Mini Review

Adsorption and Interfacial Properties of Proteins and its Relationship to Emulsification and Foaming: A Mini Review

Mingliang Li, Xiaowei Zhang and Leiyan Wu*

College of Food Science and Engineering, Jiangxi Agricultural University, China

Submission: November 30, 2022; Published: January 12, 2023

*Corresponding author: Leiyan Wu, College of Food Science and Engineering, Jiangxi Agricultural University, China

How to cite this article: Getnet Awoke Y Nadezhda Vasilevna B, Sabirov A. Preparation and Characterization of Microbial Growth Media and its Application for the Production of Microbial Feed Protein. Nutri Food Sci Int J. 2023. 11(4): 555820. DOI: 10.19080/NFSIJ.2023.11.555820.

Abstract

The interfacial properties of proteins have been extensively studied because of those properties are widely used in many food products, for example breads or cakes, ice-cream, and foamy coffee beverages. Protein interfacial behavior is significantly influenced by protein type, concentration, pH, ionic strength, sonication, and heating. Furthermore, proteins frequently work in conjunction with other substances, and these interactions have an impact on the interfacial properties of proteins. The impact of solution environment and processing techniques on the protein interfacial characteristics has been extensively studied in the past. The whole adsorption process of proteins, including protein diffusion in solutions and adsorption, permeation and rearrangement of protein at the interface has been reviewed in this work. The impact of protein type, solution environment and interfacial type on protein interfacial adsorption kinetics and interfacial swelling rheology have been discussed. Additionally, a summary of the structural characteristics of proteins that adhere readily to the interface has been provided. In addition, this review has important guiding significances for predicting and customizing protein adsorption with different process, so as to obtain varying purpose emulsion or foaming system.

Keywords: Protein; Adsorption; Interface behavior; Interface rheology; Emulsification; Foaming

Introduction

An emulsion is the dispersion of one liquid in the form of small droplets (0.1μm - 10μm) in another insoluble liquid [1]. A Foam, on the other hand, is a system in which bubbles are dispersed in a continuous aqueous phase [2]. Emulsions and foams are widely found in food products such as creams, milk powders, cakes, etc. However, due to their large interfacial areas, both foams and emulsions are thermodynamically unstable systems [3,4]. Surfactants are therefore needed to stabilize emulsions and foams over time. Surfactants are amphiphilic and can adsorb to the air-water and oil-water interfaces, thereby reducing the interfacial tension between the two phases forming foams and emulsions. In this way, they stabilize foams and emulsions by forming films at the interface. Surfactants are generally synthetic small-molecule surfactants, proteins, polysaccharides, polyphenols, and nanoparticles [5]. Synthetic surfactants have been widely used in food due to their functional characteristics, however nowadays, an increasing number of consumers prefer natural and safe food ingredients, hence natural surfactants are gradually gaining attention. Among them, proteins are frequently utilized as food surfactants due to their great functional qualities and high nutritional value.

Since the interfacial properties of proteins form the basis of their functional characteristics, they are crucial to the emergence and stability of emulsions and foams. Proteins are quickly adsorbed to the oil-water and air-water interfaces during the stirring process. After this adsorption, the proteins at the interface go through permeation and rearrangement behavior. Finally, the proteins at the interface interact with one another to form a stable and elastic interfacial film to stabilize oil droplets and foaming [6]. A deep understanding of the interfacial properties of proteins is essential for their use as surfactants in food products to improve food taste [7]. However, proteins’ interfacial characteristics, such as hydrophobicity, surface charge, particle size, etc., are directly related to their structure. The structure and interfacial characteristics of proteins can be significantly influenced by factors such as protein type, concentration, pH, temperature, and ionic strength, which can then alter their functional characteristics. Additionally, different protein treatments used in the preparation of food might alter the structure of proteins and have an impact on their interfacial and functional characteristics [8]. This article is based on a review of the changes in protein structure and interfacial properties as a function of solution environment, food processing methods, and compounding of other substances and discusses the changes in protein structure that facilitate adsorption.

