Soap is made by subjecting lard (pig fat) to saponification, in which heat and a strong alkali (NaOH or KOH) release fatty acids in the form of sodium or potassium salts from triacylglycerols. When mixed with water, the fatty acids in the soap function as amphipathic molecules that form micelles as a result of the hydrophobic effect (see Figure 2.43). With sufficient agitation, these micelles trap greasy food particles released from hands or clothing and are washed away during the rinsing phase. Free fatty acids inside cells would also act as soap and disrupt biological membranes, but fatty acids inside cells are chemically neutralized by linkage to glycerol or are biologically sequestered in the cell by binding to fatty acid carrier proteins.
Everyday BioChem 