Carotenoid decomposition products

Significant amounts of several carotenoid decomposition products were also identified in this study. Toluene, a-ionone and B-ionone are well-known decomposition products of carotenoids. In corn grain, the two most abundant carotenoids are lutein and phytoene (10). The formation of isophorone from lutein by a free radical mechanism was reported in an earlier publication (4), and phytoene... 

The volatile peroxides, other oxidation decomposition products, and odiferous compounds form reduced-boiling point azeotropes with water in the steam, at high temperatures, 250-260°C/482-500°F, and very low absolute pressures ( 3 mbar). This is above the smoke point of soybean oil, but below the flash point, and oxygen must be excluded. Considerable heat bleaching of yellow-red carotenoids also occurs at this temperature. Typically the deodorization process requires 20-40 min after come-up time, uses 0.5-2.0 percent spaiged steam (the higher level if tocopherols are recovered), operates at between 2 and 4 mbar, and produces a product with about 0.03-0.05 percent FFA.143... 

Palm oil physico-chemical properties allow it to be the most widely fractioned oil (Table 2). Fractioning involves physical or chemical refine applying high temperatures, desodorisation and deacidification of oil under vacuum, in both cases. Physical deacidification accurs at 250-270 C under vacuum up to 3-5 Torr, whereas chemical uses 220-240 °C. The high temperatures and vacuum are necessary to remove undesirable compounds as traces of metals, free fatty acids, oxidation and decomposition products. Nevertheless, those procedures also remove some tocopherols and tocotrienols, and all carotenoids presented in the oil [30, 31, 32, 33,34]. 

The basic flavour of peaches Persica vulgaris, syn. Prunus persica, Rosaceae) is typified by the presence of y-lactones (Cg-Cjj) and 8-lactones (C q and Cjj). Individual varieties differ mainly in their content of esters and monoterpenoids. As with all stone fruits, an important component is benzaldehyde, while other important compounds include benzyl alcohol, ethyl cinnamate, isopentyl acetate, hnalool, a-terpineol, hexanal, (Z)-hex-3-enal, ( )-hex-2-enal and decomposition products of carotenoids. 

Although LOX activity is important to the plant s defense against pathogens, there are negative aspects of the enzyme in foods. LOX activity and the resulting fatty acid hydroperoxide products initiate free radical chains that modify proteins (particularly residues of Trp, His, Cys, Tyr, Met, and Lys) as well as vitamins or their precursors (e.g., carotene and tocopherol). Evidence of such free radical reactions is often visibly observed as loss of carotenoid/chlorophyll pigments in improperly blanched frozen foods. Another consequence of these free radical reactions is the development of potent off-flavors, many of which originate from decomposition of the fatty acid hydroperoxide products. 

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. 

Crude fats and oils consist primarily of glycerides. However, they also contain many other hpids in minor quantitites. Com oil, for example, may contain glycerides plus phosphoUpids, glycolipids, many isomers of sitosterol and stigmasterol (plant steroids), several tocopherols (vitamins E), vitamin A, waxes, unsaturated hydrocarbons such as squalane and dozens of carotenoids and chlorophyll compounds, as well as many products of decomposition, hydrolysis, oxidation, and polymerization of any of the natural constituents. 

Recent work in the area has concentrated on the reactions of carotenoids with peroxyl radicals, generated mainly by the thermal decomposition of azo-initiators that lead to a variety of products. " Most of these products seem to be apocarotenals or apocarotenons of various chain lengths produced by cleavage of a double bond in the polyene chain, such as P-apo-12 -carotenal, P-apo-14 -carotenal, P-apo-lO-carotenal, and P-apo-13-carolenone. Kennedy and Liebler " reported that 5,6-epoxy-p,p-carotene and 15,15 -epoxy-P,P-carotene and several unidentified polar products were formed by the peroxyl radical oxidation of P-carotene by the peroxyl radicals. 

The hydrolysis of the acetal moiety and the elimination of the alkoxy group generally proceed under strongly acidic conditions. This is a weakness of the method, especially in the case of carotenoids, because it may cause isomerization and even decomposition of the products [5]. Milder conditions are achieved by the use of acetic acid/sodium acetate or formic acid [18], or formic acid/sodium formate [14]. Mild acidic hydrolysis (e.g. with dilute phosphoric acid) removes selectively the acetal group, thereby yielding the free 3-alkoxy-aldehyde [11,19]. 

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