Transglutaminase Cross-linking Research Articles

Microstructural, physicochemical properties, and interaction mechanism of hydrogel nanoparticles modified by high catalytic activity transglutaminase crosslinking

Natural protein hydrogels are commonly used in the food industry due to their versatility, making it crucial to develop hydrogels with superior properties. In this study hydrogel nanoparticles were modified with high-performance transglutaminase obtained by cavity engineering strategy. The optimal mutant, R57L/Y198F/F259W, exhibited a 3.3-fold increases (up to 103.26 U mg−1) in catalytic activity and a 3.3 °C increased in TmE value, resulting in a hydrogel with higher hardness, springiness, cohesiveness, and resilience. The hydrophilic capacity of the hydrogel, such as water holding capacity, swelling rate, and freeze-thaw stability (240 h), were also enhanced by 3.00%, 24.56%, and 9.00%, respectively. Fourier transform infrared spectroscopy (FTIR) analysis indicated a 10.76% increase in α-helix and 9.69% increase in β-sheet contents, which led to improved thermostability and textural properties. Scanning electron microscope (SEM) revealed that the structure of modified hydrogel nanoparticles had a denser, mostly polygonal honeycomb structure. Molecular dynamics (MD) simulations indicated that the mutation altered the secondary structure of C64 from a helix to a loop, which improved catalytic activity, resulting in the formation of more cross-linked structures. The W259 residue was found to play a crucial role in stabilizing the complexes. These findings provide valuable insight for the application of protein-based hydrogels in the food industry.

Effect of transglutaminase crosslinking on the protein structure and potential allergenicity of dual-protein system, with a focus on β-conglycinin

Transglutaminase (TGase)-mediated crosslinking serves as a promising strategy to mitigate soy antigenicity. β-Conglycinin is recognized as a key allergen among soy proteins. Nonetheless, our understanding of the underlying relationship between immunoreactivity and protein structure remains inadequate. This study aimed to examine the impact of TGase-mediated crosslinking on the immunoreactivity of β-conglycinin in a dual-protein system consisting of soy protein isolate (SPI) and whey protein isolate (WPI) (with SPI-WPI ratios of 10:0, 7:3, 5:5, 3:7 (w/w)). Conformational changes were also examined. Results revealed that β-lactoglobulin and α-lactalbumin in WPI were less susceptible to TGase crosslinking compared to the 7S and 11S subunits in SPI. The conformation of proteins in the dual-protein system after TGase crosslinking were altered, as demonstrated by increased ultraviolet absorption intensity, fluctuant intrinsic fluorescence intensity and surface hydrophobicity, and decreased free sulfhydryl content. As the crosslinking time of TGase increased from 1 h to 18 h, the allergenicity of β-conglycinin gradually decreased in all four SPI-WPI ratios. Notably, the SPI3-WPI7 ratio exhibited the lowest allergenicity of 77.21 ± 1.89% after 18 h of TGase catalyzation. Overall, the dual-protein system proved to be more effective in reducing the allergenicity of β-conglycinin.

Investigating the physicochemical properties and air-water interface adsorption behavior of transglutaminase-crosslinking rapeseed protein isolate

Improving the technical functionality to adapt to the application of complex food systems is an important challenge for the development of plant protein ingredients. Herein, the correlation between the physicochemical properties and interfacial adsorption behavior of rapeseed protein isolate (RPI) at the air–water interface after transglutaminase (TG) treatment was investigated. The results of cross-linking degree, Fourier transform infrared spectroscopy (FTIR) and sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) showed that the TG enzyme was able to catalyse cross-linking between lysine and glutamine residues of RPI. The foaming capacity of RPI was enhanced from 120 % to 150 % after TG cross-linking 5 h, whereas the average size (210–219 nm) of the RPI determined by dynamic light scattering did not change significantly. Besides, the hydrophobicity tended to increase overall under the enzyme treatment, while the surface electrostatic potential decreased. The former indicates the unfolding of the protein and reduces the kinetic barriers to protein adsorption at the air–water interface, with a consequent increase in disulfide bonding and surface pressure. Furthermore, as the enzyme treatment time increased, a significant increase in protein content of foam by 33.86 %. These findings provide novel insight into the foaming mechanism of TG cross-linking RPI.

