Effect of transglutaminase on rennet-induced gelation of skim milk and soymilk mixtures

Transglutaminase cross-linking ovalbumin-flaxseed oil emulsion gels: Properties, microstructure, and performance in oxidative stability

This study prepared emulsion gels by modifying ovalbumin (OVA)-flaxseed oil (FSO) emulsions with transglutaminase (TGase) and investigated their properties, structure and oxidative stability under different enzyme reaction times. Here, we found prolonged reaction times led to the transformation of α-helix and β-turn into β-sheet and random coil. The elasticity, hardness and water retention of the emulsion gels increased significantly, but the water-holding capacity decreased when the reaction time exceeded 4 h. Confocal laser scanning microscope (CLSM) indicated extended enzyme reaction time fostered oil droplet aggregation with proteins. Emulsion gel reduced FSO oxidation, especially after 4 h of the enzyme reaction, the peroxide value (PV) of the emulsion gel was reduced by 29.16% compared to the control. In summary, the enzyme reaction time of 4 h resulted in the formation of a dense gel structure and enhanced oxidative stability. This study provides the potential applications in functional foods and biomedical fields.

Characteristics of the Mixed Yogurt Fermented from Cow-Soy Milk in the Presence of Transglutaminase

The mixed yogurt was fermented from Cow-Soy milk and modified by transglutaminase (TG). The effects of mixed milk and TG on the quality characteristics of mixed yogurt were investigated by texture characteristics, rheology (rheometer) and structure (scanning electron microscopy). The findings revealed that the mixed yogurt with 50% cow milk exhibited lower hardness, viscosity and consistency. Furthermore, when TG was added, the yogurt showed better rheological properties, sensory score and a more stable microstructure. Compared with the samples without TG modification, the viscosity and cohesiveness of the modified samples increased by 10% and 100%, respectively. The combination of cow milk and soy milk improved the texture of yogurt, and the TG addition further improved the physicochemical properties of yogurt. This finding provided a meaningful reference for the development of mixed yogurt with a suitable taste from animal and plant milk, and laid a basis for the practical application of mixed yogurt in the dairy industry, which will meet the requirements for dairy products for consumers in future.

Characterizing acidified and renneted gels with different soy milk and skim milk proportions

To understand the properties of differently acidified and renneted gels with different soy milk and skim milk proportions, mixed milks were prepared and treated using sequenced renneting then acidification at 4 °C, and the formation, spontaneous whey separation, and microstructure of the gels were monitored. The results showed that both acidification and renneting promoted gel formation in mixed milk and increased gel strength. In gels, the pH range was narrow (pH ≤ 5.2) at low soy milk proportion (25%) and low renneting degrees (0%, 25% and 50%), and the pH range was extended such that gels were formed with increasing soy milk proportion and renneting degree. When compared with pH, soy milk proportion and renneting degree influenced whey separation percentages more strongly. Soy milk significantly reduced whey separation percentages in gels, and gel strength was highest at 50% soy milk. Protein aggregates sizes increased with increasing soy milk proportion at the 75% renneting degree, and the pore sizes of skim milk-dominated gels was strongly influenced by acidification. These results help us understand mixed gel properties and provide valuable information for the manufacture of mixed fermented dairy products.

Transglutaminase in Foods and Biotechnology

Stabilization and reusability of enzyme transglutaminase (TGM) are important goals for the enzymatic process since immobilizing TGM plays an important role in different technologies and industries. TGM can be used in many applications. In the food industry, it plays a role as a protein-modifying enzyme, while, in biotechnology and pharmaceutical applications, it is used in mediated bioconjugation due to its extraordinary crosslinking ability. TGMs (EC 2.3.2.13) are enzymes that catalyze the formation of a covalent bond between a free amino group of protein-bound or peptide-bound lysine, which acts as an acyl acceptor, and the γ-carboxamide group of protein-bound or peptide-bound glutamine, which acts as an acyl donor. This results in the modification of proteins through either intramolecular or intermolecular crosslinking, which improves the use of the respective proteins significantly.

Clustering of Streptococcus thermophilus Strains to Establish a Relation between Exopolysaccharide Characteristics and Gel Properties of Acidified Milk

In situ produced extracellular polysaccharides (EPS) from lactic acid bacteria are generally known to affect the texture of fermented dairy products; however, the interplay between EPS and product properties is still poorly understood. The aim of this study was to establish a relationship between concentration and properties of EPS, and gel formation of milk analysed by noninvasive Multispeckle Diffusing Wave Spectroscopy. Twenty Streptococcus thermophilus strains were classified with respect to EPS concentration (8-126 mg GE/kg) and ropiness (thread length: 15-80 mm). Five groups identified by cluster analysis demonstrate the high strain-to-strain variability even within one species of lactic acid bacteria. Results from acidification and gelation experiments averaged per cluster indicate that fermentation time and gel stiffness is higher for strains that produce ropy EPS. A further increase in gel stiffness was detected for strains that also produced cell-bound EPS, which underlines the importance of both ropy and cell-bound EPS for improving acid gel properties. The results may be helpful for a proper selection of EPS-producing starter cultures.