Influence of the chemical structure on the odor qualities and odor thresholds of guaiacol-derived odorants, Part 1: Alkylated, alkenylated and methoxylated derivatives.

Guaiacol and its derivatives are commonly found in nature and are known for their characteristic smoky, clove-like and vanilla-like smells. However, there is no systematic investigation of the smell properties of structurally related guaiacol derivatives. In order to establish a comprehensive database on this olfactorily interesting substance class, odor thresholds in air and odor qualities of guaiacol and its alkylated, alkenylated, and methoxylated derivatives were determined by means of gas chromatography-olfactometry. All compounds elicited characteristic smoky/smoked ham-like, vanilla-like/sweet and/or clove-like smell impressions. The odor thresholds of the compounds were generally very low, ranging from 0.00018 to 111ng/Lair. The lowest thresholds were determined for 5-methoxyguaiacol and guaiacol, followed by 4-ethyl- and 4-vinylguaiacol. Some inter-individual differences in the threshold values between panelists were observed, with highest variation in the individual values of cis-6-propenyl-, trans-6-propenyl- and 3-vinylguaiacol. The smell impressions, on the other hand, were quite consistent.

Monitoring aroma changes during human milk storage at +4 °C by sensory and quantification experiments.

BACKGROUND & AIMS: The effect of human milk storage in the refrigerator has been investigated with regard to sensory changes and modifications to the molecular composition of the milk odour-active volatiles. METHODS: In the present study, characteristic odorants from fat oxidation, known from previous studies, as well as free fatty acids were quantified as representative marker substances by means of stable isotope dilution assays of fresh milk samples and milk samples stored at +4 °C for one and three days, respectively. RESULTS: Sensory evaluation showed that rancid and sweaty odour attributes were generated during storage, resulting in an unpleasant aroma profile for adults; however, odour changes were not as pronounced as those observed in our previous study for freeze storage. Fatty and buttery odour notes and a cooked milk-like smell were also generated. In total eight odorants from fat oxidation were determined and some potent odorants showed slight concentration increases. Moreover, five free fatty acids were determined and these all showed drastic concentration increases, even after storage for just one day. CONCLUSIONS: These investigations support our previous findings that storage recommendations for breast milk might need to be slightly reconsidered in view of potential sensory changes; on the other hand, no negative physiological effects are to be expected from these changes.

Chemical characterization of the smallest S-nitrosothiol, HSNO; cellular cross-talk of H2S and S-nitrosothiols.

Dihydrogen sulfide recently emerged as a biological signaling molecule with important physiological roles and significant pharmacological potential. Chemically plausible explanations for its mechanisms of action have remained elusive, however. Here, we report that H(2)S reacts with S-nitrosothiols to form thionitrous acid (HSNO), the smallest S-nitrosothiol. These results demonstrate that, at the cellular level, HSNO can be metabolized to afford NO(+), NO, and NO(-) species, all of which have distinct physiological consequences of their own. We further show that HSNO can freely diffuse through membranes, facilitating transnitrosation of proteins such as hemoglobin. The data presented in this study explain some of the physiological effects ascribed to H(2)S, but, more broadly, introduce a new signaling molecule, HSNO, and suggest that it may play a key role in cellular redox regulation.