Transglutaminase Research Articles

Effects of transglutaminase cross-linking process on printability of gelatin microgel-gelatin solution composite bioink

Three-dimensional (3D) bioprinting has emerged as a powerful engineering approach for various tissue engineering applications, particularly for the development of 3D cellular structures with unique mechanical and/or biological properties. For the jammed gelatin microgel-gelatin solution composite bioink, comprising a discrete phase of microgels (enzymatically gelled gelatin microgels) and a cross-linkable continuous gelatin precursor solution-based phase containing transglutaminase (TG), its rheological properties and printability change gradually due to the TG enzyme-induced cross-linking process. The objective of this study is to establish a direct mapping between the printability of the gelatin microgel-gelatin solution based cross-linkable composite bioink and the TG concentration and cross-linking time, respectively. Due to the inclusion of TG in the composite bioink, the bioink starts cross-linking once prepared and is usually prepared right before a printing process. Herein, the bioink printability is evaluated based on the three metrics: injectability, feature formability, and process-induced cell injury. In this study, the rheological properties such as the storage modulus and viscosity have been first systematically investigated and predicted at different TG concentrations and times during the cross-linking process using the first-order cross-linking kinetics model. The storage modulus and viscosity have been satisfactorily modeled as exponential functions of the TG concentration and time with an experimentally calibrated cross-linking kinetic rate constant. Furthermore, the injectability, feature formability, and process-induced cell injury have been successfully correlated to the TG concentration and cross-linking time via the storage modulus, viscosity, and/or process-induced shear stress. By combing the good injectability, good feature formability, and satisfactory cell viability zones, a good printability zone (1.65, 0.61, and 0.31 h for the composite bioinks with 1.00, 2.00, and 4.00% w/v TG, respectively) has been established during the printing of mouse fibroblast-based 2% gelatin B microgel-3% gelatin B solution composite bioink. This printability zone approach can be extended to the use of other cross-linkable bioinks for bioprinting applications.

Tailoring the properties of double-crosslinked emulsion gels using structural design principles: Physical characteristics, stability, and delivery of lycopene

Lycopene is claimed to have numerous physiological benefits, but its poor water solubility, chemical instability, and low bioavailability limit its application in functional foods and health care products. In this study, lycopene-loaded emulsions containing oil droplets with different interfacial structures were prepared and then cross-linked using transglutaminase (TG) and/or calcium ions (Ca2+) to form emulsion gels. The oil droplets were first coated by interfacial layers comprised of whey protein isolate (WPI) and sodium alginate (SA). During emulsion preparation, the SA was added either before or after homogenization to create complex or layer-by-layer coatings, respectively. Subsequently, TG and Ca2+ were used to cross-link WPI and SA to form emulsion gels. The results show that double-crosslinking increased the gel strength and viscosity of the emulsion gels. The layer-by-layer emulsion gels were stronger and more viscous than the complex ones. The photochemical and gastrointestinal stability of lycopene encapsulated within the emulsion gels was higher than that of free lycopene. An MTT toxicity test showed that the emulsion gels exhibited no cytotoxicity to Caco-2 cells. The lycopene-loaded emulsion gels exhibited stronger anti-inflammatory activity on the Caco-2 cells than the control. In addition, the absorption of lycopene by the Caco-2 cells increased after encapsulation. This study provides a new approach of preparing edible soft materials to enhance the application of hydrophobic bioactives (like lycopene) in functional foods.

Enzymatic crosslinking and food allergenicity: A comprehensive review.

