Studies on the relationship between functional properties and hydrophobicity of rice proteins and their hydrolyzates

 Rice protein has excellent nutritional value, its amino acid ratio is reasonable, except for tryptophan and lysine, the other amino acids are in line with the needs of the human body, and the biomass value (BV) and protein value (PV) is higher than that of other plant proteins, which is the best among plant proteins. At the same time, it is also an underutilized raw material, because in products using protein as an ingredient, its functional properties are often more important than its nutritional value [1], and the functional properties of rice protein often limit its application.

 

Many researchers have found that hydrophobicity, especially surface or effective hydrophobicity, is critical to understanding the functionality of proteins. Hydrophobicity means that the solute has little or no affinity for the environment in which the water resides. Interest in protein hydrophobicity has long been focused on the mechanisms by which it stabilizes the structure of natural proteins and the folding of molecules. In order to minimize the free energy of the folded molecule, the nonpolar or hydrophobic groups should be confined to the inside of the folded molecule and not exposed to the solute molecules. In fact, when the three-dimensional structure of the protein molecule was analyzed, it was found that some of the hydrophobic groups were exposed on the surface of the molecule. These hydrophobic fragments play a key role in intermolecular interactions. For example, they bind ligands or connect other macromolecules, including protein-protein or protein-lipid interactions. Another important aspect of the hydrophobicity of proteins is its role in the functional properties of proteins, in particular quantitative structure-activity relationships (QSAR) [2]. Since functional properties are dependent on interactions between protein molecules and with other components of the food system, these interactions may occur both on the surface and in the interior. Some functional properties of food proteins such as emulsification and foaming are influenced by the molecular structure. In this paper, the relationship between hydrophobicity and functional properties of proteins is discussed.

 

1 Experimental materials and methods

1.1 Main materials

Indica protein (alkaline extraction, protein content over 90%).

Flavourzyme Activity Unit: 500 LAPU/g, NOVO, Denmark.

 

1.2 Experimental Methods

1.2.1 Determination of hydrophobicity

Using 8-anilino-1-naphthalenesulfonate (ANS) as a probe, this reagent fluoresces in nonpolar environments but not in water or polar environments, and fluoresces when ANS bonds to membranes or relatively hydrophobic regions of proteins, a property that can be exploited to detect the hydrophobicity of the surface of proteins [3].

 

1.2.2 Determination of solubility

Folin-phenol reagent method for protein content of supernatants.

 

1.2.3 Determination of emulsification and emulsion stability

The turbidity method was used [4]. The specific operation is as follows: take 0 . 5% rice protein solution 30 ml, add 10 ml of pure soybean salad oil while stirring, and then homogenize at a speed of 8 000-10 000 r/min for 2 min to form an emulsion, and then extract 50 μl of emulsion from the bottom of the microsyringe and put it into a small beaker. Then, 25 ml of 0.1% sodium dodecyl sulfate was added. Then, add 25 ml of 0.1% sodium dodecyl sulfate (SDS) solution to make a mixture. Rice protein has excellent nutritional value, its amino acid ratio is reasonable, except for tryptophan and lysine, the other amino acids are in line with the needs of the human body, and the biomass value (BV) and protein value (PV) is higher than that of other plant proteins, which is the best among the plant proteins. At the same time, it is also an underutilized raw material, because in products using protein as an ingredient, its functional properties are often more important than its nutritional value [1], and the functional properties of rice protein often limit its application.

