Fracture Mechanics of Vitreous and Mealy Wheat Endosperm

The concepts of fracture mechanics have been applied to quantify the fracture behaviour of vitreous and mealy wheat endosperm in a single wheat cultivar. Two new techniques were developed and used to measure fracture toughness (energy per unit area of fracture) of individual grains: (1) load cycling of a notched grain; and (2) instrumented microtome cutting. The load cycling method gave average fracture toughness values for vitreous endosperm of 130 ± 42 J/m² and 50 ± 12 J/m² for mealy endosperm. Fracture toughness measured using the instrumented microtome gave values of 159 ± 7·4 J/m² for vitreous endosperm and 44 ± 4·6 J/m² for mealy endosperm. The results are consistent with the hypothesis that vitreous endosperm has stronger starch-protein matrix bonding than mealy endosperm. The effect of changing grain moisture on cutting fracture properties was investigated. As moisture decreased, values of fracture toughness increased for both mealy and vitreous endosperms at the same rate down to 11% moisture content, below which fracture toughness increased more rapidly for vitreous than for mealy endosperm. Intra-grain fracture toughness was also investigated by cutting successive sections across individual wheat grains. These showed a decrease in cutting force from the outside of the grain towards the centre, and then an increase near the crease. The critical particle size at which a transition from brittle to ductile failure occurs was calculated, giving predicted values of 1·2 mm for vitreous endosperm and 0·9 mm for mealy endosperm at 15% moisture content. This shows that vitreous endosperm undergoes more ductile deformation during deformation than does mealy endosperm, and that larger particle sizes are predicted for vitreous endosperm as a result of milling.     

Factors affecting early screening of tomatoes for monogenic and polygenic resistance to Fusarium wilt

Tomatoes (cv. Bari-RVF-SMD) monogenically (I gene) resistant to Fusarium wilt (Fusarium oxysporum f.sp. lycopersici) were not affected by inoculum dilutions (10¹, 10³ and 10⁶ conidia/ml), temperature regimes (22°C and 26°C) and plant age (two and four leaves), whereas the phenotypic expression of susceptible and polygenically resistant tomatoes (cvs Rutgers and Marglobe) was conditioned by these factors. Rutgers tomatoes were found to possess a higher level of resistance than Marglobe. Early screening (33 days after inoculation) of resistant Rutgers plants could be made on plants inoculated at the two-leaf stage with an inoculum dilution of 10³ conidia/ml and grown at 22°C or 26°C. Thirty-three days after inoculation, Marglobe tomatoes inoculated at the two- and four-leaf stages with inoculum dilutions of 10³ and 10⁶ conidia/ml and grown at 22°C or 26°C proved to be susceptible. The following first-order interactions were found to be statistically significant: cultivar × inoculum dilution, cultivar × temperature, cultivar × plant age, inoculum dilution × temperature and inoculum dilution × plant age.     

Mass transport studies of model migrants within dry foodstuffs

Cereals are widely consumed foodstuffs and it is therefore important to take them into account when estimating consumer exposure to packaging-related chemicals. The mass transport of three model migrants (diphenylbutadiene, triclosan and BHT) from low-density polyethylene (LDPE) within dry foodstuffs of different particle size (rice and wheat flour) was studied because of the relationship between consumer exposure and possible harmful effects on human health. The conditions that most affect the mass transport of substances within dry foods are evaluated and discussed. The diffusion coefficients (D_F) for diphenylbutadiene (DPBD) and triclosan in the studied foodstuffs were estimated. The D_F values for DPBD and triclosan in wheat flour at 25 °C were 7.1 × 10⁻⁸ cm²/s and 3.3 × 10⁻⁸ cm²/s, respectively. The D_F values for DPBD and triclosan in rice at 25 °C were 4.7 × 10⁻⁸ and 4.3 × 10⁻⁸ cm²/s, respectively. BHT displayed different behaviour and other tests were therefore carried out to elucidate the associated mass transport process.     

