U. Kulozik

Technische Universität München, München, Bavaria, Germany

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Publications (71)122.54 Total impact

  • Magdalena Wolz · Eugenia Mersch · Ulrich Kulozik
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    ABSTRACT: Processed food protein such as whey protein, used as hydrocolloid, is a possibility to impart specific structural and physical properties of food. The specific protein properties can be achieved by controlled denaturation or rather aggregation. The resulting aggregate structure and thereby the functional properties at the macroscopic scale depend strongly on the process conditions. Heating conditions, shear stress and material composition, determine the reaction kinetics as well as the resulting particle size distribution and the structure of the aggregates. These conditions often cannot be investigated separately in industrial processes. Therefore, the impact of shear rate, heating time and protein concentration on the particle characteristics was investigated by a rotational rheometer at 80 °C. By increasing the protein concentration (from 5 to 30% w/w), smaller more compact and stable aggregates were produced. This is due to the higher viscosity and the higher shear stress. The aggregates appearance changes from long and crystalline like structure to a spherical shape. The influence of shear rate is dependent on protein concentration. In suspension with 5% protein the aggregate size initially increases with increasing shear rates because of the predominant effect of increasing number of collisions; and decreases subsequently due to limitation of the particle growth. At high concentrations the size of the aggregates decreases with the shear rate, because of increasing shear stress. The size of whey protein aggregates can thus be regulated by the applied shear rate during processing.
    No preview · Article · May 2016 · Food Hydrocolloids
  • Magdalena Wolz · Ulrich Kulozik
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    ABSTRACT: A detailed kinetic study of the thermal reaction kinetics of whey protein concentrate was conducted at high protein concentrations. Whey protein solutions with protein concentrations of up to 40% (w/w) were heated at different temperatures for varying periods of times. The denaturation of β-lactoglobulin followed a reaction order of 1.5 and depended strongly on temperature and protein concentration. The rate of denaturation was shown to increase with increasing temperature. This could be explained by the strong influence of the temperature on the unfolding reaction. Furthermore, the protein concentration induced a faster thermal denaturation, most likely due to the increased probability of collision between whey protein molecules with increasing protein concentration which promotes protein aggregation. The results of this study are of industrial relevance for extrusion processes and the production of protein concentrates in evaporators where high protein concentrations are frequently used.
    No preview · Article · Oct 2015 · International Dairy Journal
  • Patricia Meyer · Alexander Mayer · Ulrich Kulozik
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    ABSTRACT: The purpose of this work was to characterise the ultrafiltration of skim milk with a dynamic system with a rotating membrane regarding flux in milk protein concentration. The flux of the dynamic system showed a maximum at medium rotational speeds, probably due to the permeate backpressure or a shift in the deposited particle size range to smaller particles above a critical rotational speed. The flux increased almost linearly up to a transmembrane pressure (TMP) of 100 kPa. At higher TMP, the curves levelled off, especially at higher protein concentrations. The dynamic system was less limited by the increasing retentate viscosity and reached significantly higher volume reduction ratios (VRR) as compared with a spiral wound module (SWM). SWM are suitable to achieve VRR <5-6 before a dynamic system, possibly in combination with tubular ceramic membranes, could be used to achieve higher VRR >8.
    No preview · Article · Aug 2015 · International Dairy Journal
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    ABSTRACT: Caseinomacropeptide (CMP) is the 64 C-terminal amino acid residue of κ-casein, formed by chymosin cleavage during cheese manufacture. This study examined the effects of oral administration of a CMP-enriched extract (CMPEE), obtained from a local dairy plant, on the Ca content of mouse femurs. Animals received low (0.1%, w/v), normal (0.5%, w/v) or high (1.2%, w/v) Ca diet for 3 or 8 weeks and CMPEE diluted (1:10) in their drinking water. No significant differences in Ca content were observed in faeces, kidney, urine or blood serum compared with control animals. The oral administration of CMP to mice significantly enhanced the Ca content in femur under a low-Ca diet model, especially during the period of full body development (3 weeks), in which case a significant 12% Ca increase was observed. These findings pave the way for further studies aimed at supplementing infant food with industrially-obtained CMP-enriched extract for enhanced bone health.
    Full-text · Article · May 2015 · International Dairy Journal
  • Linda Voswinkel · Ulrich Kulozik
