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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Characterizing emulsion properties of microalgal and cyanobacterial protein isolates
Teuling, Emma ; Schrama, Johan W. ; Gruppen, Harry ; Wierenga, Peter A. - \ 2019
Algal Research 39 (2019). - ISSN 2211-9264
Critical protein concentration - Cyanobacteria - Emulsion behavior - Interfacial properties - Microalgae - Rubisco

Photosynthetic unicellular sources contain a large variety of proteins. The types of proteins vary between different microalgae and cyanobacteria. The aim was to study the effect of the variation in proteins and in non-proteinaceous components present in various unicellular protein isolates on their emulsion behavior. Algae soluble protein isolates (ASPIs, 66–77% w/w protein) of Nannochloropsis gaditana, Tetraselmis impellucida and Arthrospira (Spirulina) maxima were studied, using commercially available WPI as a reference (93% w/w protein). All protein isolates could form emulsions stable against creaming (d 3,2 0.2–0.3 μm) at pH 8.0. The amount of each ASPI needed (C cr ; on protein basis) to form these stable emulsions varied between the isolates, but was within the range of proteins from both similar (photosynthetic) sources (algae and sugar beet leaves) and other protein sources (dairy, legume and egg). Minor differences were observed in the pH dependence of flocculation amongst the ASPI stabilized emulsions. For the ASPIs, the expected correlation between interfacial and molecular properties (adsorption rate constant and ζ-potential) and the emulsion behavior (C cr and droplet size as a function of pH) was absent.

Investigating the effect of temperature on the formation and stabilization of ovalbumin foams
Delahaije, Roy J.B.M. ; Lech, Frederik J. ; Wierenga, Peter A. - \ 2019
Food Hydrocolloids 91 (2019). - ISSN 0268-005X - p. 263 - 274.
Concentration - Interfacial properties - Protein - Structural characterization - Viscosity

The effect of temperature (below denaturation temperature) on protein foam formation and stabilization is potentially large, but has received little attention. This study aims to identify the effect of temperature (15–60 °C) on ovalbumin-stabilized foams at different concentrations (0.05–50 g L−1), and place this in a theoretical perspective. With increasing temperature the initial adsorption rate (dΠ/dt) increased logarithmically from 0.006 mN m−1 s−1 at 5 °C to 0.084 mN m−1 s−1 at 60 °C. A concentration increase resulted in a linear increase of dΠ/dt. This concentration effect was also observed in the foam ability, although the foam ability increased logarithmically rather than linearly with concentration, as expected based on theory and dΠ/dt. The foam ability was hardly affected by temperature (in contrast to theory and dΠ/dt). This was attributed to the strong decrease of foam stability with increasing temperature, which was expected based on theory. At elevated temperatures, the poor foam stability interferes with the foam ability (i.e. foam stability ≈ timescale of foam formation), a situation also happening at low concentrations. When formation was faster than destabilization, the foam ability relates to the effective adsorption rate. The effective adsorption rate includes the decrease in adsorption probability with increasing surface coverage. The observed balance between the effect of adsorption rate and foam stability on foam ability is not quantitatively predictable based on current theoretical models.

31P NMR assessment of the phosvitin-iron complex in mayonnaise
Merkx, Donny W.H. ; Delić, Faruk ; Wierenga, Peter A. ; Hennebelle, Marie ; Duynhoven, John P.M. van - \ 2019
Magnetic Resonance in Chemistry 57 (2019)9. - ISSN 0749-1581 - p. 540 - 547.
P NMR - Fe(III)-phosvitin - Lipid Oxidation - Mayonnaise - NMR - Paramagnetic broadening

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a 31P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of 31P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin-Fe(III) loading in mayonnaise water phase by liquid NMR, whereas 31P NMR MAS could only provide a qualitative measure. The 31P NMR method showed a direct relation between loading of the Fe(III)-phosvitin complex and lipid oxidation.

