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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      We will mail you new results for this query: wurpublikatie/titelbeschrijving/classificatie/trefwoord/cab/engels==milk products
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    Adding value through health claims: an empirical analysis of the Italian yogurt market
    Bimbo, Francesco - \ 2017
    Wageningen University. Promotor(en): A.G.J.M. Oude Lansink, co-promotor(en): Alessandro Bonanno. - Wageningen : Wageningen University - ISBN 9789463434508 - 130
    milk products - yoghurt - food products - health foods - business economics - consumer preferences - nutrition labeling - italy - europe - melkproducten - yoghurt - voedselproducten - gezondheidsvoedsel - bedrijfseconomie - consumentenvoorkeuren - etiketteren van voedingsmiddelen - italië - europa

    In recent years policymakers have aimed to increase the general awareness regarding the link between diet and health, providing food companies with an opportunity to add health-enhancing features in order to differentiate their products. The European market of these products, referred to here as functional foods, is regulated according to the European regulation 1924/2006 on nutrition and health claims on foods.

    Even though the European functional foods’ market has grown steadily over the last 20 years, more than 3 out of 4 new functional products are withdrawn from the market within two years from launch. Indeed, firms have to overcome three main obstacles to market health-enhancing products successfully. First, consumer-related factors, such as the heterogeneity of consumer acceptance of, and preferences for, new functional products; second, firms' difficulties in selecting the optimal attribute profiles to meet consumer demand for health features and; third, firms' difficulties to target consumers with a high enough willingness to pay to ensure the profitability of those investments needed to develop and market functional products.

    The general objective of this thesis is to assess quantitatively the implicit price of health claims as well as to generate new knowledge that will inform firms on how to target consumers with higher WTP for functional products.

    This thesis uses the Italian yogurt market as a case study for three reasons. First, yogurt is considered intrinsically healthy and it is one of the most credible carriers of functional ingredients: the category of fermented functional dairy accounts for nearly 43 per cent of the total functional products’ market. Second, among European countries, Italy saw the launch of the highest number (592) of new healthy products in the period 2005-2009; the majority of the new products introduced were functional yogurts benefiting digestive health (336), the immune system (99) and cardiovascular health (65). Third, the Italian yogurt market is characterized by a high level of differentiation with respect of health attributes, with manufacturers offering a variety of products carrying health claims, appearing suitable to analyze the problem at hand.

    The results of this thesis show that in the Italian yogurt market the implicit prices of “risk reduction” claim is higher than that of “general function” ones (respectively, +222.6% vs +85.5% of the baseline alternative’s price in the case of cholesterol reduction health claim), and in three out of four cases, health claims supported by familiar brands have higher implicit price than those supported by less-familiar ones. Those results confirm findings collected in the systematic literature review which highlights a consensus that claims supported by familiar brands as well as “risk reduction” (vis-à-vis “general function”) ones increase consumers’ acceptance of functional dairy products. The results also point out that “natural” and “organic” claims lead to implicit prices which are (approximately) +46.6% and +102.0% over the price of the baseline alternative, comparable to those of some of the health claims. Other results indicate that manufacturers operating in the Italian yogurt market investing in credence attributes (health claims, organic and natural) gain the ability to target consumers with higher WTP by including two or more products carrying credence attribute in their portfolio. Lastly, the findings of this thesis reveal that consumers’ body image dissatisfaction, along with not reading food labels and lower knowledge about leading functional yogurt brands, are associated with lower number of functional yogurt packages purchased by Italian yogurt consumers using a virtual shelf setting.

