… or at least economically practical.
Earlier this week I noticed a retweet of this event in my twitter feed:
— Michael Eisen (@SenatorPhD) March 23, 2017
Coincidentally, someone else posted this video about the Impossible Burger (which I hadn’t heard of before this week)
I always find stories about science and food to be interesting, and this even had a connection to my alma mater: the founder of Impossible Foods is Pat Brown of Stanford’s Biochemistry Department.
Via Google, I found some interesting things about the Impossible Burger. The video talks about their general approach of using analytical methods to figure out what constitutes the constellation of perceptions that we get when eating a particular food. But what this post is about is the secret ingredient: heme. When we talk about red meat, a lot of what makes it red is the iron in heme. I first learned about heme in any real detail at Stanford when I took intro biochemistry as an undergrad (back then the undergrads could take the same course as first year med students). Heme is found in myoglobin and hemoglobin, the major oxygen carrying proteins in muscle and blood. Heme is responsible for the “smoke ring” in BBQ. Heme is also found other proteins, and based on this story, it appears that Impossible Foods first tried to get heme from spinach chloroplasts. But I’m guessing that the yield was too low to scale up production, so they looked at another source.
Leghemoglobin is a heme protein that is made for nitrogen fixation. The Impossible Burger contains soy leghemoglobin, but it’s not actually made from soybeans, because the leghemoglobin is found in the root nodules, which are not normally harvested. Digging up the roots to get the leghemoglobin would negate some of the environmental benefits claimed by Impossible Foods, but it also is probably as economically inviable as getting heme from spinach leaves, if not worse. So to get the leghemoglobin, they cloned the soy protein into Pichia pastoris, a yeast used in biotech for protein overexpression. Here’s how Impossible Foods describes their ingredients:
The Impossible Burger is made from simple ingredients found in nature, including wheat, coconut oil and potatoes. We add one more special ingredient, called “heme.” Heme contributes to the characteristic color and taste of meat, and it catalyzes all the other flavors when meat is cooked. Heme is exceptionally abundant in animal muscle — and it’s a basic building block of life in all organisms, including plants. We discovered how to take heme from plants and produce it using fermentation — similar to the method that’s been used to make Belgian beer for nearly a thousand years. Adding heme to the Impossible Burger makes it a carnivore’s delight.
This struck me as kind of odd. Is there something special about Belgian beer fermentation that makes it more similar to Pichia protein production than normal beer fermentation? Belgian beer fermentation historically uses more wild yeast than others, but as far as I can tell from my reading, Pichia is not a desirable species in any beer fermentation, and the inoculum is going to be a pure culture, not the stuff falling off the cobwebs from a Trappist monastery.
The news coverage of the Impossible Burger has been pretty clear about the source of the heme. For example:
By taking the soybean gene that encodes the heme protein and transferring it to yeast, the company has been able to produce vast quantities of the bloodlike compound. Each vat of frothy red liquid in the lab holds enough heme to make about 20,000 quarter-pound Impossible Burgers. “We have to be able to produce this on a gigantic scale,” says Brown.
Thanks to the addition of heme, an iron-rich molecule contained in blood (which the company produces in bulk using fermented yeast), it is designed to look, smell, sizzle and taste like a beef burger.
But what I don’t see is in either article is the three letter acronym with a lot of baggage: GMO. It’s understandable, but kind of a shame, IMO. Impossible Foods got applied to the FDA for their GMO-based heme to be Generally Regarded as Safe. Most scientists I know would agree with that for most, if not all, extant GMO foods. But if golden rice and virus-resistant plants for poor farmers aren’t enough to sway GMO fearmongers, vegan burgers for first-world foodies are unlikely to do much.
Speaking of GM burgers, it’s been 10 years since Nature Biotechnology published a report of GM cattle where the PRNP gene was knocked out. Will we ever see CJD-free meat in the butcher’s section? That one really is a previously impossible product made possible by GM technology.