TRANSGLUTAMINASE IN DAIRY PRODUCTS: CHEMISTRY, PHYSICS, APPLICATIONS

One-Pot Procedure for Recovery of Gallic Acid from Wastewater and Encapsulation within Protein Particles

A whey protein isolate solution was heat-denatured and treated with the enzyme transglutaminase, which cross-linked ≈26% of the amino groups and increased the magnitude of the ζ-potential value. The protein solution was microemulsified, and then the resulting water-in-oil microemulsion was dispersed within a gallic acid-rich model wastewater. Gallic acid extraction by the outlined microemulsion liquid membrane (MLM) from the exterior aqueous phase (wastewater) and accumulation within the internal aqueous nanodroplets induced protein cold-set gelation and resulted in the formation of gallic acid-enveloping nanoparticles. Measurements with a strain-controlled rheometer indicated a progressive increase in the MLM viscosity during gallic acid recovery corresponding to particle formation. The mean hydrodynamic size of the nanoparticles made from the heat-denatured and preheated enzymatically cross-linked proteins was 137 and 122 nm, respectively. The enzymatic cross-linking of whey proteins led to a higher gallic acid recovery yield and increased the glass transition enthalpy and temperature. A similar impact on glass transition indices was observed by the gallic acid-induced nanoparticulation of proteins. Scanning electron microscopy showed the existence of numerous jammed/fused nanoparticles. It was suggested on the basis of the results of Fourier transform infrared spectroscopy that the in situ nanoparticulation of proteins shifted the C-N stretching and C-H bending peaks to higher wavenumbers. X-ray diffraction results proposed a decreased β-sheet content for proteins because of the acid-induced particulation. The nanoparticles made from the enzymatically cross-linked protein were more stable against the in vitro gastrointestinal digestion and retained almost 19% of the entrapped gallic acid after 300 min sequential gastric and intestinal digestions.

Effects of yeast, carboxymethylcellulose, yoghurt, transglutaminase and cyclodextrinase on mixing properties of oat dough

The effects of yeast, carboxylmethylcellulose (CMC), plain yoghurt (YG), transglutaminase (TG) and cyclodextrinase (CG) on the mixing properties of oat dough were investigated through the use of DoughLab. A 2(5-2)fractional factorial design resolution III with yeast (1.25, 3.25 %), CMC (1, 2 %), YG (10.75, 33.75 %), TG (0.5, 1.5 %) and CG (10, 40 μl) as independent variables was implemented. The parameters measured were water absorption, arrival time, stability, energy at peak, peak resistance, development time, departure time, softening and bandwith at peak. CMC significantly (p < 0.05) increased stability, energy at peak, development and departure times, but significantly (p < 0.05) decreased water absorption, peak resistance, softening and bandwidth at peak. TG signficantly increased water absorption, peak resistance and softening, but significantly decreased energy and development time. YG significantly (p < 0.05) decreased all the parameters measured, with the exception of softening, which was significantly increased. In contrast, yeast and cyclodextrinase did not significantly affect the oat dough during mixing. Principal component analysis indicated that 85.5 % of the variation in the data could be explained by two components. Component 1 explaining 52.3 % of the variation loaded highly on dough strength (stability and departure time). Component 2 contributing 33.2 % of the variation loaded on dough resistance (water absorption and peak resistance). CMC significantly increased dough strength while yoghurt reduced it significantly. TG significantly (p < 0.05) increased the resistance of the dough to mixing while CMC and yoghurt reduced it significantly (p < 0.05). Hence, CMC, TG and yoghurt are ingredients of choice when modifying oat dough mixing properties.

Advances in gluten-free bread technology

The unattractive appearance of gluten-free bread still remains a challenge in gluten-free breadmaking. In response to this, additives such as dairy products, soya and eggs have been used to improve the quality of gluten-free bread, but with limited success. In recent years, enzymes (transglutaminase and cyclodextrinase) and hydrocolloids (carboxymethylcellulose and hydroxypropylmethylcellulose) have become the main focus for the improvement of gluten-free bread. Transglutaminase has been shown to improve the dough viscoelasticity and decrease crumb hardness (6.84-5.73 N) of the resulting bread. Cyclodextrinase also enhances dough viscoelasticity, resulting in an improvement of 53% in shape index and crumb firmness. Similarly, hydroxypropylmethylcellulose improves gas retention and water absorption of dough and reduces crumb hardening rate of the resulting bread, while carboxymethylcellulose significantly increases dough elasticity (60-70 BU) and bread volume (230-267 cm(3)/100 g bread).