Use of mechanics of cohesive granular media for analysis of hardness and vitreousness of wheat endosperm

The characterisation of the wheat endosperm by mechanical tests of compression highlighted a relation between the rupture energy and the elasticity modulus for different varieties of wheat; this relation allows us to distinguish mealy and vitreous endosperms. An approach based on the micromechanics of cohesive granular materials is used to analyse these experimental results. A geometrical model of the wheat endosperm made of grains linked by cohesive bonds is proposed. We introduced two parameters, the first one α represents the percentage of active bonds (bonds where the stiffness and strength are non-zero), and the second one β represents the threshold of the bond's rupture. The parameter β can be related to the cross-section of the bond. This model successfully describes the mechanical tests on the wheat endosperm. The comparison with the experimental tests makes it possible to clearly differentiate vitreous wheats and mealy wheats and then attribute this property to the parameter β. The model shows the same tendency as regards the evolution of the rupture energy and the elastic modulus with the parameter α. The modelling of endosperm by the mechanics of cohesive granular media provides a new theoretical framework to interpret the rheology of endosperm. This approach allows us to connect this rheology to the mechanical actions at the scale of the granules.     

Macromolecular Features of Starches Determined by Aqueous High-performance Size Exclusion Chromatography

Starches from various botanical sources, having different amylose–amylopectin levels, were treated with 95% (v/v) dimethylsulphoxide and then dissolved by microwave heating in a high pressure vessel (MWHPV). This procedure led to an almost complete dissolution of the starch sample when it was subsequently taken up in water. Various treatment times were tested, and optimal conditions corresponded to 35 s heating time in MWHPV (maximum temperature 143 °C). Under these conditions, degradation of the polymers was not noticeable and the degree of solubilisation of starch in the samples was in the range 87 to 100%. High-performance size exclusion chromatography (HPSEC) in tandem with multi-angle laser light scattering and refractive index detection was used to investigate apparent weight-average molar mass ( _w) and z-average gyration radius ( _G) of the starch components. Apparent _wand _Gvalues for samples with different amylose contents (between ≈0 and 65·8%) were between 2·2±0·2×10⁸and 2·4±0·2×10⁷g/mol and between 250±10 and 163±5 nm, respectively. These values were higher than those reported previously^1,2probably due to our more complete but less severe solubilisation procedure. When the heating time was increased from 35 to 90 s (maximum temperature 211°C), the _wand _Gdecreased, demonstrating possible polymer degradation due to temperature. Partial precipitation of high amylose samples after 24 h storage was detected by modifications in chromatograms, compared with freshly prepared samples.     

Distribution of Water between Wheat Flour Components: A Dynamic Water Vapour Adsorption Study

The water adsorption properties of hard and soft wheat flours and flour components (starch, damaged starch, gluten, soluble pentosans, and insoluble pentosans) were determined at 25 °C using a controlled atmosphere microbalance. At different levels of relative humidity (from 10% to 95%), changes in sample mass (i.e., water gain) were continuously measured versus time and described using exponential models (R²≥0·994). Water adsorption isotherms were constructed for wheat flours and flour components and described using Guggenheim-Anderson-de Boer models (R²≥0·997). It was not possible to distinguish between the selected hard and soft wheat flours by their isotherms. The water-soluble pentosans had the highest water adsorption capacity. The theoretical distribution of water between the flour components (calculated using the Guggenheim-Anderson-de Boer parameters) was starch, 88%; gluten, 10%; and pentosans, 2%.     

Study of the microstructure of durum wheat endosperm using X-ray micro-computed tomography

Durum wheat grains are used for producing food, such as pasta or couscous. The grain mechanical properties which are linked to its internal micro-structure (i.e. endosperm porosity) are known to determine its ability to produce semolina during milling. The proportion of grains having porous endosperm in a batch appears therefore as a critical quality factor for the durum wheat value chain. Our objective was to investigate the ability of X-ray micro-tomography (μCT) method to describe the porous or vitreous counterpart structures in the endosperm of durum wheat grains. We selected two different durum wheat samples displaying vitreous or partially porous endosperms. The grains were analyzed using μCT at two pixel sizes (1 μm or 7 μm). The μCT data collected at 7 μm pixel size were used for qualitative classification of grains according to apparent distribution curve of the porosity parameters. Analysis of μCT images at 1 μm pixel size allowed us to propose pore size classification in the vitreous and porous parts of the endosperm in three durum wheat grain. Results are used to better describe the durum-wheat endosperm microstructure, but requires long scanning periods.     

