Spasenija D. Milanović

Static turbulence promoter in cross-flow microfiltration of skim milk☆

The efficiency of cross-flow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The objective of this study was to investigate the influence of static turbulence promoter on permeate flux during skim milk microfiltration and the potential application of this arrangement for an industrial development. Experimental investigations were performed on 100 nm ceramic membrane using the Kenics static mixer as a turbulence promoter. The insertion of the Kenics static mixer caused improvement of permeate flux of more than 700% at the same feed flow rate. Although the hydraulic dissipated power was significantly increased (about 6 times), the decrease of more than 25% in specific energy consumption was obtained by the use of the static mixer. Moreover, the presence of the static mixer in the membrane tube provided the similar permeate flux values at about 5 times lower cross-flow velocity, thus reducing the energy consumption for more than 80%. Additional energy saving was achieved using the Kenics static mixer with the aspect ratio (ratio of element length to mixer diameter) greater than 1, especially at the volumetric concentration factors greater than 2.

Determination of heavy metals in milk and fermented milk products by potentiometric stripping analysis with constant inverse current in the analytical step.

A simple and rapid method for the direct determination of cadmium, lead and copper in milk and fermented milk products by potentiometric stripping analysis (PSA) with oxygen as an oxidant and with inverse current imposed through the stripping step is described. For the more selective metals determination a samples pretreatment by the microwave acid extraction was applied. Due to the significant increase of the modified technique sensitivity, the detection limits of 0.30, 1.7 and 3.8 μg/l were obtained, for cadmium, lead and copper, respectively. The method accuracy was confirmed by analysing the standard reference material (SRM 1577 b). The contents of cadmium, lead and copper in milk samples were in the range of 2.13-4.82, 54.3-95.2 and 112.2-124.7 μg/kg, respectively, whereas in the samples of fermented milk products in the range of 6.30-24.1, 210.1-463.6 and 260.0-320.7 μg/kg, respectively.

Kenics Static Mixer as Turbulence Promoter in Cross-Flow Microfiltration of Skim Milk

The efficiency of cross-flow membrane filtration processes is limited by membrane fouling and concentration polarization. The question of membrane fouling and membrane pore blocking during microfiltration is much more important than in the traditional ultrafiltration, not only for the maintenance of acceptable flux but also for the adequate recovery of the permeate components. The objective of this study was to demonstrate that use of a static mixer as turbulence promoter results in enhanced cross-flow microfiltration of skim milk. Experimental investigations were performed on 50-nm and 100-nm ceramic tubular membranes. The use of a static mixer provided a significant reduction of membrane fouling and an increase of more than 700% in permeate flux for both membranes compared with that obtained without a static mixer at the same feed flow rate. The similar flux enhancement indicates that surface layer resistance dominates the overall fouling resistance. Although the power consumption was significantly increased by using a static mixer, a decrease of more than 25% in specific energy consumption for both membranes was achieved with static mixer as compared to arrangement without static mixer in experiments performed at the same cross-flow velocity.

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.

Chemometric approach to texture profile analysis of kombucha fermented milk products

In the present work, relationships between the textural characteristics of fermented milk products obtained by kombucha inoculums with various teas were investigated by using chemometric analysis. The presented data which describe numerically the textural characteristics (firmness, consistency, cohesiveness and index of viscosity) were analysed. The quadratic correlation was determined between the textural characteristics of fermented milk products obtained at fermentation temperatures of 40 and 43 °C, using milk with 0.8, 1.6 and 2.8% milk fat and kombucha inoculums cultivated on the extracts of peppermint, stinging nettle, wild thyme and winter savory. Hierarchical cluster analysis (HCA) was performed to identify the similarities among the fermented products. The best mathematical models predicting the textural characteristics of investigated samples were developed. The results of this study indicate that textural characteristics of sample based on winter savory have a significant effect on textural characteristics of samples based on peppermint, stinging nettle and wild thyme, which can be very useful in the determination of products texture profile.

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.

Primena i uticaj polimernih ambalažnih materijala na pakovanje mlečnih napitaka

Functional food is positioned above the traditional, with the potential to improve human health. Thanks to very good physico-mechanical and barrier properties polymers became very popular in food industry as a packaging materials. Wild range of fermented dairy products could be packed in this packaging materials according to their’s inertness as well. Functional milk beverage was obtained from milk with 0,9% milk fat content by applying 10% v/v of kombucha’s inoculum cultivated on a black tea sweetened with sucrose. The beverage was packed in a different packaging materials: polyamid-polyethylen (PA/PE) coextruded foil bags and polyprophylen (PP) cups closed with aluminium (Al) foil lids under atmospheric conditions (ATM). Beverages were storaged for 15 days at 4°C. The quality of kombucha inoculum, milk and obtained kombucha fermented milk beverage were analysed. Characterization of the packaging materials was done by investigating physico-mechanical, barrier and structural properties. The composition and changes in the headspace atmosphere, after production and during the storage, were analysed. The influence of packaging material properties and packaging conditions on the biochemical transformations of the milk’s components (the content of: lactose, L-lactic acid, D-galactose, ethanol, B1 and B2 vitamins) influenced by kombucha starter were analysed as well. On the bases of the obtained results of characterisation of packaging materials, it can be concluded that PA/PE and PP materials are proper to be used for analysed beverage’s packaging. Also, there is no significant difference in content of components which were quantified, between analysed materials in correlation with the packed fermented milk beverage. [Projekat Ministarstva nauke Republike Srbije, br. III-46009]

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.