Transglutaminase-induced cross-linking and glucosamine conjugation of casein and some functional properties of the modified product

Fabrication and characterization of novel TGase-mediated glycosylated whey protein isolate nanoparticles for curcumin delivery

The aim of this study was to fabricate novel transglutaminase (TGase)-mediated glycosylated whey protein isolate (WPI) nanoparticles for the encapsulation and delivery of curcumin. The influences of glycosylation on the physiochemical properties, stability, bioavailability, and antioxidant properties of WPI nanoparticles loaded with curcumin were investigated. Composite nanoparticles exhibited uniform distribution and small particle sizes. The main driving forces for the formation of curcumin nanoparticles were electrostatic interactions, hydrogen bonding, and hydrophobic interactions. The encapsulation and loading efficiency of curcumin after TGase-type glycosylation were significantly increased in comparison to WPI-curcumin nanoparticles. Glycosylated WPI-curcumin nanoparticles had stronger antioxidant properties and stability to resist external environmental changes than WPI-curcumin nanoparticles. In addition, glycosylated WPI-curcumin nanoparticles showed a controlled release and enhanced curcumin bioavailability in vitro gastrointestinal digestion. This study provides novel insights for self-assembled glycosylated protein nanoparticles as delivery systems for protecting hydrophobic nutrients.

Progress in Protein-Based Hydrogels for Flexible Sensors: Insights from Casein

In recent years, the rapid advancement of flexible sensors as the cornerstone of flexible electronics has propelled a flourishing evolution within the realm of flexible electronics. Unlike traditional flexible devices, hydrogel flexible sensors have characteristic advantages such as biocompatibility, adhesion, and adjustable mechanical properties and have similar properties to human skin. Especially, biobased hydrogels have become the preferred substrate material for flexible sensors due to increased environmental pressures caused by the scarcity of petrochemical resources. In this regard, proteins possess advantages such as diverse amino acid compositions, adjustable advanced structures, chemical modifiability, the application of protein engineering techniques, and the ability to respond to various external stimuli. These enable the hydrogels constructed from them to have greater designability, flexibility, and adaptability. As a result, their applications in manufacturing various types of sensors have experienced rapid growth. This work systematically reviews the sensing mechanism of protein-based hydrogels, focusing on the preparation of protein-based hydrogels and the optimization of flexible sensors mainly from the perspective of a typical type of animal-derived protein casein. In addition, while the potential of casein is recognized, the limitations of casein-based hydrogels in flexible sensor applications are explored, and insights are provided into the development trends of next-generation sensors based on casein-based hydrogel materials.

In vitro digestion and functional properties of bovine β-casein: A comparison between adults and infants

Gastrointestinal digestibility behavior, structural and functional characteristics of bovine β-casein (β-CN) were studied in vitro under infant and adult conditions. This direct comparison helps reveal the effects of different physiological stages on the digestive behavior of β-CN. Not only was the degree of hydrolysis (DH) of β-CN analyzed, but also the changes in its digestive morphology, microstructure, and secondary structure during digestion were explored in depth. Meanwhile, we focused on the physicochemical properties of β-CN digesta, including solubility, emulsifying and foaming properties, as well as their functional properties, such as antimicrobial and antioxidant activities. Key results showed that β-CN underwent more extensive hydrolysis in the adult digestion model, with approximately twice the DH compared to the infant model. The adult model exhibited faster digestion kinetics, less protein flocculation, and a more loosened secondary structure, indicating a more efficient digestion process. Notably, the digesta from the adult model displayed significantly improved solubility and emulsifying properties, and also enhanced antioxidant capacities, with significantly better inhibition of two common pathogenic bacteria than the infant model, and an average increase in the diameter of the inhibition zone of approximately 2 mm. These findings underscore the differential digestive behavior and functional potential of β-CN across physiological stages. This comprehensive assessment approach contributes to a more comprehensive insight into the digestive behavior of β-CN. Therefore, we conclude that producing products from unmodified β-CN may be more suitable for the adult population, and that the digesta in the adult model exhibit higher functional properties.

