Improving the freeze-thaw stability of soy protein emulsions via combing limited hydrolysis and Maillard-induced glycation

Effect of Mono- and Polysaccharide on the Structure and Property of Soy Protein Isolate during Maillard Reaction

As a protein extracted from soybeans, soy protein isolate (SPI) may undergo the Maillard reaction (MR) with co-existing saccharides during the processing of soy-containing foods, potentially altering its structural and functional properties. This work aimed to investigate the effect of mono- and polysaccharides on the structure and functional properties of SPI during MR. The study found that compared to oat β-glucan, the reaction rate between SPI and D-galactose was faster, leading to a higher degree of glycosylation in the SPI-galactose conjugate. D-galactose and oat β-glucan showed different influences on the secondary structure of SPI and the microenvironment of its hydrophobic amino acids. These structural variations subsequently impact a variety of the properties of the SPI conjugates. The SPI-galactose conjugate exhibited superior solubility, surface hydrophobicity, and viscosity. Meanwhile, the SPI-galactose conjugate possessed better emulsifying stability, capability to produce foam, and stability of foam than the SPI-β-glucan conjugate. Interestingly, the SPI-β-glucan conjugate, despite its lower viscosity, showed stronger hypoglycemic activity, potentially due to the inherent activity of oat β-glucan. The SPI-galactose conjugate exhibited superior antioxidant properties due to its higher content of hydroxyl groups on its molecules. These results showed that the type of saccharides had significant influences on the SPI during MR.

Effect of glycosylation modification on structure and properties of soy protein isolate: A review

Soybean protein isolate (SPI) is a highly functional protein source used in various food applications, such as emulsion, gelatin, and food packaging. However, its commercial application may be limited due to its poor mechanical properties, barrier properties, and high water sensitivity. Studies have shown that modifying SPI through glycosylation can enhance its functional properties and biological activities, resulting in better application performance. This paper reviews the recent studies on glycosylation modification of SPI, including its quantification method, structural improvements, and enhancement of its functional properties, such as solubility, gelation, emulsifying, and foaming. The review also discusses how glycosylation affects the bioactivity of SPI, such as its antioxidant and antibacterial activity. This review aims to provide a reference for further research on glycosylation modification and lay a foundation for applying SPI in various fields.

Effects of limited enzymatic hydrolysis and polysaccharide addition on the physicochemical properties of emulsions stabilized with duck myofibrillar protein under low-salt conditions

This study aimed to investigate the role of hydrolysis and guar gum (GG) participation on the emulsification of the duck myofibrillar protein (MP) and the related stability of oil-in-water emulsion in low-salt condition. Emulsions were prepared using one of each or both treatments, and that prepared with trypsin hydrolysis and GG (T-GG) exhibited the highest stability. FTIR analysis confirmed the hydrogen bond interactions between the system components. T-GG treatment improved emulsion properties and decreased oil droplet size. Moreover, CLSM indicated that aggregation of T-GG oil droplets was prevented. Physical stability was assessed such as Turbiscan stability index, creaming index, and rheological properties. The adsorbed percentage for T-GG was the lowest. However, interfacial tension, droplet size, stability, and peroxide value analyses indicated that a denser interfacial membrane structure is formed with T-GG. Thus, T-GG treatment could be applied in the food industry, such as in nutrient delivery systems and fat mimetics.

Smart antimicrobial system based on enzyme-responsive high methoxyl pectin-whey protein isolate nanocomplex for fresh-cut apple preservation

The increase in pectin methylesterase (PME) activity on fresh-cut apple surface can smartly trigger the controlled release of bactericidal agents encapsulated within intelligent responsive Pickering emulsions. In this study, we developed a PME-responsive nanocomplex (W-H-II) to stabilize Pickering emulsion containing thyme essential oil (TEO), preserving fresh-cut apples. W-H-II, formed by heat-induced whey protein isolate (WPI) and high methoxyl pectin (HMP) (pH 4.5, 85 °C, 15 min, WPI:HMP ratio 1:2), exhibited good pH stability due to the stabilizing effects of hydrophobic, hydrogen bonding, and electrostatic interactions. The presence of PME triggered the demethylation of HMP within W-H-II, conferring PME response characteristics. Subsequently, a bacteriostasis experiment with pectinase-producing Bacillus subtilis provided evidence of PME-triggered TEO release from W-H-II-stabilized Pickering emulsion. Furthermore, microscopy techniques were employed to verify the demulsification behavior of the emulsion when PME activity ranged from 0.25 to 2.50 U mL-1. Finally, the PME-responsive TEO Pickering emulsion effectively preserved fresh-cut apples. Stored for 6 days at 5 °C and 10 °C, as the PME activity on the apple surface increased, the decay rate of the coated group was 0 %, with a total colony count below 3.0 log CFU g-1. This study introduces a novel intelligent preservation strategy for storing fresh-cut apples.

