Biomedical subjects

Jan A Delcour

Publications and source records attributed to Jan A Delcour.

At least 19 recordsLinked to original sources

PubMed2006

Impact of browning reactions and bran pigments on color of parboiled rice.

Rice color changes from white to amber during parboiling (soaking and steaming). Color parameters indicated that, during soaking, yellow bran pigments leached out in the water. The levels of the Maillard precursors (i.e., reducing sugars (RS) and free alpha-amino nitrogen (FAN)) depended on soaking temperature and time: leaching of RS was compensated by enzymic formation for long soaking times (>60 min), while proteolytic activity was too low to compensate for FAN leaching. Rice soaking under nitrogen, oxygen, or ambient conditions and determination of polyphenol oxidase activity allowed us to conclude that the effect of enzymic color changes on the soaked rice color was rather small. Color measurements of brown and milled mildly, intermediately, and severely parboiled rice samples showed that both brown and milled rice samples were darker and more red and yellow after parboiling and that the effect depended on the severity of parboiling conditions. Furthermore, steaming affected the rice color more and in a way opposite to that observed in soaking. The changes in RS and the loss of FAN during parboiling suggested that Maillard type reactions occur during brown rice steaming. Analyses of furosine levels confirmed Maillard browning of outer bran layers and endosperm during steaming. The level of this Maillard indicator increased with the severity of parboiling conditions in both brown and milled parboiled rice. Measurements of the levels of bran pigments indicated that bran pigments diffuse into the endosperm during parboiling and contribute to the parboiled rice color.

Carbohydrates↗

PubMed2006

Insight into the distribution of arabinoxylans, endoxylanases, and endoxylanase inhibitors in industrial wheat roller mill streams.

To gain insight into the distribution of arabinoxylans (AX), endoxylanases, and endoxylanase inhibitors in industrial wheat roller milling, all streams, that is, 54 flour fractions, 4 bran fractions, and the germ, were analyzed for ash, starch, and protein contents, alpha-amylase activity levels, total (TOT-AX) and water-extractable arabinoxylan (WE-AX) contents, endoxylanase activity levels, and endoxylanase inhibitor (TAXI and XIP) contents. In general, bran fractions were significantly richer in TOT-AX and WE-AX contents, endoxylanase activity levels, and endoxylanase inhibitor contents than germ and, even more so, than flour fractions. In the 54 different flour fractions, minimal and maximal values for TOT-AX and WE-AX contents differed by ca. 2-fold, whereas they differed by ca. 15-fold for endoxylanase activity levels. The latter were positively correlated with ash and negatively correlated with starch content, suggesting that the endoxylanase activity in flour is strongly influenced by the level of bran contamination. TAXI contents in the flour fractions varied ca. 4-fold and were strongly correlated with bran-related parameters such as ash content and enzyme activity levels, whereas XIP contents varied ca. 3-fold and were not correlated with any of the parameters measured in this study. The results can be valuable in blending and optimizing wheat flour fractions to obtain flours with specific technological and nutritional benefits.

Endo-1,4-beta Xylanases↗

PubMed2006

Wheat-kernel-associated endoxylanases consist of a majority of microbial and a minority of wheat endogenous endoxylanases.

The endoxylanases associated with wheat kernels consist of wheat endogenous endoxylanases on one hand and kernel-associated microbial endoxylanases on the other hand. Assessment of their presence, based on analysis of their enzymic activity, can be expected to be hampered by the presence in wheat of high levels of endogenous endoxylanase inhibitors, which are able to inhibit the wheat-kernel-associated microbial endoxylanases. On the basis of preliminary experiments aimed at clarifying the distribution of the wheat-associated endoxylanases, a method to estimate total endoxylanase activities in wheat kernels was developed. Extensive washing of wheat kernels with universal buffer of pH 8.0 provided near-quantitative separation of the microbial endoxylanases located on the surface of wheat kernels from the endogenous endoxylanases and endoxylanase inhibitors located in such kernels. The microbial or endogenous nature of the endoxylanases was confirmed by making use of the inhibition specificity of endoxylanase inhibitors. Determination of the endoxylanase activity in the washing liquid, corresponding to the microbial endoxylanase population, and the washed kernels, corresponding to the endogenous endoxylanase population, allowed estimation of the total endoxylanase activities associated with the wheat kernel. Results showed that microbial endoxylanases can account for over 90% of the total wheat-associated endoxylanase activity and that the latter can be at least 5 times higher than the apparent endoxylanase activity.

