QTL underlying plant and first branch height in cassava (Manihot esculenta Crantz)

Cassava, Manihot esculenta Crantz subsp. Esculenta was a major food crop across Asia and Africa. The crop was a highly heterozygous perennial woody shrub cultivated from stem cuttings. Cassava improvement for starchy tuberous roots requires about 5-6 years from F₁ hybrid seed germination to the selection of superior genotypes. Early selection with DNA markers could increase the number of elite genotypes identified. The aim here was to identify DNA markers associated with loci underlying plant and first branch height. In this study, 640 SSR primer pairs were used to screen for polymorphisms in two parental lines, cv. ‘Huaybong60’ (female) and cv. ‘Hanatee’ (male). There were 235 informative polymorphic markers used to genotype 100 individuals of an F₁ mapping population. Genotype data was analyzed by JoinMap^® version 3.0 software in order to construct a genetic linkage map. The map consisted of 156 linked SSR markers distributed across 25 linkage groups. The total length of the map was 845.2 cM (Kosambi cM) with 6.2 loci per linkage group, and an average distance between markers of 7.9 cM. Plant and first branch height of stem cuttings from the F₁ mapping population were collected from individual lines planted in 2007-2009. Quantitative Trait Loci (QTL) underlying these traits were identified using mapQTL^®/version 4.0. A total of seven QTL placed on four linkage groups were found for plant height. Of these, one major QTL was discovered on linkage group 2 near the marker SSRY155 with 17.9% of phenotypic variation explained (PVE). For first branch height, five QTL located on five linkage groups were identified. The two major QTL were located on linkage groups 2, and 20 at the loci SSRY323 and SSRY236 with 23.5% and 22.6% PVE, respectively. The QTL for plant and first branch height will serve as useful molecular markers in a cassava breeding program and may allow identification of the underlying genes in future.     

Changes in soil physical properties and crop root growth in dense sodic subsoil following incorporation of organic amendments

Measurements of soil physical properties, root growth and the water content in the subsurface layers of a clay Sodosol soil were carried out to determine why the incorporation of organic amendment (20 t/ha) resulted in marked increases in wheat yield in an earlier paper. The incorporation of lucerne or dynamic lifter^® pellets at a depth of 30–40 cm resulted in an almost doubling of the macroporosity from <10% to >18%, together with reductions in bulk density and the volumetric water content (θv$\theta v$) at −1500 kPa, and a 50-fold increase on saturated hydraulic conductivity in this subsurface layer. These changes in physical properties in the 30–40 cm deep layer were highly correlated (r values 0.69–0.93, P < 0.01) with increased root growth in this layer, and increases in crop yield. The practice of incorporating an organic amendment in the top clay layer of the B horizon in soils where the high density restricts root growth, which is termed ‘subsoil manuring’, shows promise for increasing crop productivity on these soils in the high rainfall zone of southern Australia.     

Pre-harvest glyphosate application effects on properties of β-glucan from oat groats

Pre-harvest glyphosate is applied to cereal grains to control weed growth. However, it has been claimed that oat (Avena sativa L.) composition is affected by pre-harvest glyphosate application. The research was conducted to evaluate differences in properties of β-glucan in grains of pre-harvest glyphosate treated versus untreated oat plants. Two oat cultivars (Rockford and Souris) were grown at Minot and Prosper, ND, in 2015, and glyphosate was sprayed during the soft dough stage, hard dough stage, or not applied. β-glucan viscosity was not significantly (p > 0.05) affected by treatment at soft dough (1082 cP) or mature (1166 cP) stages compared with untreated (1150 cP) controls. Applying glyphosate at the soft dough stage significantly (p < 0.05) reduced the content and solubility of the β-glucan versus untreated samples. β-glucan content and solubility in oat treated at soft dough were 4.35% and 52.1%, respectively, while in untreated samples were 4.65% and 60.6%, respectively. Treatment at soft dough and hard dough stages significantly (p < 0.05) increased weight average molecular weight (M_w) of the high molecular weight fraction of soluble β-glucan (4.4 × 10⁶ and 3.8 × 10⁶, respectively), compared with untreated controls (3.5 × 10⁶). The M_w of the low molecular weight fraction of soluble β-glucan fraction significantly (p < 0.05) increased at soft and hard dough treatments (5.5 × 10⁵ and 3.3 × 10⁵, respectively), versus untreated samples (3.0 × 10⁵). Therefore, glyphosate can be applied when the grain has reached physiological maturity or thereafter.     