 

Many researchers have found that hydrophobicity, especially surface or effective hydrophobicity, is critical to understanding the functionality of proteins. Hydrophobicity means that the solute has little or no affinity for the environment in which the water resides. Interest in protein hydrophobicity has long been focused on the mechanisms by which it stabilizes the structure of natural proteins and the folding of molecules. In order to minimize the free energy of the folded molecule, the nonpolar or hydrophobic groups should be confined to the inside of the folded molecule and not exposed to the solute molecules. In fact, when the three-dimensional structure of the protein molecule was analyzed, it was found that some of the hydrophobic groups were exposed on the surface of the molecule. These hydrophobic fragments play a key role in intermolecular interactions. For example, they bind ligands or connect other macromolecules, including protein-protein or protein-lipid interactions. Another important aspect of the hydrophobicity of proteins is its role in the functional properties of proteins, in particular quantitative structure-activity relationships (QSAR) [2]. Since functional properties are dependent on interactions between protein molecules and with other components of the food system, these interactions may occur both on the surface and in the interior. Some functional properties of food proteins such as emulsification and foaming are influenced by the molecular structure. In this paper, the relationship between hydrophobicity and functional properties of proteins is discussed.

 

1 Experimental materials and methods

1.1 Main materials

Indica protein (alkaline extraction, protein content over 90%).

Flavourzyme Activity Unit: 500 LAPU/g, NOVO, Denmark.

 

1.2 Experimental Methods

1.2.1 Determination of hydrophobicity

Using 8-anilino-1-naphthalenesulfonate (ANS) as a probe, this reagent fluoresces in nonpolar environments but not in water or polar environments, and fluoresces when ANS bonds to membranes or relatively hydrophobic regions of proteins, a property that can be exploited to detect the hydrophobicity of the surface of proteins [3].

 

1.2.2 Determination of solubility

Folin-phenol reagent method for protein content of supernatants.

 

1.2.3 Determination of emulsification and emulsion stability

The turbidity method was used [4]. The specific operation is as follows: take 0 . 5% rice protein solution 30 ml, add 10 ml of pure soybean salad oil while stirring, and then homogenize at a speed of 8 000-10 000 r/min for 2 min to form an emulsion, and then extract 50 μl of emulsion from the bottom of the microsyringe and put it into a small beaker. Then, 25 ml of 0.1% sodium dodecyl sulfate was added. Nakai found that the surface hydrophobicity of plant proteins has a good correlation with the emulsifying property [7], and it can be seen from Figures 3 and 4 that the enzyme hydrolyzed product has better emulsifying property than the original material. As can be seen from Figures 3 and 4, the hydrolyzed product has better emulsification than the original material. The hydrophobicity of the hydrolyzed product is increased due to the hydrolysis of the enzyme, which exposes the hydrophobic groups and increases the hydrophobicity, and this increase in hydrophobicity facilitates the binding of the hydrophobic groups to the oil droplets, thus increasing the emulsification property. Many studies have shown that solubility has an effect on emulsification, but less so than hydrophobicity. Maximum emulsification was obtained at 11% hydrolysis, and the decrease in emulsification at higher hydrolysis may be due to the decrease in viscosity, as well as the disrupted spatial structure of the proteins (mainly helical structure) and the creation of more polar groups, which make it difficult for the oil droplets to bind to the proteins, and also lead to the decrease in emulsification [8].

 

The emulsion stability decreases with increasing hydrolysis, and the decrease in emulsion stability may be due to the decreasing viscosity of the continuous phase. On the other hand, the formation of a viscous film at the oil-water interface is very important for stability, and since small peptides are not readily adsorbed onto a viscous film, the emulsion stability decreases with increasing hydrolysis [9].

 

