Search

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures. A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

Many foam products derived from milk or specific dairy ingredients suffer from drainage, coalescence and/or disproportionation. Previous studies indicated that foam properties of milk are strongly influenced by the composition of the milk as well as by the processing conditions during foam production. The aim of this research was to get a better understanding of these two factors. Interestingly, the presence of aggregates of casein micelles was found to result in very stable foams. The interfacial properties (adsorption speed, adsorption energy, dynamical interfacial tension, interfacial dilatational moduli), thin film stability (rupture time) and foam properties (foamability, drainage, coalescence) of casein micelle dispersions were determined. Based on these data, the very stable foams were concluded to result from properties of the thin films in the foam, which were affected drastically by the presence of the large aggregates of casein micelles.

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures. A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

The results of research concerning the feasibility of anaerobic treatment of domestic sewage at low temperature are summarized in this article. The batch tests demonstrated a high biodegradability of domestic sewage at 20°C (74Ž Both batch and continuous experiments for the treatment of domestic sewage showed that the removal of SS prior to anaerobic treatment of domestic sewage not only provides a stable reactor performance but also improves the removal of both colloidal (CODcol) and dissolved COD (CODdis). The results of the pre-treatment of domestic sewage in an anaerobic filter (AF) and an anaerobic hybrid (AH) reactor showed that the AF reactor is an efficient process for the removal of suspended COD (CODss), viz. 82°at an HRT of 4 h and 13°C. The novel AF reactor consists of vertical sheets of reticulated polyurethane foam with knobs, where the biomass was only in attached form. For the treatment of pre-settled sewage at 13°C, the AH reactor, with granular sludge, showed a higher total COD (CODt) removal than the UASB reactor as a result of higher CODcol removal. Therefore, the performance of a two-step system, AF AH (with granular sludge) reactor, was investigated with different HRTs at 13°C. For optimization of CODss and CODdis an HRT of 4 4 h is needed, while for optimization of CODcol removal an HRT of 4 8 h is required. A CODt removal of 71 as achieved with 60␌onversion to methane from the removed CODt when the AF AH system was operated at an HRT of 4 8 h at 13°C.

Nieuwe techniek voor onderzoek naar de mechanische eigenschappen van nanoporeus metaalschuim Het onderzoek dat in het proefschrift van Sergey Punzhin wordt beschreven, bestaat uit twee delen. Het eerste deel gaat over experimenten met nanoporeus metaalschuim en over de productie van dit materiaal. In het tweede wordt de ontwikkeling beschreven van een nieuwe en unieke experimentele techniek waarmee mechanische eigenschappen van deze metallische nanoschuimen kunnen worden bepaald. Nanoporeuze schuimen zijn moderne en veelzijdige materialen met een veelvoud aan toepassingen. Onder andere kunnen ze, omdat ze onder invloed van een elektrische spanning deformeren, dienen als actuator (een actuator is het onderdeel dan een regelsysteem dat de verandering doorvoert die door een sensor is opgemerkt). De actuatie-actie is het gevolg van het injecteren van lading. Dat veroorzaakt een verandering in de mechanische spanningstoestand aan het oppervlak met een meetbare vervorming als gevolg. Punzhin onderzocht of ordening in het nanoschuim een belangrijke invloed heeft op deformatie of niet. Het tweede deel is gewijd aan de ontwikkeling van een nieuwe techniek om de mechanische eigenschappen van metallisch nanoschuim te testen, die ionstraal-geïnduceerd buigen (IIB) is gedoopt. In het proefschrift laat Punzhin zien dat met IIB bij gebruik van een gefocusseerde bundel met geladen deeltjes (ionen) een zeer hoge precisie en reproduceerbaarheid kan worden bereikt. Een bijkomend voordeel is dat geen mechanisch contact vereist is tussen het vervormingsapparaat en het voorwerp zelf: tijdens IIB buigt het specimen dankzij de invloed van de ionen. Punzhin concludeert dat de IIB-techniek de unieke mogelijkheid biedt om de eigenschappen onderzoeken in zowel geordende als ongeordende nanoporeuze metalen.

Nieuwe techniek voor onderzoek naar de mechanische eigenschappen van nanoporeus metaalschuim Het onderzoek dat in het proefschrift van Sergey Punzhin wordt beschreven, bestaat uit twee delen. Het eerste deel gaat over experimenten met nanoporeus metaalschuim en over de productie van dit materiaal. In het tweede wordt de ontwikkeling beschreven van een nieuwe en unieke experimentele techniek waarmee mechanische eigenschappen van deze metallische nanoschuimen kunnen worden bepaald. Nanoporeuze schuimen zijn moderne en veelzijdige materialen met een veelvoud aan toepassingen. Onder andere kunnen ze, omdat ze onder invloed van een elektrische spanning deformeren, dienen als actuator (een actuator is het onderdeel dan een regelsysteem dat de verandering doorvoert die door een sensor is opgemerkt). De actuatie-actie is het gevolg van het injecteren van lading. Dat veroorzaakt een verandering in de mechanische spanningstoestand aan het oppervlak met een meetbare vervorming als gevolg. Punzhin onderzocht of ordening in het nanoschuim een belangrijke invloed heeft op deformatie of niet. Het tweede deel is gewijd aan de ontwikkeling van een nieuwe techniek om de mechanische eigenschappen van metallisch nanoschuim te testen, die ionstraal-geïnduceerd buigen (IIB) is gedoopt. In het proefschrift laat Punzhin zien dat met IIB bij gebruik van een gefocusseerde bundel met geladen deeltjes (ionen) een zeer hoge precisie en reproduceerbaarheid kan worden bereikt. Een bijkomend voordeel is dat geen mechanisch contact vereist is tussen het vervormingsapparaat en het voorwerp zelf: tijdens IIB buigt het specimen dankzij de invloed van de ionen. Punzhin concludeert dat de IIB-techniek de unieke mogelijkheid biedt om de eigenschappen onderzoeken in zowel geordende als ongeordende nanoporeuze metalen.