Emulsifying properties of plant-derived polypeptide and their conjugates: a self-consistent-field calculation study of the impact of hydrolysis

By considering the hydrolysates of soy protein produced by trypsin as an example, the emulsion stabilizing properties of plant-based protein fragments have been investigated theoretically. We apply Self-Consistent-Field (SCF) calculations to determine the colloidal interactions induced between a pair of droplets stabilized by adsorbed layers of various soy protein fragments. The study is extended to conjugates of such polypeptides, formed by covalent bonding with a suitable hydrophilic sidechain (e.g. a polysaccharide). Our results show that the relatively longer fragments, with a greater number of hydrophobic amino acids, will display a stronger degree of adsorption affinity compared to the smaller hydrolysates, even where the latter may have a higher overall ratio of hydrophobic residues. This suggested that the degree of protein hydrolysis should be carefully controlled and limited to modest values to avoid the generation of a large number of short polypeptides, while still sufficient to improve solubility. While the emulsion stabilizing performance of a protein fragment type is strongly dependent on the conformation it adopts on the interface, we find this to be less critical for the conjugated polypeptides. However, we argue that with increasing degree of hydrolysis, many small fragments will not have the chance to form bonds with polysaccharides. It is demonstrated that the abundance of these unreacted polypeptides in the system severely reduces the efficiency of the conjugated longer protein fragments, preventing their presence on the surface of the droplets through competitive adsorption process.

Effects of Pulsed Electric Field on the Physicochemical and Structural Properties of Micellar Casein

Pulsed electric field (PEF) as a green processing technology is drawing greater attention due to its eco-friendliness and potential to promote sustainable development goals. In this study, the effects of different electric field strengths (EFS, 0-30 kV/cm) on the structure and physicochemical features of casein micelles (CSMs) were investigated. It was found that the particle sizes of CSMs increased at low EFS (10 kV/cm) but decreased at high EFS (30 kV/cm). The absolute ζ-potential at 30 kV/cm increased from -26.6 (native CSMs) to -29.5 mV. Moreover, it was noticed that PEF treatment leads to changes in the surface hydrophobicity; it slightly increased at low EFS (10 kV/cm) but decreased at EFS > 10 kV/cm. PEF enhanced the protein solubility from 84.9 (native CSMs) to 87.1% (at 10 kV/cm). PEF at low EFS (10 kV/cm) intensified the emission fluorescence spectrum of CSMs, while higher EFS reduced the fluorescence intensity compared to native CSMs. Moreover, the analysis of the Amide Ι region showed that PEF-treated CSMs reduced the α-helix and increased the β-sheet content. Raman spectra confirmed that PEF treatment > 10 kV/cm buried tyrosine (Tyr) residues in a hydrophobic environment. It was also found that PEF treatment mainly induced changes in the disulfide linkages. In conclusion, PEF technology can be employed as an eco-friendly technology to change the structure and physiochemical properties of CSMs; this could improve their techno-functional properties.

