Empirical models, foods

Elizalde, B. E., Pilosof, A. M. R., and Bartholomai, G. B. (1996). Empirical model for water uptake and hydration rate of food powders by sorption and Baumann methods. /. Food Sci. 61, 407-409. 

Mason, P. L., Bistany, K. L., Puoti, M. G., and Kokini, J. L. 1982. A new empirical model to simulate transient shear stress growth in semi-solid foods. J. Food Process Eng. 6 219-233. 

Fernandez A, Cofiaudo J, Cunha EM, Ocio MJ, Martinez A (2002) Empirical model building based on Weibull distribution to describe the joint effect oh pH and temperature on the thermal resistance of Bacillus cereus in vegetale substrate. Int J Food Microbiol 77 147-153 Forney LJ, Zhou X, Brown CJ (2004) Molecular microbial ecology land of the one-eyed king. Curr Opin Microbiol 7 210-220... 

A number of models have been developed to describe transient viscoelastic behavior and one must have at hand carefully obtained rheological data in order to test the applicability of the models. Another example of the applicability of models to viscoelastic data is the study of Leppard and Christiansen (1975) in which the models proposed by Bogue and Chen, Carreau, and Spriggs were evaluated. In the case of foods, the empirical models have been developed to describe the transient data on stick butter, tub margarine (Mason et al, 1982), canned frosting (Kokini and Dickie, 1981 Dickie and Kokini, 1982), and mayonnaise (Campanella and Peleg, 1987c). 

Constitutive equations were applied to simulate viscoelasticity of concentrated food polymer dispersions. Some fundamental and empirical models have been discussed in Section V. Among them, the Bird-Carreau constitutive model [Eqs. (89-94)] have been used for food polymer dispersions (Kokini et ai, 1984 Kokini and Plutchok, 1987b Plutchok and Kokini, 1986). 

The transport properties of foods received much attention in the literature [184-188]. The main results presented by Saravacos and Maroulis [188] are summarized in this section. The results refer to moisture diffusivity and thermal condnc-tivity. Recently published values of moisture diffusivity and thermal conductivity in various foods were retrieved from the literature and were classified and analyzed statistically to reveal the influence of material moisture content and tempera-tnre. Empirical models relating moisture diffusivity and thermal conductivity to material moisture content and temperature were fitted to all examined data for each material. The data were screened carefully using residual analysis techniques. A promising model was proposed based on an Arrhenius-type effect of temperature, which uses a parallel structural model to take into account the effect of material moisture content. 

Peleg, M (1988). An Empirical Model for the Description of Moisture Sorption Curves. Journal of Food Science, Vol.53, pp. 1216-1217,1219. 

Water activity in foods is usually determined from knowledge of the equUib rium relative humidity or can be measured using various hygrometers. In some foods it can be calculated from various theoretical and empirical models that take into account the food chemical composition, the content of electrolytes such as sodium chloride and non-electrolytes such as saccharose, respectively. Equations, varying in their levels of compUcation, are numerous, but their use is limited to certain commodities. One of the simple empirical equations for water activity calculation in jams has the form = 1/(1 + 0.21n), where... 

EN Friel, RST Linforth, AJ Taylor. An empirical model to predict the headspace concentration of volatile compounds above solutions containing sucrose. Food Chem 71 309-317, 2000. 

For most practical purposes, the isotherm can be modeled by an empirical (Brunauer, Emmett and Teller BET) or theoretical (Guggenheim, Anderson, and DeBoer GAB) equation (see below) however, none of the isotherm models in the literature is valid over the entire aw range of 0 to 1. The GAB model is one of the most widely accepted models for foods over a wide range of aw (from 0.10 to 0.90). The details of the different isotherm models with their parameters have been compiled by Rahman (1995). The BET (Eq. A2.3.4) and GAB (Eq. A2.3.5) equations are given as follows ... 

Because no general theories exist even for concentrated non-food suspensions of well defined spherical particles (Jeffrey and Acrivos, 1976 Metzner, 1985), approaches to studying the influence of the viscosity of the continuous medium (serum) and the pulp content of PF dispersions, just as for non-food suspensions, have been empirical. In PF dispersions, the two media can be separated by centrifugation and their characteristics studied separately (Mizrahi and Berk, 1970). One model that was proposed for relating the apparent viscosity of food suspensions is (Rao, 1987) ... 

Several studies were conducted on the stress overshoot and/or decay at a constant shear rate. Kokini and Dickie (1981) obtained stress growth and decay data on mayonnaise and other foods at 0.1, 1.0, lO.Oand 100 s . As expected from studies on polymers, shear stresses for mayonnaise and other food materials displayed increasing degrees of overshoot with increasing shear rates. The Bird-Leider empirical equation was used to model the transient shear stresses. 

Because t] data are obtained at low strains with minimal alteration of the STD structure, they provide unique opportunities for studying applicable models. Further, empirically obtained frequency shift factor (Ferry, 1980) has been used successfully in time-temperature superposition studies on food polymer dispersions (Lopes da Silva etal., 1994), and the applicability ofsimilar, if not identical, scaling of frequency was explored for STDs (Yang and Rao, 1998a). 

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