Dissertations / Theses on the topic 'Protein fouling'

Fouling and cleaning processes impact industrial production, in terms of economics, product quality, product safety, and plant efficiency. Therefore, optimisation of fouling and cleaning processes is a significant issue, and needs a good understanding of fouling and cleaning kinetics. Ideal monitors should determine the right time when a process run should stop and when a plant will be clean in order to improve the process efficiency. This thesis investigated the fouling and cleaning behaviour of dairy fluids in a plate heat exchanger (PHE) and bench scale fouling rig, using whey protein concentrate (WPC) and WPC-/m (with added minerals) as fluid models. Fouling and cleaning monitoring methods were also investigated as new ways to operate and control the processes. Experiments displayed that fouling increased with increasing protein concentration up to a limit of approx. β-Lg 0.3 wt. %. Increasing the flow rate from 100 to 150 l/h decreased the Δ(ΔP) fouling rate for β-Lg concentrations of 0.1, 0.3 and 0.5wt.% by 34, 70 and 72.7%, respectively, due to the increasing of shear stresses at the heat transfer surface. Adding minerals to WPC has lowered the temperature at which β-Lg begins to denature. The differences in fouling behaviour of WPC and WPCm had an effect on cleaning behaviour. Increasing the mineral content in WPC deposits leads to cleaning behaviour which differs completely from that of proteinaceous deposit as no pressure peak is observed.

In this study the fouling mechanisms of various microfiltration and ultrafiltration membranes were studied when subjected to crossflow filtration using various protein solutions. Experimentation was carried out using controlled flux experiments and fouling phenomena was investigated via the monitoring of the transmembrane pressure (TMP) and rejection. Electron microscopy was employed to study fouling on microfiltration membranes when single protein solutions were filtered while a novel method involving Matrix-Assisted Laser Desorption Ionisation Mass Spectrometry (MALDI-MS) was developed to qualitatively and quantitatively analyse mixed proteins fouled on ultrafiltration membranes. An apparent critical flux was identified whereby fouling was shown to occur at fluxes where there was no increase in TMP. TMP increase is one of the common indicators of fouling in controlled flux operation. Microfiltration experiments showed that the imposition of the apparent critical flux is accompanied by rapid increases in hydraulic resistance and the membrane wall concentration. Pore blockage and narrowing occurred at somewhat higher fluxes as indicated by increases in the observed rejection. Fouling was not influenced greatly by the addition of electrolytes for microfiltration membranes but observed transmissions were found to be greater than 100% when ultrafiltration membranes were employed. For all membranes used, the actual value of the apparent critical flux was shown to be independent of the salt concentration but dependent on pH. Sub apparent-critical constant flux microfiltration showed the existence of an aggregation/deposition time lag after which the membrane experiences a rapid increase in resistance due to protein aggregates blocking a majority of pores. This phenomenon was shown to be dependent on pH and ionic strength and was concluded to be the product of a balance between electrostatic, solubility and hydrophobic interactions.

A combination of surface analytical techniques, colloid probe Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) was used to optimise the grafting density of covalently attached 5, 20 and 40 kDa methoxy-terminated PEO layers (under marginal solvation (cloud point) conditions for the PEO molecules). The combination of these techniques allowed us to relate the PEO layer density and molecular conformations to the range, magnitude and types of forces generated by coatings of various grafting densities. The key optimisation parameter was the grafting time with the concentration of PEO in solution having a weaker effect. Oxidation of the substrate occurred, but did not significantly limit the surface density of the functional groups used to chemically attach the PEO molecules. Interactions between the substrate and silica were electrostatic in origin and did not contribute to the interaction between silica and the PEO surfaces due to salt screening effects Surfaces with dense, highly stretched PEO layers (brushes) generated purely repulsive forces at all separation distances, arising from compression by the silica spherical probe used. The force profiles for lower density surfaces comprised long-ranged attractive and short-ranged repulsive forces. The attractive forces were most likely due to attractive bridging interactions between the PEO chains and the SiO2 surface. For low grafting densities, i.e. inter-chain grafting distances, s > ??RF, the PEO layers were not strongly stretched and free to adsorb onto the opposing silica surface. XPS analysis demonstrated that HSA and Fibrinogen adsorbed onto low density 20 kDa PEO coatings (s > ??RF), most likely via diffusion through the PEO layer. No protein adsorption was found (detection limit > 10 ng/cm2) on high density, ???strongly stretched brush??? coatings (s < ?? RF). Analysis of data from the more sensitive Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) techniques indicated that low amounts of adsorbed HSA, lactoferrin, lysozyme, and IgG were present on high density 20 and 40 kDa surfaces; the most likely explanation being attractive interactions between the proteins and the PEO layers during the protein adsorption experiments. ToF-SIMS data obtained for the strongly stretched (s < ?? RF) 5 kDa PEO surfaces suggested that no protein was adsorbed, in line with the XPS data for the same surfaces.

Fouling is a chronic problem in many heat transfer systems and results in the need for frequent heat exchanger (HEX) cleaning. In the dairy industry, the associated operating cost and environmental impact are substantial. Antifouling coatings are one mitigation option. In this work, the fouling behaviour of fluoropolymer, polypropylene and stainless steel heat transfer surfaces in processing raw milk and whey protein solution are studied. Methodologies to assess the economics of antifouling coatings are developed and applied. Two experimental apparatuses were designed and constructed to study fouling at surface temperatures around 90 °C. A microfluidic system with a 650 x 2000 µm flow channel enables fouling studies to be carried out by recirculating 2 l of raw milk. The apparatus operates in the laminar flow regime and the capability to probe the local composition of delicate fouling deposit $\textit{in-situ}$ with histological techniques employing confocal laser scanning microscopy. A larger bench-scale apparatus with a 10 x 42 mm flow channel was built to recirculate 17 l of solution in the turbulent flow regime which is more representative of conditions in an industrial plate HEX. Experimental results demonstrate that fluoropolymer coatings can reduce fouling masses from raw milk and whey protein solution by up to 50 %. Surface properties affect the structure and composition of the deposit. At the interface with apolar surfaces raw milk fouling layers are high in protein, whereas a strongly attached mineral-rich layer is present at the interface with steel. Whey protein deposits generated on apolar surfaces are more spongy and have a lower thermal conductivity and/or density than deposits on steel. The attraction of denatured protein towards apolar surfaces and the formation of a calcium phosphate layer on steel at later stages of fouling are explained with arguments based on the interfacial free energy of these materials in water. The financial attractiveness of coatings is considered for HEX subject to linearly and asymptotically increasing fouling resistance and using a spatially resolved fouling model. An explicit solution to the cleaning-scheduling problem is presented for the case of equal heat capacity flow rates in a counter-current HEX. Scenarios where the use of coatings may be attractive or where there is no financial benefit in cleaning a fouled exchanger are identified. Finally, experimental data are used to estimate the economic potential of fluoropolymer coated HEXs in the ultra-high-temperature treatment of milk. In the considered case, the value of a fluoropolymer coating inferred from the reduction in fouling is estimated to be around 2000 US$/m².

