Oxidation of vegetables

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

One-Stage Method of Catalytic Oxidation of Vegetal Raw Materials by Oxygen Novel Ecologically Pure Products and Perspectives of Their Practical Use... 

The major releases of terrestrial carbon result from the oxidation of vegetation and soils associated with the expansion of cultivated land. The harvest of forests for fuelwood and timber is less important because the release of carbon to the atmosphere from the oxidation of wood products is likely to be balanced by the storage of carbon in regrowing forests. The balance will occur only as long as the forests harvested are allowed to regrow, however. If wood harvest leads to permanent deforestation, the process will release carbon to the atmosphere. 

D. B. Min, S. H. Lee, and E. C. Lee, Singlet Oxygen Oxidation of Vegetable Oils, Flavor Chemistry of Lipid Foods, American Oil Chemists Society Publication, Peoria, Illinois, 1989. 

The properties of the so-called oxycellulose are also of interest from a tinctorial standpoint. On oxidation of vegetable fibre (cellulose) with chlorine, chromic acid, or similar agents, it undergoes a change, and becomes capable of fixing basic dyestuffs without a mordant. 

G. Yildiz, R. L. Wehling and S. L. Cuppett, Method for determining oxidation of vegetable oils by near-infrared spectroscopy , J Am Oil Chem Soc, 2001,78, 495-502. 

Figure 3.6 Oxidative breakdown of hydroperoxy cyclic peroxides of linoleate leading to pentane and hexanal. Reproduced from Min, D. B., Lee, S. H. and Lee, E. C., Singlet oxygen oxidation of vegetable oils, in Flavor Chemistry of Lipid Foods (eds D. B. Min and J. H.

From Frankel etal. (1996b). Oxidation of vegetable oils were carried out at 60°C for 20 days in bulk and for 12 days in emulsions oxidation of fish oil were carried out at 40°C for 10 days. Negative values represent prooxidant activity. 

Soybean oil has a high linoleic acid content of around 50.8% and 7% of linolenic acid and is thus susceptible to oxidation. Adverse effects caused by oxidation of vegetable oils include loss of essential fatty acids, production of off-flavors and toxic compounds (Sonntag, 1979). The oxidative stability becomes an important quality control parameter for the manufactures and users of vegetable oils. Although the oxidative stability of soybean oil has been greatly improved through the concerted efforts of universities, industries... 

Activated carbon (formed by the low-temperature oxidation of vegetable carbon) ... 

When vegetable oil oxidation temperatures were plotted relative to the amounts of total unsaturates, an inverse relationship was observed, i.e., the total amount of unsaturation decreased as the oxidation temperature increased, as seen in fig. 14.7 (R = 0.69). The mechanism of oxidation of vegetable oils is consistent with that of hydrocarbon oxidation. The allylic hydrogens of unsaturated fatty acids are the most susceptible sites for the initiation of oxidation. 

It is extremely doubtful that there will be any reliable instrumental method in the foreseeable future that will replace the human being for the sensory evaluation of foods. However, there are various instrumental techniques that can be used to supplement sensory analysis (7). These techniques are typically simple rapid screening procedures which reduce the burden on sensory analysis but do not eliminate it. As an example, we see very common usage of headspace gas chromatography to monitor hexanal in vegetable oils. There is a well established correlation between the oxidation of vegetable oils and hexanal. 

Antioxidants such as a-tocopherol, ascorbic acid and tea catechin can effectively inhibit the oxidation of vegetable oils and development of rancidity in food lipids. However, it has been difficult to protect fish oils containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) against oxidative deterioration and an effective antioxidant method for fish oils is required. As shown in Figure 5, oxidation of ethyl DHA was completely inhibited in the cathodic solution, although it was more easily oxidized in distilled water or in the NaCl solution, therefore, the cathodic solution may be useful as an effective antioxidant for fish oils. 

Dayma G, Togbe C, Dagaut P. Detailed kinetic mechanism for the oxidation of vegetable oil methyl esters new evidence firom methyl heptanoate. Energy Fuels. September 2009 23 4254-4268. 

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