Nieuwe techniek voor onderzoek naar de mechanische eigenschappen van nanoporeus metaalschuim Het onderzoek dat in het proefschrift van Sergey Punzhin wordt beschreven, bestaat uit twee delen. Het eerste deel gaat over experimenten met nanoporeus metaalschuim en over de productie van dit materiaal. In het tweede wordt de ontwikkeling beschreven van een nieuwe en unieke experimentele techniek waarmee mechanische eigenschappen van deze metallische nanoschuimen kunnen worden bepaald. Nanoporeuze schuimen zijn moderne en veelzijdige materialen met een veelvoud aan toepassingen. Onder andere kunnen ze, omdat ze onder invloed van een elektrische spanning deformeren, dienen als actuator (een actuator is het onderdeel dan een regelsysteem dat de verandering doorvoert die door een sensor is opgemerkt). De actuatie-actie is het gevolg van het injecteren van lading. Dat veroorzaakt een verandering in de mechanische spanningstoestand aan het oppervlak met een meetbare vervorming als gevolg. Punzhin onderzocht of ordening in het nanoschuim een belangrijke invloed heeft op deformatie of niet. Het tweede deel is gewijd aan de ontwikkeling van een nieuwe techniek om de mechanische eigenschappen van metallisch nanoschuim te testen, die ionstraal-geïnduceerd buigen (IIB) is gedoopt. In het proefschrift laat Punzhin zien dat met IIB bij gebruik van een gefocusseerde bundel met geladen deeltjes (ionen) een zeer hoge precisie en reproduceerbaarheid kan worden bereikt. Een bijkomend voordeel is dat geen mechanisch contact vereist is tussen het vervormingsapparaat en het voorwerp zelf: tijdens IIB buigt het specimen dankzij de invloed van de ionen. Punzhin concludeert dat de IIB-techniek de unieke mogelijkheid biedt om de eigenschappen onderzoeken in zowel geordende als ongeordende nanoporeuze metalen.

Metaalschuimen zijn materialen die enerzijds een microstructuur bevatten op de microschaal (de schaal van de celwanden), maar anderzijds ook een mesoscopische microstructuur hebben (op de schaal van de celstructuur). Deze micro- en mesoscopische structuren zijn gevoelig voor het productieproces van het schuim en beïnvloeden bovendien de mechanische eigenschappen. Het doel van dit proefschrift is te onderzoeken wat de invloed van deze twee structuurniveaus op de mesoscopische vervormings- en schademechanismen is en te begrijpen hoe deze de macroscopische mechanische eigenschappen beïnvloeden. Voor dit doel werd een meerschalig model van een tweedimensionaal schuim ontwikkeld, waarbij Voronoi tessellaties werden gebruikt om de cellulaire structuur te beschrijven. Door nauwgezet de plastische vloeigrens in de celwanden op cellulair niveau te volgen, kon een geometrisch verstevigingsmechanisme worden geïdentificeerd dat hand in hand gaat met het intrinsieke verstevigen van het metaal zelf. Tevens kon worden vastgesteld dat de competitie tussen versteviging door plastische deformatie en verzwakking ('softening') door inwendige schadeontwikkeling belangrijk is bij het bepalen van de macroscopische ductiliteit. Met toenemende intrinsieke versteviging wordt de ontwikkeling van buiging in de celwanden afgeremd en daarmee ook de initiatie van schade, hetgeen de treksterkte en ductiliteit van het schuim verhoogt. In onregelmatige celstructuren met een brede verdeling van celgrootten is de mesoscopische deformatieverdeling niet-uniform, hetgeen leidt tot een verlaging van de ductiliteit. Voor schuimen met een structurele anisotropie werd aangetoond dat het schuim sterker en minder ductiel is in de trekrichting parallel aan de grootste cel-as, vergeleken met een trekrichting daar loodrecht op. Op basis van de numerieke berekeningen konden eenvoudige uitdrukkingen worden afgeleid die de macroscopische versteviging, treksterkte en ductiliteit beschrijven in termen van de materiaaleigenschappen van de celwanden en geometrische parameters van de cellulaire architectuur. Ook is er onderzoek gedaan naar het effect van interne scheuren op de treksterkte. Vastgesteld werd dat proefstukken met rand-kerven ('edge-notches') verstevigingsgedrag vertonen, terwijl proefstukken met inwendige scheuren juist verzwakken. Ten slotte is in dit proefschrift ook het falen van poreus bot ('trabecular bone') onderzocht, waarbij de effectiviteit van twee klinische behandelmethoden voor osteoporose werden vergeleken.

Metaalschuimen zijn materialen die enerzijds een microstructuur bevatten op de microschaal (de schaal van de celwanden), maar anderzijds ook een mesoscopische microstructuur hebben (op de schaal van de celstructuur). Deze micro- en mesoscopische structuren zijn gevoelig voor het productieproces van het schuim en beïnvloeden bovendien de mechanische eigenschappen. Het doel van dit proefschrift is te onderzoeken wat de invloed van deze twee structuurniveaus op de mesoscopische vervormings- en schademechanismen is en te begrijpen hoe deze de macroscopische mechanische eigenschappen beïnvloeden. Voor dit doel werd een meerschalig model van een tweedimensionaal schuim ontwikkeld, waarbij Voronoi tessellaties werden gebruikt om de cellulaire structuur te beschrijven. Door nauwgezet de plastische vloeigrens in de celwanden op cellulair niveau te volgen, kon een geometrisch verstevigingsmechanisme worden geïdentificeerd dat hand in hand gaat met het intrinsieke verstevigen van het metaal zelf. Tevens kon worden vastgesteld dat de competitie tussen versteviging door plastische deformatie en verzwakking ('softening') door inwendige schadeontwikkeling belangrijk is bij het bepalen van de macroscopische ductiliteit. Met toenemende intrinsieke versteviging wordt de ontwikkeling van buiging in de celwanden afgeremd en daarmee ook de initiatie van schade, hetgeen de treksterkte en ductiliteit van het schuim verhoogt. In onregelmatige celstructuren met een brede verdeling van celgrootten is de mesoscopische deformatieverdeling niet-uniform, hetgeen leidt tot een verlaging van de ductiliteit. Voor schuimen met een structurele anisotropie werd aangetoond dat het schuim sterker en minder ductiel is in de trekrichting parallel aan de grootste cel-as, vergeleken met een trekrichting daar loodrecht op. Op basis van de numerieke berekeningen konden eenvoudige uitdrukkingen worden afgeleid die de macroscopische versteviging, treksterkte en ductiliteit beschrijven in termen van de materiaaleigenschappen van de celwanden en geometrische parameters van de cellulaire architectuur. Ook is er onderzoek gedaan naar het effect van interne scheuren op de treksterkte. Vastgesteld werd dat proefstukken met rand-kerven ('edge-notches') verstevigingsgedrag vertonen, terwijl proefstukken met inwendige scheuren juist verzwakken. Ten slotte is in dit proefschrift ook het falen van poreus bot ('trabecular bone') onderzocht, waarbij de effectiviteit van twee klinische behandelmethoden voor osteoporose werden vergeleken.