Des peptides bioactifs ont déjà été fractionnés par électrodialyse avec membrane de filtration (ÉDMF) à partir d’hydrolysats de sous-produits de crabe des neiges. L’optimisation des paramètres apparaît maintenant indispensable pour perfectionner le procédé. Ainsi, le taux de migration des peptides, leur sélectivité et l'évolution des paramètres électrodialytiques ont été étudiés pour différents paramètres (configuration, concentration en KCl et types de champ électrique). La configuration (2) de la cellule d’ÉDMF comprenant deux compartiments d'alimentation et un compartiment de récupération a démontré des valeurs de champ électrique local relativement stables par rapport à la configuration (1) constituée d’un compartiment d’alimentation et de deux compartiments de récupération. Des peptides contenant des glutamates, des aspartates, et des glycines ont été séparés avec la configuration 1 et des peptides composés d’arginines et de lysines avec la configuration 2. Un taux de migration peptidique de 13,76 ± 3,64 g/m2h a été obtenu par le maintien constant de la conductivité des solutions. La sélectivité a été accrue en augmentant la concentration en KCl de 1 à 5 g/L dans le compartiment de récupération. Une augmentation de la force ionique a amplifié la charge de surface, agrandissant ainsi la taille effective des pores et réduisant la couche d'hydratation de la membrane d’ultrafiltration. Toutefois, les membranes échangeuses d’anions et de cations ont été colmatées par des peptides et des acides aminés et détériorées pendant l’ÉDMF. Pour résoudre ces problèmes, l’effet de l’application du champ électrique pulsé (PEF) et de l'inversion de polarité (PR) a été étudié. Le taux de migration des peptides n'a pas été affecté sauf avec PR à 40 V. La sélectivité a été maximale avec PEF à 20 V. La dissociation de l'eau a été réduite tout en conservant les propriétés physico-chimiques des membranes grâce à l’application du PEF et de la PR par rapport au courant continu (DC). En outre, la plus faible quantité d'énergie a été consommée avec le PEF. Par conséquent, il a été possible d’optimiser la technologie d’ÉDMF du point de vue de l’efficacité énergétique, de la sélectivité peptidique et de l’encrassement membranaire grâce à l’application du PEF et tout en maintenant la conductivité électrique des solutions.
Des peptides bioactifs ont déjà été fractionnés par électrodialyse avec membrane de filtration (ÉDMF) à partir d’hydrolysats de sous-produits de crabe des neiges. L’optimisation des paramètres apparaît maintenant indispensable pour perfectionner le procédé. Ainsi, le taux de migration des peptides, leur sélectivité et l'évolution des paramètres électrodialytiques ont été étudiés pour différents paramètres (configuration, concentration en KCl et types de champ électrique). La configuration (2) de la cellule d’ÉDMF comprenant deux compartiments d'alimentation et un compartiment de récupération a démontré des valeurs de champ électrique local relativement stables par rapport à la configuration (1) constituée d’un compartiment d’alimentation et de deux compartiments de récupération. Des peptides contenant des glutamates, des aspartates, et des glycines ont été séparés avec la configuration 1 et des peptides composés d’arginines et de lysines avec la configuration 2. Un taux de migration peptidique de 13,76 ± 3,64 g/m2h a été obtenu par le maintien constant de la conductivité des solutions. La sélectivité a été accrue en augmentant la concentration en KCl de 1 à 5 g/L dans le compartiment de récupération. Une augmentation de la force ionique a amplifié la charge de surface, agrandissant ainsi la taille effective des pores et réduisant la couche d'hydratation de la membrane d’ultrafiltration. Toutefois, les membranes échangeuses d’anions et de cations ont été colmatées par des peptides et des acides aminés et détériorées pendant l’ÉDMF. Pour résoudre ces problèmes, l’effet de l’application du champ électrique pulsé (PEF) et de l'inversion de polarité (PR) a été étudié. Le taux de migration des peptides n'a pas été affecté sauf avec PR à 40 V. La sélectivité a été maximale avec PEF à 20 V. La dissociation de l'eau a été réduite tout en conservant les propriétés physico-chimiques des membranes grâce à l’application du PEF et de la PR par rapport au courant continu (DC). En outre, la plus faible quantité d'énergie a été consommée avec le PEF. Par conséquent, il a été possible d’optimiser la technologie d’ÉDMF du point de vue de l’efficacité énergétique, de la sélectivité peptidique et de l’encrassement membranaire grâce à l’application du PEF et tout en maintenant la conductivité électrique des solutions.
Bioactive peptides were efficiently separated by using electrodialysis with filtration membrane (EDFM) from snow crab byproduct hydrolysate. Meanwhile, optimization of parameters is indispensable for scaling-up. The peptide migration rate and selectivity as well as evolution of electrodialytic parameters were studied with different parameters such as EDFM cell configuration, KCl concentration and type of electric field. The EDFM stack with two feed and one recovery compartments (configuration 2) has relatively stable electric field strengths (local) than the configuration with one feed and two recovery compartments (configuration 1). Peptides containing anionic amino acids: glutamic and aspartic acid as well as glycine and cationic amino acids: arginine and lysine were fractionated using configuration 1 and 2, respectively. Maintenance of solution conductivity upheld the local electric field and peptide migration throughout the treatment resulting in a higher peptide migration rate of 13.76±3.64 g/m2.h never observed so far. The selectivity of cationic peptides containing arginine and lysine increased significantly with increase in KCl concentration from 1 to 5 g/L. An increase in ionic strength amplified the surface charge density of filtration membrane subsequently increasing effective pore size and reducing hydration layer. However, both anion- and cation-exchange membranes were fouled by peptides and amino acids and were deteriorated during EDFM treatment. To address these problems, the effect of applying pulsed electric field (PEF) and polarity reversal (PR) was studied. The peptide migration rate was unaffected among PEF, PR and DC modes except with PR at 40 V. The selectivity of cationic peptides was maximum with PEF at 20 V. Fouling and water dissociation were significantly reduced and physicochemical properties of IEMs were better-protected with PEF and PR than DC. Moreover, the least amount of energy was consumed with PEF mode. Therefore, the parameters affecting EDFM process were optimized in terms of energy efficiency, selectivity and lower deterioration of membranes by applying PEF regime with configuration 2 and maintaining the constant electrical conductivity of solutions.
Bioactive peptides were efficiently separated by using electrodialysis with filtration membrane (EDFM) from snow crab byproduct hydrolysate. Meanwhile, optimization of parameters is indispensable for scaling-up. The peptide migration rate and selectivity as well as evolution of electrodialytic parameters were studied with different parameters such as EDFM cell configuration, KCl concentration and type of electric field. The EDFM stack with two feed and one recovery compartments (configuration 2) has relatively stable electric field strengths (local) than the configuration with one feed and two recovery compartments (configuration 1). Peptides containing anionic amino acids: glutamic and aspartic acid as well as glycine and cationic amino acids: arginine and lysine were fractionated using configuration 1 and 2, respectively. Maintenance of solution conductivity upheld the local electric field and peptide migration throughout the treatment resulting in a higher peptide migration rate of 13.76±3.64 g/m2.h never observed so far. The selectivity of cationic peptides containing arginine and lysine increased significantly with increase in KCl concentration from 1 to 5 g/L. An increase in ionic strength amplified the surface charge density of filtration membrane subsequently increasing effective pore size and reducing hydration layer. However, both anion- and cation-exchange membranes were fouled by peptides and amino acids and were deteriorated during EDFM treatment. To address these problems, the effect of applying pulsed electric field (PEF) and polarity reversal (PR) was studied. The peptide migration rate was unaffected among PEF, PR and DC modes except with PR at 40 V. The selectivity of cationic peptides was maximum with PEF at 20 V. Fouling and water dissociation were significantly reduced and physicochemical properties of IEMs were better-protected with PEF and PR than DC. Moreover, the least amount of energy was consumed with PEF mode. Therefore, the parameters affecting EDFM process were optimized in terms of energy efficiency, selectivity and lower deterioration of membranes by applying PEF regime with configuration 2 and maintaining the constant electrical conductivity of solutions.