Structural, functional properties of protein and characteristics of tofu from small-seeded soybeans grown in the Loess Plateau of China

The structural, functional properties of protein isolated from small-seeded soybeans were investigated and characteristics of tofu were studied. Small-seeded soybean protein had obvious α', α, β, acidic and basic subunits bands and two endothermic peaks (76.02-76.63℃ and 91.94-94.25℃). Small-seeded black soybean protein isolates (SBSPI) had more β-sheet (31.90-33.54%) structure, while small-seeded yellow soybean protein isolates (SYSPI) had more α-helix (18.89-20.72%) structure. SYSPI had higher fluorescence intensity (839.10-847.80) than SBSPI (482.70-565.10). SBSPI exhibited higher surface hydrophobicity (939.51-1252.75) and water absorption capacity (8.07-8.50 g/g). Tofu made from small-seeded yellow soybeans had higher yield (549.46-560.23 g/100 g soybean) and was brighter (L*, 74.61-77.48) and more yellowish (b*, 14.83-14.95) in color. Tofu made from Fugu small-seeded black soybean (FGSBS) had the highest hardness (178.52 g), adhesiveness (-25.77 g.sec), chewiness (87.45 g) and resilience (0.26), signifying a more compact structure.

Transglutaminase-Catalyzed Glycosylation Improved Physicochemical and Functional Properties of Lentinus edodes Protein Fraction

Lentinula edodes has high nutritional value and abundant protein. In order to develop and utilize edible mushroom protein, this study was designed to investigate the effects of TGase-catalyzed glycosylation and cross-linking on the physicochemical and functional properties of Lentinus edodes protein fraction. The results showed that within a certain time, glycosylation and TGase-catalyzed glycosylation decreased the total sulfydryl, free sulfydryl, disulfide bond, surface hydrophobicity, β-fold and α-helix, but increased the fluorescence intensity, random coil, β-turn, particle size and thermal stability. The apparent viscosity and the shear stress of the protein with an increase in shear rate were increased, indicating that TGase-catalyzed glycosylation promoted the generation of cross-linked polymers. In addition, the TGase-catalyzed glycosylated proteins showed a compact texture structure similar to the glycosylated proteins at the beginning, indicating that they formed a stable three-dimensional network structure. The flaky structure of proteins became more and more obvious with time. Moreover, the solubility, emulsification, stability and oil-holding capacity of enzymatic glycosylated Lentinus edodes protein fraction were significantly improved because of the proper TGase effects of glycosylation grafting and cross-linking. These results showed that glycosylation and TGase-catalyzed glycosylation could improve the processing characteristics of the Lentinula edodes protein fraction to varying degrees.

Optimization of enzymatic soy protein isolate-glucosamine conjugates to improve the freeze-thaw stability of emulsion

BACKGROUND

Using transglutaminase (TGase) is a new method to improve protein properties in order to promote protein glycosylation. This article mainly studies soy protein isolate (SPI) and glucosamine to improve the freeze-thaw stability of emulsion under the action of TGase. The degree of glycosylation was studied by the content of free amino groups and the degree of conjugation. The optimal conditions for preparing soy protein isolate-glucosamine (SPI-G) conjugate were determined by a response surface optimization model based on single-factor experiments using the creaming index of the emulsion after the first freeze-thaw cycle as the response value.

RESULTS

The results showed that the emulsion had the lowest creaming index when the conditions of protein concentration was 20 g L^-1 , mass ratio of SPI-G was 5:3 (w/w), enzyme addition amount was 10 U g^-1 , and reaction time was 2 h. The optimized modified product was measured for the creaming index after the first freeze-thaw cycle. It was found that the creaming index of the modified product SPI-G after the first freeze-thaw cycle was 9.02%, which was less than and close to the optimized model predicted value. The creaming index and optical microscopy results after three freeze-thaw cycles confirmed that the freeze-thaw stability of the SPI-G samples was significantly enhanced after optimization of the response surface model.

CONCLUSION

It showed that glycosylation promoted by TGase could improve the freeze-thaw stability of SPI emulsion, thereby broadening the application of SPI in food. © 2022 Society of Chemical Industry.

Improved Oxidation Stability of Camellia Oil-in-Water Emulsions Stabilized by the Mixed Monolayer of Soy Protein Isolate/Bamboo Shoot Protein Complexes

The complex of soy protein isolate (SPI)/bamboo shoot protein concentrate (BPC) was developed to stabilize camellia oil-in-water (O/W) emulsions. The surface hydrophobicity of the BPC/SPI complex driven by hydrogen bonds and electrostatic attractions was improved. With the increasing ratio of BPC in the complex, a tighter network layer structure of the complex was formed due to the rearrangement of proteins, and the emulsions showed a progressive enhancement in the gel-like structures. At the SPI/BPC ratio of 2:1, the emulsions had smaller droplet size and lower creaming index of 230 nm and 30%, and the emulsifying activity and stability indices of the emulsions were 803.72 min and 11.85 g/m², respectively, indicating a better emulsifying activity and stability of emulsions. Meanwhile, the emulsions stabilized by the complex at the ratio of 2:1 showed better storage and antioxidant stability. These findings are expected to develop the application of bamboo shoots in emulsion-based food products such as mayonnaise, salad dressings, and sauces.