Isolation and Characterisation of Single Chain Amylose

Five amylose preparations of different origins (cassava, potato, smooth seeded pea, wheat and maize), obtained from native starch granules by thymol complexation, were ultracentrifuged as the final decontamination step to remove a high molecular weight population contaminating the amylose solutions. The efficiency of this ultracentrifugation procedure was assessed by dynamic light scattering (DLS): decreases in apparent hydrodynamic radii,R?_H, from 46·1–72·6 nm before ultracentrifugation to 16·1–29·3 nm after were observed. Amylose solutions were then characterised by size exclusion chromatography coupled on-line to multi-angle laser light scattering (SEC–MALLS). Under these conditionsM?_wof cassava, potato, smooth seeded pea, wheat and maize amyloses were, respectively, 1·05×10⁶, 7×10⁵, 6·2×10⁵, 5·1×10⁵and 3·4×10⁵g/mol. Using a specific optimisation algorithm, experimental molecular weight distributions (MWD) were fitted by two mathematical models of ‘Most Probable’ distribution and ‘log-normal’ distribution. The best fit was obtained for the second model, but fittedM?_wwere higher than experimentalM?_w. When a ‘Most Probable’ model was used, the fittedM?_wwere consistent with experimentalM?_wbut with a lower quality of fit. Exponentscin the power lawR_G=KM^cwere between 0·6 and 0·7, indicating an extended linear random coil in the range of MW analysed (3×10⁵–9×10⁶g/mol). This procedure was also applied to the characterisation of different commercial amylose products.     

Study of the effect of hydrothermal process conditions on pasta quality

The effect of hydrothermal treatment on the pasting, hydration properties and colour quality of commercial fresh pasta were studied following an Instantaneous Controlled Pressure Drop treatment. This hydrothermal procedure involves a physical modification at high temperature (<144 °C) and restricted moisture content (<30%) during a very short time (15–40 s) followed by a rapid pressure drop to a vacuum (50 mbar). Two process variables (steam pressure level and processing time) were investigated using response surface methodology. Steam pressure level had the greatest effect on hydration and pasting parameters. Increased pressure resulted in elevation of mass ratio between cooked and uncooked pasta (W_i/W₀)_{100 °C} and reduction of for all treated pasta. The optimum cooking time of untreated pasta was 7 min (W/W₀=2.4), whereas for the same ratio it was less than 1 min for pasta treated at pressures ranging between 2.5 and 3.5 bar. The viscosity at 10 min (V₁₀) increased linearly when the pressure level increased. V₁₀ was 146 cP for untreated pasta whereas it reached 2659 cP for pasta treated at 3.9 bar (144 °C) for 25 s. The cold paste viscosity and setback viscosity decreased when the pressure varied from 1 to 3.9 bar.     

