David B. Josephson

Retro-aldol degradations of unsaturated aldehydes: Role in the formation ofc4-heptenal fromt2,c6-nonadienal in fish, oyster and other flavors

Alterations of cucumber-, melon-like notes in aromas and flavors caused by retro-aldol degradations oft2,c6-nonadienal were confirmed using gas chromatographic measurements of volatile compounds in model systems. The data indicated that 3-hydroxy-c6-nonenal was formed first by the addition of water to the alpha/beta double bond oft2,c6-nonadienal, and this was followed by a retro-aldol condensation of 3-hydroxy-c6-nonenal to yieldc4-heptenal and ethanal. Compared to the reaction rate in aqueous systems at neutral pH, formation ofc4-heptenal was enhanced substantially at alkaline pH, but was greatly diminished at acidic pH values. Heating (to 90 C) of aqueous model systems oft2,c6-nonadienal held at neutral pH also enhanced the rate of formation ofc4-heptenal substantially compared to that at ambient temperature (21 C). Rates of formation ofc4-heptenal in aqueous model systems held under air or nitrogen atmospheres were similar.c4-Heptenal was not formed whent2,c6-nonadienal was held at 21 C for 96 hr under air or nitrogen in nonaqueous commercial corn oil.

Inhibition of trout gill and soybean lipoxygenases by organotin compounds

Activity of trout gill and soybean lipoxygenase was inhibited by various low concentrations of tri-n-butyltin, di-n-butyltin and n-butyltin chlorides at pH 7.8. Tri-n-butyltin (0.044-0.19 mM; 8-100% inhibition) was significantly more inhibitory against trout gill lipoxygenase than di-n-butyltin (0.1-0.27 mM; 17-39% inhibition) or n-butyltin (1.2-3.6 mM; 26-43% inhibition). Soybean lipoxygenase displayed a similar sensitivity to the inhibitory effects of organotin compounds at pH 7.8. Although tri-n-butyltin (0.067-0.2 mM; 13-68% inhibition) was less inhibitory to soybean lipoxygenase, di-n-butyltin (0.134-0.537 mM; 51-75% inhibition) and n-butyltin (0.41-1.23 mM; 33-75% inhibition) were more inhibitory towards soybean lipoxygenase compared with trout gill lipoxygenase. Concentrations of butyltins required to provide substantial inhibition of trout gill lipoxygenase were of the order of magnitude of those reported for lethal water exposure concentrations of these compounds for trout and other fishes when bioaccumulation factors are considered. Thus, it is proposed that inhibition of lipoxygenase likely contributes to the biocidal activity of organotin compounds.