Cell wall disruption increases bioavailability of Nannochloropsis gaditana nutrients for juvenile Nile tilapia (Oreochromis niloticus)
Teuling, Emma ; Wierenga, Peter A. ; Agboola, Jeleel O. ; Gruppen, Harry ; Schrama, Johan W. - \ 2019
Aquaculture 499 (2019). - ISSN 0044-8486 - p. 269 - 282.
Digestion - Feed ingredient - Maillard reaction products - Microalgae - Nutritive value

In this study the correlation between the accessibility of nutrients and in vivo nutrient digestibility was tested on the marine microalga Nannochloropsis gaditana in juvenile Nile tilapia (Oreochromis niloticus). It was hypothesized that disrupting the cell walls of microalgae increases the nutrient accessibility and digestibility. N. gaditana biomass was subjected to physical treatments (pasteurization, freezing, freeze drying) or mechanical treatments (bead milling) to influence its cell wall integrity. These treatments resulted in an up to 4 x increase in in vitro accessibility of N. gaditana nutrients, assessed from measurements of leaching and susceptibility to protein hydrolysis. Apparent digestibility coefficients of macronutrients, dry matter, energy, phosphorus and calcium of untreated and treated microalgae biomass were determined in triplicate, at a 30% diet inclusion level. Bead milling the algae led to the highest increase in in vivo digestibility of dry matter, energy, protein, fat, ash and calcium on ingredient level, compared to untreated algae biomass. This includes an increase in apparent digestibility coefficient (ADC) of protein and fat from 62 to 78% and from 50 to 82%, respectively. ADCs of total carbohydrates and of phosphorus were not affected by algal cell disruption. In vivo digestibilities of N. gaditana dry matter, energy, protein, and fat were positively correlated (p <.001; r ≥ 0.91) with the nutrient accessibility of N. gaditana, as estimated with in vitro nutrient leaching analyses. This shows that the in vitro methods used are effective ways to assess the effect of mechanical and physical treatments on in vivo nutrient quality of a single ingredient. The results of this study confirm that nutrient accessibility plays a significant role in the nutrient digestibility of the microalga Nannochloropsis gaditana in Nile tilapia.

Maillard induced aggregation of individual milk proteins and interactions involved
Cardoso, Hugo B. ; Wierenga, Peter A. ; Gruppen, Harry ; Schols, Henk A. - \ 2019
Food Chemistry 276 (2019). - ISSN 0308-8146 - p. 652 - 661.
Aggregation - Disulphide - Maillard - α-Lactalbumin - β-Casein - β-Lactoglobulin

The aggregation of α-lactalbumin, β-lactoglobulin and β-casein after heating in dry state was studied in absence and presence of saccharides. In absence of saccharides, differences were observed in the extent of aggregation. Differences between the proteins were mostly due to differences in covalent aggregation. The presence of glucose during the heat treatment of milk proteins significantly increased the extent of aggregation, and decreased differences between proteins. α-Lactalbumin was selected as a model protein for the study of cross-links formed after heat treatment. In the presence of saccharides, these cross-links were found to consist of 36% of disulphide bridges (compared to >75% in the absence of glucose), followed by other cross-links such as lanthionine. Larger saccharides led to a decrease in Maillard induced aggregation; maltotriose actually even inhibited the formation of α-lactalbumin aggregates.

Understanding glycation kinetics of individual peptides in protein hydrolysates
Deng, Yuxi ; Butré, Claire I. ; Wierenga, Peter A. - \ 2019
International Dairy Journal 91 (2019). - ISSN 0958-6946 - p. 98 - 109.

Protein hydrolysates contain peptides with different lengths, type (α/ε-) and number of amino groups; these properties might influence the peptide glycation kinetics during the Maillard reaction. To identify the effects of peptide properties and hydrolysate composition on glycation kinetics, the glycation kinetics of individual peptides in hydrolysates was followed using quantitative peptide analysis. α-Lactalbumin was hydrolysed and glycated with D-glucose (0–8 h, 50 °C, dry heating with 65% humidity). The hydrolysates (degree of hydrolysis 2, 4, 6, and 8%) contained 25 unique peptides, ranging from 2 to 123 AAs with 0–12 lysine(s). The glycation rate constant (kg) and the maximum average degree of glycation (DG_Pav,max) of peptides were independent of the hydrolysate composition. The maximum DG of α-NH2 and ε-NH2 groups was 12.8% and 60.0%, respectively. With this information, the DG_Pav,max of individual peptides [9–59% for peptides with 0–2 lysine(s)] could be predicted.