Rapeseed oil as the extraction solvent motivates fucoxanthin-loaded high internal phase emulsion preparation for food 3D printing

Fucoxanthin (FX), a non-provitamin A carotenoid pigment, is a well-known natural antioxidant contained in brown algae. The present study deals with an ultrasonic-assisted FX extraction process from Undaria pinnatifida with rapeseed oil as the solvent. Then, high internal phase emulsions (HIPEs) with the FX-rich rapeseed oil as the oil phase was constructed using a simple one-step method for food 3D printing. The FX-loaded HIPEs were stabilized by the gelatin (GE)-based microgel, which were prepared by GE complex coacervation with sodium alginate and transglutaminase cross-linking, for the improved delivery and stability of FX. FX-loaded HIPEs stabilized by 2 wt (wt)% GE-based microgel showed a small and uniform particle size and a stable microstructure. The HIPEs stabilized by 2 wt% GE-based microgel had the best FX stability (residual FX 84.81 ± 0.82%) and bioaccessibility (38.26 ± 1.21%). The excellent viscoelasticity, recovery rate and thixotropy of the HIPEs stabilized by 2 wt% GE-based microgel further confirmed the best 3D printing performance. Therefore, rapeseed oil as the extraction solvent motivates FX-loaded HIPEs preparation, and GE-based microgel concentration is crucial for 3D printing.

Influence of pH-shifting and transglutaminase on the freeze-thaw stability and thermal gel properties of mung bean protein-based liquid egg substitute prepared with two different oil phases

The poor freeze-thaw stability and weak thermal gel properties of plant-based egg substitutes limit their opportunity for application. In the current study, the impact of modification by pH-shifting and transglutaminase (TG) cross-linking on the freeze-thaw stability and thermal gel properties of mung bean protein-based emulsions made by two different oil phases (canola oil and coconut oil) were studied. The pH-shifting induced improved emulsifying activity (up to 77.6% increased) and smaller droplets sizes (from 39.27 to 7.03 μm). After the freeze-thaw process, no matter with TG cross-linking or in different oil phase systems, all emulsion samples prepared with pH-shifting treated mung bean protein (BMBP) exhibited a superior freeze-thaw stability than that with native mung bean protein (NMBP). The apparent viscosity of BMBP emulsion was higher than that of NMBP, and the viscosity of BMBP-based CO-emulsion (222.50 mPa s) before freeze-thaw process was closest to that of real egg liquid (184.86 mPa s). In particular, BMBP was more sensitive to TG, resulting in a superior thermal gel hardness of BMBP-based emulsion. This study could serve as a feasible solution to enhance the freeze-thaw stability and thermal gel properties of plant-based emulsions by pH-shifting and TG cross-linking, providing some novel strategies for their applications as stabilized plant-based egg substitutes.

How fractionation procedure of mung bean protein affects transglutaminase crosslinking

Transglutaminase is often used to improve functional properties of plant proteins. Here, we report on the effects of the fractionation procedure on transglutaminase susceptibility of mung bean proteins at three length scales: molecular, colloidal and bulk. Dispersions of 4 wt% mung bean protein fractions were treated with transglutaminase. The four fractions were obtained through (1) dry fractionation (fine fraction); (2) dry fractionation with additional heating; (3) lab-scale wet fractionation; and (4) a commercial protein isolate. Analysis of rheological properties (at 9.5 wt% dry matter) revealed that transglutaminase crosslinking formed tougher materials when using the fine fraction, the heated fine fraction, and the wet fractionated isolate, while the rheological properties of the protein isolate were hardly changed. Proteins in all fractions were crosslinked by transglutaminase at molecular scale, as confirmed by an increase in large molecular weight bands in gel electrophoresis, but the extent of crosslinking depended on the fraction used. The molecular changes also resulted in altered physical chemical properties for some fractions, as revealed by protein dispersibility, confocal laser scanning microscopy, and particle size distribution. At the colloidal scale, transglutaminase crosslinking led to an increased particle size in the fine fraction and heated fine fraction, while particle sizes of the wet fractionated isolate and commercial protein isolate were mostly unaffected. The differences between the fractions were explained by three mechanistic crosslinking routes. To conclude, protein fractionation procedure greatly affected susceptibility to transglutaminase.

