Vitreosity,its stability and relationship to protein content in durum wheat

High quality requirements are set on durum wheat (Triticum durum) from semolina mills and pasta producers. For the production of semolina and pasta with good cooking quality, high grain protein content and vitreosity is required. The dependency of vitreosity on protein content as well as its stability under the influence of humidity was not well investigated up to now. We (1) compared two methods to determine vitreosity, (2) investigated the relationship between vitreosity and protein content, (3) developed a method to analyze vitreosity under humidity, and (4) examined the relationship between protein content and agronomical as well as quality traits in durum wheat. The results showed that the formation of vitreous kernels greatly depends on the protein content. To evaluate the stability of vitreosity under the influence of humidity a new method was elaborated and employed to assess the durum germplasm under study. This revealed that vitreosity of a durum wheat variety depends on the potential to form vitreous kernels but also to maintain this vitreosity under the influence of humidity. Our results further show that protein content is a central trait in durum wheat that strongly influences important traits like grain yield, vitreosity, and b-value.     

Investigation of amber durum wheat for production of yellow alkaline noodles

Samples of Canadian amber durum wheat varieties, of various protein content and a composite of export cargo samples, were milled to yield straight-grade and patent flours by reducing semolina and processed into yellow alkaline noodles (YAN). Samples of Canada Hard White Spring (CWHWS) and Canada Western Red Spring (CWRS) were included for comparative purposes. YAN from durum wheat displayed a colour advantage over CWRS and CWHWS YAN. The durum YAN displayed an approximate 9–20 unit greater b* (yellowness) value than CWRS and CWHWS at 2 and 24 h after preparation. This relates to greater yellow pigment and flavonoid contents in the durum flours. All durum wheat YAN exhibited excellent noodle brightness, which was retained over time due to lower levels of the enzymes polyphenol oxidase (PPO) and peroxidase (POD). Durum noodles displayed significantly fewer specks than CWRS and were comparable to CWHWS. Durum wheat YAN cooking quality was equal to or slightly superior to CWRS and CWHWS. Durum wheat flour refinement imparted no significant effects on cooked noodle texture (maximum cutting stress, recovery, resistance to compression). However, the various texture parameters improved with durum wheat protein content and gluten strength.     

Investigation of amber durum wheat for production of yellow alkaline noodles

Samples of Canadian amber durum wheat varieties, of various protein content and a composite of export cargo samples, were milled to yield straight-grade and patent flours by reducing semolina and processed into yellow alkaline noodles (YAN). Samples of Canada Hard White Spring (CWHWS) and Canada Western Red Spring (CWRS) were included for comparative purposes. YAN from durum wheat displayed a colour advantage over CWRS and CWHWS YAN. The durum YAN displayed an approximate 9–20 unit greater b* (yellowness) value than CWRS and CWHWS at 2 and 24 h after preparation. This relates to greater yellow pigment and flavonoid contents in the durum flours. All durum wheat YAN exhibited excellent noodle brightness, which was retained over time due to lower levels of the enzymes polyphenol oxidase (PPO) and peroxidase (POD). Durum noodles displayed significantly fewer specks than CWRS and were comparable to CWHWS. Durum wheat YAN cooking quality was equal to or slightly superior to CWRS and CWHWS. Durum wheat flour refinement imparted no significant effects on cooked noodle texture (maximum cutting stress, recovery, resistance to compression). However, the various texture parameters improved with durum wheat protein content and gluten strength.     

Potato (Solanum spp.) in the hot tropics II. Soil temperature and moisture modification by mulch in contrasting environments

In order to quantify the effects of mulch on soil temperature and soil moisture regimes during the growth of the potato crop, seven experiments were conducted at three contrasting hot tropical sites (latitude 5–12 °S) varying in altitude from 180 to 800 m. Mean maximum and minimum temperatures during the crop seasons ranged from 27° and 30° and 16° to 21°C respectively. Various mulches, mostly organic, were tested either singly or in combination with other agronomic practices, and in one experiment the interactions between mulch and three radiation levels (0, 50, and 75% reduction of incoming radiation) were studied.Mulch always enhanced soil moisture retention, but the improvement was less evident under increasing shade. Daily soil temperature fluctuations at tuber depth were damped by mulch, and maximum reduction of daytime soil temperature was recorded immediately following planting, before the crop emerged.Reductions of daytime soil heating and retention of heat within the soil at night by mulch were influenced by various edaphic and weather conditions. Maximum reduction during the day was achieved under conditions favouring soil heating (e.g. high irradiance, low soil moisture content, ridged soil, soil of low albedo) whereas heat retention at night by mulch, although greater in shaded than non-shaded plots, in general was relatively greater under conditions that favoured longwave re-radiation from the soil (e.g. ridged and dry soil).     