    Intracellular & extracellular lipolysis : regulation by the PPAR targets ANGPTL4 & HILPDA
    Dijk, Wieneke - \ 2016
    Wageningen University. Promotor(en): Sander Kersten. - Wageningen : Wageningen University - ISBN 9789462579460 - 248
    foams - foaming - milk products - processing - aggregates - casein - micelles - physical properties - schuim - schuimen - melkproducten - verwerking - bodemdeeltjes - caseïne - micellen - fysische eigenschappen

    The body efficiently stores energy in the form of triglyceride (fat) molecules. However, triglycerides cannot directly enter or exit our cells, but first need to be degraded to so-called fatty acids before moving in or out a cell. This degradation process, called lipolysis, is crucial for human physiology and is tightly regulated to prevent the accumulation of fats either within organs or within the bloodstream - hallmarks of diseases such as obesity and cardiovascular disease.

    To allow for uptake by underlying organs, triglycerides in the circulation are efficiently broken down by an enzyme called lipoprotein lipase (LPL) that sits in the bloodstream of multiple organs (extracellular lipolysis). In this thesis, we characterized a protein named angiopoietin-like 4 (ANGPTL4) that potently inhibits LPL and, thereby, inhibits the breakdown of triglycerides in the bloodstream. Our data show that by adjusting the tissue expression levels of ANGPTL4, different organs collaborate to ensure that triglycerides are distributed to organs in need of energy. Moreover, we uncovered that, in the fat tissue, ANGPTL4 starts to inhibit LPL before LPL arrives in the bloodstream. By preventing the arrival of LPL in the bloodstream, ANGPTL4 is capable of rapidly adjusting the rates of triglyceride degradation and the concomitant uptake of fatty acids from the circulation to the energy requirements of the underlying organ.

    To exit our cells, stored triglycerides, such as present in our fat tissue, need to be broken down to fatty acids. Subsequently, the released fatty acids can fuel other organs in need of energy. To further clarify the mechanisms underlying this process of intracellular lipolysis, we investigated the role of a promising new protein called HILPDA. Our data show, however, that loss of HILPDA did not impact the release of fatty acids from the fat tissue, while a high abundance of HILPDA only had a mild attenuating effect on the release of fatty acids. This suggests that HILPDA is not a major physiological regulator of intracellular lipolysis in fat cells.

    In conclusion, in this thesis, we have clarified the regulation of intracellular and extracellular lipolysis by studying the respective roles of the proteins ANGPTL4 and HILPDA. Such efforts are clinically relevant, as regulators of lipolysis are potential therapeutic targets to lower cardiovascular disease risk.

    Natuurkorstkaas ontwikkelt zich goed in proeftuin
    Hettinga, Kasper - \ 2016
    milk products - cheeses - cheese ripening - cheese mites - odours - pilot farms - ghee - natamycin

    De zelfkazer : maandblad voor producenten van boerenkaasDe kazen met natuurkorst ontwikkelen zich goed in de nieuwe rijpingsruimte van boerderij De Groote Voort in Lunteren, al deden zich wel wat problemen voor, onder andere met mijten. De problemen zijn nu onder controle, vertelde Jan Dirk van de Voort op 15 februari bij de presentatie van de tussentijdse resultaten van de ‘Proeftuin Natuurlijke Kaasrijping’.

    Reststromen zuivelketen
    Dolman, M.A. - \ 2016
    LEI Wageningen UR (Factsheet / LEI Wageningen UR 2016-013d) - 11
    agro-industriële bijproducten - reststromen - zuivelindustrie - melkproductie - melkproducten - afvalhergebruik - agro-industriële ketens - biobased economy - agroindustrial byproducts - residual streams - dairy industry - milk production - milk products - waste utilization - agro-industrial chains - biobased economy
    De productie en verwerking van zuivel leidt tot producten en diverse reststromen of bijproducten. In deze factsheet worden bestaande bijproducten en reststromen en hun huidige bestemmingen in kaart gebracht. Nagegaan is in hoeverre het geheel (het huidige gebruik) duurzaam is en of er mogelijkheden zijn om het economisch rendement te verbeteren.
    Wat betekent de Russische boycot voor Nederland?
    Berkum, Siemen van - \ 2015
    agricultural economics - exports - agricultural prices - meat - milk products - vegetables - fruit - international trade - netherlands
    From Milk By-Products to Milk Ingredients : Upgrading the Cycle
    Boer, Ruud De - \ 2014
    Wiley-Blackwell - ISBN 9780470672228 - 269 p.
    milk - milk products