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.

Food protein glycation: A review focusing on stability and in vitro digestive characteristics of oil/water emulsions

Recently, increasing studies have shown that the functional properties of proteins, including emulsifying properties, antioxidant properties, solubility, and thermal stability, can be improved through glycation reaction under controlled reaction conditions. The use of glycated proteins to stabilize hydrophobic active substances and to explore the gastrointestinal fate of the stabilized hydrophobic substances has also become the hot spot. Therefore, in this review, the effects of glycation on the structure and function of food proteins and the physical stability and oxidative stability of protein-stabilized oil/water emulsions were comprehensively summarized and discussed. Also, this review sheds lights on the in vitro digestion characteristics and edible safety of emulsion stabilized by glycated protein. It can further serve as a research basis for understanding the role of structural features in the emulsification and stabilization of glycated proteins, as well as their utilization as emulsifiers in the food industry.

Changes in the functional properties of casein conjugates prepared by Maillard reaction with pectin or arabinogalactan

The aim of this study was to prepare conjugates of casein (CA) with pectin (CP) or arabinogalactan (AG) by the Maillard reaction (wet-heating) and to investigate the effects of CP or AG on the structural and functional properties of casein. The results indicated that the highest grafting degree of CA with CP or AG was observed at 90 °C for 1.5 h or 1 h, respectively. Secondary structure showed that grafting with CP or AG reduced the α-helix level and increased the random coil level of CA. Glycosylation treatment of CA-CP and CA-AG exhibited lower surface hydrophobicity and higher absolute ζ-potential values, further significantly improving the functional properties of CA (e.g., solubility, foaming property, emulsifying property, thermal stability, and antioxidant activity). Accordingly, our results indicated that it is feasible for CP or AG to improve the functional properties of CA by the Maillard reaction.

Functional and physiochemical properties of the yoghurt modified by heat lactosylation and microbial transglutaminase cross-linking of milk proteins

This study aimed to recognize the effect of Maillard reaction (MR) on the functional properties of milk proteins and the physiochemical, textural, and sensory properties of yoghurt. Heating at 100°C for 2 h increased the carbohydrate ratio in caseins, whey proteins, and total milk proteins from 2.83%, 1.93%, and 1.8% to 4.15%, 3.58%, and 5.32%, respectively. Solubility of the lactosylated caseins, whey proteins, and total milk proteins is increased at low pH values compared to that of the control caseins, whey proteins, and total milk proteins. Lactosylation at 70 and 100°C increased the emulsion activity index (EAI) of caseins at all pH values, especially at pH below 6, and this increment was higher for casein samples treated at 100°C. Foam volume of whey proteins and total milk proteins also increased for samples lactosylated at 100°C compared to control samples. The combination of heating and microbial transglutaminase (MTGase) had a synergistic and enhancing effect on the pH values of yoghurt samples, especially in yoghurt samples produced by whole milk protein compared to control samples. Viscosity and hardness of yoghurt samples were enhanced by heat lactosylation, MTGase treatment, and also storage for 21 days at 7 ± 1°C.

Walnut Protein Isolate-κ-Carrageenan Composite Gels Improved with Synergetic Ultrasound-Transglutaminase: Gelation Properties and Structure

Walnut protein is a kind of natural, high-quality plant protein resource. However, its high content of gluten, strong hydrophobicity and poor gelation ability have greatly limited its development and utilization in gel products. It was found in this experiment that ultrasonic power combined with transglutaminase (TGase) had a significant effect on the gel properties of the walnut protein isolate (WNPI)-κ-carrageenan (KC) complex. The results showed that the gel strength of the WNPI-KC complex first increased and then decreased with the increase in ultrasonic power (0-400 W). WNPI-KC composite gel had the best texture properties, rheological properties, water-holding capacity (99.41 ± 0.76%), swelling ratio (2.31 ± 0.29%) and thermal stability (83.22 °C) following 200 W ultrasonic pretreatment. At this time, the gel network was more uniform and much denser, and the water molecules were more tightly bound. Further, 200 W ultrasonic pretreatment could promote the transformation of α-helices to β-folds in protein molecules, improve the fluorescence intensity, increase the content of free sulfhydryl groups and enhance the intermolecular forces. The experimental results could provide technical support for the development of walnut protein gel food.