In vitro protein digestion kinetics of protein sources for pigs
Chen, H. ; Wierenga, P.A. ; Hendriks, W.H. ; Jansman, A.J.M. - \ 2019
Animal 13 (2019)6. - ISSN 1751-7311 - p. 1154 - 1164.
black soldier fly larvae - gastrointestinal protein degradation - plant protein sources - porcine plasma - yellow meal worm

In current feed evaluation systems, the nutritional value of protein sources in diets for pigs is based on the ileal digestibility of protein and amino acids, which does not account for the kinetics of protein digestion along the gastrointestinal tract. The objective of the present study was to determine the in vitro protein digestion kinetics of different protein sources (soya bean meal (SBM), wheat gluten (WG), rapeseed meal (RSM), whey powder (WP), dried porcine plasma protein, yellow meal worm larvae and black soldier fly larvae (BSF)). Protein sources were incubated with pepsin at pH 3.5 for 0 to 90 min and subsequently with pancreatin at pH 6.8 for 0 to 210 min at 39°C. The in vitro protein digestion kinetics were described as the kinetics of nitrogen (N) solubilisation and the release of low molecular weight peptides (LMW) (<500 Da). The N solubilisation rate ranged from 0.025 min-1 for BSF to 0.685 min-1 for WP during the incubation with pepsin, and from 0.027 min-1 for RSM to 0.343 min-1 for WP during the incubation with pancreatin. The release rate of LMW peptides ranged from 0.027 min-1 for WG to 0.093 min-1 for WP during the incubation with pepsin, and from 0.029 min-1 for SBM to 0.385 min-1 for WP. Black soldier fly larvae showed a similar release rate of LMW peptides as WP during the incubation with pancreatin. At the end of the sequential incubation with pepsin (90 min) and pancreatin (210 min), WG and WP showed the highest percentage of N present in LMW peptides relative to total N (78% and 79%, respectively), whereas SBM showed the lowest (35%). In conclusion, protein sources for pig diets show substantial differences in in vitro protein digestion kinetics as measured by the kinetics of N solubilisation and the release of LMW peptides. The rate of release of LMW peptides was not correlated to the rate of N solubilisation for each of the protein sources evaluated.

Fungal parasites of a toxic inedible cyanobacterium provide food to zooplankton
Frenken, Thijs ; Wierenga, Joren ; Donk, Ellen van; Declerck, Steven A.J. ; Senerpont Domis, Lisette N. de; Rohrlack, Thomas ; Waal, Dedmer B. van de - \ 2018
Limnology and Oceanography 63 (2018)6. - ISSN 0024-3590 - p. 2384 - 2393.

During the end of spring and throughout summer, large-sized phytoplankton taxa often proliferate and form dense blooms in freshwater ecosystems. In many cases, they are inedible to zooplankton and prevent efficient transfer of energy and elements to higher trophic levels. Such a constraint may be alleviated by fungal parasite infections on large-sized phytoplankton taxa like diatoms and filamentous cyanobacteria, as infections may provide zooplankton with a complementary food source in the form of fungal zoospores. Zoospores have been shown to support somatic growth of large filter feeding zooplankton species. Here, we tested if selectively feeding zooplankton, more specifically rotifers, also can use fungal zoospores as a food source. Our results show that chytrid fungal parasites can indeed support population growth of rotifers (Keratella sp.). Specifically, in cultures of an inedible filamentous cyanobacterium (Planktothrix rubescens), Keratella populations rapidly declined, while in Planktothrix cultures infected with chytrids, Keratella population growth rate equaled the growth observed for populations fed with a more suitable green algal diet (Chlorella sorokiniana). Feeding of Keratella on zoospores was furthermore indicated by a reduced number of zoospores during the last sampling day. These findings not only imply that rotifers may survive on zoospores, but also that the zoospores can support high rotifer population growth rates. We thus show that fungal parasites of inedible cyanobacteria can facilitate grazers by providing them alternative food sources. Together, these results highlight the important role that parasites may play in the aquatic plankton food web.

Influence of substrate concentration on the extent of protein enzymatic hydrolysis
Deng, Yuxi ; Butré, Claire I. ; Wierenga, P.A. - \ 2018
International Dairy Journal 86 (2018). - ISSN 0958-6946 - p. 39 - 48.

