Physical properties

Triglycerides are hydrophobic substances that are soluble only in some organic solvents. Unlike many other types of complex lipids, they possess no electric charges and are therefore referred to as neutral lipids. The molecular structure of a few triglycerides that have been studied in crystals indicates that the acyl chains on the 1 and 2 carbons of glycerol, together with the 1 and 2 carbons of glycerol itself, form a straight line. Carbon 3 projects at right angles to this line, but the acyl chain on its glycerol folds over at the carboxyl carbon to lie alongside the acyl chain on carbon 1. Triglyceride molecules look much like a tuning fork and, when packed together, produce layered crystals.

The melting temperatures of mixed triglycerides are roughly an average of the melting temperatures of their constituent fatty acids. In simple triglycerides, melting temperatures rise with increasing acyl chain length but drop with increasing number of double bonds. Melted triglycerides are generally quite viscous oils. From the physiological standpoint, it is important that most stored triglycerides be fluid at body temperature in order to permit their rapid mobilization as an energy source. Liquidity is also important since subcutaneous stored fats perform an insulating function that must not interfere with the mobility of the organism and its parts.