    Milk is a complex substance, and a variety of constituents can be extracted from it for use as ingredients in other foods. The main ingredients from milk are milk fat, cheese and serum, but this range is continually expanding as food companies, dairies and dairy scientists seek to utilize as many raw materials and by-products as possible, to reduce waste, maximize efficiency, and increase productivity. Ingredients from Milk is a concise, fresh approach to ingredients derived from milk, containing guidance and new techniques for dairy industry professionals and scientists. has a structure is designed to mirror the process of extracting ingredients from milk, beginning with the basic concepts and following through the processes until finally arriving at the consumer products which constitute the end uses of ingredients from milk. This book is primarily targeted at the dairy industry, but also provides a valuable insight for academics and students seeking an industry perspective.

    Voedselfraudeur ontmaskerd (interview met Saskia van Ruth en Rita Boerrigter-Eenling)
    Smit, A. ; Ruth, S.M. van; Boerrigter-Eenling, G.R. - \ 2014
    WageningenWorld 2014 (2014)1. - ISSN 2210-7908 - p. 28 - 31.
    biologische voedingsmiddelen - authenticiteit - dranken - voedselanalyse - identificatie - voedseltechnologie - melkproducten - voedselinspectie - organic foods - authenticity - beverages - food analysis - identification - food technology - milk products - food inspection
    Producenten die sjoemelen met de herkomst van levensmiddelen kunnen vaker op het matje worden geroepen. RIKILT Wageningen UR ontwikkelt steeds meer tests die duidelijk maken waar de ingrediënten vandaan komen én of ze wel echt op biologische wijze zijn gemaakt. Koffie en eieren blijken wat dat betreft verrassend herkenbaar.
    Fragiele ouderen sterker en scherper door eiwit
    Koningsbruggen, W. van; Groot, C.P.G.M. de; Zwaluw, N.L. van der - \ 2014
    VoedingsMagazine 27 (2014)1. - ISSN 0922-8012 - p. 8 - 10.
    melkproducten - eiwitbronnen - ouderenvoeding - voedingsstoffen - voeding en gezondheid - eiwitrijke voedingsmiddelen - milk products - protein sources - elderly nutrition - nutrients - nutrition and health - protein foods
    Fragiele ouderen die extra eiwit krijgen, vertonen fysieke en ook enige mentale vooruitgang. Dit is aangetoond door een onderzoeksgroep van de afdeling Humane Voeding van Wageningen Universiteit. Promovendus Nikita van der Zwaluw en prof. dr. ir Lisette de Groot vertellen over het cognitieve deel van de studie.
    Voedselprijzenmonitor van start
    Silvis, H.J. - \ 2014
    LEI Wageningen UR
    voedselprijzen - prijsvorming - voedselproductie - voedingsmiddelen - voedselketens - producentenprijzen - consumentenprijzen - vleeswaren - melkproducten - food prices - price formation - food production - foods - food chains - producer prices - consumer prices - meat products - milk products
    De voedselprijzenmonitor verschaft inzicht in de ontwikkeling van prijzen door de voedselproductieketen heen; dit wil zeggen op het niveau van het primaire agrarische bedrijf, de verwerking en de consument. De volgende ketens worden onderscheiden: tarweproducten, aardappelproducten, zuivel, eieren, pluimveevlees, varkensvlees en rundvlees. Voor groente en fruit worden vooralsnog alleen consumentenprijzen weergegeven.
    Magere of volle melk: het verschil kun je ruiken
    Boesveldt, Sanne - \ 2014
    milk products - low fat milk - low fat products - smell - fat content
    Foaming behaviour of organic and regular milk
    Pijnenburg, J. ; Sala, G. ; Valenberg, H.J.F. van; Meinders, M.B.J. - \ 2012
    Wageningen : Wageningen UR - 23
    melk - biologische voedingsmiddelen - schuimen - stabiliteit - melkproducten - milk - organic foods - foaming - stability - milk products
    Organic milk is used more and more by consumers to froth milk that is used e.g. for the preparation of a capuccino. Frequently, organic milk turns out not to foam properly. This report describes a study to find the main couse of this bad foamability of organic milk. The focus of the research was to get insight in the foaming behaviour of a specific brand, indicated as A. The foamability and stability of different milk, both organic and regular, as well as skimmed, semi-skimmed, and full fat, were tested. The foamability of the different milk varieties appeared to be about equal. However, differences were observed for the foam stability. Foams made from A showed the lowest stability of all tested milk varieties. The reason for this is not yet clear, but the bad foam stability of this milk might be probably due to a higher fatty acid content.
    Influence of calcium chelators on concentrated micellar casein solutions : from micellar structure to viscosity and heat stability
    Kort, E.J.P. de - \ 2012
    Wageningen University. Promotor(en): Toon van Hooijdonk; Erik van der Linden, co-promotor(en): M. Minor. - S.l. : s.n. - ISBN 9789461732378 - 152
    melkproducten - calcium - chelaatvormers - caseïne - micellen - viscositeit - hittebestendigheid - milk products - calcium - chelating agents - casein - micelles - viscosity - heat stability

