Food companies utilize soy protein as an ingredient to increase the plant protein content in foods. One such company, Impossible Foods, uses soy as the main source of protein in its ImpossibleTM Burger. In addition, the Impossible Burger contains a unique ingredient called soy leghemoglobin (LegH), which is responsible for much of its meaty flavor.
What is Leghemoglobin?
Leghemoglobin (short for legume hemoglobin) is naturally found in the root nodules of legumes, such as soybeans, where it plays a crucial role in nitrogen fixation.1 LegH is an oxygen-binding protein that is structurally similar to myoglobin and hemoglobin, the major oxygen-binding proteins in animal muscle and blood, respectively.1,2 What enables LegH (and myoglobin and hemoglobin) to bind oxygen is an iron-containing molecule called “heme.” The heme molecule in LegH is identical to the heme found in both myoglobin and hemoglobin.2
Why is Soy Leghemoglobin Used in the Impossible Burger?
Scientists at Impossible Foods discovered that heme plays an important role in the creation of aromas and flavors that characterize cooked meat.3 Heme is also responsible for the bloody flavor and red color of raw meat and for the color transition from red to brown during cooking. The heme-iron provided by soy LegH is the highly bioavailable form of iron that is found in animal tissue.1,4
How is Soy Leghemoglobin Made?
Impossible Foods transferred the soy LegH gene into yeast in order to produce large quantities of LegH protein as sustainably as possible. Production of this ingredient by yeast fermentation has a smaller environmental footprint than digging up soybean root nodules and extracting the protein; however, it is identical to the LegH protein found in such root nodules.5
Is Soy Leghemoglobin Safe?
Heme has a long history of safe consumption while soy LegH is a novel food ingredient. Therefore, soy LegH was subjected to rigorous safety testing, including tests for allergenicity, mutagenicity, chromosome damage, and toxicity.5,6,7 In addition to being rapidly digested by pepsin, soy LegH does not share any meaningful similarity to known allergens or toxins.5,7 Feeding studies in rats found no indication of toxicity or adverse effect at consumption levels over 100 times greater than the 90th percentile estimated daily human intake.6,7 All of these data and more were submitted to the U.S. Food and Drug Administration (FDA) as part of the Generally Recognized As Safe (GRAS) notification process; the FDA issued its “no questions” letter in mid-2018.7
- Appleby, CA. Leghemoglobin and Rhizobium respiration. Annu Rev Plant Physiol. 1984;35(1):443–478.
- Carpenter, CE, Mahoney, AW. Contributions of heme and nonheme iron to human nutrition. Crit Rev Food Sci Nutr. 1992;31(4):333–367.
- US patent 14/797,006, allowed March 22, 2017.
- Proulx, A, Reddy, M. Iron bioavailability of hemoglobin from soy root nodules using a Caco-2 cell culture model. J. Agric. Food Chem. 2006;544:1518-1522.
- Jin, Y, He, X, Andoh-Kumi, K, Fraser, RZ, Lu, M, Goodman, RE. Evaluating potential risks of food allergy and toxicity of soy leghemoglobin expressed in Pichia pastoris. Mol Nutr Food Res. 2018;62(1):1700297.
- Fraser, RZ, Shitut, M, Agrawal, P, Mendes, O, Klapholz, S. Safety evaluation of soy leghemoglobin protein preparation derived from Pichia pastoris, intended for use as a flavor catalyst in plant-based meat. Int J Toxicol. 2018;37(3):241-262.
- Agency Response Letter GRAS Notice No.GRN 000737. United States Food and Drug Administration, Center for Food Safety and Applied Nutrition. Soy leghemoglobin preparation from a strain of Pichia pastoris. July 23, 2018. https://www.accessdata.fda.gov/scripts/fdcc/index.cfm?set=GRASNotices&id=737