Food systems, structure mixtures

Furthermore, the mechanism shown in Figure 12.1 considers only the all-tnmv-carotcnoid form as the initial compound however, although the all-tran.v-isomer predominates, d.v-isomcrs are also commonly found in model solutions and even more frequently in food systems, since these isomers are in equilibrium in the solution. Therefore, the initial carotenoid system often contains a mixture of isomers, whose composition changes according to the carotenoid structure, solvent, and heat treatment. For example, the isomerization rate of P-carotene is higher in nonpolar solvents, e.g., petroleum ether and toluene, than in polar solvents (Zechmeister 1944). 

So how do small molecules competitively displace proteins This can be answered by visualizing the structural changes that occur during displacement using probe microscopes such as the atomic force microscope (AFM). Understanding the interactions between proteins and small molecules is of importance, but is not the whole story. In food systems there will almost always be mixtures of proteins present at the interface, and we need to know what sorts of structures are formed by mixtures of proteins and how they resist displacement. We need to be able to recognize and locate individual proteins. 

Most interfaces encountered in food systems will contain more than one protein. Commercial materials used to stabilize emulsions or foams are complex isolates rather than purified single proteins. To describe the behavior of protein isolates it is necessary to imderstand the types of structures formed by mixtures of proteins at the interface, and also how such mixed structures are displaced by surfactants. 

The following sections focus on the description of the state and phase transition behavior of starch systems, as schematically illustrated in Figure 8.5, with an emphasis on their molecular organization and their response to various environments (temperature, solvent, other co-solutes, etc.). Selected material properties are also discussed in an effort to demonstrate structure-function relationships of this biopolymer mixture in pure systems and in real food products. 

CLA refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12 octadecadienoic acid) with a conjugated double bond system. The structure of two CLA isomers is contrasted with linoleic and vaccenic acids in Figure 3.1. The presence of CLA isomers in ruminant fat is related to the biohydrogenation of polyunsaturated fatty acids (PUFAs) in the rumen. Ruminant fats are relatively more saturated than most plant oils and this is also a consequence of biohydrogenation of dietary PUFAs by rumen bacteria. Increases in saturated fatty acids are considered undesirable, but consumption of CLA has been shown to be associated with many health benefits, and food products derived from ruminants are the major dietary source of CLA for humans. The interest in health benefits of CLA has its genesis in the research by Pariza and associates who first demonstrated that... 

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the structure and properties of a solid phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particulady active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust CONTROL, industrial). For these kinds of applications psychrometric charts for systems other than air—water would be useful. The construction of such has been considered (54). 

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