Monday, September 26, 2011

New Results From the "Test Tubers": Paleolithic Men Could Have Been Healthier Had They Microwaved Their Potatoes.

Image 1: Potato roasting caveman-style - probably not the best way to "cook" your potatoes
As a non-native-speaker, I must admit that the first time I heard someone talk about "tubers" was on Robb Wolf's famous podcast, back in the day, when I was "listener #6" (or seven ;-). Contrary to common (foreign) belief, not all Germans subsist on potatoes and sauerkraut and, what's more, even those who do, don't really care that a potato is a "tuber", i.e. a "Knolle" in German - I suppose the idea that it grows in the dirt is not too appealing to some, while the large majority probably just doesn't care as long as those "tubers" make a good addition to their Schweinebraten... yet, whatever the reasons may be, my first encounter with "tubers" has ingrained the link of these "underground structure[s] consisting of a solid thickened portion or outgrowth of a stem or rhizome, of a more or less rounded form, and bearing ‘eyes’ or buds from which new plants may arise" (OED.com), as the venerable Oxford English Dictionary would have it, to the paleo style of eating so deeply into my brain that I have been seeing cavemen with roasted sweet potatoes on their sticks in front of a fireplace in my mind's eye, ever since. Now, if that really was the way life went, back in the paleolithic days, our ancestors did probably miss about 32% of the antioxidant magic of the tuberous roots - at least this is what the results of a recent study on the effects of different cooking methods on polyphenols, pigments, and antioxidant activity in potato tubers from the San Luis Research Center at the Colorado State University  would suggest (Perla. 2011).

In their experiment, Venu Perla, David G. Holm, and Sastry S. Jayanty
  • boiled - 1h in a sieved double-boiler,
  • microwaved + cooked - 10min in a commercial microwave oven at max. highest level +10min boiling, and
  • baked  - 1h at 204°C in a commercial pre-heated oven
six months old stored potato tubers of 5 cultivars and 9 advanced selections of Colorado state (skin-color: 4x russet; 6x red; 1x white; 3x purple) and analyzed the samples for total phenolics, total flavonoids, total flavonols, and DPPH (2,2-Diphenyl-1-pikryl-hydrazyl) radical scavenging activity.
Figure 1: Loss in total polyphenol content of 5 cultivars and 9 advanced selections of Colorado state potato tubers due to cooking, microwaving, and baking (data calculated based on Perla. 2011).
As the data in figure 1 shows, all three preparation methods led to profound reductions of the potatos' total polyphenol counts. With Purple Majesty being most and Russet Nugget being least perceptible to the heat induced reduction in total polyphenol count. The cultivars CO97222-IR/R and CO97226-2R/R exhibited the highest total polyphenol counts (+77% and +137% above average in the raw state), with the former being particularly resistant to cooking (+119% above average) and the latter being particularly resistant to microwaving and baking (+154% and +169% above average, respectively).
Figure 1: Loss in polyphenol, flavenoid and flavenol content of 5 cultivars and 9 advanced selections of Colorado state potato tubers due to cooking, microwaving, and baking (data calculated based on Perla. 2011).
The superior resistance of these red-fleshed potato cultivars to cooking treatments is yet relative polyphenol-specific, due to their extraordinary high flavenoid and flavenol content in the raw state, CO97222-IR/R and CO97226-2R/R do yet retain a 241%, 155%, 199% and 243%, 331%, 395% higher flavenoid and 78%, 34%, 17% and 80%, 98%, 181% higher flavenol content  than the average potato (in the study) even after cooking, microwaving and baking, respectively.

The scientists also observed that, contrary to the white and yellow fleshed tubers, where the major pigment was lutein, the "dominant pigments in the red and purple fleshed tubers were anthocyanins", the antioxidant activity of which has been implicated in the prevention (by some even the treatment) of obesity, cardiovascular disease, diabetes, hyperlipidemia and even cancer. Unfortunately, these pigments are just as susceptible to cooking, microwaving and baking as the polyphenols, flavenoids and flavenols, so that the total anti-oxidant activity (as measured by DPPH free radical scavenging assays) of the tubers that were tested in this study was reduced by -26%, -32% and -38% by boiling, microwaving and baking, respectively.
Please note: While it is unlikely that you will die from eating a single raw potato. The solanine that can be found in all parts of the plant, including the leaves, fruit, and tubers, is a natural fungicide and pesticide the plant produces to protect itself from insects, the ingestion of which can potentially be fatal!
Now, despite the fact that microwaving is only slightly less damaging that baking, I assume that putting the potatos directly into the fire, like the paloelithic men and women in my daydreams use to do it, probably is the worst way to prepare your tubers. Yet while even microwaving would have been a healthier option, the best and, from an evolutionary perspective, more natural solution would be to boil your potatoes.