Encapsulation of Tea Polyphenol in Zein through Complex Coacervation Technique to Control the Release of the Phenolic Compound from Gelatin–Zein Composite Film

Green tea polyphenol (TP) was encapsulated in zein and fabricated into a gelatin–zein composite film by complex coacervation. Transglutaminase (TG) crosslinking was employed to obtain a compact structural orientation of the film to prolong the release of bioactive compounds. The encapsulation efficiency of zein and the TP release rate from the composite film were investigated. The retention rate was over 30% and 80% after film fabrication and storage, respectively. Crosslinking decreased the diffusion coefficient by half, thus improving the release of TP from the film. The antioxidant properties were satisfactory after discharge from the film detected by DPPH/ABTS scavenging. The value of crosslinking degree (~60%) and increased molecular weight of the protein were investigated by SDS-PAGE, indicating the compatibility of TP and TG treatment. According to physicomechanical findings, the TG2TP1 film exhibited the best characteristics. Tensile strength and water solubility properties were ameliorated by the TG treatment of TP-encapsulated films compared to the control film. TG and TP-loaded gelatin–zein composite film had better thermal stability than the control film. Moreover, the TP loading reduced the transparency value and improved the light-barrier properties of the film. The films showed significant antimicrobial activities against two food-borne bacteria, including Staphylococcus aureus BCTC13962 and Escherichia coli BCRC10675. The result obtained shows that the encapsulation of TP and TG treatment may be used to fabricate gelatin–zein composite film with controlled release of phenolic compounds for active packaging applications.

Effect of transglutaminase cross-linking and emulsification on the stability and digestion of limonene emulsions

Transglutaminase (TG) cross-linked whey proteins are used to prepare a D-limonene emulsion, which can solve the problems of easy oxidation and poor water solubility of D-limonene. TG cross-linking can improve the emulsion stability of whey protein isolate (WPI). SDSPAGE results showed that TG cross-linked WPI and limonene were emulsified under high-pressure homogenization to form the emulsion (WPI-TG-Oil), which had more molecular polymers. The adsorption rate of interfacial protein of the WPI-TG-Oil emulsion was significantly increased by 5.15 % compared to the WPI limonene emulsion cross-linked with TG (WPI-Oil-TG). After a 10-day storage interval, the CDs and POV showed that the WPI-TG-Oil emulsion had the strongest oxidation stability and a thickened interfacial layer. It was also noted that WPI-TG-Oil was difficult to hydrolyze during the digestion process due to the large degree of cross-linking and many high molecular weight polymers. The WPI-TG-Oil emulsion was more stable with a high molecular weight and improved the overall properties. Moreover, these findings provide basic theoretical and technical support for improving the stability of D-limonene emulsions. The most suitable processing method was TG-crosslinked WPI to form a stable emulsion, which improved the physiochemical and emulsifying properties of its emulsion for potential uses in food, cosmetics, and other industries.

