Thermal degradation modeling volatilization

Kanasawud and Crouzet have studied the mechanism for formation of volatile compounds by thermal degradation of p-carotene and lycopene in aqueous medium (Kanasawud and Crouzet 1990a,b). Such a model system is considered by the authors to be representative of the conditions found during the treatment of vegetable products. In the case of lycopene, two of the compounds identified, 2-methyl-2-hepten-6-one and citral, have already been found in the volatile fraction of tomato and tomato products. New compounds have been identified 5-hexen-2-one, hexane-2,5-dione, and 6-methyl-3,5-heptadien-2-one, possibly formed from transient pseudoionone and geranyl acetate. According to the kinetics of their formation, the authors concluded that most of these products are formed mainly from all-(E) -lycopene and not (Z)-isomers of lycopene, which are also found as minor products in the reaction mixture. 

Photochemistry of Model Compounds. Preliminary photochemical studies have been carried out on l,3-diphenoxy-2-propanol (3)8 as a model compound for bisphenol A-epichloro-hydrin condensates 1. The utilization of 3 as a model compound for thermal degradation of 1 has been reported. Irradiation (254 nm) of 3 in acetonitrile (N2 purge) provides two major volatile products, which have been identified as phenol and phenoxyacetone (4), by comparison of retention times (gas chromatography) with known samples. A possible mechanism for... 

Among the other reported volatile TDP of B-carotene include B-cyclo-cltral, 5,6-epoxy-B-ionone and dihydroactinidiolide (25). These compounds were also found by Isoe et al. (30, 31), Wahlberg et al. (32) and Kawakami and Yamanishi (33) as photo-oxygenation products of B-carotene. Volatile thermal degradation of carotenoids has been extensively studied, mainly in nonfood systems. Hence, the objective of this study was to identify the volatile components of the TDP of B-carotene formed in a food model system. 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

Spectral analysis of volatile products shows that pure plasticizer evaporates before thermal degradation of PVC is recorded.Kinetic models of PVC thermal decomposition for interpretation of thermogravimetric data were proposed and verified by experimental data. ... 

The gas chromatographic profiles of the volatile compounds generated from the model reaction systems are shown in Fig. 1. The identification and quantification of the volatile compounds generated from the model systems of IMP and alliin as well as IMP and deoxyalliin are listed in Tables II and III, respectively. As shown in Fig. 1 (C), in the absence of alliin or deoxyalliin, thermal degradation of IMP produced only a few trace components. 

Oxidation is typically a very slow reaction between a solid, possibly semicrystalline, polymer and a gas. It is kinetically very complex, in the sense that the apparently simple overall behavior can be fitted by a very wide range of models, and the literature is characterized by a good deal of paper chemistry . The main differences from thermal degradation are that the reactions are slow, over weeks or years, the production of volatiles may be almost negligible, and diffusion of oxygen into the polymer is required. 

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