Metaalschuimen zijn materialen die enerzijds een microstructuur bevatten op de microschaal (de schaal van de celwanden), maar anderzijds ook een mesoscopische microstructuur hebben (op de schaal van de celstructuur). Deze micro- en mesoscopische structuren zijn gevoelig voor het productieproces van het schuim en beïnvloeden bovendien de mechanische eigenschappen. Het doel van dit proefschrift is te onderzoeken wat de invloed van deze twee structuurniveaus op de mesoscopische vervormings- en schademechanismen is en te begrijpen hoe deze de macroscopische mechanische eigenschappen beïnvloeden. Voor dit doel werd een meerschalig model van een tweedimensionaal schuim ontwikkeld, waarbij Voronoi tessellaties werden gebruikt om de cellulaire structuur te beschrijven. Door nauwgezet de plastische vloeigrens in de celwanden op cellulair niveau te volgen, kon een geometrisch verstevigingsmechanisme worden geïdentificeerd dat hand in hand gaat met het intrinsieke verstevigen van het metaal zelf. Tevens kon worden vastgesteld dat de competitie tussen versteviging door plastische deformatie en verzwakking ('softening') door inwendige schadeontwikkeling belangrijk is bij het bepalen van de macroscopische ductiliteit. Met toenemende intrinsieke versteviging wordt de ontwikkeling van buiging in de celwanden afgeremd en daarmee ook de initiatie van schade, hetgeen de treksterkte en ductiliteit van het schuim verhoogt. In onregelmatige celstructuren met een brede verdeling van celgrootten is de mesoscopische deformatieverdeling niet-uniform, hetgeen leidt tot een verlaging van de ductiliteit. Voor schuimen met een structurele anisotropie werd aangetoond dat het schuim sterker en minder ductiel is in de trekrichting parallel aan de grootste cel-as, vergeleken met een trekrichting daar loodrecht op. Op basis van de numerieke berekeningen konden eenvoudige uitdrukkingen worden afgeleid die de macroscopische versteviging, treksterkte en ductiliteit beschrijven in termen van de materiaaleigenschappen van de celwanden en geometrische parameters van de cellulaire architectuur. Ook is er onderzoek gedaan naar het effect van interne scheuren op de treksterkte. Vastgesteld werd dat proefstukken met rand-kerven ('edge-notches') verstevigingsgedrag vertonen, terwijl proefstukken met inwendige scheuren juist verzwakken. Ten slotte is in dit proefschrift ook het falen van poreus bot ('trabecular bone') onderzocht, waarbij de effectiviteit van twee klinische behandelmethoden voor osteoporose werden vergeleken.

The research presented in this thesis aimed at controlling the horseradish peroxidase-catalyzed cross-linking of bovine α lactalbumin and the implications of this cross-linking for the foam stabilizing properties. Attention is also given to microreactors and their potential to control the enzymatic cross-linking of proteins. The proportion of cross-linked α lactalbumin dimers, oligomers and polymers could be directed by variations in ionic strength, pH, H2O2, and temperature. Covalent α lactalbumin dimers were proteolytic digested. FTMS analysis of the peptide mixture resulted in the unambiguous identification of a Tyr18 Tyr50 dityrosine cross-link. Structural modeling of the α lactalbumin dimer indicated that favorite electrostatics direct the selectivity of the cross-linking reaction and, hence, the formation of an intermolecular cross-link. The formation of the Tyr18-Tyr50 cross-link suggests that further cross-linking of α lactalbumin dimers enables the formation of linear polymers. A microreactor system was set up to obtain control over the reaction conditions to cross-link proteins. The enzymatic cross-linking of α lactalbumin was analyzed as a function of enzyme and substrate(s) feed. The increase in absorption at 318 nm due to dityrosine formation was found to be directly correlated to the decrease in monomeric α lactalbumin and was shown to be a good tool to monitor the cross-linking reaction. The α lactalbumin oligomers produced were investigated for their foam stabilizing properties. Cross-linked α lactalbumin oligomers did not stabilize foams, whereas α lactalbumin polymers acted as an anti-foam, destabilizing other protein films.

The research presented in this thesis aimed at controlling the horseradish peroxidase-catalyzed cross-linking of bovine α lactalbumin and the implications of this cross-linking for the foam stabilizing properties. Attention is also given to microreactors and their potential to control the enzymatic cross-linking of proteins. The proportion of cross-linked α lactalbumin dimers, oligomers and polymers could be directed by variations in ionic strength, pH, H2O2, and temperature. Covalent α lactalbumin dimers were proteolytic digested. FTMS analysis of the peptide mixture resulted in the unambiguous identification of a Tyr18 Tyr50 dityrosine cross-link. Structural modeling of the α lactalbumin dimer indicated that favorite electrostatics direct the selectivity of the cross-linking reaction and, hence, the formation of an intermolecular cross-link. The formation of the Tyr18-Tyr50 cross-link suggests that further cross-linking of α lactalbumin dimers enables the formation of linear polymers. A microreactor system was set up to obtain control over the reaction conditions to cross-link proteins. The enzymatic cross-linking of α lactalbumin was analyzed as a function of enzyme and substrate(s) feed. The increase in absorption at 318 nm due to dityrosine formation was found to be directly correlated to the decrease in monomeric α lactalbumin and was shown to be a good tool to monitor the cross-linking reaction. The α lactalbumin oligomers produced were investigated for their foam stabilizing properties. Cross-linked α lactalbumin oligomers did not stabilize foams, whereas α lactalbumin polymers acted as an anti-foam, destabilizing other protein films.

The thesis is about the characterization of the microstructure of several aluminium foams and its relation to the failure behavior of these materials under monotonic tension and fatigue. Due to the production processes brittle inclusions are present in the microstructure of the foams investigated. Because damage is introduced before the peak strain, which is the strain at the ultimate tensile strength (UTS), the peak strain and the UTS depend on the particular damage evolution before the peak strain. To monitor the damage evolution the electrical resistance and acoustic emission was measured during tensile tests. Brittle fracture increases the rate of damage accumulation and therefore decreases the peak strain and UTS. For decreasing relative densities below 5.5%, more bending and less stretching of struts decreases the damage accumulation and therefore increases the peak strain and UTS of Duocel open cell aluminium 6101 foam. Above 5.5% relative density annealing the foam samples or orienting the long axis of the elliptical cells transverse to the loading direction, in stead of longitudinal, has the same effect. For Replicated open cell aluminium 6101 foam densities below 5.5%, the increase in bending of struts results in the ability to shift deformation from a highly strained and damaged band to another band, thereby increasing the peak strain and UTS.