Influence of extrudate to SPI-gel-binder ratios and transglutaminase crosslinking on texture of a plant-based salami analogue

A plant-based salami-type sausage analogue was manufactured with a glucono-δ-lactone- or transglutaminase+glucono- δ -lactone-induced soy protein isolate-gel as binder to hold together fat mimetic particles and extruded proteins with fibrous structure to resemble the structure of classical dry-fermented sausages. The objective was to study the influence of the binder content on the texture of this complex meat analogues. The sausage analogues were processed similarly to traditional sausages. Texture, sensory and composition were analyzed. The hardness of dry-fermented sausages was found to decrease with increasing binder content (e.g. at 45% dry matter from ∼ 110 N to ∼ 80 N), whereas the cohesiveness increased with increasing binder content (e.g. at 45% dry matter from ∼ 0.21 to ∼ 0.41). Results from sensory and texture analysis correlated well and showed that both a high firmness and cohesiveness could not be reached in a single formulation. Furthermore, the addition of transglutaminase slightly increased firmness and cohesiveness, however, drying of sausages had a significantly higher impact on increasing hardness. These results indicate that, at lower binder contents, the structure is dominated by the extrudate particles, leading to an increased firmness but a lack of cohesiveness, whereas higher binder contents increased the cohesiveness but decreased hardness.

Transglutaminases are oncogenic biomarkers in human cancers and therapeutic targeting of TGM2 blocks chemoresistance and macrophage infiltration in pancreatic cancer.

Transglutaminases (TGs) are multifunctional enzymes exhibiting transglutaminase crosslinking, as well asatypical GTPase/ATPase and kinase activities. Here, we usedan integrated comprehensive analysis to assess the genomic, transcriptomic and immunological landscapes of TGs across cancers. Gene expression and immune cell infiltrationpatterns across cancers were obtained from The Cancer Genome Atlas (TCGA) database and Gene Set Enrichment Analysis (GSEA) datasets. Western blotting, immunofluorescence staining, enzyme-linked immunosorbent assays, and orthotopic xenograft models were used to validate our database-derived results. We found that theoverall expression of TGs (designated as the TG score) is significantly upregulated in multiple cancers and related to aworse patient survival. The expression of TG family members can be regulated through multiple mechanisms at the genetic, epigenetic and transcriptional levels. The expression of transcription factors crucial for epithelial-to-mesenchymal transition (EMT) is commonly correlated with the TG score in many cancer types. Importantly, TGM2 expression displays a close connection with chemoresistance to a wide range of chemotherapeutic drugs. We found thatTGM2 expression, F13A1 expression and the overall TG score were positively correlated with the infiltration of immune cells in all cancer types tested. Functional and clinical verification revealed that ahigher TGM2 expression is linked with aworse patient survival, an increased IC50 value of gemcitabine, and a higher abundance of tumor-infiltrating macrophages in pancreatic cancer. Mechanistically, we found thatincreased C-C motif chemokine ligand 2 (CCL2) release mediated by TGM2 contributes to macrophage infiltration into the tumor microenvironment. Our results reveal the relevance and molecular networks of TG genes in human cancers and highlight the importance of TGM2 in pancreatic cancer, which may provide promising directions for immunotherapy and foraddressing chemoresistance.

Microbial Transglutaminase Cross-Linking Enhances the Textural and Rheological Properties of the Surimi-like Gels Made from Alkali-Extracted Protein Isolate from Catfish Byproducts and the Role of Disulfide Bonds in Gelling.

The texture of surimi-like gels made from the protein isolate extracted from catfish byproducts has been proven to be brittle and lack elasticity. To address this issue, varying levels of microbial transglutaminase (MTGase) from 0.1 to 0.6 units/g were applied. MTGase had little effect on the color profile of gels. When MTGase at 0.5 units/g was employed, hardness, cohesiveness, springiness, chewiness, resilience, fracturablity, and deformation were increased by 218, 55, 12, 451, 115, 446, and 71%, respectively. A further increase in added MTGase did not lead to any textural improvement. In comparison to the gels made from fillet mince, the gels made from protein isolate were still lower in cohesiveness. Due to the activated endogenous transglutaminase, a setting step enhanced the textural properties of gels made from fillet mince. However, because of the endogenous proteases-induced protein degradation, the setting step led to a texture deterioration of the gels made from protein isolate. Gels made from protein isolate showed 23-55% higher solubility in reducing solution than in non-reducing solution, suggesting the vital role of disulfide bonds in the gelation process. Due to the different protein composition and conformation, fillet mince and protein isolate exhibited distinct rheological properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed the highly denatured protein isolate was susceptible to proteolysis and prone to disulfide formation during the gelation process. It also revealed that MTGase had an inhibitory effect on the proteolysis induced by endogenous enzymes. In view of the susceptibility of the protein isolate to proteolysis during gelation, future research should consider including other enzyme inhibitory agents in the presence of MTGase to improve the gel texture.