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    ABSTRACT: A radial flow membrane adsorber system with improved fluid distribution, thereby avoiding high back pressures, was investigated for the complete fractionation of whey proteins. A 50-fold scale-up of the chromatographic separation of all major and minor proteins in acid whey was achieved. The process with anion and cation exchanger membranes consists of two steps. In the first step β-lactoglobulin (β-Lg) and bovine serum albumin are removed. In the second step the minor proteins lactoferrin, lactoperoxidase and immunoglobulin G are isolated and α-lactalbumin remains in the serum phase. The membrane performance over five repeated cycles without cleaning was stable at both scales. The loaded β-Lg equalled the dynamic binding capacity, which was 0.5 mg cm-² and depletion of β-Lg was 96-99.8%. The yield and purity of the minor whey proteins were consistent at both scales in a range between 80-97%, with a concentration factor between 6 and 14.
    No preview · Article · Nov 2014 · International Dairy Journal
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    ABSTRACT: Membrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10 kPa). At higher cross-flow velocities (around 0.141 m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12 kg/h·m(2) for skim milk of 20% dry matter concentration and approximately 20 kg/h·m(2) after 18 h of operation with whey at 20% dry matter concentration.
    Preview · Article · Nov 2013 · Journal of Dairy Science
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    S. A. W. Bauer · U. Kulozik · P. Foerst
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    ABSTRACT: The aim of this work was to investigate the influence of process parameters on water content, water activity, survival rate, and membrane integrity during low-temperature vacuum drying for Lactobacillus paracasei F19. Early stationary-phase cells were dried for different lengths of time. The drying rates did not affect the cell survival and the membrane integrity. Additionally, it could be seen that the membrane integrity strongly correlated with the water activity. However, the loss of membrane integrity was sublethal at water contents between 40 and 20%; beyond this range water content reduction started to become lethal due to the irreversible loss of cell membrane integrity.
    Full-text · Article · Oct 2013 · Drying Technology
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    ABSTRACT: In the production of a fresh type traditional Lithuanian cottage type cheese acid gelation, induced by lactic acid producing cultures, without rennet addition is used for casein coagulation. The aim of this study was to investigate the possibility to increase the yield of cottage type cheese and to improve the textural properties of cheese using additional cross linking of milk proteins by transglutaminase. The influence of transglutaminase induced cross-linked milk proteins degree on the acid gel formation, rheological properties of acid gel and its impact on the textural properties and yield of cottage type cheese was evaluated. Milk was incubated with 1-4 U g-1 protein of transglutaminase for 20, 30 and 60 min at 40°C or 50°C temperature. Acid gel was formed by adding lactic acid bacteria after pre-treatment of milk with enzyme or simultaneously with enzyme. Results demonstrated that degree of cross-linked proteins depends on transglutaminase amount, incubation time and temperature. The increase of enzyme amount expanded degree of proteins polymerization from 9.37% at 1 U g-1 protein of transglutaminase to 19.83% at 4 U g-1 protein of transglutaminase after 20 min incubation period at 40°C temperature or from 18.51% at 1 U g-1 protein of transglutaminase to 36.75% at 4 U g-1 protein of transglutaminase after 60 min incubation time at 50°C temperature. Fermentation process was slowed down by cross-linking of proteins at transglutaminase content (2 and 4 U g-1 protein) fermentation time increased up to 369 min while the pH at which gel formation started remained at the same level. However, that caused higher gel firmness and incorporation of whey into gel, therefore the increase in cottage cheese yield produced from this gel was observed. The highest cheese yield was obtained in the sample produced from acid gel pre-treated with 3.6 U g-1 protein transglutaminase at 40°C for 60 min. The excessive protein cross-linking led to the deterioration of textural properties of the cottage type cheese.
    Full-text · Article · Oct 2013 · Journal of Food Agriculture and Environment
  • Thomas Strixner · Ulrich Kulozik
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    ABSTRACT: The egg yolk main fractions, granules and plasma, show considerable different emulsifying properties. In order to use this potential, the present study investigates the influence of variable process conditions on the continuous centrifugal separation process of liquid egg yolk. It is shown that the granule fraction represents no homogeneous component, but consists of three different subfractions with different size, density and structure. It was confirmed by SDS–PAGE that each granule subfraction incorporated different amounts of LDL. The inhomogeneity leads to a subfraction depending sedimentation behaviour of the whole granule-fraction in egg yolk which could be clearly classified. Based on these findings, the impact of variable rheological properties on the sedimentation behaviour of polydisperse suspensions with high particle concentrations is discussed. However, fluid temperatures of 50 °C, a dry matter reduction below 29% prior to the centrifugal fractionation and g-forces up to 10,000g resulted in excellent separation efficiencies of the granule-fraction.
    No preview · Article · Jul 2013 · Journal of Food Engineering
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    ABSTRACT: This chapter contains sections titled: Introduction Isolation of Dairy Components Using Resin-Based Chromatography Membrane Adsorption Chromatography (MAC) Conclusions
    No preview · Chapter · Jan 2013
  • Iris Schmitz-Schug · Petra Foerst · Ulrich Kulozik