Changes in protein conformation and surface hydrophobicity upon peroxidase-catalyzed cross-linking of apo-α-lactalbumin

In this study, we explore the effect of peroxidase-catalyzed cross-linking on the molecular conformation of apo-α-lactalbumin (apo-α-LA) and the resulting changes in protein surface hydrophobicity. In studying conformational changes, we distinguish between early stages of the reaction ("partial cross-linking"), in which only protein oligomers (10(6) Da > Mw ≥ 10(4) Da) are formed, and a later stage ("full cross-linking"), in which larger protein particles (Mw ≥ 10(6) Da) are formed. Partial cross-linking induces a moderate loss of α-helical content. Surprisingly, further cross-linking leads to a partial return of α-helices that are lost upon early cross-linking. At the same time, for partially and fully cross-linked apo-α-LA, almost all tertiary structure is lost. The protein surface hydrophobicity first increases for partial cross-linking, but then decreases again at full cross-linking. Our results highlight the subtle changes in protein conformation and surface hydrophobicity of apo-α-LA upon peroxidase-catalyzed cross-linking.

Transglutaminases: recent achievements and new sources

Transglutaminases are a family of enzymes (EC 2.3.2.13), widely distributed in various organs, tissues, and body fluids, that catalyze the formation of a covalent bond between a free amine group and the γ-carboxamide group of protein or peptide-bound glutamine. Besides forming these bonds, that exhibit high resistance to proteolytic degradation, transglutaminases also form extensively cross-linked, generally insoluble, protein biopolymers that are indispensable for the organism to create barriers and stable structures. The extremely high cost of transglutaminase of animal origin has hampered its wider application and has initiated efforts to find an enzyme of microbial origin. Since the early 1990s, many microbial transglutaminase-producing strains have been found, and production processes have been optimized. This has resulted in a rapidly increasing number of applications of transglutaminase in the food sector. However, applications of microbial transglutaminase in other sectors have also been explored, but in a much lesser extent. Our group has identified a transglutaminase in the oomycete Phytophthora cinnamomi, which is able to induct defense responses and disease-like symptoms. In this mini-review, we report the achievements in this area in order to illustrate the importance and the versatility of transglutaminases.

A novel approach for improving the yield of Bacillus subtilis transglutaminase in heterologous strains

The transglutaminase (BTG) from Bacillus subtilis is considered to be a new type of transglutaminase for the food industry. Given that the BTG gene only encodes a mature peptide, the expression of BTG in heterologous microbial hosts could affect their normal growth due to BTG's typical transglutaminase activity which can catalyze cross-linking of proteins in the cells. Therefore, we developed a novel approach to suppress BTG activity and reduce the toxicity on microbial hosts, thus improving BTG yield. Genes encoding the respective regions of transglutaminase propeptide from seven species of Streptomyces were fused to the N-terminal of the BTG gene to produce fusion proteins. We found that all the fused propeptides could suppress BTG activity. Importantly, BTG activity could be completely restored after the removal of the propeptides by proteolytic cleavage. Of the seven propeptides tested, the propeptide proD from Streptomyces caniferus had the strongest suppressive effect on BTG activity (70 % of the activity suppressed). Moreover, fusion protein proD-BTG (containing proD) also exhibited the highest yield which was more than twofold of the expression level of BTG in an active form in Escherichia coli. Secretion expression of BTG and proD-BTG in Corynebacterium glutamicum further showed that our novel approach was suitable for the efficient BTG expression, thus providing a valuable platform for further optimization of large-scale BTG production.

Transglutaminase-induced crosslinking of gelatin-calcium carbonate composite films

The effects of transglutaminase (TGase) on the rheological profiles and interactions of gelatin-calcium carbonate solutions were studied. In addition, mechanical properties, water vapour permeability and microstructures of gelatin-calcium carbonate films were also investigated and compared. Fluorescence data suggested that the interaction of TGase and gelation-calcium carbonate belonged to a static quenching mechanism, and merely one binding site between TGase and gelatin-calcium carbonate was identified. Moreover, differential scanning calorimetry (DSC), the mechanical properties and the water vapour permeability studies revealed that TGase favoured the strong intramolecular polymerisation of the peptides in gelatin. The microstructures of the surfaces and cross sections in gelatin-calcium carbonate films were shown by scanning electron microscope (SEM) micrographs. The results of the fourier transform infrared spectroscopy (FTIR) indicated that TGase caused conformational changes in the proteins films. Therefore, TGase successfully facilitated the formation of gelatin-calcium carbonate composite films.

