Functional properties enzymatic protein processing

The earliest commercial milk protein enzymatic modification dates back to the 1940s, when the first formulas for allergenic infants were made. The aims of this process were to reduce allergenicity as well as to change the functional properties of proteins while preserving their nutritional value for clinical use. Unfortunately the hydrolysates thus obtained were characterized by bitter taste, and for mainly this reason proteolysis, as a technological process, enjoyed very little popularity. 

Treatments used in food processing may modify the native structure of proteins independently of or in concomitance with chemical/enzymatic modification of the amino acids in their primary structure. In most cases, such structural changes are a highly desirable result of processing, and process conditions are chosen that result in extensive (but controlled) protein denaturation and in the exposure of reactive functional groups. In many other cases, however, protein denaturation represents a major drawback, in that it may alter the nutritional and functional properties of the processed material. 

Discarded fish bones and cutoffs may contain considerable amounts of muscle proteins. These muscle proteins are nutritionally valuable and easily digestible with well-balanced amino acid composition (Venugopal et al., 1996). Therefore, fish proteins derived from seafood processing by-products can be hydrolyzed enzymatically to recover protein. Protein hydrolysates from several marine species have been analyzed for their nutritional and functional properties, and researches have mainly explored the possibility of obtaining biologically active peptides (Benkajul and Morrissey, 1997). Moreover, skipjack tuna muscle (Kohama et al., 1988), sardine muscle (Bougatef et al., 2008), and shark meat (Wu et al., 2008) have been used to separate potential peptides. 

It is essential to consider the physico-chemical properties of each WPC and casein product in order to effectively evaluate their emulsification properties. Otherwise, results merely indicate the previous processing conditions rather than the inherent functional properties for these various products. Those processing treatments that promote protein denaturatlon, protein-protein Interaction via disulfide interchange, enzymatic modification and other basic alterations in the physico-chemical properties of the proteins will often result in protein products with unsatisfactory emulsification properties, since they would lack the ability to unfold at the emulsion interface and thus would be unable to function. It is recommended that those factors normally considered for production of protein products to be used in foam formation and foam stabilization be considered also, since both phenomena possess similar physico-chemical and functionality requirements (30,31). 

Enzymatic hydrolysis of food proteins generally results in profound changes in the functional properties of the proteins treated. Protein hydrolysates may therefore be expected to fulfil certain of the food industry s demands for proteins with particular, well-defined functional properties. A wide-spread use of protein hydrolysates in food requires, however, a careful control of the taste and functionality of the protein during its hydrolysis and subsequent processing to obtain a reproducible product quality. 

Reactions in proteins and other nitrogenous compounds catalyzed by endogenous enzymes are responsible for desirable and undesirable sensory attributes of foods — color, flavor, and texture — as well as for the development of compounds that are nutritionally beneficial or have detrimental effects on human health. The use of added enzymes or enzyme sources is also an essential part of many traditional methods of food processing. Since the conditions of enzymatic reactions are much milder than those applied in chemical treatments, different added enzymes are being used to an increasing extent to modify the functional properties of food proteins. 

Both the protein and fat components in milk influence the properties of food, but the ability of the milk to impart desirable properties to food is mostly influenced by the physical functional properties of the milk protein components (Kinsella, 1984 Mulvihill and Fox, 1989). The inherent functionality of milk proteins is related to the structural/ conformational properties of protein, which is influenced by both the intrinsic properties of the protein and extrinsic factors. Modification of the protein composition or structure and the organization of the proteins within the dairy ingredient through the application of physical, chemical, or enzymatic processes, alone or in combination, enable the differentiation of the functionality of the ingredient and designing the required functionality for specific applications (Chobert, 2003 Foegeding et al., 2002). 

Application of membrane processes during production of purified food proteins is a mild treatment which ensures that the functional properties of the native proteins are retained. (1 ) These properties are mostly found to be superior to those of denatured proteins. However, not all possible needs of the modern food industry are fulfilled by using native proteins instead of denatured ones. Therefore, enzymatic modification of proteins has been demonstrated as a possible means of meeting the needs of the food industry for high-quality protein ingredients ( ), (13), (14). 

A proteinase-catalyzed reaction including splitting and synthesis of peptide bonds is a process also suitable for covalent amino acid incorporation into peptide chains. This type of enzymatic modification reaction of food proteins is useful for different purposes alteration of sensory properties, solubility, nutritional quality, functional properties, antifreeze character, and different biological activities. Recently, special proteinase-catalyzed reactions have been elaborated by which proteins can be modified with particular respect to their primary structure and conformation. 

Enzymatic techniques can be used to endow proteins with surface-active functionality. An enzymatic technique that has shown promise in enhancing surface properties of proteins is a modified version of the classical plastein reaction. The plastein reaction is known to be a protease-catalyzed reverse process in which a peptide-peptide condensation reaction [11,12] proceeds through the peptidyl-enzyme intermediate formation [13]. It is essentially a two-step process enzymatic hydrolysis of a protein and plastein formation from the hydrolysate peptides. A novel one-step process was developed as a modified type of the plastein reaction by Yamashita et al. [14,15], which... 

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