The thesis is about the characterization of the microstructure of several aluminium foams and its relation to the failure behavior of these materials under monotonic tension and fatigue. Due to the production processes brittle inclusions are present in the microstructure of the foams investigated. Because damage is introduced before the peak strain, which is the strain at the ultimate tensile strength (UTS), the peak strain and the UTS depend on the particular damage evolution before the peak strain. To monitor the damage evolution the electrical resistance and acoustic emission was measured during tensile tests. Brittle fracture increases the rate of damage accumulation and therefore decreases the peak strain and UTS. For decreasing relative densities below 5.5%, more bending and less stretching of struts decreases the damage accumulation and therefore increases the peak strain and UTS of Duocel open cell aluminium 6101 foam. Above 5.5% relative density annealing the foam samples or orienting the long axis of the elliptical cells transverse to the loading direction, in stead of longitudinal, has the same effect. For Replicated open cell aluminium 6101 foam densities below 5.5%, the increase in bending of struts results in the ability to shift deformation from a highly strained and damaged band to another band, thereby increasing the peak strain and UTS.

Onderzoek naar de relatie tussen moleculaire structuur van eiwitten en het schuimgedrag van de oplossing

Keywords: Sunflower protein, Helianthusannuus ,helianthinin, albumins, solubility, structure,denaturation, pH, temperature, ionic strength,phenoliccompounds,chlorogenicacid, foams, emulsions, functionalityThe research described in this thesis deals with the relation between specific sunflower proteins, their structure and their functional properties as a function of extrinsic factors as pH, ionic strength and temperature.Sunflower protein isolate (SI) devoid ofchlorogenicacid (CGA), the mainphenoliccompound present, was obtained withoutdenaturationof the proteins. Sunflower proteins were found to be composed of two main protein fractions: 2S albumins or sunflower albumins (SFAs) andhelianthinin. Subsequently, these protein fractions werebiochemicallyand structurally characterized under conditions relevant to food processing.Depending on pH, ionic strength, temperature and protein concentration,helianthininoccurs in the 15-18S (high molecular weight aggregate), 11 S (hexamer), 7S (trimer) or 2-3S (monomer) form. Dissociation into 7S from 11S gradually increased with increasing pH from 5.8 to 9.0. Enhancing the ionicstrengthresulted in stabilization of the 11S form. Heating and lowering the pH resulted in dissociation into themonomericform ofhelianthinin. The 11S and 7S form ofhelianthinindiffer in their secondary structure, tertiary structure, and thermal stability. With respect to solubilityas a function of pH,helianthininshows a bell shaped curve with a minimum at approximately pH 5.0 at low ionic strength. At high ionic strength,helianthininis almost insoluble at pH< 5.0.The second main sunflower fraction,SFAs, revealed to be very stable against pH changes (pH 3.0 to 9.0) and heat treatment (up to 100°C), and their solubility was only marginally affected by pH and ionic strength. The solubility of the SI as a function of pH seems to be dominated by that ofhelianthinin.Foam and emulsion properties of the sunflower isolate as well as those of purifiedhelianthinin,SFAsand combinations thereof were studied at various pH values and ionic strengths, and after heat treatment. Sunflower proteins were shown to form stable emulsions, with the exception ofSFAsat alkaline and neutral pH values. Increasing amount ofSFAsimpaired the emulsifying properties. Regarding foam properties, less foam could be formed fromhelianthininthan fromSFAs, but foam prepared withhelianthininwas more stable againstOstwaldripening and drainage than foam prepared withSFAs. Increasing amounts ofSFAshad a positive effect on foam volume and a negative one on foam stability and drainage. It was found that treatments that increase conformational flexibility improve the emulsion and foam properties of sunflower proteins.

Keywords: protein film, protein conformation, air/water interface, network formation, foam formation, foam stability, interfacial rheology, fracture behaviour.The aim of this thesis was to obtain systematic information on the importance of mechanical and conformational aspects for the formation of a visco-elastic protein network at the air/water interface. Such a protein network is formed upon adsorption at the interface and is assumed to play a role in the formation and stabilisation of emulsions and foams. To understand the formation of a visco-elastic layer with specific mechanical properties, one has to study the molecular processes occurring at the interface, namely protein adsorption, conformational changes that occur upon adsorption and the interactions between the adsorbed proteins. A series of proteins was studied with a tertiary structure varying from random coil (flexible) to rigid (globular):b-casein,b-lactoglobulin, ovalbumin and (soy) glycinin. Glycinin has only been studied preliminary in the past but, being an interesting substitute for animal proteins, it was investigated quite extensively in this thesis. The conformation of glycinin was found to be pH-dependent and this change in conformation strongly affected the adsorption behaviour and rheological properties of interfacial glycinin layers. The monomeric glycinin form present at pH3 behaved as a good foaming agent whereas at pH 6.7 (hexamer form) no foam could be formed. Infrared Reflection Absorption Spectroscopy (IRRAS) showed that only minor changes occurred in the secondary structure of a protein upon adsorption at the interface. Ovalbumin andb-lactoglobulin showed a 10% loss ofb-sheet structures whereas glycinin (pH3) formed intermolecular anti-parallelb-sheets. The latter is an indication for interfacial aggregation. Mechanical properties were determined by deformation in shear and dilation. Upon large deformations most protein films were found to exhibit fracture behaviour. The differences observed for ovalbumin,b-lactoglobulin and glycinin indicated a transition from a more yielding behaviour to a more brittle fracture behaviour. A correlation was found between several mechanical properties of adsorbed protein films and the stability against disproportionation of foams made with the corresponding proteins. Furthermore, correlations between macroscopic film properties and molecular properties of the proteins in terms of molecular dimensions and secondary structure were studied. It was discovered that the molecular area at the onset of surface pressure per unit protein molecular weight was strongly correlated to the steady-state shear stress of a saturated protein film. This means that protein 'hardness' largely determines the film properties but a quantitative model is yet to be developed. Practical relevance of the mechanical properties of adsorbed protein layers for the stability of emulsions and foams is discussed.