Changes in substrate concentration were shown to affect the experimental maximum degree of hydrolysis (DHmax,exp). Such changes may affect the outcome of in vitro protein digestion models. To study this effect, apo α-lactalbumin (0.5–10%) was hydrolysed by digestive enzymes, bovine, porcine and human trypsins, bovine α-chymotrypsin or Bacillus licheniformis protease (BLP), at a constant enzyme to substrate ratio (E:S). Hydrolysis by human trypsin was not sensitive to changes in substrate concentration. The DHmax,exp by bovine and porcine trypsins, or bovine α-chymotrypsin increased with an increasing substrate concentration, while the DHmax,exp by BLP decreased. For hydrolyses with different DHmax,exp, a change in the percentage of intact protein versus DH was observed, meaning that the peptide concentrations differed during the hydrolyses. If some peptides could be protease inhibitors, the differences in DHmax,exp could be explained. This was confirmed by performing the hydrolysis at a higher E:S, which reached a higher DHmax,exp.

Apparent ileal digestibility of Maillard reaction products in growing pigs
Salazar-Villanea, Sergio ; Butré, Claire I. ; Wierenga, Peter A. ; Bruininx, Erik M.A.M. ; Gruppen, Harry ; Hendriks, Wouter H. ; Poel, Antonius F.B. van der - \ 2018
PLoS ONE 13 (2018)7. - ISSN 1932-6203

The absorption of Maillard reaction products (MRP) from dietary origin has been linked to the occurrence of chronic diseases. The aim of the present study was to determine the effects of toasting time of rapeseed meal (RSM) and the processing method of the diets (pelleting and extrusion) that included RSM on the apparent ileal digestibility (AID) of total lysine, fructosyl-lysine (FL), carboxymethyl-lysine (CML), carboxyethyl-lysine (CEL), lanthionine (LAN) and lysinoalanine (LAL) in growing pigs. The study consisted of a 2×3 factorial design with toasting time of RSM (60, 120 min) and diet processing method (mash, pelleted, extruded) as factors. Fifty growing pigs were individually fed one of the experimental diets for 4.5 consecutive days. Following euthanasia, samples of digesta were collected from the terminal 1.5 m of the small intestine. Increasing the toasting time of RSM increased the contents of FL, CML and CEL, whereas the additional effects of the diet processing methods were relatively small. Lysinoalanine and lanthionine were not detected in the diets; therefore, digestibility of these compounds could not be determined. The contents of FL, CML and CEL in the ileal chyme were positively correlated to their contents in the diets. The AID of the MRP from thermally-treated RSM were overall low and were not related to their contents in the diets. The AID of FL ranged between -8.5 and 19.1%, whilst AID of CML and CEL ranged from -0.2 to 18.3 and 3.6 to 30%, respectively. In conclusion, thermal treatments have clear effects on the contents of MRP in the diets. These compounds have relatively low digestibility in growing pigs.

Geeft 'De Staat van de Boer' een juist beeld?
Wiskerke, Han - \ 2018

De Staat van de Boer | Opinie

De Staat van de Boer is het grootste opinieonderzoek dat ooit onder agrariërs is gehouden. Geeft het onderzoek een juist beeld? Daar verschillen de meningen over.