Biomimetic materials for medical application through enzymatic modification

Living organisms synthesize functional materials, based on proteins and polysaccharides, using enzyme-catalyzed reactions. According to the biomimetic approach, biomaterial matrices for tissue engineering are designed to be able to mimic the properties and the functions of the extracellular matrix (ECM). In this chapter, the most significant research efforts dedicated to the study and the preparation of biomimetic materials through enzymatic modifications were reviewed. The functionalizations of different polymeric matrices obtained through the catalytic activity of two enzymes (Transglutaminase, TGase and Tyrosinase, TYRase) were discussed. Specifically, the biomimetic applications of TGase and TYRase to confer appropriate biomimetic properties to the biomaterials, such as the possibility to obtain in situ gelling hydrogels and the incorporation of bioactive molecules (growth factors) and cell-binding peptides into the scaffolds, were reviewed.

Characterization of recombinant Zea mays transglutaminase expressed in Pichia pastoris and its impact on full and non-fat yoghurts

BACKGROUND

Transglutaminases catalyze post-translational modification of proteins by ε-(γ-glutamyl) links and covalent amide bonds. Research on properties and applications of plant transglutaminases is less developed than in animals and micro-organisms. In a previous study, optimized Zea mays transglutaminase was purified from recombinant Pichia pastoris strain. The main objective of the present study was to characterize this enzyme and assess its effect on the properties of yoghurt.

RESULTS

The purified recombinant transglutaminase presented a Km of 3.98 µmol L(-1) and a Vmax of 2711 min(-1) by the fluorometric method. The enzyme was stable after incubation for 30 min below 50 °C and over a broad pH range of 5-8 at -20 °C for 12 h. The results showed that the crosslinking reaction catalyzed by this enzyme could effectively improve the properties of full and non-fat yoghurts. Also, the properties of non-fat yoghurt could be improved similar to the full-fat product by recombinant transglutaminase.

CONCLUSION

The application of recombinant transglutaminase in yoghurt indicated that this enzyme could be used as a substitute for microbial transglutaminase in the production of yoghurt, thus providing experimental evidence for the future application of plant transglutaminases in the food industry.

Nanoscale understanding of thermal aggregation of whey protein pretreated by transglutaminase

Nanoscale structures of whey protein isolate (WPI) pretreated by microbial transglutaminase (mTGase) and subsequent heating were studied in this work and were correlated to zeta-potential, surface hydrophobicity, thermal denaturation properties, and macroscopic turbidity and viscosity. Dispersions of 5% w/v WPI were pretreated by individual or sequential steps of preheating at 80 °C for 15 min and mTGase, used at 2.0-10.2 U/g WPI for 1-15 h, before adjustment of the pH to 7.0 and to 0-100 mM NaCl for heating at 80 °C for 15 and 90 min. The zeta potential and surface hydrophobicity of WPI increased after all pretreatment steps. Preheating increased cross-linking reactivity of WPI by mTGase, corresponding to significantly increased denaturation temperature. Particle size analysis and atomic force microscopy revealed that structures of sequentially pretreated WPI remained stable after heating at 100 mM NaCl, corresponding to transparent dispersions. Conversely, WPI pretreated by one step aggregated at only 100 mM NaCl and resulted in turbid dispersions. Besides reporting a practical approach to produce transparent beverages, nanoscale phenomena in the present study are important for understanding whey protein structures in relevant applications.

Enzyme-catalyzed protein crosslinking

The process of protein crosslinking comprises the chemical, enzymatic, or chemoenzymatic formation of new covalent bonds between polypeptides. This allows (1) the site-directed coupling of proteins with distinct properties and (2) the de novo assembly of polymeric protein networks. Transferases, hydrolases, and oxidoreductases can be employed as catalysts for the synthesis of crosslinked proteins, thereby complementing chemical crosslinking strategies. Here, we review enzymatic approaches that are used for protein crosslinking at the industrial level or have shown promising potential in investigations on the lab-scale. We illustrate the underlying mechanisms of crosslink formation and point out the roles of the enzymes in their natural environments. Additionally, we discuss advantages and drawbacks of the enzyme-based crosslinking strategies and their potential for different applications.

Aspects of physical and chemical alterations to proteins during food processing – some implications for nutrition

In this paper, we give an overview of our research exploring the impact of physical and chemical processing on food proteins. There are three themes, applied to the proteins of wheat, soya, egg and dairy foods. Firstly, the impact of the Maillard reaction on food proteins is discussed, with a particular focus on how the reactions might be harnessed to manipulate food texture. Secondly, the potential of enzymatic protein-protein crosslinking is considered, especially the enzyme transglutaminase. Thirdly, the broader question of how the aggregation of proteins within a food is altered by chemical and physical modification and how, in turn, this might impact on the overall nutritional quality of the food is considered.