Keywords: Sunflower protein, Helianthusannuus ,helianthinin, albumins, solubility, structure,denaturation, pH, temperature, ionic strength,phenoliccompounds,chlorogenicacid, foams, emulsions, functionalityThe research described in this thesis deals with the relation between specific sunflower proteins, their structure and their functional properties as a function of extrinsic factors as pH, ionic strength and temperature.Sunflower protein isolate (SI) devoid ofchlorogenicacid (CGA), the mainphenoliccompound present, was obtained withoutdenaturationof the proteins. Sunflower proteins were found to be composed of two main protein fractions: 2S albumins or sunflower albumins (SFAs) andhelianthinin. Subsequently, these protein fractions werebiochemicallyand structurally characterized under conditions relevant to food processing.Depending on pH, ionic strength, temperature and protein concentration,helianthininoccurs in the 15-18S (high molecular weight aggregate), 11 S (hexamer), 7S (trimer) or 2-3S (monomer) form. Dissociation into 7S from 11S gradually increased with increasing pH from 5.8 to 9.0. Enhancing the ionicstrengthresulted in stabilization of the 11S form. Heating and lowering the pH resulted in dissociation into themonomericform ofhelianthinin. The 11S and 7S form ofhelianthinindiffer in their secondary structure, tertiary structure, and thermal stability. With respect to solubilityas a function of pH,helianthininshows a bell shaped curve with a minimum at approximately pH 5.0 at low ionic strength. At high ionic strength,helianthininis almost insoluble at pH< 5.0.The second main sunflower fraction,SFAs, revealed to be very stable against pH changes (pH 3.0 to 9.0) and heat treatment (up to 100°C), and their solubility was only marginally affected by pH and ionic strength. The solubility of the SI as a function of pH seems to be dominated by that ofhelianthinin.Foam and emulsion properties of the sunflower isolate as well as those of purifiedhelianthinin,SFAsand combinations thereof were studied at various pH values and ionic strengths, and after heat treatment. Sunflower proteins were shown to form stable emulsions, with the exception ofSFAsat alkaline and neutral pH values. Increasing amount ofSFAsimpaired the emulsifying properties. Regarding foam properties, less foam could be formed fromhelianthininthan fromSFAs, but foam prepared withhelianthininwas more stable againstOstwaldripening and drainage than foam prepared withSFAs. Increasing amounts ofSFAshad a positive effect on foam volume and a negative one on foam stability and drainage. It was found that treatments that increase conformational flexibility improve the emulsion and foam properties of sunflower proteins.

Keywords: protein film, protein conformation, air/water interface, network formation, foam formation, foam stability, interfacial rheology, fracture behaviour.The aim of this thesis was to obtain systematic information on the importance of mechanical and conformational aspects for the formation of a visco-elastic protein network at the air/water interface. Such a protein network is formed upon adsorption at the interface and is assumed to play a role in the formation and stabilisation of emulsions and foams. To understand the formation of a visco-elastic layer with specific mechanical properties, one has to study the molecular processes occurring at the interface, namely protein adsorption, conformational changes that occur upon adsorption and the interactions between the adsorbed proteins. A series of proteins was studied with a tertiary structure varying from random coil (flexible) to rigid (globular):b-casein,b-lactoglobulin, ovalbumin and (soy) glycinin. Glycinin has only been studied preliminary in the past but, being an interesting substitute for animal proteins, it was investigated quite extensively in this thesis. The conformation of glycinin was found to be pH-dependent and this change in conformation strongly affected the adsorption behaviour and rheological properties of interfacial glycinin layers. The monomeric glycinin form present at pH3 behaved as a good foaming agent whereas at pH 6.7 (hexamer form) no foam could be formed. Infrared Reflection Absorption Spectroscopy (IRRAS) showed that only minor changes occurred in the secondary structure of a protein upon adsorption at the interface. Ovalbumin andb-lactoglobulin showed a 10% loss ofb-sheet structures whereas glycinin (pH3) formed intermolecular anti-parallelb-sheets. The latter is an indication for interfacial aggregation. Mechanical properties were determined by deformation in shear and dilation. Upon large deformations most protein films were found to exhibit fracture behaviour. The differences observed for ovalbumin,b-lactoglobulin and glycinin indicated a transition from a more yielding behaviour to a more brittle fracture behaviour. A correlation was found between several mechanical properties of adsorbed protein films and the stability against disproportionation of foams made with the corresponding proteins. Furthermore, correlations between macroscopic film properties and molecular properties of the proteins in terms of molecular dimensions and secondary structure were studied. It was discovered that the molecular area at the onset of surface pressure per unit protein molecular weight was strongly correlated to the steady-state shear stress of a saturated protein film. This means that protein 'hardness' largely determines the film properties but a quantitative model is yet to be developed. Practical relevance of the mechanical properties of adsorbed protein layers for the stability of emulsions and foams is discussed.

Whey protein and sodium caseinate were hydrolysed with commercially available enzyme preparations. The resulting hydrolysates were characterised using several analytical characterisation methods and by determination of several functional properties. Subsequently, correlations between the biochemical characteristics themselves and between biochemical and functional properties were studied using multivariate regression analysis.Biochemical characteristics of hydrolysates were determined using unifactorial methods like the degree of hydrolysis, and by multifactorial methods, i.e . reversed phase (RPC) and size exclusion chromatography (SEC), and Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy appeared to discriminate most effectively between hydrolysates made from different protein sources and classes of proteolytic enzymes, followed by RPC and SEC.Emulsion and foam properties of hydrolysates were similar or inferior to those of the parental proteins. Casein hydrolysates generally showed better emulsion and foam forming ability than whey protein hydrolysates. Foam forming ability of whey protein hydrolysates was correlated to the molecular weight distribution (MWD) of the peptides, showing that especially peptides with MW of 3-5 kDa contributed to foam forming ability.Concerning prevention of emulsion instability due to coalescence it was shown that peptides with a molecular weight larger than 2 kDa are needed. Foam stabilising ability of casein hydrolysates also depended on the MWD of hydrolysates, but higher molecular weight peptides, i.e. larger than 7 kDa, were needed to obtain good foam stability.The ability of the three multifactorial characterisation methods (SEC, RPC, FTIR spectroscopy) to predict functional properties was investigated. It appeared that SEC profiles were able to predict emulsion and foam stability of all hydrolysates, as well as foam forming ability, Angiotensin Converting Enzyme (ACE) inhibiting ability and bitterness of whey hydrolysates. RPC profiles were also able to predict these properties and additionally predicted solubility and bitterness of casein hydrolysates. FTIR spectra were best suited to predict a variety of hydrolysate properties, since apart from the before-mentioned properties, the spectra can also be used to predict emulsion forming ability and to improve prediction of bitterness of hydrolysates.Finally, the influence of hydrolysis process conditions on ACE inhibiting ability of whey hydrolysates was investigated, showing that ACE inhibiting activity could be optimised by using process optimisation techniques like experimental design and response surface optimisation.