Le colmatage des membranes reste la principale limitation pour le développement du bioréacteur à membrane (BAM). Dans cette thèse, l'objectif principal se concentre sur les effets des micropolluants pharmaceutiques qui se retrouvent dans les eaux usées domestiques sur le colmatage de la membrane du BAM. Carbamazépine (CBZ), un médicament antiépileptique, a été choisi. Les effets de la CBZ sur le colmatage du BAM ont été étudiés de deux manières: un pic de pollution pour étudier les effets des pics de CBZ à court terme sur le pouvoir colmatant et une pollution continue pour examiner les effets de CBZ à long terme sur le colmatage du BAM. Les résultats ont montré que, pendant 3 heures contact avec CBZ de 100 µg L-1, le pouvoir colmatant des boues activées a augmenté en raison de l'augmentation des protéines de 100-1000 kDa dans le surnageant, ce qui pourrait être complètement retenu par la membrane du BAM et les membranes utilisées dans les essais de filtrabilité. L'augmentation des protéines de 100-1000 kDa dans le surnageant peut probablement être causé par la décomposition bactérienne face aux médicaments. L'effet réduit a été observée pour les boues provenant du BAM fonctionné sous la charge organique plus élevée. Pendant le contact continue, la vitesse du colmatage plus élevée a été observé après l'addition en continu de CBZ dans le BAM (90 µg L-1 dans l'alimentation), qui pourrait être lié à l'augmentation importante des protéines de 10-100 kDa dans le surnageant. Des protéines de 10-100 kDa s’accumulent dans le dépôt de la membrane du BAM, modifient de la structure de dépôt et changent les caractéristiques de rétention de BAM. L'augmentation des protéines de 10-100 kDa a probablement été causée par la réaction de défense des bactéries face en permanence des médicaments. Légère inhibition de l'activité microbienne a été trouvée plusieurs jours après l'addition de la CBZ dans le BAM, puis il a été stabilisé à un certain niveau en raison de l'acclimatation des boues au stress pharmaceutique. Similaire, l'augmentation significative de la concentration en protéine a été observée au début plusieurs jours après l'addition de la CBZ dans le BAM, puis retourne à son niveau initial. Aucun changement significatif de la taille des flocs des boues et de la concentration en polysaccharides dans le surnageant n’a été constaté au cours de la période de contact continu à long terme. Cette étude pourrait contribuer à améliorer la compréhension des interactions complexes entre les micropolluants pharmaceutiques, boues activées et le colmatage du BAM
Membrane fouling still remains the main limitation for the development of membrane bioreactor (MBR). In this thesis, the main objective focuses on the effects of pharmaceutical micropollutants which are frequently found in domestic wastewater on MBR fouling. Carbamazepine (CBZ), an anti-epileptic drug, was chosen in this study due to its occurrence in domestic wastewater and persistency in MBR process. The effects of CBZ on MBR fouling were investigated in two different ways of contact, i.e. short-term peak contact and long-term continuous contact. The results showed that during only 3 hours contact with 100 µg L-1 CBZ, the fouling propensity of the sludge increased due to the increase in 100-1000 kDa protein-like substances in the supernatant, which could be completely retained by the MBR membrane and the membranes used in the filterability tests. The increase of 100-1000 kDa protein-like compounds in the supernatant may probably be caused by the bacterial decay when facing the pharmaceutical stress. Besides, the reduced effect was observed for sludge obtained from MBR operated under higher organic loading rate. During the long-term continuous contact, significantly higher MBR fouling rate was observed after the continuous addition of CBZ in the MBR via the feed (90 µg L-1 CBZ in the feed), which could be related to the significant increase of 10-100 kDa protein-like compounds in the supernatant after addition of CBZ. The 10-100 kDa protein-like compounds could accumulate in the biocake, which was formed on MBR membrane surface, modify the biocake structure and change the retention characteristics of MBR. The increase of 10-100 kDa protein-like compounds was probably caused by the defensive response of bacteria when continuously facing the pharmaceutical stress. Slight inhibition of microbial activity was found several days after addition of CBZ in MBR, and then it was stabilized to some constant level due to the acclimation of sludge to the pharmaceutical stress. Similar, significant increase of protein concentration was observed at the beginning several days after addition of CBZ in MBR, then returned to the initial level. No significant change in sludge floc size and polysaccharide concentration in supernatant was found during the long-term continuous contact period. This study could help to enhance the understanding of complex interactions among pharmaceutical micropollutants, activated sludge and MBR fouling

Les protéines extraites des feuilles de luzerne sont une source importante de protéines. La filtration membranaire, technologie de séparation respectueuse de l’environnement avec une productivité élevée et de faible coût a été utilisée pour séparer et concentrer les protéines des feuilles de luzerne à partir de leur jus. Cependant le phénomène du colmatage de la membrane qui réduit sérieusement le flux et la séparation des protéines est un facteur limitant important dans l'application de la filtration membranaire. Pour améliorer la récupération des protéines et amenuiser le phénomène du colmatage, la filtration membranaire associée à fort cisaillement a été utilisée pour la filtration du jus de luzerne. Toujours dans l’objectif d'optimiser le processus de la filtration, "le mode de la filtration" et "les paramètres de fonctionnement" ont été étudiés pour réduire le colmatage de la membrane et améliorer le rendement de la filtration. Puis, l’effluent du jus de luzerne a été filtré par des membranes dans des conditions de fort cisaillement afin de recycler les protéines. En outre, le mécanisme du colmatage a été étudié et a permis d’évaluer les stratégies de contrôle du colmatage. L'optimisation du procédé membranaire, via l’étude du "mode de filtration" et des "paramètres de fonctionnement" a été conduit dans le but d’améliorer la séparation et la concentration des protéines et de réduire le colmatage. Trois types de « mode de filtration » ont été testés : la filtration frontale sur le module de la cellule amicon (DA), la filtration tangentielle dynamique sur le module à disque rotatif (CRDM) et la filtration frontale sur le module à disque rotatif (DRDM)). Les « paramètres de fonctionnement » qui ont été étudiés sont les suivants : le type de membranes (ultrafiltration (UF) et microfiltration (MF)), la vitesse de rotation, la température et la pression transmembranaire (TMP). Le comportement du débit (évolution du flux du perméat au cours de la filtration), les performances de la séparation (taux de clarification et de concentration), l’efficacité du nettoyage de la membrane (récupération de la perméabilité membranaire) et la productivité lors des tests de recyclage et de concentration ont été étudiés dans le but de définir des stratégies dans le contrôle du colmatage. Puis, l’effluent de luzerne a été filtré par UF afin de séparer et purifier les protéines. Le mécanisme du phénomène du colmatage des membranes lors de la filtration du jus de luzerne a été étudié. Le processus du colmatage de la membrane a montré une tendance d’un colmatage multi-site progressif. Le modèle du colmatage multisite progressif selon la loi de Darcy (SMDM) a été proposé afin de mieux décrire et comprendre le processus du colmatage. Les effets de la composition du fluide d’alimentation, du choix de la membrane et des conditions hydraulique ont joué un rôle important dans le processus progressif du colmatage. De plus, les coefficients de résistance et de compressibilité dans les différentes étapes et sites ont été calculés afin d’expliquer le processus complexe du colmatage et d’évaluer l'efficacité des stratégies du contrôle du colmatage. Une série d'essais avec de longues durées de filtration a été réalisée pour étudier le déclin du flux et le colmatage de la membrane à diverses étapes du processus. Ces résultats présentent une utilité pour améliorer la récupération des protéines et contrôler le colmatage dans le processus de la filtration membranaire à fort cisaillement du jus de luzerne. Ces résultats sont aussi utiles pour la conception et la mise en place des technologies membranaires dans les processus industriels
Alfalfa leaf proteins extracted from plants are an important protein source. As an environmentally friendly separation technology with high productivity and low cost, membrane filtration was used to separate and concentrate leaf protein from alfalfa juice. However membrane fouling seriously reduces flux and protein separation and is an important limitation in the application of membrane filtration. To improve protein recovery and fouling control, dynamic shear-enhanced membrane filtration with high shear rate on membrane surface and excellent anti-fouling capacity was used for alfalfa juice filtration in this work. In order to optimize filtration process, filtration mode and operation parameters were investigated to reduce membrane fouling and improve separation performance. Then, alfalfa wastewater was also treated by dynamic shear-enhanced membrane filtration to recycle proteins. Furthermore, the fouling mechanism was studied and served as a valuable evaluation for fouling strategies. In this study, process optimization including “Filtration mode” and “Operation parameters” was studied to improve protein recovery and fouling control. In “Filtration mode”, three types of filtration modules (dead end filtration using laboratory Amicon cell (DA), dynamic cross filtration using rotating disk module (CRDM) and dead end filtration using rotating disk module (DRDM)) were used to investigate the filtration performance. As for “Operation parameters”, the operation parameters including membranes (ultrafiltration (UF) and microfiltration (MF)), rotating speed, temperature and transmembrane pressure (TMP) were studied to optimize the filtration process. Flux behavior (permeate flux and flux decline), separation performance (clarification and concentration capacity), membrane cleaning efficiency (permeability recovery) and productivity in full recycling tests and concentration tests were utilized to evaluate the various operation strategies. In addition, alfalfa wastewater was treated by UF membrane, while waste proteins were recycled. Fouling mechanism for alfalfa juice filtration was investigated. The fouling process showed significantly stepwise multisite patterns. Based on Darcy’s law, the stepwise multisite Darcy’s law model (SMDM) was proposed to better describe and understand the fouling process. The effects of feed composition, membrane and hydraulic conditions played an important role in stepwise fouling process. Moreover, the resistance coefficient and compressibility for different steps and sites were calculated to explain the complex fouling process and estimate the efficiency of flux decline control strategies. Besides, a series of long tests were utilized to study flux decline and membrane fouling at various fouling step process. These results can be used to understand the protein recovery and fouling control during shear-enhanced membrane filtration process of alfalfa juice. They have important implications for process design of membrane technology in industrial scale

