Tomato Nutrition

While anyone following this nutritional series might already be aware of the pressure cooker’s amazing nutritional conservation and magnification prowess there is a little something extra that the pressure cooker can do and it’s pretty exciting.

tomatoes & eggplant

Researchers in India, tested eight techniques for washing tomatoes including cooking under pressure, to find out which was best for removing pesticide residue.

The techniques they tried were: washing under tap water; a 10-minute soak in a 2% salt solution; 10-minute soak in a 2%  tamarind solution (comprised of tartaric acid); 10-minute soak in lemon water; 10-minute soak in  0.1% Sodium Bicarbonate (baking soda) solution ; dipping the fruits for a minute in 4% Acetic acid (vinegar) solution;  dipping the fruits in a formula that combined some of the previous methods (vinegar, baking soda lemon); 10-minute soak in commercial “Bio Wash” solution; and pressure cooking.

Out of all treatments, dipping in 2% salt solution for 10 minutes is very effective in removing 45%, 43%, 52%, 50%, 54%, 48% and 76% of dimethoate, chlorpyriphos, quinalphos, profenophos, phosalone, -cyhalothrin and malathion, respectively, and [pressure] cooking removed insecticides in the range 55-80%. Dipping fruits and vegetables in 2% salt solution for 15 minutes is the best household method for removal of pesticide residues, and also the method is effective in reducing the
residues below MRL (Maximum Residue Limits). 1

While the salty soak was the easiest to do, the pressure cooker actually performed better than any other method. The study’s data clearly show that pressure cooking out-paced or matched the residue reduction the salt rinse for five of the seven tested pesticides.

Percentage of Pesticide Residue Reduction In Veggies


2% salt solution


pressure cooking

"direct cooking"

pressure cooking+

2% salt solution
Dimethoate 45%64%56%99%
* Shashi BV et al.; IJFH 2016; 2(1):19-24.
** Shashi BV et al.; Sch J Agric Vet Sci 2015; 2(1A):27-30.


While the tomato study only published the results of pressure cooking tomatoes,  without sharing any data to what would happen when the tomato is just conventionally boiled, the same lab did earlier experiments with Eggplant which includes “direct cooking.”  Unfortunately, the paper does not describe in detail what that means (perhaps it was pan frying) but it did show that “direct cooking” also did not reduce pesticide residue as much as pressure cooking . 2

So…could a cook achieve the same results with plain boiling or steaming without using any pressure?

cauliflower florets

Well, thankfully, a study that measured pesticide residue in cauliflower compared not only the pressure cooked but also boiled and microwaved florets. A chart from the study clearly illustrates that both rinsing and pressure cooking florets gave the optimal results. So don’t skimp on washing veggies just because they’re going to be pressure cooked, later.

As the excerpted chart shows, although the pesticide residue reduction from pressure cooking is quite high, there are two other methods that performed similarly.  Those two columns illustrate the results of rinsing the veggie with sodium hydroxide and hydrochloric acid solution.  Since most people don’t ordinarily know how to safely handle – much less use-  lye or the main ingredient that’s in drain cleaners, the researchers recommended that the chemical treatments are best left to industrial processing. 3

Washing of [cauliflower] vegetables with water followed by pressure cooking removed maximum residues up to 70% as compared to the other processes and proved good household practice.

There isn’t too much other published to show how pesticide residue is reduced for other veggies.  But I did find a couple of papers with a different finding for two veggies: pressure cooked potatoes did not reduce any more pesticide residues compared to boiling4; and,  pressure cooking curry leaves only reduced pesticide residue for just one of the out of the five tested – the best method was to rinse an dip the leaves in a salt solution.5

So far, we’ve found evidence that for some veggies, pressure cooking them reduces pesticide residue.  Could this also apply to meat and fish?

water buffalo & meat

Water Buffalo

Water buffalo is a cousin of the cow, under the same bovine branch in the animal kingdom.  While in the western world they’re most famous for their milk products (mozzarella di buffala) in other parts of the world water buffalo are used as work animals for tilling fields and as a meat source. Due to the water buffalo’s close relation to cows, some of these findings could also apply to beef (keep reading for data on this).

The study I looked at measured residues of Cyclodiene-type pesticides in buffalo meat that was boiled, broiled, microwaved and pressure cooked6.  It’s important to note that this class of pesticide has been banned for use in the United States since 19737  and severely restricted within the European Union8 but is still being used in Australia9 (the largest beef importer into the US10) and other countries.