Rheological and textural properties of acid-induced soybean protein isolate gel in the presence of soybean protein isolate hydrolysates or their glycosylated products

Enzymatic hydrolysis and glycosylation were successively applied to modify soybean protein isolate (SPI) and rheological and textural properties of acid-induced SPI gel added with the obtained SPI hydrolysates and their glycosylated products were then investigated. The incorporation of SPI hydrolysates decreased the elastic modulus (G') and hardness of SPI gel, which might be related to the random aggregation between SPI hydrolysates and native SPI molecules via hydrophobic interactions. In addition, as the molecular weight of SPI hydrolysates decreased, the reduction in G' and hardness became more significant. Although glycosylation of SPI hydrolysates weakened the adverse effects of hydrolysates on the SPI gel formation to some extent, the glycosylated SPI hydrolysates were still unable to improve the gel quality compared with the control. However, results of this research may provide important information for understanding the influencing mechanism of SPI hydrolysates and their glycosylated products on the formation of SPI gel.

Bacteria Single-Cell and Photosensitizer Interaction Revealed by Quantitative Phase Imaging

Quantifying changes in bacteria cells in the presence of antibacterial treatment is one of the main challenges facing contemporary medicine; it is a challenge that is relevant for tackling issues pertaining to bacterial biofilm formation that substantially decreases susceptibility to biocidal agents. Three-dimensional label-free imaging and quantitative analysis of bacteria-photosensitizer interactions, crucial for antimicrobial photodynamic therapy, is still limited due to the use of conventional imaging techniques. We present a new method for investigating the alterations in living cells and quantitatively analyzing the process of bacteria photodynamic inactivation. Digital holographic tomography (DHT) was used for in situ examination of the response of Escherichia coli and Staphylococcus aureus to the accumulation of the photosensitizers immobilized in the copolymer revealed by the changes in the 3D refractive index distributions of single cells. Obtained results were confirmed by confocal microscopy and statistical analysis. We demonstrated that DHT enables real-time characterization of the subcellular structures, the biophysical processes, and the induced local changes of the intracellular density in a label-free manner and at sub-micrometer spatial resolution.

Effect of temperature of preheated soy protein isolate on the structure and properties of soy protein isolate heated-vitamin D3 complex

In this paper, soy protein isolate (SPI) was preheated and combined with vitamin D₃ (VD₃ ) to study the protective effect of modified SPI on VD₃ . The structure and properties of the SPI with heat treatment-VD₃ (SPI(H)-VD₃ ) complex were determined. The secondary and tertiary structure of SPI(H)-VD₃ results showed that the content of α-helix decreased and the content of random coil increased, indicating that the rigid structure of the protein decreased, the flexibility increased, and the maximum fluorescence intensity wavelength was red shifted. When the heat treatment temperature was 85°C, the embedding rate of SPI(H)-VD₃ composite was the highest. As the heat treatment temperature increased, the internal hydrophobic groups of SPI were exposed, and the average particle size decreased significantly. The light stability results showed that the content of VD₃ in the SPI(H)-VD₃ composite at a heat treatment temperature of 85°C was significantly increased compared with the unheated SPI. PRACTICAL APPLICATIONS: This article mainly discusses the structure and properties of modified soy protein isolates bound to VD₃ by preheating soy protein isolates at different temperatures. It provides more possibilities for the application of VD₃ in food.