    In practice it is challenging to prepare a concentrated medical product with high heat stability
    and low viscosity. Calcium chelators are often added to dairy products to improve heat stability,
    but this may increase viscosity through interactions with the casein proteins. The aim of this
    thesis was to obtain a better understanding of the influence of different calcium chelators on the
    physico-chemical properties of casein micelles and the resulting effect on viscosity and heat
    stability of concentrated micellar casein isolate (MCI) solutions. The calcium chelators disodium
    uridine monophosphate (Na2UMP), disodium hydrogen phosphate (Na2HPO4), trisodium citrate
    (TSC), sodium phytate (SP), and sodium hexametaphosphate (SHMP) were studied.
    Initially, the calcium-binding capacity of the phosphates was investigated and found to be
    directly related to the amount of charges. The resulting effects on physical changes of casein
    micelles were subsequently explored before and during heating. The viscosity of the MCI
    solutions increased upon addition of the calcium chelators, which was attributed to swelling of
    the caseins at decreasing calcium-ion activity. The calcium chelators induced different changes
    in turbidity of the MCI solutions, which could be related to the degree of dissociation of the
    casein micelles. Simulations of the ion equilibria indicated that the extent of casein micelle
    dissociation followed the calcium-binding capacity of the calcium chelators. Micelle
    dissociation occurred in the order of SHMP > SP > TSC > Na2HPO4 > Na2UMP. The results on
    heat stability indicated that the calcium-ion activity and state of the micellar structure before and
    during heating determined the heat stability of the MCI solutions. Na2UMP was the most
    effective heat stabilizer, as it bound sufficient free calcium ions to reduce protein aggregation
    without affecting the micellar structure. SHMP was the least effective heat stabilizer because of
    heat-induced changes occurring during heating. For polyphosphates, SHMP and SP, it was
    found that they decreased the isoint of casein by forming direct bindings with the caseins, for
    which calcium ions were not required.
    In conclusion, this thesis has provided new insights in the relationships between calcium
    chelators and their influence on the casein micelle structure and on the physico-chemical
    properties of concentrated MCI solutions. Also, the practical relevance for the dairy industry
    was described, demonstrating how different calcium chelators can manipulate the viscosity and
    heat stability of dairy products.

