This database contains bibliographic descriptions of all Wageningen University PhD theses from 1920 onwards. It is updated on a daily basis by WUR Library.
Author abstracts and/or summaries are added to all descriptions. A link to the full text dissertation is added to the bibliographic description. In a few cases, no electronic version is available, mostly because of copyright issues.
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pectins - characterization - chemical structure - mass spectrometry - degradation - capillary electrophoresis
Abstract: Pectine wordt in levensmiddelen vooral gebruikt als geleermiddel, stabilisator of verdikkingsmiddel in producten zoals jam, yoghurtdranken, vruchten-zuiveldranken en ijs. Daarnaast is er in toenemende mate interesse in het mogelijk gezondheidbevorderend effect van dit polysaccharide. Kennis van de exacte structuur zal bijdragen aan het begrip van de fysiologische functie van pectine in de plant en aan een verdere optimalisering van industriële en medische toepassingen van dit polymeer. Om meer inzicht te krijgen in de structuur werden nieuwe LC-MS en CE-MS methoden ontwikkeld, waarmee verbindingen tussen verschillende structuurelementen konden worden aangetoond. Als gevolg van de verkregen inzichten over de opbouw van pectine, wordt een aanpassing aan het structuurmodel van pectine voorgesteld, waarbij homogalacturonan ketens zowel lineair als vertakt aan rhamnogalacturonan I worden gepositioneerd. De ontwikkelde methoden, kunnen worden toegepast in onderzoek gericht op de opheldering van techno- en biofunctionele eigenschappen van complexe polysaccharidestructuren.
Abstract: During berry juice production, polysaccharides are released from the cell walls and cause thickening and high viscosity when the berries are mashed. Consequences are a low juice yield and a poor colour. This can be prevented by the use of enzymes that degrade these polysaccharides. To use these enzymes most efficiently, the structure and composition of the cell walls had to be known. This thesis describes a detailed composition of the cell walls of bilberries and black currants. The obtained results were used to monitor changes in the cell walls during different treatments such as enzyme treatment and high pressure processing. A higher viscosity and lower juice yield after high pressure processing were assigned to changes in pectin structure and extractability. Based on this knowledge, a synergistic effect was obtained by combining high pressure processing with treatment with commercial enzyme preparations.
Abstract: Cowpea, chickpea and yellow pea starches were studied and the results showed that their properties were strongly related to the chemical fine structures of the starches. Furthermore, granular starches were modified using two types of chemical acetylation reagents and then separated into different size fractions. The amount of introduced acetyl groups was found to depend on the size of the granules for the reaction with rapidly reacting reagent acetic acid anhydride, whereas the amount of introduced acetyl groups was independent from the granule size for reaction with the slowly reacting reagent vinyl acetate. Modification with the two types of reagents resulted in significant difference in physical properties of the starches. The investigation on the chemical fine structure of modified starches suggested that the distribution of acetyl groups over both the amylose and amylopectin populations of the starches was different, not only at molecular level but also at granular level.
soya protein - hydrolysis - aggregation - carbohydrates - protein extraction - protein digestion - protein digestibility - peptides
Abstract: Soy is a commonly used ingredient is food and animal feed. With particular focus on the in-soluble fractions, this thesis deals with the effects of proteases and carbohydrate degrading enzymes on different soybean meals subjected to different extent of heating. The primary aim is to improve the understanding of enzymatic hydrolysis of SBM with emphasis on proteins and to identify barriers limiting the efficiency of the process. The results show that aggregation behavior of peptides during enzymatic processing of soy proteins is potentially a limiting factor for efficacy of protein extraction. Surprisingly, it is also demonstrated that aggregation is not limited to in vitro incubations, but is also occurring in vivo in the digestive system of pigs.
Abstract: Food chemistry is amongst others about the components and chemical reactions that are part of food products, about the effect of chemical reactions on the quality and about the techniques used to research food products. To support students in acquiring the knowledge and skills of food chemistry, in this design research it is investigated whether, but especially also how, digital learning materials can be developed. The biggest advantage of digital material opposed to non-digital material is that students can be activated easily. The computer can respond directly to an answer of the student for a question (feedback). The computer can also give a hint how to solve the question. Different kinds of learning materials were designed: 1. material with which students independently can solve a quantitative problem 2. material with which students can acquire knowledge in an active and efficient manner, and 3. material with which students learn how to design experiments. From evaluations with students a positive appreciation of these materials was noticed. Furthermore, it can be concluded from this research that giving feedback, just-in-time information and visual information is of importance for the success of digital learning materials.