Micronization using combined alkaline protease hydrolysis and high-speed shearing homogenization for improving the functional properties of soy protein isolates

The present study aimed to investigate the functional properties of soybean protein isolate (SPI) treated with alkaline protease and high-speed shearing homogenization. Alkaline protease-hydrolyzed SPIs that were characterized by varying degrees of hydrolysis between 0 and 6% were treated with high-speed shearing homogenization to obtain different micro-particulate proteins. The results showed that this combined treatment could significantly reduce the particle size of SPI by markedly degrading the structure of both the 7S and 11S subunits, thereby resulting in a significantly reduced content of β-sheet and β-turn structures. The surface hydrophobicity increased considerably for samples with hydrolysis below the threshold of 2% and then declined gradually above this threshold. Furthermore, the combination of hydrolysis and homogenization significantly improved the emulsion stability of SPI hydrolysates. It also significantly improved the foaming properties of SPI. These results demonstrated that alkaline protease hydrolysis combined with high-speed shearing homogenization represents a promising approach for improving the functional and structural properties of SPI.

Effects of ultrasound synergized with microwave on structure and functional properties of transglutaminase-crosslinked whey protein isolate

In the present study, ultrasound (400 W, U), microwave heating (75 ℃ for 15 min, M) and ultrasound synergized with microwave heating (UM) pretreatments of whey protein isolate (WPI) were applied to investigate and compare their influence on structure, physicochemical and functional characteristic of transglutaminase (TGase)-induced WPI. From the results of size exclusion chromatography, it could be seen that all three physical pretreatments could promote the formation of polymers in TGase cross-linked WPI, whose polymer amounts were increased by the order of U, UM and M pretreatment. Among three physical methods, M pretreatment had the strongest effect on structure and functional characteristics of TGase-induced WPI. Furthermore, compared with TGase-induced WPI, α-helix and β-turn of M-treated TGase-induced WPI (M-WPI-TGase) were reduced by 7.86% and 2.93%, whereas its β-sheet and irregular curl were increased by 15.37% and 7.23%. Zeta potential, emulsion stability and foaming stability of M-WPI-TGase were increased by 7.8%, 59.27% and 28.95%, respectively. This experiment exhibited that M was a more effective pretreatment method than U, UM for WPI, which could promote its reaction with TGase and improve its functional properties.

Sources, chemical synthesis, functional improvement and applications of food-derived protein/peptide-saccharide covalent conjugates: a review

Proteins/peptides and saccharides are two kinds of bioactive substances in nature. Recently, increasing attention has been paid in understanding and utilizing covalent interactions between proteins/peptides and saccharides. The products obtained through covalent conjugation of proteins/peptides to saccharides are shown to have enhanced functional attributes, such as better gelling property, thermostability, and water-holding capacity. Additionally, food-derived protein/peptide-saccharide covalent conjugates (PSCCs) also have biological activities, such as antibacterial, antidiabetic, anti-osteoporosis, anti-inflammatory, anti-cancer, immune regulatory, and other activities that are widely used in the functional food industry. Moreover, PSCCs can be used as packaging or delivery materials to improve the bioavailability of bioactive substances, which expands the development of food-derived protein and saccharide resources. Thus, this review was aimed to first summarize the current status of sources, classification structures of natural PSCCs. Second, the methods of chemical synthesis, reaction conditions, characterization and reagent formulations that improve the desired functional characteristics of food-derived PSCCs were introduced. Third, functional properties such as emulsion, edible films/coatings, and delivery of active substance, bio-activities such as antioxidant, anti-osteoporosis, antidiabetic, antimicrobial of food-derived PSCCs were extensively discussed.