    Vol smaak en variatie; Kansen voor producten van geiten- en schapenzuivel op de consumentenmarkt
    Haaster-de Winter, M.A. van; Berg, I. van den; Dvortsin, L. - \ 2011
    Den Haag : LEI, onderdeel van Wageningen Universiteit (Rapport / LEI : Onderzoeksveld Consument & gedrag ) - ISBN 9789086155712 - 35
    marktonderzoek - geitenmelk - ooienmelk - melkproducten - biologische voedingsmiddelen - consumentenonderzoeken - marktverkenningen - consumentengedrag - market research - goat milk - ewe milk - milk products - organic foods - consumer surveys - market surveys - consumer behaviour
    De melk van Nederlandse geiten en schapen wordt grotendeels verkaasd en geëxporteerd. Organic Goatmilk Coöperatie, De Groene Geit en Nederlandse Vereniging van Professionele Melkschapenhouders vragen zich af welke kansen de thuismarkt biedt. De volgende punten komen als belangrijkste uitkomsten uit het onderzoek. Smaak en variatie zijn sterke punten van geiten- en schapenzuivelproducten. Daarmee is de aantrekkingskracht van algemene aard en zijn de producten voor veel meer mensen aantrekkelijk dan alleen mensen met een koemelkallergie. Geiten- en schapenzuivelproducten hebben een goede uitgangspositie om in te haken op de voor consumenten relevante thema's van gezondheid en genieten en beleving. Inspelen op gemak en betaalbaarheid bieden meer uitdaging. Gebruikers van geiten- en schapenzuivelproducten zijn nieuwsgierige mensen en vinden eten leuk. Ofwel, zij zijn eerder dan anderen geneigd om nieuwe producten uit te proberen. Bovendien vinden gebruikers van geitenzuivelproducten het leuker om te eten of er mee bezig te zijn.
    Innovations in the dairy chain: bio-economic analysis of novel breeding opportunities
    Demeter, R.M. - \ 2011
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Alfons Oude Lansink; Miranda Meuwissen; A.R. Kristensen. - [S.l.] : S.n. - ISBN 9789461732088 - 192
    dierveredeling - melkkoeien - zuivelindustrie - kunstmatige selectie - melkproducten - genomica - melkvetpercentage - melkeiwitpercentage - animal breeding - dairy cows - dairy industry - artificial selection - milk products - genomics - milk fat percentage - milk protein percentage
    In recent years, there has been a growing interest in the dairy sector to move from producing bulk dairy commodities towards producing specialized dairy products aimed at niche markets. Dairy farmers consider shifting from commodity milk to raw milk with specialized composition to meet consumer or industrial demands. In this context, the objectives of the thesis were 1) to assess qualitatively future scenarios to create value added in the dairy chain and 2) to ex-ante assess quantitatively the technical and economic implications at farm level of producing differentiated raw milk by using genetic selection. A two-step approach was applied, where the first step assessed qualitatively the strategic opportunities offered by a wide range of novel methods emerging at various stages in the production chain, whereas the second step assessed quantitatively the implications of specific strategies on farm level. The main findings indicate that creating value added is vital for the sustainable growth of the dairy industry, and producing raw milk with specialized characteristics by using novel breeding concepts can play an important role in this process. The ex-ante quantitative assessments have found no evidence that implementing novel genetic selection strategies to change fat or protein composition in milk would have large effects on herd production and profitability. The stakeholders of the dairy industry should initiate joint action plans to capitalize on the opportunities offered by recent milk genomics research.
    Gezondheidsraad onderschat rendement van de Nederlandse koe : simpele rekensom weerlegt eiwitfabel over melk
    Dijkstra, Jan - \ 2011
    dairy cows - milk products - milk composition - milk production characteristics - nutrients - nutrient content - nutrient sources
    Zuivelproducten zijn belangrijke bronnen van micronutriënten
    Groot, C.P.G.M. de - \ 2011
    VoedingsMagazine 24 (2011)3. - ISSN 0922-8012 - p. 11 - 13.
    melkproducten - melk - voedingsstoffen - aanbevolen dagelijkse hoeveelheden - voeding en gezondheid - voedingsstoffentekorten - voedingsstoffenbehoeften - sporenelementen - milk products - milk - nutrients - recommended dietary allowances - nutrition and health - nutrient deficiencies - nutrient requirements - trace elements
    Het network of excellence EURRECA heeft tien micronutriënten geselecteerd die prioriteit verdienen bij de Europese harmonisatie van de voedingsaanbevelingen. Voor veel van de micronutrienënten zijn melk en zuivelproducten belangrijke bronnen. Zo bleek tijdens een symposium in Parijs.