Properties of Frozen Wheat Doughs at Subzero Temperatures

The subzero properties of wheat doughs were measured by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA) over the temperature range −90 to +40 °C and by¹H-nuclear magnetic resonance (NMR) T₂relaxation over the range −45 to 0 °C. The experiments revealed two transitions in the dough: one independent of frequency at −10 °C (attributed to ice melting) and one dependent on frequency at −30 °C (attributed to a glass transition). The glass transition temperatures measured by DMTA moved to higher temperatures during frozen storage when the optimal water content of dough was used. A reduction in the water content eliminated this phenomenon. A similar effect of water reduction was observed by NMR studies, in which amplitude ratios and decay times were used to calculate the phase transitions. However, the glass transition recorded by NMR was independent of frozen storage with optimal water content. The changes of water state in frozen doughs were studied by ultracentrifugation (the amount of liquid phase) and NMR (freezable water based on liquid amplitude ratios). Frozen storage increased the liquid phase in dough with optimal water content. Thus, ice crystals are growing during frozen storage resulting in the concentration of polymers and a higher glass transition observed by DMTA. The increase of liquid phase during storage was substantially lower when the water content of dough was decreased. Ice crystals» growth can be minimised by reducing water content. The experiments were carried out with four different flours. The measurement of glass transition temperature by DMTA, DETA or NMR did not reveal great differences in doughs made from different flours. The amount of liquid phase was strongly flour dependent.     

Metabolic profiling and analysis of volatile composition of durum wheat semolina and pasta

Although pasta is generally not considered for its aromatic properties, some evidence proves that cereal flours release volatile compounds and they might have an effect on the aroma of the transformed products. This work reports on the characterization of the volatile components of semolina and pasta obtained from four durum wheat cultivars (Triticum durum Desf., cvs. PR22D89, Creso, Cappelli, Trinakria). Semolina samples were characterized through polar metabolite profiling and fatty acid analysis to identify potential precursors of the volatile components. The results show significant differences among the samples tested with cv. Trinakria characterized by the highest content of sugars and fatty acids. Volatile composition was investigated both in semolina and in cooked pasta using headspace solid-phase micro-extraction (HS-SPME) and identified by GC–MS. Thirty-five volatile compounds including aldehydes, ketones, alcohols, terpenes, esters, hydrocarbons and a furan were identified. Significant differences were observed between semolina and pasta samples in terms of composition and amount of the volatile compounds. During cooking an increase in aldehyde content, the appearance of ketones and a decrease in alcohol content were observed. Correlations between metabolites and volatiles demonstrate that the flavour of cooked pasta may differ significantly depending on the durum wheat cultivar employed.     

Effect of incorporation of an i-type low-molecular-weight glutenin subunit and a modified γ-gliadin in durum and in bread wheat doughs as measured by micro-mixographic analyses

The effects of incorporation of an i-type low-molecular-weight glutenin subunit (LMW-i) and of a modified γ-gliadin showing an additional cysteine residue, on 2 g Mixograph parameters of durum (biotypes 42 and 45 of the Italian cv. Lira) and bread wheat (Australian cv. Kukri) doughs were studied. In bread wheat flour incorporation of the modified γ-gliadin resulted in a significant decrease in dough strength (decreased mixing time and peak resistance), but at the same time it produced a slight increase in dough stability (decreased resistance to breakdown). The incorporation of the LMW-i type into bread wheat dough had minimal effects on dough mixing requirements. The incorporation of both LMW-i type and modified γ-gliadin in durum wheat doughs produced a significant decrease in the overall dough strength, especially in Lira 45 biotype doughs. Reversed phase high-performance liquid chromatography (RP-HPLC), size exclusion high-performance liquid chromatography (SE-HPLC) and two-dimensional gels analyses of control and reconstituted semolina doughs showed that the two polypeptides were in the polymeric fraction. The effect of the incorporation of the two polypeptides in durum and bread wheat doughs showed remarkable differences and the reasons for this is discussed in terms of both intrinsic differences between wheat flour and durum semolina and in methodological approaches.     