Transglutaminase-Mediated Caseinate Oligochitosan Glycation Enhances the Effect of Caseinate Hydrolysate to Ameliorate the LPS-Induced Damage on the Intestinal Barrier Function in IEC-6 Cells

Some food components can regulate the intestinal barrier function. Herein, the effect of transglutaminase-type oligochitosan glycation on caseinate hydrolysate for its ability to maintain intestinal epithelial integrity and the tight junction (TJ) structure was investigated by assessing and comparing the bioactivities of glycated caseinate hydrolysate and caseinate hydrolysate against the lipopolysaccharide-induced barrier damage in the model cells (rat intestinal epithelial IEC-6 cells). The results from liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis demonstrated that oligochitosan glycation occurred at the Gln residues of α-S1-casein and α-S2-casein. The two hydrolysates retarded the lipopolysaccharide cytotoxicity toward IEC-6 cells and enhanced the barrier integrity by increasing the transepithelial electrical resistance or decreasing the paracellular permeability. In addition, these two hydrolysates could upregulate both mRNA and protein expression of three TJ proteins in IEC-6 cells. More importantly, the glycated caseinate hydrolysate had higher potential than caseinate hydrolysate to protect IEC-6 cells against the lipopolysaccharide-induced barrier damage, suggesting that the transglutaminase-mediated oligochitosan glycation of proteins is a useful approach to enforce protein biofunctions in the intestine.

Green synthesis of glyco-phenol by enzymatic coupling between ferulic acid and glucosamine: An ecofriendly procedure

A new glyco-phenol was produced by the coupling between glucosamine (Glu) and ferulic acid (FA) using Myceliophthora thermophila laccase as biocatalyst in mild conditions (distilled water and 30°C) as an environmentally friendly process. Results indicated that the enzymatic reaction created a new derivative (FA-Glu), produced from coupling between Glu and FA by covalent bonds. By the high production of (FA-Glu) derivative and its stability, the optimal ratio of (FA:Glu) was of (1:1) at optimal time reaction of 6 h. Under these optimal conditions, almost 55% of -NH₂ groups on Glu were bound with FA oxidation products. The new derivative showed higher hydrophobic character than Glu due to the presence of FA in its structure. Liquid chromatography-mass spectrometry analysis showed that (FA-Glu) derivative exhibited a molecular mass at MM 713 g/mol containing one Glu molecule and three FA molecules after decarboxylation. Furthermore, the new derivative presented good antioxidant and antiproliferative activities in comparison with Glu and FA. These results suggest that the enzymatic conjugation between Glu and FA is a promising process to produce a new glyco-phenol having good functional properties for potential applications.

The non-covalent interaction between two polyphenols and caseinate as affected by two types of enzymatic protein crosslinking

Caseinate was crosslinked by horseradish peroxidase (HRP) or microbial transglutaminase (TGase) and mixed with kaempferol and quercetin at 293-313 K (i.e. 20-40 °C), respectively. Generally, these two polyphenols dose-dependently induced fluorescent quenching in caseinate or its crosslinked products via a static mechanism, while enzymatic crosslinking endowed caseinate with higher affinity for the polyphenols with increased apparent binding constants [(9.94-168.77) × 10⁵versus (4.92-6.53) × 10⁵ L/mol], unchanged binding site number and slightly shortened binding distance. To form protein-polyphenol complexes, hydrophobic force was the main driving force for the HRP-crosslinked caseinate and unreacted caseinate, while hydrogen-bonds and van der Waals force were the main driving forces for the TGase-crosslinked caseinate. Overall, quercetin was more potent than kaempferol to bind to the proteins, while TGase-mediated caseinate crosslinking induced the highest affinity to the polyphenols with the largest ΔG decrease. Thus, two types of crosslinking impacted the driving forces, apparent binding constant and thermodynamic indices of caseinate-polyphenol interaction.

