August 29, 2017 at 6:05 am #302669
…and here’s is why I’m not going to write an article about it.
I recently found a really promising research paper that tested THIRTEEN different frozen vegetables for nutrition after boiling, pressure cooking, steaming and microwaving. Whenever I find a research paper before bearing down and reading it I always look at the data tables.
Initially, I was so excited to find this jackpot of nutritional data on comparing different cooking methods on so many vegetables.
As I went through one vegetable after another, pressure cooking was either worse than or slightly better than boiling and retained VERY LITTLE folates, carotenoids, and vitamin C compared to non-pressure steaming and microwaving.
I was confused because this data went against EVERYTHING else I’d found so far – if true it would completely turn one of the values of pressure cooking on its head. But, it didn’t take me long to find a BIG FLAW in the data.
At the beginning of a paper, the researchers detail what equipment they used and how they measured the data. And that’s where something jumped out at me right away. For Boiling, Steaming and Microwaving the researchers instantly froze the cooked vegetable in liquid nitrogen for storage until they could measure the nutrient levels. BUT, the pressure cooked vegetables were thrown in an ice-water bath for 5 minutes first and then dipped in liquid nitrogen.
Hmm…. so how could this small alteration affect the results?
Well, I kept searching and found out that folates, carotenoids, and vitamin C are all WATER SOLUBLE. That means, they dissolve in water. So, it is feasible that the pressure cooked vegetables lost additional nutrients in the ice water bath compared to all of the other cooking methods.
So basically, the data on the pressure cooked vegetables is totally useless and cannot be compared to vegetables with other cooking methods that WERE NOT thrown in an ice bath for 5 minutes.
I have contacted the lead researcher to ask if they also measured the nutrients in the ice water – I haven’t heard back from them but it’s unlikely since they did not state doing it in the paper.
I’m just putting this out there, in case anyone else stumbles on this research thinking they found a GOTCHA and in the interest of full disclosure.
If Dr. Bureau answers my query, I’ll share her response here as well.
Bureau, S., Mouhoubi, S., Touloumet, L., Garcia, C., Moreau, F., Bédouet, V., & Renard, C. M. (2015). Are folates, carotenoids and vitamin C affected by cooking? Four domestic procedures are compared on a large diversity of frozen vegetables. LWT-Food Science and Technology, 64(2), 735-741.
Full Research Paper Copy:
And, if you want to read the articles I DID write on pressure cooker nutrition, you can find them here:
https://www.hippressurecooking.com/category/news-and-articles/nutrition/August 29, 2017 at 11:25 am #302733
WOW, that is some sloppy science. I wonder what their reasoning could possibly be for not carrying out this study in a consistent, scientific manner. It sounds as though maybe they performed the pressure cooking method first, only later realizing the error of their ways (measuring post-ice bath).August 29, 2017 at 11:34 am #302740
Well, the study was sponsored by the frozen veggie outfit, so it’s not like they couldn’t get any more of them to test.
What is ironic is that in the conclusion they acknowledge that Vitamin C is soluble and veggies can lose 2-10% of it in the cooking liquid. So they are aware of it but still did the ice bath.
But, you’re right, actually, many research papers can be written on a single set of data collection so it could just be that the data for the pressure cooker was collected for a different purpose and re-utilized in this study.
Can’t wait to hear back from the lead author to find out if they measured the ice water – sometimes they don’t present ALL the data they have available for a study because of space constraints, or it doesn’t fit the narrative, or they’re saving it for another paper.
Every researcher I’ve ever contacted for my articles has always been really excited to discuss their work and give more details, photos and illustrations – the ones that answer, anyway. : )
LSeptember 5, 2017 at 6:19 pm #303739
I know that pressure cooked food – especially vegetables – are more nutritious. My veg are only ever cooked in the pressure cooker and never overcooked.
I’m healthy, very rarely get colds etc.
The study is definitely flawed. I remember previously seeing on this website a different study which proved that pressure cooking vegetables preserved the most vitamins.
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