Discussion

Diffusion of proteins to the interface

In the initial stage of protein adsorption, the adsorption is primarily controlled by diffusion. The interfacial tension decreases rapidly during this phase. The diffusion rate can be calculated by Ward and Tordai model [9]:

where C₀ is the initial protein concentration, K is the Boltzmann constant, T is the absolute temperature, and D is the diffusion coefficient. It has been demonstrated previously that proteins diffuse more quickly at the oil-water interface than at the air-water interface because the oil phase is more attractive to proteins than the air phase [10]. The structural differences between individual proteins lead to differences in their diffusion rates. Loosely structured chain-disordered proteins (e.g., β-casein) have a faster diffusion rate than compact globular proteins (e.g., bovine serum proteins) [11]. Due to the higher hydrophobicity of pea proteins, they have a higher diffusion rate in comparison to milk proteins [12]. Polyglycerol polyricinoleate has a smaller molecular weight (MW) than proteins and can adsorb faster to the oil-water interface [13]. According to the Stokes-Einstein diffusion model, the diffusion coefficient is inversely proportional to the molecular size [9]. Many studies have shown that the diffusion rate is driven by the concentration gradient and increases with the increase in the concentration of the bulk phase [14,15]. However, it has also been noted that adsorption barriers and electrostatic repulsion cause the protein diffusion rate to decrease with increasing concentration [16]. In the diffusion phase, in addition to the concentration gradient, chemical potential gradients produced by hydrophobic and electrostatic forces also act as a driving factor for protein diffusion to the interface [8]. Therefore, the solution environment such as pH and ionic strength are also important factors that influence the diffusion of proteins to the interface. For β-lactoglobulin and β-lactoglobulin aggregates, there is less spatial resistance at a pH close to PI (Isoelectric Point), due to the lower net charge compared to positively or negatively charged particles which can diffuse to the interface faster [17]. However, the lower surface charge near the PI may lead to the formation of protein aggregates of large particles, which reduces the diffusion rate [16,18]. At low ion concentrations, the electrostatic shielding effect of ions accelerates protein adsorption to the interface [16,19,20]. A further increase in ion concentration may lead to an increase in particle size but will decrease the diffusion rate [20]. In the diffusion phase, chemical potential gradients produced by hydrophobic and electrostatic forces also act as a driving factor for protein diffusion to the interface in addition to the concentration gradient [21]. Moreover, ultrasound has been shown to increase the hydrophobicity of proteins and reduce their particle size, which accelerates the diffusion rate of proteins [20,22]. The pace of protein diffusion can be influenced by a variety of interactions with other substances in addition to how the protein is processed. For instance, the maize protein hydrolysate’s reduced hydrophobicity following compounding with tannic acid and the high viscosity of xanthan gum both lower the protein’s rate of diffusion [15,23]. However, Ali Rafe reported that β-lactoglobulin and high methoxyl pectin synergistically interact at the air-water interface to accelerate the K_diff of β-lactoglobulin [24].

Permeation and rearrangement of protein at the interface

After a short period of diffusion, the protein undergoes permeation and rearrangement behavior at the interface. During this phase, the interfacial tension decreases slowly. A first-order equation can be used to monitor the rates of penetration and rearrangement of adsorbed protein [9]:

where π0, πt, and π are the interfacial pressures at the beginning, at any time point, and at equilibrium, respectively. The first linear region corresponds to the rate constant of penetration (K_P). The second linear region corresponds to the rate constant of rearrangement (K_R). According to a theory, globular proteins partially denature at the interface and unfold to produce molten globules, which in turn increases interactions with exposed hydrophobic groups and results in a protein with KR greater than K_P [25]. Also, this theory supports that proteins with flexible conformations are easier to permeate and rearrange behavior at interfaces [14]. Numerous studies have demonstrated that proteins have quicker penetration and rearrangement rates at high concentrations, but after a certain point, due to spatial site resistance, the rate of permeation and rearrangement drops [26,27]. However, at high concentrations, the protein forms a more compact conformation [28]. According to this theory, the permeation and rearrangement rate of protein should be worse at higher concentrations, but this is not the case. This is likely because the concentration gradient’s favorable impact on the initial adsorption at the interface outweighs the structure’s unfavorable impact on the protein’s conformational differences [14]. Proteins also form different conformations at different pHs resulting in differences in adsorption behavior [29]. Zhou et al. reported that the higher hydrophobicity of whey protein isolate at pH 3 resulted in faster permeation and unfolding rates [30]. Tian et al. showed that pH2-shifted β-conglycinin resulted in lower permeation and rearrangement rates due to its larger particle size [31]. High ionic concentrations hindered the penetration rate of -conglycinin and walnut protein-xanthan gum combinations, likely as a result of attractive interactions between the polyelectrolytes, although the electrostatic shielding effect benefited the rate of rearrangement [16,32]. In addition, it has been previously shown that heating causes proteins to form aggregates and increases electrostatic repulsion between proteins thereby reducing the rate of permeation and rearrangement [30,33,34]. However, in medium ratios, mixes of ovalbumin and lysozyme form an aggregate with lower free energies, enabling faster penetration and rearrangement behavior [35] (Figure 1).

