Food systems, structure importance

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. 

Time-dependent rheological properties reflect the nature of a system s structure and can be due to viscoelasticity, structural changes, or both (Cheng and Evans, 1965 Harris, 1972). Structure breakdown can result in a decrease in the viscosity of a substance. It occurs in emulsions, suspensions, and sols. The characterization of the time-dependent flow properties of food systems is important for process design and control, for product devel-... 

Quaternary structure of proteins in food systems is important for a number of reasons. Firstly, many food proteins are large and oligomeric in nature, composed of either identical or heterogeneous subunits. Examples include p-lactoglobulin (dimer), avidin... 

It is important to understand the characteristic interactions involved at an interface containing each of the main types of surface-active molecules, i.e., biopolymers (proteins, polysaccharides) and low-molecular-weight surfactants (lipids). But that is not the whole story. In real food systems there are almost always mixed ingredients at the interface. So it is necessary to understand what sorts of mixed interfacial structures are formed, and how they are influenced by the intermolecular interactions. 

Other Protein Components. Other protein components In complex food systems and In protein Ingredient preparations may Interfere with or modify gelation reactions. Protein Interaction between whey protein and casein upon heating has a profound Influence on the characteristics of the casein gel structure In cheesemaking. Similarly protein Interactions are Important to meat structures. Protein-protein Interaction between soy and meat proteins has also been demonstrated with heat treatment (28). While concrete Interaction data have not been collected on protein gels formed from protein combinations, gelation properties of whey proteln/peanut flour blends have been Investigated GU) ... 

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. 

It is often best to begin with purified proteins when studying the relationships between protein structure and function at the molecular level. The presence of multiple proteins often complicates data interpretation, as it is not clear if effects are due to protein interactions, variations in the ratio of proteins, or to other factors. In these studies it is advisable to select tests based on a fundamental physical or chemical property, since results are less likely to vary with the test conditions or instrumentation used. Unfortunately, it becomes less likely that the property under study will relate directly to function in a food system when such simplified (often dilute) systems are used. Something as seemingly insignificant as protein concentration in the model system can have a large influence on the results obtained. Also, the relative importance or contribution of a functional property to a complex food system can be misinterpreted in a purified model system. 

This book gives an informative, yet relatively concise and well-referenced, summary of the structure and catalytic mechanism of selected food-related enzymes. A ll enzymes covered play an important role in food systems and all have their catalytic mechanism described at the molecular level. 

One of the most important factors that determine whether or not a protein is usable in the fabrication of a food product is its functionality. The functionality results from a combination of physico-chemical properties that define the behavior of the food protein in food systems. It is evident that a detailed understanding of food protein functionality requires an intimate knowledge of the protein structure. The bovine milk protein system has been studied in great detail. Although providing useful structure-function... 

Fig. 1 A diorama of a Phaeocystis ecosystem, in which physical, chemical, geological, and biological components interact to varying degrees to influence food web structure, biogeochemical flows, and ecosystem function. For simplicity, only well-documented components are illustrated. Current extent of our knowledge base is qualitatively related to font size. Arrow magnitude and direction indicate major known flows increasingly smaller and more numerous arrows imply unknown connections, the importance of indirect flows among ecosystem compartments, and overall system complexity...

In the food area, protein supplies are emphasized more frequently and are mostly studied for the nutritional properties. It should be pointed out, in the strongest terms, that protein foods are rarely used as crude powders or in their native forms. They are ingested most frequently as part of a complex food system where their functionality, rather than their nutrition, is the property most obvious to the consumer. In fact, many projects to alleviate protein malnutrition in less-developed countries have floundered because the introduced food forms did not fit the accepted pattern (i.e., the functionality) of the foods normally used in the region. Therefore, it is now commonly recognized, for improved nutritional standards, that any new food introduced into a population must, of necessity, be considered for its functional properties. Improving these properties will be a major factor in the successful adoption of the new food by the people in the area. Understanding the relation between protein structure and functionality is an important step in accomplishing these tasks. 

Application of data obtained from simple clean reaction systems in biological or chemical studies of heme catalysis also has its problems. Chemical model systems use chelators, model hemes, and substrate structures that are quite different from those existing in foods. Reaction sequences change with heme, substrate, solvent, and reaction conditions. Intermediates are often difficult to detect (141), and derivations of mechanisms by measuring products and product distributions downstream can lead to erroneous or incomplete conclusions. It is no surprise, then, that there remains considerable controversy over heme catalysis mechanisms. Furthermore, mechanisms determined in these defined model systems with reaction times of seconds to minutes may or may not be relevant to lipid oxidation being measured in the complex matrices of foods stored for days or weeks under conditions where phospholipids, fatty acid composition, heme state, and postmortem chemistry complicate the oxidation once it is started (142). Hence, the mechanisms outlined below should be viewed as guides rather than absolutes. More research should be focused on determining, by kinetic and product analyses, which reactions actually occur and are of practical importance in specific food systems. 

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. 

The interaction between proteases and their inhibitors is, at least by comparison with interactions which take place in food systems, a remarkably simple and straightforward association. Simple correlations of functional properties with different kinds of molecular forces cannot be made. It is possible, however, to illustrate the importance of protein structure and of protein—protein interactions as determinants of the functional properties of food proteins. I would like therefore to look at several food systems in which protein—protein or protein—other constituent interactions play a role and examine the relationship between functionality and protein structure in these systems. One of the simplest areas in which to examine this relationship is the well studied collagen-gelatin transition. 

In many lipid-based food systems, in addition to performing rheological experiments to determine global structure, the measurement of surface rheological properties can play a crucial role in determining the quality of the final product. Therefore, the measurement of interfacial tension is sometimes a matter of utmost importance. It is particularly valuable for dispersed lipid food systems, primarily for W/O or... 

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