Fabrication of a double-network high internal phase emulsion gel stabilized by bacterial cellulose nanofibrils: Enhancement of heat stability and 3D printing

The semi-fluid properties required for 3D printing of high internal phase emulsion (HIPE) gels are incompatible with high mechanical strength, thereby limiting the application of HIPE gels in simulated meat products. In this study, pea protein (PeaP)-stabilized HIPEs reinforced with bacterial cellulose nanofibrils (BCNFs) were constructed and deformed into PeaP/sodium alginate (SA) double-network HIPE gels by further cross-linking of transglutaminase (TGase) and Ca2+. Increasing the BCNF concentration decreased the interfacial tension of water-in-oil HIPE emulsions from 11.91 mN/m to 9.49 mN/m, and reduced the average diameter of the droplets from 27 ± 3.1 μm to 11.3 ± 0.6 μm. The HIPEs also showed a thicker interfacial layer and improved viscoelastic properties at higher BCNF concentrations. The HIPEs were transformed from a semi-solid material to a rigid solid HIPE gel after the formation of a double-network structure. The fracture stress of the double-network HIPE gel containing 0.16% BCNFs was 0.015 MPa, which was greater than that of 0.001 MP and 0.007 MPa for the single-network SA and PeaP HIPE gels. The double-network HPIE gels fabricated with 0.08%–0.16% BCNF concentrations had high-temperature stability. The synergistic effect of the PeaP covalent network and the SA-Ca2+ ionic network produced a HIPE gel with good extrusion printability and strong self-supporting properties. This work could provide new insights into the design of high-strength HIPE gels with 3D printability that will facilitate the use of emulsion gels in plant-based meat products.

Hofmeister anion effects synergize with microbial transglutaminase to enhance the techno-functional properties of pea protein

Pea protein are emerging as the most potential alternative for meat products, but its application was hindered by their weaker gelling properties. Here, the feasibility of combining the Hofmeister anion (CO32–, Citrate3-, and SO42-) effect with microbial transglutaminase (MTG) cross-linking strategy to improve the techno-functional properties of pea protein was studied. Hofmeister anions or/and MTG treatment of pea protein caused a clear shift in far-UV CD spectra towards β-turn and random coil structures. Furthermore, Hofmeister anion and MTG-induced crosslinking caused a reduction of surface hydrophobicity in contrast with anions-treated. Compared to CO32– and SO42-, Citrate3- treatment can better improve the efficiency of MTG-crosslinking, as demonstrated by a reduction in free amino group contents and an increase in mean diameter size. Using MTG in combination with Hofmeister anions showed significantly improved foam property and gel hardness as well as decrease gelation temperature of pea protein, specifically Citrate3- treatment. Thus, this research provides a novel and effective method to improve the effect of MTG-cross-linked pea protein, which will play an essential role in future food production.

Secondary structure characterization of mixed food protein complexes using microfluidic modulation spectroscopy (MMS)