Endo-1,4-beta Xylanases↗

PubMed2006

Amylose-lipid complexes as controlled lipid release agents during starch gelatinization and pasting.

The effect of amylose-lipid (AM-L) complexes consisting of amylose populations with different peak degrees of polymerization (DP) and complexed with glyceryl monostearate (GMS) or docosanoic acid (C22) on the pasting properties of wheat and rice starches was evaluated with a rapid visco analyzer (RVA). AM-L complexes were formed by both (i) addition of lipids to amylose fractions with peak DP 20, 60, 400, or 950 at 60 degrees C or (ii) potato phosphorylase-catalyzed amylose synthesis in the presence of lipids. All AM-L complexes affected pasting properties in line with their dissociation characteristics. AM-L complexes therefore have potential as "controlled lipid release agents" with effects markedly different from those observable with emulsifier addition in starch pasting. More in particular, short chain AM-L complexes resulted in a starch pasting behavior comparable to that of cross-linked starch, as evidenced by reduced granule swelling, good viscosity stability in conditions of high temperature and shear, and a stable cold paste viscosity.

Amylose↗

PubMed2006

Structural transformations during gelatinization of starches in limited water: combined wide- and small-angle X-ray scattering study.

Rice flour (18-25% moisture) and potato starch (20% moisture) were heated with continuous recording of the X-ray scattering during gelatinization. Rice flours displayed A-type crystallinity, which gradually decreased during gelatinization. The development of the characteristic 9 nm small-angle X-ray scattering (SAXS) peak during heating at sub-gelatinization temperatures indicated the gradual evolution into a stacked lamellar system. At higher temperatures, the crystalline and lamellar order was progressively lost. For potato starch (B-type crystallinity), no 9 nm SAXS peak was observed at ambient temperatures. Following the development of lamellar structures at sub-gelatinization temperatures, B-type crystallinity and lamellar order was lost during gelatinization. On cooling of partially gelatinized potato starch, A-type crystallinity steadily increased, but no formation of stacked lamellar structures was observed. Results were interpreted in terms of a high-temperature B- to A-type recrystallization, in which the lateral movement of double helices was accompanied by a shift along their helical axis. The latter is responsible for the inherent frustration of the lamellar stacks.

Chemical Phenomena↗

PubMed2006

Gelatinization of starch in excess water: beyond the melting of lamellar crystallites. A combined wide- and small-angle X-ray scattering study.

The gelatinization of waxy rice, regular rice, and potato starch suspensions (66% w/w moisture) was investigated by real-time small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) during heating and by fast ramp differential scanning calorimetry (DSC). The high-angle tail of the SAXS patterns suggested the transition from surface to mass fractal structures in the DSC gelatinization range. Amylose plays a major role in determining the dimensions of the self-similar structures that develop during this process as the characteristic power-law scattering behavior extends to lower scattering angles for regular than for waxy starches. Crystallinity of A-type starches is lost in the temperature region roughly corresponding to the DSC gelatinization range. At the end of the gelatinization endotherm, the B-type potato starch showed residual crystallinity (WAXD), while SAXS-patterns exhibited features of remaining lamellar stacks. Results indicate that the melting of amylopectin crystallites during gelatinization is accompanied by the (exothermic) formation of amorphous networks.

Amylose↗

PubMed2006

Non-digestible oligosaccharides with prebiotic properties.

The search for functional foods or functional food ingredients, i.e. foods or food ingredients that can enhance health, is beyond any doubt one of the leading trends in today's food industry. In this context, probiotics, i.e. living microbial food supplements, and prebiotics, i.e. non-digestible food ingredients, receive much attention. Both popular concepts target the gastrointestinal microbiota. While in the Western world, intake of probiotics has been recommended for long, prebiotics in general, and non-digestible oligosaccharides in particular, have only recently received attention. This review deals with production and characterization of non-digestible oligosaccharides and focuses on their role in promoting health and treating diseases. Attention is paid to the effects of non-digestible oligosaccharides on constipation, mineral absorption, lipid metabolism, cancer prevention, hepatic encephalopathy, glycemia/insulinemia, and immunomodulation.

