Josef Kerler

VANILLA PRODUCTION: TECHNOLOGICAL, CHEMICAL, AND BIOSYNTHETIC ASPECTS

This review covers the most recent literature on vanilla research. Besides the curing process, chemistry in green and cured beans, as well as studies on the biosynthetic pathways of the most important aroma compounds are discussed. Despite intensive research on the curing process, the traditional curing procedures are still widely used. The role of enzymes involved in the curing process is not fully understood. The biosynthesis of vanilla aroma compounds is still under investigation. Data obtained from plant cell cultures are not always in accordance with those from the plant. The glycosylation of the compounds in vivo is still a point of study. Alternative routes to vanillin involving microbial biotransformations are outlined.

Identification of glucosides in green beans of Vanilla planifolia Andrews and kinetics of vanilla β-glucosidase

Natural vanilla is extracted from the fruits of Vanilla planifolia. In the overall vanilla aroma, minor compounds p-cresol, creosol, guaiacol and 2-phenylethanol have a high impact. This is shown by GC-Olfactometry analysis of cured vanilla beans. The presence of β-D-glucosides of these compounds was investigated, in order to determine if these compounds are derived from glucosides or if they are formed during the curing process via different pathways. Glucosides of vanillin, vanillic acid, p-hydroxy benzaldehyde, vanillyl alcohol, p-cresol, creosol and bis[4-(β-d-glucopyranosyloxy)-benzyl]-2-isopropyltartrate and bis[4-(β-d-glucopyranosyloxy)-benzyl]-2-(2-butyl)tartrate have been identified in a green bean extract. The kinetics of the β-glucosidase activity from green vanilla beans towards eight glucosides naturally occurring in vanilla and towards p-nitrophenol were investigated. For glucosides of p-nitrophenol, vanillin and ferulic acid the enzyme had a Km of about 5 mM. For other glucosides (vanillic acid, guaiacol and creosol) the Km-values were higher (>20 mM). The Vmax was between 5 and 10 IU mg−1 protein for all glucosides tested. Glucosides of 2-phenylethanol and p-cresol were not hydrolysed. β-Glucosidase does not have a high substrate specificity for the naturally occurring glucosides compared to the synthetic p-nitrophenol glucoside (Km 3.3 mM, Vmax 11.5 IU mg−1 protein).

α‐Acetyl‐N‐heterocycles in the Maillard reaction

Abstract α‐Acetyl‐N‐heterocycles are a special class of Maillard reaction products with typical roasty flavor characteristic and generally low odor thresholds. A total of 12 α‐acetyl‐N‐heterocycles have so far been reported to occur in heated foodstuffs or process flavorings. The partially unsaturated α‐acetyl‐N‐heterocycles 2‐acetyltetrahydropyri‐dine, 2‐acetyl‐1‐pyrroline, 2‐acetyl‐2‐thiazoline, and 5‐acetyl‐2,3‐di‐hydro‐1,4‐thiazine are reported to have very low odor thresholds (in water) between 0.1 and 1.6 ppb, whereas the odor thresholds for the corresponding aromatic α‐acetyl‐N‐heterocycles as well as for ace‐tylpyrazines range from 10 ppb to 170 ppm. Seven of the 12 α‐acetyl‐N‐heterocycles, especially those with partially unsaturated monocy‐clic ring systems have been described as important aroma compounds, and therefore their formation has been studied extensively. In particular, the amino acids proline, hydroxyproline, ornithine, citrulline and cysteine have been considered efficient precursors ...

Lipid Derived Flavours

Lipid derived flavour substances play an important role in the aroma of all foods. They can be enzymatically generated, or formed by the process of autoxidation or photooxidation from lipids. Primary oxidation products are prone to secondary oxidation, often resulting in further C-C cleavage.