Tristearin, also known as glyceryl tristearate, is a saturated long-chain triacylglycerol (TAG) composed of three stearic acid (octadecanoic acid, C18:0) molecules esterified to a glycerol backbone. It is predominantly found in animal fats such as beef tallow and in fully hydrogenated vegetable oils. Tristearin represents the terminal compound of the saturated TAG series following tripalmitin and is well known for its sharp melting profile, making it valuable in confectionery, pharmaceutical, and cosmetic formulations.

Chemical Structure

Tristearin has the molecular formula C₅₇H₁₁₀O₆ and a molecular weight of approximately 891.5 g/mol. Its symmetric sn-glycerol backbone bears three linear stearoyl chains esterified at the sn-1, sn-2, and sn-3 positions. This highly ordered structure confers pronounced hydrophobicity (logP ≈ 18.77; log10WS ≈ −20.38), promotes dense β-crystalline packing, and enables enzymatic hydrolysis by lipases to release free stearic acid.

Physical Properties

Tristearin is a white, odorless crystalline solid with a melting point between 71 and 73 °C and a density ranging from 0.86 to 0.91 g/cm³. It has a high boiling point (~813 °C) and a flash point of approximately 299 °C. Insoluble in water, it dissolves readily in hot organic solvents such as benzene, chloroform, and ether. Its stable β-polymorphic form, characterized by high enthalpy of fusion (ΔH_fus ≈ 115–203 kJ/mol), allows precise thermal processing without eutectic softening.

Biological Functions

In biological systems, tristearin serves primarily as an energy storage lipid. Upon digestion, it is hydrolyzed to stearic acid, a saturated fatty acid known to exert a neutral effect on serum LDL cholesterol compared with palmitic acid. Stearic acid contributes approximately 4% of membrane phospholipid fatty acids and is metabolized more slowly than medium-chain triglycerides, supporting prolonged energy release and increased satiety without adverse effects on lipid profiles.