When a tomato is a just tomato

Image of tomatoes by Rachel Andrew via Flickr. Text added by Anastasia Bodnar.

Another paper comparing organic and conventional tomatoes (sort of) was published in PLOS One on 20 February 2013: The impact of organic farming on quality of tomatoes is associated to increased oxidative stress during fruit development.

In contrast to so many other studies that aim to see if there is a difference between conventional and organic produce, these researchers used the same cultivar: Débora, a typical tomato variety used in Brazil. We know that different varieties can vary a lot in things like mineral and antioxidant content. So, removing this variability from the experiment helps a lot.

Unfortunately, they didn’t do every thing in a way that would present the most  objective results, in my humble opinion.

Tomato nutrient content is based on density

Tomatoes, like many other fruits, can vary in water content based on the environment in which they were grown. As the authors of this paper say: “Mass and size were about 40% higher in fruits from conventional growing systems than in fruits from organic farming. Such differences could originate either from differences in nitrogen availability or from limitations to growth imposed by the more stressing conditions prevailing in organic farming.” In other words, if the plants are more stressed out (as they often are in organic farming, at least in theory due to higher pest pressure and less applied nutrients) then they will grow smaller, more dense fruits. Perhaps the title of the paper should be “The impact of organic farming on density of tomatoes is associated with increased oxidative stress during fruit development”.

The researchers “correct” for the difference in mass, which means that tomatoes that are less dense will look like they are more nutritious. Why does this matter? Well, are you going to eat a serving of tomato based on mass, or are you going to eat a whole or half of a tomato? Sometimes a tomato is just a tomato, not a health food supplement.

The researchers don’t seem to think so, though, concluding: “Our work clearly demonstrates that tomato fruits from organic farming have indeed a smaller size and mass than fruits from conventional growing systems, but also a substantially better quality in terms of concentrations in soluble solids and phytochemicals such as vitamin C and total phenolic compounds.” Except, we know the “quality” depends on the density!

If you re-correct the values, it turns out that there isn’t much difference between organic and conventional tomatoes, and as many studies have shown previously, some nutrients are higher in organic while some are higher in conventional. Conclusion: choose organic if that is what you prefer, but nutritional differences are not a good reason. For nutrition, simply eating more fruits and veggies is the way to go!

The values below were not corrected. As expected, the organic tomatoes were a little bit smaller and weighed a lot less. I’ve bolded the higher of each pair.

Item Units Organic Conventional
Size centimeters 4.20 5.46
Weight grams 75.15 124.93
Citric acid % of total acid 0.36 0.28
Total chlorophyll soil plant analysis development 40.18 40.29

These values were corrected, some by the fresh weight (which means the less dense aka more water filled conventional tomatoes will have lower values) and some by protein. The ones that were corrected by fresh weight I simply multiplied by the weight per tomato*. The protein values weren’t reported in the paper for some reason, but protein was also based on fresh weight, so I uncorrected those values by the fresh weight too (it’s not perfect, but should give us a decent estimate). Site note: along with the missing protein values, something called “thiobarbituric acid reactive substances” was described in the methods but the values were not reported.

Item Units Corrected Uncorrected
Organic Conventional Organic Conventional
Soluble Solids °Brix (concentration of sucrose w/w) 6.00 3.83 0.45 0.48
Total phenolic content mg galic acid equivalents / kg FW 556.50 232.50 41.82 29.05
Anthocyanins mg / kg FW 3.60 9.90 0.27 1.24
Yellow flavonoids mg / kg FW 43.70 25.70 3.28 3.21
Vitamin C mg / kg FW 264.70 170.90 19.89 21.35
Lipid peroxidation nnmol MDA / g FW 19.24 8.06 1.45 1.01
Total antioxidants umol Trolox / g FW 128.34 136.28 9.64 17.03
Phenylalanine ammonia-lyase µmol trans-cinnamic acid / mg P 11.43 4.79 0.86 0.60
Ascorbate peroxidase µmol H2O2 / min * mg P 1.01 0.98 0.08 0.12
Catalase µmol H2O2 / min * mg P 5.07 16.46 0.38 2.06
Superoxide dismutase UA / mg P 121.76 22.70 9.15 2.84

Cilantro Peach Tomato Salad by Margaret in Minnesota via Flickr.

As you can see, the number of values where organic is higher than conventional changes from 8:3 to 5:5, and many of the differences shrink. We also have to consider that we are not fruit flies being forced to eat only tomatoes. Tomatoes are just one part of a healthy diet, and we get nutrients from many sources. Antioxidants and flavnoids of various types are found in all fruits and veggies, so add some variety to that tomato salad to get variety in nutrients! How about some yellow peaches and red onion? Then add cilantro, basil, or mint! Yum!