    No preview · Article · Jan 2013 · Dairy Science and Technology
  • R Gebhardt · T Steinhauer · P Meyer · J Sterr · J Perlich · U Kulozik
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    ABSTRACT: Casein micelles undergo shape changes when subjected to frontal filtration forces. Grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) allow a quantification of such structural changes on filtration cakes deposited on smooth silicon micro-sieves. A trans-membrane pressure of deltap = 400 mbar across the micro-sieve leads to an immediate film formation after deposition of casein solution. We observe significant changes in the GISAXS pattern depending on how many layers are stacked on top of each other. Compared to a deposit formed by one layer, GISAXS on a deposit formed by three layers of casein micelles leads to less scattering in the vertical and more scattering in the horizontal direction. Simulations show that the experimental results can be interpreted by a structural transformation from an originally spherical micelle shape to an ellipsoidal-deformed shape. The results are supported by AFM measurements showing a reduced lateral size of casein micelles deposited on top of a membrane pore. The observed shape changes could be due to filtration forces acting on densely packed deposits confining the micelles into ellipsoidal shapes.
    No preview · Article · Dec 2012 · Faraday Discussions
  • Petra Foerst · Ulrich Kulozik
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    ABSTRACT: In order to better understand inactivation of cells during a drying process, the inactivation kinetics of concentrated Lactobacillus paracasei ssp. paracasei (F19) was measured under stationary conditions for different combinations of water activities and temperatures in a water activity range of a w = 0.23–a w = 0.75 and temperatures between 4°C and 50°C. It was shown that the inactivation kinetics of the probiotic bacterium L. paracasei at moderate temperatures could, for all conditions, be formally described by a first-order reaction with activation energies that are much lower than for thermal inactivation (E a = 61 kJ/mol). With regard to the water activity, the reaction rate constants exhibit a maximum inactivation rate at intermediate water activity a w = 0.52. As this behavior has direct implications for the stability of cells in a drying process, the stationary data were used to model the inactivation during test vacuum drying processes, where both temperature and water activity dynamically change. It is shown that—depending on the drying rate—dynamic effects have to be taken into account when modeling the survival during drying. Nevertheless, the model based on stationary inactivation data is capable to predict the characteristics of inactivation during a drying process. Therefore, it can serve as basis to optimize the drying process with regard to maximum survival of cells. However, a further refinement of the model with regard to the drying rate is necessary.
    No preview · Article · Aug 2012 · Food and Bioprocess Technology
  • Barbaros Özer · Christopher Guyot · Ulrich Kulozik
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    ABSTRACT: The objective of the present study was to assess competitive interactions between transglutaminase (TGase) and rennet during rennet coagulation of skim milk. Rennet coagulation was achieved at two different renneting temperatures (30 °C and 34 °C), three initial milk pH levels (6.5, 6.3 and 6.1) and two TGase concentrations (0.6 U g−1 protein and 1.8 U g−1 protein). Results of the relative caseinomacropeptide in serum and degree of polymerization revealed that TGase influenced both the primary and secondary phases of rennet coagulation, respectively. Overall, the higher the renneting temperature and the lower the TGase level, the lower were the yields of the rennet gels. The coagulation times (tc) of the gels decreased with decreased initial milk pH and increased coagulation temperature. The optimum initial milk pH, coagulation temperature and TGase concentration were determined to be 6.3, 30 °C and 1.8 U g−1 protein.
    No preview · Article · May 2012 · International Dairy Journal
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    ABSTRACT: There is still lack of the insight into the storage stability of dry probiotics produced by vacuum drying. Therefore, in this study we assessed the stability of a vacuum-dried Lactobacillus paracasei F19 under varying storage conditions. L. paracasei F19 was vacuum-dried with and without sorbitol and trehalose. The dried cells were stored at 4, 20 and 37°C, and at aw=0.07, 0.22 and 0.33. The survival was determined by viable counts on MRS agar plates. The inactivation rate constants were determined for each storage condition. The survival after drying of cells dried without and with trehalose and sorbitol was 29, 70 and 54%, respectively. All vacuum-dried cells were very stable at 4°C. However, high stability at non-refrigerated temperatures was obtained only in the presence of sorbitol. In contrast to sorbitol, the supplementation of trehalose did not stabilize cells during storage. This is supposedly due to the rapid crystallization of trehalose during storage. While glass transition temperatures of dry cell-sorbitol increased from −32°C to 12°C during storage at 37°C and aw=0.07, Tg of dry cell-trehalose (−15°C after drying) could not be determined after storage for only 24h. In conclusion, we showed that high stability of probiotic cells at non-refrigerated temperatures could be obtained by vacuum drying process with appropriate protectant.
    No preview · Article · Apr 2012 · Food and Bioproducts Processing
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    A Piry · A Heino · W Kühnl · T Grein · S Ripperger · U Kulozik
