Enals dienals

Aldehydes, enals, dienals, ketones, and hydrocarbons, which are responsible for disagreeable odors, generally bok at lower temperatures than fatty acids. Analysis showkig a free fatty acid concentration of less than 0.05% is an kidication that deodorization is sufficientiy complete. Some of the dienals have very low odor thresholds and sensory evaluation of the finished ok is a judicious quaHty assurance step. 

Loss of Flavor Compounds in UHT Processed Cream. Table 1 shows the concentrations of flavor compounds in UHT processed cream packaged in Tetra Brik packages over 12 mo storage. The concentration of flavor compounds represents an average of four processes. Butanal concentration decreased 50%, aldehydes (C -C,0) decreased 75-85% and total carbonyls (aldehydes, Ketones, enals, dienals, ketoacids, ketoglycerides, and dicarbonyls) decreased 97%. 

A ruthenium(n)-indenyl complex, which is an efficient catalyst for the isomerization of allylic alcohols, is also an effective catalyst for the isomerization of propargylic alcohols to both a,/3-enals and a,/ -enones (Scheme 57).96 In this reaction, the addition of 20—40 mol% InClj is highly effective. The reaction exhibits extraordinary chemoselectivity and a variety of functional groups are unaffected, which allows a highly efficient synthesis of dienals (R1 =Me2C = CH, R2 = H). 

Other studies suggest that the preponderance of certain carbonyls or group of carbonyls is involved in the off-flavors of various dairy products. Forss et al (1955A.B) reported that the C6 to Cn 2-enals and the C6 to Cu 2,4-dienals—and, more specifically, 2-octenal, 2-nonenal,... 

Bassette and Keeney (1960) ascribed the cereal-type flavor in dry skim milk to a homologous series of saturated aldehydes resulting from lipid oxidation in conjunction with products of the browning reaction. The results of Parks and Patton (1961) suggest that saturated and unsaturated aldehydes at levels near threshold may impart an off-flavor suggestive of staleness in dry whole milk. Wishner and Keeney (1963) concluded from studies on milk exposed to sunlight that C6 to Cn alk-2-enals are important contributors to the oxidized flavor in this product. Parks et al. (1963) concluded, as a result of quantitative carbonyl analysis and flavor studies, that alk-2-4-dienals, especially... 

A primary alcohol and amines can be used as an aldehyde precursor, because it can be oxidized by transfer hydrogenation. For example, the reaction of benzyl alcohol with excess olefin afforded the corresponding ketone in good yield in the presence of Rh complex and 2-amino-4-picoline [18]. Similarly, primary amines, which were transformed into imines by dehydrogenation, were also employed as a substrate instead of aldehydes [19]. Although various terminal olefins, alkynes [20], and even dienes [21] have been commonly used as a reaction partner in hydroiminoacylation reactions, internal olefins were ineffective. Recently, methyl sulfide-substituted aldehydes were successfully applied to the intermolecu-lar hydroacylation reaction [22], Also in the intramolecular hydroacylation, extension of substrates such as cyclopropane-substituted 4-enal [23], 4-alkynal [24], and 4,6-dienal [25] has been developed (Table 1). 

Note that the suffixes -anal, -enal, and -dienal signify the saturated form and the forms with one and two double bonds, respectively note also that the numbering of the carbon atoms begins from the— CHO, or aldehydic group, at the end of the chain, with the double bonds occurring at the 2 and 6... 

Dienals. The cyclohexylimine (2) of 1 reacts with carbonyl compounds in THF to give (E,E)-dienals in 65-80% yield. The reaction of 2 with a,p-enals to provide trienals proceeds in generally lower yield (25-45%). 

It was pointed out that the ylide 20 can be regarded as a j5-formylvinyl anion equivalent 21 it reacts with aldehydes to give oxiranes, which can readily be converted under mild conditions into 4-hydroxy-2-( )-enals (equation 7). A vinylogue of 20 has been converted in the same way into a 6-hydroxy-2, 4-( , F)-dienal this reaction enables a five carbon atom homologation of aldehydes to be achieved. ... 

