Determination of Organic Acids During the Fermentation and Cold Storage of Yogurt

¹ Instituto de Productos Lacteos de Asturias, Consejo Superior de Investigaciones Cientificas (CSIC), Carretera Infiesto s/n. Ap. Correos 85, 33300 Villaviciosa, Spain
² Department of Dairy Science, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803

The objective of the present study was the separation and quantification of orotic, citric, pyruvic, lactic, uric, formic, acetic, propionic, butyric, and hippuric acids in a single isocratic analysis by HPLC. Two methods of extraction were compared: 1) acetonitrile and water and 2) .01N H₂SO₄. Recoveries of orotic, lactic, acetic, and propionic acids were 90% for both methods. Recoveries of citric, pyruvic, uric, butyric, and hippuric acids were not satisfactory with the acetonitrile method, but were acceptable using the H₂SO₄ extraction procedure. Yogurts were manufactured under laboratory-scale conditions, and samples were analyzed during fermentation and after storage at 4°C. Samples were analyzed for pH and organic acids. All of the organic acids exhibited varying degrees of increases and decreases during fermentation and storage. Formic and butyric acids were not detected under the conditions of this study.

Key Words: high performance liquid • chromatography • organic acids • fermentation • yogurt

Submitted on November 29, 1993
Accepted on May 10, 1994

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