Thermal degradation food systems

Rios, A.O., Borsarelli, C.D., and Mercadante, A.Z., Thermal degradation kinetics of bixin in an aqneons model system, J. Agric. Food Chem., 53, 2307, 2005. 

The thermal degradation of anthocyanins, both in extracts and model systems, was reported to follow first-order reaction kinetics in all studies. The stability of anthocyanins and all pigments found in foods decreased with increases in temperature. 

Observed Rate Constant (Arobs) and Activation Energy ( a) Values Found for Carotenoid Thermal Degradation in Food Systems... 

Zepka, L. Q., C. D. Borsarelli, M. A. A. R da Silva et al. 2009. Thermal degradation kinetics of carotenoids in a cashew apple juice model and its impact on the system color. J. Agric. Food Chem. in press, doi 10. 1021/jf900558a. 

The importance of direct gas chromatography and combined direct GC/MS to the food industry is demonstrated by the analysis of volatile flavor components and contaminants in experimental samples of rice, food blends, and raw and roasted peanuts. By examining these samples, we are able to investigate flavor systems that are probably associated with lipid oxidation, thermal degradation of protein, or protein interactions with other compounds. 

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. 

The one-pass, plug flow operation of a thin-film evaporator is an advantage for minimizing thermal degradation of a heat sensitive product in an evaporation step. The mean residence time in the evaporator can be just seconds, rather than minutes or hours in a recirculating evaporation system. For this reason, thin-film evaporators are widely used for heat sensitive food, pharmaceutical, and other chemical products. Also, it should be noted that the thin-film evaporator can be operated at a higher temperature to make a better separation, whereas care must usually be taken to keep the product temperature lower in an evaporation system with longer residence times (see Fig. 21, later in this chapter). 

FIGURE 45.10 Droplet temperature T and thermal degradation Aj. in maltose-water system vs. reduced time t/R for two air temperatures (1) to 100°C, and (2) to 80°C. (From Kerkhof, P.J.A.M. and Schoeber, W.J.A.H., Theoretical modeling of the drying behavior of droplets in spray dryers, in Advances in Preconcentration and Dehydration of Foods, A. Spicer (Ed.), Elsevier Applied Science, London, U.K., pp. 349-397, 1974. With permission.)... 

Stadler R.H., Varga N.,HauJ.,ArceV.F.,WdtiD.H. Alkylpyridiniums. 1. Formation in model systems via thermal degradation of trigonelline. Journal of Agricultural and Food Chemistry, 50 1192-1199 (2002). 

XPE can be rotational moulded to produce automotive parts, toys, food handling systems, and chemical tanks. It also provides higher heat/chemical resistance and stiffness than normally achieved by rotational mouldable LLDPE. LDPE with an MER of 2-20 g/10 min and a density of 916-939 kg/m is recommended, followed by EVA copolymer and HOPE. HOPE is more difficnlt to melt than LDPE. It also shows a tendency to thermal degradation and more prononnced deformation on cooling, mainly for flat surfaces. PP is avoided because of its susceptibility to degradation. 

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