The Null-4A Allele at the Waxy Locus in Durum Wheat affects Pasta Cooking Quality

Granule-bound starch synthase, also known as the waxy protein catalyses the synthesis of amylose in wheat endosperm starch. In durum wheats, the genes encoding GBSS are present at the two Wx loci on chromosome 7A and 4A (a segment of 7B that has been translocated). Several null Wx-B1 (missing GBSS protein from chromosome 4A) durum lines were produced from crosses with null-4A bread wheats backcrossed to durum wheats. Semolina milled from 4 normal and 7 null-4A durum wheat lines grown over two seasons (1999 and 2000) in South Australia were analysed for amylose content, starch pasting properties as measured by the Rapid Viscoanalyzer (RVA), swelling power and starch damage, protein content and electrophoretic protein analysis. Spaghetti was prepared with a micro-scale extruder and the cooked pasta evaluated for cooking loss, firmness, stickiness and water absorption. The null-4A lines had significantly lower (ca. 5%) amylose content, higher starch peak viscosities and semolina swelling power. The pasta derived from the null-4A lines had lower cooking loss and in 1999 was more adhesive than the non-waxy lines. Cooking loss was correlated with amylose content, peak starch viscosity, swelling power of semolina and cooked pasta adhesiveness. Semolina swelling power was highly correlated with RVA peak viscosity. Waxy durum wheats appear to have an advantage over the normal types in terms of lower cooking loss, widely used as an indicator of pasta cooking quality.     

Effect of thermal processing and storage on digestibility of starch in whole wheat grains

Gelatinisation and retrogradation of starch in wheat flour systems and whole wheat grains were studied using DSC and the impact of these events on starch digestibility was investigated. Gelatinisation of starch was possible in wheat flours with more than 60% moisture content (dwb) and gelatinised samples had higher digestibility values. Retrogradation of starch was studied with partially and fully cooked (boiled at 100 °C for 12 min and 32 min, respectively) wheat grains that were subjected to storage at 22 °C for 48 h. Stored samples had lower digestibility values when compared to the freshly cooked counterparts. The effect of moisture on retrogradation was studied with fully cooked wheat grains that were dried to a range of moisture contents (14.6–35.9%, wwb) and stored at 20 °C for 24 h. Retrogradation enthalpy increased with increasing moisture content; however, digestibility values did not reflect the changes in retrogradation enthalpy. The possibility of estimating the degree of retrogradation in fully cooked grains (32 min cooking) was investigated using a wheat flour-water system. The retrogradation enthalpy of fully cooked grains was slightly higher than the wheat flour-water system (at a moisture content of 49%, wwb) during the course of storage at 22 °C.     

Genetic and Agronomic Variation in Arabinoxylan and Ferulic Acid Contents of Durum Wheat (Triticum durumL.) Grain and Its Milling Fractions

Total arabinoxylan (AXt), water-extractable arabinoxylan (WeAX) and ferulic acid (FA) from five cultivars of durum wheat (Triticum durumL.), grown under four different agronomic conditions, were measured. Among the varieties analysed, AXt, WeAX and FA contents ranged between 4·07%–6·02%, 0·37%–0·56% and 0·784 mg/g–7·98 mg/g, respectively. High genetic and agronomic variability was detected for AXt, WeAX and FA. AXt and FA increased sharply in milling products for extraction rates above 60%. FA was quantified in durum wheat milling fractions. High concentrations of FA esterified to cell-wall arabinoxylans were found in the aleurone layer (69% of total FA), germ and seedcoat (26·6% of total FA). Only trace amounts were detected in the starchy endosperm (1·4% of total FA). A highly significant correlation appeared between AXt and FA contents.     

