Acid-induced gelation of enzymatically modified, preheated whey proteins

Whey filtration: a review of products, application, and pretreatment with transglutaminase enzyme

In the cheese industry, whey, which is rich in lactose and proteins, is underutilized, causing adverse environmental impacts. The fractionation of its components, typically carried out through filtration membranes, faces operational challenges such as membrane fouling, significant protein loss during the process, and extended operating times. These challenges require attention and specific methods for optimization and to increase efficiency. A promising strategy to enhance industry efficiency and sustainability is the use of enzymatic pre-treatment with the enzyme transglutaminase (TGase). This enzyme plays a crucial role in protein modification, catalyzing covalent cross-links between lysine and glutamine residues, increasing the molecular weight of proteins, facilitating their retention on membranes, and contributing to the improvement of the quality of the final products. The aim of this study is to review the application of the enzyme TGase as a pretreatment in whey protein filtration. The scope involves assessing the enzyme's impact on whey protein properties and its relationship with process performance. It also aims to identify both the optimization of operational parameters and the enhancement of product characteristics. This study demonstrates that the application of TGase leads to improved performance in protein concentration, lactose permeation, and permeate flux rate during the filtration process. It also has the capacity to enhance protein solubility, viscosity, thermal stability, and protein gelation in whey. In this context, it is relevant for enhancing the characteristics of whey, thereby contributing to the production of higher quality final products in the food industry. © 2023 Society of Chemical Industry.

Fractal Dimension Analysis of Texture Formation of Whey Protein-Based Foods

Whey protein in the form of isolate or concentrate is widely used in food industries due to its functionality to form gel under certain condition and its nutritive value. Controlling or manipulating the formation of gel aggregates is used often to evaluate food texture. Many researchers made use of fractal analysis that provides the quantitative data (i.e., fractal dimension) for fundamentally and rationally analyzing and designing whey protein-based food texture. This quantitative analysis is also done to better understand how the texture of whey protein-based food is formed. Two methods for fractal analysis were discussed in this review: image analysis (microscopy) and rheology. These methods, however, have several limitations which greatly affect the accuracy of both fractal dimension values and types of aggregation obtained. This review therefore also discussed problem encountered and ways to reduce the potential errors during fractal analysis of each method.

Effects of high intensity ultrasound on acid-induced gelation properties of whey protein gel

Pre-heated whey protein isolate (WPI) solution (10% w/v, 85°C for 30min) was prepared and subjected to high-intensity ultrasound (HUS, 20kHz) at different durations (5-40min) before acidification to determine the effects of HUS on glucono-δ-lactone (GDL)-induced gelation properties of whey protein gel. Results showed that HUS reduced the particle size and increased surface free sulfhydryl groups of pre-heated whey protein solution. Free sulfhydryl (-SH) content of the acid-induced WPI gels (GIWG) and protein solubility in presence of 8M urea were significantly reduced (P<0.05) by HUS (20 or 40min), indicating that HUS facilitated formation of more disulfide bonds during/after the gelation process. HUS significantly increased (P<0.05) the water holding capacity (WHC), gel strength, gel firmness (G') as well as the frequency dependence of GIWG. The WHC, gel strength and gel firmness were positively correlated with surface free -SH content of pre-heated WPI and negatively correlated with particle size of pre-heated WPI and free -SH content of GIWG. The results indicated that high intensity ultrasound could be used for modifying whey protein to improve its gelling properties.

Silk protein-based hydrogels: Promising advanced materials for biomedical applications

Hydrogels are a class of advanced material forms that closely mimic properties of the soft biological tissues. Several polymers have been explored for preparing hydrogels with structural and functional features resembling that of the extracellular matrix. Favourable material properties, biocompatibility and easy processing of silk protein fibers into several forms make it a suitable material for biomedical applications. Hydrogels made from silk proteins have shown a potential in overcoming limitations of hydrogels prepared from conventional polymers. A great deal of effort has been made to control the properties and to integrate novel topographical and functional characteristics in the hydrogel composed from silk proteins. This review provides overview of the advances in silk protein-based hydrogels with a primary emphasis on hydrogels of fibroin. It describes the approaches used to fabricate fibroin hydrogels. Attempts to improve the existing properties or to incorporate new features in the hydrogels by making composites and by improving fibroin properties by genetic engineering approaches are also described. Applications of the fibroin hydrogels in the realms of tissue engineering and controlled release are reviewed and their future potentials are discussed.

STATEMENT OF SIGNIFICANCE

This review describes the potentiality of silk fibroin hydrogel. Silk Fibroin has been widely recognized as an interesting biomaterial. Due to its properties including high mechanical strength and excellent biocompatibility, it has gained wide attention. Several groups are exploring silk-based materials including films, hydrogels, nanofibers and nanoparticles for different biomedical applications. Although there is a good amount of literature available on general properties and applications of silk based biomaterials, there is an inadequacy of extensive review articles that specifically focus on silk based hydrogels. Silk-based hydrogels have a strong potential to be utilized in biomedical applications. Our work is an effort to highlight the research that has been done in the area of silk-based hydrogels. It aims to provide an overview of the advances that have been made and the future course available. It will provide an overview of the silk-based hydrogels as well as may direct the readers to the specific areas of application.

