Browsing by Subject "acetoin"

Diacetyl and acetoin are typical butter flavours, which are also present in other fermented dairy products such as sour milk. Diacetyl and acetoin are mainly produced from their precursor ?-acetolactate (ALA) by lactic acid bacteria as a product of their metabolism. In the literature review the formation of diacetyl and acetoin were examined along with the typical techniques to analyse diacetyl. The aim of the experimental work was to develop and validate a method for the determination of diacetyl and acetoin in sour milk by gas-chromatographic technique coupled with flame ionisation detector (GC-FID). In this study a suitable column and gas-chromatographic parameters to analyse diacetyl and acetoin were obtained and two sample preparation techniques were tested. In addition, the reactivity of diacetyl and acetoin and their interactions with the sample matrix were examined. Finally the method was validated. In the complete method, the proteins of the sample were precipitated with acetone and the sample was centrifuged. ALA along with protein-bound diacetyl and acetoin were extracted from the supernatant by solid-phase extraction (SPE), followed by the GC-FID-analysis of free diacetyl and acetoin in the SPE-permeate. GC-FID-analysis was performed using a polar ZB-FFAP-column, split-ratio 30:1 and inlet and detector temperatures 200 ?C and 250 ?C, respectively. Diacetyl and acetoin are reactive and easily evaporated, which complicated their analysis. ALA was mainly decomposed to acetoin in the hot injector. This finding resulted in extraction of ALA from the sample by SPE. In the sour milk matrix, diacetyl and acetoin were believed to appear in three different forms: free and strongly or weakly bound to proteins. The compounds were easily transformed from one form to another. Possibly, also cyclopentanone, the internal standard, was partly bound to the sample matrix. The reactivity of the compounds prevented the determination of total diacetyl and acetoin. Therefore, the method was suitable only for the determination of free diacetyl and acetoin, which, in fact, constitute the buttery aroma in sour milk. Sour milk contained more free acetoin than diacetyl. The method was found to be selective and sensitive for the determination of diacetyl and acetoin. However, the reactivity of the compounds impaired the repeatability of the results. Further research is needed to discover factors affecting the binding of diacetyl and acetoin to the sample matrix. Furthermore, different internal standards and solvents ought to be tested in place of cyclopentanone and acetoin.