In light of the recent Cyclospora outbreak linked to bagged lettuce (and the past outbreaks of e.coli, norovirus, salmonella, and HepA linked to spinach, raspberries, and frozen mixed berries), I wanted to investigate how dirty our produce really is and how well our produce washing methods work. So far I have tested raspberries, strawberries, blueberries, grapes, broccoli, carrots, bagged lettuce, heads of lettuce, and raw chicken breasts. I have many experiments still to do.
In case you are new to my website, my name is Annie Pryor. I am a mother with 3 young children and have a Ph.D. in biochemistry from the Ohio State University. I am passionately interested in decreasing the prevalence of stomach bugs in the world. I have years of experience growing bacteria in a research lab, so I am completely qualified to do these experiments with bacteria. In fact, they are pretty simple experiments and would be great for anyone looking for a science fair project. In case you don't know, I am growing bacteria on agar plates. The small white spots are piles of bacteria.
What has more bacteria, a raw chicken breast or bagged lettuce?
For this experiment, I purchased bagged romaine lettuce and Tyson raw chicken breasts from Walmart. With clean gloves, I rubbed a small handful of the romaine lettuce onto a sterile agar plate.
Then with clean gloves, I rubbed one raw chicken breast all over another sterile agar plate. Then I rubbed a second raw chicken breast all over the same agar plate to make sure it got good and dirty.
I incubated the agar plates overnight in a warm incubator (about 95 degrees F) and examined the plates in the morning. Much to my surprise, the bagged lettuce had much more bacteria than the raw chicken breasts! (This does not mean you should start eating raw chicken breasts. Please continue cooking chicken to 180 degrees F.) I will repeat this experiment as soon as I can with organic chicken to see how that compares. Now nobody panic. We have all been eating bagged lettuce for years and don't usually get sick. Most of these bacteria are probably harmless. Our intestines require good bacteria to function, and our bodies need to learn to handle the regular flora in our food. That being said, bagged lettuce has been responsible for many outbreaks and recalls including the latest cyclospora outbreak. My goal is to determine if buying heads of lettuce and washing it ourselves is any better or safer than buying the bagged stuff. If you scroll down, you will see that I have tested a few other bagged lettuces already.
I wanted to make absolutely certain that my tap water and clean gloves were not contributing bacteria to my experiments. So, I put on a clean pair of gloves, got them wet under the tap water, and rubbed them on a clean agar plate.
I incubated the plate overnight and was pleased that there was no bacterial growth at all the next day.
For this experiment, I wanted to determine if simply rinsing fresh raspberries in tap water was good enough to remove most of the germs. First I took a dirty raspberry right out of the box and rubbed it all over one half of an agar plate. I used a sterile swab to hold the raspberry. I got a second dirty raspberry and rubbed the same half of the agar plate. So, there were 2 dirty raspberries rubbed on that half of the plate.
Then I used a sterile swab to rub this clean raspberry on the other half of the agar plate.
I repeated this with one more clean raspberry. So, two clean raspberries were rubbed on that half of the agar plate.
The agar plate was then placed in my warm (about 95 degrees F) incubator for 15 hours.
I repeated the same experiment with the raspberries but this time I rinsed several raspberries in a strainer together. I mixed them gently with my hand while the water was running so each raspberry got rinsed. I rinsed them for 2 minutes. Then I rubbed 2 dirty raspberries and 2 rinsed raspberries onto an agar plate and incubated them overnight.
As you can see, giving raspberries a good rinse with water seems to be very effective at removing bacteria.
For this experiment, I wanted to determine if simply rinsing fresh blueberries in tap water would be enough to remove most of the bacteria. I used a sterile swab to roll 2 dirty blueberries around on one half of an agar plate.
Then I rinsed the blueberries under cool tap water for 2 minutes. I used my hand to gently mix the blueberries so each one got rinsed.
I used another sterile swab to roll 2 clean blueberries around on the other half of the agar plate. I incubated the plates overnight. As you can see, just rinsing with water did a good job removing the bacteria. There is a little bacteria at the bottom on the clean side. However, that was caused when one of the dirty blueberries that I was rolling on the other side accidentally rolled out of bounds. It seems that just giving blueberries and raspberries a good rinse with tap water does a good job removing germs.
