Water-food structure interactions

Slade, L. and Levine, H. 1991. Beyond water activity Recent advances based on an alternative approach to the assessment of food quality and safety. Crit. Rev. Food Sci. Nutr. 30, 115-360. Slade, L. and Levine, H. 1995. Glass transitions and water-food structure interactions. Adv. Food Nutr. Res. 38, 103-269. 

Slade, L. and Levine, H. Glass transitions and water-food structure interactions, Adv. Food Nutr. Res., 38,103,1995. 

Finally, food processing implies the conversion of biological systems based on specific interactions of components into foods with nonspecific interactions between components. For this reason the thermodynamic approach is especially applicable for studying the role of food polymers and water in structure-property relations. The logical starting point is therefore to consider mixed aqueous solutions of biopolymers. 

Water behaves differently in different environments. Properties of water in heterogenous systems such as living cells or food remain a field of debate. Water molecules may interact with macromolecular components and supramolecular structures of biological systems through hydrogen bonds and electrostatic interactions. Solvation of biomolecules such as lipids, proteins, nucleic acids, or saccharides resulting from these interactions determines their molecular structure and function. 

Another proportion of bound water (3 2% of the total water content) exists at water activities ranging from 0.2 to 0.7. This water occupies the remaining first-layer sites and forms several layers around the monomolecular layer. In these layers mutual hydrogen bonds between water molecules already dominate, but there are also interactions between water molecules and ions or dipoles. Some water molecules penetrate into the capillary pores in the food structures by physical sorption. This water has the limited function of a solvent and the main proportion of this water does not freeze at 40 °C. The boundary between the first and second category water is the value of water activity of about 0.25. This water is known as multilayer water. 

The movement of fluoride through the atmosphere and into a food chain illustrates an air-water interaction at the local scale (<100 km) (3). Industrial sources of fluoride include phosphate fertilizer, aluminum, and glass manufacturing plants. Domestic livestock in the vicinity of substantial fluoride sources are exposed to fluoride by ingestion of forage crops. Fluoride released into the air by industry is deposited and accumulated in vegetation. Its concentration is sufficient to cause damage to the teeth and bone structure of the animals that consume the crops. 

In food chemistry, the water distribution and its interaction with polymeric structures plays a fundamental role as it determines important food quality parameters. low resolution NMR proved to be an... 

Little data is available on the interaction of protein modification for improved functionality and vitamin bioavailability from modified food-stuffs. Some water-soluble and fat-soluble vitamins are protein-bound in their transport, storage and/or active forms. Therefore, methods used to cause dramatic alteration of protein conformation or chemical structure can be assumed to alter some vitamins as well. 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

For simple fluids, also known as Newtonian fluids, it is easy to predict the ease with which they will be poured, pumped, or mixed in either an industrial or end-use situation. This is because the shear viscosity or resistance to flow is a constant at any given temperature and pressure. The fluids that fall into this category are few and far between, because they are of necessity simple in structure. Examples are water, oils, and sugar solutions (e.g., honey unit hi.3), which have no dispersed phases and no molecular interactions. All other fluids are by definition non-Newtonian, so the viscosity is a variable, not a constant. Non-Newtonian fluids are of great interest as they encompass almost all fluids of industrial value. In the food industry, even natural products such as milk or polysaccharide solutions are non-Newtonian. 

Materials science associated with fracture mechanics has mainly been confined to composite materials such as concrete, ceramics and metals. Much of the emphasis of the research has been on preventing fatigue and failure rather than designing for it to occur. The way a structure deforms and breaks under stress is crucial for properties such as flow and fracture behaviour, sensory perception of structure, water release and the mobility and release of active compounds. In the case of foods, the ability to break down and interact with the mouth surfaces provides texture and taste attributes. The crack propagation in a complex supramolecular structure is highly dependent on the continuous matrix, interfacial properties and defects and the heterogeneity of the structure. Previous structure-fracture work has dealt with cellular plant foods, and it has been demonstrated that the fracture path differs between fresh and boiled carrots due to cellular adhesion and cell wall strength as well as cell wall porosity and fluid transport (Thiel and Donald 1998 Stoke and Donald 2000 Lillford 2000). 

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