**5. Industrial properties and applications**

Functional properties affect the behavior of proteins during processing, storage and in preparation of food and food components (**Table 3**). Among different proteins, glycinin is nutritionally superior to the 7S con-glycinins [69], and possesses superior intrinsic functional properties for processed foods [70]. Processing technology has the capability of altering the protein structure, function, and physicochemical properties of peanuts [71–76].

#### **5.1 Protein solubility, emulsification**

Protein solubility is the first and foremost property that is determined in testing a new protein isolate. The functional properties of proteins are often affected by


**129**

*Functional Uses of Peanut (*Arachis hypogaea *L.) Seed Storage Proteins*

protein solubility and those most affected are foaming, emulsification and gelation. The solubility of a protein is the thermodynamic manifestation of the equilibrium between protein–protein and protein solvent interactions [77]. These properties are affected by the intrinsic factors of protein such as molecular structure and size, and many other factors including the method of protein separation, production, pH, ionic strength and the presence of other components in the food system. The importance of these properties varies with the type of food products in which the

Interactions of water and oil with proteins are very important in food systems because of their influence on the flavor and texture of foods. Proteins with high oil and water binding are desirable for use in meats, sausages, breads, and cakes [78]. Emulsification of proteins is closely related to the conformation of proteins and interaction of adsorbed molecules at the oil/water interface. Proteins with high emulsifying and foaming capacity are good for salad dressing, sausages, bologna, soups, confectionery, frozen desserts, and cakes [78]. Researchers [79–81] have determined the functional properties of several plant proteins concentrates using alkali solutions with isoelectric precipitation produced from peas and beans. The functional properties of peanut proteins have been subjects of limited studies that focused mainly on peanut flour [82–84]. According to some, protein isolates (PPI) have higher purity of proteins and better functional properties than other peanut

Functional properties of protein are influenced by many factors. For the end product uses, pH, temperature and ionic strength of the food system are important factors to consider. For initial extraction of proteins, methods and conditions of protein extraction, as well as downstream processing of extracted proteins such as purification, drying are the factors that are important [82]. Methods used to develop plant protein isolate/concentrate include isoelectric precipitation, alcohol

Peanut protein concentrates were isolated from defatted peanut flour by various methods such as isoelectric precipitation, alcohol precipitation, combined isoelectric and alcohol precipitation, and combined alkali solution with isoelectric precipitation [80]. Their functional properties (protein solubility, water holding/oil binding capacity, emulsifying capacity and stability, foaming capacity and rheology) were evaluated. Protein prepared by alcohol precipitation was found to have better functional properties particularly water holding/oil binding capacity, which were significantly different from other protein products such as of isoelectric and alkali precipitates [80]. The study concluded that it could be effectively used for making protein concentrates and suitable for use in various food formulations such as weaning foods, dry mixes, baked foods, whipped toppings and salad dressings

Heating destroys anti-metabolites such as trypsin inhibitor in beans and nuts [85] and amylase inhibitors in legumes, thus improving the bioavailability or digestibility of the protein [86]. Roasting of peanuts significantly decreased protein solubility in peanut flour in the pH range 3.5–10.0 compared to that in raw peanut flour. Heating of peanut in water at 100–120 °C for 15 min decreased the protein solubility [16]. This might be due to the increase of surface hydrophobicity of protein via unfolding of molecules upon heat. The pH range also had a significant effect on the solubility of peanut protein [16]. The minimum protein solubility was observed at pH 3.5–4.5 and maximum solubility at pH 10 or higher 16]. The study suggested that solubility was pH dependent with the lowest solubility being

*DOI: http://dx.doi.org/10.5772/intechopen.96871*

protein products, such as flour or concentrate [82].

**5.2 Influence of extraction procedure, pH, temperature**

precipitation, alkali solution and hot water extraction [83].

owing to its high water and oil binding capacities.

protein concentrate is used.

**Table 3.**

*Uses of protein functional properties in food types (adapted from [70]).*

#### *Functional Uses of Peanut (*Arachis hypogaea *L.) Seed Storage Proteins DOI: http://dx.doi.org/10.5772/intechopen.96871*

*Grain and Seed Proteins Functionality*

Stilbenes contain two phenyl compounds connected by a 2- carbon methylene

Functional properties affect the behavior of proteins during processing, storage and in preparation of food and food components (**Table 3**). Among different proteins, glycinin is nutritionally superior to the 7S con-glycinins [69], and possesses superior intrinsic functional properties for processed foods [70]. Processing technology has the capability of altering the protein structure, function, and

Protein solubility is the first and foremost property that is determined in testing a new protein isolate. The functional properties of proteins are often affected by