Interfacial dilatational rheology

Interfacial dilatational rheology provides a good response to the mechanical strength of the protein film formed at the interface and the degree of interaction at the interface [36]. Because spherical proteins have greater molecular interactions at the interface, interfacial membranes consisting of flexible proteins (like β-casein) are less flexible than membranes formed of spherical proteins with a rigid structure (like lysozyme) [37,38]. It is important to note that the type of protein leads to differences between interfacial film strengths, and the non-aqueous phase also leads to differences between interfacial film strengths. It has been previously shown that due to salvation, oil-water interfaces form less elastic interfacial films compared to air-water interfaces [39]. In general, as the protein concentration increases more protein molecules tend to adsorb onto the interface to increase the stacking density, thus forming a more powerful membrane [16,40,41]. However, many studies have also pointed out that when the protein concentration continues to increase, the protein molecules become less elastic upon reaching a critical concentration value due to imperfect alignment or blocking by adjacent molecules, resulting in weakened molecular interactions and a consequent decrease in the elasticity of the interfacial membrane [42-44]. The effect of pH on the interfacial modulus of proteins can be attributed primarily to the change in their structure and the effect of surface charge. According to Jose María Ruiz- Alvarez, various charges of the peptides led to a better unfolding of whey protein hydrolysates and blue whiting protein hydrolysates at pH 8 and pH 2, respectively, generating stronger interfacial films at the oil-water interface [45]. Generally, proteins form more rigid interfaces at a pH close to PI, and higher charges reduce the interaction between proteins, forming poor elastic membranes [46-48]. However, similar to diffusion, when the pH approaches PI, the proteins start aggregating which weakens the membrane elasticity [16]. The surface charge of proteins is also dramatically affected by the ionic strength in the solution. The effect of ions on protein swelling modulus depends on pH and increasing the ionic strength at pH away from PI decreases the electrostatic repulsion between protein molecules, while simultaneously increasing the interaction between them and thus increasing the swelling modulus [13]. Xiong et al. investigated the effect of ultrasonic treatment of bound ions on protein interface rheology [20]. After the ultrasound the ovalbumin and ovotransferrin apparently had enhanced intermolecular interactions, forming a more robust film [20,49]. Peanut isolate protein becomes more hydrophobic when heated, which encourages adsorption at the interface and the formation of an interfacial membrane that is more elastic [50]. While many researchers have elaborated on the interfacial rheology of protein complex systems, the majority of the aforementioned studies have solely focused on single protein systems. In accordance with previously published research studies, combining proteins with xanthan gum, chitosan, and cinnamaldehyde improves protein adsorption at the interface and encourages the generation of more elastic protein films while improving the stability of the emulsion [36,51,52].

Conclusion

The effects of different processing methods and environmental conditions on the adsorption kinetics and interfacial swelling rheology of proteins have been reviewed. Based on previous studies, it is known that proteins with relatively loose structures can adsorb to the interface faster in comparison to dense spherical proteins, but form less elastic interfacial films. The interfacial affinity of a protein determines the concentration at which its monolayer is saturated, beyond which the diffusion, permeation, and rearrangement rates of the protein as well as the strength of the interfacial membrane are reduced. Since proteins have a high degree of hydrophobicity, those with a low charge and tiny particle size will adsorb at the interface more readily than others with a higher charge and larger particle size. This is crucial for predicting how well proteins would emulsify and foaming. Emulsification and foaming qualities are intimately related to a protein’s interfacial activity and the rate at which it adsorbs at the interface. The stability of emulsions and foams is closely correlated with the nature of the interfacial film. We can increase product quality by modifying processing procedures and environmental factors by comprehending the effects of various processing techniques and environments on protein interface and functional properties.