Under more vigorous conditions (100 °C) the dienal is formed in good yield and it is even possible to combine two enals to form a trienal, e.g. 50, regiospeciflcally. 

The volatiles in the frying oil increase in the beginning, but then decrease as frying continues. The most important volatiles for the quality of frying oil are saturated aldehydes Cg-Cg, enals (e.g., 2-decenal), dienals (e.g., 2,4-heptadienal), and hydrocarbons (hexene, hexane, heptane, octane, nonane, and decane). The presence of volatile oxidation products formed during the frying process was discussed by Perkins (1996) and Nawar (1998). 

A rise in free fatty acids may also cause changes in the flavour components. Increased P-oxidation of the free fatty acids leads to P-keto acids which are decarboxylated to methyl ketones. There are also increases in unsaturated aldehydes, especially 2-enals and 2,4-dienals, probably formed by oxidation of unsaturated fatty acids. This marked increase in carbonyls and unsaturated aldehydes may cause a significant alteration in the flavour, as these compounds have considerable organoleptic properties. 

The corresponding reaction with 2,3-dienyl alcohols 21 provided a new entry to substituted enal/enone 22, dienal/dienone 23 (Scheme... 

The four hydroperoxides from autoxidation of oleate give four aldehydes (8 0, 9 0, 10 1 2t, 11 1 2t) and the two hydroperoxides from autoxidized linoleate give hexanal and deca-2,4-dienal. The aldehydes produced from other hydroperoxides (Tables 10.2 and 10.3) can be derived from the equation given above. Hept-cw-4-enal is reported to give a creamy flavour to butter but a... 

While the preparation of 12 was secured, the preparation of the dienyl side chain 21 was undertaken according to a biomimetic strategy using an aldol condensation of enal 19, which was synthesized from p-nitrobenzaldehyde and propanal. Since this transformation worked superbly for accessing -19, it was tempting to produce , -dienal 23 by iteration, a procedure that was actually described by Suzuki with modest efficiency (Scheme 17). Despite numerous attempts from Matthias to enhance the process, dienal 23 could not be obtained in yield higher than 22%. 

Alkanals (C5—C7) hex-2-enal 2,4-dienals (C5-C10) 2-/-pentenylfuran Alkanals (C5—CIO) alk-2-enals (C5—CIO) hepta-2-t,4-t-dienal 2-heptanone pent-2-/-enal but-2-/-enal... 

As with alkanals, the carbonyl group of alk-2-enals is oxidised to a carboxyl group via the corresponding peroxy acid. Retroaldolisation creates acetaldehyde and an aldehyde containing two fewer carbon atoms, whereas aldolisation with acetaldehyde produces alka-2,4-dienals (Figure 3.52). 

Autoxidation of alka-2,4-dienals accompanied by retroaldolisa-tion leads temporarily to epoxides and finally to relatively stable end products. Similarly to alk-2-enals, the main reaction products include alkanals, alkenals, dialdehydes (including malondialde-hyde) and hydrocarbons. Some secondary reactions of alka-2,4-dienals are shown in Figure 3.53. 

Alk-2-enals, alka-2,4-dienals, ketones, lactones, other products... 

Some compounds formed from meat lipids have an important role. Such compounds include some carbonyl compounds, such as oct-l-en-3-one, hexanal, octanal, nonanal, (Z)- and ( )-non-2-enal, (2 ,6Z)-nona-2,6-dienal, (2 ,4Z)-deca-2,4-dienal and 12-methyltridecanal (8-181). Other important fatty acid oxidation products include ( )-4,5-epoxydec-2-enal (8-182), (Z)-octa-l,5-dien-3-one, (2 ,6Z)-nona-2,6-dienal. Also important... 

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