Food allergy has become a major global public health concern. In the past decades, enzymatic crosslinking technique has been employed to mitigate the immunoreactivity of food allergens. It is an emerging non-thermal technique that can serve as a great alternative to conventional food processing approaches in developing hypoallergenic food products, owing to their benefits of high specificity and selectivity. Enzymatic crosslinking via tyrosinase (TYR), laccase (LAC), peroxidase (PO), and transglutaminase (TG) modifies the structural and biochemical properties of food allergens that subsequently cause denaturation and masking of the antigenic epitopes. LAC, TYR, and PO catalyze the oxidation of tyrosine side chains to initiate protein crosslinking, while TG initiates isopeptide bonding between lysine and glutamine residues. Enzymatic treatment produces a high molecular weight crosslinked polymer with reduced immunoreactivity and IgE-binding potential. Crosslinked allergens further inhibit mast cell degranulation due to the lower immunostimulatory potential that assists in the equilibration of T-helper (Th)1/Th2 immunobalance. This review provides an updated overview of the studies carried out in the last decade on the potential application of enzymatic crosslinking for mitigating food allergenicity that can be of importance in the context of developing hypoallergenic/non-allergenic food products.

Novel tissue-engineered skin equivalent from recombinant human collagen hydrogel and fibroblasts facilitated full-thickness skin defect repair in a mouse model

Tissue-engineered skin equivalent (TESE) is an optimized alternative for the treatment of skin defects. Designing and fabricating biomaterials with desired properties to load cells is critical for the approach. In this study, we aim to develop a novel TESE with recombinant human collagen (rHC) hydrogel and fibroblasts to improve full-thickness skin defect repair. First, the bioactive effect of rHC on fibroblast proliferation, migration and phenotype was assayed. The results showed that rHC had good biocompatibility and could stimulate fibroblasts migration and secrete various growth factors. Then, rHC was cross-linked with transglutaminase (TG) to prepare rHC hydrogel. Rheometer tests indicated that 10% rHC/TG hydrogel could reach a oscillate stress of 251 Pa and remained stable. Fibroblasts were seeded into rHC/TG hydrogel to prepare TESE. Confocal microscope and scanning electronic microscope observation showed that seeded fibroblasts survived well in the hydrogel. Finally, the therapeutic effect of the newly prepared TESE was tested in a mouse full-thickness skin defect model. The results demonstrated that TESE could significantly improve skin defect repair in vivo. Conclusively, TESE prepared from rHC and fibroblasts in this study exhibits great potential for clinical application in the future.

Protective Effect of Potentilla glabra in UVB-Induced Photoaging Process.

Maintaining skin homeostasis is one of the most important factors for skin health. UVB-induced skin photoaging is a difficult problem that has negative impacts on skin homeostasis. So far, a number of compounds have been discovered that improve human skin barrier function and hydration, and are thought to be effective ways to protect skin homeostasis. Potentilla glabra var. mandshurica (Maxim.) Hand.-Mazz. Ethanol Extract (Pg-EE) is a compound that has noteworthy anti-inflammatory properties. However, its skin-protective effects are poorly understood. Therefore, we evaluated the capacity of Pg-EE to strengthen the skin barrier and improve skin hydration. Pg-EE can enhance the expression of filaggrin (FLG), transglutaminase (TGM)-1, hyaluronic acid synthase (HAS)-1, and HAS-2 in human keratinocytes. Moreover, Pg-EE down-regulated the expression of pro-inflammatory cytokines and up-regulated the production of FLG, HAS-1, and HAS-2 suppressed by UVB through inhibition of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) pathways. Given the above, since Pg-EE can improve skin barrier, hydration and reduce the UVB-induced inflammation on skin, it could therefore be a valuable natural ingredient for cosmetics or pharmaceuticals to treat skin disorders.

Enhanced bone regeneration via spatiotemporal and controlled delivery of a genetically engineered BMP-2 in a composite Hydrogel