Whey protein and sodium caseinate were hydrolysed with commercially available enzyme preparations. The resulting hydrolysates were characterised using several analytical characterisation methods and by determination of several functional properties. Subsequently, correlations between the biochemical characteristics themselves and between biochemical and functional properties were studied using multivariate regression analysis.Biochemical characteristics of hydrolysates were determined using unifactorial methods like the degree of hydrolysis, and by multifactorial methods, i.e . reversed phase (RPC) and size exclusion chromatography (SEC), and Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy appeared to discriminate most effectively between hydrolysates made from different protein sources and classes of proteolytic enzymes, followed by RPC and SEC.Emulsion and foam properties of hydrolysates were similar or inferior to those of the parental proteins. Casein hydrolysates generally showed better emulsion and foam forming ability than whey protein hydrolysates. Foam forming ability of whey protein hydrolysates was correlated to the molecular weight distribution (MWD) of the peptides, showing that especially peptides with MW of 3-5 kDa contributed to foam forming ability.Concerning prevention of emulsion instability due to coalescence it was shown that peptides with a molecular weight larger than 2 kDa are needed. Foam stabilising ability of casein hydrolysates also depended on the MWD of hydrolysates, but higher molecular weight peptides, i.e. larger than 7 kDa, were needed to obtain good foam stability.The ability of the three multifactorial characterisation methods (SEC, RPC, FTIR spectroscopy) to predict functional properties was investigated. It appeared that SEC profiles were able to predict emulsion and foam stability of all hydrolysates, as well as foam forming ability, Angiotensin Converting Enzyme (ACE) inhibiting ability and bitterness of whey hydrolysates. RPC profiles were also able to predict these properties and additionally predicted solubility and bitterness of casein hydrolysates. FTIR spectra were best suited to predict a variety of hydrolysate properties, since apart from the before-mentioned properties, the spectra can also be used to predict emulsion forming ability and to improve prediction of bitterness of hydrolysates.Finally, the influence of hydrolysis process conditions on ACE inhibiting ability of whey hydrolysates was investigated, showing that ACE inhibiting activity could be optimised by using process optimisation techniques like experimental design and response surface optimisation.

The results of research concerning the feasibility of anaerobic treatment of domestic sewage at low temperature are summarized in this article. The batch tests demonstrated a high biodegradability of domestic sewage at 20°C (74Ž Both batch and continuous experiments for the treatment of domestic sewage showed that the removal of SS prior to anaerobic treatment of domestic sewage not only provides a stable reactor performance but also improves the removal of both colloidal (CODcol) and dissolved COD (CODdis). The results of the pre-treatment of domestic sewage in an anaerobic filter (AF) and an anaerobic hybrid (AH) reactor showed that the AF reactor is an efficient process for the removal of suspended COD (CODss), viz. 82°at an HRT of 4 h and 13°C. The novel AF reactor consists of vertical sheets of reticulated polyurethane foam with knobs, where the biomass was only in attached form. For the treatment of pre-settled sewage at 13°C, the AH reactor, with granular sludge, showed a higher total COD (CODt) removal than the UASB reactor as a result of higher CODcol removal. Therefore, the performance of a two-step system, AF AH (with granular sludge) reactor, was investigated with different HRTs at 13°C. For optimization of CODss and CODdis an HRT of 4 4 h is needed, while for optimization of CODcol removal an HRT of 4 8 h is required. A CODt removal of 71 as achieved with 60␌onversion to methane from the removed CODt when the AF AH system was operated at an HRT of 4 8 h at 13°C.

The aim of the investigation described in this thesis was to increase the level of understanding of the role that proteins play in the preparation and subsequent stabilisation of foams and emulsions. One aspect of this role is facilitation of break-up, due to surface tension lowering. A second aspect is the formation of a viscoelastic interfacial layer, which affects both the short-term and long-term stability of the dispersion. Therefore, a systematic study of the changes in static and dynamic interfacial properties induced by proteins was carried out.For part of this study, dealing with the interfacial rheology, several experimental techniques were used. These techniques were either properly modified existing techniques (Chapter 3, modified longitudinal wave set-up) or newly developed (Chapter 4, Dynamic Drop Tensiometer; Chapter 5, Concentric Ring Surface Shear Rheometer) to meet the requirements for measuring the rheology of adsorbed protein layers at liquid/liquid interfaces. These requirements are (i) isotropic deformation, without leakage of the interfacial layer, for the dilational modulus measurements at air/water and oil/water interfaces and (ii) shear modulus measurements at small oscillatory deformation.The proteins chosen for this study wereβ-casein,β-lactoglobulin (BLG), bovine serum albumin (BSA), ovalbumin and lysozyme. This set of proteins was chosen, because they differ considerably in relevant aspects, such as molecular weight, molecular structure and iso-electric point.In Chapter 1 the scope and context of this study are given including a brief introduction into (i) the molecular properties of these proteins, that are relevant to the adsorption, (ii) protein adsorption and interfacial rheology, and (iii) the relation between interfacial properties and the properties of emulsions and foams.Chapter 2 deals with the adsorption of proteins at the air/water interface. The adsorption was determined by ellipsometry, a method by which not only the adsorbed amount but also the layer thickness and protein concentration in the adsorbed layer could be determined. The ellipsometric studies were combined with surface tension measurements at the same surface.All proteins examined show high affinity adsorption, i.e. strong adsorption at low concentration in solution. The initial rate of adsorption of all proteins is well described by a simple diffusion equation. For all proteins examined, the value of the surface pressure (Π) are protein-specific, but otherwise unique, time-independent functions of the adsorption (Γ). Time independence of theΠ(Γ) curve was concluded from the finding thatΠandΓpairs measured at different bulk concentrations and at different stages of adsorption, all collapse into one single curve. In other words, each protein has a unique surface equation of state indicated by its measuredΠ(Γ) curve. This curve reflects the relative rigidity of the protein molecule. For flexible molecules likeβ-casein and PVA ,Γ min (=ΓwhereΠstarts to deviate measurably from zero) is low and from this point onward the surface pressure increases gradually with increasingΓ. For rigid globular proteins (BSA, ovalbumin and lysozyme)Γ min is higher and with further increase of the surface concentration the surface pressure increases steeply. At high protein concentration and long adsorption times, for most proteins multilayer adsorption takes place.For ovalbumin, in the pH range 4-8 the effect of pH on theΠ-Γcurve is small, which indicates that electrostatic intermolecular forces do not contribute much to the surface pressure.In Chapter 3 a longitudinal wave technique, modified to ensure isotropic surface deformation, was used to determine the dilational modulus,ε, of adsorbed protein layers, at the air/water interface. This modification fully eliminated the complicating shear effects that became apparent in dilational modulus measurements with adsorbed layers of proteins in a conventional set-up.For all proteins examined at frequencies in the range from 0.01 to 1 rad/s, the initial part of theε(Π) plot is a straight line through the origin. The slope of this initial part ranges between +4 and +12 . No clear relationship between the slope and the rigidity of the protein molecule was found. However, the extent of this linear range is smaller for the flexible molecules (β-casein and PVA). From the fact that this slope significantly exceeds the ideal value of +1, it must be concluded that the behaviour of the adsorbed layer is far from ideal. In the linear range, the measured moduli coincide with the limiting moduli,ε 0 , calculated from theΠ(Γ) curve. This indicates that the surface pressure adjusts "instantaneously" to the changing adsorption during a compression-expansion cycle in time-scales ranging from 1 to 100 s. This also means that the modulus is purely elastic, i.e. the effect of relaxation processes is negligible. In this elastic range, differences between individual proteins are related to different degrees of non-ideality, reflected in the surface equation of state.At higher surface concentrations a relaxation mechanism becomes operative, which is most probably not caused by diffusional exchange between surface and solution. This conclusion is based on calculations of the diffusional transport rate and the theoretical frequency spectrum of the modulus. Relaxation due to conformational changes is plausible. In the visco-elastic regionε≥ε 0 for all proteins examined. This is an extra argument against diffusional exchange.The modulus increases in the order: PVA 1g/l), during the first minutes after adsorption a situation exists that differs from the equilibriumΠ(Γ) curve. At low interfacial pressures, during a modulus measurement, the adaptation of the conformation is faster (< 1 s.). Non-ideality of the adsorbed layer increases in the sequence TAG-oil < tetradecane < air, which is probably related to a decrease of solution quality for the more hydrophobic amino acids, which decreases in the same sequence. At each of the different interfaces non-ideality increases with increasing rigidity of the protein molecule (β-casein

