Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Factors governing partial coalescence in oil-in-water emulsions
Fredrick, E. ; Walstra, P. ; Dewettinck, K. - \ 2010
Advances in Colloid and Interface Science 153 (2010)1-2. - ISSN 0001-8686 - p. 30 - 42.
complex food emulsions - hydrophobic emulsifier additives - dispersed phase crystallization - temperature cycling stability - surfactant sucrose ester - thermally treated creams - dairy whipped emulsions - adsorbed milk-proteins - palm mid-fraction - competitive a
The consequences of the instability mechanism partial coalescence in oil-in-water food emulsions show a discrepancy. On the one hand, it needs to be avoided in order to achieve an extended shelf life in food products like sauces, creams and several milk products. On the other hand, during the manufacturing of products like ice cream. butter and whipped toppings partial coalescence is required to achieve the desired product properties. It contributes to the structure formation, the physicochemical properties (stability, firmness....) and the sensory perception, like fattiness and creaminess of the final food products. This review critically summarises the findings of partial coalescence in oil-in-water emulsions in order to provide insight in how to enhance and retard it. Next to the pioneering work, a large set of experimental results of more recent work is discussed. First, the general mechanism of partial coalescence is considered and a distinction is made between partial and 'true' coalescence. The main differences are: the required solid particles in the dispersed oil phase, the formation of irregular clusters and the increased aggregation rate. Second, the kinetics of partial coalescence is discussed. In more detail, potential parameters affecting the rate of partial coalescence are considered by means of the encounter frequency and capture efficiency of the fat globules. The flow conditions, the fat volume fraction and the physicochemical properties of continuous aqueous phase affect both the encounter frequency and capture efficiency while the actual temperature, temperature history and the composition and formulation of the emulsion mainly affect the capture efficiency.
Dispersed systems: Basic considerations
Walstra, P. ; Vliet, T. van - \ 2007
In: Fennema's Food Chemistry: 4th ed. / Damodaran, s., Parkin, K., Fennema, O.R., New York : Marcel Dekker (Food Science and Technology 169) - ISBN 9780849392726 - p. 783 - 847.
The estimated accuracy of the EU reference dissection method for pig carcass classification
Nissen, P.M. ; Busk, H. ; Oksama, M. ; Seynaeve, M. ; Gispert, M. ; Walstra, P. ; Hansson, I. ; Olsen, E. - \ 2006
Meat Science 73 (2006)1. - ISSN 0309-1740 - p. 22 - 28.
This experiment was designed to describe the accuracy of the EU-reference dissection method, and to describe the types of factors influencing the accuracy and assess their size. The experiment was conducted in four different European countries at two abattoirs within each country. A total of 128 carcasses was selected according to carcass weight, fat class and sex, and 8 butchers from different countries dissected the carcasses. Due to the experimental design of the experiment a variation in pig type was found between countries. The accuracy was expressed by the repeatability and reproducibility standard deviation, which were found to be 0.87 and 1.10, respectively, and by the reliability, found to be 0.87. This indicates a high accuracy, although a significant effect was found on the estimation of lean meat percentage (LMP) of butcher, and also that jointing of the carcass was of overall importance to the accuracy of the EU-reference dissection method.
Effects of Protein Composition and Enzymatic Activity on Formation and Properties of Potato Protein Stabilized Emulsions
Koningsveld, G.A. van; Walstra, P. ; Voragen, A.G.J. ; Kuijpers, I.J. ; Boekel, M.A.J.S. van; Gruppen, H. - \ 2006
Journal of Agricultural and Food Chemistry 54 (2006)17. - ISSN 0021-8561 - p. 6419 - 6427.
lipid acyl hydrolase - emulsifying properties - tuber protein - patatin - oil - solubility - water - purification - selectivity - expression
In the present study emulsions were made with various potato protein preparations, which varied in protease inhibitor and patatin content. These emulsions were characterized with respect to average droplet size, plateau surface excess, and the occurrence of droplet aggregation. Droplet aggregation occurred only with potato protein preparations that contained a substantial amount of protease inhibitors and could be prevented only at pH 3. The average droplet size of the emulsions made with potato proteins appeared to be related to the patatin content of the preparation used. Average droplet size was found to be dominated by the patatin-catalyzed lipolytic release of surface active fatty acids and monoglycerides from the tricaprylin oil phase during the emulsification process. Addition of monoglycerides and especially fatty acids, at concentrations representative of those during emulsification, was shown to cause a stronger and much faster decrease of the interfacial tension than that with protein alone and to result in a drastic decrease in droplet size. The patatin used was shown to have a lipolytic activity of 820 units/g with emulsified tricaprylin as the substrate. Because of the droplet aggregating properties of the protease inhibitors, the patatin-rich potato preparations seem to be the most promising for food emulsion applications over a broad pH range, provided the lipolytic activity can be diminished or circumvented
Voedsel en voeding: Zin en onzin
Walstra, P. ; Boekel, M.A.J.S. van - \ 2006
Wageningen : Wageningen Academic Publishers - ISBN 9789086860098 - 172
voedsel - voedingsmiddelen - voeding - voedselwetenschappen - voedseltechnologie - voedselovertuigingen - food - foods - nutrition - food sciences - food technology - food beliefs
Voedsel en voeding staan voortdurend in de belangstelling. Iedereen heeft er een mening over en er wordt veel zinnigs maar ook veel onzinnigs over gezegd en geschreven. De auteurs zetten in dit boek de feiten op een rij, beschrijven de complexiteit van de huidige voedselproductie, maar ontrafelen deze ook en scheiden aldus de zin van de onzin. De meest relevante zaken op het gebied van voedsel en voeding worden met elkaar in verband gebracht
Mechanical properties of fat dispersions prepared in a mechanical crystallizer
Kloek, W. ; Vliet, T. van; Walstra, P. - \ 2005
Journal of Texture Studies 36 (2005)5-6. - ISSN 0022-4901 - p. 544 - 568.
