Microbial transglutaminase and its application in the food industry. A review

The extremely high costs of manufacturing transglutaminase from animal origin (EC 2.3.2.13) have prompted scientists to search for new sources of this enzyme. Interdisciplinary efforts have been aimed at producing enzymes synthesised by microorganisms which may have a wider scope of use. Transglutaminase is an enzyme that catalyses the formation of isopeptide bonds between proteins. Its cross-linking property is widely used in various processes: to manufacture cheese and other dairy products, in meat processing, to produce edible films and to manufacture bakery products. Transglutaminase has considerable potential to improve the firmness, viscosity, elasticity and water-binding capacity of food products. In 1989, microbial transglutaminase was isolated from Streptoverticillium sp. Its characterisation indicated that this isoform could be extremely useful as a biotechnological tool in the food industry. Currently, enzymatic preparations are used in almost all industrial branches because of their wide variety and low costs associated with their biotechnical production processes. This paper presents an overview of the literature addressing the characteristics and applications of transglutaminase.

Raw-appearing Restructured fish models made with Sodium alginate or Microbial transglutaminase and effect of chilled storage

Restructuring by adding Sodium Alginate or Microbial Transglutaminase (MTGase) using cold gelation technology make it possible to obtain many different raw products from minced and/or chopped fish muscle that are suitable for being used as the basis of new restructured products with different physicochemical properties and even different compositions. Special consideration must be given to their shelf-life and the changes that may take place during chilling, both in visual appearance and physicochemical properties. After chilled storage, the restructured models made with different muscular particle size and composition at low temperature (5 °C), it was observed that microbial growth limited the shelf-life to 7-14 days. Mechanical properties increased (p < 0.05) during that time, and higher values were observed in samples elaborated by joining small muscle particle size than in those elaborated by homogenization. There was no clear increase in the cooking yield and purge loss, and no significant colour change (p > 0.05) was detected during storage.

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.

Infrared study of structural characteristics of Frankfurters formulated with olive oil-in-water emulsions stabilized with casein as pork backfat replacer

This article reports an infrared spectroscopic (FT-IR) study on lipids and protein structural characteristics in frankfurters as affected by an emulsified olive oil stabilizing system used as a pork backfat replacer. The oil-in-water emulsions were stabilized with sodium caseinate, without (F/SC) and with microbial transglutaminase (F/SC+MTG). Proximate composition and textural characteristics were also evaluated. Frankfurters F/SC+MTG showed the highest (P < 0.05) hardness and lowest (P < 0.05) adhesiveness. These products also showed the lowest (P < 0.05) half-bandwidth of the 2922 cm(-1) band, which could be related to the fact that the lipid chain was more orderly than that in the frankfurters formulated with animal fat and F/SC. The spectral results revealed modifications in the amide I band profile when the olive oil-in-water emulsion replaced animal fat. This fact is indicative of a greater content of aggregated intermolecular β-sheets. Structural characteristics in both proteins and lipids could be associated with the specific textural properties of frankfurters.

Effects of microfluidization treatment and transglutaminase cross-linking on physicochemical, functional, and conformational properties of peanut protein isolate

Peanut protein isolate (PPI) was treated by high-pressure microfluidization (40, 80, 120, and 160 MPa) and/or transglutaminase (TGase) cross-linking. It was found that individual microfluidization at 120 MPa was more effective in improving the solubility, emulsifying properties, and surface hydrophobicity of PPI than at other pressures (e.g., 40, 80, or 160 MPa). Individual TGase cross-linking also effectively changed the physicochemical and functional properties of PPI. Microfluidization (120 MPa) or TGase cross-linking caused the unfolding of PPI structure, resulting in the decrease of α-helix and β-turns levels and the increase of β-sheet and random coil levels, as proved by Fourier transform infrared (FTIR) and circular dichroism (CD) spectra. Compared with individual treatments, microfluidization followed by TGase cross-linking significantly (p < 0.05) improved the emulsion stability during long-term storage (20 days). Moreover, the combined treatments led to looser structure of PPI and resulted in more obvious changes in physicochemical properties.