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    ABSTRACT: We investigated the fractionation of casein micelles and the whey protein β-lactoglobulin (β-LG) of skim milk by crossflow microfiltration (0.1 μm) for the first time by a novel approach as a function of membrane length and membrane resistance. A special module was constructed with 4 sections and used to assess the effects of membrane length by measuring flux and β-LG permeation (or transmission) as a function of transmembrane pressure and membrane length. Depending on the position, the membranes were partly controlled by a deposit layer. A maximum for β-LG mass flow through the various membrane sections was found, depending on the position along the membrane. To study the effect of convective flow toward the membrane, membranes with 4 different intrinsic permeation resistances were assessed in terms of the permeation and fouling effects along the flow channel. From these findings, we derived a ratio between transmembrane pressure and membrane resistance, which was useful in reducing the effect of deposit formation and, thus, to optimize the protein permeation. In addition, the fouling effect was investigated in terms of reversible and irreversible fouling and, in addition, by differentiation between pressure-induced fouling and adsorption-induced (pressure-independent) fouling, again as a function of membrane length.
    Full-text · Article · Apr 2012 · Journal of Dairy Science
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    Linda Voswinkel · Ulrich Kulozik
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    ABSTRACT: The separation of different major and minor proteins from acid whey with membrane adsorption chromatography at lab scale was investigated. Macroporous membranes with strong anionic or cationic ligands for fast operation (Sartobind Q and S nano) were used in order to bind and subsequently elute the proteins. Food grade buffers were applied for equilibration and elution steps. Desorption was realized by ionic strength gradient with sodium chloride. A two step process was developed where the six target proteins could be efficiently isolated. For maximum exploitation of membrane capacity as well as for highest purity of the various protein fractions potential displacement effects on both anion and cation exchanger have been investigated. (C) 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of 11th International Congress on Engineering and Food (ICEF 11) Executive Committee.
    Preview · Article · Dec 2011
  • R Gebhardt · C Vendrely · U Kulozik
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    ABSTRACT: The objective of this study was to determine the effect of size-fractionation by centrifugation on the film structure of casein micelles. Fractionated casein micelles in solution were asymmetrically distributed with a small distribution width as measured by dynamic light scattering. Films prepared from the size-fractionated samples showed a smooth surface in optical microscopy images and a homogeneous microstructure in atomic force micrographs. The nano- and microstructure of casein films was probed by micro-beam grazing incidence small angle x-ray scattering (μGISAXS). Compared to the solution measurements, the sizes determined in the film were larger and broadly distributed. The measured GISAXS patterns clearly deviate from those simulated for a sphere and suggest a deformation of the casein micelles in the film.
    No preview · Article · Nov 2011 · Journal of Physics Condensed Matter
  • Martin Heinrich · Ulrich Kulozik
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    ABSTRACT: The re-association of disintegrated casein micelles was investigated using a combined high pressure and enzymatic treatment with chymosin at 20°C and 150 or 200MPa. The amphiphilic, growth-limiting character of κ-casein was altered in the pressure-disintegrated state of the casein micelle. With increasing amounts of κ-casein being hydrolysed, less micellar surface can be covered with intact κ-casein after high pressure treatment. Therefore, larger particles with shifted surface-to-volume ratio were expected to occur with increasing degree of hydrolysis (DH) of κ-casein. Higher DH values led to larger reformed casein micelles. As compared with a control sample, the relative particle diameter showed a strong correlation to DH. This could be attributed to the re-association of caseins or micellar fragments forming micelles similar in structure as compared with native ones. Gelling similar to that in standard renneting, only occurred at DH levels above 0.80.
    No preview · Article · Sep 2011 · International Dairy Journal
  • C. Guyot · U. Kulozik
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    ABSTRACT: A novel method of transglutaminase (TGase) treatment for skim milk yoghurt production was investigated. In contrast to previous studies, TGase pre-treated skim milk powder (SMP) was used as protein fortification for yoghurt making, instead of treating the entire yoghurt milk. When the TGase concentration for powder production was increased from 0 to 10 U g−1 protein, the viscosity of stirred skim milk yoghurt produced with addition of TGase-treated SMP increased from 247 to 453 mPas and the serum loss assessed using a centrifugation method decreased from 57.1% to 52.6%. Furthermore, by using enzyme-modified SMP, only half of the protein addition was required to obtain an equivalent viscosity compared to the control. The study showed that crosslinking the caseins by TGase only in the added SMP yields the desired positive effects while allowing for a complete elimination of the residual enzyme activity.
    No preview · Article · Sep 2011 · International Dairy Journal

Publication Stats

800 Citations
122.54 Total Impact Points


  • 2002-2015
    • Technische Universität München
      • Chair of Food Process Engineering and Dairy Science
      München, Bavaria, Germany
  • 2010
    • Pontifical Catholic University of Chile
      • Departamento de Ingeniería Química y Bioprocesos
      CiudadSantiago, Santiago, Chile