Scaffolds functionalized with bone morphogenetic protein-2 (BMP-2) have shown great potential for bone regeneration. However, structural instability and the necessity for supra-physiological dose have thus far limited practical applications for BMP-2. Protein modification and site-specific covalent immobilization of BMP-2 to carrier materials might be optimal strategies to overcome these problems. Here, we report a broadly applicable strategy where the polyhistidine tag-T4 Lysozyme (His6-T4L) was genetically fused at the N-terminus of BMP-2 and used as a protein spacer, which on one hand enhanced protein solubility and stability, and on the other hand mediated site-specific covalent anchoring of BMP-2 upon binding to nickel-chelated nitrilotriacetic acid (Ni-NTA) microparticles (denoted as MPs-His6-T4L-BMP2) to further maximize its rescued activity. We also constructed a novel gelatin-based hydrogel that was crosslinked by transglutaminase (TG) and tannic acid (TA). This hydrogel, when incorporated with MPs-His6-T4L-BMP2, displayed excellent in-situ injectability, thermosensitivity, adhesiveness and improved mechanical properties. The effective loading mode led to a controlled and long-term sustained release of His6-T4L-BMP2, thereby resulting in enhancement of bone regeneration in a critical-sized bone defect. We believe that the protein modification strategy proposed here opens up new route not only for BMP-2 applications, but can be used to inform novel uses for other macromolecules.

Influence of Transglutaminase on Glucono-δ-lactone-Induced Soy Protein Gels

Enzymatic cross-linking of proteins can be used to create a variety of foods with appealing textures and facilitate further processing such as slicing or packaging. Transglutaminase (TG), a protein-glutamine-γ-glutamyltransferase, has been used in the production of processed meat and fish products. However, it has a reaction optimum at pH 7 and is therefore typically unsuitable for application in up-and-coming acidic food products such as fermented vegan meat product alternatives. To determine whether a simultaneous addition of slowly acidifying glucono-δ-lactone (GDL) and TG can facilitate protein cross-linking prior to the pH becoming too low, TG and GDL were added separately or in combination to soy protein suspensions composed of 10–15% soy protein concentrates or isolates (SPI). Texture analysis showed that SPI gels at pH 5–6, induced by GDL and TG combined, were harder than only GDL-induced gels and as hard as TG-induced gels at the optimum pH of 7. Decreased tan δ values and confocal laser scanning microscopy images indicated that protein cross-linking had taken place in combined gels. The results suggest an initial network formation induced by TG, which later in the acidification is being supplemented by an agglomeration of proteins due to weakened electrostatic repulsion. Taken together, the combination of slow acidification by GDL and TG addition leads to acidic gels with enhanced textural properties and shelf life.

The Role of the PFNA Operon of Bifidobacteria in the Recognition of Host's Immune Signals: Prospects for the Use of the FN3 Protein in the Treatment of COVID-19.

Bifidobacteria are some of the major agents that shaped the immune system of many members of the animal kingdom during their evolution. Over recent years, the question of concrete mechanisms underlying the immunomodulatory properties of bifidobacteria has been addressed in both animal and human studies. A possible candidate for this role has been discovered recently. The PFNA cluster, consisting of five core genes, pkb2, fn3, aaa-atp, duf58, tgm, has been found in all gut-dwelling autochthonous bifidobacterial species of humans. The sensory region of the species-specific serine-threonine protein kinase (PKB2), the transmembrane region of the microbial transglutaminase (TGM), and the type-III fibronectin domain-containing protein (FN3) encoded by the I gene imply that the PFNA cluster might be implicated in the interaction between bacteria and the host immune system. Moreover, the FN3 protein encoded by one of the genes making up the PFNA cluster, contains domains and motifs of cytokine receptors capable of selectively binding TNF-α. The PFNA cluster could play an important role for sensing signals of the immune system. Among the practical implications of this finding is the creation of anti-inflammatory drugs aimed at alleviating cytokine storms, one of the dire consequences resulting from SARS-CoV-2 infection.