What about yield?

While there are a lot of different things to consider when it come to agriculture (taste is a big one!), I’m always interested to know how efficient a system is with regard to land use. Using this tomato study, can we find out the yield of various nutrients per acre?

In this particular study, the  rows 1 m apart with 0.4 m between plants for both organic and conventional fields. It’s great that they were consistent, but unfortunately they do not tell us how many fruits each plant produced, so we can’t determine yield from the data. Happily, we can use data that the USDA collected about tomato yields.

The USDA collected organic tomato yield data during the last Census of Agriculture in the 2008 Organic Production Survey. The Economic Research Service collects conventional tomato yield data every year. Here’s how the tomatoes stack up (yield in tons):

  • Conventional (fresh) 14.79
  • Conventional (processing) 41.5
  • Conventional (total) 34.51
  • Organic (certified only) 23.05
  • Organic (certified and exempt) 22.32
  • Organic (exempt only) 1.81

Some of these values are a little weird… I’m guessing that the processing yields are so much higher because the tomatoes can be a bit uglier than those sold as fresh tomatoes. It’s frustrating that the organic tomatoes aren’t similarly separated out because we can expect a similar difference between fresh and processed in organic. Farms that are exempt for certification make less than $5,000 per year, possibly because their yields are so low. And what is up with the bizarrely high yield for conventional total in 1964? Anyway…

In 2008, the total conventional yield is over 10 tons per acre higher than certified organic yield. To put it another way, you’d need 1.5 organic acres to grow the same amount of tomatoes. Note: I used total conventional here because the organic numbers also include tomatoes for fresh and processing uses.


See Today’s Organic, Yesterday’s Yields by Steve Savage for a great summary of the USDA yield data.

Now, let’s look at the nutrients per acre.

Item Organic Conventional
Soluble Solids 10.39 16.51
Total phenolic content 963.97 1002.39
Anthocyanins 6.24 42.68
Yellow flavonoids 75.70 110.80
Vitamin C 458.52 736.81
Lipid peroxidation 33.33 34.75
Total antioxidants 222.31 587.55
Phenylalanine ammonia-lyase 19.80 20.65
Ascorbate peroxidase 1.75 4.23
Catalase 8.78 70.96
Superoxide dismutase 210.91 97.87

With such a small difference in nutrients per tomato, does it make sense to sacrifice so many nutrients per acre? Instead, let’s see some research in agronomic practices to see what can be done to boost nutrients while keeping yields high. A bonus: integrating key organic methods into conventional agriculture could have a positive impact on sustainability, and since there are far more conventional farms than organic, that translates to a lot of positive change. Another option could be choosing tomato varieties that accumulate more nutrients while maintaining high yields. How about some purple tomatoes?

.
Citation:  Oliveira A.B., Moura C.F.H., Gomes-Filho E., Marco C.A., Urban L., Miranda M.R.A. & El-Shemy H.A. (2013). The Impact of Organic Farming on Quality of Tomatoes Is Associated to Increased Oxidative Stress during Fruit Development, PLoS ONE, 8 (2) e56354. DOI:

There seem to be two articles about this particular paper already in Science Seeker: Stress Makes Organic Fruits Healthier Than Conventional and Organic Tomatoes Contain More Vitamin C Than Conventionally Grown. So, I’m late to the party but hopefully this post will be useful because I take a more skeptical and in depth view than these folks did.

Want to redo the analysis yourself? Here’s my Excel file.

* Yes, I ignored the metric units when I uncorrected. Otherwise, some of the values became very large and hard to compare. Plus it doesn’t matter if you are comparing 5 and 6 or 5000 and 6000 since the ratio is the same.

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Anastasia is a Board Member of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes! Learn more about Anastasia at about.me. Disclaimer: Anastasia's words are her own and views expressed do not necessarily represent the views of her employer(s). She is not paid to blog or conduct any social media activities. Any mention of a specific company or product does not indicate endorsement of that company or product.


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4 comments to When a tomato is a just tomato

  • Science Based RD

    Hi Anastasia,

    This is a very interesting study regarding organic vs. conventional tomatoes. After reading the study I do agree that it was well done in some areas but future research could use some changes. But that is not why I am writing.

    You state that “Well, are you going to eat a serving of tomato based on mass, or are you going to eat a whole or half of a tomato? Sometimes a tomato is just a tomato, not a health food supplement.”

    Yes, a tomato is just a tomato but not all tomatoes are equal. I hope you will agree that for tomatoes the quality for consumers based upon culinary aspects will vary depending upon many variables. The concentration of the various compounds measured, along with others not measured, each tomato may be different in taste and appearance. That will be important to some consumers, such as me (taste especially since I tend to have a very violent, well not that strong, taste aversion to most but a few types of tomatoes) and many of my nutrition classmates and culinary friends, but of course not to others.

