Triolein, also known as glyceryl trioleate, is an unsaturated triacylglycerol (TAG) composed of three oleic acid (C18:1 cis-9) chains esterified to a glycerol backbone. It is a predominant lipid component of vegetable oils such as olive, canola, and sunflower oils, accounting for approximately 55–80% of the total lipid content in olive oil. Compared with saturated triacylglycerols such as tristearin, triolein confers enhanced fluidity and low-temperature stability to lipid matrices.
Chemical Structure
Triolein has the molecular formula C57H104O6 and a molecular weight of 885.4 g/mol. Each oleoyl chain contains a cis double bond at the Δ9 position, generating a kinked molecular geometry that limits tight lipid packing. The ester linkages exhibit partial double-bond character, with characteristic bond lengths of approximately 1.23 Å for the carbonyl (C=O) and 1.36 Å for the C–O bond.
Physical Properties
At room temperature, triolein is a colorless, viscous liquid with a density of 0.9078 g/cm³ at 25°C. It has a low melting point of approximately 5°C and a boiling point near 471°C under reduced pressure (10 mmHg). Triolein is extremely hydrophobic, with a logP value of approximately 18.1 and very low aqueous solubility (log10WS ≈ −19.94). It is readily soluble in organic solvents such as chloroform, ethanol, and ether but is immiscible in water. The low melting point results from cis-unsaturation, which disrupts crystalline packing.
Biological Functions
In biological systems, triolein is hydrolyzed by pancreatic lipases to release oleic acid, a monounsaturated fatty acid associated with reduced LDL cholesterol levels and maintenance of membrane fluidity, where oleic acid can account for approximately 15–20% of membrane phospholipids. Triolein serves as a sustained energy source through β-oxidation and is digested more slowly than saturated triacylglycerols, contributing to prolonged postprandial satiety.