The researchers found …

Among the cooking methods, pressure cooking was most effective in reducing both α- and β-endosulfan.6

Percentage of Pesticide Residue Reduction In Meat



Muthukumar M et al.; JFST (2010) 47(3):325–329


An ambitious thesis of a budding veterinarian in India published last year measured pesticide residue reduction of ten pesticides when boiling, pressure cooking and microwaving local beef, lamb, pork, and chicken. The data was collected by testing 30 samples of each food item and the results are illuminating. Pressure cooking the meats outperformed microwaving and boiling. All pesticides measured were reduced the most with pressure cooking in pork, lamb, and chicken while for beef nine of the ten pesticides measured were reduced.11

But, a published paper, found that grilling lamb, compared to roasted and pressure cooked12. And freshwater fish doesn’t seem to get any additional pesticide reducing benefits from pressure cooking, either – faring better with baking13 and frying14.

what’s going on?!?

Actually, no paper or thesis referenced for writing this article actually spelled out why pressure cooking some vegetables can reduce their pesticide residue. But, since pesticides are made with volatile compounds that sensitive to high temperatures, the theory so far is that the higher temperatures of the pressure cooker (at least for some foods) accelerates the degradation of the pesticide to the point where it is more difficult to detect.

Although there are still more questions and than answers on this topic, this new pressure cooker super-power was worth sharing because although everyone wants to purchase and eat high-quality foods, at the moment bio/organic foods cannot be priced for every budget.

See Also: Pressure Cooker Nutritional Information


PRESSURE COOKER NUTRITION: Reduce Pesticide Residue in Foods by Pressure Cooking




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Vemuri S, Cherukuri SR, Reddy H, . Swarupa S, Kavitha K, Anitha V. Risk Mitigation Methods for Removal of Pesticide Residues in Tomato for Food Safety. IJFH. 2016;2(1):19-24.
Vemuri S, Rao CS, Swarupa S, Darsi A, Reddy HA. Simple decontamination methods for removal of pesticide residues in brinjal. Sch J Agric Vet Sci. 2015;2(1):27-30.
Banshtu T, Kumar Patyal S. Decontamination Processing of Chlorpyrifos and Cypermethrin  Residues in Cauliflower. I. 2018;7(05):859-868. doi:10.20546/ijcmas.2018.705.105
Lamb FC, Farrow RP, Elkins ER, Cook RW, Kimball JR. Behavior of DDT in potatoes during commercial and home preparation. J. 1968;16(2):272-275. doi:10.1021/jf60156a018
Priyadarshini G, Vemuri S, Reddy CN, Swarupa S, Kavitha K. Risk Mitigation for Removal of Pesticide Residues in Curry Leaf for Food Safety. ijaf. 2017;7(1):13-22. doi:10.5923/j.ijaf.20170701.03 [Source]
Muthukumar M, Sudhakar Reddy K, Narendra Reddy C, et al. Detection of cyclodiene pesticide residues in buffalo meat and effect of cooking on residual level of endosulfan. J. 2010;47(3):325-329. doi:10.1007/s13197-010-0052-y
Learn more about DDT. ScienceDirect. Learn more about DDT. Accessed July 12, 2018.
HEXACHLOROCYCLOPENTADIENE (HCCP)  SUMMARY RISK ASSESSMENT REPORT – FINAL APPROVED VERSION. European Union:  ECHA – European Chemicals Agency. Published 2017. Accessed July 12, 2018.
C. Radcliffe J. Pesticide Use in Australia. Australian Academy of Technological Sciences and Engineering; 2002.
U.S. Beef Imports: Ranking Of Countries. FarmCentric: Beef 2 Live. Published 2015. Accessed July 12, 2018.
Conchello MP, Herrera A, Ari�o A, L�zaro R, P�rez-Arquillu� MC. Effect of grilling, roasting, and cooking on the natural hexachlorobenzene content of ovine meat. B. 1993;50(6). doi:10.1007/bf00209946
Goyal A, Aulakh RK. Effect of Processing on Pesticide Residues in Some Edible Fresh Water Fishes. J. 2017;7(1):191. doi:10.5958/2277-940x.2017.00026.2


  1. Laura:

    those are good news, thanks for sharing them!