Rheological Behaviour of Wheat Endosperm—Proposal for Classification Basedon the Rheological Characteristics of EndospermTest Samples

A simple, rapid method for the preparation of parallelepiped-shaped samples from a grain is used in the proposal of a study of the rheological behaviour of wheat endosperm. Compression rupture, creep and relaxation tests are used. A series of compression tests on mealy and vitreous endosperm of different wheat varieties (soft, hard and durum) shows that the rheological properties are influenced by both the genetic origin and grain vitreousness. The main mechanical characteristics—Young's modulus, elastic and rupture stresses, rupture energy and rupture strain—were determined at moisture contents of 12 to 17%. The influence of the moisture content on rheological behaviour is demonstrated. The vitreous endosperm of some wheat varieties displays considerable ductility before rupture. The nature of this plasticity was analysed by creep and relaxation tests on hard and soft wheats. Comparison of the different endosperm rheology values clarifies the notions of vitreousness and hardness. Wheat classification based on endosperm mechanical characteristics is proposed. It seems that Young's modulus characterises hardness whereas rupture energy is related to the vitreousness of the different varieties studied. Entering the results in a Young's modulus–rupture energy system leads to a classification of wheats according to two essential factors: hardness of varietal origin and vitreousness of cultural origin.     

A Comparative Analysis of Free, Bound and Total Lipid Content on Spelt and Winter Wheat Wholemeal

Free lipids (FL), bound lipids (BL) and total lipids (TL) were determined by the Soxhlet method in whole ground spelt (Triticum aestivum ssp. spelta L.) and hexaploid winter wheat (T. aestivum) samples. Ninety-one samples of spelt and 78 samples of winter wheat were analysed in the present study. The available material is representative of the wide variability found in spelt (true spelt forms compared with spelt wheat hybrid material). The results show that spelt differs from winter wheat by a higher FL and TL content (on average, 1·3 times and 1·2 times respectively). Furthermore, our results demonstrate that FL account for most of the high TL content of spelt as compared to winter wheat. Lipid content is a parameter which allows a distinction between spelt and winter wheat. This could be useful for breeders to classify spelt varieties.     

Spring wheat response to timing of water deficit through sink and grain filling capacity

Water and nitrogen (N) availability are the main factors influencing crop growth globally. Poorly distributed or insufficient water for crop growth requirements decreases yields in drought-prone areas such as those with a Mediterranean type environment. Cereal grain yield is a complex trait of interrelated components: plants per unit land area, spikes per plant, spikelets per spike, grains per spikelet, and single grain weight (SGW). The effect of water limitation and timing on development of yield components was studied in detail at the spike level in spring wheat (Triticum aestivum L.) cultivar Amaretto. An experiment with three watering treatments (control watering, CONT; drought prior to pollination, DR1 and terminal drought, DR2) was arranged in a large greenhouse (20 m × 30 m), with the use of standard field-trial machinery. Automated blackout curtains were used to control day length, which was set to correspond to that at 40°N. With watering treatments, two N application rates (60 and 120 kg N ha⁻¹) were used to investigate the N effect and potential watering × N interaction on yield formation and realisation. The water deficit effect exceeded the effect of N on fertile floret and grain number and SGW. DR1 strongly reduced the number of fertile florets and grains, whereas terminal drought reduced the number of grains per spike. Resuming the watering at pollination markedly enhanced photosynthesis, and hence grain filling capacity, resulting in the highest SGW in DR1. Enhancement in availability of key resources was associated with reduced rate of fertile floret and grain abortion, which resulted in higher grain to fertile floret ratio in DR1. Spikelets in the mid-section of the spike dominated yield formation in all treatments. In DR1 this was especially emphasised as 53% of the grain yield was produced in spikelets 4–6, whereas in DR2 and CONT this was 45 and 41%, respectively. Grains in proximal position in the spikelets produced about 80% of the spike grain yield, the proportion being slightly higher in stressed plants and plants receiving 60 kg N. No marked N × water deficit treatment interaction occurred for any of the measured parameters.     

