Oxidation secondary products

A number of methods are available for following the oxidative behaviour of food samples. The consumption of oxygen and the ESR detection of radicals, either directly or indirectly by spin trapping, can be used to follow the initial steps during oxidation (Andersen and Skibsted, 2002). The formation of primary oxidation products, such as hydroperoxides and conjugated dienes, and secondary oxidation products (carbohydrides, carbonyl compounds and acids) in the case of lipid oxidation, can be quantified by several standard chemical and physical analytical methods (Armstrong, 1998 Horwitz, 2000). 

The origin of many of the components of black tea aroma has been studied. Aldehydes are produced by catechin quinone oxidation of amino acids. Enzymic oxidation of carotenoids during manufacture generates ionones and their secondary oxidation products such as theaspirone and dihydroactinidolide. Oxidation of linoleic acid is responsible for the formation of trans-2-hexenal.82... 

In this case, the mineralogical studies on the mechanism of sulfide alteration and on the genesis and evolution of secondary oxidation products are of paramount environmental relevance because they allow a better understanding of the source and the mechanisms of release of the ecotoxic elements and the effective... 

Refined, bleached, and deodorized oils may contain some nutritionally objectionable compounds - secondary oxidation products, di- and tri-enoic... 

CASRN 13071-79-9 molecular formula C9H21O2PS3 FW 288.43 Soil. Oxidized in soil to its primary and secondary oxidation products, terbufos sulfoxide and terbufos sulfone, respectively (Bowman and Sans, 1982 Chapman et al, 1982 Wei, 1990). Both... 

According to the Cd 18-90 AOCS ° official method, the ANV is 100 times the optical density measured in a 1 cm cell, at 350 nm, of a solution containing 1.00 g of oil in 100 ml of the test solution. The measured absorbance is due to Schiff bases (167) formed when p-anisidine (166) undergoes condensation reaction with carbonyl compounds, according to equation 55. The carbonyl compounds are secondary oxidation products of lipids, such as a, S-unsaturated aldehydes and ketones derived from the hydroperoxides (see Scheme 1 in Section n.A.2.c), and their presence points to advanced oxidation of the oil. 

Alkanals, secondary oxidation products, 665 n-Alkanals, lipid peroxidation, 614 Alkanes... 

Conjugated dienes value (CDV), secondary oxidation products, 663, 671-2 Coordination compounds O NMR spectroscopy, 185 silyl peroxides, 808-10 Coordination ionospray mass spectrometry,... 

Oxidation indices, 656-72 peroxide determination, 762-3 peroxide value, 656, 657-64 colorimetry, 658-61 definition, 657 direct titration, 657 electrochemical methods, 663-4 IR spectrophotometry, 661-3 NIR spectrophotometry, 663 UV-visible spectrophotometry, 658-61 secondary oxidation products, 656, 665-72 tests for stability on storage, 664-5, 672 thermal analysis, 672 Oxidative amperometiy, hydroperoxide determination, 686 Oxidative cleavage alkenes, 1094-5 double bonds, 525-7 Oxidative couphng, hydrogen peroxide determination, 630, 635 Oxidative damage... 

Secondary oxidation products oxidation indices, 656, 665-72 acid value, 672 anisidine value, 656, 666 carbonyl compounds, 656, 669-71 conjugated dienes value, 671-2 thiobarbituric acid reactive substances, 656, 666-9... 

Thus, if a particle secondary oxidation product does not get partitioned efficiently into the condensed phase (i.e., KtmJ is small) or the available organic condensed phase for uptake of the semivolatile product is small, Eq. (LL) reduces to Y M(lE ,/fnlI1/ and the secondary organic aerosol yield is proportional to the amount of condensed phase available for uptake of the low-volatily gaseous products. On the other hand, if KomJ and M are large, Eq. (LL) becomes Y Ea, independent of the amount of condensed phase available for product uptake. 

The primary products from autoxidation are hydroperoxides, which are often simply referred to as peroxides. Peroxides are odorless and colorless, but are labile species that can undergo both enzymatic and nonenzymatic degradation to produce a complex array of secondary products such as aliphatic aldehydes, alcohols, ketones, and hydrocarbons. Many of these secondary oxidation products are odiferous and impart detrimental sensory attributes to the food product in question. Being able to monitor and semi-quantitate the development of peroxides by objective means (e.g., PV determination) over time is important for food scientists who want to characterize the quality of an oil or a lipid-containing food product, even though the peroxides themselves are not directly related to the actual sensory quality of the product tested. 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

It should be noted that both linoleic and a-linolenic acids form hydroperoxides that absorb UV radiation at 233 nm (i.e., the same wavelength as that of CDs). Furthermore, CDs are formed upon decomposition of hydroperoxides from a-linolenic acid, absorbing at 233 nm, whereas secondary oxidation products, particularly ethylenic diketones and a-unsatu-rated ketones, show a maximum absorbance at -268 nm. Carotenoid-containing oils may interfere in the assay by giving higher than expected absorbance values at 233 nm, due to the presence of double bonds in the conjugated structures of carotenoids. 

The results from the TBA test, known in older literature as the TBA number, are usually expressed as mg malonaldehyde/kg sample for methods a to c cited above (note that results have also been reported as nmol malonaldehyge/kg or g sample) and as mg of malonaldehyde per unit of lipid for method d. Since it is known that malonaldehyde is not the only aldehyde present in the sample extract and because other aldehydes are capable of producing the same red pigment with TBA when the conditions are favorable, the TBA number/value is more appropriately expressed as the TBARS value, i.e., mg malonaldehyde equivalents/kg sample. To confuse the matter, the AOCS method, which is based on the protocol reported by Pokomy and Dieffenbacher (1989) and permits the direct determination of TBA value in oils and fats without preliminary isolation of secondary oxidation products, defines the TBA value as the increase of absorbance measured at 532 nm due to the reaction of the equivalent of 1 mg of sample per 1 ml volume with... 

This method permits the direct determination of TBARS in oils and fats without preliminary isolation of secondary oxidation products. This protocol is applicable to animal and vegetable fats and oils, fatty acids and their esters, partial glycol esters, and similar materials (AOCS, 1998). 

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