Soy Protein: Molecular Structure Revisited and Recent Advances in Processing Technologies

Rising health concerns and increasing obesity levels in human society have led some consumers to cut back on animal protein consumption and switch to plant-based proteins as an alternative. Soy protein is a versatile protein supplement and contains well-balanced amino acids, making it comparable to animal protein. With sufficient processing and modification, the quality of soy protein can be improved above that of animal-derived proteins, if desired. The modern food industry is undergoing a dynamic change, with advanced processing technologies that can produce a multitude of foods and ingredients with functional properties from soy proteins, providing consumers with a wide variety of foods. This review highlights recent progress in soy protein processing technologies. Using the current literature, the processing-induced structural changes in soy protein are also explored. Furthermore, the molecular structure of soy protein, particularly the crystal structures of β-conglycinin and glycinin, is comprehensively revisited.

Glycation of Plant Proteins Via Maillard Reaction: Reaction Chemistry, Technofunctional Properties, and Potential Food Application

Plant proteins are being considered to become the most important protein source of the future, and to do so, they must be able to replace the animal-derived proteins currently in use as techno-functional food ingredients. This poses challenges because plant proteins are oftentimes storage proteins with a high molecular weight and low water solubility. One promising approach to overcome these limitations is the glycation of plant proteins. The covalent bonding between the proteins and different carbohydrates created via the initial stage of the Maillard reaction can improve the techno-functional characteristics of these proteins without the involvement of potentially toxic chemicals. However, compared to studies with animal-derived proteins, glycation studies on plant proteins are currently still underrepresented in literature. This review provides an overview of the existing studies on the glycation of the major groups of plant proteins with different carbohydrates using different preparation methods. Emphasis is put on the reaction conditions used for glycation as well as the modifications to physicochemical properties and techno-functionality. Different applications of these glycated plant proteins in emulsions, foams, films, and encapsulation systems are introduced. Another focus lies on the reaction chemistry of the Maillard reaction and ways to harness it for controlled glycation and to limit the formation of undesired advanced glycation products. Finally, challenges related to the controlled glycation of plant proteins to improve their properties are discussed.

Fabrication and Characterization of a Microemulsion Stabilized by Integrated Phosvitin and Gallic Acid

The purpose of this work was to conjugate phosvitin (Pv) with gallic acid (GA) to explore a new emulsifier that had both good emulsifying properties and antioxidant activity. The Pv-GA complex was prepared at a GA concentration of 1.5 mg/mL with pH 9.0. The Pv-GA complex obtained was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and characterized with infrared, ultraviolet, and fluorescence spectra. The emulsifying activity and stability of the Pv-GA complex were slightly improved, and antioxidant activities was significantly enhanced. Furthermore, the Pv-GA complex was used to load conjugated linoleic acid (CLA) for microemulsion preparation. Results showed that the Pv-GA complex could increase the viscosity and lipid antioxidant capacity of Pv-GA/CLA microemulsion. The Pv-GA/CLA microemulsion had remarkable emulsifying activity, emulsifying stability, pH, and thermal stability and poor salt stability.

Analysis of the glycosylation products of peanut protein and lactose by cold plasma treatment: Solubility and structural characteristics

Cold plasma (CP) treatment was used to prepare the glycosylation conjugates of high-temperature peanut protein isolate (HPPI) and lactose to improve the solubility of HPPI. We observed that by increasing the CP treatment time to 3 min, the solubility of the conjugates increased to 1.34 mg/mL. An increase in the degree of glycosylation and a decrease in the degree of browning indicated that although CP treatment accelerated the glycosylation of HPPI and lactose, it interfered with the formation of melanoidin. The analysis of protein tertiary structure showed that tryptophan and tyrosine residues in proteins undergoing CP treatment were the primary sites for the Maillard reaction. The relative decrease in surface hydrophobicity and FT-IR analysis indicated that the increase in the -OH stretching vibration intensity on the protein surface represented the formation of the covalent bonds between HPPI and lactose during the CP treatment. An increase in the denaturation temperature of proteins was observed after grafting with lactose. Changes in the secondary structure and surface structure of proteins showed that lactose covalently bonded to the surface of HPPI during CP treatment, forming a more stable ordered structure.