2.3 Foaming

Foaming is a property that occurs at the liquid/gas interface and is strongly related to the tension at the interface between the two phases. cherry suggests that to form stable foams, proteins should be (1) soluble in water, (2) readily concentrated at the liquid/gas interface, and (3) able to form a mucilage layer of sufficient viscosity and strength, which requires that the protein's structure be hydrophobic, pliable, and disordered. limited hydrolysis can increase the exposure of hydrophobic groups and cross-linking of polypeptide chains, which can increase the viscosity of the lamellae and enhance the foaming ability. Limited hydrolysis increases the exposure of hydrophobic groups and cross-linking of peptide chains, which increases the viscosity of the lamellae and the stability of the foam, while increased hydrophobicity enhances the foaming ability. As can be seen in Fig. 5, we get the maximum foaming degree when the hydrolysis degree is 7%. If the hydrolysis degree is too large, the excessive self-crosslinking causes the loss of elasticity of the lamellae, which leads to the collapse of the foam, and the foaming property will be reduced, and the stability will be reduced [10]. It is theorized that the net charge concentration affects protein adsorption at the air/water interface, and that an increase in net charge increases the foamability, so that limited hydrolysis increases the degree of foaming; on the other hand, excessive hydrolysis results in a high net charge concentration, which leads to repulsion between molecules, resulting in the collapse of the bubbles, and a decrease in stability. The flexibility of the protein molecules, their size, and the degree of cross-linking of the molecules all have an effect on foaming, and since viscosity is a characteristic that reflects this aspect, the degree of foaming is also related to viscosity, with the greater the viscosity, the greater the degree of foaming. Excessive hydrolysis decreases the viscosity of the solution, which also contributes to poor foaming, and Leandros suggests that proteins with a dispersibility greater than 40% and a hydrophobicity greater than 700 (using the cis-pnA probe) are favored for foaming. Therefore, in order to obtain the best foaming characteristics, it is important to balance solubility, hydrophobicity and viscosity to achieve a good balance between hydrophilicity and hydrophobicity.

 

3 Conclusion

Hydrophobicity plays an important role in the functional properties of proteins, and numerous studies have shown that solubility, emulsification, and foaming properties of hydrophobic proteins have been reasonably well resolved using hydrophobicity. Enzymatic hydrolysis of hydrophobic protein

The water property is improved to effectively improve its solubility, emulsification and foaming properties.

 

References:

［1］ Johson D w. Functional properties of oilseed proteins［J］.  J Amer oil chem soc, 1970, 47:402 .

[2] wolf wJ. soybeans: chemistry and Technolgoy [c].  smith A K, cir- cle s J, Eds: Avi: westprot, cT, 1972, 93 .

［3］ Horiuchi T, Fukushima D, sugimoto H .  Studies on Enzyme - Modified proteins as Foaming Agents: effects of structure on Foam stability［J］.  Food chem, 1978(3):35 .

［4］ Kevin N p, John E K .  Emulsifying properties of protein: Evaluation of a Turbidimetic Technique [J].  J Agri Food chem, 1978, 26(3):716 .

［5］ shigeru Hayakaya, shuryo Nakai. Relationships of Hydrophobicity and net charge to the solubility of Milk and soy proteins［J］.  J Fod sci, 1985, 50:486 .

［6］ Bigelow c c. on the Average Hydrophobicity of protein and the Rela- tion Between it and protein structures［J］.  J Theoret Biol, 1967, 16: 187 .

［7］ Nakai s, Ho L, Heibig N, et al. Relationship Between Hydrophobicity and Emusifying properties of som plant proteins［J］.  can Inst Food sci Technol J, 1980, 13:23 .

［8］ Leandrosp. voutsinas, Elainecheung. Relationships of Hydrophobicity to Emulsifying properties of Heat Denatured proteins［J］.  J Food sci, 1983, 48:26 .

［9］ Qi M, Hettiarachchy N s, Kalapathy U. Solubilicity and Emusifying properties of soy protein Isolates Modified by pancreation［J］.  Solubilicity and Emusifying properties of soy protein Isolates Modified by pancreation [J].  J Food sci, 1997, 62:1 110 .

［10］ cheery Jp, Mcwatters K H .  Protein Functionality in Food［A］.  A c s. symposium series 147 [c]. (Ed).  cherry J p. American chemi- cal society, washington Dc.

[11] Kinsella J E .  Functional properties of protein in Food: a survey cRc Rev [J].  Food sci Nutr, 1976(3):219 .