Tensile behavior and structural evolution of poly(lactic acid) monofilaments in glass transition region

A series of amorphous poly(lactic acid) (PLA) monofilaments with various D-isomer contents of 1∼9 mol% have been prepared and then elongated uniaxially at 25∼65 °C in the glass transition region. Both initial modulus and maximum strength of PLA monofilaments are appreciably decreased with increasing the temperature, especially at ∼50 °C, and they were somewhat lower for the monofilament with higher D-isomer content. Structural evolution, chain orientation, and thermal properties of PLA monofilaments drawn uniaxially with various draw ratios at 65 °C were then investigated by using wide-angle X-ray diffraction, polarized Raman spectroscopy, and differential scanning calorimetry, respectively. X-ray diffraction patterns clearly exhibited the development of chain orientation and stain-induced crystallization of the monofilaments as a function of draw ratio (DR). The dichroic ratio, a measure of the chain orientation, was quantitatively evaluated from the polarized Raman spectra. It was revealed that the dichroic ratios increased up to DR=4 and decreased slightly at DR>4 owing to the strain-induced crystallization for PLA monofilaments with D-isomer contents of 1 and 4 mol%. The glass transition and cold-crystallization temperatures of PLA monofilaments increased and decreased, respectively, with the increment of DR. The strain-induced enthalpy relaxation endothermic peak appearing in glass transition region became intense with increasing the DR.     

Usage of undersize bulgur flour in production of short-cut pasta-like couscous

Couscous is a traditional cereal product produced by rubbing durum semolina particles with water by hand, but can be produced by using pasta pressing technique. This study aimed to produce a short-cut pasta type couscous by substitution of semolina with undersize bulgur at 25, 50, 75 and 100%, by determining optimum parameters. Bulk density, cooking loss, volume and weight increases, protein and ash contents, color, sensory, texture and functional properties were determined. Couscous samples were prepared and dried using packed bed (60 and 80 °C) and microwave dryers (180 and 360 W) to determine optimum parameters. It was found that the quantity of bulgur flour was significantly (p ≤ 0.05) effective on the sensory attributes, bulk density, cooking loss, volume and weight increases, protein and ash contents in contrast to functional properties. Weight and volume increase values decreased with increasing quantity of bulgur flour. Couscous samples containing bulgur flour have higher protein than the control due to higher protein content of bulgur. According to texture profile, hardness of couscous containing bulgur flour was lower than the semolina control for each drying technique. Results revealed the fact that the production of pasta type couscous is possible using totally undersize bulgur instead of semolina.     

Texture,processing and organoleptic properties of chickpea-fortified spaghetti with insights to the underlying mechanisms of traditional durum pasta quality

Nutritionally enhanced spaghetti was prepared from durum semolina fortified with 0–30% desi chickpea ‘besan’ flour. This study examined the dough rheology, processing ease and quality attributes of the fortified spaghetti including protein, starch, texture (firmness, resilience and stickiness), colour, cooking loss, and organoleptic acceptability. Chickpea-fortified spaghetti was acceptable to consumers, had reasonable pasta quality, including lower cooking loss and less stickiness than the control spaghetti and retained firmness better than durum after refrigeration. This study suggests that chickpea-fortified spaghetti may be suited to uses such as fresh pasta, in soups, canning, and microwave re-heating. In addition, this study has added to the understanding of the underlying mechanisms of pasta quality. The main findings were: (1) gluten content/composition appears to be more important than protein content for pasta firmness; (2) the protein–polysaccharide matrix appears to be more important than the starch composition for cooking loss; (3) increased protein and amylose contents were associated with decreased pasta stickiness; (4) cooking loss and stickiness were not necessarily as strongly related as commonly believed. Further research into these theories is necessary to fully understand the underlying mechanisms of pasta quality.     

Estimated Glycemic Index and Dietary Fiber Content of Cookies Elaborated with Extruded Wheat Bran