Unicellular protein: isolation, techno-functionality and digestibility
Teuling, Emma - \ 2018
Wageningen University. Promotor(en): H. Gruppen, co-promotor(en): P.A. Wierenga; J.W. Schrama. - Wageningen : Wageningen University - ISBN 9789463438537 - 168
Comparison of Protein Hydrolysis Catalyzed by Bovine, Porcine, and Human Trypsins
Deng, Yuxi ; Gruppen, Harry ; Wierenga, Peter A. - \ 2018
Journal of Agricultural and Food Chemistry 66 (2018)16. - ISSN 0021-8561 - p. 4219 - 4232.
LC-MS - peptide release kinetics - protein digestibility - secondary specificity - tryptic hydrolysis
Based on trypsin specificity (for lysines and arginines), trypsins from different sources are expected to hydrolyze a given protein to the same theoretical maximum degree of hydrolysis (DHmax,theo). This is in contrast with experiments. Using α-lactalbumin and β-casein, this study aims to reveal if the differences among experimental DHmax (DHmax,exp) by bovine, porcine, and human trypsins are due to their secondary specificity. Peptide analysis showed that ∼78% of all the cleavage sites were efficiently hydrolyzed by porcine trypsin, and ∼47 and ∼53% were efficiently hydrolyzed by bovine and human trypsins, respectively. These differences were explained by the enzyme secondary specificity, that is, their sensitivities to the amino acids around the cleavage sites. The DHmax predictions based on the secondary specificity were 4 times closer to the DHmax,exp than the predictions based on trypsin specificity alone (DHmax,theo). Proposed preliminary relations between binding sites and trypsin secondary specificity allow DHmax,exp estimations of tryptic hydrolysis of other proteins.
Towards predicting enzymatic protein hydrolysis
Deng, Yuxi - \ 2018
Wageningen University. Promotor(en): H. Gruppen, co-promotor(en): P.A. Wierenga; H.A. Schols. - Wageningen : Wageningen University - ISBN 9789463432351 - 190
Maillard induced glycation behaviour of individual milk proteins
Cardoso, Hugo B. ; Wierenga, Peter A. ; Gruppen, Harry ; Schols, Henk A. - \ 2018
Food Chemistry 252 (2018). - ISSN 0308-8146 - p. 311 - 317.
Reactivity - α-Lactalbumin - β-Casein - β-Lactoglobulin
This paper set out to differentiate the Maillard induced glycation reactivity of individual milk proteins using different saccharides under well-defined reaction conditions. α-Lactalbumin, β-lactoglobulin and β-casein were incubated with mono-, di- and trisaccharides in the dry state under standardised buffered conditions and glycation was expressed relative to the available reactive groups per protein (DG). Protein reactivity, described by the DG max and initial speed of glycation (v), followed the same order for each protein-saccharide incubation: α-lactalbumin > β-lactoglobulin ≫ β-casein. Glycation of whey proteins by different monosaccharides was double that of β-casein. Differences in DG between whey proteins and β-casein decreased with increased saccharide size. A two-fold difference was found for glycation in the presence of the dimers lactose and maltose for β-casein but not for the whey proteins. The percentage of glycated lysines increased with increased lysine to protein size ratio.
Towards predicting protein hydrolysis by bovine trypsin
Deng, Yuxi ; Veer, Frank van der; Sforza, Stefano ; Gruppen, Harry ; Wierenga, Peter A. - \ 2018
Process Biochemistry 65 (2018). - ISSN 1359-5113 - p. 81 - 92.
LC-MS - Peptide quantification - Peptide release kinetics - Protein digestion - Secondary specificity - Trypsin hydrolysis
The extent of protein enzymatic hydrolysis is considered to be mostly determined by protease specificity and the number of cleavage sites (CS) on the substrate. However, this theoretical maximum is typically not reached. The limited hydrolysis of certain CS may be due to the differences in enzyme preference resulting from neighbouring amino acids (AA) of the CS (secondary specificity). This study aims to find the link between enzyme secondary specificity and the relative hydrolysis rate constants (selectivity) of individual CS in a protein, to better predict the maximum experimental degree of hydrolysis. Bovine tryptic hydrolysis of α-lactalbumin and β-casein showed that ≥50% of the CS were inefficiently hydrolysed. The selectivity depended on the number of charged AA at P2 and P2' positions of a CS. Trypsin efficiently cleaves CS with neutral AA at these two positions. The selectivity towards 12 out of 18 (67%) CS in β-lactoglobulin was correctly predicted. The predicted maximum degree of hydrolysis is within ~13% error of the experimental value, which is ~5 times better than the prediction based only on enzyme specificity. This work helps to estimate the extent of hydrolysis and the peptide formation of bovine tryptic hydrolysis of other substrates.
Degradation of Collagen Increases Nitrogen Solubilisation During Enzymatic Hydrolysis of Fleshing Meat
Anzani, Cecilia ; Prandi, Barbara ; Tedeschi, Tullia ; Baldinelli, Chiara ; Sorlini, Giovanni ; Wierenga, Peter A. ; Dossena, Arnaldo ; Sforza, Stefano - \ 2018
Waste and Biomass Valorization 9 (2018)7. - ISSN 1877-2641 - p. 1113 - 1119.
Amino acid analysis - Degree of hydrolysis - Enzymatic hydrolysates - Fleshing meat - Peptide analysis