Evaluation of main-crop stubble height on ratoon rice growth and development

Rice (Oryza sativa L.) ratooning is the production of a second rice crop from the stubble left behind after the main-crop harvest. Lowering the main-crop stubble height by harvesting the main crop at a lower than traditional height is believed to alter growth parameters and increase ratoon yields. The objectives of this study were to evaluate the effect of main-crop stubble height on ratoon grain yield, agronomics, and cumulative/weekly panicle growth parameters (density, point of origin, and weight). Main-crop ‘Cocodrie’ and ‘Trenasse’ rice cultivars were harvested to leave either a 40- or 20-cm stubble height. When the main-crop stubble was harvested at 20 cm, ratoon rice grain yield in 2007 was increased by 375 and 190 kg ha⁻¹ for Cocodrie and Trenasse, respectively. Yield was not improved in 2006 using the low (20 cm) harvest height. The yield advantage in 2007 was associated with the increased weight of the basal panicles when the main crop was harvested at 20 cm. When the main-crop stubble was 20 cm, basal and axial panicle points of origin were numerically similar 5 weeks after main-crop harvest (WAH), while panicles originating from basal nodes were predominant 6 WAH and beyond. In contrast, when the main-crop stubble was 40 cm, approximately 75% of the emerged panicles originated from axial nodes 5 WAH, panicles from both axial and basal points of origin were nearly identical 6 WAH, and basal panicles were dominant thereafter. Results from this study indicate that when the initial stubble height is reduced from 40 to 20 cm the growth of the ratoon crop is altered by shifting panicle point of origin during the early growth period and delaying maturity.     

Expansion capacity of doughs: methodology and applications

An instrument for measuring the expansion capacity of dough was developed based on the application of a known negative pressure and measurement of the height reached by the dough using a dough height tracker. At a negative pressure of 74 cm of Hg, the same maximum heights were reached after expansion at all stages of processing from after mixing to end of proof. For this negative pressure (74 cm Hg), the expanded dough heights measured immediately after mixing for doughs from 9 hard and 10 soft wheat flours coincided closely with the heights reached by corresponding baked loaves (r=0.99). Pizza doughs were also found to give a good correlation with baked pizza height (r=0.78, significant at 1% level). The method was used to obtain information about the timing of the effects of bromate addition and flour lipid extraction during processing. An increase in dough expansion capacity from bromate addition was observed only after the final proofing stage. Gas cell fineness of the bread crumb, measured by CrumbScan software, was decreased by bromate addition but gas cell elongation was increased. Effects of lipid removal were different. An increase in expansion capacity occurred at all processing stages and gas cell fineness of the bread crumb was increased. Expansion capacity appears to be an inherent property of a dough and may have potential as a rapid measurement to predict baking performance.     

Postharvest harpin or Bacillus thuringiensis treatments suppress citrus black spot in ‘Valencia’ oranges

Citrus black spot (CBS) caused by Guignardia citricarpa represents an important threat to citriculture in Brazil. Limited information is available regarding potential biological control agents and new alternative compounds that may provide protection of orange fruits against the disease. In this study, the effects of commercial products based on Bacillus thuringiensis var. kurstaki (Bt) bacterium, Bt pure isolates and Harpin protein (Messenger^®) on the postharvest control of CBS, were evaluated in ‘Valencia’ sweet orange fruits harvested for three consecutive years in a citrus grove. The fruits were sprayed with the following products: DiPel^® WP (Bt, subspecies, kurstaki strain HD-1, 16,000 International Units mg⁻¹, 32 g active ingredient kg⁻¹) (1, 20 and 50 mg ml⁻¹), Dimy Pel^® WP (Bt, subspecies, kurstaki, strain HD-1, 17,600 IU mg⁻¹, 26 g active ingredient l⁻¹) (2, 20 and 50 mg ml⁻¹), Messenger^® (3% harpin protein) (1 and 2 mg ml⁻¹) and fungicide Tecto^® Flowable SC (thiabendazole, 485 g l⁻¹) (0.8 g active ingredient l⁻¹), besides the Bt isolates, Bt- HD-567, Bt- DiPel and Bt- Dimy (9 × 10⁸ CFU ml⁻¹). Ten days after treatment, the number of newly developed CBS lesions and pycnidia produced were evaluated using fifty fruits per treatment. The Dimy Pel^® and Messenger^® reduced the number of new developed CBS lesions on fruits in up to 67% and 62%, respectively. All applied treatments drastically decreased the number of pycnidia produced in the CBS lesions on orange fruits with 85% to 96% reductions compared to the untreated control. Volatile compounds produced by the isolates Bt- HD-567, Bt- Dimy and Bt- DiPel, reduced the number of lesions on treated fruits by 70%, 65% and 71% compared to the control, respectively. In addition, the survival of Bt isolates on orange fruit surfaces were evaluated by recovering and quantifying the number of CFU every seven days for up to 28 days. The declines in survival rates on orange fruit surfaces were drastic for the three strains of Bt in the first week. The CFU numbers of all applied isolates declined by 4 to 5 orders of magnitude after storage at room temperature for 28 days. In vitro assays revealed that the Bt isolates significantly reduced the mycelial growth of the pathogen, ranging from 32% to 51%, compared to the control, whereas no inhibitory effect was observed in the presence of Messenger^®.     