Acknowledgment

We gratefully acknowledge the financial support by the National Natural Science Foundation of China (32060583 and 31660481). The authors would like to thank all the reviewers who participated in the review, as well as Dr. Lei-Yan Wu for providing structural arranging during the preparation of this manuscript.

Conflict of Interest

The authors declare that they have no known competing financial interests or personal relationships that could influence the work reported in this paper.

References

1. Yan X, Ma C, Cui F, McClements DJ, Liu X, et al. (2020) Protein-stabilized Pickering emulsions: Formation, stability, properties, and applications in foods. Trends in Food Science & Technology 103: 293-303.
2. Walsh DJ, Russell K, FitzGerald RJ (2008) Stabilisation of sodium caseinate hydrolysate foams. Food research international 41(1): 43-52.
3. Zhan F, Hu J, He C, Sun J, Li J, et al. (2020) Complexation between sodium caseinate and gallic acid: Effects on foam properties and interfacial properties of foam. Food Hydrocolloids 99: 105365.
4. Niu H, Wang W, Dou Z, Chen X, Chen X, et al. (2022) Multiscale combined techniques for evaluating emulsion stability: A critical review. Adv Colloid Interface Sci 311: 102813.
5. Mao L, Wang D, Liu F, Gao Y (2018) Emulsion design for the delivery of β-carotene in complex food systems. Critical Reviews in Food Science and Nutrition 58(5): 770-784.
6. Hu L, Wu L, Lai C, Li M, Yang W (2021) The influence of pH and concentration on the zeta potential, hydrophobicity of OVT and the relationship between its structure and interfacial behaviors. Journal of Dispersion Science and Technology 43(12): 1755-1765.
7. Zheng H (2019) Introduction: measuring rheological properties of Foods. In: Rheology of semisolid foods. Springer, Germany, p. 3-30.
8. Zhou B, Tobin JT, Drusch S, Hogan SA (2021) Interfacial properties of milk proteins: A review. Adv Colloid Interface Sci 295: 102347.
9. Henestrosa RVP, Sánchez CC, Escobar MdMY, Jiménez JJP, Rodríguez FM, et al. (2007) Interfacial and foaming characteristics of soy globulins as a function of pH and ionic strength. Colloids and Surfaces A: Physicochemical and Engineering Aspects 309(1-3): 202-215.
10. Sengupta T, Damodaran S (1998) Role of dispersion interactions in the adsorption of proteins at oil− water and air− water interfaces. Langmuir 14(22): 6457-6469.
11. Chen M, Sala G, Meinders MB, Valenberg HJ, Linden E, et al. (2017) Interfacial properties, thin film stability and foam stability of casein micelle dispersions. Colloids Surf B Biointerfaces 149: 56-63.
12. Wierenga PA, Meinders MB, Egmond MR, Voragen FA, De Jongh HH (2003) Protein exposed hydrophobicity reduces the kinetic barrier for adsorption of ovalbumin to the air - water interface. Langmuir 19(21): 8964-8970.
13. Zhu Q, Wang C, Khalid N, Qiu S, Yin L (2017) Effect of protein molecules and MgCl2 in the water phase on the dilational rheology of polyglycerol polyricinoleate molecules adsorbed at the soy oil-water interface. Food Hydrocolloids 73: 194-202.
14. Tang CH, Shen L (2015) Dynamic adsorption and dilatational properties of BSA at oil/water interface: Role of conformational flexibility. Food Hydrocolloids 43: 388-399.
15. Liu L, Zhao Q, Liu T, Zhao M (2011) Dynamic surface pressure and dilatational viscoelasticity of sodium caseinate/xanthan gum mixtures at the oil–water interface. Food Hydrocolloids 25(5): 921-927.
16. Tian Y, Taha A, Zhang P, Zhang Z, Hu H, et al. (2021) Effects of protein concentration, pH, and NaCl concentration on the physicochemical, interfacial, and emulsifying properties of β-conglycinin. Food Hydrocolloids 118.