The objective of this study was to investigate the effects of preheat treatments on fouling by fresh whole milk (FWM), recombined whole milk (RCB) and reconstituted whole milk (Recon) in the high-temperature heater of indirect UHT plants. Various preheat treatments prior to evaporation during milk powder manufacture were applied to skim milk powder (SMP, 75 °C 2 s, 85 °C, 155 s and 95 °C, 155 s) and whole milk powder (WMP, 95 °C, 33 s). These preheat treatments were so-called “evaporator preheat treatments”. Skim milk powder (SMP) and whole milk powder (WMP) were derived from the same original batch of pasteurised FWM to remove the effects of the variation in milk composition between different milk batches. These SMPs were recombined with anhydrous milk fat and water to prepare RCB, and WMPs were reconstituted with water to prepare Recon. Then, (homogenized) FWM, RCB and Recon were subjected to various preheat treatments (75 °C, 11 s, 85 °C, 147 s and 95 °C, 147 s) prior to UHT processing. These preheat treatments were so-called “UHT preheat treatments”. Temperature difference (hot water inlet temperature – milk outlet temperature) was taken as a measure of the extent of fouling in the high-temperature heater. The slope of the linear regression of temperature difference versus time (for two hours of UHT processing) was taken as fouling rate (°C/h). Increasing both evaporator and UHT preheat treatments resulted in increasing fouling rate and total deposit weight for all three whole milk types for several milk batches. In the case of FWM, there was no reduction in fouling rate with increasing UHT preheat treatment whether FWM was homogenized then preheated, preheated then homogenized or not homogenized at all. These findings, which are wholly consistent and well replicated, are in apparent conflict with the results of most previous comparable studies. Possible reasons for this are explained. Further investigations of the effects of homogenization relating to the role of whey protein on the surface of the fat globules showed that whey protein associated with the membrane covering the surface of fat globules for homogenized then preheated FWM, RCB and Recon and that association increased with increasing heating process stage. The increasing association of whey protein with the milk fat globules membrane with increasing severity of heating process stage became faster when preheat treatment was more severe: the association of whey protein plateaued on intermediate temperature heating when the milks were preheated at 75°C, 11 s and on preheating when the milks were preheated at 95°C, 147 s. In the case of FWM, the thickness of the membrane covering the surface of fat globules for homogenized then preheated FWM, which increased with the severity of heating process stage, was greater than the thickness of the membrane in preheated then homogenized FWM. Preheating then homogenization resulted in the greater interfacial spreading of small molecules on the surface of fat globules, i.e. whey protein or small molecules from the disintegration of casein micelles during preheating. Possible basic mechanisms for UHT fouling in the high-temperature heater include: the reduction in the solubility of calcium phosphate and the deposition of protein as fat-bound protein and non-fat-bound protein. When non-fat-bound protein in milk plasma deposited, it could be a carrier for the deposition of mineral, such as, the precipitate of calcium phosphate in the casein micelles or the deposition of complexes between whey protein and casein micelles.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1990.
Includes bibliographical references (leaves 274-284).
by Arun Suresh Chandavarkar.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1990.

Malgré une longue histoire de développement, l'hémodialyse (rein artificiel) possède encore quelques limitations, telles que la perte des propriétés initiales de la membrane en cours de traitement à cause du colmatage et la mauvaise élimination des toxines urémiques de taille moyenne. La présente étude fait partie d'un projet européen nommé BioArt dont le but est d'apporter des solutions à ces limites. Dans cet objectif, l'un des partenaires du projet a proposé le développement d'un nouveau concept de membrane double couche au sein de laquelle sont incorporées des particules adsorbantes. Une caractérisation complète de cette nouvelle membrane était alors nécessaire, plus précisément l'impact de la matrice mixte sur l'élimination des toxines urémiques de divers groupes devait être évalué, ainsi que la propension du matériau membranaire à se colmater. Les études des phénomènes de colmatage sont classiquement menées à l'échelle macroscopique (faisceau de fibres creuses) sans analyse à l'échelle d'une fibre isolée. Le but premier de la présente thèse a alors été de proposer un dispositif permettant une étude du colmatage membranaire induit par la protéine à l'échelle microscopique. Un dispositif microfluidique transparent dans lequel la membrane polymère est insérée a été élaboré et mis en œuvre pour la filtration des protéines modèles : l'albumine de sérum bovin (BSA) et l'a-lactalbumine. Grâce au couplage avec la microscopie de fluorescence, différents modes d'adsorption des protéines sur la surface de la membrane ont été observés et liés aux variations des conditions hydrodynamiques à l'intérieur de la puce. Il a été constaté, sous certaines conditions, une différence dans l'accumulation de protéines entre l'entrée, le centre et la sortie du canal tandis que dans d'autres conditions cet effet s'annule. En outre, un phénomène inattendu, l'agrégation de l'a-lactalbumine, a été observé au cours de la filtration. La localisation dans le canal et la forme des agrégats dépendent également des conditions hydrodynamiques et de la pression transmembranaire appliquée. Dans le but d'optimiser la conception de la membrane vis à vis de son aptitude à éliminer des molécules de taille moyenne de la circulation sanguine, un modèle mathématique a été proposé. L'objectif du modèle était, en prenant en compte la présence de particules adsorbantes à l'intérieur de la membrane double couche, de rendre compte de la combinaison des trois mécanismes d'élimination du soluté : la convection, la diffusion et l'adsorption. Le modèle permet de prédire l'influence de divers paramètres tels que la diffusivité de la molécule, l'épaisseur de la membrane, la présence de la convection, la charge en particules adsorbantes, sur l'intensification des flux à travers la membrane. Le modèle semble être un outil utile pouvant être appliqué à l'optimisation de membranes pour l'élimination des toxines
Despite a long history of development, the hemodialysis procedure (artificial kidney) still possesses some limitations, such as loss of the initial properties of the membrane due to fouling and poor removal of the middle sized uremic toxins. The present study is part of an European project named BioArt the aim of which was to overcome these limitations. In that objective, one of the partners of BioArt project reported on the development of the novel promising concept of double layer membrane with embedded adsorptive particles. A thorough characterization of the new membrane was then necessary, more precisely the extent to which mixed matrix layer can improve the removal of the uremic toxins from various groups needed to be evaluated, as well as the propensity of the membrane material to become fouled. The studies of the fouling phenomena are conventionally performed at the macro scale (bundle of hollow fibers) without insights of what is happening at the scale of an isolated fiber. Therefore, the primary aim of the present Thesis was to transfer the research of the protein-induced membrane fouling from the macro to the micro scale. A novel transparent microfluidics device with the polymeric membrane inside has been developed and applied for the filtration of model proteins: bovine serum albumin (BSA) and a-lactalbumin. Thanks to the coupling of the microchip with the fluorescent microscopy, different patterns of protein deposition on the membrane surface were observed and related to the variations in the hydrodynamic conditions inside the microchip. It was found that at certain conditions one may observe the difference in protein accumulation in the inlet, the middle, and the outlet of the channel while at other conditions this effect vanishes. Additionally, the unexpected phenomena of a-lactalbumin aggregation was observed over the course of filtration. The location and shape of the aggregates were also dependent on the hydrodynamic conditions and the applied transmembrane pressure. Aiming to address the problem of membrane design optimization for the enhancement of the middle molecules elimination from the bloodstream, a mathematical model, which accounts for the presence of adsorptive particles inside the complex double-layer membrane, has been proposed. The objective of the model was to understand the interplay of three solute removal mechanisms: convection, diffusion, and adsorption. The model allows predicting the influence of various parameters such as molecule diffusivity, membrane thickness, the presence of convection, content of adsorptive particles on the flux intensification across the membrane. The developed model seems to be a useful tool, which may be applied to design optimized membranes for the removal of toxins

Barnacles are dominant hard–fouling organisms in marine waters. They attach to substrates by secreting a complex proteinaceous adhesive. Understanding the chemical composition of this multi–protein underwater adhesive and how it is affected by environmental variables, such as oceanic temperatures, is critical for developing nontoxic solutions to control biofouling. Previous experiments in our lab revealed an inverse relationship between critical removal stress (CRS) and temperatures at which barnacles were reared. Further investigations showed that this correlation is not attributed to differences in physical properties such as barnacle size or short–term changes in the viscosity of adhesive. Therefore, the observed effects may be influenced by a physiological response to temperature during initial growth and development. We hypothesized that rearing temperature affects the expression of proteins found in the adhesive matrix. To elucidate the underlying mechanisms responsible for the temperature effect, we analyzed uncured barnacle adhesive using two-dimensional gel electrophoresis (2DGE) and matrix-assisted laser desorption/ionization-tandem time-of-flight (MALDI-TOF/TOF) mass spectrometry (MS). In our analysis, we 1) detected differences in protein expression at two experimental temperatures (15°C and 25°C) and 2) identified several proteins that may serve functional roles in the process of adhesion. Our data are also consistent with a model that the curing process of barnacle adhesive may be analogous to the process of wound healing in animals.