Characterization of nit sheath protein functions and transglutaminase-mediated cross-linking in the human head louse, Pediculus humanus capitis

BackgroundHead louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. Recently, two homologous proteins, named louse nit sheath protein (LNSP) 1 and LNSP 2, were identified as adhesive proteins but the precise mechanism of nit sheath solidification is unknown.MethodsWe determined the temporal transcriptome profiles of the head louse accessory glands plus oviduct, from which putative major structural proteins and those with functional importance were deduced. A series of RNA interference (RNAi) experiments and treatment of an inhibitor were conducted to elucidate the function and action mechanism of each component.ResultsBy transcriptome profiling of genes expressed in the louse accessory glands plus uterus, the LNSP1 and LNSP2 along with two hypothetical proteins were confirmed to be the major structural proteins. In addition, several proteins with functional importance, including transglutaminase (TG), defensin 1 and defensin 2, were identified. When LNSP1 was knocked down via RNA interference, most eggs became nonviable via desiccation, suggesting its role in desiccation resistance. Knockdown of LNSP2, however, resulted in oviposition failure, which suggests that LNSP2 may serve as the basic platform to form the nit sheath and may have an additional function of lubrication. Knockdown of TG also impaired egg hatching, demonstrating its role in the cross-linking of nit sheath proteins. The role of TG in cross-linking was further confirmed by injecting or hair coating of GGsTop, a TG inhibitor.ConclusionsBoth LNSP1 and LNSP2 are essential for maintaining egg viability besides their function as glue. The TG-mediated cross-linking plays critical roles in water preservation that are essential for ensuring normal embryogenesis. TG-mediated cross-linking mechanism can be employed as a therapeutic target to control human louse eggs, and any topically applied TG inhibitors can be exploited as potential ovicidal agents.Graphical abstract

Impact of sourdough and transglutaminase on gluten-free buckwheat bread quality

Gluten-free (GF) bread based on starch has low sensory quality and stales faster than conventional wheat bread. At the same time, it is characterized by low nutritional value. Buckwheat flour can be used as an ingredient of GF bread improving favourably its nutritional properties. The application of transglutaminase (TG) that modifies proteins through cross-linking can further improve the overall quality of GF bread. In the present study, we investigated the effectiveness of TG used together with various doses of buckwheat sourdough, prepared using starter cultures L. plantarum ŁOCK 860 and L. brevis ŁOCK 1267, on the quality features of GF buckwheat bread. Compared to control, the exclusive addition of sourdough reduced significantly (p < 0.05) the specific volume of the bread, whereas the crumb was more cohesive and springy with a parallel TG addition. The crumb had lower density, similar to that of conventional bread. The flavor and aroma of the GF buckwheat bread were also improved noticeably. The use of sourdough had a significant effect on the mechanical properties of the crumb. Its structure became more springy. Moreover, the overall sensory quality of experimental bread increased, as the characteristic bitter aftertaste of buckwheat was less noticeable. In conclusion, the simultaneous use of buckwheat sourdough and TG had a positive effect on the total quality score which can lead to the increased sensory acceptability of the GF buckwheat bread.

Differential white spot syndrome virus-binding proteins in two hemocyte subpopulations of Chinese shrimp (Fenneropenaeus chinensis)

A number of white spot syndrome virus (WSSV)-binding proteins have been identified previously in the hemocytes of Fenneropenaeus chinensis. In order to further investigate the differential WSSV-binding proteins in hemocyte subpopulations, granular hemocytes and hyalinocytes were sorted from WSSV-infected shrimp by immunomagnetic bead (IMB) method. The results of ELISA and immuno-dot blot assay showed that the WSSV-binding activity of granular hemocytes proteins was much stronger than that of hyalinocytes proteins. And the percentage of WSSV-positive granular hemocytes was significantly higher than that of hyalinocytes post WSSV infection, indicating that granular hemocytes were more susceptible to WSSV infection. Moreover, a total of 9 WSSV-binding proteins were successfully identified in granular hemocytes and hyalinocytes by two-dimensional virus overlay protein binding assay (2D-VOPBA) and MALDI-TOF MS analysis, of which 3 binding proteins (arginine kinase, protease 1 and transglutaminase) existing in both hyalinocytes and granular hemocytes and 6 proteins (F1ATP synthase β-chain, hnRNPs, GAPDH, RACK1, β-actin and cellular retinoic acid) detected only in granular hemocytes. Among these identified WSSV-binding proteins, the transglutaminase (TG) was further recombinantly expressed, and the recombinant TG could be bound with WSSV. Subsequently, quantitative real-time PCR analysis showed that differential expression levels of WSSV-binding proteins were observed in granular hemocytes and hyalinocytes. The results of this study revealed that the WSSV-binding proteins were differentially expressed in granular hemocytes and hyalinocytes, which provided a deeper insight into the interaction between WSSV and hemocyte subpopulations.