Abstract: The meat portion directly attached to bovine hides (fleshing meat) is a by-product of leather industry that is a potential new source of proteins. In literature different enzymatic and chemical methods have been proposed to hydrolyze and solubilize fleshing meat. Enzyme hydrolysis is preferable for the mildness and the lower environmental impact. Enzymatic hydrolysates have never been deeply characterized, nor the specific enzyme efficiency, deeply investigated. In this study, the activity of six proteolytic enzymes was tested in order to determine their efficiency in solubilizing fleshing meat and to characterize at the molecular level the composition of the nitrogen fraction of the obtained hydrolysates. Total nitrogen content and the degree of hydrolysis were determined by Kjeldhal and o-phthaldialdehyde (OPA) methods. Amino acids and peptides were analysed by high performance liquid chromatography (HPLC) and mass spectrometry techniques. The results showed that papain and Alcalase appear to be the most efficient enzymes, and the corresponding hydrolyzates were rich in peptides and amino acids characteristic of collagen, notably absent in the hydrolyzates obtained with other enzymes. Thus, the ability to efficiently hydrolyze collagen seems to be related to the efficiency in fleshing meat hydrolysis. Graphical Abstract: [Figure not available: see fulltext.]

Protein digestion kinetics in pigs and poultry
Chen, Hsuan - \ 2017
Wageningen University. Promotor(en): W.H. Hendriks, co-promotor(en): A.J.M. Jansman; P.A. Wierenga. - Wageningen : Wageningen University - ISBN 9789463437974 - 168

Increasing the protein efficiency is considered a main strategy for sustainable feeding of pigs and poultry. In practice, protein in pig and poultry diets originates from different ingredients, selected in diet formulation based on their nutritional value and cost. Currently, the nutritional value of protein sources in pig and poultry diets is based on the concentration of essential amino acids (AAs), and their digestibility up to the end of the ileum or the gastrointestinal tract (GIT) (NRC, 2012; CVB, 2016). The ileal and faecal digestibility of protein and AAs, however, only provide information on the quantity of protein and AAs apparently absorbed up to the end of the ileum or over the entire GIT, respectively. They, however, do not provide information on the kinetics of protein digestion, which might affect the post-absorption metabolism of dietary AAs. The aim of this thesis, therefore, was to provide further insights into digestion kinetics of dietary protein sources in the GIT of pigs and poultry, and the consequences of differences in digestion kinetics of dietary protein for the growth performance of broilers.

Protein digestion kinetics in pigs and poultry

In Chapter 2, in vitro protein digestion kinetics of various protein sources (soybean meal (SBM), wheat gluten (WG), rapeseed meal (RSM), whey powder (WP), dried porcine plasma protein (DPP), yellow meal worm larvae (MW), and black soldier fly larvae (BSF)) were determined using a two-step method. Protein sources were incubated with pepsin at pH 3.5 for 0-90 min and subsequently with pancreatin at pH 6.8 for 0-210 min at 39 °C. Protein sources showed substantial differences in in vitro protein digestion kinetics as measured by the kinetics of N solubilisation and the release of low molecular weight peptides (< 500 Da). The N solubilisation rate ranged from 0.025 min-1 for BSF to 0.685 min-1 for WP during the incubation with pepsin, and from 0.027 min-1 for RSM to 0.343 min-1 for WP during the incubation with pancreatin. The rate of release of low molecular weight peptides ranged from 0.027 min-1 for WG to 0.093 min-1 for WP during the incubation with pepsin, and from 0.029 min-1 for SBM to 0.385 min-1 for WP. Over all protein sources evaluated, no correlation was found between the rate of N solubilisation and the rate of release of low molecular weight peptides.

Based on the in vitro results, SBM, RSM, WG, DPP and BSF were selected for further investigations into in vivo protein digestion kinetics in both pigs (Chapter 3) and broiler chickens (Chapter 4). Forty pigs were randomly allocated to one of the five experimental diets containing the respective protein sources as the only source of protein. Four pigs per experimental diet were fitted with an ear-vein catheter and blood samples were collected before and after a morning meal. At dissection, digesta samples from the stomach and the small intestine, divided into four segments of equal length, were quantitatively collected. Apparent digestibility of crude protein (CP), and retention time (RT) of the solid fraction of digesta along the stomach and the SI were determined to calculate protein digestion kinetics. The initial protein digestion rate ranged from 0.68 % · min-1 for the RSM based diet to 3.04 % · min-1 for the DPP diet. A higher digestion kinetics of dietary protein resulted in a more rapid and pronounced postprandial appearance of AAs and peptides in systemic blood of pigs.

