Protein during food processing

Deterioration of the physical properties of proteins during food processing or food storage can be ascribed primarily to an irreversible insolubilization of proteins. However, a deteriorative change for one purpose can be a favorable one for another purpose. In Japan, for instance, the irreversible insolubilization of soybean proteins has been utilized effectively for production of soybean protein foods, such as tofu, kori-tofu, and yuba. 

Biopolymer incompatibility seems to provide phase-separated liquid and gel-like aqueous systems. In highly volume-occupied food systems aggregation, crystallisation and gelation of biopolymers and their adsorption at oil/water interfaces favour an increase in the free volume, which is accessible for other macromolecules. Denatura-tion of proteins during food processing decreases their solubility and co-solubility of proteins with one another and with polysaccharides and induces phase separation of the system. 

During food processing, interactions of antioxidants with proteins and other food constituents take place, and the activity of some antioxidants may change as a result of hydrolytical processes because glycosides and esters are converted... 

The Maillard reaction commonly occurs in food products and during food processing. A typical or pure Maillard reaction is simply the reaction of a sugar and an amino acid. Strictly speaking, the sugar must be a reducing carbohydrate and the amino acid can be either free or bound, as a peptide or protein. The reaction generates not only volatile compounds, which provide odor, but also odorless nonvolatile compounds, some of which are colored. 

Nutritional and Metabolic Aspects of Protein Modification During Food Processing... 

There have been a number of well-documented examples of the formation of chemical derivatives of the amino acid side chains in proteins during the processing of foods and feeds. It would be wrong to believe that there are not many more examples of at least minor amounts of undesirable substances introduced by similar procedures, but, fortunately, none of major importance have surfaced other than the two discussed below. 

Lysinoalanine formation in casein, lactalbumin, and wheat gluten was measured at 65°C at various pH s for 3 hours. Factors that control the extent of formation of the unnatural amino acid lysinoalanine during food processing and thus the degree of crosslinking in structurally different proteins are discussed. 

Proteins are commercially important in foodstuffs, along with carbohydrates and fats, and are often used as emulsifiers during food processing. Inducing protein denaturation is also important when cooking food for example, egg white changing from a liquid to a solid arises from the denaturation of albumin. Because protein... 

It is apparent that the structures of proteins, at both molecular and microstructural levels, such as those found at an interface, are dynamic and prone to changes during food processing and storage. The structural alterations may be accelerated or delayed upon further modifications of such parameters as pH and ionic strength, or upon addition of polysaccharides. 

Harsh treatments used during food processing can have deleterious effects on the nutritional quality of the processed protein. Decreases in digestibility (enzymatic hydrolysis) (8 10 ... 

Formation of allergens during food processing (e.g., neoallergen generation) either due to protein modification, protein interaction with nonprotein components (e.g., sugars or lipids), or both,... 

Protein conformational stability Is not only of fundamental Interest for protein chemistry, but also relevant to questions of food safety and quality. High stability of proteinase Inhibitors may necessitate use of conditions for their Inactivation that denature other proteins first and lead to other reactions that have undesirable consequences for protein digestibility (Richardson, 1977). In discussing Inactivation of enzymes during food processing. Balls (1942) stated, "Until we know more about It, we shall probably overheat our products rather than underheat them, just to be safe. When we know more about It we may be able to moderate our enthusiasm and our technique". Basic studies on stabilities of protein enzyme Inhibitors and lectins, as well as enzymes, can contribute to development of methods that avoid overheating or underheating food or feed products. 

In a similar way, EPR spectroscopy of orange-brown melanoidins, which were isolated from heated aqueous solutions of bovine serum albumin and glycolaldehyde, revealed the protein-bound l,4-bis(5-amino-5-carboxy-l-pentyOpyrazinium radical cation (CROSSPY) as a previously unknown type of cross-linking of proteins in vivo and during food processing (i). CROSSPY could be found in wheat bread crust, roasted cocoa, as well as coffee beans. 

The amount of copper in the body is 80-100 mg. Copper is a component of a number of oxido-reductase enzymes (cytochrome oxidase, superoxide dismutase, tyrosinase, uricase, amine oxidase). In blood plasma, it is bound to ceruloplasmin, which catalyzes the oxidation of Fe + to Fe +. This reaction is of great significance since it is only the Fe + form in blood which is transported by the transferrin protein to the iron pool in the liver. The daily copper requirement is 1-1.5 mg and it is supplied in a normal diet. Copper is even less desirable than iron during food processing and storage since it catalyzes many unwanted reactions. Cu +-Ions are taste bearing. The threshold value 2.4-3.8 mg/1 was determined with aqueous solutions of CuSOa or CuCl2. 

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