Next, I wanted to determine if rinsing strawberries in tap water was enough to get them clean. First I rubbed 2 unwashed strawberries (one at a time) onto an agar plate. I used a sterile swab to push them around.
Then I rinsed 2 different strawberries (one at a time) under running tap water for 1 minute. I used my other hand to gently rub the outside of the strawberry.
I rubbed the 2 clean strawberries on another agar plate and pushed them around with a sterile swab. (I took a photo of that but it was blurry.) Then I incubated the plates overnight in my warm incubator.
As you can see, rinsing with water for 1 minute is a great way to clean strawberries! I realize that most of us don't want to spend 1 full minute cleaning each strawberry.
I repeated this experiment with strawberries a different day. This time I only rinsed and rubbed each strawberry for 15 seconds under WARM running water. As you can see, the 2 strawberries got almost perfectly clean.
For this experiment, I wanted to determine if simply rinsing grapes with tap water (like I have done my entire life) was enough to get them clean. First, I rubbed 3 dirty grapes on one half of an agar plate using sterile swab.
Then, I rinsed a bunch of red grapes under tap water for 1 minute.
I incubated the plate overnight and examined it in the morning. The dirty grapes had a lot of bacteria and rinsing them in water for 1 minute made a big improvement. Even though, I think the just the water rinse is good enough, I am going to test the Fit fruit and vegetable wash on grapes later this week.
I rolled 3 dirty grapes around on an agar plate using a sterile swab.
I rinsed some grapes under warm water for 1 minute. I used my other hand to mix them around.
I rolled 3 of those rinsed grapes around on another agar plate.
Then I sprayed a small bunch of grapes with 5 sprays of Fit Fruit and Vege wash. I mixed the grapes up with my hand for 30 seconds. Then I rinsed the grapes under warm water for 1 minute.
Then I rolled 3 of these washed and rinsed grapes around on another agar plate.
The plates were incubated overnight. As you can see, rinsing for 1 minute in warm water gets the grapes very clean. Washing with Fit first, gets them really, really clean. The Fit spray smells a little bad when you first use it but the smell is gone after you rinse the grapes. My very picky son taste tested all of the grapes and could not tell which ones were sprayed with Fit. It did not affect the taste. The Fit sprayed grapes looked significantly cleaner than the grapes rinsed with just water. I am going to keep using Fit on my grapes.
For this experiment, I wanted to determine if simply rinsing in tap water did a good job cleaning broccoli. First, I rubbed an unwashed piece of broccoli on one half of an agar plate.
Then I rinsed another piece of broccoli under WARM tap water for 20 seconds. I rubbed it while I was rinsing it.
I rubbed the rinsed broccoli onto the other half of an agar plate. The plates were incubated overnight.
The results show that just rinsing in WARM water and rubbing does a good job cleaning broccoli. I have repeated this experiment a few times and warm water is more effective than cold water.
For these experiments, I compared ready-to-eat carrots and whole carrots.
First, I rolled 3 baby carrots (directly out of a new bag) around on an agar plate using a sterile swab.
Then I peeled a large carrot under running warm water.
I cut the carrot into 3 sections and rolled them around on another agar plate using a sterile swab.
I incubated the plates in my warm incubator overnight and examined the plates in the morning. I have repeated this experiment several times with 4 different brands of carrots (some organic and some not organic). The ready-to-at carrots all contain much more bacteria than a big carrot peeled under running water. I am buying the big carrots from now on. My children actually prefer eating a big, long carrot because they like to pretend to be "Bugs Bunny".
Brace yourselves, this isn't pretty. I wanted to find out if ready-to-eat triple washed bagged lettuce was germy and if washing it with tap water helped. First I rubbed a small handful of the bagged lettuce onto an agar plate.
Then I washed the lettuce in tap water. I filled up the bowl with water, mixed it up with my hand and let it sit for 2 minutes. I emptied the water and filled it up again with clean tap water. I swished it around with my hand again. I emptied the water and spun the lettuce to get rid of most of the water.