The increasing demand for high-fiber products has favored the design of numerous bakery products rich in fiber such as bread, cookies, and cakes. The objective of this study was to evaluate the dietary fiber and estimated glycemic index of cookies containing extruded wheat bran. Wheat bran was subjected to extrusion process under three temperature profiles: TP1;(60, 75, 85 and 100 °C), TP2;(60, 80, 100 and 120 °C), and TP3;(60, 80, 110 and 140 °C) and three moisture contents: (15, 23, and 31 %). Cookies were elaborated using extruded wheat bran (30 %), separated into two fractions (coarse and fine). The dietary fiber content of cookies elaborated with extruded wheat bran was higher than the controls; C0 (100 % wheat flour) and C1 (30 % of no extruded bran coarse fraction) and C2 (30 % of no extruded bran fine fraction). The higher values of dietary fiber were observed on cookies from treatments 5 (TP1, 31 % moisture content and coarse fraction) and 11 (TP2, 31 % moisture content and coarse fraction). The estimated glycemic index of cookies ranged from 68.54 to 80.16. The dietary fiber content of cookies was increased and the lowest glycemic index corresponded to the cookies elaborated with extruded wheat bran. Cookie made with the treatment 11 had a better dietary fiber content and lower estimated glycemic index.     

Dynamic viscoelastic, calorimetric and dielectric characteristics of wheat protein isolates

Dynamic oscillatory rheology of two wheat protein isolate (Prolite 100 and Prolite 200) doughs (≈48% moisture content, wet basis) were studied over a frequency range of 0.1–10 Hz during temperature sweep from 20 to 90 °C at a heating rate of 2 °C/min. Both doughs behaved similarly during heating; showed a threshold value and increased sharply, thereafter. Prolite 200 dough had a higher elastic modulus (G′) and lower phase angle (δ) whereas Prolite 100 showed a distinct gel point at 52.2 °C followed by significant increase up to 90 °C. Rheological data of doughs after isothermal heating at 90 °C for 15 min followed by cooling to 20 °C resulted in strong mechanical strength. However, Prolite 100 dough showed more viscoelastic characteristics with significant transformation from liquid-like to solid-like behavior after heating than Prolite 200. Thermal analysis of isolates indicated distinct endothermic peaks in wider temperature range (50–130 °C) at various moisture levels. Lower temperatures could be associated with denaturation of various fractions of proteins whereas higher temperature linked to glass transition temperature of isolates. SDS–PAGE did not show any clear distinction among protein subunits between two isolates. Dielectric measurements of isolates at frequencies from 500 to 3000 MHz and temperature range between 30 and 80 °C indicated Prolite 200 had higher dielectric constant (ε′) and loss factor (ε″) than Prolite 100. Isolates showed significant changes in dielectric properties above 50 °C indicating protein denaturation and supported rheological and calorimetric data.     

Partial purification and characterization of polyphenoloxidase from durum wheat (Triticum durum L.)

A bright yellow color of pasta is an important qualitative trait for the durum wheat industry. Final color is the result of the balance between yellow and brown components in semolina. Polyphenoloxidase (PPO) is implicated as playing a significant role in darkening. This study aimed to characterize PPO activity of durum wheats. PPO was extracted and partially purified by ion-exchange chromatography on a column packed with diethyaminoethyl cellulose (DEAE). This procedure led to 26.33-fold purification with 24.7% recovery. The optimum temperature and pH of PPO were found to be 40 °C and 6.5, respectively. Heat stability of durum wheat PPO decreased as the temperatures increased from 30 to 80 °C. The z-value was calculated as 23.4 °C. It increased to 26.3 and 48.4 °C in the presence of 40% sucrose and 1 M NaCl, respectively. Durum wheat PPO was shown to use several phenolic compounds as substrate. Among the substrates used, the greatest substrate specificity was observed with catechol. Durum wheat PPO was sensitive to inhibitors such as ascorbic acid, cysteine, oxalic acid and citric acid. Ascorbic acid was the most effective inhibitor.     

Effect of Extrusion Conditions and the Optimization of Phenolic Compound Content and Antioxidant Activity of Wheat Bran Using Response Surface Methodology

