By Michele Repo, MD
Berries have received no shortage of good press and are firmly established as a “healthy” food. But, are all berries created equal? Or are there factors that can make one bowl of berries more nutritious than another? Well, as a start, we can look at the work of researchers hoping to answer this question: “Does the nutritional content of berries that have been grown conventionally differ from those that have been grown organically?”
What do the studies tell us so far? That’s an important question but before delving into the answer(s), let’s first establish what is being compared. When it comes to the nutritional content of berries, some of the molecules of particular interest are phytonutrients (quite simply, plant nutrients). These chemicals are also referred to as “bioactive compounds” (or BAC for short). Why the interest in these BACs? Well, it’s thought that they have certain functions (e.g. anti-inflammatory and anti-oxidant) that may prove beneficial to humans. Naturally, if you’re a health-conscious consumer, it becomes important to know which berries offer the most potential benefit. And, with an aging population and an impressive list of chronic diseases to address in North America, it is understandable that foods that offer the greatest nutritional benefit have caught the attention of scientists far and wide. Despite health being an important driver of studies on berries, keep in mind that the studies reviewed in this report make no function or health-related claims. They are simply comparing levels of certain phytonutrients in organic and conventionally produced berries.
It would be great if all studies on nutrient levels in berries compared the same BACs. Unfortunately, that’s not the case. For that reason, research on organic versus conventionally grown berries can’t simply be thrown together to arrive at a single conclusion. Likewise, the studies don’t always look at the same berries. As a particularly popular berry, research on strawberries currently far outweighs research on other berries such as blueberries, blackberries, and elderberries.
Rather than inundate you with a long list of numbers, perhaps a table (or three) will better illustrate some of the relevant research findings. And apologies for the long chemical names that sometimes surface in the tables. Such is the nature of BACs!
Let’s start by looking at blueberries grown in New Jersey. When they were compared, statistically significant differences in BAC content were found between organic and conventionally grown fruit. Based on this study, we can score one for organic berries.1Wang, S.Y., Chen, C.T., Sciarappa, W., Wang, C.Y., & Camp, M.J. (2008). Fruit quality, antioxidant capacity, and flavonoid content of organically and conventionally grown blueberries. J Agric Food Chem, 56(14),
|Sample||Anti-oxidant activity (micromoles/ g of fwt)||Total anthocyanins (mg/100 g fwt)||Total phenolics
(mg/100 g fwt)
|Conventionally grown blueberries||30.76||82.36||190|
fwt = fresh weight
Moving on to two different types of strawberries grown in Maryland, significant differences in some BAC levels were found when comparing conventionally and organically grown fruit. Again, the organic berries came out ahead.2Jin, P., Wang, S.Y., Wang C.Y., & Zheng, Y. (2011). Effect of cultural system and storage temperature on antioxidant capacity and phenolic compounds in strawberries. Food Chem, 124, 262–270. doi:
|CULTIVAR||ORGANIC/CONVENTIONAL||BAC #11||BAC #21||BAC #32||BAC #43|
1 Data expressed as microgram of ellagic acid equivalents per gram of fresh weight.
2Data expressed as microgram of quercetin 3-glucoside equivalents per gram of fresh weight.
3 Data expressed as microgram of kaempferol 3-glucoside per gram of fresh weight.
* statistically significant differences
Lastly, moving west to California, a study of organic strawberries showed that they too contained significantly higher levels of certain phytonutrients.3Reganold, J.P., Andrews, P.K., Reeve, J.R., Carpenter-Boggs, L., & Schadt C.W. (2015). Fruit and Soil Quality of Organic and Conventional Strawberry Agroecosystems. PLoS ONE, 5, 1-14. doi: 10.1371/annotation/1eefd0a4-77af-4f48-98c3-2c5696ca9e7a.
|Sample||Anti-oxidant activity1||Total phenolics2||Total ascorbic acid3|
|Conventionally grown strawberries||10.95||1.24||0.566|
1 mmol Trolox equivalents/grams fruit
2 mg gallic acid equivalents/gram fruit
3 mg/g fruit
This study also demonstrated that the organically grown strawberries had lower potassium and phosphorus levels compared to the conventionally grown berries.
Organic raspberries have also been found to offer higher amounts of antioxidant activity and flavonoids.4Jin, P., Wang, S.Y., Gao, H., Chen H., Zheng, Y., & Wang C.Y. (2012). Effect of cultural system and essential oil treatment on antioxidant capacity in raspberries. Food Chem, 132, In the same vein, the phytonutrient level of both blueberries and blackberries has been found to be higher in wild (and therefore organic) versus conventionally grown crops.5Koca, I., & Karadeniz, B. (2009). Antioxidant properties of blackberry and blueberry fruits grown in the Black Sea Region of Turkey. Scientia Horticulturae, 121(4), 447-450.
