Food materials, interactions

This paper organizes some of the how and why of flexible package-food product interactions by discussing a few specific examples of food packaging development, as well as some overall factors of packaging material application. 

In aqueous food materials Tj and T2 relaxation behavior of water are related to different aspects of the interaction and motion of the water molecules. The relationship is not so simple, especially in heterogeneous food materials [63-65]. There are at least four types of protons to be considered, namely free (or bulk) water, bound (or hydrated) water, exchangeable macro-moleculc protons such as those found in hydroxyl and amino groups, and unexchangeable macromolecule protons. Under such circumstances measurement of Ti is more reliable than T2 measurement, but can be complicated by the spin diffusion, while T2 relaxation can be complicated by slow translational diffusion and proton exchanges. 

The values of e and e" of a food material play a critical role in determining the interaction of the microwave electric field with the material. A discussion of these interactions follows. A "map" of foods plotted against their dielectric parameters was introduced by Bengtsson and Risman (1971). Table 1 gives values for the dielectric constant, loss factor and penetration depth, and Figure 1 shows a "map" of these values for common foods. 

The rate of migration of low molecular weight residual molecules from plastics into foods and interactions of the plastics with food components or other filled products depends on the molecular structure and the macroscopic (aggregate) nature of the plastic material. In order to perform useful estimations of mass transfers, for example from plastics to food, a basic knowledge of the structure of the plastic and food components and their influences on this phenomenon is necessary. 

The physical state of materials is often defined by their thermodynamic properties and equilibrium. Simple one-component systems may exist as crystalline solids, liquids or gases, and these equilibrium states are controlled by pressure and temperature. In most food and other biological systems, water content is high and the physieal state of water often defines whether the systems are frozen or liquid. In food materials science and characterization of food systems, it is essential to understand the physical state of food solids and their interactions with water. Equilibrium states are not typical of foods, and food systems need to be understood as nonequilibrium systems with time-dependent characteristics. 

Understanding the physical state of food materials requires that food composition and properties of individual food components and their interactions with each other are well known. The physical characterization of a food system needs to consider all components within the system, the molecular environment of the components and all micro- and nanostructural aspects of factors contributing to the properties of the material. The first studies referring to glass formation by food components were those on dairy powders (Supplee 1926) and glucose (Parks and Thomas 1934). These... 

Fabrication of protein nanotubes has the potential to lead food science and engineering to new heights. However further studies need to be conducted to fulfill the promise in many potential food applications. Interactions of nanotubes with the materials to be encapsulated— their structures, characteristics and controlled release properties—should be studied using the model or actual food systems. Another important area of future research is the investigation of the self-assembly characteristics of other food proteins that can be used for similar purposes. 

Control of moisture is one area of great value to food systems. Low molecular weight carbohydrate materials interact with water in ways that can be measured physically and used to predict physical properties. For example, the influence of molecular weights of saccharides on glass transition temperature has been studied [77] to understand their impact on food system proper-... 

Milling results in particle size reduction. Milling techniques have long been used for size reduction of pharmaceutical powders to improve body absorption (Bentham et al, 2004). An increased surface area of food materials will increase the rate of water absorption of materials, improve solubility of dry products, and increase accessibility of sites for chemical reactions (e.g., oxidation, digestion, flavor release, catalyst, and enzyme activity). The structure of food is also important as it dictates how, when, and where food nutrients and flavors may be released. The effectiveness of nutrient bioavailability in food is in part related to its size although other factors such as interactions of the component with a matrix also influence how the component is released. 

The ramifications of nanotechnology in the food arena have yet to be fully realized. This requires further research into biopolymer assembly behavior and applications of nanomaterials in the food industry. Researchers should keep abreast of the development of research tools and what is being done to push resolution limits for techniques such as atomic force spectroscopy or the synchrotron coupled to various spectroscopic techniques and higher resolution microscopy. New techniques should be exploited and the knowledge gained used to understand the dynamics and interactions of food materials at the single-molecule level and to describe assembly behavior in quantitative thermodynamic terms. There are questions about the interactions of nanoparticles with the food matrix and within the human body. These questions need to be addressed by future research (Simon and Joner, 2008 Sletmoen et ah, 2008). 

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