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The determination of acetic, propionic and butyric acids in cheese

Summary A method has been developed for the routine determination of acetic, propionic and butyric acids in cheese. The cheese sample is homogenized with water (1:2) at 40°C for 15 min and the slurry centrifuged at −5°C and 12000 g for 10 min. The free fatty acids in a portion of the aqueous centrifugate are adsorbed on to a column of anion-exchange resin in the hydroxide form. After washing the column with water to remove extraneous material the acids are eluted from the resin with aqueous formic acid. Amino acids in the acidic eluate which interfere with subsequent analyses are removed by a cation-exchange resin column in the hydrogen ion form. The concentrations of acetic, propionic and butyric acids in the cation-exchange resin eluate are determined by isothermal gas chromatography using a glass column (1·8m×2mm i.d.) packed with Chromosorb 101 (100/120mesh). Cheese oil-water partition coefficients are then used to calculate the concentrations of acetic, propionic and butyric acids in the cheese sample.