Insecticidal Sweeteners

August 11, 2016

While not a fanatic, I'm always leery about food whose ingredient labels read like the index of a chemistry textbook. I've learned to read ingredient labels more carefully, now, since I've found that I'm somewhat allergic to psyllium. This is something I discovered earlier this year while eating a high-fiber bread. The bread was so tasty, that I was eating about four slices per day; and, after a few days, my skin began to itch. A little Internet sleuthing led to my easy diagnosis.

Artificial sweeteners are ubiquitous in foods and drinks. In the United States, they're certified to be harmless by the Food and Drug Administration, a respected government agency. That's why I'm not afraid to use sucralose (the "yellow packets") in my coffee, still adding a little sugar. I tried Truvia (the "green packets"), but that sweetener changes the taste of the coffee.

Choose your color. Green packets, a recent market entry, are missing from this image. The apparent color convention for packets of natural sugar (sucrose) is white for refined sugar, and brown for raw sugar. (U.S. Department of Health and Human Services image.)

These yellow and green packets join the "pink packets" containing saccharin (C₇H₅NO₃S, 2H-1λ⁶,2-benzothiazol-1,1,3-trione) along with ingredients to reduce its bitter aftertaste. There are also the "blue packets" containing Aspartame (C₁₄H₁₈N₂O₅, N-(L-α-Aspartyl)-L-phenylalanine, 1-methyl ester) along with aftertaste-reducing ingredients. People with a condition known as phenylketonuria need to avoid aspartame.

Truvia is the trade name for the sweetener containing rebaudioside A, an extract of the Stevia rebaudiana plant, along with the simple sugar alcohol, erythritol (C₄H₁₀O₄, (2R,3S)-butane-1,2,3,4-tetraol).[1] Erythritol, an approved food additive in the US and many other countries, occurs naturally in some fruits.

Erythritol molecular structure. (Via Wikimedia Commons.)

Since the ingredients of Truvia have been shown to be safe for human consumption, it was a surprise when it was found to be toxic to fruit flies (Drosophila melanogaster).[2] Fruit flies fed Truvia died in six days, and further study showed that the culprit wasn't stevia; rather, it was the erythritol.[2] I wrote about this finding in a previous article (One Man's Food..., June 13, 2014). Another sugar alcohol, mannose, is toxic to honey bees, but not fruit flies.[2]

Drosophila melanogaster (female, left, and male, right) (Via Wikimedia Commons.)

This same Drexel University research team that made this discovery has just published results of fruit fly experiments using polyols similar to erythritol, all of which have been approved for human consumption.[3-4] They fed these to adult Drosophila melanogaster along with controls that included sucrose and non-sweetened food to determine the affect on their longevity.[3] All of the polyols, except for D-mannitol, had no affect. The D-mannitol, however, was slightly toxic, but only to the female of the species (see graph).[3] Female fruit flies were five times more likely to die than males after D-mannitol consumption.[4]

D-mannitol is selectively toxic to female fruit flies. (Fig. 2 of Ref. 3, published under a Creative Commons Attribution Non-Commercial License.[3])

In the experiments, groups of fruit flies were fed with particular sweeteners mixed with their food, and there were two control groups which were fed food mixed with the naturally occurring sugar, sucrose, and unmodified feed.[4] As previously found, erythritol was especially effective in killing fruit flies, all of which were dead by the sixth day; however, two other polyols, malitol and xylitol, appeared to have no effect.[4]

Polyol toxicity to fruit flies. (Fig. 1 of Ref. 3, published under a Creative Commons Attribution Non-Commercial License.[3])

When fruit flies were fed with D-mannitol, a sweetener used in chewing gum, and as a coating to hard candy or dried fruit to prevent sticking, there was no apparent effect for the first week. After the seventh day, these fruit flies displayed a higher death rate than the controls, and the effect had statistical significance at the twelfth day. The 50% survival point was reached at day 17.[4]

There is no known reason why the female fruit flies should be more susceptible than males to the toxicity of D-mannitol. Says Sean O'Donnell, a professor and associate department head of Biodiversity, Earth & Environmental Science at Drexel,

"Implications for insect control could exist, because females are the real reproducers and affecting females can reduce population growth... Furthermore, many social insect pests — such as Hymenoptera, which includes ants and wasps — have female-based colonies."[4]

O'Donnell further clarifies that there is nothing in these experiments that should dissuade human use of these sweeteners. "All the compounds we tested are vetted and human-safe... The effects on insects don't really inform human health issues in this case."[4]

References:

1. Steven J. Catani, "Erythritol-containing tabletop sweeteners and methods of producing same," US Patent Application No. 12/147,075, Publication No. 20090004355, Priority Date, June 29, 2007. Also published as CA2691547A1, EP2173191A1, and WO2009006200A1.
2. Kaitlin M. Baudier, Simon D. Kaschock-Marenda, Nirali Patel, Katherine L. Diangelus, Sean O'Donnell and Daniel R. Marenda, "Erythritol, a Non-Nutritive Sugar Alcohol Sweetener and the Main Component of Truvia®, Is a Palatable Ingested Insecticide," PLoS ONE, vol. 9, no. 6 (June 4, 2014), Document No. e98949, doi:10.1371/journal.pone.0098949. This is an open access article, available as a PDF file, here.
3. Sean O'Donnell, Kaitlin Baudier, and Daniel R. Marenda, "Non-Nutritive Polyol Sweeteners Differ in Insecticidal Activity When Ingested by Adult Drosophila melanogaster (Diptera: Drosophilidae)," Journal of Insect Science, vol. 16, no. 1 (June 7, 2016), Article no, 47, doi: 10.1093/jisesa/iew031. This is an open access article with a PDF file here.
4. Frank Otto, "Ladykiller: Artificial Sweetener Proves Deadly for Female Flies," Drexel University Press Release, June 27, 2016.