Much to my dismay, the lettuce was filthy! Washing it with water really didn't improved it at all! I will continue to experiment with this to determine if any cleaning methods improve this kind of lettuce. I will try vinegar and food grade hydrogen peroxide. If you have any suggestions, please e-mail me, phd.annie at gmail.com. But before you panic, remember that we have all been eating lettuce like this forever and it usually never makes us sick. Our bodies can handle a lot of germs.
I used that same container of organic spring mix for an experiment the following day. This time I soaked some spring mix in tap, and I soaked more spring mix in 25% white vinegar in water. (1.5 cups of vinegar and 4.5 cups of water.) I let them soak for 10 minutes.
After 10 minutes, I rinsed them under running water for 2 minutes. I moved them around with my hand to thoroughly rinse them. I rinsed the spring mix soaked with vinegar first and left the other spring mix soaking in the water. So, the spring mix that was soaked in the water really sat there for about 12 minutes instead of 10. I washed the strainer between each one.
After I had rinsed both spring mixes, I set them on paper towel briefly.
Then I rubbed a small handful of each onto an agar plate.
I will repeat this experiment with another container of bagged lettuce soon to be absolutely certain that this vinegar method is as good as it looks right now. (Experiments always need repeated before you can totally believe the results.)
BAGGED ROMAINE COMPARED TO A HEAD OF ROMAINE
For this experiment, I wanted to determine if bagged ready-to-eat romaine lettuce is dirtier than a whole head of romaine. Wearing clean gloves, I rubbed a small handful of bagged romaine onto a sterile agar plate.
Then I took one of the inner leaves from one of the heads of romaine. This romaine was NOT WASHED and the bag says that you need to wash it before you eat it. I did NOT WASH it for this experiment. I tore up the leaf so it was similar in size to the bagged romaine and rubbed it on another agar plate.
I incubated the plates overnight and examined them in the morning. In my opinion, the bagged romaine is about as dirty as the whole unwashed romaine.
At the same time that I was doing the previous romaine experiment, I also took one of the inner romaine leaves, tore it up, and rinsed it under tap water for 30 seconds.
2 days later, I repeated the experiment with another whole head of romaine lettuce. I tore up one of the dirty leaves and rubbed it on an agar plate. Then, I rinsed another leaf for 30 seconds under tap water, tore it up, and rubbed it on the agar plate. Then, I took another leaf and soaked it for 10 minutes in tap water. I also soaked another leaf in tap water with 25% white vinegar for 10 minutes.
After the 10 minute soak, I rinsed each leaf for 30 seconds under tap water, tore them up, and rubbed them each on a sterile agar plate.
I incubated the 4 plates overnight and examined them in the morning. As you can see, the quick 30 second rinse under tap water did a great job cleaning the romaine. Soaking for 10 minutes in both 25% vinegar and plain water made the lettuce even better.
SHREDDED ICEBERG LETTUCE
Then I rinsed the lettuce in a strainer under cool water for 30 seconds. I used my other hand to mix it up so it all got rinsed.
Then I put a small handful of this cleaned lettuce onto an agar plate. I used a sterile swab to push it around.
I incubated the agar plates overnight. Unfortunately, the shredded iceberg was filthy even after washing it! I repeated this experiment the following week with a new bag of Dole Shredded iceberg and it was still full of bacteria.
Head of Iceberg Lettuce
After seeing how much bacteria bagged chopped iceberg lettuce has, I wanted to find out if a regular head of iceberg lettuce has that much bacteria. First I peeled off the outer 3 layers of the lettuce and threw them away. Then I split the next leaf into 2 pieces. One piece I kept "dirty" and chopped it up. (I had previously washed my knife, sprayed it with 3% hydrogen peroxide, and rinsed it again.)
I rubbed this unwashed chopped iceberg lettuce all over a sterile agar plate using a sterile swab.
Then I took the other half of the iceberg leaf and rinsed it under tap water for 30 seconds.
I incubated the plates overnight in my warm incubator (about 95 degrees F) and examined the plates the next day. The iceberg barely had any bacteria.