Aroma profiles of the curry leaf, Murraya koenigii (L.) Spreng. chemotypes: Variability in north India during the year

Murraya koenigii (L.) Spreng. (Rutaceae) is characterized by a large chemical intraspecific variability among the land races. This fact makes it difficult to detect real changes occurring in their essential oil composition during annual cycle. Based on this, variations of essential oil yield and composition in two chemotypes (‘A’ and ‘B’) of M. koenigii were assessed in spring, summer, rainy, autumn and winter seasons under foot hill conditions of northern India. The essential oil yield ranged from 0.15% to 0.18% in chemotype ‘A’, while it varied from 0.12% to 0.14% in chemotype ‘B’. Essential oils of both chemotypes from different seasons were analysed by gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). A total of fifty-eight constituents representing 93.7-98.8% of chemotype ‘A’ and fifty-six constituents forming 96.1-98.7% of the total composition of chemotype ‘B’ were identified. Chemotype ‘A’ was characterized by higher percentages of α-pinene (34.6-41.9%), sabinene (26.1-36.1%), (E)-caryophyllene (2.4-5.4%) and terpinen-4-ol (1.5-5.3%), whereas chemotype ‘B’ was dominated by higher amount of α-pinene (52.7-65.3%), β-pinene (10.7-12.9%), (E)-caryophyllene (3.1-10.3%) and limonene (5.1-7.8%). Comparative results showed considerable variations in the essential oil composition of both chemotypes due to season of collection. Present study concluded that the M. koenigii leaves of desired quality may be obtained by selecting suitable chemotype and season.     

Impact of guar and xanthan gums on proofing and calorimetric parameters of frozen bread dough

The influence of guar and xanthan gum and their combined use on dough proofing rate and its calorimetric properties was investigated. Fusion enthalpy, which is related to the amount of frozen water, was influenced by frozen dough formulation and storage time; specifically gum addition reduced the fusion enthalpy in comparison to control formulation, 76.9 J/g for formulation with both gums and 81.2 J/g for control, at 28th day. Other calorimetric parameters, such as T_g and freezable water amount, were also influenced by frozen storage time. For all formulations, proofing rate of dough after freezing, frozen storage time and thawing, decreased in comparison to non-frozen dough, indicating that the freezing process itself was more detrimental to the proofing rate than storage time. For all formulations, the mean value of proofing rate was 2.97 ± 0.24 cm³ min⁻¹ per 100 g of non-frozen dough and 2.22 ± 0.12 cm³ min⁻¹ per 100 g of frozen dough. Also the proofing rate of non-frozen dough with xanthan gum decreased significantly in relation to dough without gums and dough with only guar gum. Optical microscopy analyses showed that the gas cell production after frozen storage period was reduced, which is in agreement with the proofing rate results.     

