional values that are presented in the books and this implies that reader should be able to ascertain that his home grown products satisfy this values or not (because of bad soil, weather, etc.) and what steps to do to approach the right values. –  xralf Nov 4 '11 at 12:08
    
@TeaDrinker Thank you for question edit, I only corrected the heading to match better the question. –  xralf Nov 4 '11 at 12:10
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I would just like to point out, in a friendly as possible way, that this question is out of scope for G&L. But totally in scope for biology or biochemistry. There's an Area 51 proposal for biology you might like to commit to here: area51.stackexchange.com/proposals/12502/biology –  Lisa Nov 8 '11 at 23:10
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1 Answer 1

An article at slate.com describes how food labs measure calories, and where the calorie numbers come from on food labels. It's good for background info on the process.

Unless you have a remarkably well-stocked and well-equipped lab in your basement, you're not going to be able to test vitamin content at home. As far as I can tell, literature dealing with these topics is aimed at industrial users and/or academic papers. See, for example, this abstract on testing vitamin D using liquid chromatography [pdf].

Furthermore, you can't even really trust the labels on the foods you buy to be accurate: producers can just use the values from government tables. So if there are differences, they won't necessarily be reflected on the label of a particular batch of food that you've purchased.

I know of no literature regarding "home grown" vs "supermarket", but there is info on the nutritional content of organic vs conventionally grown fruits and veg:

  • This article at the Mayo Clinic says "a study" (uncited) found that organic and conventional are comparable for nutrition.
  • The same Mayo Clinic article says that the USDA (uncited) has found that organic foods contain significantly fewer pesticide residues than conventional.
  • This report [pdf] for the UK Food Standards Agency might be the one referenced by the Mayo Clinic article above. They surveyed the literature and found:

    There is no good evidence that increased dietary intake, of the nutrients identified in this review to be present in larger amounts in organically than in conventionally produced crops and livestock products, would be of benefit to individuals consuming a normal varied diet, and it is therefore unlikely that these differences in nutrient content are relevant to consumer health.

    There were small differences in the content of some things in some foods.

  • Another survey study out of New Zealand [abstract] finds that the "findings are inconsistent".

  • Yet another survey study [abstract] found that there are significant differences in the levels of some nutrients.

Local (backyard!) food may be more nutritious for a few reasons: cultivars are selected for taste and nutrition above yield and transportability, processing is reduced or eliminated, and damage from transport is reduced or eliminated.

Unfortunately I don't see any literature that can give you concrete guidance or hard numbers.

For what it's worth, my personal experience is that home-grown and locally-produced food has far superior flavor and texture compared to supermarket food from "far away". (And we don't have to worry when there are massive recalls on lettuce, tomatoes, beef, eggs, etc.)

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Vitamin C is something that can be tested at home - I've judged far too many Vit.C science fair experiments! But yes measuring most of these nutrients requires equipment,reagents; & to do it accurately you need a lab. Garden food can be as fresh as it gets - so everything being equal it will be the most nutritious, but remember that cooking also destroys&removes a lot of vitamins. Local/garden food also has seasons - something we remember from our childhoods! –  winwaed Nov 4 '11 at 13:19
    
Good point on vitamin C... but given that it's really easy to get enough vitamin C, it might be the least important nutrient to measure. –  bstpierre Nov 4 '11 at 18:08
    
@bstpierre Thank you, I need some time to read it and process it. –  xralf Nov 9 '11 at 8:29
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