Limited hydrolysis and conjugation of zein with chitosan oligosaccharide by enzymatic reaction to improve functional properties

In order to improve its aqueous solubility and emulsifying function, zein was partially hydrolyzed by trypsin and conjugated to chitosan oligosaccharide lactate by transglutaminase. Hydrolysis and covalent linkage to chitosan oligosaccharide was confirmed by free amine content, gel electrophoresis, and infrared spectroscopy. Enzymatic glycosylation was optimized at pH 6, 44 °C, and 4 h to bind approximately 95% of the free amines in the hydrolysates to chitosan oligosaccharide. Hydrolysis and conjugation increased solubility of zein by 47.60% and 72.93%. Hydrolysis and conjugation also decreased surface hydrophobicity by more than 20% and more than doubled emulsifying activity index, emulsion stability index, and foaming capacity. This enzymatic modification has potential to be applied to improve functional properties of other prolamins.

Acid-Induced Gelation of Enzymatically and Nonenzymatically Cross-Linked Caseins-Texture Properties, and Microstructural Insights

Casein gels consist of a fractal organized network of aggregated casein particles. The gel texture thereby depends on the structure, the spatial distribution, and the interaction forces of the network's elementary building blocks. The aim of this study was to explore the technofunctional consequences of a possible specificity of Maillard reaction-induced cross-linking reactions on casein with respect to texture and microstructure of acid gels. Therefore, sodium caseinate glycated with lactose in the dry state (60 °C, a_w 0.5) was compared with casein samples cross-linked with methylglyoxal, with glutaraldehyde, or via microbial transglutaminase, respectively, at similar levels of protein cross-linking as confirmed by size-exclusion chromatography under denaturing conditions. Casein gels prepared by acidification with glucono-δ-lactone were characterized concerning pH kinetics during gelation, mechanical texture properties under large deformation, and water-holding capacity, while viscometric properties of casein suspensions were obtained prior to gelation. The gel microstructure was captured by confocal laser scanning microscopy and evaluated by means of image texture analysis. All protein cross-linking reactions studied led to an enhanced gel strength which was accompanied by an increased interconnectivity of the gel network and a decrease in apparent pore sizes. Gels with more densely packed strands, as was the case for enzymatically modified casein, exhibited pronounced mechanical stability. The spontaneous destabilization of the gel network upon prolonged glycation reactions, which was not obviously displayed by microstructural features but connected to an increased viscosity and pronounced pseudoplastic flow of the unacidified suspension, suggests a limitation of particle rearrangements and the weakening of interparticle protein-protein interactions by additional structure attributes formed during the early Maillard reaction (glycoconjugation).

Property changes of caseinate in response to its dityrosine formation induced by horseradish peroxidase, glucose oxidase and d-glucose

BACKGROUND

A ternary system containing horseradish peroxidase (HRP), glucose oxidase and d-glucose using one- or two-step treatment was evidently able to cross-link proteins via dityrosine formation and thus was assessed for its possible impact on several properties of a protein ingredient caseinate.

RESULTS

HRP, glucose oxidase and d-glucose were used at 200 U, 6 U and 0.05 mmol g^-1 protein to treat caseinate by one- and two-step methods, producing two cross-linked caseinates named CLCN-I and CLCN-II, respectively. In response to the conducted cross-linking, both CLCN-I and CLCN-II gained slightly reduced dispersibility at pH 5-10, enlarged hydrodynamic radius (particle size distribution, 266.37 and 258.33 versus 226.67 nm) and negative zeta-potential (-26.60 and -22.27 versus -14.30 mV) in dispersions, increased water-binding (3.70 and 3.09 versus 2.68 kg kg^-1 protein), decreased oil-binding (1.75 and 2.74 versus 2.87 kg kg^-1 protein) and emulsifying activity (76.2 and 82.3 versus 94.3 m² g^-1 protein), increased emulsion stability (84.3% and 82.5% versus 78.6%), and enhanced thermal stability with lower mass loss (58.5% and 59.6% versus 64.3%) or higher decomposition temperatures (331.2 °C and 328.7 °C versus 327.6 °C) upon heating at 105-450 °C. In addition, CLCN-I and CLCN-II had decreased gelling temperatures and shortened gelling times when forming acid-induced gels, and the gels were endowed with increased values in four textural indices and finer microstructure. Moreover, CLCN-I with a higher cross-linking extent showed greater property changes than CLCN-II.