    Actualisatie ketenrendement in de Nederlandse agribusiness: 2000-2009 : varkensvlees, zuivel, groente en fruit
    Backus, G.B.C. ; Pierick, E. ten; Galen, M.A. van; Jager, J.H. - \ 2011
    Den Haag : LEI Wageningen UR - 10
    landbouwindustrie - ketenmanagement - kosten-batenanalyse - rendement - melkproducten - fruit - groenten - varkensvlees - bedrijfsresultaten in de landbouw - agribusiness - supply chain management - cost benefit analysis - returns - milk products - fruit - vegetables - pigmeat - farm results
    In 2007 zijn door het LEI in opdracht van de Rabobank de ketenrendementen in de Nederlandse agribusiness onderzocht. Voor de periode 2002-2004 werden de rendementen in de verschillende schakels van vier Nederlandse agroketens berekend voor zuivel, varkensvlees, groente en fruit. Het onderzoek maakte duidelijk hoe de rendementsverhouding tussen de schakels en tussen de ketens was, en droeg daarmee bij aan de discussie hierover. Het was voor de Rabobank aanleiding de resultaten van de studie uit 2007 te laten actualiseren.
    Het gaat bij melk om het samenspel tussen de vele nutrienten
    Hooijdonk, A.C.M. van - \ 2011
    ZuivelZicht 103 (2011)7. - ISSN 0165-8573 - p. 12 - 14.
    melkproducten - voedingsstoffen - voedingsstof-voedingsstof interacties - voeding en gezondheid - voedingswaarde - voedingsstoffengehalte - voedingsstoffenconcentratie - milk products - nutrients - nutrient nutrient interactions - nutrition and health - nutritive value - nutrient content - nutrient density
    Regelmatig wordt Toon van Hooijdonk er mee geconfronteerd dat mensen weinig meer weten van melk dan alleen dat er calcium in zit. Dat er zoveel meer nutriënten aanwezig zijn in melk is spaarzaam bekend. 'Juist de samenhang tussen al die nutriënten is belangrijk', zegt de hoogleraar Zuivelkunde.
    Verse melk voor de Filippino's
    Lee, J. van der; Schiere, J.B. - \ 2010
    V-focus 7 (2010)2. - ISSN 1574-1575 - p. 28 - 29.
    melkveehouderij - melkvee - melk - melkproducten - dairy farming - dairy cattle - milk - milk products
    Op de Filippijnen neemt de consumptie van melkproducten toe. Lokale productie staat nog in de kinderschoenen, met volop kansen om aan de toenemende vraag te voldoen. Wageningen UR adviseert het ministerie van LNV over Nederlandse steun aan de ontwikkeling van de sector. Dat zorgt voor interessante uitdagingen.
    Bioavailability of lysine in heat-treated foods and feedstuffs
    McArtney Rutherfurd, S. - \ 2010
    Wageningen University. Promotor(en): Wouter Hendriks; Martin Verstegen, co-promotor(en): P.J. Moughan. - [S.l. : S.n. - ISBN 9789085856825 - 139
    lysine - biologische beschikbaarheid - voer - voedingsmiddelen - melkproducten - huisdierenvoer - ontbijtgranen - warmtebehandeling - maillard-reactie - maillard-reactieproducten - verteerbaarheid - lysine - bioavailability - feeds - foods - milk products - pet foods - breakfast cereals - heat treatment - maillard reaction - maillard reaction products - digestibility
    During the processing of foodstuffs, lysine can react with other compounds present to form nutritionally unavailable derivatives, the most common example of which are Maillard products. Maillard products can cause serious problems when determining the available lysine content of processed foods or feedstuffs as they can revert to lysine during amino acid analysis. Several methods have been developed to determine the dietary lysine available for the metabolic processes of animals including animal growth-based assays, reactive lysine chemical methods and digestibility assays. However, growth-based assays are laborious, highly variable and tend to determine utilization rather than availability. Chemically reactive lysine assays do accurately determine the unmodified lysine in a food or feedstuff, but do not determine available lysine as they incorrectly assume that reactive lysine digestion and absorption is 100%. Ileal digestibility assays measure digestible total lysine rather than digestible reactive lysine (available lysine) and so are inaccurate, especially when applied to processed protein sources. This thesis describes the development of a true ileal digestible reactive lysine assay for determining dietary (bio)available lysine. This assay couples the guanidination reaction, for determining reactive lysine, with a true ileal digestibility assay. The resulting apparent digestibility estimate is corrected to a true digestibility value by accounting for the endogenous ileal lysine flow.