Microfluidic modulation spectroscopy (MMS) has been recognised as a novel technology for producing high quality and reproducible data at a wide concentration range to characterise protein structure. In this study, the use of MMS for food applications was explored through the structural analysis of pea protein, whey protein, and pea/whey protein complexes prepared by transglutaminase cross-linking. MMS generated reproducible data with >99.5% repeatability in all protein samples. The cross-linking seemed to alter the structure of whey protein with isopeptide and hydrogen bond formation, more significantly than that of pea protein. The larger secondary and tertiary structural changes were observed with higher whey protein content in cross-linked pea/whey protein complex, which eventually increased the surface hydrophobicity. According to the second derivatives analysis by MMS, β-sheet and random coil increased and β-turn decreased in the pea protein, whereas α-helix, β-sheet, and β-turn decreased and random coil increased in the whey protein after cross-linking. In the pea/whey protein complex, β-turn shifted to β-sheet due to cross-linking. There are some discrepancies between the relative secondary structure contents obtained from MMS data compared to the data acquired from circular dichroism. However, MMS has the considerable advantage of being able to directly measure original samples without significant dilution as required for circular dichroism measurements. This study provides evidence that MMS technology could be a robust technique to quantify the secondary structures of typical proteins in food with high reliability.

Modified whey protein isolate gel prepared by thermal aggregation combined with transglutaminase crosslinking achieves Casein-like slow digestion in vitro and in vivo

Our study aimed to fabricate a modified slow-digestive whey protein isolate (WPI), which can supply enough branched-chain amino acids (BCAAs) during long-term fasting. The WPI aqueous solution (10 % w/v) was treated by heat (80 ℃) to unfold the protein tertiary structure, and subsequently treated with transglutaminase to form a gel via cross-linking. The powder of the WPI gel was obtained by spray drying, which can dissolve in water easily and self-assemble into gels again. This modified WPI contained protein aggregates with high molecular weight, and kept a stable gel-like structure under simulated gastric digestion conditions (pH = 3, 37 ℃). A dense honeycomb internal microstructure of the freeze-dried gel was observed. Further, we found that the WPI gel successfully achieved a casein-like digestible ratio (37.37 %) and released more BCAAs (0.18 mg/mL) than casein during the 4 h of in vitro simulated digestion based on the INFOGEST method. Finally, our results showed that the C57BL/6 mice oral administrated with the modified WPI gel had consistently higher BCAAs concentration (0.052 mg/mL) in their blood serum than the mice with normal WPI intake during the 6 h of in vivo digestion.

Construction of transglutaminase covalently cross-linked hydrogel and high internal phase emulsion gel from pea protein modified by high-intensity ultrasound.

The poor gelling and emulsification properties of pea protein (PeaP) limit its application in gel-based products. In this study, a strong hydrogel and a high internal phase emulsion (HPLE) gel of PeaP were constructed by covalent cross-linking of transglutaminase (TGase) assisted by high-intensity ultrasound. Ultrasound promoted the catalytic efficiency of TGase, with the gel-point temperature dropping from 44 °C to 28 °C after 10min of ultrasound. As the ultrasound time increased from 1min to 10min, the microstructure of the hydrogel also changed from an irregular macropore structure to a relatively homogeneous honeycomb structure. This was accompanied by an improvement in gel strength, water holding capacity, and ultimate stress. Ultrasound enhanced the binding of water to PeaP, but had little effect on the water-locking ability of the network structure. Ultrasonication improved the self-supporting ability of the HPIE gels. The oil droplets within the HPIE gels were closely aligned to form a hexagonal structure. The PeaP layer was further cross-linked by TGase, strengthening the network structure. High internal phase emulsion gel displayed a higher gel strength, viscosity, and good self-healing ability under 1min ultrasound. Meanwhile, HPIE gel at 1min of ultrasound could be printed with the highest clarity. This work provided some insights into improving the functional properties of PeaP, which is helpful for the design and development of PeaP-based gel products. © 2022 Society of Chemical Industry.

Synergistic effect of microfluidization and transglutaminase cross-linking on the structural and oil–water interface functional properties of whey protein concentrate for improving the thermal stability of nanoemulsions