Purification and Characterization of a Glutenin Hydrolysing Proteinase from Wheat Damaged by the New Zealand Wheat Bug, Nysius huttoni

A glutenin hydrolysing enzyme (bug proteinase), present in New Zealand wheat damaged by Nysius huttoni, was purified 50000-fold by anion exchange, hydrophobic interaction, immobilized metal ion affinity and gel filtration chromatography. The enzyme had an apparent M_r of 14·1k as determined by gel filtration chromatography. SDS-PAGE showed a major protein band of M_r 30k and six minor bands of M_r 13·2-28·5k, none of which was a glycoprotein. Isoelectric focusing revealed two major enzyme active bands (pI 9·6 and 9·2) and three minor activity bands (pI 9·9, 8·8 and 8·2). IEF showed no protein contaminants in the most purified sample. The enzymes had optimum activity at pH 8·9 and 45°C. The activity was stable in the pH range 4·5-11 and at 50°C for 20 min at pH 8·9. The bug proteinase was shown to be a serine proteinase by inhibition with phenylmethylsulphonyl fluoride and potato proteinase inhibitors (POT-IC and POT-ID). Thirty other proteinaceous serine proteinase inhibitors did not inhibit the enzyme. Bread baking with partially purified enzyme produced loaves with the poor quality characteristics of loaves made with bug-damage wheat.     

Influence of storage temperature on rate of potato tuber tissue infection caused byPhytophthora infestans (mont.) de bary estimated by digital image analysis

Summary Potato tubers were inoculated with two biotypes ofPhytophthora infestans then stored at 3,7, 10 and 15°C. Image analysis quantified average reflective intensity (ARI) of diseased tissue from cut surfaces of sample tubers. Tuber tissue infection and infection rate were measured by calculating Mean ARI of samples. Average tuber tissue infection and infection rate was minimal at 3°C (P.i.-US8 orP.i.-US1). Tuber tissue infection increased at temperatures >3°C, from 220 Mean ARI seven days after inoculation (dai) to 190–150 Mean ARI 50 dai (depending on cultivar and biotype ofP. infestans). Rate of tuber tissue infection caused byP.i.-US1 at 7°C was about zero in cv. Snowden but greater than −0.2 ARI day⁻¹ (cvs Russet Burbank and Superior). Rate of late blight infection in tuber tissue generally increased with temperature from −0.2 ARI day⁻¹ (at 7°C) in all cultivars to a maximum of −0.8 ARI day⁻¹ (10°C).     

Development of wheat kernels with contrasting endosperm texture characteristics as determined by magnetic resonance imaging and time domain-nuclear magnetic resonance

Spikes and seeds from diploid ‘einkorn’ wheat Triticum monococcum and two near-isogenic hard and soft common wheat (Triticum aestivum) lines were harvested at regular intervals from 7 days post-anthesis (dpa) and analysed by non-destructive magnetic resonance imaging (MRI) and time domain-nuclear magnetic resonance (TD-NMR). A large amount of free water occurred in rachises, glumes and awns of spikes collected at 7 dpa, and accumulated in the physiologically active cells of the endosperm at 21 dpa. In the final stages of kernel development, awns and seed embryos exhibited a high MR signal due to the presence of free water likely associated with biological activities. TD-NMR relaxation time distributions obtained by discrete exponential fitting, distributed exponential fitting and SLICING multivariate analysis offered detailed information on mobility behaviour of water molecules in developing seeds and were able to differentiate two soft and hard isolines from common wheat cv. Enesco at early stages of seed development.     

