Structure modification of stirred fermented milk gel due to laccase-catalysed protein crosslinking in a post-processing step

Mild Enzyme-Induced Gelation Method for Nanoparticle Stabilization: Effect of Transglutaminase and Laccase Cross-Linking

Low-environment-sensitive nanoparticles were prepared by enzymatic cross-linking of electrostatic complexes of dextran-grafted whey protein isolate (WPI-Dextran) and chondroitin sulfate (ChS). The effect of transglutaminase (TG) and laccase cross-linking on nanoparticle stability was investigated. Covalent TG cross-linking and grafted dextran cooperatively contributed to the stability of nanoparticles against dissociation and aggregation under various harsh environmental conditions (sharply varying pH, high ionic strength, high temperature, and their combined effects). However, fragmentation induced by laccase treatment did not promote nanoparticle stability. Structural characterization showed that the compact structure promoted by TG-induced covalent isopeptide bonds repressed dissociation against varying environmental conditions and thermal-induced aggregation. Furthermore, the increasing α-helix and decreasing random coil contents benefited the formation of disulfide bonds, further contributing to the enhanced stability of nanoparticles cross-linked by TG, whereas weak hydrophobic interactions and hydrogen bonding as evidenced by the increase in β-sheet and microenvironmental changes were not able to maintain the stability of nanoparticles treated with laccase. Encapsulated cinnamaldehyde presented sustained release from TG-cross-linked nanoparticles, and the bioaccessibility was considerably enhanced to 50.7%. This research developed a novel mild strategy to enhance nanoparticle stability in harsh environments and digestive conditions, which could be an effective delivery vehicle for hydrophobic nutrients and drug applications in food and pharmaceutical industries.

Impact of polymerized whey protein/pectin thickening (PP) system on physical properties and volatile compounds of goat milk kefir mild and kefir

Polymerized whey protein and low-methoxyl pectin were used as thickening agents in fermented dairy food formulations. Effects of polymerized whey protein and pectin (PP) system on particle size distributions, rheological properties, molecular weight distributions of polysaccharides, microstructures, and volatile compounds of goat milk kefir mild and kefir were investigated. Clustering analysis indicated that the PP system addition could increase the particle size distributions and rheological properties of both kefir products. Molecular weight distributions of polysaccharides shown that an intermolecular aggregation occurred between pectin and exopolysaccharides (produced by microorganisms from starter cultures). Micrographs suggested that polymerized whey protein interacted with casein network to form a dense structure. Meanwhile, PP system did not change the characteristics flavor of goat milk kefir mild and kefir. Results indicated that the PP system may be a good combination to improve the physical properties of kefir products. PRACTICAL APPLICATION: Goat milk kefir has gained more and more attention due to its specific flavor and functional properties. However, poor texture of milk curd limits the consumption of fermented goat milk. As a new combination of thickening agents, PP system could specifically improve the particle size distributions and rheological properties of fermented goat milk. And the characteristic flavor of goat milk kefir was not changed. Results indicated that PP system can be used as thickening agents for formulations of different fermented goat milk products.

Laccase-catalyzed oxidative cross-linking of tyrosine and potato patatin- and lysozyme-derived peptides: Molecular and kinetic study

Laccase can catalyze the oxidative cross-linking of peptides, which is useful in the production of proteinaceous materials with enhanced functional properties. However, the kinetics and the pathway of this reaction remain unclear. In the present study, laccase-catalyzed oxidative cross-linking reaction was investigated through a combination of computational analysis, kinetic studies and end-product profiling using selected substrate models, including peptide AG-10 (AKKIVSDGNG) (without tyrosine) derived from lysozyme and tyrosine-containing peptide ST-10 (SYMTDYYLST) from potato protein (patatin), and tyrosine. Both laccases from Trametes versicolor (LacTv) and Coriolus hirsutus (LacCh) were used as biocatalysts. Laccase exhibited higher binding affinity and catalytic efficiency (k_cat/K_m) towards ST-10 and AG-10 than tyrosine. Among the laccases, LacCh showed higher k_cat towards the substrate models than LacTv. Through the molecular docking, this result was attributed to the presence of the ASN206 at the cavity of LacCh. The end product profiles reveal the formation of homo-oligomers (> 5 units) of ST-10 in the reaction catalyzed by LacTv, while polymerization was favored by LacCh. These cross-linked products were identified to have a mix of oligo-tyrosine linkages. In contrast, the cross-linking of AG-10 required the presence of ferulic acid as mediator, which resulted in the formation of hetero-oligomers and polymers of AG-10. The knowledge obtained in the present study provide insight into an effective reaction for peptide cross-linking.

Enzyme-Based Strategies for Structuring Foods for Improved Functionality

Enzyme technologies can be used to create food dispersions with novel functional attributes using structural design principles. Enzymes that utilize food-grade proteins and/or polysaccharides as substrates have gained recent interest among food scientists. The utilization of enzymes for structuring foods is an ecologically and economically viable alternative to the utilization of chemical cross-linking and depolymerization agents. This review highlights recent progress in the use of enzymes to modify food structures, particularly the interfacial and/or bulk properties of food dispersions with special emphasis on commercially available enzymes. Cross-linking enzymes such as transglutaminase and laccase promote the formation of intra- and intermolecular bonds between biopolymers to improve stability and functionality, whereas various degrading enzymes such as proteases alter the native conformation of proteins, leading to self-assembly of hierarchically ordered colloids. Results of this bio-inspired approach show that rational use of structure-affecting enzymes may enable food manufacturers to produce food dispersions with improved physical, functional, textural, and optical properties.