I repeated this experiment several more times to compare bags of shredded iceberg to balls of iceberg.
My results show that if you buy a ball of iceberg and discard the outer 2 layers, you are eating MUCH LESS bacteria than if you eat bagged shredded iceberg. I did not even wash the balls of iceberg in these experiments. I just compared a leaf from an unwashed ball of iceberg to the bagged shredded iceberg.
--soaked in tap water or tap water with white vinegar
Leafy greens like kale are very healthy but seem like they would be hard to clean. I have always just rinsed them in water, and I want to see how well that works. For this experiment, I divided a large kale leaf into 3 similar sized sections.
I rubbed one dirty piece of kale all over an agar plate.
Then I soaked the 2 other pieces of kale in clean containers of tap water. The containers contained 2.5 cups of water. One container also contained 1 tablespoon of white vinegar (creating a 2.5% solution). I left the Kale sit in the water for 5 minutes. Twice during that time I used sterile swabs to mix them up a bit which would aid in the cleaning.
When I removed them from the water, I set them on clean paper towel briefly. I did not let them dry.
Then I rubbed the cleaned kale all around agar plates.
I incubated the plates in my incubator which was about 95 degrees F for 15 hours.
After 15 hours, I examined the plates. The kale definitely improved after the soaking, but I did not see a significant difference with the white vinegar. I would like to improve my kale cleaning methods more. I will try rinsing the kale under running tap water and soaking it in a 25% vinegar and water solution in future experiments.
A few days later, I had a new head of kale and decided to try more experiments. This time, I compared dirty kale, kale that had been rinsed under tap water for 30 seconds, and kale that had been sprayed with Fit fruit and vegetable wash. First I tore up a leaf of dirty kale and rubbed it onto a sterile agar plate.
Then I rinsed another leaf of kale under tap water and rubbed it for 30 seconds.
I sprayed 2 sprays of Fit fruit and vegetable wash to a third piece of kale and rubbed it in for 30 seconds. Then I rinsed this leaf for 30 seconds under tap water.
I tore up this leaf and rubbed it onto an agar plate.
Next, I decided to find out how much bacteria is in ready-to-eat spinach. After all of my previous experiments, I did not have high hopes.
First, I rubbed 5 spinach leaves onto a clean agar plate.
Then I rinsed a handful of spinach under warm water for 30 seconds. I mixed it around with my other hand.
I rubbed 5 of those rinsed leaves onto another agar plate.
Then I soaked a handful of spinach leaves in either warm tap water or warm tap water with 25% white vinegar for 10 minutes.
After 10 minutes, I rinsed the spinach under warm tap water for 30 seconds.
Then I rubbed 5 spinach leaves onto clean agar plates.
I incubated the agar plates overnight and examined them in the morning. As you can see, the ready-to-eat spinach (like any bagged lettuce) has tons of bacteria. Rinsing it in water for 30 seconds does almost nothing. Soaking in 25% white vinegar for 10 minutes helps a little. I am going to do another experiment soaking the spinach in hydrogen peroxide.
I repeated this experiment using food grade hydrogen peroxide. I purchased the food grade hydrogen peroxide at a local healthy food store. It is 35% hydrogen peroxide and supposedly contains less stabilizing chemicals. It needs to be kept refrigerated and is harmful if you get it on your skin.
First, I rubbed 5 unwashed leaves of spinach onto a clean agar plate. Then, I soaked a handful of spinach in 25% white vinegar for 10 minutes. I soaked another handful of spinach in a 3% solution of hydrogen peroxide in water for 10 minutes. To make the 3% solution, I put about 1/6 cup of 35% hydrogen peroxide (which is half of 1/3 cup) into a large measuring cup and then added tap water until it came to 2 cups total.
Then I rinsed the spinach in warm tap water for 30 seconds.
I rubbed 5 leaves of the spinach onto clean agar plates.
