Hexanal

Abstract: There are at least five lipoxygenases (TomloxA, TomloxB, TomloxC, TomloxD, and TomloxE) present in tomato (Lycopersicon esculentum Mill.) fruit, but their role in generation of fruit flavor volatiles has been unclear. To assess the physiological role of TomloxC in the generation of volatile C6 aldehyde and alcohol flavor compounds, we produced transgenic tomato plants with greatly reduced TomloxC using sense and antisense constructs under control of the cauliflower mosaic virus 35S promoter. The expression level of the TomloxC mRNA in some transgenic plants was selectively reduced by gene silencing or antisense inhibition to between 1% and 5% of the wild-type controls, but the expression levels of mRNAs for the four other isoforms were unaffected. The specific depletion of TomloxC in transgenic tomatoes led to a marked reduction in the levels of known flavor volatiles, including hexanal, hexenal, and hexenol, to as little as 1.5% of those of wild-type controls following maceration of ripening fruit. Addition of linoleic or linolenic acid to fruit homogenates significantly increased the levels of flavor volatiles, but the increase with the TomloxC-depleted transgenic fruit extracts was much lower than with the wild-type control. Confocal imaging of tobacco (Nicotiana tabacum) leaf cells expressing a TomloxC-GFP fusion confirmed a chloroplast localization of the protein. Together, these results suggest that TomloxC is a chloroplast-targeted lipoxygenase isoform that can use both linoleic and linolenic acids as substrates to generate volatile C6 flavor compounds. The roles of the other lipoxygenase isoforms are discussed.

Abstract: The antioxidant activity of several anthocyanins was tested in vitro on human low-density lipoproteins (LDL) and on a lecithin−liposome system. Samples were incubated at 37 °C, and the extent of oxidation was measured by determining the formation of conjugated diene and hexanal. The inhibition of oxidation increased with concentration of the antioxidant. In the LDL system, when the oxidation was catalyzed with 10 μM copper, malvidin was the best oxidation inhibitor, followed by delphinidin, cyanidin, and pelargonin. When the oxidation was catalyzed with 80 μM copper, the order of antioxidant activity changed and decreased in the following order at all concentrations tested: delphinidin, cyanidin, malvidin, and pelargonin. In the liposome system, catalyzed with either 3 or 10 μM copper, malvidin was the best inhibitor of both conjugated diene and hexanal formation. At 3 μM copper, delphinidin, cyanidin, and pelargonin showed prooxidant activity. At 10 μM copper, pelargonin followed malvidin in antioxidant...

Abstract: The concentrations of 44 of the major aroma components of tomato paste were determined. Comparison with studies for fresh tomatoes showed marked decreases in concentration for some compounds, particularly aliphatic aldehydes ((Z)-3-hexenal and hexanal >400 times lower) in the paste. Other compounds, however, such as the potent odorant beta-damascenone (also 6-methyl-5-hepten-2-one, other ketones, linalool, and alpha-terpeneol) show severalfold increases in concentration in the paste. The observation by other workers of the formation of relatively large (0.5-10 ppm) concentrations of dimethyl sulfide in processed tomato was confirmed. Considerations of the odor thresholds of components and their determined concentrations indicated that the compounds most important to tomato paste aroma include dimethyl sulfide, beta-damascenone, beta-ionone, 3-methylbutanal, 1-nitro-2-phenylethane, eugenol, methional, 3-methylbutyric acid, 6-methyl-5-hepten-2-one, phenylacetaldehyde, and linalool.

Abstract: Evening primrose meal (EPM: 1% and 2%, w/w) reduced (p ≤ 0.05) the formation of 2-thiobarbituric acid-reactive substances (TBARS), hexanal, and total volatiles in cooked comminuted pork by 43.6−72.6%. Phenolic compounds in the EPM were extracted under optimum conditions (with 56% acetone at 71 °C for 47 min) predicted by a multivariate analysis. The resulting evening primrose crude extract (EPCE) inhibited the bleaching of β-carotene in a model system. After 2 h of assay, the system containing 200 ppm EPCE [as (+)catechin equivalents] retained 86% of the initial β-carotene whereas the control retained only 11%. Inhibition of the formation of TBARS, hexanal, and total volatiles in the cooked comminuted pork containing 200 ppm EPCE [as (+)catechin equivalents] ranged from 67.3% to 97.5%. The EPCE inhibited the formation of conjugated dienes, hexanal, and total volatiles in stripped-bulk corn oil (18.5−63.6% inhibition) and stripped-corn oil-in-water emulsion systems (31.7−65.6% inhibition). Hydrogen peroxi...