In the broiler trial, a total of 378 26-day-old male broilers with average body weight of 1430 ± 48 g were randomly allocated to 42 pens. Pens were randomly allocated to one of the seven diets (i.e. a basal diet and six experimental diets with SBM, soy protein isolate (SPI), WG, RSM, DPP or BSF as the main protein source). At dissection, digesta samples from the crop, gizzard, duodenum, proximal jejunum, distal jejunum, and ileum were quantitatively collected. The CP digestion kinetics of the experimental diets were calculated by relating the apparent CP digestibility coefficient at each segment of the small intestine to the sum of digesta retention up to that segment. The initial protein digestion rate ranged from 1.76 % · min-1 for the RSM based diet to 30.7 % · min-1 for the WG based diet.

Mechanism of protein hydrolysis in the GIT of pigs and poultry

It was hypothesised that proteins present in highly digestible protein sources (i.e. WG and DPP) are more susceptible to hydrolysis by digestive enzymes than slow digestible protein sources (i.e. SBM, RSM and BSF) and that enzymatic hydrolysis of protein progress stepwise in the small intestinal intestine, resulting in hydrolysis products (peptides) becoming smaller in size towards the end of the small intestine. As a consequence, relatively more low and intermediate molecular weight peptides were expected to be present in ileal digesta of pigs and broilers fed highly digestible protein sources, compared to sources with a lower digestibility. The molecular weight distribution of soluble proteins and peptides in digesta from the different segments of the GIT of pigs and broilers was analysed using size exclusion chromatography (Chapter 3 and 4). The molecular weight distribution of proteins and peptides in ileal digesta of pigs and broilers fed highly digestible protein sources was comparable to those of pigs and broilers fed low digestible protein sources. In addition, the molecular weight distributions were rather similar throughout segments of the GIT. These results indicate that proteins from both highly and low digestible sources follow a “one-by-one” type of hydrolysis mechanism, meaning intact proteins are hydrolysed to low molecular weight peptides and free AAs and absorbed by the intestinal mucosa in one sequence. As a result, proteins and peptides with a wide range of molecular weights were not observed in digesta of different segments of the GIT. Approximately 30 % of peptides present in ileal digesta of pigs are < 10 kDa in dependent of protein source, whereas almost no peptides < 10 kDa were found in the ileal digesta of broilers.

Synchronisation the supply of dietary starch and protein

The effects of synchronising the supply of dietary protein and starch using information on their kinetics of digestion on the growth performance and carcass characteristics in broilers was investigated (Chapter 5). Two starch and two protein sources were used: pea starch (PS) and SBM as slowly digestible sources while rice starch (RS) and SPI as fast digestible sources. Broilers fed diets synchronised for digestion rate of starch and protein (i.e. PS-SBM (slow-slow) and RS-SPI (fast-fast)) did not show a higher growth performance and breast meat yield compared to broilers fed the asynchronised diets (i.e. RS-SBM (fast-slow) and PS-SPI (slow-fast)). The evaluation of the effect of synchronising the supply of dietary starch and protein, however, was hindered by feed intake being affected by dietary protein and starch source. Feed intake of birds was higher when fed diets with SBM compared to SPI and when PS was fed instead of RS.

Conclusions

The results of the present thesis indicate that the kinetics of protein digestion in the GIT of pigs and poultry differs substantially among protein sources. Wheat gluten and DPP can be regarded as fast digestible protein sources while SBM, RSM and BSF are more slowly digestible protein sources in both pigs and broilers. Broilers showed on average a 2.7-fold higher small intestinal protein digestion rate than pigs, excluding and with the exception of WG, for which the protein digestion rate was very high in broilers compared to pigs. However, despite differences in intrinsic characteristics (e.g. AA composition, protein conformation, physicochemical properties) of protein sources and in digestive physiology of pigs and poultry, the mechanism of hydrolysis of dietary proteins in the gut seems rather similar. Synchronising the digestion kinetics of dietary starch and protein using both fast digestible sources or both slowly digestible sources did not improve the performance nor the breast muscle yield of ad libitum fed broilers kept under an intermittent light regime.