Cohesion –adhesion Meats, Sausages, baked goods, cheeses, pasta products

Foaming Whipped toppings, chiffon deserts, angel food cakes

bridge. They occur in nature in a rather restricted distribution. Stilbenes like isoflavonoids, are also classified as phytoestrogens. Most stilbenes in plants act as antifungal phytoalexins, compounds that are usually synthesized only in response to infection or injury. The most studied one is resveratrol. Resveratrol is one of the major stilbene phytoalexin compounds produced by grape berries and peanuts in response to stress like fungal infection, the presence of heavy metal ions, or ultraviolet (UV) irradiation [66]. Resveratrol was found to be present in substantial amounts in the leaves, roots, and shells of peanuts, but very little was found in developing seeds and seed coats of field-grown peanuts [67]. The phytoalexin content of peanuts, however, increases during germination and is enhanced by microbial infection, postharvest induction procedures such as soaking and drying; wounding (slicing and incubation); UV light exposure, among others. Raw peanuts soaked in water for about 20 hours and dried for 66 hours increased the resveratrol content between 45 and 65 times after the soaking treatment [66]. Boiled peanuts contain more resveratrol than peanut butter and roasted peanuts. Resveratrol has been associated with reduced CVD and reduced cancer risk. Resveratrol has been shown from in vitro, ex vivo, and animal studies to have many attributes that may provide protection from atherosclerosis, antiproliferative, and proapoptotic proper-

ties against breast, colon, prostatic, and leukemia cells [68].

**5. Industrial properties and applications**

physicochemical properties of peanuts [71–76].

**Functional Property Food type** Solubility Beverages

Viscosity Soups, gravies Gelation Meats, curds, cheese

Fat absorption Meats, sausages

Water absorption and binding Meats, Sausages, breads, cakes

Elasticity Meats, bakery products Emulsification Sausages, bologna, Soup, cakes

*Uses of protein functional properties in food types (adapted from [70]).*

Flavor binding Simulated meats, bakery goods

**5.1 Protein solubility, emulsification**

**128**

**Table 3.**

protein solubility and those most affected are foaming, emulsification and gelation. The solubility of a protein is the thermodynamic manifestation of the equilibrium between protein–protein and protein solvent interactions [77]. These properties are affected by the intrinsic factors of protein such as molecular structure and size, and many other factors including the method of protein separation, production, pH, ionic strength and the presence of other components in the food system. The importance of these properties varies with the type of food products in which the protein concentrate is used.

Interactions of water and oil with proteins are very important in food systems because of their influence on the flavor and texture of foods. Proteins with high oil and water binding are desirable for use in meats, sausages, breads, and cakes [78]. Emulsification of proteins is closely related to the conformation of proteins and interaction of adsorbed molecules at the oil/water interface. Proteins with high emulsifying and foaming capacity are good for salad dressing, sausages, bologna, soups, confectionery, frozen desserts, and cakes [78]. Researchers [79–81] have determined the functional properties of several plant proteins concentrates using alkali solutions with isoelectric precipitation produced from peas and beans. The functional properties of peanut proteins have been subjects of limited studies that focused mainly on peanut flour [82–84]. According to some, protein isolates (PPI) have higher purity of proteins and better functional properties than other peanut protein products, such as flour or concentrate [82].

#### **5.2 Influence of extraction procedure, pH, temperature**

Functional properties of protein are influenced by many factors. For the end product uses, pH, temperature and ionic strength of the food system are important factors to consider. For initial extraction of proteins, methods and conditions of protein extraction, as well as downstream processing of extracted proteins such as purification, drying are the factors that are important [82]. Methods used to develop plant protein isolate/concentrate include isoelectric precipitation, alcohol precipitation, alkali solution and hot water extraction [83].

Peanut protein concentrates were isolated from defatted peanut flour by various methods such as isoelectric precipitation, alcohol precipitation, combined isoelectric and alcohol precipitation, and combined alkali solution with isoelectric precipitation [80]. Their functional properties (protein solubility, water holding/oil binding capacity, emulsifying capacity and stability, foaming capacity and rheology) were evaluated. Protein prepared by alcohol precipitation was found to have better functional properties particularly water holding/oil binding capacity, which were significantly different from other protein products such as of isoelectric and alkali precipitates [80]. The study concluded that it could be effectively used for making protein concentrates and suitable for use in various food formulations such as weaning foods, dry mixes, baked foods, whipped toppings and salad dressings owing to its high water and oil binding capacities.