Effect of cooking on physical and sensory properties of fresh yellow alkaline noodles prepared by partial substitution of wheat flour with soy protein isolate and treated with cross-linking agents

Yellow alkaline noodles (YAN) prepared by partial substitution of wheat flour with soy protein isolate and treated with microbial transglutaminase (MTG) and ribose were investigated during cooking. Cooking caused an increase in lightness but a decrease in redness and yellowness, pH, tensile strength and elasticity values of noodles. The extents of these changes were influenced by formulation and cross-linking treatments. The pH and lightness for YAN-ribose were lowest but the yellowness and redness were the highest whilst the tensile strength and elasticity values remained moderate. For YAN-MTG, the color and pH values were moderate, but tensile strength and elasticity values were the highest. YAN prepared with both cross-linking agents had physical values between YAN-ribose and YAN-MTG. Although certain sensory parameters showed differences in score, the overall acceptability of all 10-min-cooked YAN was similar. It is possible to employ cross-linking agents to improve physical properties of cooked YAN.

Emulsifying properties of the transglutaminase-treated crosslinked product between peanut protein and fish (Decapterus maruadsi) protein hydrolysates

BACKGROUND

Defatted peanut meal, a protein-rich by-product from the oil extraction industry, is underutilised owing to its inferior functional properties. In this study, transglutaminase (TGase) crosslinking and proteolysis were used to improve the emulsifying properties of peanut protein isolate (PPI) extracted from the meal. PPI and PPI hydrolysate (PPIH) were conjugated separately with fish (Decapterus maruadsi) protein hydrolysate (DPH), catalysed by TGase to obtain improvements in the emulsifying properties.

RESULTS

Analyses by electrophoresis and high-performance liquid chromatography indicated that polymers were formed in all TGase-treated samples. In emulsions of PPIH, PPI-DPH and PPIH-DPH the volume/surface average particle diameter (d(32) ), creaming and instability phenomenon were decreased and the zeta-potential was increased after TGase treatment, showing improved emulsifying activity and emulsion stability. In the case of PPI, TGase treatment had no effect on the emulsifying activity, but the emulsion stability of TGase-treated PPI was improved.

CONCLUSION

The study showed that TGase crosslinking and proteolysis could improve the emulsifying properties of PPI, while proteolysis followed by TGase crosslinking proved more efficient. The emulsifying properties of the heterologous protein systems of PPI-DPH and PPIH-DPH were also improved by TGase treatment.

Cross-linking of hen egg white lysozyme by microbial transglutaminase under high hydrostatic pressure: localization of reactive amino acid side chains

After incubation of hen egg white lysozyme (HEWL) with microbial transglutaminase (mTG) under high pressure (400-600 MPa for 30 min at 40 °C), the formation of HEWL oligomers was observed via SDS electrophoresis. At atmospheric pressure, HEWL represents no substrate for mTG. Likewise, enzymatic treatment following a pretreatment with high pressure did not lead to oligomerization. Reactive amino acid side chains were identified by peptide mapping after tryptic digestion using RP-HPLC with ESI-TOF-MS. Isopeptide-containing peptide fragments were found only in HEWL samples simultaneously treated with enzyme and pressure. It was found that mTG exclusively cross-links HEWL under high pressure by formation of an isopeptide between lysine at position 1 and glutamine at position 121 in the peptide chain. Therefore, a pressure-induced partial and reversible unfolding of the protein with exposure of lysine and glutamine side chains has to occur, resulting in a site-directed oligomerization of HEWL by mTG. The enzymatic modification of HEWL by mTG under high pressure offers interesting perspectives for further functionalization reactions.

Nutritional Effects of Mechanically Deboned Chicken Meat and Soybean Proteins Cross-linking by Microbial Transglutaminase

This work studied the nutritional effects of protein cross-linking as mediated by microbial transglutaminase (TGase) using rats as biological models. Rats were divided into six groups that received diets containing casein (standard protein diet), cross-linked meat protein (CMP), meat protein (MP), cross-linked soy protein, or soy protein (SP) as the protein sources of their diets, which were compared against an aproteic diet (basal diet). The cross-linking process showed a significant (p < 0.05) impact on the true digestibility (TD) of meat and SPs, decreasing it for the first and increasing it for the second. As a consequence, the TD of modified SP became similar to that observed for CMP, although, the biological value, net protein utilization, net protein ratio, and protein retention efficiency values of meat and SPs were not affected in the process. These results suggest that the use of TGase for the reticulation of isolated SP can improve its nutritional quality.