Simultaneous determination of acetoin and diacetyl in yogurt by a spectrophotometric method

Abstract

The aim of this study was to develop a rapid and relatively simple protocol for the simultaneous quantitative determination of the main volatile compounds acetoin and diacetyl found in yogurt. Both these substances are the common flavor components in cultured dairy products. Acetoin/diacetyl determination is important because its concentrations represent criteria for the quality appreciation of the lactic starter cultures. This proposed method employs the reactions of acetoin and diacetyl with 1-naphthol and creatine in an alkaline medium that lead to the formation of a purple chromogenic compound that can be quantified spectrophotometrically. Under these conditions diacetyl reacted fast during the first 10 minute causing a large increase in peak height (absorbance). The recoveries of acetoin and diacetyl were in range between 90.60-100.86%, while the detection limits were 0.24 and 0.45 ppm, respectively. The method showed linearity in a concentration up to 20.00 ppm for both acetoin and diacetyl. The relative standard deviation (RSD%) ranged from 2.75 to 3.45%. Reliability of the method was established by parallel determination using GC/MS method. The proposed spectrophotometric method was applied for the monitoring of these flavor compounds in yogurt samples, after separation of them by steam distillation, during a 21 days period time. The concentration of acetoin decreased very slowly through 0–21 days while the concentration of diacetyl increased from 0.50 to 17.53 ppm during the first 14 days and remained constant through the rest of the analyzed period.