Sugar beet leaves: from biorefinery to techno-functionality
Kiskini, Alexandra - \ 2017
Wageningen University. Promotor(en): H. Gruppen, co-promotor(en): P.A. Wierenga. - Wageningen : Wageningen University - ISBN 9789463436793 - 141
sugarbeet - sugarbeet tops - biorefinery - bioprocess engineering - proteins - isolation techniques - physiological age - suikerbieten - suikerbietenloof - bioraffinage - bioproceskunde - eiwitten - isolatietechnieken - fysiologische leeftijd

Sugar beet leaves (SBL), which are a side stream of the sugar beets cultivation, are currently left unexploited after sugar beets have been harvested. The general aim of this thesis was to study the biorefinery of SBL, with a special focus on the isolation of proteins. To reach this aim the research was divided into three sub-aims: 1) to determine whether there is variability in the chemical composition of the leaves due to pre-harvest conditions (plant age), 2) to evaluate the variability of the techno-functionality of leaf soluble protein concentrate (LSPC) due to system conditions and 3) to extend current product and process synthesis approaches to enable the design of biorefining process. To address the first aim, SBL collected at different time points were used. Despite a small variation in the chemical composition of the leaves of different plant ages, a large effect of the plant age on the quality of LSPC was observed. In particular, LSPC from old plants was brown (indicative of polyphenol oxidase - PPO - activity), whereas LSPC from young plants was yellow. Based on these data, samples extracted with sodium disulfite (to inhibit PPO-mediated browning) were used for further experiments. The obtained LSPC consisted mainly of protein (69.3% w/w db (N∙5.23)) and carbohydrates (5.1% w/w db; half of which was charged carbohydrates). The main protein present in LSPC was Rubisco. The emulsion and foam properties of LSPC were studied as a function of protein concentration (Cp), pH and ionic strength (I). The minimal Cp of LSPC needed to form a stable emulsion (Ccr) was comparable to that of other widely used plant proteins, such as soy protein isolate. A critical ζ-potential (ζcr ~ 11 mV) was identified, below which flocculation occurs. At pH 8.0 and high I (0.5 M) the Ccr was higher than at low I (0.01 M), which relates to a higher protein adsorbed amount at the interface (Γmax). The foam ability (FA) of LSPC increased with Cp at all conditions tested. The FA was related to the soluble and not to the total Cp in the bulk. Interestingly, the minimal Cp; i.e.CcrFA needed to reach highest FA was constant as a function of pH. At high I (0.5 M) LSPC had higher FA than at low I (0.01 M), which was related to the faster adsorption of proteins at the interface. A minimum Cp was required to form stable foams. At pH 3.0 and 5.0 the foam stability of LSPC was higher than at pH 8.0. This was postulated to be due to formation of aggregates (between proteins or between proteins and charged carbohydrates). From these data it was shown that the techno-functional properties of LSPC could be linked to the molecular and interfacial properties of the dominant proteins in the concentrates. Thus, predictions for the techno-functional properties of impure systems, such as LSPC, can be made using only the known molecular properties of the dominant proteins and a small set of experiments. The knowledge acquired through the previous studies was used to adapt an existing methodology; namely the product-driven-process synthesis (PDPS) methodology, to extend its use in biorefinery. The adapted PDPS contained 4 novel steps, which facilitated its use in biorefinery. To illustrate how this new approach can be used in practice, a case study of a sugar beet leaves biorefinery was presented.

Comparison of Protein Extracts from Various Unicellular Green Sources
Teuling, Emma ; Wierenga, Peter A. ; Schrama, Johan W. ; Gruppen, Harry - \ 2017
Journal of Agricultural and Food Chemistry 65 (2017)36. - ISSN 0021-8561 - p. 7989 - 8002.
amino acid composition - carbohydrate composition - cyanobacteria - Microalgae - physicochemical properties - single-cell protein
Photosynthetic unicellular organisms are considered as promising alternative protein sources. The aim of this study is to understand the extent to which these green sources differ with respect to their gross composition and how these differences affect the final protein isolate. Using mild isolation techniques, proteins were extracted and isolated from four different unicellular sources (Arthrospira (spirulina) maxima, Nannochloropsis gaditana, Tetraselmis impellucida, and Scenedesmus dimorphus). Despite differences in protein contents of the sources (27-62% w/w) and in protein extractability (17-74% w/w), final protein isolates were obtained that had similar protein contents (62-77% w/w) and protein yields (3-9% w/w). Protein solubility as a function of pH was different between the sources and in ionic strength dependency, especially at pH < 4.0. Overall, the characterization and extraction protocol used allows a relatively fast and well-described isolation of purified proteins from novel protein sources.
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