Temperature food systems

The sweet taste of sucrose is its most notable and important physical property and is regarded as the standard against which other sweeteners (qv) are rated. Sweetness is induenced by temperature, pH, sugar concentration, physical properties of the food system, and other factors (18—20). The sweetening powers of sucrose and other sweeteners are compared in Table 3. The sweetness threshold for dissolved sucrose is 0.2-0.5% and its sweetness intensity is highest at 32-38°C (19). 

The two main assumptions underlying the derivation of Eq. (5) are (1) thermodynamic equilibrium and (2) conditions of constant temperature and pressure. These assumptions, especially assumption number 1, however, are often violated in food systems. Most foods are nonequilibrium systems. The complex nature of food systems (i.e., multicomponent and multiphase) lends itself readily to conditions of nonequilibrium. Many food systems, such as baked products, are not in equilibrium because they experience various physical, chemical, and microbiological changes over time. Other food products, such as butter (a water-in-oil emulsion) and mayonnaise (an oil-in-water emulsion), are produced as nonequilibrium systems, stabilized by the use of emulsifying agents. Some food products violate the assumption of equilibrium because they exhibit hysteresis (the final c/w value is dependent on the path taken, e.g., desorption or adsorption) or delayed crystallization (i.e., lactose crystallization in ice cream and powdered milk). In the case of hysteresis, the final c/w value should be independent of the path taken and should only be dependent on temperature, pressure, and composition (i.e.,... 

A food system can experience rather large fluctuations in temperature during its lifetime, depending on a variety of factors, such as the location and time of year the product is manufactured and the conditions of distribution, storage, and display. For example, if a food product, such as an intermediate moisture cheese, is manufactured and packaged with an aw] equal to 0.66 at... 

FIG. 13 Illustration of the effect of temperature (T) on aw for (A) a complex food system, (B) a small molecular weight solute, such as fructose, and (C) foods containing large amounts of solutes, such as raisins. In all case, Ti[Pg.26]

State diagrams are very useful tools in the characterization of amorphous ingredients and food systems (Roos, 1995 Slade and Levine, 1991). Slade and Levine (1988, 1991), acknowledging the earlier work of Franks et al. (1977) and MacKenzie (1977), formulated a state diagram (called a dynamics map or mobility transformation map ) for food systems that includes four dimensions temperature, concentration, pressure, and time. This state... 

Differences in mobility of various components (e.g., starch, sucrose, water) within a food system (e.g., a cookie), as well as the inherent heterogeneity of many food systems (e.g., crust versus crumb of a cookie), suggest the need to measure more than an average Tg for a system. Ruan and Chen (1998) proposed the creation of a Tg map to capture the distribution of Tg values within a food system. Since conventional techniques used to measure Tg do not have the capacity at the present time to provide spatial information, Ruan and Chen (1998) suggested the use of MRI, as a function of temperature, to produce a Tg map. ... 

As pointed out previously, Ts is not a single or unique value, even for a well-defined sample rather, it occurs over a temperature range and is dependent on the measurement method used and the system involved (recall Figure 33). In addition, it is quite possible that complex, multiphase food systems possess more than one Tg. The complexity inherent in many food systems sometimes makes it difficult to observe a Tg value at all (Labuza et al., 2001 Vittadini et al., 2002). 

The yield of HAs in food systems is affected by the concentration of substrates, enhancers and inhibitors, duration and temperature of heating, water activity, and pH. Some HAs are formed in mixtures of substrates heated for several weeks at relatively low temperature, about 37 to 60°C at 150 to 200°C the rate of reaction is much higher. However, in model systems prolonged heating may also bring about a decrease of the concentration of some HAs. Low water activity in the surface layers of the heated products favors the formation of HAs. In presence of lipids, Fe, and Fe, the rate of reaction increases, probably due to oxidation and generation of radicals (Jagerstad et ah, 2000). 

Environment. The physical and chemical environments have been shown to affect the functional performance of proteins. Factors, such as concentration, pH, temperature, ionic strength, and presence of other components, affect the balance between the forces underlying protein-protein and protein-solvent interactions (9). Most functional properties are determined by the balance between these forces. Although the comparison of discrete data from various studies might be of limited value, consideration of the response patterns of protein additives to changes in the environment of simple and/or food systems might be fruitful. 

Due to the presence of various solutes, the vapour pressure exerted by water in a food system is always less than that of pure water (unity). Water activity is a temperature-dependent property of water which may be used to characterize the equilibrium or steady state of water in a food system (Roos, 1997). 

Freshly cut oranges or their juices may be exposed in an open glass for several hours without appreciable loss of I he vitamin because of the protective effect of the acids present and the practical absence of enzymes that catalyze its destruction. In potatoes, when baked or boiled, there is a slight loss of the vitamin, blit if they are whipped lip with air while hot, as in the production of mashed potatoes, a large fraction of the initial vitamin content usually will be lost. In freezing foods, it is common practice to dip them in boiling water or to treat them briefly with steam to inactivate enzymes, after which they arc frozen and stored at very low temperatures. In this state, the vitamin is reasonably stable. Vuamin C degradation in dehydrated food systems is described shortly. 

The composition of volatiles released from a food is different when it is sniffed (via orthonasal route) and when it is eaten (via retronasal route). This is partially due to conditions in the mouth that selectively affect volatility, thus altering the ratio of compounds that volatilize from a food system. Mouth temperature, salivation, mastication, and breath flow have all been shown to affect volatilization (de Roos and Wolswinkel, 1994 Roberts et al., 1994 Roberts and Acree, 1995 van Ruth et al., 1995c). The ideal gas law describes the effects of temperature. Saliva dilutes the sample, affects the pH, and may cause compositional changes through the action of the enzymes present (Burdach and Doty, 1987 Overbosch et al., 1991 Harrison, 1998). Mastication of solid foods affects volatility primarily by accelerating mass transfer out of the solid matrix. The gas flow sweeps over the food, creating a dynamic system. The rate of the gas flow determines the ratio of volatiles primarily based on individual volatilization rates and mass transfer. 

III., using the temperature control system developed by the Quartermaster Food and Container Institute 46), The amino acid solutions and the samples used in the evaluation of carcass variation, grade, and cut by consumer acceptance panels were irradiated in the cobalt-60 source at the U. S. Army Natick Laboratories, Natick, Mass. 

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