The Effects of Transglutaminase and Refrigerated Storage on the Physicochemical Properties of Whole Wheat Dough and Noodles.

This study investigated the effects of transglutaminase (TG) concentrations (0, 0.1% and 1%) on the physicochemical properties of whole wheat dough (WWD) and noodles (WWN) during refrigerated storage (0, 1, 2, and 3 days). The yield, ferulic acid (FA) content, molecular weight (Mw), and apparent viscosity (AV) of water extractable arabinoxylan (WEAX) from refrigerated WWDs were analysed. The WEAX yield and FA tended to increase with refrigerated storage, while the Mw decreased. WEAX FA of from WWD with TG tended to be smaller than the control during refrigeration. The AV for all WEAXs gradually decreased during refrigeration. The TG concentration effects on WWD resistance to extension and extensibility and the WWN cooking properties and texture profile analysis (TPA) were studied. The water absorption and swelling index tended to decrease in WWNs with TG depending on refrigeration time compared to the control samples. The TPA results showed that WWNs with TG were significantly harder than the control after two days of refrigeration. This study demonstrated that TG affected not only WWD composition but also WWN physical properties during refrigerated storage.

Improving the texture and rheology of set and stirred kombucha fermented milk beverages by addition of transglutaminase

The possibilities of manufacturing fermented milk beverages by applying kombucha inoculum concentrated by evaporation and with addition of transglutaminase have been investigated. The main aims of this study were to investigate influence of concentrated kombucha inoculum and the addition of transglutaminase (TG) on textural, rheological and sensory properties of set and stirred fermented milk beverages. The results showed that the addition of transglutaminase had a great influence on textural characteristics and rheological properties of kombucha fermented milk beverages. Firmness and consistency of kombucha fermented milk products were significantly increased with the incorporation of TG compared to the control sample. Set samples with TG addition had approximately 90% higher hysteresis loop area compared to stirred samples, while hysteresis loop area of stirred samples without TG was 60% lower compared to set samples. The enzymatic treatment of milk with TG improved texture, rheology and sensorial characteristics of set and stirred fermented milk beverages obtained by concentrated kombucha inoculum.

Unique autoantibody prevalence in long-term recovered SARS-CoV-2-infected individuals

The variability in resolution of SARS-CoV-2-infections between individuals neither is comprehended, nor are the long-term immunological consequences. To assess the long-term impact of a SARS-CoV-2-infection on the immune system, we conducted a prospective study of 80 acute and former SARS-CoV-2 infected individuals and 39 unexposed donors to evaluate autoantibody responses and immune composition. Autoantibody levels against cyclic citrullinated peptide (CCP), a specific predictor for rheumatoid arthritis (RA), were significantly (p = 0.035) elevated in convalescents only, whereas both acute COVID-19 patients and long-term convalescents showed critically increased levels of anti-tissue transglutaminase (TG), a specific predictor of celiac disease (CD) (p = 0.002). Both, anti-CCP and anti-TG antibody levels were still detectable after 4–8 months post infection. Anti-TG antibodies occurred predominantly in aged patients in a context of a post-SARS-CoV-2-specific immune composition (R2 = 0.31; p = 0.044). This study shows that increased anti-CCP and anti-TG autoantibody levels can remain long-term after recovering even from mildly experienced COVID-19. The inter-relationship of the lung as viral entry side and RA- and CD-associated autoimmunity indicates that a SARS-CoV-2-infection could be a relevant environmental factor in their pathogenesis.