The extrusion process (EP) consists of heat and mechanical treatments under different conditions of moisture, shear, and pressure and rapidly causes structural alterations and changes in the functional properties of the extruded material. The aim of this study was to evaluate the effect of extrusion conditions and optimize the wheat bran extrusion conditions to achieve the greatest content of phenolic compounds and antioxidant activity using response surface methodology. The EP factors evaluated were feed moisture (FM) (25–33.54%) and final extrusion temperature (T) (140–180 °C). The properties evaluated in the extruded material were bound total phenol content (BTPC), total phenolic compounds and antioxidant activity (AOX). Analysis of variance (ANOVA) and response surface methodology were used in the evaluation. The determination coefficients, (FM)² and (T)², very significantly affected the BTPC and bound 2,2-diphenyl-1-picrylhydrazyl content (BDPPHC). The optimization was performed by overlaying two contour plots to predict the best combination regions. The optimized extrusion conditions were the following: FM?=?30% and T?=?140 °C, which provided BTPC?=?3547.01 μgGAE/g (predicted: 3589.3 μgGAE/g) and BDPPHC?=?9.5 μmolTE/g (predicted: 10.4 μmolTE/g); and FM?=?30% and T?=?180 °C, which provided BTPC?=?3342.3 μgGAE/g (predicted: 3727.7 μgGAE/g) and BDPPHC?=?9.5 μmolTE/g (predicted: 9.3 μmolTE/g). The EP increased the phenolic compounds and AOX, and enhancement of these properties in wheat bran products could make them functional foods.     

The antioxidant potential of milling fractions from breadwheat and durum

The effect of primary processing, namely milling, on the phenolic content and antioxidant capacity of two wheat cultivars, namely Canada Western Amber Durum (Triticum turgidum L. var. durum) and Canada Western Red Spring (Triticum aestivum L.) was studied. The milling products: bran, flour, shorts and feed flour fractions were examined. In addition, semolina was an end-product of durum wheat milling. Antioxidant activity of wheat phenoliocs was evaluated using oxygen radical absorbance capacity, inhibition of photochemiluminescence, the Rancimat method, and inhibition of oxidation of low-density lipoprotein cholesterol and deoxyribonucleic acid. The phenolic composition of wheat extracts was determined using high performance liquid chromatography. Bran showed the highest antioxidant activity whereas the endosperm possessed the lowest in both cultivars examined. The phenolic compounds are concentrated in the outermost layers namely the bran. The consumption of wheat with bran in the form of whole grain may provide beneficial health effects.     

The influence of temperature extremes on some quality and starch characteristics in bread,biscuit and durum wheat

Environmental conditions during grain-fill can affect the duration of protein accumulation and starch deposition, and thus play an important role in grain yield and flour quality of wheat. Two bread-, one durum- and one biscuit wheat were exposed to extreme low (−5.5 °C for 3 h) and high (32 °C/15 °C day/night for three days) temperatures during grain filling under controlled conditions for two consecutive seasons. Flour protein content was increased significantly in one bread wheat, Kariega, under heat stress. Cold stress significantly reduced SDS sedimentation in both bread wheats. Kernel weight and diameter were significantly decreased at both stress treatments for the two bread wheats. Kernel characteristics of the biscuit wheat were thermo stable. Kernel hardness was reduced in the durum wheat for the heat treatment. Durum wheat had consistently low SDS sedimentation values and the bread wheat high values. Across the two seasons, the starch content in one bread wheat was significantly reduced by both high and low temperatures, as is reflected in the reduction of weight and diameter of these kernels. In the durum wheat, only heat caused a significant reduction in starch content, which is again reflected in the reduction of kernel weight and diameter.     

Glass transitions and the fracture behaviour of gluten and starches within the glassy state

Granular particles (crumbs) of gluten, wheat starch, and waxy maize starch were obtained by extrusion in a twin-screw cooker extruder and conditioned to a range of moisture contents (4–18%). The textures of the granules were assessed by a small sensory panel and the sounds produced during crushing (acoustic emission) measured. Solid, essentially amorphous, bars of gluten, wheat starch and waxy maize starch were produced by heat setting under pressure. The glass transition temperatures were measured by differential scanning calorimetry and dynamic mechanical thermal analysis, crystallinity by X-ray diffraction and the fracture behaviour examined using a three-point bend test. Heat-set gluten failed via elastic (brittle) fracture below its glass transition temperature, whereas, as the moisture content was increased, the glassy gelatinised starches underwent a brittle-ductile transition while still in the glassy state. This change in fracture mechanism explains why extruded gluten granules exhibited crispness at higher moisture contents than extruded starch granules, despite gluten having a lower glass transition temperature. The results suggest that the prediction of brittle textures (crisp, crunchy) from a knowledge of the glass transition temperature alone is not possible because bipolymers can exhibit different fracture mechanisms when in the glassy state.