fractal nature - networks - oil
Dispersions of hydrogenated palm oil (HP) in sunflower oil were crystallized in a scraped-surface heat exchanger (SSHE), where local strain rates are high. The HP crystallized completely or partially under shear, possibly followed by crystallization at rest. The Young's moduli scaled with the fraction solid fat to powers 2.5 and 1.5 for dispersions partially and completely crystallized under shear, respectively. Dispersions completely crystallized under shear leave the SSHE as a dispersion of compact aggregates in which the crystals are strongly sintered. The aggregates attract each other by relatively weak Van der Waals forces. Possibly, recrystallization causes a slow increase in consistency over about 16 days as a result of sintering between the aggregates. Dispersions partly crystallized under shear and partly at rest obtained their final consistency within 1 day. This is explained by ongoing crystallization at rest, which causes rapid sintering between aggregates and thereby formation of strong bonds. Any additional recrystallization then did not result in an increased consistency. The final consistency of the dispersions was comparable for both crystallization conditions.
Large deformation behavior of fat crystal networks
Kloek, W. ; Vliet, T. van; Walstra, P. - \ 2005
Journal of Texture Studies 36 (2005)5-6. - ISSN 0022-4901 - p. 516 - 543.
fractal nature - casein gels - crystallization - oil
Compression and wire-cutting experiments on dispersions of fully hydrogenated palm oil in sunflower oil with varying fraction solid fat were carried out to establish which parameters are important for the large deformation behavior of fat crystal networks. Compression experiments showed that the apparent Young's modulus, yield stress, yield deformation and Bingham extensional viscosity scaled with the volume fraction solid fat according a power law. For the Young's modulus and yield stress, the exponent was about 3.8¿3.9. The scaling exponent is close to the one relating the storage modulus and the fraction solid fat at deformations within the linear region. The specific fracture energy obtained from wire cutting also increased with volume fraction solid fat. That of a 10% solid fat dispersion was about 4 J/m2. Combination of the energy input from compression experiments and the specific fracture energies from wire-cutting experiments yielded defect lengths of the order of 20 ¿m. This length scale corresponds to the size of a fat crystal aggregate at the gel point.
Dairy Science and Technology, Second Edition
Walstra, P. ; Wouters, J.T.M. ; Geurts, T.J. - \ 2005
Boca Raton, FL, USA : CRC (Food science and technology 147) - ISBN 0824727630 - 782
zuivelwetenschap - zuiveltechnologie - melk - melkproducten - kazen - melkbewerking - handboeken - dairy science - dairy technology - milk - milk products - cheeses - milk processing - handbooks
This book discusses the transformation of milk into high-quality produces, emphasizing the principles of physical, chemical, enzymatic, and microbial transformation. The text begins with an introduction to the chemistry, physics and microbiology of milk and then explains the manufacturing processes. After an extensive discussion of various dairy products and the procedures necessary for consumer safety, the book concludes with details on the manufacture and ripening of cheese.