Heating destroys anti-metabolites such as trypsin inhibitor in beans and nuts [85] and amylase inhibitors in legumes, thus improving the bioavailability or digestibility of the protein [86]. Roasting of peanuts significantly decreased protein solubility in peanut flour in the pH range 3.5–10.0 compared to that in raw peanut flour. Heating of peanut in water at 100–120 °C for 15 min decreased the protein solubility [16]. This might be due to the increase of surface hydrophobicity of protein via unfolding of molecules upon heat. The pH range also had a significant effect on the solubility of peanut protein [16]. The minimum protein solubility was observed at pH 3.5–4.5 and maximum solubility at pH 10 or higher 16]. The study suggested that solubility was pH dependent with the lowest solubility being

observed for both raw and roasted peanuts, at the isoelectric point of pH around 4.0. Protein solubility reduced as pH increased until reached an isoelectric point. At pH above the isoelectric point an increase in protein solubility was observed.

#### **5.3 Gel forming ability or foaming**

The abilities of protein to form gels and to provide a structure for holding water, flavors, sugars, and food ingredients are useful in food applications, and in newproduct development that provide an added dimension of protein functionality. Foams are 2 phase systems composed of air bubbles surrounded by a continuous liquid lamellar phase [87]. Defatted peanut flour is not a good foaming agent, with a foaming capacity of only 6 ml/100 ml liquid, whereas, roasted peanuts showed half of the raw peanuts foaming capacity. Therefore, defatted peanut protein isolates may not be suitable in the food system that requires foaming such as cake and ice cream. Overall, roasting decreased functionality of peanut protein isolates, while fermentation significantly increased all functional properties of both raw and roasted peanut flours [16].

Recent studies have shown that high pressure treatment can change not only the functional characteristics of food proteins, but also their physical and chemical properties as well as molecular conformation [88–90]. In peanut protein isolates, high pressure treatment from 50–200 MPa, a non-thermal processing, significantly improved water binding capacity (WBC) and oil binding capacity (OBC). Additionally, pressure treatment could result in intensity denaturation of conarrachin II fraction [91]. It was evident by SDS PAGE (**Figure 2**). This way protein isolates can be used as food supplementary material with improved characteristics.

Effect of membrane processing were analyzed on the functional properties, structural changes, subunit profile and sensory attributes of the groundnut protein concentrate [92]. Results indicated an increase in the nitrogen solubility and foaming capacity of the protein concentrate over pH ranges of 2–10, acid precipitated protein isolate. Protein concentrate also showed higher emulsion stability index, less hydrophobicity but reduced nutty flavor as compared to control flour and acid protein isolate. Thus, membrane technology could give a protein concentrate with improved functionality and sensory characteristics similar to roasted wheat and improved digestibility, which will have potential application in the development of

#### **Figure 2.**

*Effect of high pressure on protein concentrates lanes 2(untreated) and 3–7(treated with 50-100 MPa). (adapted from [91]).*

**131**

storage proteins [104–107].

*Functional Uses of Peanut (*Arachis hypogaea *L.) Seed Storage Proteins*

**5.4 Water holding capacity and oil binding capacity**

food product formulations. Increased thermal stability, protein solubility at 4.5–6 pH, improved foaming and emulsifying properties were noticed by conjugating

Hydration or rehydration is the first and perhaps most critical step in imparting desirable functional properties to proteins in a food system. Water retention is defined as the ability of the food material to hold water against gravity [93]. Water holding capacity and oil absorption capacity both were significantly higher in raw peanut protein isolates [16]. Intrinsic factor affecting the water binding capacity of food proteins includes amino acid composition, protein conformation, and surface polarity/hydrophobicity [94]. The water retention capacity is the sum of bound, hydrodynamic and physically entrapped water [95]. During roasting, peanut proteins were denatured by high temperature, exposing more hydrophobic sites, which explained the reduced water retention of peanut protein [96]. With respect to water-holding capacity, the denatured proteins bind more water through exposure

Oil binding capacity and water holding capacity are increased by high pressure treatment [91]. Both properties are important for food texture and flavor. They are

The peanut protein isolates with improved functional food properties are critically needed in many developing countries, because animal protein is more expensive and is getting beyond the reach of many people in developing countries. Abundant proteins in peanuts are cheaper sources of proteins that would serve the purpose. Research data show that peanut and peanut butter consumption improved the feeling of fullness and satisfied the consumers better than the carbohydrates snacks like rice cakes in equal quantities [98]. Another study has shown that peanut consumption can curb the appetites due its fullness effect [99]. Evidence has emerged in favor of type of healthy monounsaturated fat in peanuts that may stimulate a hormone which helps a person to feel satisfied after consumption [100]. Apart from this, it has been seen that daily nutrition peanut consumption leads to long term health benefits. Compared to well-known foods like green tea and red

Groundnut-based 'Plumpy'nut, a ready to use therapeutic food, has helped save

Recent research studies suggest that boiling enhances antioxidant concentration in the peanuts. It has been found that boiled peanuts have 2–4 folds increase in isoflavone antioxidants biochanin A and genistein content, respectively [103].

the lives of thousands of malnourished children in Niger, by UNICEF [102].