Generally, whey protein concentrate (WPC) undergoes high-temperature denaturation and aggregation, which reduces its emulsifying properties and is not conducive to as an emulsifier to maintain the thermal stability of emulsions. In this study, dynamic high-pressure microfluidization technology (DHPM) combined with TGase (TG) cross-linking was applied to prepare DHPM-TG-WPC, and the thermal stabilization mechanism of nanoemulsions prepared with DHPM-TG-WPC was explored. Results showed DHPM treatment could promote the formation of TG-crosslinked WPC polymers. Compared to WPC, the free sulfhydryl and free amino group content of DHPM-TG-WPC was significantly decreased (P < 0.05), the surface hydrophobicity and interfacial tension of DHPM-TG-WPC were increased by 45.23 % and 62.34 %, respectively. And its emulsifying stability index and interface protein adsorption was significantly enhanced (P < 0.05). Furthermore, compared to WPC, DHPM-WPC and TG-WPC, DHPM-TG-WPC-stabilized nanoemulsions showed the best 15 days of storage stability after thermal sterilization. This study provides a theoretical basis for the application of modified-WPC emulsion.

Modification of fermented whey protein concentrates: Impact of sequential ultrasound and TGase cross-linking

This study aimed to examine the impact of fermentation process on whey protein and improve the general properties of fermented whey protein concentrate (FWPC) recovered by a combined ultrafiltration-diafiltration (UF-DF) operation. Impacts of sequential ultrasound (US) pretreatment and transglutaminase (TGase) crosslinking on structural, functional, and physicochemical properties of FWPCs were investigated. Partially denatured and hydrolyzed fermented whey protein could replace heat denaturation prior to the TGase addition to a whey protein system. Sequential treatment increased the molecular weight of FWPCs as exhibited by both SEM and SDS-PAGE, which demonstrates that modification can lead to the polymers and oligomers production. The zeta potential value increased significantly after US treatment and enzyme catalysis, and all the modified FWPCs were strongly negatively charged. Compared with the secondary structure of untreated FWPCs, the percentage of α-helix and random coil in modified FWPCs significantly increased, while the percentage of β-sheet and β-turns reduced. Solubility, free sulfhydryl groups, and surface hydrophobicity of all FWPCs were significantly improved compared to non-fermented WPC (P < 0.05). Sequential treatment induced a substantial impact on the emulsifying activity and stability of modified samples in comparison with untreated FWPCs. Scanning electron microscope pictures confirmed the positive effects of sequential treatments on texture and void size reduction. Therefore, the application of recovering modified FWPCs is fully recommended as a commercially viable approach for enhanced protein production at the industrial scale.

Improved properties of gelatin films involving transglutaminase cross-linking and ethanol dehydration: The self-assembly role of chitosan and montmorillonite

In this study, the chitosan and montmorillonite (MMT) were synergistically introduced to improve the properties of the gelatin films through self-assembly. The preparation of gelatin films (G), gelatin + MMT composite films (G + MMT), gelatin-chitosan bilayer films (G-CS), and gelatin + MMT-chitosan composite bilayer films (G + MMT-CS) involved transglutaminase (TG) cross-linking followed by ethanol precipitation and self-assembly process. The water contact angle of the composite bilayer films (G-CS and G + MMT-CS) was higher than 110° due to the formation of surface hydrophobic layer formed by self-assembly via hydrogen bonding and electrostatic interaction between gelatin and chitosan, but the MMT alone cannot improve the hydrophobicity of gelatin films. The water solubility (WS) of G + MMT, G-CS and G + MMT-CS films was significantly lower than that of G films. The mechanical and barrier properties were significantly improved due to the introduction of MMT and the surface deposition of chitosan, attributing to the increase of triple helix content and formation of bilayer structure, respectively. Moreover, MMT caused the decrease of sterilization thermal shrinkage from 49.54% to 34.00%. Interestingly, MMT facilitated the surface deposition of chitosan during self-assembly process. The mold growth of bread wrapped with G + MMT-CS was effectively inhibited during storage, implying potential application as antimicrobial food packaging materials. • Self-assembly of gelatin and chitosan improved hydrophobicity of gelatin (G) films. • Chitosan and montmorillonite improved mechanical and barrier properties of G films. • Sterilization thermal shrinkage of G films was reduced by montmorillonite. • Introducing montmorillonite facilitated the self-assembly deposition of chitosan.

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 2h 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.