Competitive Adsorption between B-Casein or B-Lactoglobulin and Model Milk Membrane Lipids at Oil-Water Interfaces
Waninge, R. ; Walstra, P. ; Bastiaans, J. ; Nieuwenhuijse, H. ; Nylander, T. ; Paulsson, M. ; Bergenstahl, B. - \ 2005
Journal of Agricultural and Food Chemistry 53 (2005)3. - ISSN 0021-8561 - p. 716 - 724.
fat globule-membrane - phase-equilibria - phospholipid surfaces - orogenic displacement - protein adsorption - cryo-tem - emulsions - surfactants - stability - lecithin
This study investigated the competitive adsorption between milk proteins and model milk membrane lipids at the oil-water interface and its dependence on the state of the lipid dispersion and the formation of emulsions. Both protein and membrane lipid surface load were determined using a serum depletion technique. The membrane lipid mixture used was a model milk membrane lipid system, containing dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine, milk sphingomyelin, dioleoylphosphatidylserine, and soybean phosphatidylinositol. The model composition mimics the lipid composition of natural milk fat globule membranes. The interactions were studied for two proteins, -lactoglobulin and -casein. The mixing order was varied to allow for differentiation between equilibrium structures and nonequilibrium structures. The results showed more than monolayer adsorption for most combinations. Proteins dominated at the oil-water interface in the protein-emulsified emulsion even after 48 h of exposure to a vesicular dispersion of membrane lipids. The membrane lipids dominated the oil-water interface in the case of the membrane lipid emulsified emulsion even after equilibration with a protein solution. Protein displacement with time was observed only for emulsions in which both membrane lipids and -casein were included during the emulsification. This study shows that kinetics controls the structures rather than the thermodynamic equilibrium, possibly resulting in structures more complex than an adsorbed monolayer. Thus, it can be expected that procedures such as the mixing order during emulsion preparation are of crucial importance to the emulsification performance
Emulsions (chapter 8)
Walstra, P. - \ 2005
In: Fundamentals of interface and colloid science, volume V Soft Colloids Elsevier Academic Press - ISBN 9780124605305 - 94 p.
Foams (chapter 7)
Bergeron, V. ; Walstra, P. - \ 2005
In: Fundamentals of interface and colloid science, volume V Soft Colloids Elsevier Academic Press - ISBN 9780124605299 - 38 p.
The Syneresis of Rennet-coagulated Curd
Dejmek, P. ; Walstra, P. - \ 2004
In: Cheese: Chemistry, Physics and Microbiology Elsevier - ISBN 012263652X - 33 p.
Functional properties in industrial applications
Walstra, P. ; Vliet, T. van - \ 2003
Progress in Biotechnology 23 (2003). - ISSN 0921-0423 - p. 9 - 30.
Accuracy of prediction of percentage lean meat and authorization of carcass measurement instruments: adverse effects of incorrect sampling of carcasses in pig classification.
Engel, B. ; Buist, W.G. ; Walstra, P. ; Olsen, E. ; Daumas, G. - \ 2003
Animal Science 76 (2003)2. - ISSN 1357-7298 - p. 199 - 209.
regression experiments - precision - expense
Classification of pig carcasses in the European Community is based on the lean meat percentage of the carcass. The lean meat percentage is predicted from instrumental carcass measurements, such as fat and muscle depth measurements, obtained in the slaughter-line. The prediction formula employed is derived from the data of a dissection experiment and has to meet requirements for authorization as put down in EC regulations. Requirements involve the sampling procedure and sample size for the dissected carcasses and the accuracy of prediction. Formulae are often derived by linear regression. In this paper we look at a particular type of sampling scheme. This involves selection of carcasses on the basis of carcass measurements not all of which are intended to be used as prediction variables. This sampling scheme frequently appears in requests for authorization of carcass measurement instruments and accompanying prediction formulae, despite the fact that it lacks formal statistical justification when used in conjunction with linear regression. The objective of this work was to assess the performance of the prediction formula that follows from this potentially faulty combination of sampling scheme and linear regression in relation to the requirements in the EC regulations. We show that this sampling scheme may produce poor predictions for lean meat percentage compared with proper sampling procedures with selection on prediction variables only or random sampling. We do so by computer simulation. Initially, simulated data were based on recent and historic data from The Netherlands. Prediction variables are fat and muscle depth measurements. The additional variable involved in sampling, but not included in the regression, was carcass weight. We also show that due to this faulty sampling scheme there is a serious risk that a new measurement instrument may not be authorized because performance criteria in the EC-regulations are not met.
Physical chemistry of foods
Walstra, P. - \ 2003
New York [etc.] : Marcel Dekker (Food science and technology 121) - ISBN 0824793552 - 807
fysische chemie - fysische eigenschappen - voedsel - fysica - voedselchemie - voedselwetenschappen - studieboeken - physical chemistry - physical properties - food - physics - food chemistry - food sciences - textbooks
Exploring the structure and physical and chemical properties of solutions, dispersions, soft solids, fats, and cellular systems, this text describes the physicochemical principles essential to the comprehension and prediction of reactions and conversions that occur during the manufacture, handling, and storage of foods. The book contains practical examples of starch gelatinization and retrogradation, protein denaturation, lipid crystallization, foam and emulsion formation, colloidal interactions, glass transitions, and food freezing and structure, etc.
