When it comes to managing water and providing texture, gums are effective ingredients in the product-development arsenal, and locust bean gum (LBG) is no exception. It is extracted with water and alcohol from the endosperm of the seeds of the European carob tree, Ceratonia siliqua, an evergreen that grows in the Mediterranean area. The seeds grow in pods and have a uniform size—about 200 mg—leading medieval jewelers to use them as a standard weight, hence the origin of the carat. (Locust beans were known as keration in Greek, or qirat in Arabic.)
Function follows form
Today, the seeds are used to produce locust bean (or carob) gum, a galactomannan polysaccharide with a molecular weight of 400,000 to 1,000,000, made up of long chains of the sugars galactose and mannose. The main chain consists of (1-4) linked β-D mannose residues, and the side chains are (1-6) linked α-D galactose. Its composition varies, but it usually has approximately 3.5 randomly distributed mannose residues for every galactose residue, although that number can range from 2.8 to 4.9. This structure can affect the properties: Less galactose increases the chains’ flexibility, but increases their extensibility. This structure is similar to that of guar gum, but the uneven side-chain distribution makes it less soluble and less viscous. It forms weak, thermally irreversible gels due to the association of the parts of the chains lacking galactose residues. Reducing temperature and water activity can increase this association, allowing the formation of a 3-D network and gel. This is the reason LBG works so well in ice cream: The weak gel produces a smooth texture and doesn’t give ice cream a slimy mouthfeel, plus the gum provides meltdown resistance.
The structure also influences LBG’s hydration properties. While it can undergo some swelling in room-temperature water, it requires higher temperatures, 60 to 90ºC, for complete hydration. “Locust bean gum reacts differently dependent upon the temperature used,” explains Rodger Jonas, national business development manager, P.L. Thomas & Co., Morristown, NJ. “Higher temperatures will result in full activation, but room temperature will result in an approximate 35% utilization of the gum’s capabilities.” Salt, sugar and other ingredients that compete for water can slow the hydration rate.
To avoid lumps when using LBG, proper dispersion is needed. “There are a few ways to help disperse LBG,” says Grace Wang, food scientist, TIC Gums, Inc, Belcamp, MD. “Use an agglomerated powder, use an aspirator, dry blend with sugar, or disperse in oil. The first two methods don’t require any extra blending steps, unlike the other two. Once dispersed, though, LBG does need to be heated to at least 165°F for full hydration and functionality.”