Le présent travail est une contribution pour mieux comprendre l’influence des micelles de caseine sur l’encrassement de solutions de protéines sériques. En particulier, des approches expérimentales et numériques ont été réalisées, à des tailles laboratoires et pilotes, pour décrire les phénomènes de dénaturation et mieux cerner le rôle du calcium dans les mécanismes d’encrassement. Tout d'abord, l'effet du ratio massique caséine / lactosérum sur les performances d'encrassement des protéines de lactosérum a été étudié dans un échangeur à Plaques à l'échelle pilote. La masse totale du dépôt d'encrassement chute d’abord de manière significative avec l'augmentation de la concentration en caséine, atteignant un minimum quand le ratio vaut 0,2. Au-delà de cette valeur, la masse de dépôt réaugmente. La chute de la masse du dépôt, pour un ratio ≤ 0,2, ne semble pas être corrélée à la dénaturation thermique du BLG mais plus probablement due à la modification des interactions minérales introduites par la caséine. L'augmentation de la masse de dépôt, pour un ratio ≥ 0,2, semble être liée à une co-précipitation du complexe BLG-caséine qui augmente l'encrassement. Il est suggéré que la présence de caséine micellaire modifie profondément l'équilibre calcique en solution et que la teneur en nanocluster de Ca-P modifie fortement les interactions entre les espèces protéiques et les minéraux (calcium ionique, Ca-P) affectant ainsi la dénaturation des protéines et la précipitation des minéraux. Un nouveau modèle cinétique concernant le dépliement thermique et l'agrégation de BLG a été établi. Ce modèle est en mesure de justifier la rupture de pente dans le diagramme d'Arrhenius et de fournir des informations thermodynamiques détaillées pour les processus de dépliement et d'agrégation. Sur la base de ce modèle, il a été confirmé que le calcium ionique avait un rôle protecteur sur le dépliement thermique du BLG à basse température. En revanche, à des températures plus élevées, le calcium favorise l'agrégation et la formation d'espèces BLG dépliées. Un dispositif d'encrassement à l'échelle laboratoire a été construit et tester avec des protéines de lactosérum en régime laminaire. Un modèle CFD 3D réaliste a été implémenté simulant à la fois les réactions au cœur du fluide et en surface. Les résultats ont montré une relation linéaire entre le facteur pré-exponentiel et la concentration de calcium, ce qui suggère que l'encrassement nécessite qu’une seule molécule de calcium soit associée à une protéine de BLG. Il est confirmé que le calcium est essentiel à l'encrassement avec des effets significatifs à la fois sur les processus de dénaturation thermique et sur la croissance du dépôt. Enfin, l'effet du ratio caséine / lactosérum sur l'encrassement a été étudié avec un dispositif d'encrassement de laboratoire. Les résultats laboratoires montrent que la caséine réduit l’aptitude à l’encrassement comme déterminé précédemment avec l’installation pilote. Cependant, dans ce cas, l'encrassement reste à un niveau faible y compris pour des ratios élevés (jusqu'à 4). La présence de caséines individuelles dans la phase sérique a été considérée comme responsable de cette atténuation de l'encrassement, probablement par leurs activités de type chaperon. Cependant, quand le pH de la solution d'encrassement est fixé à 6,6, il est démontré que la caséine perd son effet d'atténuation de l'encrassement pour des ratios plus élevés. Ce comportement est lié à sa faible capacité de micelle de caséine à contrôler le calcium ionique dans la phase sérique à un pH plus bas, entraînant une concentration plus élevée en calcium facilitant la dénaturation de la BLG et l'accumulation de dépôts. Une quantité plus faible de caséines dissociées dans la phase sérique à pH 6,6 pourrait aussi expliquer l'augmentation de la masse d'encrassement car elles ne sont pas en concentration suffisantes pour remplir des fonctions de type chaperon
The present work is a contribution to better understand the influence of casein micelles on the fouling of serum whey protein solutions. In particular, experimental and numerical approaches have been carried out, at laboratory and pilot scales, to describe denaturation phenomena and better understand the role of calcium in fouling mechanisms. First of all, the effect of casein/whey mass ratio on the whey protein fouling performance was investigated in a pilot-scale PHE. The total fouling deposit mass drop significantly with the addition of casein, resulting in a minimum value located at Casein/WPI of 0.2. Exceeding this critical ratio, fouling deposit increased with elevated casein concentrations. The deposit mass drop (Casein/WPI ≤ 0.2) is unlikely to be linked to the thermal denaturation of BLG and is more probably due to the change in mineral interactions introduced by casein. The increased fouling mass (Casein/WPI ≥ 0.2) was attributed to a co-precipitation of BLG-casein complex that enhances the fouling. It is proposed that micellar casein change deeply the calcium balance and the content of CaP nanocluster modifies sharply the interactions which occur between protein species (BLG, caseins) and mineral elements (ionic calcium, Ca-P) thereby affecting the protein denaturation and fouling behavior. A novel kinetic model concerning thermal unfolding and aggregation of BLG was established. This model interprets mathematically the break-slope behavior in the Arrhenius plot and provides detailed thermodynamic information for both unfolding and aggregation processes. Based on this model, it was confirmed that ionic calcium has a protective role on the thermal unfolding of BLG at low temperature. In contrast, at higher temperatures, calcium promotes aggregation and the formation of unfolded BLG species. A bench-scale fouling rig was built to perform whey protein fouling experiments in a laminar regime. A realistic 3D CFD model was achieved to simulate both the bulk and surface reactions. Results showed a linear relationship between the deposition pre-exponential factor and calcium concentration, suggesting the fouling is built in such a pattern that only one calcium ion per BLG molecule is involved. Calcium was confirmed to be essential to fouling growth with significant effects both on the thermal denaturation and deposition processes. Finally, the effect of casein/whey ratio on the whey protein fouling was investigated in the laboratory-scale fouling device. Results revealed a similar effect of casein on fouling mitigation as those found in the pilot plant. However, in this case, the fouling was suppressed and maintained at a low extent even at high Casein/WPI ratios (up to 4). The presence of individual caseins in the serum phase was considered to be responsible for this fouling mitigation probably through their chaperon-like activities. However, when the pH of the fouling solution is set at 6.6, casein is shown to lose its fouling-mitigating effect at higher ratios. This behavior is related to its weak ability of casein micelle to control ionic calcium in the serum phase at lower pH, resulting in higher calcium concentration facilitating BLG denaturation and deposition accumulation. A lower amount of dissociated caseins in the serum phase at pH 6.6 could also explain the increase in fouling mass because they are not in sufficient concentration to perform chaperone-like functions

碩士
國立臺灣大學
化學工程學研究所
88
Protein fouling is one of the critical factors governing the performance and overall effectiveness of microfiltration processes. The adsorption and deposition of protein on microfiltration membrane would result in decline of filtration rate and alteration of selectivity of membrane as well. Hence, experiments were performed with bovin serum albumin (BSA) and track-etched polycarbonate (PC) membranes to evaluate how fouling phenomena affects the microfiltration process. The significant flux decline observed in the present work is initiated by the deposition of BSA aggregates near the membrane pores, and, in turn, an external cake composed of BSA aggregates forms which can further increase the irreversible filtration resistance. Then, the reversible BSA deposition on the cake of aggregates occurs which could dominate the filtration resistance in the continuing microfiltration process. The analysis suggests that both the irreversible adsorption of BSA aggregates and the reversible adsorption of monomers are two major mechanisms for the fouling phenomena. In addition, the effects of operation variables, such as BSA concentration, pH of solution and operating pressure, on the reversible and irreversible fouling mechanism are also discussed.