I incubated the plates overnight and examined the results in the morning. The 10 minute soak in hydrogen peroxide cleaned about as well as the soak in white vinegar. I repeated this experiment again and got similar results. However, it seems that bagged lettuce and spinach is always going to have a lot of bacteria. Please remember that most of the bacteria is harmless. Consider it a "probiotic". I think it is important for our bodies to learn to deal with the regular bacteria in our food. In addition, it has been shown that bacteria and viruses can enter lettuce through the roots and be INSIDE the leaves1. So, no manner of cleaning is going to get rid of all of the germs. Moderation is the key here.
Then I rubbed 5 spinach leaves on to each agar plate and incubated the plates overnight. As you can see, rinsing in hot water killed a significant amount of bacteria. The heat was killing it. This isn't really cleaning it so much as it is "cooking" it.
I repeated the experiment rinsing spinach in hot water for 1 minute again. As you can see, the hot water does kill most of the germs.
I had a request to test hydroponic lettuce. This lettuce is grown without soil so one would think it would be pretty clean.
I tested 2 of the inner leaves. I tore them up and rubbed them on agar plates without washing them at all. After incubating the plates overnight, almost no bacteria grew. The hydroponic lettuce was very clean. I repeated this experiment with another bunch of the same brand of lettuce and it was also very clean.
Pre-Sliced Apples vs Whole Apples
After testing ready-to-eat carrots and bagged salad and finding them full of bacteria, I did not have a lot of hope for ready-to-eat sliced apples. For this experiment, I washed a whole apple using Fit Fruit And Vegetable Wash and dried it with clean paper towel. I grabbed a clean knife out of the dishwasher and sliced up the apple while wearing clean gloves.
I placed one slice of the freshly cut apple on an agar plate and put a slice of the pre-cut apple next to it. I left them on there for about 5 seconds and then removed them.
I let the agar plate incubate overnight it my warm incubator. The next day, I was sad to see the huge amount of bacteria on the pre-cut apple compared to almost no bacteria on the freshly cut apple.
I repeated this experiment another day with a different brand of pre-cut apples.
Like last time, I washed an apple with Fit Fruit And Vegetable Wash and sliced it up. This time I rubbed 3 slices of apple all around the agar plate. I rubbed 3 slices of the pre-cut apple all over 1 agar plate. Then I rubbed 3 slices of the freshly sliced apple all over another agar plate. I also sliced up an apple that I DID NOT WASH and rubbed 3 slices of that all over another agar plate. I moved the apple around so the peel was in contact with the plate as well as the inside of the apple.
My results show that the ready-to-eat apple was full of bacteria. The washed and UNWASHED apple had almost no bacteria on it.
I decided to repeat this experiment one more time with ORGANIC apples. I used Organic sliced apples from Trader Joes and an organic Gala apple.
This time, I did not wash the whole apple at all. I sliced it up and rubbed 3 slices of each apple all over an agar plate. Although, the organic UNWASHED apple had a small amount of bacteria, it does not even compare to the huge amount of bacteria in the pre-sliced apples. So, why do the pre-sliced apples have so much bacteria? Even unwashed apples don't have that much bacteria. Where did all of this bacteria come from? The processing facility? Hopefully, most of these bacteria are harmless. However, there have been recalls of sliced apples due to contamination with bad bacteria. I'm going to be cutting up my own apples from now on.
I have a lot more experiments to do. Please e-mail me and tell me how YOU wash your fruits vegetables? Is there a specific vegetable wash or method that I should test? Any particular fruits or vegetables that you want to see tested? Please let me know. phd.annie at gmail dot com. If you would like to be notified when more results are posted, please like my facebook page.
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Have you ever seen reports on the levels of salmonella on chicken raised in hardcore factory facilities (like Tyson) v. organic/ free range chicken? The organic versions are usually far worse in detectable levels of disease-causing bacteria like listeria, E. coli, salmonella, etc. So yes it is still very important to cook your chicken! ;) That said, factory farms also douse their products with chemical baths during the packaging process. They are so filthy that if they didn't they would sicken people right and left... so I was not surprised at your "clean" result with the chicken. I doubt you have the bandwidth to key out your colonies to species but it would be interesting to see if any of the bacterial growth you are seeing on the agar plates is disease causing as opposed to "benign".