When a potato is pressure cooked and cooled a large portion of its starch is converted into “resistant starch” – a healthier starch that isn’t fully digested and instead used by the body like fiber – lowering blood cholesterol and fats.
Resistant starch is usually found in beans, whole grains and some fruits (bananas); but, it can also be created by cooking typically starchy foods (such as potatoes, rice, pasta and bread) and then cooling them. This “retrograded resistant starch” isn’t naturally present in these foods and can only be produced by converting common starch with cooking and cooling.
Scientists in Spain measured pressure cooked potato starch samples at 100°C (boiling), and with pressure to 120°C (equivalent 15 psi) and 250°C using an autoclave to find out how much of the potato’s own starch would convert into resistant starch. An autoclave is a pressure vessel used for research and industrial applications that can operate from 1 to 50psi or more (depending on the model) – they can be brought up to pressure using water-generated steam, just like a pressure cooker. Although their paper doesn’t give exact data from their findings, their conclusion was..
…. [Resistant Starch] RS yields obtained in the [High-pressure Autoclave] HPA process were greater than the ones obtained using a boiling water bath as gelatinization system.
Which basically means you can convert more of the potato’s starch into the better-for-you “resistant starch” by pressure cooking compared to boiling. If eating cold mashed potatoes isn’t appealing, that’s OK. Reheating doesn’t destroy this newly created resistant starch – apparently it can increase it.
A BBC TV Show (Trust Me, I’m A Doctor) conducted a small experiment with cooked, cooled and reheated pasta and found that reheating continues the process of converting a food’s starch to resistant starch. All 10 volunteers had a 50% lower blood glucose response to the “cooked, cooled & reheated” pasta compared to the “cooked” or “cooked & cooled.” Evidence, according to the experiment’s author, that even more resistant starch was converted during reheating.
no acrylamide? no problem!
The potato research continues with Swiss researchers who took a bunch of potatoes to steam, roast, and fry to measure how much acrylamide was produced. Acrylamide is a carcinogenic compound that forms during high temperature cooking. The Swiss found that this compound is primarily created during dry cooking methods like roasting or deep frying. It turns out that steaming potatoes under pressure produced almost no acrylamide compared to dry cooking methods where the potatoes reached the same temperatures (25 μg/kg versus 1500 μg/kg ). BUT, if the pressure cooking temperature is raised from the 120°C (equivalent to 15 psi) to 160°C (only achievable with an autoclave) then acrylamide will start to develop even in the presence of steam and pressure (800 μg/kg).
Don’t worry, most potatoes need only 10 minutes at high pressure (115-120°C) to be fully cooked and these researchers pressure cooked theirs for 20.
It is not possible to create carcinogenic acrylamide when cooking potatoes at the high temperatures that can be achieved by household pressure cookers.
Pressure cooking and cooling potatoes produces a nutritional insoluble starch which has a lower glycemic impact. It’s likely that reheating pressure cooked potatoes will increase this resistant starch further for more nutritional benefits.
Aren’t your leftovers starting to look good right about now?!?
potato pressure cooker recipes
Start your quest for resistant starch with one of our pressure cooker potato recipes…
- Visit the new Pressure Cooker Nutrition section of this website, where we report on the latest research!
Andrews, Rayan. “Resistant Starch: What Is It? And Why Is It so Good for You?.” Precision Nutrition Inc, 2011. Web. 25 May 2016.
Escarpa, A., et al. “Resistant starch formation: Standardization of a high-pressure autoclave process.” Journal of Agricultural and food chemistry44.3 (1996): 924-928.
van Tulken, Chris, MD. “Is Reheated Pasta Less Fattening?” BBC News Magazine, 16 Oct. 2014. Web. 20 May 2016.
Biedermann, Maurus, et al. “Methods for determining the potential of acrylamide formation and its elimination in raw materials for food preparation, such as potatoes.” Mitteilungen aus Lebensmitteluntersuchung und Hygiene 93.6 (2002): 653-667.