CONCLUSION

This ternary system could be used in caseinate cross-linking to improve properties such as aggregation, emulsification, gelation and thermal stability. © 2020 Society of Chemical Industry.

Influence of Microbial Transglutaminase on Physicochemical and Cross-Linking Characteristics of Individual Caseins

The effects of microbial transglutaminase (MTGase) cross-linking on the physicochemical characteristics of individual caseins were investigated. MTGase was used to modify three major individual caseins, namely, κ-casein (κ-CN), α_S-casein (α_S-CN) and β-casein (β-CN). The SDS-PAGE analysis revealed that MTGase-induced cross-linking occurred during the reaction and that some components with high molecular weights (>130 kDa) were formed from the individual proteins κ-CN, α_S-CN and β-CN. Scanning electron microscopy (SEM) and particle size analysis respectively demonstrated that the κ-CN, α_S-CN and β-CN particle diameters and protein microstructures were larger and polymerized after MTGase cross-linking. The polymerized κ-CN (~749.9 nm) was smaller than that of β-CN (~7909.3 nm) and α_S-CN (~7909.3 nm). The enzyme kinetics results showed K_M values of 3.04 × 10⁻⁶, 2.37 × 10⁻⁴ and 8.90 × 10⁻³ M for κ-CN, α_S-CN and β-CN, respectively, and, furthermore, k_cat values of 5.17 × 10⁻⁴, 1.92 × 10⁻³ and 4.76 × 10⁻² 1/s, for κ-CN, α_S-CN and β-CN, respectively. Our results revealed that the cross-linking of β-CN catalyzed by MTGase was faster than that of α_S-CN or κ-CN. Overall, the polymers that formed in the individual caseins in the presence of MTGase presented a higher molecular weight and larger particles.

Preparation and Evaluation of New Glycopeptides Obtained by Proteolysis from Corn Gluten Meal Followed by Transglutaminase-Induced Glycosylation with Glucosamine

New glycopeptides were generated by proteolysis from corn gluten meal (CGM) followed by transglutaminase (TGase)-induced glycosylation with glucosamine (GlcN). The glycopeptides exhibited desirable antioxidant and intracellular ROS-scavenging properties. The amount of conjugated GlcN quantified by high-performance liquid chromatography (HPLC) was 23.0 g/kg protein. The formed glycopeptides contained both glycosylated and glycation types, as demonstrated by the electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS/MS). The glycopeptides exhibited scavenging capabilities against free radical diphenylpicrylhydrazyl (DPPH) and hydroxyl radicals by reducing their power. The potential protection of glycopeptides against ethanol-induced injury in LO2 cells was assessed In Vitro based on methyl thiazole tetrazolium (MTT) testing and intracellular reactive oxygen species (ROS) scavenging capacity, respectively. Glycopeptide cytoprotection was expressed in a dose-dependent manner, with the glycopeptides exhibiting good solubility ranging from 74.8% to 83.2% throughout a pH range of 2-10. Correspondingly, the glycopeptides showed good emulsifying activity (36.0 m2/g protein), emulsion stability (74.9%), and low surface hydrophobicity (16.3). These results indicate that glycosylation of CGM significantly improved its biological and functional properties. Glycopeptides from CGM could be used as potential antioxidants as well as comprising a functional food ingredient.

