Quantitation of Nine Lactones in Dairy Cream by Stable Isotope Dilution Assays Based on Novel Syntheses of Carbon-13-Labeled γ-Lactones and Deuterium-Labeled δ-Lactones in Combination with Comprehensive Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometry

Lactones are well-known aroma compounds in, e.g., fruits and fermented foods as well as in dairy products, such as cream or milk powders. The latter are often used in confectionary products, e.g., milk chocolate. Lactones are suggested to contribute to the distinct aroma of dairy products and have also been reported in milk chocolate. However, data on their contribution to the overall aroma of this type of chocolate are scarce. As a result of their pH-dependent instability and their low volatility, a reliable quantitation of lactones is a challenge. Thus, to allow for a quantitation of nine lactones in one single comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry in electron ionization mode run, new synthetic routes were developed for five carbon-13-labeled γ-lactones and four deuterium-labeled δ-lactones, with the isotope label in the ring to be used in stable isotope dilution assays. The concentrations of the nine lactones were then analyzed in raw and pasteurized cream as well as in a heat-treated raw cream. δ-Dodecalactone and δ-decalactone showed the highest concentrations in both the raw and pasteurized cream. In the latter, δ-dodecalactone reached a 2.5-fold higher concentration compared to the raw cream. Subsequent heat treatments in a lab scale showed a further increase by factors of 13 and 19, respectively, suggesting a high potential of lactone precursors in cream. The results serve as a basis for further studies on lactone formation in other thermally processed products, such as milk chocolate.