Protein-protein and protein-molecule interactions are complicated phenomena due to the tendency of proteins to change shape and function in response to their environment. Protein aggregation whether onto surfaces or in solution, can pose numerous problems in industry. Surface plasmon resonance (SPR) devices and quartz crystal microbalances (QCM) are two real-time, label free methods that can be used to detect the interactions between molecules on surfaces. These devices often employ self-assembled monolayers (SAMs) to produce specific surfaces for studying protein-protein interactions. The objective of this work was to develop methodologies utilizing SPR to better understand protein-protein and protein-molecule interactions with possible applications in the food and separation industrial sectors. A very well characterized whey protein, β-lactoglobulin (BLG), is used in numerous applications in the food industry. BLG can undergo different types of self-aggregation due changes in external environment factors such as buffer strength, pH or temperature. In this work, a hydrophilic SAM was developed and used to study the interaction and non-specific adsorption of BLG and palmitic acid (PA), a molecule which is known to bind to BLG. It was found that PA tended to reduce BLG conformational changes once on the surface, resulting in a decrease in its surface adhesion. Fluorescent excitation emission matrices (EEM’s) using a novel fluorescence probe technique were utilized to detect protein on the surface as well as conformational changes on the surface of the sensor, although the extent these changes could not be quantified. Another whey protein, α-lactoglobulin (AL), was utilized as a surrogate protein to study the adsorption of colloidal/particulate and protein matter (CPP) extracted from filtration studies of river water. A large fraction of natural organic matter (NOM), the major foulant in membrane based water filtration, is CPP and protein. Understanding the interactions between these components is essential in abating NOM membrane fouling. Several SPR methods were investigated in order to verify the interactions. A mixture of AL and CPP particles in solution prevented the non-specific adsorption of AL to the SAM surface. This change in association was then detected through SPR. Fluorescent EEM’s of the sensor surface verified that CPP and AL bound to the surface. This finding has fundamental significance in the interpretation of NOM-based membrane fouling. To better understand the mechanisms behind non-specific adsorption, a mechanistic mathematical model was developed to describe the adsorption of BLGs onto the hydrophilic SAM. The resulting model performed well in terms of predicting adsorption based on SPR data. The model incorporated the monomer-dimer equilibrium of BLG in solution, highlighting the impact of protein aggregation on non-specific adsorption mechanisms. For future studies, improvement in fluorescent FOP surface scan methodology would help identify different protein/molecules and conformations on the surface.

Title: Thin films of plasma polymers as stable supports for biomedical applications Author: Ivan Gordeev Institute: Charles University in Prague, Department of Macromolecular Physics Supervisor of the doctoral thesis: Doc. Ing. Andrey Shukurov, Ph.D, Charles University in Prague, Department of Macromolecular Physics. Abstract: Plasma polymers have been widely considered for use as bio-active coatings. In biomedicine, the surfaces that withstand accumulation of biofilms are of particular importance. This thesis is focused on development of new plasma-based methods for deposition of bio-resistant (non-fouling) plasma polymers. Poly(ethylene oxide) was the subject material. R.f. magnetron sputtering, plasma-assisted thermal vapour deposition and amplitude modulated atmospheric pressure surface dielectric barrier discharge were the methods adapted to fabricate thin films with tunable chemical composition, cross-link density and biological response. A new insight was gained into the processes of plasma polymerization as well as into composition/structure relationship and its effect on biological properties of resultant films. Keywords: plasma polymerization, PEO, 'non-fouling' properties, protein adsorption, cell adhesion

Hollow fiber ultrafiltration is a viable low cost alternative technology for the concentration or separation of protein solutions. However, membrane fouling and solute build up in the vicinity of the membrane surface decrease the performance of the process by lowering the permeate flux. Major efforts have been devoted to study membrane fouling and design more efficient ultrafiltration membrane systems. The complexity of membrane fouling, however, has limited the progress to better understand and predict the occurrence of fouling. This work was motivated by the desire to develop a microscopic Computational Fluid Dynamics (CFD) model to capture the complexity of the membrane fouling during hollow fiber ultrafiltration of protein solutions. A CFD model was developed to investigate the transient permeate flux and protein concentration and the spatial fouling behavior during the concentration of electroacidified (pH 6) and non- electroacidified (pH 9) soy protein extracts by membrane ultrafiltration. Electroacidification of the soy protein to pH 6 was found to decrease the permeate flux during UF which resulted in longer filtration time. Lower electrostatic repulsion forces between the proteins at pH 6 (near the protein isoelectric point) resulted in a tighter protein accumulation on the membrane surface suggested to be responsible for the lower permeate flux observed in the UF of the electroacidified soy protein extract. A new transient two-component fouling resistance model based on the local pressure difference, permeate velocity and protein concentration was implemented in the resistance-in-series flux model to describe the dynamics of the reversible and irreversible fouling during the filtration and the effect of pH on the membrane fouling. Good agreement between the experimental data and the model predictions was observed. Mathematical modeling was performed to estimate the osmotic pressure and diffusion coefficient of the proteins bovine serum albumin (BSA) and soy glycinin, one of the major storage proteins in soy, as a function of protein concentration, pH, and ionic strength. Osmotic pressure and diffusion coefficient of proteins play vital roles in membrane filtration processes because they control the distribution of particles in the vicinity of the membrane surface, often influencing the permeation rate. Therefore, understanding the behavior of these properties is of great importance in addressing questions about membrane fouling. An artificial neural network was developed to analyze the estimated data in order to find a simple relation for osmotic pressure as a function of protein concentration, pH, and ionic strength. For both proteins, the osmotic pressure increased as pH diverged from the protein isoelectric point. Increasing the ionic strength, however, reversed the effect by shielding charges and thereby decreasing the osmotic pressure. Osmotic pressure of glycinin was found lower than that of BSA. Depending on how much pH was far from the isoelectric point of the protein, osmotic pressure of BSA could be up to three times more than the glycinin’s. Two different trends for diffusion coefficient at specified pH and ionic strength were observed for both proteins; diffusion coefficient values that decreased with protein concentration and diffusion coefficient values that passed through a maximum. A rigorous CFD model based on a description of protein interactions was developed to predict membrane fouling during ultrafiltration of BSA. BSA UF was performed in a total recycle operation mode in order to maintain a constant feed concentration. To establish a more comprehensive model and thereby alleviate the shortcomings of previous filtration models in literature, this model considered three major phenomena causing the permeate flux decline during BSA ultrafiltration: osmotic pressure, concentration polarization, and protein adsorption on the membrane surface. A novel mathematical approach was introduced to predict the concentration polarization resistance on the membrane. The resistance was estimated based on the concentration and thickness profile of the polarization layer on the membrane obtained from the solution of the equation of motion and continuity equation at a previous time step. Permeate flux was updated at each time step according to the osmotic pressure, concentration polarization resistance, and protein adsorption resistance. This model had the ability to show how microscopic phenomena such as protein interactions can affect the macroscopic behaviors such as permeate flux and provided detailed information about the local characteristics on the membrane. The model estimation was finally validated against experimental permeate flux data and good agreement was observed.

