How pure is potato starch?
May 7, 2012 3:41 PM   Subscribe

How pure is potato starch? Can I rely on it not to include the high amounts of potassium that potatoes do?

I've been unable to find potassium content information for potato starch - the purified, white powder, like corn starch. A lot of products include potato starch, and some, like noodles, are made primarily out of it. As part of my medically-mandated diet, I need to limit my potassium intake. As potato starch is a dried, concentrated product, it might be dangerous for me to eat it if it retains and concentrates potassium as well.

Do you know about the process(es) used to create potato starch, or the actual potassium content of the final product? Is the process standardized enough to have the same result, even across international manufacturers?
posted by WasabiFlux to Food & Drink (7 answers total)
You could probably get this information from the nutritionist at your local dialysis center. People with low or no kidney function have to keep pretty close tabs on the amount of potassium they take in and nutritionists at dialysis centers are experts in helping them find which foods are high or low in it.
Of course, I don't know who your local dialysis provider is, but you could search for nephrologists in your area. In the US, the two biggest dialysis provider companies are Fresinius and DaVita.
posted by Quizicalcoatl at 4:04 PM on May 7, 2012

Not a nutritionist here, but I've always been under the impression that it's the skin of the potato that contains all the nutrients, including potassium - and that without the skin, a potato is nothing but a big lump of carbs.

That said - your profile indicates you are in the US. Packaged foods need nutrition labels here, so that should tell you how much is in each serving, regardless of what materials, potato starch or otherwise, are used to make the final product. If you are cooking with potato starch, that label should also have the relevant nutrition info. And if you are worried about dining out, you can create (or possibly find elsewhere) a cheat sheet showing what typical restaurant foods have high or low levels of potassium based on their ingredients, similar to Weight Watchers point values for restaurant chains.

If you're not finding what you want on nutrition labels, you could probably check with a name-brand manufacturer. To your point about standardization, pretty much every food manufacturing process in this day and age is standardized enough that getting an answer from one manufacturer should translate to most, if not all, others - unless they are marketing a different line of products that specifies how it's different.
posted by trivia genius at 4:16 PM on May 7, 2012

You can extract potato starch by grating potatoes, throwing them in a bowl of water, swooshing it around for a minute, pull the potatoes out, then wait a few minutes for the liquid to separate into white goo and water. If you spread the white goo out on a sheet pan and let it dry, you'll have potato starch. I have no idea how accurate this is, but livestrong says potato starch has 46% of your RDA of potassium.
posted by foodgeek at 4:21 PM on May 7, 2012

AFAIK potato starch contains 15mg potassium on 100g starch vs. a fresh potato has around 600 mg on 100g. (100g = 100000mg)
Potassium in the human body is actually needed (in a healthy person) for nerve transmissions, blood pressure, release of hormones like insulin and the digestion of carbs, among others. The recommended daily intake is often cited between 2000mg to 4000mg.

Potassium deficiency (hypokalemia) can have unpleasant effects, so if you have a condition that requires a cap on your potassium intake, I would recommend a visit with a nutritionist.
I think the idea to call up a few manufacturers is good, just to give you an idea. However, I question if a manufacturer really tests for all vitamins, mineral nutrients and micronutrients in a product like starch.
posted by travelwithcats at 4:41 PM on May 7, 2012

Response by poster: I do have kidney failure, and I am on dialysis. Renal dietitians range from good to terrible, and when it comes to the nutritional content of a food, not one of the four I've talked to in the last 4 years has ever been able to help me - in terms of concrete numbers or sources - beyond what I can find on the internet.

Potatoes contain high amounts of potassium in the flesh. I can't eat potatoes, peeled or otherwise.

Potassium is not required to be measured or listed on a nutritional label. Many many food products leave potassium content off the label. The USDA database doesn't include potato starch, so I'm out of luck there as well.

The USDA database does include potato flour, which is different. That must be what foodgeek's livestrong link talks about. I try to stick to primary sources, or sources with verifiable references. I can't verify the information in that article.

travelwithcats, do you have a source for those numbers? Yes, hypokalemia can have unpleasant effects. My problem is hyperkalemia, which can be just as unpleasant, and just as deadly.
posted by WasabiFlux at 6:31 PM on May 7, 2012 [1 favorite]

Best answer: WasabiFlux: 'do you have a source for those numbers?'

Of course I do. :-) However it's a little bit tricky this time.
I checked a food database for dialysis patients that lists 11000 food items, the caveat is it's in german. The german word for potassium is kalium (K). Here it says potato starch contains 15mg potassium on 100g starch (highlighted in yellow, rather on top of the page). They call potato starch 'Kartoffelstärke Mehl' (Mehl being the word for flour but it translates to 'potato starch flour', it's really the white starch that they mean). I think the USDA database has almost 8000 food items listed, so this one has a few more.

Potassium is water soluble (they often advice dialysis patients to thoroughly wash and soak veggies to get as much of it out as possible). If we look at the manufacturing process of potato starch, it seems that they use a lot of water to wash the starch out. Following this logic, potato starch, although you say it 'is a dried, concentrated product', does not contain any concentrated amounts of potassium. Starch is only a part of the potato. This is a paper explaining starch production (pdf, for potato starch check pages 19 & 20)

Another approach could be to look up a recipe (for dialysis patients) that calls for potato starch and lists the potassium content of the overall meal. If you know how much potassium the other ingredients contain, you could figure out how much would have to come from the starch. However, this would be more of an estimate than a definitive number.

I'll happily check/translate anything for you, just memail me.
I am sorry you have to deal with kidney failure. I hope you will get better soon and wish you the best.
posted by travelwithcats at 8:07 AM on May 8, 2012

Best answer: Hi, WasabiFlux. I work in the tech services/nutrition dept of a food manufacturer, so I have a bit of info on this.

First of all, the potassium in potato starch is going to differ greatly depending on how it's processed. The "purest" potato starch is going to go through some pretty serious chemical/enzymatic processing, and typically contains 5 to 10 mg of potassium/100g. However, the closer you come to the "natural products" end of the spectrum, the less refined it will be, with manufacturers coming close to 100mg/100g since potato starch doesn't have a standard of identity that requires a certain level of refinement/"purity". These numbers are pulled from a pretty standard industry database; if you'd like more details feel free to memail me.

The second thing I wanted to mention is that unfortunately very few manufactured foods are going to have accurate potassium info available. When adding raw material info into their records, manufacturers will frequently only log info that is relevant to labeling requirements. Adding to the problem is the fact that many raw material suppliers will provide their nutrition info based on standard database values, not necessarily lab analysis. So in short, most food manufacturers simply aren't going to have accurate numbers for you.

Seeing as this is a major health concern for you, it may be best to buy products that are specifically marketed to have low-potassium, with the manufacturer either having their product sent out for lab analysis or requiring all raw material suppliers to provide certificates of analysis (preferably, they'd be doing both). This is a total pain in the ass, but may be the only option if your health depends on it.
posted by a box and a stick and a string and a bear at 11:42 AM on May 8, 2012

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