17. Dombrowski J, Gschwendtner M, Kulozik U (2017) Evaluation of structural characteristics determining surface and foaming properties of β-lactoglobulin aggregates. Colloids and Surfaces A: Physicochemical and Engineering Aspects 516: 286-295.
18. Zhang X, Lei Y, Luo X, Wang Y, Li Y, et al. (2021) Impact of pH on the interaction between soybean protein isolate and oxidized bacterial cellulose at oil-water interface: Dilatational rheological and emulsifying properties. Food Hydrocolloids 115.
19. Tan Y, Deng X, Liu T, Yang B, Zhao M, et al. (2017) Influence of NaCl on the oil/water interfacial and emulsifying properties of walnut protein-xanthan gum. Food Hydrocolloids 72: 73-80.
20. Xiong W, Li J, Li B, Wang L (2019) Physicochemical properties and interfacial dilatational rheological behavior at air-water interface of high intensity ultrasound modified ovalbumin: Effect of ionic strength. Food Hydrocolloids 97.
21. Choe U, Chang L, Ohm JB, Chen B, Rao J (2022) Structure modification, functionality and interfacial properties of kidney bean (Phaseolus vulgaris L.) protein concentrate as affected by post-extraction treatments. Food Hydrocolloids 133.
22. Sha L, Koosis AO, Wang Q, True AD, Xiong YL (2021) Interfacial dilatational and emulsifying properties of ultrasound-treated pea protein. Food Chem 350: 129271.
23. Wang YH, Lin Y, Yang XQ (2019) Foaming properties and air-water interfacial behavior of corn protein hydrolyzate-tannic acid complexes. J Food Sci Technol 56(2): 905-913.
24. Rafe A, Selahbarzin S, Kulozik U, Hesarinejad MA (2022) Dilatational rheology-property relationships of β-lactoglobulin /high methoxyl pectin mixtures in aqueous foams. Food Hydrocolloids 130.
25. Beverung C, Radke CJ, Blanch HW (1999) Protein adsorption at the oil/water interface: characterization of adsorption kinetics by dynamic interfacial tension measurements. Biophysical chemistry 81(1): 59-80.
26. Patino RJM, Sánchez CC, Ortiz MSE, Niño RMR, Añón MC (2004) Adsorption of soy globulin films at the air - water interface. Industrial & engineering chemistry research 43(7): 1681-1689.
27. Luo Y, Zheng W, Shen Q, Zhang L, Tang C, et al. (2021) Adsorption kinetics and dilatational rheological properties of recombinant Pea Albumin-2 at the oil-water interface. Food Hydrocolloids 120.
28. Li R, Fu N, Wu Z, Wang Y, Wang Y (2015) Protein aggregation in foam fractionation of bovine serum albumin: Effect of protein concentration. Biochemical Engineering Journal 103: 234-241.
29. Gochev GG, Kovalchuk VI, Aksenenko EV, Fainerman VB, Miller R (2021) β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH. Colloids and Interfaces 5(1).
30. Zhou B, Tobin JT, Drusch S, Hogan SA (2021) Dynamic adsorption and interfacial rheology of whey protein isolate at oil-water interfaces: Effects of protein concentration, pH and heat treatment. Food Hydrocolloids 116.
31. Tian Y, Zhang Z, Zhang P, Taha A, Hu H, et al. (2020) The role of conformational state of pH-shifted β-conglycinin on the oil/water interfacial properties and emulsifying capacities. Food Hydrocolloids 108.
32. Yao X, Xu K, Shu M, Liu N, Li N, et al. (2021) Fabrication of iron loaded whey protein isolate/gum Arabic nanoparticles and its adsorption activity on oil-water interface. Food Hydrocolloids 115.
33. Liu F, Tang CH (2016) Soy glycinin as food-grade Pickering stabilizers: Part. I. Structural characteristics, emulsifying properties and adsorption/arrangement at interface. Food Hydrocolloids 60: 606-619.
34. Xiong W, Ren C, Li J, Li B (2018) Characterization and interfacial rheological properties of nanoparticles prepared by heat treatment of ovalbumin-carboxymethylcellulose complexes. Food Hydrocolloids 82: 355-362.