    Additionally, to use myself as an example, I do not just simply use a whole or half tomato. I will often use mass, physical volume, or visual estimates based upon need when using a tomato for preparing a meal. I am assuming I am not the only person who uses any of those criteria for cooking or processing food.

    Regardless of my cooking technique or diet, those in populations that could use an increase in fruits and vegetables intake in their diet via fresh or processed foods the increase in density of nutrients, phytochemicals, and bioactive compounds *may* be beneficial to their overall health.

    Maybe at some point a study will (or have any been done that you know of?) examine how to best increase the density of nutrients while increasing yields.

    So much to learn, so little time.

    Jeff

    • You are right – not all tomatoes are equal when you are looking for a particular taste or texture. There is a lot of variety in tomatoes, mostly due to the specific cultivar grown. In general, if one is looking for more dense tomatoes they may find organic tomatoes are more likely to fit their needs. However, if a recipe calls for a certain mass of tomato and doesn’t specify density, one may have too much or too little tomato solids depending on if organic or conventional is used.

      Personally, I find that the season matters most, followed closely by cultivar. I look for conventionally grown heirloom tomatoes in season. That way I get superior taste and presumably more nutrients, but I hope the conventional growing methods increase yields to balance out the lower yields of heirloom cultivars. I don’t know if it matters, but I don’t cook with tomatoes a lot, so the raw taste is important to me more so than the cooking properties.

      One thing that I didn’t discuss in this post but that I would be interested to know is the sauce yield per acre for conventional vs organic tomatoes. If organic tomatoes are more dense, then less water needs to be cooked off to create a nice, thick tomato sauce. So, even though conventional processing tomatoes have a very high yield, the effective yield for sauce may be closer or even lower than organic.

      Still, while this information may be interesting and even useful from agronomic or culinary perspectives, I do not believe the evidence shows that organic tomatoes are superior nutritionally, at least not enough to be biologically significant. I’m not a dietician, but I’m not able to think of any person who would benefit from such a tiny increase in a few tomato nutrients who would not be better served with a simple “eat more fruits and vegetables” recommendation. If one is consuming a variety of plant foods, then they will get enough antioxidants, minerals, and vitamins from the different sources. One should not depend on just one food as a source for any nutrient.

      I find it dangerous when the media and celebrity doctors recommend organic as more healthy for whatever reason because the implication is that conventional is less healthy. This could have a negative impact on consumption of fruits and vegetables for most people because the majority can’t afford the increased cost of organic.

  • Science Based RD

    I agree that a tiny increase in nutrients and bioactives may be insignificant. I do think that for people that don’t eat a wide variety of plant foods, as too many people do in our society, that if there was to be in increased concentration of nutrients and bioactives in the vegetables and fruits that people do eat that it *may* be beneficial overall. I’m being very careful not to reach on potential benefits. :)

    Also, I do agree seasonality does matter. Whatever the source, organic or conventional, the season and freshness does matter most to me for cooking. Usually, in my area the best produce at the best price tend to be organics at the farmers markets. My choices are wide (Fred Meyer vs Safeway vs Co-ops vs Whole Foods) but unfortunately the larger companies tend to have the worse produce year round.

  • Sjoerd van der Meulen

    Hi Anastasia,

    That is an interesting story you wrote about the comparison of organic and conventional tomatoes! Your comments on the paper make sense if you read it from an objective perspective. However, I have to agree with the previous comments that most of the time you add vegetables onto your menu based on weight/volume. So the denser a product, the more valuable nutrients will be consumed. And if you offer what we call in Holland ‘water bomb tomatoes’, then one would rather not eat tomatoes (in principle this can account for any food of course) at all. For me, the tomatoes grown (in an organic way) in an old greenhouse of my grandfather beat even the commercially organic ones, but that is very personal.

    About the yield per acre story, I am not really in favor of taking land space as a single factor. Not only since a lot of land is used to grow crops for biodiesel and other non-food applications that have alternatives elsewhere, but also because in the end the amount of land will not be the (only) limiting factor to produce our food. I think that phosphate levels in the world will drop before that. Not to mention chemicals used in the production of conventional crops that, even though not a lot of research is focused on long-term effects on human health (guess why!), might partly undo the positive effect of taking in vitamins by eating for example tomatoes. I would say, a good comparison takes all these factors, use of land, renewability of fertilizers, chemicals used and other energy demanding factors in the process, along.

    It is an interesting discussion, which will continue for a while…

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