Bacteria↗

PubMed2005

Molecular identification of wheat endoxylanase inhibitor TAXI-II and the determinants of its inhibition specificity.

Wheat grains contain Triticum aestivum xylanase inhibitor (TAXI) proteins which inhibit microbial xylanases, some of which are used in cereal based food industries. These inhibitors may play a role in plant defence. Among the TAXI isoforms described so far, TAXI-II displays a deviating inhibition specificity pattern. Here, we report on the molecular identity of TAXI-II and the basis of its inhibition specificity. Three candidate TAXI-II encoding sequences were isolated and recombinantly expressed in Pichia pastoris. To identify TAXI-II, the resulting proteins were tested against glycoside hydrolase family (GHF) 11 xylanases of Aspergillus niger (ANX) and Bacillus subtilis (BSX). One of these proteins (rTAXI-IB) inhibited both enzymes, like natural TAXI-I. The other candidates (rTAXI-IIA and rTAXI-IIB) showed an inhibition pattern typical for natural TAXI-II, only clearly inhibiting BSX. Comparative analysis of these highly similar sequences with distinct inhibition activity patterns, combined with information on the structural basis for ANX inhibition by TAXI-I [S. Sansen, C.J. De Ranter, K. Gebruers, K. Brijs, C.M. Courtin, J.A. Delcour, A. Rabijns, Structural basis for inhibition of Aspergillus niger xylanase by Triticum aestivum xylanase inhibitor-I, J. Biol. Chem. 279 (2004) 36022-36028], indicated a crucial role for Pro294 of TAXI-IIA and Gln376 of TAXI-IIB in determining the reduced inhibition activity towards ANX. Consequently, single point mutants rTAXI-IIA[P294L] and rTAXI-IIB[Q376H], both displaying the Leu/His combination corresponding to TAXI-I, were able to inhibit ANX. These results show that TAXI-II inhibition specificity bears on the identity of two key residues at positions 294 and 376, which are involved in the interaction at the -2 glycon subsite and the active site of GHF 11, respectively.

Amino Acid Sequence↗

PubMed2005

Evidence for the involvement of arabinoxylan and xylanases in refrigerated dough syruping.

The relationship between syruping in refrigerated doughs upon prolonged storage and different aspects of arabinoxylan (AX) hydrolysis was investigated using Triticum aestivum xylanase inhibitor (TAXI) and different xylanases in the dough formula. Dough characteristics were evaluated with strong emphasis on the AX population and its fate as a function of storage time. Selective reduction of part of the flour endogenous xylanase activity in dough by added TAXI reduced dough syruping after 12 and 20 days of storage by 50%, providing straightforward evidence for the involvement of xylanases and, thus, AX in the syruping phenomenon. Addition of xylanases with different inhibitor sensitivities [an inhibition-sensitive Bacillus subtilis xylanase (XBS(i)) as well as a noninhibited mutant (XBS(ni)) thereof] to dough confirmed the importance of xylanases in dough syruping, on one hand, and the power of wheat flour TAXI to constitute a significant barrier against xylanase-mediated dough syruping, on the other hand. Use of xylanases with different substrate selectivities [an Aspergillus aculeatusxylanase (XAA) versus XBS(ni)] showed degradation of water-extractable AX (WE-AX) and solubilized AX to low molecular weight molecules rather than the conversion of water-unextractable AX (WU-AX) to high molecular weight water extractable components to be the main factor influencing dough syruping.

Bread↗

PubMed2005

Enzymic degradability of hull-less barley flour alkali-solubilized arabinoxylan fractions by endoxylanases.

