Quantitative determination of volatile compounds using TD-GC-MS and isotope standard addition for application to the heat treatment of food

For many foods that undergo thermal treatment, the generation of numerous process-induced compounds has strong implications for food quality and safety. Today, increasing attention is payed to the generation and occurrence of particular classes of newly formed compounds in processed foods for their potential health implication. It is therefore of the utmost importance to monitor the process with fit-for-purpose methods that are appropriate for use in quality control or in research and innovation. Since many quality-related compounds are volatile, there is a need for robust methods that can quantify a broad range of volatile markers and are applicable to on-line monitoring.To meet this need, an original and reliable method based on thermal desorption has been developed for the quantification of volatile compounds sampled on-line by sorbent tubes. For the first time, this method combines in-tube calibration and deuterated standard addition. Ten volatile compounds that are likely to form during heat processing of food (i.e. baking of cereal products), were chosen as target analytes for their relevance to food quality and their different physicochemical properties: 3-methylbutanal, pyrazine, 2-methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, acetic acid, furfural, 5-methylfurfural, furfuryl alcohol and 5-hydroxymethylfurfural. The key steps in the analytical procedure were optimized and carefully characterized in terms of recovery, repeatability and reliability. The TD-GC-MS method displayed good linearity over extended ranges for all compounds (R²: 0.9950 to 0.8880) with low limits of quantification (LOQs) ranging from 0.0141 to 11.5 ng. The matrix effect was negligible for most compounds, except for 5-hydroxymethylfurfural (21.5%), the most polar and least volatile compound.The method was applied to determining process-induced compounds generated during the baking of a model cake and sampled from baking vapors at three different times during the heat treatment. Of all the compounds extracted, the target analytes exhibited concentrations spread over very broad ranges. This highly sensitive method could therefore be used for the early quantification of relevant markers during the processing of food matrices, for quality or mitigation purposes.Quantitative TD-GC-MS with in-tube calibration and isotope standard addition is particularly well-suited for applications where an accurate determination is required of both trace level and major volatile compounds over time. This method may therefore be relevant for monitoring either industrial or domestic food processes (e.g. baking, frying, roasting), for multi-residue analyses linked to quality and safety, or reaction kinetics for multi-response modeling. It can also be transferable to emerging non-food applications.