[Fine Chemicals] Properties of xanthan gum and its use in food

Xanthan gum is built from a five-sugar repeating unit made of D-glucose, D-mannose, D-glucuronic acid, acetic acid, and pyruvic acid. The molar ratio of glucose, mannose, and glucuronic acid is 2.8:3.0:2.0. Xanthan gum is produced from a fermentation medium containing sugars (such as glucose, sucrose, starch, hydrolyzed starch) with a suitable nitrogen source, dipotassium hydrogen phosphate, and a small amount of trace elements, acted on by a strain of Xanthomonas campestris, then fermented, extracted, dried, and ground. Xanthan gum is tasteless, odorless, non-toxic, safe to eat, and easily soluble in water. In aqueous solution it appears as a polyanion and has unique physicochemical properties. In industrial production it's mainly used as a thickener, and also as a suspending agent, emulsifier, and stabilizer. So far, xanthan gum is considered the best-performing biological gum internationally, and is widely used in food, fruit juice, beverages, feed, cosmetics, medicine, ceramics, firefighting, petroleum, and other industries; its market growth potential exceeds all hydrophilic gums. This article reviews the structure, properties, and production of xanthan gum, and describes its applications in the food industry. 01 Structure Xanthan gum is a pale white or light cream-yellow powder made of repeating five-sugar units. Its main chain is the same as cellulose, i.e., glucose linked by β-1,4 glycosidic bonds, and three linked monosaccharides form its side chain: mannose–glucose–mannose. The mannose attached to the main chain is usually modified by an acetyl group, the mannose at the end of the side chain is modified by an acetal reaction with pyruvic acid, and the middle glucose is oxidized to glucuronic acid. Besides its regular primary structure, xanthan gum also has a secondary structure. By X-ray diffraction and electron microscopy, xanthan gum molecules form a regular helical structure through hydrogen bonding. The double helices form a networked three-dimensional structure through weak forces—this is xanthan gum's tertiary structure, and it exists in aqueous solution in liquid crystal form. 02 Properties Xanthan gum is called the "industrial MSG" and is currently the microbial polysaccharide with the largest production scale and the widest use in the world. Its main properties are as follows. (1) Xanthan gum is tasteless, odorless, and highly safe to use, with high viscosity—a 1% aqueous solution has about 100 times the viscosity of gelatin, so it works as a good thickener and stabilizer. (3) Unique rheology: under shear, the solution's viscosity drops rapidly, and once the shear is removed the viscosity immediately recovers. This property gives foods like ice cream, ham sausage, fruit juice, plant-protein drinks, and baked goods a good mouthfeel. It also makes xanthan gum widely used in oil drilling and extraction. (4) Good heat stability: it keeps its special functions over a wide temperature range (−18 to 130°C), making it a good auxiliary material for frozen and baked foods. (5) Acid-base stability: its viscosity is basically unaffected by acids and bases, and it keeps its original properties within pH 1–12, giving it a wide range of applications. (6) Strong antioxidant and anti-enzymatic action: it still works even in the presence of sodium hypochlorite, hydrogen peroxide, and bioactive enzymes. (7) Broad compatibility.