Expansion profiles of wheat doughs fermented by seven commercial baker's yeasts

Commercial baker's yeast consists of Saccharomyces cerevisae, however the strain can vary in each baker's yeast, which might influence the dough fermentation time. The scope of this research was to investigate the dough expansion of wheat doughs fermented by seven commercial baker's yeasts at different yeast concentrations (2.88·10¹¹, 5.76·10¹¹ and 8.64·10¹¹ colony forming units/kg flour) and fermentation temperatures (5 °C, 15 °C, 25 °C and 35 °C). Dough expansion was investigated by monitoring the dough height and it was found to be described well by a first order kinetic model. Doughs fermented with four of the seven yeasts generally had higher kinetic rate constants and hence shorter fermentation times compared to fermentation with the other three yeasts. The shortest fermentation times were found for doughs fermented at 25 °C and the highest yeast concentration, a trend found for all the yeasts tested. The differences in the kinetic rate constants indicate a differentiation in yeast strain among the commercial baker's yeasts emphasising the great importance of the choice of baker's yeast for the dough fermentation time.     

Effect of temperature on seed germination parameters in Kalmegh (Andrographis paniculata Wall. ex Nees.)

Kalmegh (Andrographis paniculata Wall. ex Nees) is a medicinal herb of tropical south east Asia and native to India and Sri Lanka. It has been used herb for liver ailment in all prevailing systems of medicine viz. Ayurvedic, Unani, Homeopathic and modern throughout most of the south East Asian countries viz. China, India, Sri Lanka, Indonesia, Thailand, Burma, and Vietnam, etc. Commercially cultivation of Kalmegh is done through seeds. Optimal germination potential, temperature and first as well as final count day are three primary parameters for developing the seed quality standards. Germination of Kalmegh variety ‘CIM-Megha’ was carried out at six constant temperatures at an interval of every ‘5 °C’ from ‘15 to 40 °C’ temperatures coupled with 16 h light and 8 h dark photo period. The temperature of ‘25 °C’ was found optimally suitable with ‘94.6’ and ‘23.6’ percentage of germination and germination energy, respectively, while the temperature at ‘40 °C’ was deleterious with no germination. Significant decrease in percentage of germination and germination energy was observed at ‘15 °C’, ‘20 °C’, ‘30 °C’ and ‘35 °C’ of temperature in comparison to ‘25 °C’. The study further revealed that days 5-6 and days 7-9 after seed sowing were the ideal for first and final count, respectively for seed germination of Kalmegh.     

Simulation of the effects of genotype and N availability on rice growth and yield response to an elevated atmospheric CO2 concentration

The objective of this study was to identify physiological processes that result in genotypic and N fertilization effects on rice yield response to elevated atmospheric CO₂ concentrations ([CO₂]). This study conducted growth and yield simulations for 9 rice genotypes grown at 4 climatically different sites in Asia, assuming the current atmospheric [CO₂] (360 ppm) and elevated [CO₂] (700 ppm) using 5 levels of N fertilizer (4, 8, 12, 16, 20 g m⁻² N fertilizer). A rice growth model that was developed and already validated for 9 different genotypes grown under 7 sites in Asia was used for the simulation, integrating additional components into the model to explain the direct effect of [CO₂] on several physiological processes. The model predicted that the relative yield response to elevated [CO₂] (RY, the ratio of yield under 700 ppm [CO₂] to that under 360 ppm [CO₂]) increased with increasing N fertilizer, ranging from 1.12 at 4 g m⁻² N fertilizer to 1.22 at 20 g m⁻² N fertilizer, averaged overall genotypes and locations. The model also predicted a large genotypic variation in RY at the 20 g N treatment, ranging from 1.08 for ‘WAB450-I-B-P-38-HB’ to 1.41 for ‘Takanari’ averaged overall locations. Combining all genotypes grown at the 5N fertilization conditions, a close 1:1 relationship was predicted between RY and the relative [CO₂] response in spikelet number for crops with a small number of spikelets (less than 30,000 m⁻²) under the current atmospheric [CO₂] (n = 18, r = 0.89^***). In contrast, crops with a large number of spikelets under the current atmospheric [CO₂] showed a significantly larger RY than the relative [CO₂] response for spikelet number per unit area. The model predicted that crops with a larger number of spikelets under the current atmospheric [CO₂] derived great benefit from elevated [CO₂] by directly allocating increased carbohydrate to their large, vacant sink, whereas crops with a smaller number of spikelets primarily required an increased spikelet number to use the increased carbohydrate to fill grains. The simulation analyses suggested that rice with a larger sink capacity relative to source availability under the current atmospheric [CO₂] showed a larger yield response to elevated [CO₂], irrespective of whether genotype or N availability was the major factor for the large sink capacity under the current [CO₂]. The model predicted that the RY response to nitrogen was brought about through the N effects on spikelet number and non-structural carbohydrate accumulation. The genotypic variation in RY was related to differences in spikelet differentiation efficiency per unit plant N content. Further model validation about the effects of [CO₂] on growth processes is required to confirm these findings considering data from experimental studies.     