The aim of the investigation described in this thesis was to increase the level of understanding of the role that proteins play in the preparation and subsequent stabilisation of foams and emulsions. One aspect of this role is facilitation of break-up, due to surface tension lowering. A second aspect is the formation of a viscoelastic interfacial layer, which affects both the short-term and long-term stability of the dispersion. Therefore, a systematic study of the changes in static and dynamic interfacial properties induced by proteins was carried out.For part of this study, dealing with the interfacial rheology, several experimental techniques were used. These techniques were either properly modified existing techniques (Chapter 3, modified longitudinal wave set-up) or newly developed (Chapter 4, Dynamic Drop Tensiometer; Chapter 5, Concentric Ring Surface Shear Rheometer) to meet the requirements for measuring the rheology of adsorbed protein layers at liquid/liquid interfaces. These requirements are (i) isotropic deformation, without leakage of the interfacial layer, for the dilational modulus measurements at air/water and oil/water interfaces and (ii) shear modulus measurements at small oscillatory deformation.The proteins chosen for this study wereβ-casein,β-lactoglobulin (BLG), bovine serum albumin (BSA), ovalbumin and lysozyme. This set of proteins was chosen, because they differ considerably in relevant aspects, such as molecular weight, molecular structure and iso-electric point.In Chapter 1 the scope and context of this study are given including a brief introduction into (i) the molecular properties of these proteins, that are relevant to the adsorption, (ii) protein adsorption and interfacial rheology, and (iii) the relation between interfacial properties and the properties of emulsions and foams.Chapter 2 deals with the adsorption of proteins at the air/water interface. The adsorption was determined by ellipsometry, a method by which not only the adsorbed amount but also the layer thickness and protein concentration in the adsorbed layer could be determined. The ellipsometric studies were combined with surface tension measurements at the same surface.All proteins examined show high affinity adsorption, i.e. strong adsorption at low concentration in solution. The initial rate of adsorption of all proteins is well described by a simple diffusion equation. For all proteins examined, the value of the surface pressure (Π) are protein-specific, but otherwise unique, time-independent functions of the adsorption (Γ). Time independence of theΠ(Γ) curve was concluded from the finding thatΠandΓpairs measured at different bulk concentrations and at different stages of adsorption, all collapse into one single curve. In other words, each protein has a unique surface equation of state indicated by its measuredΠ(Γ) curve. This curve reflects the relative rigidity of the protein molecule. For flexible molecules likeβ-casein and PVA ,Γ min (=ΓwhereΠstarts to deviate measurably from zero) is low and from this point onward the surface pressure increases gradually with increasingΓ. For rigid globular proteins (BSA, ovalbumin and lysozyme)Γ min is higher and with further increase of the surface concentration the surface pressure increases steeply. At high protein concentration and long adsorption times, for most proteins multilayer adsorption takes place.For ovalbumin, in the pH range 4-8 the effect of pH on theΠ-Γcurve is small, which indicates that electrostatic intermolecular forces do not contribute much to the surface pressure.In Chapter 3 a longitudinal wave technique, modified to ensure isotropic surface deformation, was used to determine the dilational modulus,ε, of adsorbed protein layers, at the air/water interface. This modification fully eliminated the complicating shear effects that became apparent in dilational modulus measurements with adsorbed layers of proteins in a conventional set-up.For all proteins examined at frequencies in the range from 0.01 to 1 rad/s, the initial part of theε(Π) plot is a straight line through the origin. The slope of this initial part ranges between +4 and +12 . No clear relationship between the slope and the rigidity of the protein molecule was found. However, the extent of this linear range is smaller for the flexible molecules (β-casein and PVA). From the fact that this slope significantly exceeds the ideal value of +1, it must be concluded that the behaviour of the adsorbed layer is far from ideal. In the linear range, the measured moduli coincide with the limiting moduli,ε 0 , calculated from theΠ(Γ) curve. This indicates that the surface pressure adjusts "instantaneously" to the changing adsorption during a compression-expansion cycle in time-scales ranging from 1 to 100 s. This also means that the modulus is purely elastic, i.e. the effect of relaxation processes is negligible. In this elastic range, differences between individual proteins are related to different degrees of non-ideality, reflected in the surface equation of state.At higher surface concentrations a relaxation mechanism becomes operative, which is most probably not caused by diffusional exchange between surface and solution. This conclusion is based on calculations of the diffusional transport rate and the theoretical frequency spectrum of the modulus. Relaxation due to conformational changes is plausible. In the visco-elastic regionε≥ε 0 for all proteins examined. This is an extra argument against diffusional exchange.The modulus increases in the order: PVA 1g/l), during the first minutes after adsorption a situation exists that differs from the equilibriumΠ(Γ) curve. At low interfacial pressures, during a modulus measurement, the adaptation of the conformation is faster (< 1 s.). Non-ideality of the adsorbed layer increases in the sequence TAG-oil < tetradecane < air, which is probably related to a decrease of solution quality for the more hydrophobic amino acids, which decreases in the same sequence. At each of the different interfaces non-ideality increases with increasing rigidity of the protein molecule (β-casein

