The Exposition Universelle in 1855 in Paris was quite a spectacle. It drew more than 5 million visitors, including Queen Victoria and Prince Albert, the first British royals to set foot in France for over 400 years. Visitors were treated to exhibits of the crown jewels of France, the world’s first sewing machine, carved caskets made of Goodyear’s novel vulcanized rubber, and a Parisian inventor’s 10-foot-high percolator that brewed 2,000 cups of coffee an hour. Crowds gathered around McCormick’s reaper, a machine that revolutionized agriculture by making it possible to harvest grain more efficiently than men wielding scythes. Thanks to the reaper, food shortages were less likely, because far more land could be now be farmed.
Also on display were items of medical interest, such as a sample of “Trehala,” a powdered substance popular in the Islamic world with a reputation for relieving respiratory ailments. The name apparently was a corruption of “Teherani,” meaning coming from Tehran, the capital of Persia. Trehala was made from the crushed cocoons of Larinus maculates, a beetle that spends its life crawling on the leaves of a host plant. Whether Trehala ever had any medicinal value is questionable, but it certainly has importance in the history of chemistry. It was the raw material from which in 1859 famed French chemist Marcellin Berthelot isolated “trehalose,” a simple sugar would go on to have a variety of applications.
Long before Berthelot’s experiments, Trehala had made its mark under quite a different name. According to some biblical scholars, this insect residue was the “manna” that God had sent from heaven to feed the starving Israelites as they wandered through the desert after Moses had led them out of slavery in Egypt. The Bible describes manna as tasting like a wafer made with honey, which could well be a description of the taste of trehalose, which being composed of two molecules of glucose joined together is indeed sweet. This sugar is widespread in nature, found in mushrooms, shellfish, algae, honey, yeast and anything made from yeast, such as wine, beer and bread.
What makes trehalose interesting is its ability to preserve the cell structure in foods, especially after heating and freezing. It appears to replace the moisture in cells that is driven out by heat and thereby prevents the collapse of the network of proteins that is key to cell integrity. Undesirable changes in texture can also occur when cell structure is disrupted through the formation of crystals. Trehalose interferes with crystal formation in ice as well as in starch and therefore finds a use in ice cream, frozen foods and baked goods.
Furthermore, foods and pharmaceuticals with added trehalose can be dehydrated and reconstituted with little damage. This protective effect is particularly handy when it comes to preserving the proteins that constitute vaccines, antibodies and blood coagulation factors. With trehalose these can be stored in a dehydrated fashion requiring no refrigeration, ready to be reconstituted as needed, solving the problem of a high percentage of vaccines in developing countries being wasted due to lack of refrigeration. Trehalose-dried blood is also a possibility and could be important in fighting critical blood shortages that are sometimes experienced.
Today trehalose is produced on a large scale from starch with the aid of bacterial enzymes and is used by the food and pharmaceutical industries as an additive primarily because of its preservative properties. Extensive feeding studies involving both animals and humans have failed to reveal any adverse effects. Until now.
The heretofore sweet science of trehalose may be souring with the finding that some strains of Clostridium difficile bacteria have the ability to use trehalose as a nutrient. C. diff infections plague hospitals since these bacteria are resistant to many antibiotics and frolic when competing bacteria are killed off.
Since about 2000, C. diff infections have become not only more common, but more serious, puzzling scientists. Now there may be an explanation. A study published in the prestigious journal Nature in 2018 showed that some strains of C. diff can use trehalose as a nutrient, and when it is available, these strains outcompete others. Unfortunately, these are also strains that produce a higher level of the toxins that cause gastrointestinal distress. Interestingly, the increase in severity of the C. diff infections coincides with the discovery of an easy method to produce trehalose from corn starch and its introduction into the food supply.
At this point, the connection between trehalose and C. diff infections is best described as intriguing but in need of further exploration. Calls for banning trehalose are premature, especially given that this sugar doesn’t cause blood glucose to spike the way that other sugars do. However, the potential connection between trehalose and C. diff bacteria is an illustration of the complex interplay among our diets, our microbes and our health. Even additives that have passed all regulatory safety requirements may have unintended consequences.
Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss).
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