Stefan Brennecke

High-impact sulfur compounds: constitutional and configurational assignment of sulfur-containing heterocycles.

To unambiguously identify their structures and to evaluate their organoleptic properties, several constitutional und configurational isomers of dialkyl‐tetrathianes and dialkyl‐pentathiepanes were synthesized by two different synthetic protocols, and separated by preparative gas chromatography. Raman and NMR spectroscopy were used to differentiate between the constitutional 3,6‐dialkyl‐1,2,4,5‐tetrathiane and the 4,6‐dialkyl‐1,2,3,5‐tetrathiane isomers. Furthermore, cis‐ and trans‐isomers of 3,6‐dialkyl‐1,2,4,5‐tetrathianes were distinguished by temperature‐dependent NMR experiments. Static, quantum‐chemical simulations of the NMR spectra for these cis‐ and trans‐isomers were calculated in the gas layer in order to confirm our experimental assignments. In addition, the assignment of 4,7‐alkyl‐1,2,3,5,6‐pentathiepanes were deducted from their Raman spectra. Dialkyl‐tetrathianes and dialkyl‐pentathiepanes are interesting components to be used in flavor applications due to their unique olfactory impact and facets.

The flavour chemistry of culinary Allium preparations

Abstract In culinary preparations cooked, roasted and fried Allium products play a major role in the taste and the aroma of the final product. In this study the correlation of various culinary preparation techniques such as cooking and frying and the resulting differences in the flavour chemistry (volatiles and non-volatiles) are demonstrated. Different preparation techniques performed on shallots, garlic and/or scallions influence the profile of volatiles and non-volatiles in culinary preparations significantly.

Chapter 45 – Studies on Stability of Citrus Flavors and Insights into Degradation Pathways of Key Aroma Compounds

Model studies have been performed with individual citrus related aroma compounds such as citral, α-terpineol, α-terpinene, and others, in order to de-couple the complexity of citrus flavors. Degradation pathways and transformation rates have been determined for the most relevant compounds leading to the most prominent off-note compound p-methyl acetophenone. Citral is one of the main precursors. Catechins (flavan-3-ols) are often used as antioxidants for stabilization of flavor mixtures. The reactivity of catechins towards aldehydes is underestimated. In our study, we demonstrate the formation of covalent catechin–citral adducts – a reaction that might influence the aroma stability of citrus flavors in the presence of catechins. As a result, the freshness of citrus flavors and stability of key aroma-active substances can be improved, on the result of this study.