    I guess I´ll add a water salt bath before my usual pressure cooking of vegetables,


  2. Peeling or washing fruit and vegetables does more to reduce pesticide levels than cooking, but the only way to be entirely sure is to stick to organic produce.

    1. No, because organic agriculture uses chemical pesticides too, just from a different list than conventionally grown produce (those deemed to be natural versus those that are synthesized, although some synthesized chemicals are allowed in organic agriculture and some natural chemicals are not allowed). It is a common misconception that they do not use chemicals at all. And conventional agriculture may, of course, use the same chemicals as organic agriculture, just not vice versa. The allowed chemicals in organic agriculture were originally grandfathered without actual safety studies. We are slowly catching up with testing and it turns out that natural pesticides are carcinogenic at about the same rate as synthesized pesticides.

    2. And:

      “When people are buying organic food, they often make the incorrect assumption that there are no pesticides. It’s true that organic production often uses fewer dangerous chemicals, but certain pesticides are allowed.”

  3. I agree with Anna’s information. Thanks Anna.

    None of the information floating around the internet covers the transportation of food in relation to health and pesticides and insecticides. I would also like to add that my Uncle, while he was a transport driver coast to coast, was forced by government regulations to spray his load with pesticides and insecticides (instructions included the use of gloves and breathing apparatuses) when crossing boarders or state lines to prevent the spread of unwanted insects and plant diseases. Further proof of this, for me, is that I am very sensitive to pesticides and insecticides and have found that even after washing organically grown fruit & veggies I still am affected. So even if it is grown ‘organically’ it isn’t always free of pesticides and insecticides. Since he told us this I have ignored the ‘organically grown’ labels and just buy the best looking fruit and veggies and wash them well. I still have to cook them to death to be able to eat them. I’ve known for a long time that heat/cooking reduces the ‘cides’.

    An additional FYI: my experience has shown canned and frozen foods have less to none of the ‘cides’. It may be because they do not come under the same government regulations. Canned is obviously already cooked which kills bugs and diseases but freezing maybe kills the bugs and diseases, too.

    Laura, thank you so much for letting us know that the magic pressure cooker makes this a faster way to achieve safer food. You are the best.

    1. That’s very interesting information about produce in transit being sprayed to meet different states’ different regulatory requirements regarding pests, Sheila, but it makes sense that that could happen. (Some states have unknowingly imported pests in the past that have been industry threatening.)

      I had a wake up call about organic produce when a small local farmer whom we know switched from conventional to organic to meet the demand of his Washington, DC farmer’s market customers. (Switching was a massive undertaking for him but it was worth it because of demand and his ability to charge more for his organic produce.) He told us that his farming methods weren’t actually changing, just the chemicals that he used on his crops. So I stopped paying more for organic (after a little research into the fact that the chemicals used in organic agriculture hadn’t even been tested for safety and were probably just as likely to be unsafe as any chemical used in conventional agriculture) and I started making sure I washed my produce well.

      And then there is the issue of fraud in organic labeling, especially with regard to imported organic products. The extra money that can be charged for a product labelled “organic” is an incentive for this fraud.

  4. Very enlightening article but I wonder about if the act of pressure cooking the vegetable and meat will get rid of the pesticides what happens to the liquid that is left in the pot especially since I usually use that liquid to flavor other recipes?

    1. Since pesticides are heat-sensitive the theory is that they are “deactivated” and their presence can no longer be detected. However, I do wonder what remains as well!



  5. That’s a great read. Last year, my family and I went to my Nan’s farm. We picked a lot of fresh tomatoes! and when I say a lot, we loaded huge bins as big as the truck parts. Will take note of those tips when using tomatoes and other veggies.

  6. Two big questions I had after reading this article:

    1. What PSI and duration are required for these effects? Most produce can only be pressure cooked briefly, with instant release, or it’s mush.

    2. This may be validly denature the chemicals that are pesticides (much like cooking protein powder or fats can change them), but we don’t know that this doesn’t make it more harmful and/or simply more easily absorbed by our body, instead of less. I mean, we hope so! :-) But I’d say that’s a question that needs to be studied.

    A tiny bit of GSE (grapefruit seed extract) in a big bowl of water to rinse produce in allegedly works very well to cover the ‘other’ element of stuff-bad-for-you, bacteria/fungus/etc. on the outside (even from the hands of other store shoppers and things like that).

  7. Happily, even a small container garden can give many a chance to grow their own, and have total control over the inputs (short of air pollution).

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