Comparative Study on the Use of Transglutaminase Enzyme in Making Labneh from Different Kinds of Milk

Present research aims to make labneh from different kinds of milk (buffalo , cow and goat)(BM,CM, and GM, respectively), and to compare the effect of the addition of transglutaminase (TG) on the examined treatments. Results show that the addition of TG did not considerably affect the development of acidity during the fermentation process, while the increase of acidity in B and C was faster than in G. On the other hand, an increase in the yield of labneh made with added enzyme, compared with samples without TG from was 43.16 to 50.55% ,38.78 to 48.16 % and 22.50 to 37.20%, in the same order. In addition, an improvement in the gel strength and decrease in the synersis were observed. The chemical composition and sensory properties was determined during 21 days showed an increase in the total solid (TS),total protein(TP) and total volatile fatty acid (TVFA) in the samples treated with TG, while there was no noticeable effect on acidity and PH. The addition of TG in all of the examined samples led to improvement in the sensory value and accessed to creamy body, particularly in the labneh made from cow milk with added TG.

Secalin enzymatically cross-linked by either papain and N-acetyl-dl-homocysteine thiolactone or transglutaminase: Improving of protein functional properties and film manufacturing

With the aim to create new food ingredients and packaging, cross-linked secalin (SCL) was synthesized by papain-catalyzed disulfide bond formation in the presence of N-acetyl-dl-homocysteine thiolactone (AHTL). The effects of SCL structural modification on the protein functional properties, as well as of the derived films, were investigated at several concentrations of AHTL and compared to those produced by the iso-peptide bonds formed in the presence of different concentrations of transglutaminase (TG). Cross-linked SCL exhibited improved emulsifying and foaming properties, whereas the derived films showed increased mechanical, barrier and water resistance properties. In particular, AHTL/papain mediated cross-linking was more effective in increasing the elongation at break (200%), Young's modulus (200 MPa), surface hydrophobicity and barrier properties of SCL-based films (water permeability halved, that to oxygen one tenth and that to carbon dioxide one twentieth), while films obtained with TG cross-linked SCL showed higher tensile strength (4 MPa) and lower swelling index (83%). SEM analyses showed a more compact structure in the films obtained with AHTL/papain-cross-linked SCL, whereas thicker films (50% more) with porous surface fractures were observed when SCL was formerly modified by TG. The different behavior of the two groups of films prepared with SCL differently cross-linked was probably due to the different microstructure of the derived films dependent on the shorter distance of iso-peptide bonds obtained by TG with respect to the disulfide bonds resulting from AHTL/papain reaction. These findings indicate that the two different enzymatic cross-linking methods can be used to prepare SCL with improved functional properties to be utilized as food ingredient or for potential packaging applications.

High Tissue Transglutaminase Antibody Titers Are Diagnostic for Celiac Disease

Celiac disease (CD) currently is diagnosed using both serologic testing (i.e., IgA anti–tissue transglutaminase [tTG] and anti-endomysial antibodies)

Premenopausal Osteoporosis &amp; Perfluoroalkyl Substance Exposure; Is There a Link?