The impacts of the arabinose to xylose (A/X) ratio of arabinoxylans (AX) and the endoxylanase substrate specificity on the enzymic degradability of hull-less barley flour AX by endoxylanases were studied by using alkali-solubilized AX (AS-AX) fractions with different A/X ratio, on the one hand, and glycoside hydrolase family 10 and 11 endoxylanases of Aspergillus aculeatus (XAA) and Bacillus subtilis (XBS), respectively, on the other hand. AS-AX were obtained by saturated barium hydroxide treatment of hull-less barley flour water-unextractable AX. Fractionation of AS-AX by stepwise ethanol precipitation resulted in structurally different hull-less barley flour AS-AX fractions. Their A/X ratios increased with increasing ethanol concentration, and this increase in A/X ratio was reflected in their xylose substitution levels. For both XAA and XBS, the enzymic degradability of AX and apparent specific endoxylanase activity decreased with increasing A/X ratio of the AS-AX substrates, implying that both endoxylanases were sterically hindered by arabinose substituents. However, for all AS-AX fractions, hydrolysis end products of lower average degree of polymerization were obtained after incubation with XAA than with XBS, indicating that the former enzyme has a lower substrate specificity toward hull-less barley flour AS-AX than the latter. In addition, apparent specific endoxylanase activities indicated that XBS was approximately 2 times more sensitive to variations in the A/X ratio of AS-AX fractions than XAA. Furthermore, AS-AX with higher A/X ratio were relatively resistant to degradation by XBS.

Aspergillus↗

PubMed2005

Endoxylanase substrate selectivity determines degradation of wheat water-extractable and water-unextractable arabinoxylan.

The relative activity of an endoxylanase towards water-unextractable (WU-AX) and water-extractable arabinoxylan (WE-AX) substrates, referred to as endoxylanase substrate selectivity, impacts the enzyme functionality in cereal-based biotechnological processes such as bread-making and gluten starch separation. A set of six endoxylanases representing a range of substrate selectivities as determined by a screening method using chromophoric substrates [Anal. Biochem.2003, 319, 73-77] was used to examine the impact of such selectivity on changes in structural characteristics of wheat WU-AX and WE-AX upon enzymic hydrolysis. While WE-AX degradation by the selected endoxylanases was very comparable with respect to apparent molecular mass (MM) profiles and arabinose to xylose ratio of the hydrolysates formed, WU-AX solubilisation and subsequent degradation of solubilised fragments gave rise to widely varying MM profiles, depending on the substrate selectivity of the enzymes. Enzymes with high selectivity towards WU-AX de facto generated higher MM fragments from WU-AX than enzymes with low selectivity. The arabinose to xylose ratios of solubilised fragments were independent of the degree of solubilisation.

Arabinose↗

PubMed2005

Purification and characterization of a XIP-type endoxylanase inhibitor from rice (Oryza sativa).

A rice XIP-type inhibitor was purified by affinity chromatography with an immobilized Aspergillus aculeatus family 10 endoxylanase. Rice XIP is a monomeric protein, with a molecular mass of ca. 32 kDa and a pI of ca. 5.6. Its N-terminal amino acid sequence was identical to that of a rice chitinase homologue, demonstrating the difficulty when using sequence information to differentiate between endoxylanase inhibitors and (putative) chitinases in rice. Rice XIP inhibited different endoxylanases to a varying degree. In particular, it most strongly inhibited family 10 endoxylanases from A. niger and A. oryzae, while several family 11 enzymes from Bacillus subtilis, A. niger and Trichoderma sp. were not sensitive to inhibition. The above mentioned A. aculeatus endoxylanase was not inhibited either, although gel permeation chromatography revealed that it complexed rice XIP in a 1:1 molar stoichiometric ratio.

Chromatography, Affinity↗

PubMed2005

His374 of wheat endoxylanase inhibitor TAXI-I stabilizes complex formation with glycoside hydrolase family 11 endoxylanases.