Of course, research results are not uncommonly contradictory. So, it shouldn’t come as any surprise that a 2011 study described the differences in phytonutrient levels between organically and conventionally produced blueberries to be “subtle” rather than significant.6You, Q., Wang, B., Chen, F., Huang, Z., Wang, X., & Luo, P. G. (2011). Comparison of anthocyanins and phenolics in organically and conventionally grown blueberries in selected cultivars. Food A 2012 review of organic versus conventional foods concluded that there was no strong evidence that the former is more nutritious than the latter. However, this review was not specific to either berries or BACs. The authors of the review also acknowledged that organic foods may reduce the risk of exposure to pesticide residue and antibiotic-resistant bacteria.7Smith-Spangler, C., Brandeau, M.L., Hunter, G.E., Bavinger, J.C., Pearson, M., Eschbach, P.J., Sundaram, V., Liu, H., Schirmer, P., Stave, C., Olkin, I., & Bravata, D.M. (2012). Are Organic Foods Safer It’s also important to recognize that organic versus conventional is only part of the BAC story. There are many other factors that can have an impact on phytonutrient levels in berries. These variables include time of year, maturity of the berries, cultivar and growing season. In other words, it may make sense to consider more than just growing method when looking for the berries with the best BAC scores.
WHY THEN THE DIFFERENCE?
It seems fair to say that differences in phytonutrient content between organic and conventionally produced berries is not a one-off finding. This then begs the question of why does the cultivation method influence a berry’s BAC level? Several theories have been put forth including one based on how plants allocate resources.8Stamp, N.E. (2003). Out of the quagmire of plant defense hypotheses. Q. ReV. Biol, 78, 23-55. With a finite supply of energy, plants must distribute it between competing functions, two important ones of which are growth and defense. When fungicides and/or insecticides are applied (as per conventional agriculture), the berries are provided an external source of protection. This presumably allows them to move some of their resources away from defense and more towards growth. How is that relevant to phytonutrients? Well, phytonutrients play an important role in plant defense mechanisms – when the need for them is less, it makes sense that the plant decreases its production of, for example, antioxidants. Presto, you end up with less BACs. Add to this the rapid growth that is facilitated by the fertilizers and you end up with an even lower amount of BACs/100 g fruit. In other words, plants give up some of their BAC based protection to make the most of the opportunity to grow like stink in the presence of fertilizer. This may seem like a good deal to the plant, but may be less so for the consumer who wants berries with optimized phytonutrient content.
CAN’T I JUST WASH MY BERRIES – AND PRESTO, ORGANIC BERRIES EMERGE?
Given the economic value of berries, it perhaps comes as no surprise that strawberries, blueberries, and currants have been described as “intensively chemically protected”.9Wolejko, E., Kozowicka, B., & Kaczyński, P. (2014). Pesticide residues in berries fruits and juices and the potential risk for consumers. Desalination and Water Treatment, 52(19-21), 3804-3818, DOI:10.1080/19443994.2014.883793 Also, not surprising is that some of this “protection” ends up on the fruit as chemical residue. Given the health consciousness of today’s consumers, the possibility that they may be ingesting pesticides, even at levels considered non-toxic, often doesn’t sit very well. As a result, consumers often want to know if certain berries pose more of a pesticide problem than others. In the USA, and based on information from the EPA, strawberries have been classified by the Environmental Working Group as being the worst of the “dirty dozen,” i.e., the twelve fruits and vegetables with the most pesticide residue. In comparison, domestic blueberries came in at #17, imported blueberries at #20 and raspberries at #24.
In an attempt to contribute to the discussion about pesticide residue on berries, researchers from Poland had these results to offer with regards to a common fungicide, dithiocarbamate:
|BERRY||% CONTAMINATED WITH DITHIOCARBAMATE||AMOUNT OF RESIDUE (mg/kg)|
|.09 – 1.49|
|.08 – .58|
|.09 – .24|
|.06 – .28|
|.05 – .10|
Again, strawberries came out on top in terms of the concentration of pesticide. (Unfortunately for this berry, this is one of those times when being on top isn’t good news).
Having established that pesticide residue is in fact a real possibility in berry crops, what then do we know about washing said berries? As a hotbed of berry production, researchers from Poland again have something to add to the discussion. In a 2016 report, researchers demonstrated that five minutes of washing berries with water removed more residue than washing for one or two minutes. That was the good news. The bad news was that even after five minutes, pesticide residue could still be detected on the strawberries.10Lozowicka, B., Rutkowska, E., Jankowska, M., Kaczyński, P., & Hyrnko, I. (2012). Health risk analysis of pesticide residues in berry fruit from north-eastern Poland. J Fruit Orna Plant Res, (Further, one wonders, how many consumers wash their berries for a full five minutes?). This finding was supported by an earlier study out of Italy which showed that both washing with water and washing with detergent reduced but did not eliminate pesticide residue on strawberries.11Angioni, A., Schirra, M., Garau, V.L., Melis, M., Tuberoso, C.I.G., & Cabra, P. (2004) Residues of azoxystrobin, fenhaxamid and pyrimethanil in strawberry following field treatments and the effects of domestic
Closer to home, in a study of low bush blueberries in Michigan, washing them with distilled water reduced the amount of phosmet, an organophosphate insecticide, found on the fruit.12Crowe-White, K.M. (2002). Effects of Post-harvest treatments on the microbiological quality and pesticide residues of Lowbush Blueberries. (Masters Dissertation). University of Michigan. Although the post-washing level of phosmet was below the level considered safe by the EPA, this may not be a reassuring finding for those people who consider any amount of pesticide a cause for concern. This is particularly so because fungicides are one of the most likely contaminants of conventional berries and, given their adverse health effects, also particularly unwelcome guests.9Wolejko, E., Kozowicka, B., & Kaczyński, P. (2014). Pesticide residues in berries fruits and juices and the potential risk for consumers. Desalination and Water Treatment, 52(19-21), 3804-3818, DOI:10.1080/19443994.2014.883793 Lastly, washing does nothing to address any differences in nutrient content between conventionally and organically grown berries.