碩士
淡江大學
化學工程與材料工程學系碩士班
94
In this study, the inorganic tubular membranes(1000, 5000 MWCO) were employed in a cross-flow filtration system to investigate the effect of operation conditions, solutions and membrane properties on protein solutions filtration. The way for cleaning the membrane fouling were also discussed. The solution fluxes and solute rejection were measured under various operating parameters such as membrane MWCO, transmembrane pressure, pH value and solution composition. In addition, in this work also calculate experimental resistance value with resistance-in-series model and predicting flux of BSA solution with osmotic pressure model which will compare with experiment flux. Experimental results indicate that the NaOH solution could removal the BSA fouling on the membrane and the required concentration of NaOH solution increase as the feed BSA concentration increases. Under the turbulent flow pattern, the increase in BSA concentration just slightly reduces the flux. For BSA and β-cyclodextrin binary solution, the rejection of β-cyclodextrin varies with the pH value. In the case of 5k Da membrane, the rejection of β-cyclodextrin is higher than 80% at pH=6.87 and less than 30% in pH=10. This is due to the fact that the porosity of the polarization layer of BSA on the membrane surface varies with pH value. Therefore, the present membrane can be applied for the separation of small molecule from BSA solution by choosing a suitable pH value. In resistance-in-series model, fouling resistance value in all solution concentration of BSA are almost the same and far smaller than membrane resistance value. But in β-cyclodextrin solution, the values become higher than membrane. When in binary solution, fouling layer form by BSA on membrane surface could reject β-cyclodextrin transmembrane, so that the pore blocked resistance value can be decreased. In osmotic pressure model, the trend of theoretical flux agree with experiment flux but higher than it. This is could be the osmotic pressure model just only to consider the concentration rise in membrane surface but the influence of fouling layer was neglected.

It is crucial to understand the fundamental mechanisms of cleaning milk protein fouling to optimise Cleaning-in-place (CIP) process. Using Whey Protein Concentrate (WPC) gel as a model material and a rapid ultraviolet (UV) spectrophotometry, a comprehensive laboratory study on the cleaning of the WPC gel deposits from hard surface with alkaline cleaning solutions has been conducted. The kinetics of the cleaning process has been established and mathematical models have been developed in order to elucidate the influences of various parameters on cleaning process. This study has provided sound evidence that whey protein concentrate gel is a reliable simulation of the whey protein fouling deposits used in most milk protein fouling and cleaning studies. Based on treating denatured whey protein gels as biopolymers, a chemical reaction controlled polymer dissolution cleaning mechanism has been proposed. The polymer dissolution plays a major role of removing proteinaceous deposits when treated with alkaline solutions under the flow conditions tested. Similar to the diffusion of cleaning chemicals and chemical reactions, the reptation (induction) is also one of essential steps for the dissolution of WPC gels in alkaline solutions. The disengagement of intermediate reaction products (altered protein molecules) from a gel-solution interface and subsequent mass transfer of these reaction products to the bulk cleaning solutions are the rate-limiting steps for the cleaning process. The typical dissolution cleaning rate curve of WPC gels in alkaline solutions includes swelling, uniform and decay cleaning stages. This study on cleaning kinetics shows that increasing the cleaning temperature can improve the cleaning efficiency. The apparent activation energy for these three stages is 32.6, 40.5, and 38.3 kJ/mol, respectively, which is in agreement with previous research works. Increasing flow velocity enhances the cleaning process. However, this effect could be reduced when and the cleaning process gradually changes from a mass transfer-controlled process to a disengagement-controlled process, where the flow velocity is very high. The introduction of the hydrolysis, β-elimination reactions and some competing chemical reactions have highlighted the complex of chemical reactions involved in cleaning of proteinaceous fouling using alkaline solutions. The changes in molecular mass distribution and SH content of WPC gel dissolved at various temperatures observed has confirmed the assumption that all these chemical reactions are temperature dependent. The investigation on the swelling, microstructural and mechanical properties of WPC gels treated with alkaline solutions also illustrates the concentration dependency of these chemical reactions. The mechanical property studies demonstrate that the chemical treatment could make WPC gel weaker and easier to be destroyed. However, the relationship between the mechanical properties and the cleaning process needs to be further studied. Based on the polymer dissolution and mass transfer theory, a mathematical model of chemical cleaning has been proposed. Various parameters, such as tr (reptation time), Rm, (constant cleaning rate), mc, (the critical mass), ξ (rate constant in swelling stage), kA (rate constant in decay stage) and Ψ (a dimensionless parameter) have been used to characterise the whole cleaning process. Among the parameters used in the cleaning model, the constant cleaning rate (Rm) is the most important one and determines the overall efficiency of a cleaning process, which has been further predicted and expressed as a product of mass transfer coefficient and solubility of disengaged protein molecules. The successful model formulations for the cleaning rate and cleaning time under various operation conditions are a good outcome of the rational mechanisms proposed for the removal of proteinaceous fouling. This research has provided a good foundation for further fundamental research in this area and for optimising the cleaning processes.

Efficient separation of target protein from impurities is crucial in bioseparation for large scale production and purity of the target protein. Two separation process approaches were considered in this study. The first approach focused on identifying major impurity and optimization of solution properties for target protein purification. The second approach consisted of designing an adsorbent that interacted specifically with the target molecule. The first study included modification of protein solution properties (pH, ionic strength, buffer ions) in order to maximize lysozyme purification by a strong cation exchange resin. The interaction of phytic acid, a major impurity, present in transgenic rice extracts, that contributes to decreased lysozyme adsorption capacity on SP Sepharose was evaluated. The target protein was lysozyme, which is used in a purified form as a baby formula additive to reduce gastrointestinal tract infections. At constant ionic strength, lysozyme in pH 4.5 acetate buffer had a higher binding capacity and stronger binding strength than at pH 6.0. Lysozyme in sodium phosphate buffer of pH 6.0 exhibited lower adsorption capacity than in pH 6 Tris buffer. Binding capacity and strength were significantly affected by phytic acid in all studies buffers. The second study consisted of surface modification of microfiltration membranes for protein purification and separation and reduces fouling. This study describes adsorption and fouling of chemically modified microfiltration membranes with bovine serum albumin (BSA) and immunoglobulin G (IgG). Least fouling resulted with polyethylene glycol (PEG) membranes when BSA protein was used. Amine-functionalized membranes showed specific interaction with BSA. There was multi-layer deposition of IgG on amine-functionalized membrane. G3 membrane synthesized to selectively bind IgG seemed a noble option to separate IgG from a protein mixture.

In dairy processing, dairy ingredients need to be thermally treated to ensure product quality and safety for an extended shelf life. During thermal processes, milk protein denatures and interacts with other dairy ingredients to form a layer of deposit on heated surfaces, known as fouling which can deteriorate process efficiency and product safety. Milk is a complex mixture of proteins, fats, carbohydrates, minerals and vitamins. The heat-sensitive B-lactoglobulin (B-lg) is known to be a key component in fouling formation (constituting 50% of type A fouling deposits) during milk pasteurization, as B-lg unfolds when heated and exposes the reactive sulfhydryl groups that can interact with other proteins and ingredients to form deposits. Although casein (80% of milk proteins) is known to interact with denatured B-lg, no fouling studies have been performed with particular focus on the effect of casein on whey protein fouling.

Carbohydrates are an ingredient widely added in various dairy products as sweetener, stabilizer, texturizer, and fat replacer. Simple sugars have a protective effect on whey protein denaturation, but their effect on dairy fouling is not known. Polysaccharides can interact with milk proteins through electrostatic and hydrophobic interactions, as well as hydrogen bonding. The addition of polysaccharide (carrageenan) has been reported to cause opposite effects on protein deposition, however, no conclusive mechanism has been proposed to elucidate how protein-polysaccharide interaction at pasteurization temperatures affects the fouling behavior of dairy products.

In this dissertation, different model dairy solutions and real dairy products were used to study the effect of composition, including protein distribution and additions of simple sugars and polysaccharides, on dairy fouling. Fouling deposits were formed and analyzed using a bench-top spinning disc apparatus operating under well-controlled temperatures and shear stresses characterized by computational fluid dynamics simulations. By studying the fouling behavior of camel milk and comparing with bovine milk, milk without B-lg was found to still foul and form deposits containing casein, α-lactalbumin, serum albumin with a reduced thermal resistance due to a more porous structure. Results also showed that the addition of 10 wt% sugar reduced whey protein fouling by more than 30% and affected the structure and adhesion strength of deposits. Furthermore, the presence of carrageenan in dairy solutions can promote the denaturation of B-lg when heated and form a more compact deposit, resulting in more severe fouling. Overall, this dissertation provides a fundamental understanding of the fouling characteristics of complex dairy products. The knowledge gained is expected to help the dairy industry select suitable ingredients to mitigate or prevent the fouling problem.