Spreading of oil from protein stabilised emulsions at air/water interfaces
Schokker, E.P. ; Bos, M.A. ; Kuijpers, A.J. ; Wijnen, M.E. ; Walstra, P. - \ 2002
Colloids and Surfaces. B: Biointerfaces 26 (2002). - ISSN 0927-7765 - p. 315 - 327.
thin viscous film - deep fluid layer - insoluble surfactant - water interface - isolate
Spreading of a drop of an emulsion made with milk proteins on air/water interfaces was studied. From an unheated emulsion, all oil molecules could spread onto the air/water interface, indicating that the protein layers around the oil globules in the emulsion droplet were not coherent enough to withstand the forces involved in spreading. Heat treatment (90oC) of emulsions made with whey protein concentrate (WPC) or skim milk powder reduced the spreadability, probably because polymerisation of whey protein at the oil/water interface increased the coherence of the protein layer. Heat treatment of emulsions made with WPC and monoglycerides did not reduce spreadability, presumably because the presence of the monoglycerides at the oil/water interface prevented a substantial increase of coherence of the protein layer. Heat treatment of caseinate-stabilised emulsions had no effect on the spreadability. If proteins were already present at the air/water interface, oil did not spread if the surface tension () was
Physical chemistry of foods
Walstra, P. - \ 2002
In: Gums and stabilisers for the food industry 11 : the proceedings of theEleventh Gums and Stabilisers for the Food Industry Conference-Crossing Boundaries held on 2-6 July 2001 at The North East Wales Institute, Wrexham,UK / ed. by A. Peter [S.l.] : S.n. - p. np - np.
Formation and Stability of Foam Made with Various Potato Protein Preparations
Koningsveld, G.A. van; Walstra, P. ; Gruppen, H. ; Wijnaards, G. ; Boekel, M.A.J.S. van; Voragen, A.G.J. - \ 2002
Journal of Agricultural and Food Chemistry 50 (2002). - ISSN 0021-8561 - p. 7651 - 7659.
functional-properties - beta-lactoglobulin - air-water - hydrolysis - fractions - behavior - plasmin - patatin - isolate - ph
In the present study, foam-forming and -stabilizing properties of potato proteins were studied using whipping and sparging tests. The soluble potato proteins-are mainly composed of patatin and protease inhibitors. The whipping tests showed that less foam was formed from untreated patatin than from the protease inhibitors, but patatin foam was much more stable. The foam-forming properties of patatin could be strongly improved by partial unfolding of the protein. Whipping tests, at both low (0.5 mg/ mL) and high (10 mg/mL) protein concentration, also indicated that foams made with,an ethanol-precipitated protein isolate were more stable than those made with beta-casein and beta-lactoglobulin. More generally, it can be concluded that when proteins are used as a foaming agent, a high concentration is required, because the protein available is inefficiently used. Also, there are several variables that may all, in different ways, affect both foam formation (amount of foam, bubbles size distribution) and foam stability. These variables include the type and concentration of protein, solvent conditions (pH, l), and the method used to make the foam.
The Roles of Proteins and Peptides in Formation and Stabilisation of Emulsions
Walstra, P. - \ 2002
In: Gums and stabilisers for the Food Industry, Conference 2nd - 6th July 2001 / ed. by P.A. Williams. Vol. 11, 2002 Cambridge : Royal Society of Chemistry - ISBN 0854048367 - p. 237 - 244.
Effects of structural rearrangements on the rheology of rennet-induced casein particle gels
Mellema, M. ; Walstra, P. ; Opheusden, J.H.J. van; Vliet, T. van - \ 2002
Advances in Colloid and Interface Science 98 (2002)1. - ISSN 0001-8686 - p. 25 - 50.
cluster-cluster aggregation - finite binding-energies - skim milk gels - computer-simulation - fractal structure - scaling behavior - micelles - gelation - syneresis - model
During ageing of casein or skim milk gels, structural changes take place that affect gel parameters, such as pore size and storage modulus. These changes can be explained in terms of rearrangements of the gel network at various length scales. In this paper, rheological experiments on rennet-induced casein gels and a general model on rearrangements are presented. The results of experiments (e.g. microscopy, permeametry) and computer simulations, the model, and recent literature on casein gels and other types of particle gels are compared to each other. Experiments presented include measurements of storage and loss moduli and maximum linear strain of the casein gels. Parameters varied were pH (5.3 and 6.65) and temperature (25 and 30degreesC). In addition, the casein volume fraction (5-9 vol.%) was varied, which enables application of fractal scaling models. For rennet-induced casein gels, it is demonstrated that at the lower pH, all types of rearrangements proceed significantly faster. The rearrangements include: an increase in the size of compact building blocks; partial disappearance of fractal structure; and the formation of straightened strands, some of which eventually break. All of these rearrangements seem to be a consequence of particle fusion. There are indications of universality of the relation between particle fusion and gel syneresis for gels composed of viscoelastic particles. (C) 2002 Elsevier Science B.V. All rights reserved.
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