Wheat endoxylanase inhibitor TAXI-I inhibits microbial glycoside hydrolase family 11 endoxylanases. Crystallographic data of an Aspergillus niger endoxylanase-TAXI-I complex showed His374 of TAXI-I to be a key residue in endoxylanase inhibition. Its role in enzyme-inhibitor interaction was further investigated by site-directed mutagenesis of His374 into alanine, glutamine or lysine. Binding kinetics and affinities of the molecular interactions between A. niger, Bacillus subtilis, Trichoderma longibrachiatumendoxylanases and wild-type TAXI-I and TAXI-I His374 mutants were determined by surface plasmon resonance analysis. Enzyme-inhibitor binding was in accordance with a simple 1 : 1 binding model. Association and dissociation rate constants of wild-type TAXI-I towards the endoxylanases were in the range between 1.96 and 36.1 x 10(4)m(-1) x s(-1) and 0.72-3.60 x 10(-4) x s(-1), respectively, resulting in equilibrium dissociation constants in the low nanomolar range. Mutation of TAXI-I His374 to a variable degree reduced the inhibition capacity of the inhibitor mainly due to higher complex dissociation rate constants (three- to 80-fold increase). The association rate constants were affected to a smaller extent (up to eightfold decrease). Substitution of TAXI-I His374 therefore strongly affects the affinity of the inhibitor for the enzymes. In addition, the results show that His374 plays a critical role in the stabilization of the endoxylanase-TAXI-I complex rather than in the docking of inhibitor onto enzyme.

Alanine↗

PubMed2004

Water-extractable and water-unextractable arabinoxylans affect gluten agglomeration behavior during wheat flour gluten-starch separation.

Water-extractable arabinoxylan (WE-AX) of variable molecular weight (MW) and water-unextractable arabinoxylan (WU-AX) were added to wheat flour to study their effect on gluten agglomeration in a dough and batter gluten-starch separation process with recovery of gluten from the batter with a set of vibrating sieves (400, 250, and 125 microm). Low MW WE-AX had almost no impact on the distribution of the gluten on the different sieves. High MW WE-AX decreased yields of the largest (400 microm sieve) gluten aggregates, more than their medium MW counterparts, indicating the importance of AX MW for their effect on gluten interactions. Correlations between the total level of gluten protein recovered on the three sieves and the batter extract viscosity as well as between the proportion of gluten protein recovered on the 400 microm sieve to that on the three sieves and the batter extract viscosity pointed to the importance of viscosity as an indicator for gluten agglomeration, as did the fact that another viscosity increasing plant polysaccharide (guar gum) also negatively influenced gluten agglomeration. However, the obtained data cannot rule out that AX and guar gum also exert steric effects on gluten agglomeration. WU-AX, present as discrete cell wall fragments, had a negative impact on the level of large gluten aggregates. Taken together, the results show that both native WE-AX and WU-AX detrimentally impact gluten agglomeration.

Flour↗

PubMed2004

Impact of inhibition sensitivity on endoxylanase functionality in wheat flour breadmaking.

A Bacillus subtilis endoxylanase (XBS(i)) sensitive to inhibition by Triticum aestivum L. endoxylanase inhibitor (TAXI) and a mutant thereof (XBS(ni)), uninhibited by TAXI, were used in straight-dough breadmaking to assess the importance of endoxylanase inhibition sensitivity on endoxylanase functionality in the process. With two European wheat flours, the loaf volume improving effect of XBS(ni) at much lower enzyme dosages was substantially larger than that brought about by XBS(i). This coincided with differences in arabinoxylan (AX) hydrolysis. Although XBS(ni) had a lower substrate selectivity for water-unextractable arabinoxylan (WU-AX) than XBS(i), the former solubilized significantly more WU-AX than XBS(i). Because of inhibition, XBS(i) solubilized most of the WU-AX during mixing, whereas, with XBS(ni), the rate of solubilization decreased less with increasing processing time than that with XBS(i). During fermentation and baking and at the highest dosage (600 U/kg of flour of XBS(i) and 60 U/kg of flour of XBS(ni)), XBS(ni) induced a stronger degradation of enzymically solubilized and water-extractable AX than XBS(i). Taken together, the data clearly demonstrate that endoxylanases, which in vitro are inhibited by endoxylanase inhibitors and still are active in the breadmaking process, as demonstrated by their functional (bread volume) enhancing effect, gradually lose their activity in the process.

Bacillus subtilis↗

PubMed2004

Enrichment of higher molecular weight fractions in inulin.