Effect of particle size on kinetics of starch digestion in milled barley and sorghum grains by porcine alpha-amylase

The influence of milled grain particle size on the kinetics of enzymatic starch digestion was examined. Two types of cereals (barley and sorghum) were ground, and the resulting grounds separated by size using sieving, with sizes ranging from 0.1 to 3 mm. In vitro enzymatic digestion was performed, using pancreatic alpha-amylase, amyloglucosidase and protease, to determine fractional-digestion rates over 24 h. The resulting glucose production rate data were well fitted by simple first-order kinetics. For each sieve screen size, the digestion rate of barley was always higher than that of sorghum. The rate coefficients for digestion showed a decrease with increasing size, and could be well fitted by an inverse square relationship. This is consistent with the supposition that starch digestion in these systems is controlled by diffusion of enzyme through the grain fragment. Apparent diffusion coefficients of alpha-amylase obtained by fitting the size dependence were 0.76 (sorghum) and 1.7 (barley) × 10⁻⁷ cm² s⁻¹, 9 (sorghum) and 4 (barley) times slower than predicted for a molecule of the size of alpha-amylase in water.     

Water Sorption and Dielectric Relaxations of Wheat Dough (Containing Sucrose, NaCl, and their Mixtures)

Dielectric relaxations of wheat doughs with different water contents and effects of sucrose, NaCl, and their mixture on relaxation temperatures were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency. Before analysis, samples were stored at room temperature in vacuum desiccators over a_w range of 0·225–0·753. Dynamic DEA measurements were made at a heating rate of 2 °C/min from 40 °C below and above the observed relaxation zone. The frequencies used were 0·1, 0·5, 1, and 5 Hz. Steady state water contents varied from 3·21 to 10·89 g H₂O/100 g dm over a_w range used for the plain dough (flour+water). Added ingredients increased sorption of doughs. The tan δ of DEA showed an α-relaxation (glass transition) in all doughs at all frequencies used. The relaxation peak temperature, taken as T_g, increased with increasing frequency. Added sucrose decreased the T_g of doughs, as well as added NaCl. A dramatic depressing effect of NaCl on T_g was probably due to an increase in conductivity of doughs.     

Effect of endosperm starch granule size distribution on milling yield in hard wheat

Increased flour yield in hard wheat is associated with increased endosperm rheology index, calculated from strength and stiffness as measured by the SKCS. A study of the fractured endosperm of hard wheat varieties grouped according to similar rheology index values was performed using environmental scanning electron microscopy (ESEM). Differing microstructures and fracture patterns were observed between each group. Specifically, the group representing high rheology index had a greater concentration of small starch granules in prismatic cells. Samples of diverse wheat germplasm were grown at two sites and subjected to laboratory milling. Starch granule size distribution (SGSD) analysis using a laser diffraction method was undertaken on a subset of samples in triplicate representing a range in flour yield. The results supported an hypothesis for a significant influence of SGSD on flour yield of hard wheat varieties. In addition, a significant part (R²>0.40 (p<0.05) at two sites) of the association appeared to be under genetic control. Results indicate a more even gradation of distributions involving an increase in the sample volume % of small granule (types B and C) and decrease in type A granules. This was associated with increased rheology index values and higher flour yield. The ratio of type A:C starch granules accounted for up to 58% (p<0.05) of the variation in flour yield in the samples studied. Thus, rheological parameters measured using a rapid SKCS screening method can be linked to the genetic regulation of SGSD with implications for the improvement of commercial processing performance of hard wheat.     

Hydrothermal Processing of Barley (cv. Blenheim): Optimisation of Phytate Degradation and Increase of FreeMyo-inositol

Optimal conditions were developed for hydrothermal processing of whole barley kernels (cv. Blenheim) to degrade phytate (myo-inositol hexaphosphate) and to increase the content of freemyo-inositol. The hydrothermal treatment comprised of two wet steeps, where lactic acid solution of different concentrations was used, and two dry steeps followed by successive drying. Experiments were performed as a central composite design and evaluated by multiple linear regression. The variables in the experiments were temperature in the first wet and dry steep (T₁), temperature in the second wet and dry steep (T₂) and lactic acid solution concentration in both wet steeps (C) and mathematical models were developed in these variables. Optimal conditions for maximal phytate degradation and for maximal increase of freemyo-inositol wereT₁=48 °C,T₂=48–50 °C andC=0·8%, at these conditions the amount of phytate was reduced by 95–96% and the freemyo-inositol concentration was increased from 0·56 to 2·45 μmol/g d.m. We conclude that this hydrothermal process can be used to produce a barley product (cv. Blenheim) with a low phytate content and a high level of freemyo-inositol.     

