Isovaleraldehyde, concentration

For determination of the absolute isovaleraldehyde concentrations known amounts of solutions containing known concentrations of isovaleraldehyde were added to the samples and the resulting peak areas in the gas chromatogram were measured. In this way the isovaleraldehyde peak areas could be correlated with the isovaleraldehyde concentrations present in the standard solutions and the sample. 

Table I shows that an increase of Amadori compounds occurs parallel with an increase of isovaleraldehyde formed by Strecker degradation of the amino acid leucine (18 ). It becomes evident from Table I that the flavor impression "burnt arises if certain concentrations of isovaleraldehyde are exceeded this flavor change is increased by increasing isovaleraldehyde concentrations. By this means an analytical control of undesirable sensory changes caused by the Maillard reaction in carrots is available.

From Table II it can be seen that at air temperatures of 90 °C and 60 °C there is only a minor increase in isovaleraldehyde concentrations, correlating with very little or no sensory changes. 

According to Table V the tolerable limits of iso-valeraldehyde concentration seem to be variety dependent while "Rubika" containing 1.8 ppm isovaleralde-hyde does not exhibit distinct undesirable flavor changes, "Rubin" having the same isovaleraldehyde concentration and "Pariser Markt" with an even lower amount of isovaleraldehyde already show a burnt flavor character. These findings may be attributed to the fact that... 

Rubika" has a higher concentration of the amino acid leucine therefore in this case more isovaleraldehyde may be generated compared to other volatile products contributing to off-flavor. 

The syntheses of dithiopyr (1), thiazopyr (2) and related compounds [4, 5] begin with a Hantzsch-type base-catalyzed intermolecular cyclization [22], which provides the dihydropyridines 4 (R = Me or Et). Two equivalents of methyl or ethyl trifiuoroacetoacetate (5, R = Me or Et) are allowed to react with one equivalent of isovaleraldehyde (6) in the presence of a base, like piperidine, in a suitable solvent at temperatures varying from room temperature to reflux. The intermediate dihydroxytetrahydropyran (structure not shown) is converted into the dihy-droxypiperidine 7 by reaction with a nitrogen source, such as ammonium hydroxide or ammonia gas. Reaction of 7 with a dehydrating agent, such as concentrated sulfuric acid, toluenesulfonic acid, or trifluoroacetic anhydride, gives a mixture... 

Ethyl 2-(triphenylphosphoranylidene)propanoate (87) (42.7 g, 118 mmol) was added in one portion to a stirred solution of isovaleraldehyde (86) (8.50 mL, 79.0 mmol) in CH2CI2 (300 mL), and the resultant solution heated at reflux for 72 h. The reaction mixture was cooled to rt. and pentane (80 mL) was added, causing precipitation of the triphenylphosphine oxide by-product, which was ranoved by filtration. The filtrate was carefuUy concentrated under reduced pressure and the residue purified by flash column chromatography (Et20), affording (i )-ethyl 2,5-dimethylhex-2-enoate (88) as a colourless oil (13.2 g, 98 %). 

Chan and Reineccius [35] also have published some kinetic work on other aroma compounds (isovaleraldehyde, phenylacetaldehyde, 2-acetyl-l-pyrroline, 2-acetyl-furan, and di(H)di(OH)-6-methyl pyranone). All of these volatiles followed pseudo zero order reaction kinetics in their early stages of reaction (Table 5.2). The fact that the concentrations of isovaleraldehyde, phenylacetaldehyde, and the methylpyr-anone reached plateaus late in heating suggests that a first order fit, as proposed by Jusino et al. [32], might be more appropriate. 

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