Xanthan Gum

Humans have been breeding plants for thousands of years, and agriculture was a watershed in our evolution. Plants are bred to exhibit desirable traits, a process that was sometimes helped along by spontaneous mutations – such as the mutation that brought us sticky rice about 1,000 years ago (Ronald, 88). New techniques have developed over the past century, driven by new technologies and an ever deeper understanding of genetics.

No longer must plant breeders wait around for a spontaneous mutation to bring us the greatest thing since sticky rice. A method called “mutation breeding” is used to create different varieties of plants. Mutations are deliberately induced by exposing plant seeds to radiation or placing them in carcinogenic solutions. Any seeds that survive are grown and examined for desirable traits. There are more than 2,000 plant varieties developed by mutation breeding, which is considered a form of conventional breeding and is acceptable in organic agriculture. Lundberg Family Farms, for example, produces an organic short-grain brown rice, a variety called Calrose 76 (Ronald, 88-91), which was developed by the California Agricultural Research Station at UC Davis. Calrose 76 was the end product of efforts to produce a short rice plant that matured early, during which rice seeds were mutated by exposure to gamma-ray-emitting cobalt isotopes (Sleper, 249).

Just as some crop varieties were developed by mutation breeding, deliberate mutation by exposure to mutagens is also used to create microorganisms capable of producing food ingredients as byproducts of their metabolism. This technology predates genetic engineering, and is considered acceptable practice in making foods that are certified organic. These microbes can also be genetically engineered rather than exposed to mutagens to achieve the same ends. Food products created by microbes include xanthan gum.

Xanthan Gum: some produced via mutagenesis; some produced via genetic engineering

In nature, Xanthomonas campestris is a bacterial plant pathogen, infecting vascular tissues and consuming the glucose therein, producing a gummy byproduct called xanthan that eventually interferes with nutrient transport. It is safe for human ingestion and is used as a thickener for food, in gluten-free baking, and in applications in other industries (Tortora, 801). Every year, 30,000 tons of xanthan gum are commercially produced (Silva).

A 1993 paper describes a new, mutated strain of Xanthomonas campestri™ that could degrade lactose in lieu of the usual glucose or corn syrup (Paz). A strain of X. campestris that can turn a waste product into a profitable polymer is useful for food scientists, because lactose is available in abundance as a byproduct of cheese making – nine pounds of whey are produced for every pound of cheese, and Americans eat a lot of cheese. Scientists selected for strains of X. campestris that grew on a lactose substrate, allowing them to harness the power of microbes to create the viscous material that we call xanthan gum. The newly developed lactose-utilizing bacteria produced 30 g/L of xanthan gum for every 40 g/L of whey powder (Tortora, 801).

Earlier, in the 1980s, a β-galactosidase gene from Escherichia coli was inserted into X. campestris to create a genetically modified xanthan-gum producer; its ability to ferment xanthan gum from a whey substrate was comparable with the ability of the unmodified bacterium to ferment xanthan gum from the traditional glucose-based substrate. Despite success in genetically engineering a xanthan-producing bacterium, there were two concerns. The first concern seemed to be the public’s fears about inserting foreign DNA into organisms. The second was that the plasmid containing the gene coding for β-galactosidase also included an antibiotic-resistance gene as a marker (Yang). These concerns led to efforts to create a strain of X. campestris by induced mutation rather than transgenic modification.

A Chinese team describes a method for identifying strains of X. campestris that can ferment xanthan gum on a lactose substrate. Such a bacteria strain would need to contain the gene coding for β-galactosidase, the enzyme capable of cleaving lactose. They sought a strain that occurred without genetic modification, to avoid using an antibiotic-resistance gene as a marker. A strain of X. campestris, Xc17, was determined to carry this gene, and then was exposed to a mutagen (nitrous acid) to create a strain, Xc17L, capable of 20 times more β-galactosidase activity than the original, unmutated strain. It was found to produce as much xanthan gum on a lactose substrate as X. campestris can traditionally ferment on a glucose substrate (Yang).

Is Xanthan Gum Vegan?

Regardless of your feelings about GMOs, as a vegan you might want to avoid xanthan gum that was grown on a lactose substrate. I emailed the manufacturers of two salad dressings that are currently in my refrigerator, both of which contain xanthan gum (and one of which explicitly labeled their product as vegan). I asked if they knew what substrate the xanthan gum was fermented on. I also wrote to Bob’s Red Mill, a natural foods maker whose xanthan gum is available in health-food stores, and asked the same question. It turned out that both of my salad dressings were manufactured by Drew’s, and they said that their xanthan gum is produced on a corn-sugar or corn-starch substrate. Bob’s Red Mill says they use corn and soy products to feed the bacteria that produce their xanthan gum.

The question of whether xanthan gum produced on a substrate of whey is vegan is probably best left to the individual vegan to determine. On the one hand, the use of an animal product in its manufacture should disqualify it from being considered vegan, even if no whey is present in the final product. On the other hand, it seems that the demand for xanthan gum does not drive the production of whey; rather, it is the production of whey as a byproduct that drives food scientists to find uses for it. Vegans, by abstaining from cheese, are not driving the production of millions of pounds of whey. It seems better to find a use for whey than to dispose of it, not only to minimize waste but also because whey disposal can have negative ecological impacts (Silva).

References

Paz, F., Trebbau, G., Vierma, L. (1993). Comparison of the Properties of Commercial Xantham Gum with a Xanthan Gum Produced by Xanthomonas campestri™ Using Lactose as Sole Source of Carbon. Developments in Petroleum Science, 39, 427. (Abstract only)

Ronald, P.G., Adamchak, R.W. (2008). Tomorrow’s Table: Organic Farming, Genetics, and the Future of Food. Oxford University Press.

Silva, M.F., et al. (2009). Production and characterization of xantham gum by Xanthomonas campestris using cheese whey as sole carbon source. Journal of Food Engineering, 90(1), 119-123.

Sleper, D.A. (2006). Breeding Field Crops. Wiley-Blackwell.

Tortora, G.J., Funke, B.R., Case, C.L. (2010). Microbiology: An Introduction. San Francisco: Pearson Benjamin Cummings.

Yang, T. C., Wu, G. H., & Tseng, Y. H. (2002). Isolation of a Xanthomonas campestris strain with elevated β-galactosidase activity for direct use of lactose in xanthan gum production. Letters in Applied Microbiology, 35(5), 375-379. doi:10.1046/j.1472-765X.2002.01202.x

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