Encapsulation of Lutein in Nanoemulsions Stabilized by Resveratrol and Maillard Conjugates

Lutein is incorporated into foods as a natural yellow pigment and nutraceutical. The introduction of lutein into many foods and beverages, however, is problematic because of its strong hydrophobicity and poor chemical stability. In this research, lutein-loaded nanoemulsions were prepared to overcome this problem. Casein-dextran Maillard conjugates or physical complexes were utilized as emulsifiers, while either medium chain triglycerides (MCT) or grape seed oil (GSO) were used as carrier oils. The impact of resveratrol addition on nanoemulsion stability was also examined. The influence of storage temperature, pH, and CaCl₂ concentration on the chemical and physical stability of the nanoemulsions was measured. The casein-dextran conjugates were highly effective at improving the physical resistance of the nanoemulsions to environmental stresses, but had a detrimental effect on their color stability. Conversely, nanoemulsions prepared from casein-dextran physical complexes were unstable around the protein's isoelectric point (pH 4.6), as well as upon addition of CaCl₂ . Incorporation of resveratrol and GSO into the nanoemulsions decreased lutein degradation and color fading at all temperatures. This study shows that casein-dextran conjugates are highly effective at improving the physical stability of lutein-loaded nanoemulsions, while resveratrol and GSO are effective at improving their chemical stability. PRACTICAL APPLICATION: Lutein can be used by the food industry to create "clean label" and functional food products. The major challenges in incorporating lutein in foods are its poor chemical stability and its high hydrophobicity, which makes it difficult to incorporate. Emulsion-based delivery systems assembled from natural ingredients may address these challenges. In this study, the impact of Maillard conjugates fabricated from caseinate and dextran, as well as resveratrol addition, on the formation and stability of lutein-enriched nanoemulsions was determined. The information obtained from this study will help the formulation of more effective functional foods and beverage products.

Relationship between Molecular Flexibility and Emulsifying Properties of Soy Protein Isolate-Glucose Conjugates

At present, the structure-activity relationships of soy protein isolate are still not well understood. In this paper, the relationship between molecular flexibility and emulsifying properties of soy protein isolate and soy protein isolate-glucose conjugates were investigated. The Maillard reaction was carried out at different temperature conditions (50 °C, 60 °C, 70 °C, 80 °C, and 90 °C) under a specific wet condition. Meanwhile, structural properties including surface hydrophobicity ( H₀), molecular flexibility and secondary, tertiary, quaternary structures, and the free sulfhydryl group ( -SH) content were measured. The results showed that there was a good correlation between molecular flexibility and emulsifying properties, and the correlation coefficients was 0.920 ( P < 0.01) for emulsifying activity and 0.952 ( P < 0.01) for emulsion stability. Compared with soy protein isolate, the H₀ of samples at different temperatures first increased and then decreased reaching a maximum at 70 °C, a red shift occurred during the whole given reaction conditions shown by the intrinsic fluorescence spectrum, and the free sulfhydryl content also displayed a marked increase ( P < 0.05). At the same time, the particle size gradually became smaller as the degree of grafting increased. The contents of β-turn and random coil increased at the cost of α-helix and β-sheet contents, as evidenced by Fourier transform infrared results. The findings could provide a deep insight into the structure-function relationship of soy protein isolate-glucose conjugates, thus providing theoretical guidance for further research of soy proteins.

Eco-Innovation in Reusing Food By-Products: Separation of Ovalbumin from Salted Egg White Using Aqueous Two-Phase System of PEG 1000/(NH₄)₂SO₄

For the purpose of reducing pollution and the rational use of salted egg white, which is a byproduct of the manufacturing process of salted egg yolk, an aqueous two-phase system (ATPS) composed of polyethylene glycols (PEG 1000) and (NH₄)₂SO₄ was investigated to selectively separate ovalbumin (OVA) from salted egg white. With the aim of optimizing the selective separation of OVA using ATPS, a response surface method (RSM) experiment was carried out on the basis of a single-factor experiment. The OVA was characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS⁻PAGE), reversed-phase high-performance liquid chromatography (RP-HPLC), liquid chromatography-nano electrospray ionization mass spectrometry (Nano LC-ESI-MS/MS), and Fourier transform infrared spectroscopy (FT-IR). Under the optimal conditions, the recovery yield of OVA through ATPS (Y) and the purity of OVA (P) could reach 89.25% and 96.28%, respectively. In conclusion, OVA was successfully separated from the salted egg white by PEG/(NH₄)₂SO₄ ATPS.