**7. Methods to improve nutrition and manage allergenic properties**

Seed storage peanut proteins (such as Ara h 3 and Ara h 4) are less severe in allergenicity compared to their vicilin (Ara h 1) and conglutin (Ara h 2) type seed

Many methods are tried in peanut protein extracts to reduce their allergenic effect. Among them, roasting, boiling or another heat treatments are most common and require less labour and effort. Though heat treatments sometimes

high in raw peanut proteins but affected by high temperatures.

wine, peanuts have higher antioxidant capacity [101].

*DOI: http://dx.doi.org/10.5772/intechopen.96871*

protein isolates (PPI) with dextran [84].

of hydrophilic groups [97].

**6. Role in hunger management**

*Grain and Seed Proteins Functionality*

**5.3 Gel forming ability or foaming**

roasted peanut flours [16].

observed for both raw and roasted peanuts, at the isoelectric point of pH around 4.0. Protein solubility reduced as pH increased until reached an isoelectric point. At

The abilities of protein to form gels and to provide a structure for holding water, flavors, sugars, and food ingredients are useful in food applications, and in newproduct development that provide an added dimension of protein functionality. Foams are 2 phase systems composed of air bubbles surrounded by a continuous liquid lamellar phase [87]. Defatted peanut flour is not a good foaming agent, with a foaming capacity of only 6 ml/100 ml liquid, whereas, roasted peanuts showed half of the raw peanuts foaming capacity. Therefore, defatted peanut protein isolates may not be suitable in the food system that requires foaming such as cake and ice cream. Overall, roasting decreased functionality of peanut protein isolates, while fermentation significantly increased all functional properties of both raw and

Recent studies have shown that high pressure treatment can change not only the functional characteristics of food proteins, but also their physical and chemical properties as well as molecular conformation [88–90]. In peanut protein isolates, high pressure treatment from 50–200 MPa, a non-thermal processing, significantly improved water binding capacity (WBC) and oil binding capacity (OBC). Additionally, pressure treatment could result in intensity denaturation of conarrachin II fraction [91]. It was evident by SDS PAGE (**Figure 2**). This way protein isolates can be used as food supplementary material with improved characteristics. Effect of membrane processing were analyzed on the functional properties, structural changes, subunit profile and sensory attributes of the groundnut protein concentrate [92]. Results indicated an increase in the nitrogen solubility and foaming capacity of the protein concentrate over pH ranges of 2–10, acid precipitated protein isolate. Protein concentrate also showed higher emulsion stability index, less hydrophobicity but reduced nutty flavor as compared to control flour and acid protein isolate. Thus, membrane technology could give a protein concentrate with improved functionality and sensory characteristics similar to roasted wheat and improved digestibility, which will have potential application in the development of

*Effect of high pressure on protein concentrates lanes 2(untreated) and 3–7(treated with 50-100 MPa). (adapted* 

pH above the isoelectric point an increase in protein solubility was observed.

**130**

**Figure 2.**

*from [91]).*

food product formulations. Increased thermal stability, protein solubility at 4.5–6 pH, improved foaming and emulsifying properties were noticed by conjugating protein isolates (PPI) with dextran [84].

### **5.4 Water holding capacity and oil binding capacity**

Hydration or rehydration is the first and perhaps most critical step in imparting desirable functional properties to proteins in a food system. Water retention is defined as the ability of the food material to hold water against gravity [93]. Water holding capacity and oil absorption capacity both were significantly higher in raw peanut protein isolates [16]. Intrinsic factor affecting the water binding capacity of food proteins includes amino acid composition, protein conformation, and surface polarity/hydrophobicity [94]. The water retention capacity is the sum of bound, hydrodynamic and physically entrapped water [95]. During roasting, peanut proteins were denatured by high temperature, exposing more hydrophobic sites, which explained the reduced water retention of peanut protein [96]. With respect to water-holding capacity, the denatured proteins bind more water through exposure of hydrophilic groups [97].

Oil binding capacity and water holding capacity are increased by high pressure treatment [91]. Both properties are important for food texture and flavor. They are high in raw peanut proteins but affected by high temperatures.