A novel approach for the production of soy protein isolates was investigated integrating electroacidification and membrane ultrafiltration. The effect of electroacidification on the ultrafiltration performance and physicochemical properties of the soy protein extracts was obtained by comparing an electroacidified (pH 6) and a non-electroacidified (pH 9) soy protein extract. The effect of membrane fouling on the permeate flux decline was studied in a hollow fiber and a dead end ultrafiltration system. Due to more significant membrane fouling, the permeate flux was always lower for the electroacidified extract, resulting in at least 1.5-fold increase in the total fouling resistance compared to the non-electroacidified extract. The total amount of protein deposited on the membrane surface during unstirred dead-end ultrafiltration was comparable (about 7 mg/cm2) for both soy protein extracts. The discrepancy between the total fouling resistance and the protein deposition estimates was attributed to the formation of denser (less permeable) fouling deposit for the electroacidified extract, which was supported by scanning electron microscopy studies of fouled membranes. The removal of carbohydrates and minerals was evaluated for direct ultrafiltration and two-stage discontinuous diafiltration using a hollow fiber system. The carbohydrate removal results were always consistent with the theoretical predictions, indicating that the carbohydrates were freely permeable across the membrane. In contrast, the minerals were partially retained by the membrane, but to a higher extent for the non-electroacidified extract, which demonstrated that the electroacidification pretreatment enhanced the mineral removal during the ultrafiltration. Incorporation of the diafiltration step improved the ash (mineral) and carbohydrate removal. Stronger electrostatic interactions between soy proteins, calcium/magnesium, and phytic acid (antinutrient) at alkaline pH resulted in less efficient removal of calcium, magnesium, and phytic acid during the ultrafiltration of the non-electroacidified extract compared to the electroacidified extract. Consequently, the soy protein isolates produced by electroacidification and the hollow fiber ultrafiltration had a lower mineral and phytic acid content. The protein content was at least 88 % (dry basis), with or without the electroacidification pretreatment. The study of the viscosity revealed that the electroacidification pretreatment reduced the viscosity of the soy protein extract, which resulted in a lower axial pressure drop increase during the ultrafiltration of the electroacidified extract compared to the non-electroacidified extract. Adjusting the pH of the electroacidified extract to 9 and the pH of the non-electroacidified extract to 6 had a great impact on the particle size distribution but only a marginal effect on the viscosity of the pH adjusted extracts. This indicated that the pH and the particle size distribution were not responsible for the viscosity difference between the electroacidified and the non-electroacidified soy protein extracts. It was proposed that the electroacidification pretreatment had some impact on the water hydration capacity of the soy proteins, which consequently affected the viscosity.

Master of Science
Food Science Institute
Jayendra K. Amamcharla
Fouling and biofilm formation on stainless-steel (SS) surfaces can be sources for cross-contamination and pose a great threat to the public health and food quality. The dairy industry needs an intervention strategy focusing on technologies discouraging the biofilm attachment and developing a sustainable eco-friendly approach for biofilm removal from the dairy processing surfaces. Since fouling encourages the attachment of bacteria to the SS surfaces, it becomes important to study the ways of reducing the fouling. The bacterial attachment to the fouled SS surfaces can be prevented by modifying the SS surface properties by chemical (using coatings) or mechanical methods. On the other hand, the degree of fouling can also be reduced by using good quality raw materials. The objective-1 of the study was focused on understanding the relationship between effect of milk protein concentrate (MPC80) solubility characteristics and fouling on SS surfaces during thermal processing. The powders were stored at different temperatures (25 ºC and 40 ºC) for 2 weeks to generate powders with different dissolution characteristics. Fouling characteristics of reconstituted MPC80 powder were studied using a custom-built benchtop plate heat exchanger. Exposing the MPC80 powder to a higher temperature during storage (40 ºC) significantly decreased the solubility and increased the amount of foulant on SS coupons (P < 0.05). Microscopic investigations (scanning electron microscopy and laser scanning confocal microscopy) of resulting fouled layers revealed heterogeneous fouling layers of varying tomographies, consisting of lipids, proteins, and calcium. In the second study, the efficacy of Micro- and Nano-bubble aqueous ozone (MNAO) as a disinfectant was studied in removal of Bacillus cereus and Bacillus licheniformis biofilm from the SS surface. For the Bacillus cereus biofilm removal, a log reduction of only 0.68 cfu/cm2 was observed after the de-ionized water wash. Whereas both MNAO and cleaning-in-place (CIP) treatments significantly reduced the bacterial counts by 2.43 and 2.88 log10 cfu/cm2, respectively. On the other hand, for the Bacillus licheniformis biofilm removal from SS surfaces, a significant log reduction observed was 1.45, 3.03, 2.92 log10 cfu/cm2, respectively after de-ionzed water, MNAO, and CIP treatments. Thus, it was observed that MNAO has great potential for removal of Bacillus cereus and Bacillus licheniformis biofilms from the SS surface, and can be used in the dairy industry as an effective sanitizer/disinfectant

碩士
中原大學
土木工程研究所
97
Development of membrane bioreactors has been limited by problems of membrane fouling, which will decrease the flux but increase the TMP (trans-membrane pressure) and cost for maintenance and operation. Many literature has indicated the major constituent of fouling is extracellular polymeric substances(EPS) which is composed by protein, carbohydrate, humic substances, nucleic acid and lipid. And,the most part of EPS is protein. Recently, many research has aimed at the quantitative analysis of protein in order to find out the relationship between protein and membrane fouling. However, no research focuses on the qualitative analysis of protein. Therefore, this research set membrane of different material(PAN,PVDF,PTFE) in the reactor, and performed biological technique to identify the species of proteins on fouling and discuss the relativity of protein and materials. Results showed the surface morphology of membrane(pore formation, size, roughness) will affect the forming of fouling.We analyzed the distribution of the molecular weight of protein and found out the membranous surface with larger pores will cause higher ratio of small protein to aggregate. There is no significant connection between species of proteins and hydrophilicity or hydrophobicity of surface , while hydrophobic protein aggregated on the surface more easier than hydrophilic protion. The location of 29%~58% of protein with functions relation to translation. More than 67% of protein located within bacteria, this may be related to the lysis of bacteria. We will apply our research to identity surface foulant of membranes and reduce fouling effect on MBR.

碩士
國立中央大學
化學工程與材料工程研究所
95
The characteristics of preventing nonspecific adsorption of protein has lead to extensive usage of PEG and its derivatives for biomedical applications. We consider that the interaction of water with the PEG is a major determinant of preventing protein adsorption. However, the thermodynamics aspect of the mechanism has not been well addressed. Therefore, in this study, we described the hydration behavior of PEG by measuring the dilution heat of PEG with various salt concentration, types of salt ions, temperature and molecular weight of PEG. In addition, we measured the isotherms and the interaction enthalpy between protein and Ether-650S with various salt concentrations, salt types and temperature by batch isotherms and ITC. From the results of dilution heat, we observed that all the dilution heat are exothermic at all condition (i.e. salt conc. and types, temperature, PEG MW). It indicated that the PEG molecule is prefer to hydrate with water than aggregation in the conditions investigated. At high salt concentration, temperature and molecular weight of PEG, the dilution heat of PEG is less exothermic due to the poor hydration of PEG. In thermodynamics, the dilution of PEG is more energy unfavorable at high salt concentration, temperature and molecular weight of PEG. And the extent of salt ions which affect the hydration of PEG is consistent with the Hofmeister series. Besides, we also observed that all the values of Flory-Huggins parameter(χ) are negative at each condition. It also indicated that all the solvent which we used are good solvent for PEG. From the results of isotherm, the amount of lysozyme adsorb on Ether-650 will decrease with increase the salt concentration. We considered that both of hydrophobic and electrostatic interaction affect the binding affinity of lysozyme. The enthalpy of lysozyme adsorbed on Ether-650S are almost endothermic. It indicated that the hydrophobic force is the driving force during the adsorption process. However, the enthalpy of adsorption is exothermic at 1M KCl. This lead to the suggestion that the adsorption of lysozyme with the Ether-650 is of the “nonclassical” hydrophobic type interaction at 1M KCl. In this study, we also calculated the number of water molecules released during the adsorption by preferential interaction model. From the results of P.I Model, we can conclude : (1) when we adding ammonium chloride to the solution, the system released more water molecules than add that of potassium chloride during the binding process.(2)compare with literature data, PEG ligand have stronger capability of hydration than other hydrophobic ligands.