Functional and biological properties of Maillard conjugates and their potential application in medical and food: A review

Protein and peptides are usually sensitive to environmental stresses, such as pH changes, high temperature, ionic strength, and digestive enzymes amongst other, which limit their food and medicinal applications. Maillard reaction (also called Maillard conjugation or glycation) occurs naturally without the addition of chemical agents and has been vastly applied to boost protein/peptide/amino acid functionalities and biological properties. Protein/peptide-saccharide conjugates are currently used as emulsifiers, antioxidants, antimicrobials, gelling agents, and anti-browning compounds in food model systems and products. The conjugates also possess the excellent stabilizing ability as a potent delivery system to enhance the stability and bioaccessibility of many bioactive compounds. Carbonyl scavengers such as polyphenols are able to significantly inhibit the formation of advanced glycation end products without a significant effect on early Maillard reaction products (MRPs) and melanoidins, which are currently applied as functional ingredients. This review paper highlights the technological functionality and biological properties of glycoconjugates in food model systems and products. Recent applications of MRPs in medical sciences are also presented.

Characterization of transglutaminase from Bacillus subtilis and its cross-linking function with a bovine serum albumin model

Finding new crosslinking enzymes for enzyme-mediated protein conjugation is a great need in the food industry. In this research, the properties of Bacillus subtilis transglutaminase (BTG) were characterized in detail and its protein crosslinking functions with bovine serum albumin (BSA) as a model were studied. Compared to the commercial transglutaminase from Streptoverticillium mobaraense, BTG was more stable in a broad range of temperatures (30-60 °C) and pH values (pH 5.0-9.0), with its maximum enzymatic activity at 60 °C and pH 8.0. The protein function evaluation results demonstrated that the BTG-modified BSA showed better emulsifying and foaming properties (p < 0.05) compared with the native one. Additionally, significant improvements (p < 0.05) were observed in the rheological properties, water holding capacity, and textural properties of the BTG-treated BSA gels. With good thermal and pH stability and excellent crosslinking effects, BTG would be a potential enzyme for food structure engineering to improve the functional properties of food proteins and expand their applications.

Effect of caseinate glycation with oligochitosan and transglutaminase on the intestinal barrier function of the tryptic caseinate digest in IEC-6 cells

The oligochitosan-glycated caseinate digest has higher activity than the caseinate digest to strengthen the intestinal barrier function of IEC-6 cells.

Impacts of glycation and transglutaminase-catalyzed glycosylation with glucosamine on the conformational structure and allergenicity of bovine β-lactoglobulin

β-Lactoglobulin (β-LG) is recognized as the major milk allergen. In this study, the effects of transglutaminase (TGase) and glucosamine (GlcN)-catalyzed glycosylation and glycation on the conformational structure and allergenicity of β-LG were investigated. The formations of cross-linked peptides were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and GlcN-conjugated modification was identified using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Structural analysis revealed that glycosylation and glycation of β-LG induced unfolding of the primary protein structure followed by a loss of the secondary structure. As revealed by circular dichroism (CD) spectroscopy, glycosylated β-LG exhibited the highest increase in the β-sheets from 32.6% to 40.4% (25 °C) and 44.2% (37 °C), and the percentage of α-helices decreased from 17.7% to 14.4% (25 °C) and 12.3% (37 °C), respectively. The tertiary and quaternary structures of β-LG also changed significantly during glycosylation and glycation, along with reduced free amino groups and variation in surface hydrophobicity. Immunoblotting and indirect enzyme-linked immuno sorbent assay (ELISA) analyses demonstrated that the lowest IgG- and IgE-binding capacities of β-LG were obtained following glycosylation at 37 °C, which were 52.7% and 56.3% lower than that of the native protein, respectively. The reduction in the antigenicity and potential allergenicity of glycosylated β-LG was more pronounced compared to TGase treated- and glycated β-LG, which correlated well with the structural changes. These results suggest that TGase-catalyzed glycosylation has more potential compared to glycation for mitigating the allergenic potential of milk products.