    Selected reaction conditions for the guanidination of lysine in a heated lactose/casein mixture and digesta of rats fed unheated casein and heated lactose/casein was examined. Overall, suitable reaction conditions were 0.6 M O-methylisourea for 7 d in a shaking waterbath at 21 ± 2 °C with an O-methylisourea to lysine ratio of 1000 and a reaction mixture pH of 10.6 for casein and heated lactose/casein and 11.0 for digesta. The accuracy of the guanidination method for determining reactive lysine in a range of “ready-to-eat ” cereal-based breakfast foods and selected feedstuffs was tested by comparison with the reactive lysine content of the same protein sources when determined using the fluorodinitrobenzene method. Overall, there was excellent agreement between the two methods. The accuracy of the newly developed bioassay for determining digestible reactive (available) lysine for predicting lysine deposition was also tested using a heated skim milk powder. The true ileal total and reactive lysine digestibilities were determined for the heated skim milk powder which was then fed to pigs, along with two control diets which were formulated based on either total lysine digestibility or reactive lysine digestibility. All diets were limiting in lysine. The pigs fed the heated skim milk powder deposited the same (P > 0.05) amount of lysine (9.1 g d-1) as the pigs fed the control diet that was formulated based on reactive lysine digestibility (9.1 g d-1) but deposited significantly (P < 0.05) more than the pigs fed the control diet that was formulated based on total lysine digestibility (5.4 g d-1). Consequently for the heated skim milk powder at least, the true ileal digestible reactive lysine assay accurately determined the available lysine content.

    The new assay demonstrated that for a range of milk protein-based foods, there was little difference between digestible total lysine and digestible reactive lysine for most of the milk products tested. In contrast, for a range of “ready-to-eat” cereal-based breakfast foods, available lysine was 5 – 50% lower than that determined using the traditional assay, which is of concern given that breakfast cereals are perceived to be “healthy” foods. Similarly, the available lysine content of a range of moist and dry commercial cat foods was significantly (P < 0.05) lower (15-55% lower) than previously estimated using the traditional true ileal digestible total lysine assay. The assay was also used to examine the effect of storage for extended periods at elevated temperatures on a hydrolysed-lactose skim milk powder and overall, there was a significant decrease in the available lysine content over time, as much as 60% over 6 mth when the powder was stored at 40 °C. In addition, the decrease in available lysine content of the hydrolysed-lactose skim milk powder was 2 – 5.5 times greater than observed for a normal skim milk powder depending on the storage time and temperature. Overall, foods and feedstuffs that have undergone processing often contain lower amounts of available lysine than thought previously. This new assay not only highlights the inaccuracy of the traditional true ileal digestible total lysine assay as a method for determining available lysine in processed protein sources, but permits the accurate assessment of the available lysine content of processed foods and feedstuffs.

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