Determination of Free Fatty Acid Content of Cheddar Cheese by a Copper Soap Method

Abstract

A relative index of hydrolytic rancidity in Cheddar cheese was developed from Cu soap method to measure free fatty acid content of Cheddar cheese. Cu soap derivatives of free fatty acids were extracted by a mixture of chloroform, heptane and methanol. Extracted Cu soaps were reacted with a color reagent, sodium diethyl dithiocarbamate and the Cu-color complex was quantitated spectrophotometrically at 440 nm. Recovery experiments with caprylic acid indicated that the Cu soap method does not recover completely short chain fatty acids. Long chain free fatty acids make up the major portion of free fatty acids in Cheddar cheese even though the short chain fatty acids may have a more significant impact on flavor. Large increases of total fatty acids in a Cheddar cheese sample correlate with development of rancid flavors. Coefficients of variation for this method ranged from 1.9-4.4% for replicate analysis of individual cheese samples. Total free fatty acid content of nonrancid Cheddar cheese samples determined by the Cu soap method were comparable to reported contents.