Susceptibility of the individual caseins in reconstituted skim milk to cross-linking by transglutaminase: influence of temperature, pH and mineral equilibria

The susceptibility of total casein and the individual caseins in reconstituted skim milk to transglutaminase (TGase)-induced cross-linking was studied as a function of incubation temperature (5–40 °C), pH (5·0–7·0) and mineral addition. Within the ranges studied, the level of total casein cross-linked increased with increasing temperature, pH and concentration of added trisodium citrate, whereas adding calcium chloride had the opposite effect. These effects can be largely related to the effects of these parameters on TGase activity. In addition, the parameters were also found to influence the susceptibility of κ-casein, and to a lesser extent β-casein, to cross-linking, whereas the susceptibility of αs1-casein was not affected. The susceptibility of κ-casein to cross-linking increased with increasing temperature and calcium chloride addition, but decreased with increasing pH and citrate content, whereas the susceptibility of β-casein to TGase-induced cross-linking decreased with increasing temperature, but was not affected by other parameters. These findings highlight the fact that selection of environmental conditions during cross-linking can be applied to tailor the surface, and hence possibly colloidal stability, of casein micelles in TGase-treated milk.

Crosslinking with transglutaminase does not change metabolic effects of sodium caseinate in model beverage in healthy young individuals

Background

Postprandial metabolic and appetitive responses of proteins are dependent on protein source and processing technique prior to ingestion. Studies on the postprandial effects of enzymatic crosslinking of milk proteins are sparse. Our aim was to study the effect of transglutaminase (TG)-induced crosslinking of sodium caseinate on postprandial metabolic and appetite responses. Whey protein was included as reference protein.

Methods

Thirteen healthy individuals (23.3 ± 1.1 y, BMI 21.7 ± 0.4 kg/m²) participated in a single-blind crossover design experiment in which the subjects consumed three different isovolumic (500 g) pourable beverages containing either sodium caseinate (Cas, 29 g), TG-treated sodium caseinate (Cas-TG, 29 g) or whey protein (Wh, 30 g) in a randomized order. Blood samples were collected at baseline and for 4 h postprandially for the determination of plasma glucose, insulin and amino acid (AA) concentrations. Gastric emptying (GE) was measured using the ¹³ C-breath test method. Appetite was assessed using visual analogue scales.

Results

All examined postprandial responses were comparable with Cas and Cas-TG. The protein type used in the beverages was reflected as differences in plasma AA concentrations between Wh and Cas, but there were no differences in plasma glucose or insulin responses. A tendency for faster GE rate after Wh was detected. Appetite ratings or subsequent energy intake did not differ among the protein beverages.

Conclusions

Our results indicate that the metabolic responses of enzymatically crosslinked and native sodium caseinate in a liquid matrix are comparable, suggesting similar digestion and absorption rates and first pass metabolism despite the structural modification of Cas-TG.

Structure modification of a milk protein-based model food affects postprandial intestinal peptide release and fullness in healthy young men

Physico-chemical and textural properties of foods in addition to their chemical composition modify postprandial metabolism and signals from the gastrointestinal tract. Enzymatic cross-linking of protein is a tool to modify food texture and structure without changing nutritional composition. We investigated the effects of structure modification of a milk protein-based model food and the type of milk protein used on postprandial hormonal, metabolic and appetitive responses. Healthy males (n 8) consumed an isoenergetic and isovolumic test product containing either whey protein (Wh, low-viscous liquid), casein (Cas, high-viscous liquid) or Cas protein cross-linked with transglutaminase (Cas-TG, rigid gel) in a randomised order. Blood samples were drawn for plasma glucose, insulin, cholecystokinin (CCK), glucagon-like peptide 1 and peptide YY analysis for 4 h. Appetite was assessed at concomitant time points. Cas and Wh were more potent in lowering postprandial glucose than Cas-TG during the first hour. Insulin concentrations peaked at 30 min, but the peaks were more pronounced for Cas and Wh than for Cas-TG. The increase in CCK was similar for Cas and Wh in the first 15 min, whereas for Cas-TG, the CCK release was significantly lower, but more sustained. The feeling of fullness was stronger after the consumption of Cas-TG than after the consumption of Cas and Wh. The present results suggest that food structure is more effective in modulating the postprandial responses than the type of dairy protein used. Modification of protein-based food structure could thus offer a possible tool for lowering postprandial glucose and insulin concentrations and enhancing postprandial fullness.