Mirela D. Iličić

VISCOSITY CHANGES OF PROBIOTIC YOGHURT WITH TRANSGLUTAMINASE DURING STORAGE

The aim of this study was to determine the effect of the quantity of transglutaminase as well as conditions of its application (direct, or after activation by milk heating for 2 h at 40°C and for 1 min at 80°C), on yoghurt viscosity manufactured from two kinds of low fat milk (0.1 % w/w fat and 0.5% w/w fat) during 10 days of storage. The fermentation in both series started after the adequate amounts of probiotic starter culture ABT-4 (Chr. Hansen A/S Denmark) were added to the milk at 43°C. After milk fermentation at pH 4.5, probiotic yoghurt samples were cooled to 8°C, gently homogenized and packed in plastic containers and stored for 10 days, at +4oC. Viscosity of all samples was measured at 5°C on a Haake Rheostress 600 viscosimeter. On the basis of the obtained results it can be concluded that yoghurt samples produced with low level of transglutaminase activated prior to fermentation have significantly better rheological properties than the samples produced without activation and yoghurt control. Generally, the application of low level transglutaminase in low - fat yoghurt production improves overall rheological properties of the final product.

In silico identification of milk antihypertensive di- and tripeptides involved in angiotensin I–converting enzyme inhibitory activity

Identification of bioactive milk peptides could improve food technology through improved selection of food supplements with a focus on antihypertensive properties. We hypothesized that angiotensin I-converting enzyme (ACE) inhibitory activities of milk di- and tripeptides could be predicted using 3-dimensional quantitative structure activity relationship methods and that these activities could be explained through evaluation of structural features (hydrogen bond donor/acceptor, hydrophobic, steric, and electrostatic) that are responsible for this bioactivity. We aimed to build comparative molecular field analysis (CoMFA) models combined with in silico digestion to predict the peptide sequences released from enzymatic digestion and to evaluate peptides without experimental data. Furthermore, molecular docking simulation was performed with the aim to evaluate structural features. Molecular docking simulations revealed that the most potent inhibitory peptides contain hydrophobic amino acids that enter deep into the hydrophobic pocket of the ACE active site and make interactions with its residues. CoMFA results point out favorable steric interactions and electronegativity at the C-terminus of the milk dipeptides. The CoMFA model appears to favor electropositive amino acids at the second place in tripeptides and electronegative interaction with Tyr520. Furthermore, predicted values of ACE inhibitory activity of dipeptides obtained by peptide cutter are relatively high, which recommend them for application as functional food supplements and natural alternatives to ACE inhibitory drugs. This research suggests that obtained 3-dimensional quantitative structure activity relationship models are able to successfully identify milk-derived di- and tripeptides that have significant antihypertensive activity and provide information for screening and design of novel ACE inhibitors that could be used as supplements in human nutrition.

Comparative Molecular Modeling and Docking Analysis of β-galactosidase Enzymes from Commercially Important Starter Cultures Used in the Dairy Industry

β-Galactosidases from S. thermophillus, L. acidophilus, and B. animalis lactis are essential enzymes which hydrolyze lactose during commercial yogurt and cheese production. S. thermophillus β-galactosidase is active in the human digestive tract, improving digestion in lactose-intolerant individuals. Because X-ray crystal structures have not been determined, molecular models of these β-galactosidases were created for comparative structural analysis and molecular docking against lactose. Modeling and docking results were validated using crystal structures of homologous β-galactosidase enzymes from E. coli and B. circulans. The structure of E.coli β-galactosidase in complex with lactose was used as a docking control. Structure-based sequence alignment and molecular docking identified catalytically active residues as GLU458/GLU546 in S. thermophillus, GLU148/GLU307 in L. acidophilus and GLU164/GLU324 in B. animalis ssp. lactis, and predicts residues involved in lactose recognition. These models provide a framework for future engineering of improved β-galactosidase variants with commercial applications.

Novel Fermented Dairy Products

Health benefits of milk and dairy products have been known for thousands of years in many diet cultures around the world. In response to the increasing consumer’s interest in functional foods which is part of the challenges nowadays, dairy industry has developed a variety of new functional dairy products, particularly fermented dairy products. The high nutritional value and the health benefits of dairy products are the result of biologically active components that are present in native milk and due to their suitable modification through the fermentation process. Application of novel technological processing is of great importance for preservation of existing and formation of the additional nutritional value of final products. This chapter offers a brief overview of the current knowledge of fermented dairy product development focusing on different factors determining the quality, functionality and acceptance of the products. Furthermore, some featured types of fermented dairy products which are presented on the market are pointed out.

Prediction of Active Residues of β -galactosidase from Bacteroides thetaiotaomicron

Bacteroides thetaiotaomicron, a Gram-negative anaerobe and symbiotic commensal microbe, dominates the human intestinal tract; where it provides a range of beneficial metabolic tasks not encoded in the human genome. B. thetaiotaomicron uses various polysaccharides as its carbon and energy source, providing valuable monosaccharides for its host. Regarding dairy technology, the most important characteristic of B. thetaiotaomicron is its ability to degrade lactose.β-galactosidase from B. thetaiotaomicron belongs to thesubfamily GH-35. There is a lack of structural information about B. thetaiotaomicron β-galactosidase, including the active site and residues involved in lactose degradation. The aim of this research was to predict the residues of B. thetaiotaomicron β-galactosidase involved in substrate catalysis, to construct a model of its active site, and to predict residues involved in substrate binding.Amino acid sequences were retrieved from UNIPROT database. Sequence clustering and alignments were performed using UGENE 1.11.3.Docking studies were performed using Surflex-Dock. Our results indicate that proton donor and nucleophillic residues could be GLU182 and GLU123, respectively.These active residues of B. thetaiotaomicron β-galactosidase have not been reported previously.