Inulin (general formulas GFn and Fm, with G = anhydroglucose and F = anhydrofructose) naturally occurs as a homologous series of oligo- and polysaccharides with different chain lengths. For reasons of growing interest in the food and pet food industries, the short chain inulins have to be separated from their long chain analogues because their properties (digestibility, prebiotic activity and health promoting potential, caloric value, sweetening power, water binding capacity, etc.) differ substantially. To study these properties in relation to the number average degree of polymerization (DPn), ultrafiltration, specific crystallization from aqueous solution, and precipitation from solvent/water mixtures were used to enrich native chicory and dahlia inulin in the higher molecular weight fractions. Depending on the membrane module used, the DPn of chicory inulin (DPn = 8.1) and dahlia inulin (DPn = 29) could be increased by ultrafiltration to a maximum value of, respectively, 22 and 43. With crystallization from aqueous solutions (25 degrees C), similar results were obtained but at a much higher yield. Finally, long chain inulin could be precipitated from aqueous solutions in the presence of high concentrations of methanol, ethanol, and acetone. Acetone demonstrated to be the best solvent system to increase the DPn, followed by ethanol and methanol. However, for safety reasons and food purposes, ethanol was evaluated to be the best choice. With ethanol, the DPn could be raised to 25 for chicory inulin and up to 40 for dahlia inulin.

Chemical Precipitation↗

PubMed2004

Structural basis for inhibition of Aspergillus niger xylanase by triticum aestivum xylanase inhibitor-I.

Plants developed a diverse battery of defense mechanisms in response to continual challenges by a broad spectrum of pathogenic microorganisms. Their defense arsenal includes inhibitors of cell wall-degrading enzymes, which hinder a possible invasion and colonization by antagonists. The structure of Triticum aestivum xylanase inhibitor-I (TAXI-I), a first member of potent TAXI-type inhibitors of fungal and bacterial family 11 xylanases, has been determined to 1.7-A resolution. Surprisingly, TAXI-I displays structural homology with the pepsin-like family of aspartic proteases but is proteolytically nonfunctional, because one or more residues of the essential catalytical triad are absent. The structure of the TAXI-I. Aspergillus niger xylanase I complex, at a resolution of 1.8 A, illustrates the ability of tight binding and inhibition with subnanomolar affinity and indicates the importance of the C-terminal end for the differences in xylanase specificity among different TAXI-type inhibitors.

Aspergillus niger↗

PubMed2004

Heterogeneity in the fine structure of alkali-extractable arabinoxylans isolated from two rye flours with high and low breadmaking quality and their coexistence with other cell wall components.

The alkali extractable (AE) arabinoxylans from two rye flours differing in baking quality were studied following sequential extraction of water-unextractable and starch-free rye flour residue with saturated barium hydroxide solution, water and 1 M sodium hydroxide solution (Ba, BaH, and Na, respectively), and further fractionation of isolated fractions by ammonium sulfate precipitation. (1)H NMR and sugar analyses of AE subfractions provided evidence for the presence of lowly branched arabinoxylans (average arabinose-to-xylose ratio, Ara/Xyl approximately 0.5), containing mainly un- and monosubstituted xylopyranosyl residues (Xylp) in the chain. The proportion of this subfraction decreased from 50% in the Ba fraction to 35 and 17% in the Na and BaH fractions, respectively. Other subfractions, rich in both mono- and disubstituted Xylp, represented arabinoxylan populations with intermediate (Ara/Xyl approximately 0.8) and high substitution degree (Ara/Xyl approximately 1.1). The Ba and Na fractions contained phenolic compounds, whereas they were absent in the BaH fraction. The higher ratio of such phenolic compounds to arabinose (PhC/Ara) found in AE arabinoxylans from rye flour of inferior baking quality was one of the most pronounced differences between arabinoxylan populations from rye flours with high and low baking quality. The arabinoxylans from rye flour of high baking quality present in Ba and Na fractions had slightly higher apparent molecular weights (MWs) when compared to those from rye flour with low baking quality. The arabinoxylans present in the BaH fractions, characterized by the highest MWs, had similar MWs.

Barium Compounds↗