Dough and bread made from high- and low-protein flours by vacuum mixing: Part 1: Gluten network formation

The effects of reduced headspace pressure on the development of gluten network in doughs made from both high-protein flour (HPF) and low-protein flour (LPF) were investigated. The effect of vacuum mixing was found to be dependent on both flour-type and mixing-time. A significant increase in dough extensibility was observed when the HPF dough was mixed under moderate vacuum of −0.04 MPa for 3 min as compared to the one mixed under atmospheric pressure for the same duration. This was attributed to the formation of a more extensive gluten network associated with an increased disulphide bond density and a significantly higher β-sheet to β-turn ratio. On the other hand, over-mixing was observed in the LPF dough that was mixed for 5 min under atmospheric pressure. Applying moderate vacuum of −0.04 MPa allowed the LPF dough to withstand longer mixing time, as indicated by its increased disulphide bond density and biaxial extensibility compared to the control dough mixed under atmospheric pressure. Results of this study suggest the potential of applying vacuum to reduce the mixing time required for high protein flour and to prevent the over-mixing of low protein flour.     

Properties of bread made from frozen dough containing waxy wheat flour

The quality of bread made from frozen dough is diminished, and staling rate is increased by changes that occur during freezing and storage. New cultivars of waxy wheat flour (WWF), containing higher levels of amylopectin, may help improve the quality of baked products. Bread quality and staling were investigated for bread containing 0–45% WWF and 55–65% water after freezing and 90-day frozen storage. The specific volume was highest with 15% WWF substitution and 60% water in bread made from both unfrozen and frozen dough. With higher levels of WWF and lower water content, bread staling rates decreased. Bread with higher levels of WWF were darker and had greater color variation. ¹H NMR studies showed that bread with greater WWF and water had higher transverse relaxation (T₂) times (9–11 ms), but less change in T₂ during storage. This research demonstrated that specific combinations of WWF and water produced a better quality of bread after dough freezing.     

Hybanthus parviflorus (Violaceae): Insecticidal activity of a South American plant

Hybanthus parviflorus is a perennial shrub, widely distributed in the tropical and subtropical regions of America, and is known as ‘violetilla’ in Argentina. Previous phytochemical studies of this species led us to the isolation and determination of the primary structure of a novel macrocyclic polypeptide, the cyclotide hypa A. Here the insecticidal activities of extracts of H. parviflorus were determined against Ceratitis capitata Wied., the Mediterranean fruit fly or ‘Medfly’. Mortality in the different life stages of Medfly, total mortality and modifications of the insect’s physiology caused by 50% EtOH and CH₂Cl₂ extracts of H. parviflorus were evaluated. In addition, we determined the occurrence of ursolic acid, β-sitosterol and the polyphenols quercetin, quercetin-3-methyl ether, apigenin, luteolin, kaempferol, rutin, caffeic acid and chlorogenic acid. The promising insecticidal activity of 50% EtOH extracts of H. parviflorus and its purified fractions was related to the presence of cyclotides. The insecticidal activity of CH₂Cl₂ extracts could be related to the presence of polyphenols, ursolic acid and β-sitosterol.     