Introduction: Perfluoroalkyl substances (PFAS) like Perflouroctanoate (PFOA) and Perflurooctane sulfonate (PFOS) are ubiquitous environmental contaminants that have been in industrial use for many years. Many known adverse effects include malignancies, reproductive and thyroid dysfunction. However, there is limited literature regarding PFAS causing low bone density. We report a case of a premenopausal woman with a history of exposure to PFAS who was recently diagnosed with osteoporosis.Clinical Case: A 36-year-old lady with a history of hypothyroidism, on levothyroxine, presented to the orthopedics clinic with complaints of sudden onset right foot pain with no trauma. She was found to have a fracture of her right second metatarsal bone. Notably, over a period of five years she had suffered multiple fractures including metatarsal, elbow and a wrist fracture, all with minimal or no trauma. She denied smoking, alcohol, chronic steroid or PPI use, history of malabsorption, celiac disease, kidney stones, malignancy or liver problems. Her menstrual cycles were regular; she was on oral contraceptives in the past for dysmenorrhea. She is on Vitamin D supplementation and consumes adequate dairy products daily. There is no family history of hip fracture or osteoporosis. Labs showed: Calcium 8.9mg/dl, Phosphorus 2.4mg/dl (2.5–4.5mg/dl), intact PTH was 92.7pg/ml (8-97pg/ml), 24-hour urine calcium was undetectable. Vitamin D was 56.6ng/ml (30-100ng/ml). CBC, TSH, FSH, liver & kidney functions were all normal. Anti-endomysial, anti-gliadin and anti-tissue trans glutaminase antibodies were all unremarkable. IgA level was 362mg/dl (8–352 mg/dl). DXA scan revealed the lowest Z-score (-3.1) in the lumbar spine. She reported a history of exposure to PFAS with a blood level of 22.3ng/ml for PFOA and 48.4ng/ml for PFOS in the year 2005. Plan is to initiate bisphosphonate therapy for the treatment of osteoporosis.Discussion: PFAS are known endocrine disruptive agents that have been used widely in making a wide range of consumer products including nonstick and stain-resistant coatings of cookware, food containers. Recent studies suggest that serum PFAS concentrations were associated with lower bone density. There was a higher incidence of lower lumbar spine bone density in patients exposed to PFOS. PFOA is believed to compete with calcitriol at the same binding site on Vitamin D receptor resulting in changes in the osteoblasts thereby decreasing bone mineralization.Conclusion: There needs to be increased awareness about the association of low bone density in patients exposed to PFAS. This is especially important in the evaluation of premenopausal osteoporosis.

Development and characterization of whey protein isolate and xylan composite films with and without enzymatic crosslinking

Biodegradable food packaging provides an environmentally-conscious alternative to plastic food packaging options. This study investigated whey protein edible films containing 10–40 g xylan/100 g whey protein isolate (WPI). Transglutaminase (TG) was used as a cross-linking agent in WPI-only and 40 g xylan/100 g WPI films. The food packaging properties investigated were water vapor permeability (WVP), oxygen permeability (OP), tensile stress, and % elongation at break. Thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Crystallinity and microstructure were assessed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Composite films containing 40 g xylan/100 g WPI that were also treated with TG showed the greatest improvement in properties important to food packaging. Compared to the WPI-only control films, WVP decreased from 6.41 to 3.89 g mm/m2 day kPa (p < 0.05), OP decreased from 21.85 to 7.32 cc μm/m2 day kPa (p < 0.05), and tensile stress increased from 6.73 MPa to 15.96 MPa (p < 0.05). The % elongation at break decreased significantly from 12.5% in WPI-only films to 5.8–1.4% in all xylan and TG treated films (p < 0.05). The temperature of melting increased from 121 °C in control films to a maximum of 166 °C in the 20 g xylan/100 g WPI films, indicating increased intermolecular strength. Film microstructure showed separate organization of xylan within films. Crystallinity was identified with increasing xylan content through XRD analysis, suggesting increased polymer packing.

Synergistic recovery and enhancement of gelling properties of oxidatively damaged myofibrillar protein by l-lysine and transglutaminase

The influence of combined Lysine (Lys) and transglutaminase (TG) on the conformation and gelling properties of oxidatively damaged myofibrillar protein (MP) was investigated. The addition of Lys (5 mM) significantly increased the α-helix content (by 47.8%) and decreased the particle size of oxidatively damaged MP, and improved the cooking yield (by 16.8%) and the breaking strength of MP gels (by 65.5%). The treatment with TG (E:S = 1:500) led to a slightly reduced α-helix content but improved breaking strength (by 41.8%) and cooking loss (by 13.3%) of the gels. Their combination (Lys + TG) showed the greatest and synergistic overall improvement, with the set gel displaying a fine, smooth and compact network structure. Notably, the gelling ability of oxidatively damaged MP upon Lys + TG treatment was significantly stronger than that of non-oxidized MP far exceeding its recovery. Therefore, significantly enhanced gelling properties of oxidatively damaged MP can be attained through the combination Lys and TG.