Gas chromatographic determination of free fatty acids in olive mill waste waters

A method was developed for the gas chromatographic (GC) determination of free fatty acids (FFA) in olive mill waste waters (OMW). The sample under examination was acidified to pH 2-3 to cause protein precipitation. Elimination of the colloidal fraction was obtained by addition of acetone. Polyvynilpirrolidone was added to eliminate the interference by phenolic compounds. The sample was then clarified by centrifugation and an aliquot was injected into the GC system. Both the C2-C8 FFA coming from microbial metabolism and the C16-C18 FFA coming from the oil originally present in the olives were quantified in a single run by employing nonanoic acid as the internal standard. Rather high amounts in particular of acetic acid were generally found, usually in the range from 1000 to 4000 mg/L of OMW.