Microbial Transglutaminase: General Characteristics and Performance in Food Processing Technology

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

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

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

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

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.

Effects of transglutaminase glycosylated soy protein isolate on its structure and interfacial properties

BACKGROUNDS

The structural and interfacial properties of soybean protein isolate (SPI) after glycosylation by the transglutaminase method were studied. It is hoped that preliminary explorations will find a new food ingredient and broader application of SPI in the food industry.

RESULTS

The contents of free amino proves that transglutaminase can insert glucosamine into SPI through its transamination, and realize the enzymatic glycosylated SPI. The results of structure properties showed that a decrease in the content of the α-helical structure indicates that the rigid structure of the protein is opened and the flexibility is increased. The blue shift of the maximum fluorescence intensity of soy protein isolate-glucosamine with transglutaminase (SPI-G) indicates the formation of a new substance; scanning electron microscopy shows that the SPI-G powder can be seen at a magnification of 2000×, and the protein structure becomes soft. The results of interfacial properties found that enzymatic protein glycosylation exposes the internal hydrophobic groups of SPI, resulting in increased surface hydrophobicity, increased emulsification and emulsification stability, and reduced surface tension.

CONCLUSION

It shows that SPI-G effectively improves the interfacial properties of SPI, providing a theoretical basis for the application of enzymatic glycosylation of SPI in the food industry. © 2021 Society of Chemical Industry.

Intein-mediated intracellular production of active microbial transglutaminase in Corynebacterium glutamicum

The microbial transglutaminase (mTGase) from Streptomyces mobaraense is widely used in the food industry. However, recombinant production of mTGase is challenging because the mTGase is synthesized as an inactive zymogen, and needs to be activated by proteolytic processing. In this study, self-cleaving intein Ssp DnaB was applied to activate the mTGase in Corynebacterium glutamicum. Premature cleavage of intein Ssp DnaB also occurred, but instead of suppressing premature cleavage, this phenomenon was used to produce active mTGase in C. glutamicum. Both SDS-PAGE analysis and mTGase activity assays indicated that the premature cleavage of intein Ssp DnaB activated the mTGase intracellularly in C. glutamicum. The subsequent N-terminal amino acid sequencing and site-directed mutagenesis studies further showed that the premature cleavage activated the mTGase intracellularly, in a highly specific manner. Moreover, the growth performance of C. glutamicum was not noticeably affected by the intracellular expression of active mTGase. Finally, the mTGase was produced in a 2 L bioreactor, with activity up to 49 U/mL, the highest intracellular mTGase activity ever reported. Using premature cleavage of intein Ssp DnaB to activate mTGase in C. glutamicum, we produced high levels of intracellular active mTGase. Moreover, this approach did not require any further processing steps, such as protease treatment or lengthy incubation, greatly simplifying the production of active mTGase. This efficient and simple approach has great potential for the large-scale industrial production of active mTGase.

Transglutaminases: part I-origins, sources, and biotechnological characteristics

The transglutaminases form a large family of intracellular and extracellular enzymes that catalyze cross-links between protein molecules. Transglutaminases crosslinking properties are widely applied to various industrial processes, to improve the firmness, viscosity, elasticity, and water-holding capacity of products in the food and pharmaceutical industries. However, the extremely high costs of obtaining transglutaminases from animal sources have prompted scientists to search for new sources of these enzymes. Therefore, research has been focused on producing transglutaminases by microorganisms, which may present wider scope of use, based on enzyme-specific characteristics. In this review, we present an overview of the literature addressing the origins, types, reactions, and general characterizations of this important enzyme family. A second review will deal with transglutaminases applications in the area of food industry, medicine, pharmaceuticals and biomaterials, as well as applications in the textile and leather industries.

Effect of microbial transglutaminase cross-linking on the quality characteristics and potential allergenicity of tofu

Microbial transglutaminase (MTGase) has been developed as a new tofu coagulant in recent years due to its good hydrophilicity, high catalytic activity, and strong thermal stability. This study aimed to investigate the effect of MTGase on the physicochemical properties and immunoreactivity of tofu relative to conventional coagulants [brine and glucono-δ-lactone (GDL)]. Structural changes of the MTGase cross-linked soymilk protein were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD) spectroscopy, ultraviolet (UV) absorption spectroscopy, and fluorescence spectroscopy. The IgE-binding capacity of MTGase cross-linked proteins was tested by enzyme-linked immunosorbent assay (ELISA). The physicochemical properties, quality characteristics, and surface microstructures of five different types of tofu were determined by the Kjeldahl nitrogen method, texture analysis, and scanning electron microscopy (SEM). The digestibility of tofu was evaluated in vitro by simulated gastrointestinal (GIS) digestion. A cell sensitization experiment was performed in vitro to evaluate the capability of tofu digestion products to induce the release of bioactive mediators from human basophil leukemia (KU812) cells. Results indicated that MTGase significantly changed the advanced structure of the soymilk protein. Compared with tofu without MTGase, the composite coagulant tofu containing MTGase exhibited better quality. MTGase improved the water-holding capacity (WHC) of the internal mesh structure and increased the yield of tofu. The digestion products of the composite coagulant tofu, especially the GDL plus MTGase tofu, induced KU812 cells to release fewer bioactive mediators compared with those of MTGase-free tofu. MTGase can not only improve the quality of conventional coagulant tofu but also reduce the potential allergenicity of tofu to a certain extent.

Expression of Zea mays transglutaminase in Pichia pastoris under different promoters and its impact on properties of acidified milk protein concentrate gel

BACKGROUND

Transglutaminase (TGase) catalyzes post-translational modification of proteins by γ-glutamyl-ϵ-lysine chain links, covalent conjugation of polyamines, and deamidation. Zea mays TGase (TGZ) is a plant TGase with potential application prospects in the food industry. In this study, two promoter types, P_FLD1 and P_TEF1 , were compared to improve the expression of TGZ, and the cross-linking effect of recombinant TGZ on the properties of acid-induced milk protein concentrate (MPC) gel was assessed.

RESULTS

A higher expression of TGZ was obtained under the induction of P_FLD1 with a production of 635 U L^-1 . After purification using chromatography, TGZ activity was 0.4 U mg^-1 . The results indicated that TGZ treatment has effectively improved the textural properties of MPC gel at strength level and water-holding capacity. Optimal texture of MPC gel was achieved after TGZ treatment using 2 U g^-1 TGZ for 2 h at 35 °C and pH 7.

CONCLUSION

Comparative analysis of the promoters has greatly contributed to the production of TGZ in the industrial field. Furthermore, the modification of MPC gel texture by TGZ indicated that this recombinant enzyme has a practical value in dairy product, especially in yoghurt industry. © 2019 Society of Chemical Industry.

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.