Determination of organic acids and sugars in cheese, milk and whey by high performance liquid chromatography

Abstract

This report details fast economical methods for extraction and quantitation of organic acids and simple sugars using high performance liquid chromatography (HPLC). The extraction method does not require a clean up step since the HPLC columns are not susceptible to contamination by co-extractants. The methods were used to survey Cheddar cheese-making trials as well as commercial cheeses. In the Cheddar cheese, the lactic acid (11.53–13.37mg g −1, formic acid (0.28–0.50mg −1g), citric acid (2.10–2.13mg g −1) and acetic acid (0.14–0.15mg g −1) varied very little between trials and between batches within the trials. Analysis of commercial cheeses showed a range of concentrations of organic acids between varieties and between samples of the same variety. The lactose content was high enough in the milk and whey from the cheese trials (39.11–46.21 mg ml −1) to use a refractive index detector (RI). The residual lactose concentration in Cheddar and commercial cheeses was too low to be measured accurately by RI, so a different and more sensitive system with a pulsed amperometric detector (PAD) was used for this assay. A significant amount of lactose was found in Cottage cheese (4.31-0.00 mg g −1); only very low residues of mono- and disaccharides were found in the other commercial and Cheddar cheese samples.