ANY OTHER FACTORS TO CONSIDER BEFORE I BUY A PINT OF ELDERBERRIES (0R, BLUEBERRIES, OR BLACKBERRIES)?
Just as there is no shortage of interest in berries and their nutrients, there is also no shortage of interest in urban farming. There are many factors driving this interest, including food security, finding a use for marginal or abandoned land, and helping city dwellers forge a closer connection to the food they eat. But are berries grown in the city nutritionally on par with berries grown in the country? Answering that question definitively will require more work but research out of, (you guessed it!), Poland is certainly relevant to this discussion. A 2009 study in the south-eastern part of that country looked at the flavonoid (phytonutrient) content of elderberries in relation to where they were collected. Berries picked at sites that were closer to high traffic transportation routes had lower levels of flavonoids (bad), and higher levels of heavy metals such as lead, chromium, cadmium and copper (also bad).13Kołodziej, B., Maksymiec, N., Drożdżal, K., & Antonkiewicz, J. (2012). Effect of traffic pollution on chemical composition of raw elderberry (Sambucus nigra L.). Journal of Elementology, 17(1) 67-78. An earlier study in Denmark found that when grown in contaminated soil, elderberries had higher levels of cadmium than their grocery store counterparts. Similarly, berries that grow in bushes (as opposed to trees) had higher levels of lead contamination – presumably due to dust drifting up from the contaminated soil.14Samsøe-Petersen, L., Larsen, E.H., Larsen, P.B., & Bruun, P. (2002). Uptake of Trace Elements and PAHs by Fruit and Vegetables from Contaminated Soils. Environ Sci Technol, 36(14), 3057-63.
When it comes to the impact of traffic on the BAC levels found in berries, North American research is not easy to come by. What is more readily available are multiple studies that document increases in heavy metals such as lead and cadmium in soil plots closer to major roads. What this means is that even if plants don’t incorporate these heavy metals into their berries, surface contamination can be a concern in those kinds of plots.15McBride, M.B. Shayler, H.A., Spliethoff, H.M., Mitchell, R.G., Marquez-Bravo, L.G., Ferenz, G.S., Russell-Anelli, J.M., Casey, L., & Bachman, S. (2014) Concentrations of lead, cadmium and barium in urban garden-grown vegetables: 16Clarke, L.W., Jenerette, G.D., & Bain, D.J. (2015). G. Urban legacies and soil management affect the concentration and speciation of trace metals in Los Angeles community garden soils Environ Pollut, And so, the “health” of berries grown in urban settings may be significantly influenced by the quality of the soil, which in turn is influenced by the amount of local traffic pollution, amongst other factors. Okay, understood. But is soil contamination in urban gardens a big problem or a once-in-a-lifetime situation? Well, a study published in 2014 demonstrated that of 55 community gardens in New York City, 70% had at least one soil sample with higher than recommended levels of metals. Leading the pack were the heavy metals, barium and lead, which exceeded healthy levels in 12 and 9% of samples respectively.17Mitchell, R.G., Spliethoff, H.M., Ribaudo, L.N., Lopp, D.M., Shayler, H.A., Marquez-Bravo, L.G., Lambert, V.T., Ferenz, G.S., Russell-Anelli, J.M., Stone, E.B., & McBride, M.B. (2014). Lead (Pb) and other metals in There are many benefits to urban gardening but it is imperative that soil safety be confirmed. With these results in mind, “location, location, location”, may be as relevant to growing berries as it is to real estate!
Apparently when it comes to nutrient content, a berry is not necessarily a berry. There are many factors that can influence nutrient content, not the least of which is whether organic or conventional growing methods have been used. It would also be nice to know whether the berries have been grown far enough away from traffic pollution to be spared some of its heavy metals. Although not providing a sure-fire guarantee that you’re about to eat the most nutritious berry possible, the literature does provide some evidence that you may get more phytonutrient bang for your berry buck when you opt for the organically grown version. But, if at all possible, make sure your organic berries aren’t grown near a major roadway or in soil that has become contaminated with toxins in another way. Otherwise, the luster of organic berries may lose some of its sheen.
Related article: DOES NUTRITIONAL CONTENT VARY BY GROWING PRACTICE?