Impact of guar and xanthan gums on proofing and calorimetric parameters of frozen bread dough

The influence of guar and xanthan gum and their combined use on dough proofing rate and its calorimetric properties was investigated. Fusion enthalpy, which is related to the amount of frozen water, was influenced by frozen dough formulation and storage time; specifically gum addition reduced the fusion enthalpy in comparison to control formulation, 76.9 J/g for formulation with both gums and 81.2 J/g for control, at 28th day. Other calorimetric parameters, such as T_g and freezable water amount, were also influenced by frozen storage time. For all formulations, proofing rate of dough after freezing, frozen storage time and thawing, decreased in comparison to non-frozen dough, indicating that the freezing process itself was more detrimental to the proofing rate than storage time. For all formulations, the mean value of proofing rate was 2.97 ± 0.24 cm³ min⁻¹ per 100 g of non-frozen dough and 2.22 ± 0.12 cm³ min⁻¹ per 100 g of frozen dough. Also the proofing rate of non-frozen dough with xanthan gum decreased significantly in relation to dough without gums and dough with only guar gum. Optical microscopy analyses showed that the gas cell production after frozen storage period was reduced, which is in agreement with the proofing rate results.     

Dough and bread made from high- and low-protein flours by vacuum mixing: Part 2. Yeast activity,dough proofing and bread quality

The combined effects of reduced mixer headspace pressure and mixing duration on the yeast activity, proofing and quality of dough and bread made from both high-protein flour (HPF) and low-protein flour (LPF) were addressed in this study. Rheofermentometer analysis showed that a reduction in mixer headspace pressure up to 0.08 MPa did not affect the overall gassing power of yeast in either of the two dough matrices. An increase in mixing duration sped up the mass transfer rate of CO₂ at the initial stage of fermentation, leading to a faster expansion of dough volume at the beginning. Moreover, an increase in mixing time promoted dough development and gas inclusion, which resulted in a increased volume of dough and bread, as well as a softer texture of both baked bread and steamed bread. In general, reduced headspace pressure produced baked bread of smaller volume, denser structure and harder texture. On the other hand, vacuum mixing produced steamed bread with softer texture without significantly changing the bread’s volume and porosity.     

Comparison of the impact of dextran and reuteran on the quality of wheat sourdough bread

This study investigates the influence of in situ exopolysaccharides (EPS) and organic acids on dough rheology and wheat bread quality. Dextran forming Weissella cibaria MG1 was compared to reuteran forming Lactobacillus reuteri VIP. For in situ production of EPS, sourdoughs were supplemented with 15% sucrose. Control sourdoughs were prepared with the same strain but without sucrose. W. cibaria MG1 and L. reuteri VIP formed 5.1 and 5.8 g kg⁻¹ dextran and reuteran, respectively. Formation of EPS from sucrose led to production of high amounts of acetate by L. reuteri VIP, but only small amounts were detected in W. cibaria MG1 sourdough. EPS containing sourdough or control sourdough was incorporated at 10% and 20% in wheat dough. EPS significantly influenced the rheological properties of the dough, with dextran exhibiting the strongest impact. The addition of dextran enriched W. cibaria MG1 sourdough significantly increased CO₂ production, whereas increased acidity in reuteran containing dough reduced gas production. The quality of wheat bread was enhanced when 10% of L. reuteri-sucrose sourdough was added. The positive effect of reuteran was masked by increased acidification after 20% sourdough addition. Incorporation of dextran enriched sourdough (10% and 20%) provided mildly acidic wheat bread with improved bread quality.     

Effect of fat level,mixing pressure and temperature on dough expansion capacity during proving

In this work the effect of fat content on dough aeration during proving was investigated using dynamic dough density measurements. Doughs of three different fat levels (0%, 0.04% and 0.2% flour basis) were mixed under various pressures using a Tweedy mixer and proved at five different temperatures (30, 35, 40, 45 and 50 °C) in the dynamic dough density system. The dough expansion capacity and the time of the gas loss of each dough sample were measured and related to fat level, mixing pressure and proving temperature.