Alk-2-enals

Canonero, R., Martelli, A., Marinari, U.R. and Brambilla, G. (1990). Mutation induction in Chinese hamster lung V79 cells by five alk-2-enals produced by lipid peroxidation. Mutat. Res. 244, 153-156. 

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... 

Kosugi, H., Kato, T., and Kikugawa, K. 1987. Formation of yellow, orange, and red pigments in the reaction of alk-2-enals with 2-thiobarbituric acid. Anal. Biochem. 165 456-464. 

Creamy flavors in butter have been associated with 4-cis heptenal produced for autoxidation of isolinoleic acid (Begeman and Koster, 1964). Drier flavor in foam spray-dried milk has been associated with 6-rra x-nonenal, which has a flavor threshold in fresh milk of 0.07 pg/kg (Parks et al., 1969). Bassette and Keeney (1960) implicated a homologous series of autoxidation-derived saturated aldehydes, together with products of Maillard browning, in cereal-type off-flavors in powdered skim milk. Staleness in dry whole milk may be associated with saturated and unsaturated aldehydes (Parks and Patton, 1961). 2,4-Decadienal has been reported to be the principal compound responsible for the off-flavor associated with spontaneously oxidized milk (Parks et al., 1963). Oxidized flavors in sunlight-exposed milk are commonly related to C6 to Cn alk-2-enals... 

Forss et al. (1960a,c) compared the qualitative and quantitative distribution of carbonyl compounds in dairy products with fishy, tallowy or painty off-flavor. Total content of volatile carbonyl compounds was approximately 10 times greater in the tallowy and 100 times greater in the painty butterfat than in fishy butterfat. Tallowy butterfat contained greater amounts of -heptanal, -octanal, -nonanal, 2-heptanone 2-heptenal and 2-nonenal, while painty butterfat contained greater amounts of K-pentanal and C5 to C10 alk-2-enals. 

Zone 3 non-polar carbonyls including the alkanals, and alk-2-enals. These can be further resolved into two fractions comprising osazones and a mixture of alkanals and alkenals using silica-gel 60 and chloroform/hexane (7 3, v/v) as developer. In all cases, the hydrazones corresponding to standards run concomitantly are scraped off and eluted in chloroform/methanol (9 1, v/v). 

The disadvantage of normal phase HPLC for the separation of carbonyl dinitrophenylhydrazones is the difficulty in maintaining reproducible retention times due to absorption of water from the solvent and interaction with the active groups on the column (Fig. 5.10). To overcome this problem, a cyano-propyl bonded phase (Exsil 100, 5 /im Chromtech, U.K.) column may be used for isolation of hy-droxyalkenals and a mixture of alkanals and alk-2-enals from rat liver microsomes. The less polar carbonyls can be separated under isocratic conditions as follows. 

Individual alk-2-enal dinitrophenylhydrazones can be resolved under the conditions described for individual alkanals using a mobile phase of methanol/water (9 1, v/v). The carbonyls are eluted in order of decreasing polarity between 4 and 12 min after injection (Fig. 5.12). 

Fig. 5.12. HPLC separation of a reference mixture of alk-2-enals. The numbers indicate the chain length of the aldehyde, thus 4 but-2-enal 5 pent-2-enal etc. (Benedetti et...

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... 

The continued autoxidation of alk-2-enals leads to a number of products that are formed by similar mechanisms that give rise to products arising from alkanals. An important product... 

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. 

Figure 3.50 Oxidation fission of alk-2-enals formed by decomposition of lipid hydroperoxides.

Alk-2-enals also react to form adducts with 2 -deoxyguanosine (the corresponding base guanine) and other bases in DNA. If the damaged DNA is not repaired, these adducts may be mutagenic. The proposed reaction mechanism involves a Michael addition of the N -amino group of deoxyguanosine at the C-3 position... 

Figure 3.75 Formation of 2 -deoxyguanine adducts with alk-2-enals and malondialdehyde R = H (acrolein), R = CH(0H)CH2CH3 (4-hydroxyhex-2-enal, R = ChKOHXCHjLCHj (4-hydroxynon-2-enal).

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

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