Proteins, functional properties emulsification

The valuable component of cheese whey is not the lactose but the whey proteins, primarily lactalbumin. The amino acid profile of these proteins is superior nutritionally to casein and is equal to or better than whole egg protein. The heat-denatured form of these proteins has been manufactured for many years usually by heating the cheese whey to precipitate the proteins. The product was tan colored and completely insoluble. With the advent of UF, these proteins could be recovered, concentrated and demineralized athermally. The result was a "whey protein concentrate" (WPC) with improved solubility and other functional properties (emulsification, foamability, water binding, gelation and cloud stability). 

Oilseed proteins are used as food ingredients at concentrations of 1—2% to nearly 100%. At low concentrations, the proteins are added primarily for their functional properties, eg, emulsification, fat absorption, water absorption, texture, dough formation, adhesion, cohesion, elasticity, film formation, and aeration (86) (see Food processing). Because of high protein contents, textured flours and concentrates are used as the principal ingredients of some meat substitutes. 

Characteristically, legume seeds are rich in protein and contain intermediate to high levels of lysine and threonine which are important in balancing the deficiencies of these essential amino acids in cereal diets. Certain legume proteins, such as soybean, also exhibit strong functional properties, especially water solubility, water and fat binding and emulsification. Thus soybean flours, protein concentrates and isolates have been used widely as nutritional supplements and functional ingredients in foods. 

Pin milling alone improved one functional property, oil emulsification (Table III). The pin-milled flours, protein fractions and proteinates gave oil emulsification values of 70.0-79.0% compared to values of less than 18.0% for starch products. 

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). 

Kuehler and Stine (43) studied the functional properties of whey protein with respect to emulsifying capacity as affected by treatment with three proteolytic enzymes. Two microbial proteases and pepsin were examined. The emulsion capacity decreased as proteolysis continued, suggesting that there is an optimum mean molecular size of the whey proteins contributing to emulsification. 

The functional properties that govern the role of proteins in food applications are color flavor texturization solubility viscosity adhesion or cohesion gelation coagulation aeration or foamability water and oil absorption and emulsification. 

A whey protein hydrolysate BioZate , containing ACE-inhibitory peptide was recently developed by Davisco Foods International Inc. The effect on blood pressure was studied with 30 unmedicated, non-smoking, borderline hypertensive men and women, and daily dose was 20 g. The results indicated that there was a significant drop in both systolic and diastolic blood pressure after 1-week treatment, which persisted throughout the study of 6 weeks. The application of this product is varied and flexible. In addition to the bioactive peptides, it has functional properties such as emulsification and foaming (Klink, 2002). 

Groninger (38) succinylated fish myofibrillar protein and examined some of its chemical and functional properties. The fish myofibrillar proteins were succinylated at different levels and the degree of succinyla-tion was related to a functional property such as emulsification capacity. The protein efficiency ratio for succinylated protein was lower than that of untreated fish protein. Grant (39) succinylated wheat flour proteins and analyzed their solubility, viscosity, and chromatographic behavior. The effects of acetylation and succinylation on the physicochemical and functional properties of several plant proteins was reviewed recently by Kinsella and Shetty (6). 

Reversibly insolubilized soybean protein products possess various functional properties, such as binding, emulsification effect, etc. These functionalities may appear when the native protein molecules are unfolded during heating in food processing. Therefore these products, such as soybean protein isolate, are useful as binders or emulsifiers for sausage, hams, etc. 

Solubility is a critical functional characteristic because many functional properties depend on the capacity of proteins to go into solution initially, e.g. gelation, emulsification, foam formation. Data on solubility of a protein under a variety of environmental conditions (pH, ionic strength, temperature) are useful diagnostically in providing information on prior treatment of a protein (i.e. if denaturation has occurred) and as indices of the potential applications of the protein, e.g. a protein with poor solubility is of little use in foams). Determination of solubility is the first test in evaluation of the potential functional properties of proteins and retention of solubility is a useful criterion when selecting methods for isolating and refining protein preparations (1). Several researchers have reported on the solubility of extracted microbial proteins (69,82,83,84). In many instances yeast proteins demonstrate very inferior solubility properties below pH 7.5 because of denaturation. 

One of the current approaches to the improvement of the functional properties of proteins is enzymatic hydrolysis [148], The emulsifying ability of soy protein isolate can be increased by treatment with neutral fungal protease however, this treatment decreases emulsion stability [163], Partial hydrolysis of fish protein concentrate improves both emulsification and stability [164]. On the other hand, treatment of whey protein concentrate with pepsin, pronase, and pro-lase leads to a decrease in emulsification ability, suggesting that there... 

Morr [97] has listed a number of requirements related to different properties of proteins as food ingredients, as indicated in Table 2. The major functional properties of food proteins that influence their choice in specific applications are emulsification, aeration/foam formation, gelation, solubility/water binding, dispersibiliy, film formation (cohesion/adhesion), heat stability, and acid stability. 

Proteins are biopolymers that are encountered in many applications, such as food emulsions, hair conditioners, photographic emulsions, and various medical diagnostic products. Many of these applications are frequently based on the unique surface activity of the proteins, which is reflected in functional properties such as foaming, emulsification, and gelling. The proteins are composed of polymeric chains containing many hydrophobic and hydrophilic domains, often giving the molecules an amphipathic structure somewhat similar to that of polymeric surfactants. 

In addition to pH and temperature, the native structure of p-LG is also sensitive to ionic strength, high-pressure, and the presence of surfactant, and other physicochemical factors. The protein structural features and transitions have a major impact on its functional properties, including emulsification, gelling properties, and ligand binding. 

The emulsification properties of NFDM were slightly better than for caseinate at all protein levels. However. NFDM exhibited lowest emulsification properties at pH 10.4 and highest emulsification at pH 5.6, which was directly opposite the results with caseinate. Thus, the molecular state of caseins, whether in the. micellar or soluble complex form is important in determining their functionality as an emulsifier. 

Whey protein concentrates (WPC), which are relatively new forms of milk protein products available for emulsification uses, have also been studied (4,28,29). WPC products prepared by gel filtration, ultrafiltration, metaphosphate precipitation and carboxymethyl cellulose precipitation all exhibited inferior emulsification properties compared to caseinate, both in model systems and in a simulated whipped topping formulation (2. However, additional work is proceeding on this topic and it is expected that WPC will be found to be capable of providing reasonable functionality in the emulsification area, especially if proper processing conditions are followed to minimize protein denaturation during their production. Such adverse effects on the functionality of WPC are undoubtedly due to their Irreversible interaction during heating processes which impair their ability to dissociate and unfold at the emulsion interface in order to function as an emulsifier (22). 

In spite of the above limitations and the relatively small number of Studies involved, it is evident that the functionality of proteins as protein concentrates can be modified substantially by enzymes. Solubilities of proteins can be altered (generally increased) by hydrolytic reactions viscosities and gelation of protein solutions can be decreased dramatically by limited proteolysis the volume of foams of whipped hydrolysates is generally greater than that of the parent protein, but the foam stability is usually less. Emulsification properties of hydrolysates are affected in different ways depending on the protein. From the very limited number of studies on partial hydrolysis of food proteins it appears that water binding is increased as a result of proteolysis. ... 

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