The self-assembly, aggregation and phase transitions of food protein systems in one, two and three dimensions

The aggregation of proteins is of fundamental relevance in a number of daily phenomena, as important and diverse as blood coagulation, medical diseases, or cooking an egg in the kitchen. Colloidal food systems, in particular, are examples that have great significance for protein aggregation, not only for their importance and implications, which touches on everyday life, but also because they allow the limits of the colloidal science analogy to be tested in a much broader window of conditions, such as pH, ionic strength, concentration and temperature. Thus, studying the aggregation and self-assembly of proteins in foods challenges our understanding of these complex systems from both the molecular and statistical physics perspectives. Last but not least, food offers a unique playground to study the aggregation of proteins in three, two and one dimensions, that is to say, in the bulk, at air/water and oil/water interfaces and in protein fibrillation phenomena. In this review we will tackle this very ambitious task in order to discuss the current understanding of protein aggregation in the framework of foods, which is possibly one of the broadest contexts, yet is of tremendous daily relevance.

Changes in morphology and activity of transglutaminase following cross-linking and immobilization on a polypropylene microporous membrane

Transglutaminase (TGase) was cross-linked with glutaraldehyde, and cross-linked crystalline transglutaminase was immobilized on a polypropylene microporous membrane by UV-induced grafting. Immobilized enzyme activity were calculated to be 0.128 U/cm² polypropylene microporous membrane. The microstructure and enzyme characteristics of free, cross-linked and immobilized transglutaminase were compared. The optimum temperature of free transglutaminase was determined to be approximately 40 °C, while cross-linking and immobilization resulted in an increase to approximately 45 °C and 50 °C. At 60 °C, immobilized, cross-linked and free transglutaminase retained 91.7 ± 1.20%, 63.2 ± 1.05% and 37.9 ± 0.98% maximum activity, respectively. The optimum pH was unaffected by the state of transglutaminase. However, the thermal and pH stabilities of cross-linked and immobilized transglutaminase were shown to increase.

Effect of hydrophilic and hydrophobic interactions on the rheological behavior and microstructure of a ternary cellulose acetate system

The effect of hydrophilic and hydrophobic interactions on the rheological and microstructural behavior of cellulose acetate (CA) in a ternary CA, N,N-dimethylacetamide (DMA), nonsolvent (alcohol) system was examined. Increasing nonsolvent concentration increased the viscosity and dynamic viscoelastic properties of the system. At a critical nonsolvent concentration, a sol-gel transition was observed, which was dependent on nonsolvent structure. Increasing the available hydrogen bonding groups within the nonsolvent led to higher modulus (stronger gels) and a sol-gel transition at lower nonsolvent concentration. Likewise, increasing the alkyl chain length (hydrophobicity) of the nonsolvent also enhanced the viscoelastic properties; however, hydrogen bonding, specifically the ability to hydrogen bond donate was critical for gel formation. For all gels studied, the elastic modulus shifts to higher values with increasing hydrophilicity and hydrophobicity of the nonsolvent and exhibits a power-law behavior with nonsolvent content. All of the gels exhibit similar fractal dimensions; however, confocal images of the different systems reveal distinct differences. Increasing the hydrophilicity of the nonsolvent led to a more uniform denser gel microstructure, whereas increasing the hydrophobicity resulted in a larger more heterogeneous network structure despite the increase in moduli.

Viscoelastic Behavior of Cellulose Acetate in a Mixed Solvent System

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.

Influence of Processing on Functionality of Milk and Dairy Proteins

The inherent physical functionality of dairy ingredients makes them useful in a range of food applications. These functionalities include their solubility, water binding, viscosity, gelation, heat stability, renneting, foaming, and emulsifying properties. The suitability of dairy ingredients for an application can be further tailored by altering the structure of the proteins using appropriate processes. The processes discussed include physical modification (heat treatment, acidification, addition of mineral slats, homogenization, and shear), enzymatic modification (renneting, hydrolysis, and transglutamination), and chemical modification (use of chemical agents and the Maillard reaction). Emerging food processes (high pressure and ultrasound) are also discussed. The challenges for using dairy ingredients for the delivery of nutrients and bioactive components, while maintaining physical functionality, are also highlighted. There is a need for continued research into the fundamental aspects of milk proteins and their responses to various stresses for further differentiation of milk products and for the delivery of ingredients with consistent quality for target applications.

Enzymatic Cross-Linking of β-Lactoglobulin: Conformational Properties Using FTIR Spectroscopy

In this study, we use FTIR spectroscopy to probe the conformational changes of beta-lactoglobulin (beta-LG)-the main constituent of whey proteins-as subjected to enzymatic cross-linking by transglutaminase. We investigate both the amide I region (1600-1700 cm(-1)) and the C-H stretching region (2800-3100 cm(-1)). In the amide I region, spectra of denatured conformations of beta-LG, known to be necessary for cross-linking, differ according to the denaturation procedure, i.e., chemical or thermal treatment. Denaturation by chemical denaturants, dithiothreitol (DTT) or beta-mercaptoethanol, show no effect on the alpha-helix, while shifting the monomer dimer equilibrium toward higher monomer concentration. On the other hand, denaturing by thermal treatment dissociates the beta-sheets in the native structure, leading to new intermolecular beta-sheets being formed. Preheated then enzyme cross-linked beta-LG molecules show very similar spectra in the amide I region to the molecules with no cross-linking, indicating minimal effects of the cross-links on the carbonyl stretching mode. However, chemically denatured (using beta-mercaptoethanol) then enzyme cross-linked beta-LG molecules show noticeable diminution in the alpha-helix band and formation of strong hydrogen-bonded intermolecular beta-sheets. In the C-H stretching region, preheated then enzyme cross-linked beta-LG molecules exhibit a different degree of exposure of aliphatic amino acids due to the enzyme action. The same behavior is observed for DTT-treated then enzyme cross-linked beta-LG molecules. Generally, the changes in the C-H stretching region clearly indicate that hydrophobic interactions are altered upon enzymatic cross-linking.