Combined Use of Trisodium Citrate and Transglutaminase to Enhance the Stiffness and Water-Holding Capacity of Acidified Yak Milk Gels

In this research, the synergistic effect of trisodium citrate (TSC) and microbial transglutaminase (TGase) treatment on the textural properties of acidified yak skim milk gels was investigated. TSC was added to yak skim milk to concentrations of 0, 20, and 40 mmol/L, followed by adjusting the pH to 6.7. The samples were incubated with TGase for the cross-linking reaction, after which the samples were acidified with 1.4% (w/v) gluconodelta-lactone (GDL) at 42°C for 4 h to form gels. The stiffness and water holding capacity (WHC) of gels exhibited higher values at 20 or 40 mmol/L than without TSC. The final storage modulus (G′) of yak milk gels was positively related to the concentration of TSC prior to TGase treatment. Cryoscanning electron microscopy observations showed that the gel networks were more rigid with higher TSC concentrations. Overall, TSC dissociated particles in yak milk into smaller ones. The newly formed particles in yak skim milk could form acid-induced gels with greater stiffness and higher WHC in the presence of TGase.

Transglutaminase Applications in Dairy Technology

Consumers' expectations from a dairy product have changed dramatically during the last two decades. People are now more eager to purchase more nutritious dairy foods with improved sensory characteristics. Dairy industry has made many efforts to meet such expectations and numerious production strategies and alternatives have been developed over the years including non-thermal processing, membrane applications, enzymatic modifications of milk components, and so on. Among these novel approaches, transglutaminase (TG)-mediated modifications of milk proteins have become fairly popular and such modifications in dairy proteins offer many advantages to the dairy industry. Since late 1980s, a great number of researches have been done on TG applications in milk and dairy products. Especially, milk proteins-based edible films and gels from milk treated with TG have found many application fields at industrial level. This chapter reviews the characteristics of microbial-origin TG as well as its mode of action and recent developments in TG applications in dairy technology.

Transglutaminase-set colloidal properties of wheat gluten with ultrasound pretreatments

The low solubility of wheat gluten limits its accessibility. This work aimed to study the impact of ultrasonic pretreatments on the gelation of wheat gluten. The pretreatments included ultrasound combined with alkali, urea, Na₂SO₃, with or without the addition of transglutaminase (TGase). The gel strength of wheat gluten was 287g/cm² after treatment with Na₂SO₃/ultrasound/TGase. The free sulfhydryl and disulfide bond content was significantly affected by ultrasound treatment. After treatments including TGase crosslinking, the molecular weight of wheat gluten complexes became larger. The network formed by the wheat gluten was transformed into a dense and homogenous structure after the pretreatment with Na₂SO₃/ultrasound/TGase. The content of random coil of wheat gluten increased. The gelation of wheat gluten could also be significantly enhanced by Na₂SO₃/ultrasound treatment followed by TGase treatment. Using physical and chemical pretreatments to allow TGase to enhance the gelation of wheat gluten may increase its uses as a food additive.

Caseinate-gelatin and caseinate-hydrolyzed gelatin composites formed via transglutaminase: chemical and functional properties

BACKGROUND

Treatment of food proteins by enzymatic crosslinking and other reactions can confer modified properties on the treated proteins. Bovine gelatin and hydrolyzed bovine gelatin were used to generate two caseinate-based composites via transglutaminase, and potential useful properties to food processing were investigated for both composites.

RESULTS

Caseinate-gelatin and caseinate-hydrolyzed gelatin composites contained 33.4 and 10.3 g kg(-1) protein of 4-hydroxyproline, respectively. Caseinate conjugation with gelatin and hydrolyzed gelatin resulted in two composites with stronger absorption at five wavenumbers during Fourier transform-infrared analysis, demonstrating that they were rich in hydroxyl and carboxyl groups. Both composites exhibited higher viscosity values in aqueous dispersions, lower thermal stability (i.e. higher mass loss) during thermogravimetric analysis and worse emulsifying properties than original caseinate, owing to conjugation and crosslinking via transglutaminase. However, confocal laser scanning microscopy (CLSM) analysis revealed that both composites actually had better emulsion stability after 2 weeks of storage.

CONCLUSION

The composites generated were different in chemical characteristics and better in viscosity and emulsion stability than original caseinate. They might have potential as protein thickeners and emulsifiers. CLSM is a better technique to assess emulsion stability of food proteins than the classic turbidity method.