proteins - food - aggregation - chemical structure - molecular conformation - protein engineering
Abstract: Protein functionality in food products strongly relies on the fact that proteins can undergo intermolecular interactions, called aggregation. It was found that very subtle dynamics inherent to the protein of interest can have consequences for the functional properties of proteins. The aim of this thesis is to explore structural features of proteins of importance to the generation of aggregation prone protein molecules. The approach selected involves chemical engineering in which functional groups of the protein are converted into a chemical group with different properties. This led to a detailed description of the structural impact of the modifications in relation to aggregate formation. It was found that the various modifications applied interact with the aggregation process in a rather diverse (but predictable) manner. The accumulation of data from this work in combination with results from literature was used to significantly improve the understanding of factors relevant to aggregation and to develop a model to predict aggregation propensity. This model can be used within the food and pharmaceutical industry to determine the aggregation propensity of proteins used in formulae and medication.
pectins - chemical properties - physical properties - food additives
Abstract: Commercial pectins are mainly used for the gelling, thickening and stabilizing properties in food products. The different physical properties of pectins strongly depend on the galacturonic acid level and the level of methyl-esterification as well as on the molecular weight distribution. However, the conventional chemical analysis of the pectins does not always show differences between pectins while they behave differently. Two highly methyl-esterified pectins with similar chemical characteristics but different reactivity towards calcium were analysed. They were found to be a mixture of pectic populations differing in the degree of methyl-esterification as well as in the distribution of these methyl-esters. Amidated pectins with similar chemical features but different calcium sensitivity were also found to be a mixture of different pectic populations. Even for pectins having a similar degree of substitution, the ratio of amide groups versus methyl-esters varied significantly. In addition, the distribution of these substituents was found to differ.
Abstract: In order to modulate the functional properties of food proteins, the interactions between globular proteins and the monomeric phenolic, caffeoylquinic acid (CQA, chlorogenic acid), and the oligomeric phenolics, procyanidins, were characterized and investigated for their effect on protein functional properties. Non-covalent interactions between proteins and CQA involved a low affinity and did not affect protein solubility. Proteins show a medium affinity for procyanidins of an average degree of polymerization (DP) of 5.5, but weakly interacted with smaller procyanidins. Procyanidins of DP 5.5 strongly decreased protein solubility. Covalent interactions between proteins and CQA oxidised by polyphenol oxidase (PPO) or oxidised at alkaline pH resulted in protein modification mainly via dimeric CQA quinones. The covalent modifications of proteins with CQA strongly reduced protein solubility. Lysine, tyrosine, histidine and tryptophan were able to interact with CQA quinones. It can be concluded that for food non-covalent interactions are restricted to oligomeric phenolic.
Abstract: This research is part of the multidisciplinary program, PROFETAS (PROtein Foods Environment Technology And Society), which aimed to feasibly shift from animal proteins to pea proteins for the development of Novel Protein Foods (NPFs) with desirable flavour. The aim of this research is to investigate the flavour aspects of peas and its protein fractions, as being potential ingredients for NPFs. To achieve this objective, the type and amount of flavour compounds from pea flour and pea protein preparations, as well as the stability and sensory characteristics of some of these compounds were investigated. The interactions of flavour compounds and pea protein fractions, as well as the effect of heating and presence of non-protein components on these interactions were also studied. With the results obtained, PROFETAS will be able to provide essential information for food industries and research institutes, to aid in the production of food with superior quality. Food manufacturers can better manipulate their ingredients and processing, optimising production conditions, which in turn lead to cost saving.
Abstract: The human intestine contains many bacteria, among which bifidobacteria. These can have a positive effect on human health. By consuming products containing dietary fibres (prebiotics), the amount of these intestinal bacteria can be stimulated, because they contain enzymes, which are able to degrade the fibres. Knowing which enzymes are present in the bacteria, will help to determine which kind of dietary fibres are suitable for use as a prebiotic. In this research, enzymes present in bifidobacteria, which were able to degrade the fibres galactan and galacto-oligosaccharides, were investigated. Three different enzymes were examined: a beta-galactosidase, an endo-galactanase, and an alpha-galactosidase. The results of this thesis gave more insight in how galactans and galacto-oligosaccharides can be degraded by bifidobacteria.
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