35. Jin H, Sun Y, Pan J, Fang Y, Jin Y, et al. (2022) Adsorption kinetics of ovalbumin and lysozyme at the air-water interface and foam properties at neutral pH. Food Hydrocolloids 124.
36. Xiong W, Ren C, Tian M, Yang X, Li J, et al. (2018) Emulsion stability and dilatational viscoelasticity of ovalbumin/chitosan complexes at the oil-in-water interface. Food Chem 252: 181-188.
37. Freer EM, Yim KS, Fuller GG, Radke CJ (2004) Interfacial rheology of globular and flexible proteins at the hexadecane/water interface: comparison of shear and dilatation deformation. The Journal of Physical Chemistry B 108(12): 3835-3844.
38. Rouimi S, Schorsch C, Valentini C, Vaslin S (2005) Foam stability and interfacial properties of milk protein–surfactant systems. Food Hydrocolloids 19(3): 467-478.
39. Hinderink EBA, Sagis L, Schroen K, Carabin BCC (2020) Behavior of plant-dairy protein blends at air-water and oil-water interfaces. Colloids Surf B Biointerfaces 192: 111015.
40. Peng D, Jin W, Li J, Xiong W, Pei Y, et al. (2017) Adsorption and Distribution of Edible Gliadin Nanoparticles at the Air/Water Interface. J Agric Food Chem 65(11): 2454-2460.
41. Dachmann E, Nobis V, Kulozik U, Dombrowski J (2020) Surface and foaming properties of potato proteins: Impact of protein concentration, pH value and ionic strength. Food Hydrocolloids 107.
42. Qiao X, Miller R, Schneck E, Sun K (2020) Foaming properties and the dynamics of adsorption and surface rheology of silk fibroin at the air/water interface. Colloids and Surfaces A: Physicochemical and Engineering Aspects 591.
43. Kirtil E, Svitova T, Radke CJ, Oztop MH, Sahin S (2022) Investigation of surface properties of quince seed extract as a novel polymeric surfactant. Food Hydrocolloids 123.
44. Kirtil E, Kurtkaya E, Svitova T, Radke CJ, Oztop MH, et al. (2021) Examination of interfacial properties of quince seed extract on a sunflower oil-water interface. Chemical Engineering Science 245.
45. Álvarez RJM, Santaella CT, Valderrama MJ, Guadix A, Guadix EM, et al. (2022) pH influences the interfacial properties of blue whiting (M. poutassou) and whey protein hydrolysates determining the physical stability of fish oil-in-water emulsions. Food Hydrocolloids 122.
46. Ulaganathan V, Retzlaff I, Won J, Gochev G, Gunes D, et al. (2017) β-Lactoglobulin adsorption layers at the water/air surface: 2. Dilational rheology: Effect of pH and ionic strength. Colloids and Surfaces A: Physicochemical and Engineering Aspects 521: 167-176.
47. Ishii T, Matsumiya K, Matsumura Y (2021) Combinational effects of acid and salt addition on colloidal, interfacial, and emulsifying properties of purified soybean oil bodies. Food Hydrocolloids 111.
48. Wouters AGB, Joye IJ, Delcour JA (2020) Understanding the air-water interfacial behavior of suspensions of wheat gliadin nanoparticles. Food Hydrocolloids 102.
49. Li S, Zhang S, Liu Y, Fu X, Xiang X, et al. (2022) Effects of ultrasound-assisted glycosylation on the interface and foaming characteristics of ovotransferrin. Ultrason Sonochem 84: 105958.
50. Zhang Y, Xiong W, Lei L, Pei Y, He L, et al. (2019) Influence of heat treatment on structure, interfacial rheology and emulsifying properties of peanut protein isolate. Czech Journal of Food Sciences 37(3): 212-220.
51. Cai Y, Deng X, Liu T, Zhao M, Zhao Q, et al. (2018) Effect of xanthan gum on walnut protein/xanthan gum mixtures, interfacial adsorption, and emulsion properties. Food Hydrocolloids 79: 391-398.
52. Felix M, Yang J, Guerrero A, Sagis LMC (2019) Effect of cinnamaldehyde on interfacial rheological properties of proteins adsorbed at O/W interfaces. Food Hydrocolloids 97.