Investigation of the fracture mode for hard and soft wheat endosperm using the loading–unloading bending test

Investigation of the fracture mode for hard and soft wheat endosperm was aimed at gaining a better understanding of the fragmentation process. Fracture mechanical characterization was based on the three-point bending test which enables stable crack propagation to take place in small rectangular pieces of wheat endosperm. The crack length can be measured in situ by using an optical microscope with light illumination from the side of the specimen or from the back of the specimen. Two new techniques were developed and used to estimate the fracture toughness of wheat endosperm, a geometric approach and a compliance method. The geometric approach gave average fracture toughness values of 53.10 and 27.0 J m⁻² for hard and soft endosperm, respectively. Fracture toughness estimated using the compliance method gave values of 49.9 and 29.7 J m⁻² for hard and soft endosperm, respectively. Compressive properties of the endosperm in three mutually perpendicular axes revealed that the hard and soft endosperms are isotropic composites. Scanning electron microscopy (SEM) observation of the fracture surfaces and the energy–time curves of loading–unloading cycles revealed that there was a plastic flow during crack propagation for both the hard and soft endosperms, and confirmed that the fracture mode is significantly related to the adhesion level between starch granules and the protein matrix.     

Purification and Characterisation of Ascorbate Oxidase from Flour and Immature Wheat Kernels

White flour from wheat was shown to contain basic-ascorbate oxidase (AOX) enzymes (pI 7·6–9·6) and acidic-AOX enzymes (pI 5·1–6·6) in a ratio of 0·4:1, based on chromatography data. Immature wheat kernels (two weeks post-anthesis) contained about 12 times more AOX activity (units/g dry weight) than flour from mature grain, and the ratio of basic- to acidic-AOX was 5:1. Acidic-AOX was purified 90-fold from flour by hydrophobic interaction, gel filtration and anion exchange chromatography. Basic-AOX was purified 20 000-fold from immature wheat by hydrophobic interaction, anion exchange, cation exchange and gel filtration chromatography in a yield of 5%. The acid-AOX had a M of 140 k, was optimally active at pH 6·3 and 40 °C, and was stable in the pH range 5–9 and at 30 °C for 0·5 h at pH 6·2. The Km values were 0·26 m for L-ascorbic acid and 0·93 m for D-iso ascorbic acid. The basic-AOX had a M of 139 k and subunit M of 72 k. The enzyme was optimally active at pH 6·2 and 50 °C, and was stable in the pH range 5–9 and at 40 °C for 0·5 h at pH 6·2. The Km values were 0·30 m for L-ascorbic acid and 0·53 m for D-iso ascorbic acid. The absorption spectrum of basic-AOX had absorption maxima at 280 nm and 607 nm of similar magnitude to those measured in AOX fromCucurbita species (squash). This indicates that wheat AOX contains protein-bound copper similar to other plant AOX.     

Variability in dehydrodiferulic acid composition of durum wheat (Triticum durum Desf.) and distribution in milling fractions

The dehydrodiferulic acid content of different common and durum wheat grains and milling fractions was determined by an HPLC procedure. The 8-O-4′, 5–8′ benzofuran, 5–8′ and 5-5′ dehydrodimers were identified in all samples studied and occurred in decreasing relative amounts, respectively. Durum wheats were twice as concentrated in dimers as common wheats. An important genetic variation for dehydrodiferulic acid content was shown within durum wheat grains, whereas the agronomic conditions had no effect. There was 10 to 20 times more dehydrodiferulic acids in external layers (aleurone, bran) than in the starchy endosperm of durum wheat grains. The content and composition in dimers of the inner endosperm did not vary according to genotypes and cultivation conditions. The ratio of dehydrodimers to monomers of ferulic acid which represented an index of dimerisation, was 1·6 times higher in the external layers of the grain than in the endosperm. No relation was found, however, between the degree of ferulic acid dimerisation and the milling behaviour of durum wheat grains.