Onderzoek naar de relatie tussen moleculaire structuur van eiwitten en het schuimgedrag van de oplossing

The influence of spreading particles on the stability of thin liquid films was investigated. Due to the spreading of a particle, i.e. an oil droplet, over a surface of a thin liquid film the latter becomes thinner and may rupture. The following steps in the whole process were distinguished: 1) transport of the particle to the film surface, 2) dewetting of the particle ensuring physical contact between the particle surface and the film surface, 3) spreading of the particle over the film surface and 4) movement of the film bulk liquid induced by the surface movement due to spreading material.An attempt was made to develop a theory that describes the spreading process quantitatively. It describes the film thinning process as a result of the liquid drag due to the surface motion initiated by the spreading material by using the parameters film thickness, droplet radius, liquid bulk viscosity, liquid bulk density and the surface rheological properties of the oil droplet and the film liquid.Model systems of foaming liquid and lipid material were used to study this spreading process. The latter was done on a relative macroscopic scale over bulk surfaces which is different compared to the dimensions and conditions which are valid for spreading particles on a foam film. It was assumed that the developed theory could be applied to both dimensions. The experimental results pointed in this direction. This was verified by the experimental results of introducing small spreading emulsion droplets on thin liquid films. A clear correlation between the above mentioned parameters and film rupture initiated by the spreading droplets was found.

Onderzoek naar de relatie tussen moleculaire structuur van eiwitten en het schuimgedrag van de oplossing

The influence of spreading particles on the stability of thin liquid films was investigated. Due to the spreading of a particle, i.e. an oil droplet, over a surface of a thin liquid film the latter becomes thinner and may rupture. The following steps in the whole process were distinguished: 1) transport of the particle to the film surface, 2) dewetting of the particle ensuring physical contact between the particle surface and the film surface, 3) spreading of the particle over the film surface and 4) movement of the film bulk liquid induced by the surface movement due to spreading material.An attempt was made to develop a theory that describes the spreading process quantitatively. It describes the film thinning process as a result of the liquid drag due to the surface motion initiated by the spreading material by using the parameters film thickness, droplet radius, liquid bulk viscosity, liquid bulk density and the surface rheological properties of the oil droplet and the film liquid.Model systems of foaming liquid and lipid material were used to study this spreading process. The latter was done on a relative macroscopic scale over bulk surfaces which is different compared to the dimensions and conditions which are valid for spreading particles on a foam film. It was assumed that the developed theory could be applied to both dimensions. The experimental results pointed in this direction. This was verified by the experimental results of introducing small spreading emulsion droplets on thin liquid films. A clear correlation between the above mentioned parameters and film rupture initiated by the spreading droplets was found.

Bread dough is a foam and the stability of the gas bubbles towards disproportionation and coalescence during the breadmaking process determines for a large part the final appearance of the baked bread with respect to crumb structure and loaf volume. Gas bubble behaviour in bread dough is determined by both surface and bulk rheological properties of dough (components). These properties were studied and their relevance to breadmaking was established.Surface dilational moduli of different dough components were determined. It appears that wheat lipids and added surfactants as SSL and DATEM can retard disproportionation to a large extent if these components are present in the right concentration and modification. Wheat proteins will hardly retard this foam instability mechanism.Dynamic measurements and biaxial extension tests on wheat and rye flour as well as wheat gluten doughs were performed. Both flour and gluten doughs show strain hardening at 20 and at 55°C. Wheat cultivars with good breadmaking performance exhibit stronger strain hardening properties than poor baking ones and rye. Next to strain hardening, biaxial stress and extensibility are important parameters determining bread quality.During mixing both the surface tension and the viscosity of the dough determine the (minimum) radii of the entrapped gas bubbles. Directly after mixing surface properties dominate primarily gas bubble behaviour by retarding disproportionation, especially if surfactants like SSL or DATEM are added. Already during first proof bulk properties, especially biaxial stress, extensibility and strain hardening, start to dominate gas bubble stability and this remains as such during almost the remainder of the breadmaking process. In the final stage of oven rise surface properties may contribute to the stability of some dough films that have become very thin.

The mechanism which explains extensive particle aggregation in topping emulsions, that contain a relatively large amount of the α-tending emulsifier glycerol lacto palmitate (GLP) , was studied.From x-ray and neutron diffraction and from differential scanning calorimetry it appeared that GLP forms an α-gel phase with water below the crystallization temperature of the emulsifier. From this phase study it was concluded that the process of particle aggregation in these emulsions is a result of the formation of this α-gel phase at the o/w-interface of the dispersed particles.The results of both bulk and surface rheological experiments, performed with these emulsions, are discussed in relation to the physical properties of these systems. The results are interpreted by assuming that the physical properties of these whippable emulsions are determined by the formation of this α-gel phase at the interface of the fat particles.

The mechanism which explains extensive particle aggregation in topping emulsions, that contain a relatively large amount of the α-tending emulsifier glycerol lacto palmitate (GLP) , was studied.From x-ray and neutron diffraction and from differential scanning calorimetry it appeared that GLP forms an α-gel phase with water below the crystallization temperature of the emulsifier. From this phase study it was concluded that the process of particle aggregation in these emulsions is a result of the formation of this α-gel phase at the o/w-interface of the dispersed particles.The results of both bulk and surface rheological experiments, performed with these emulsions, are discussed in relation to the physical properties of these systems. The results are interpreted by assuming that the physical properties of these whippable emulsions are determined by the formation of this α-gel phase at the interface of the fat particles.