Isolation and properties of Aspergillus niger IBT-90 xylanase for bakery

Xylanase of low molecular weight (K II) was isolated from the fungus Aspergillus niger IBT-90 cultivated in medium with wheat bran. K II was purified by precipitation with ammonium sulphate (20–80% saturation) and gel filtration on Biogel P-10. This enzyme is most active in hydrolysis of birchwood xylan at 50°C and pH 5.5. Xylanase K II has an ability to degrade 1,4-β-bonds and to debranch substrates. It degrades not only xylans but also cellulose, an important factor for its application in bakery. Ag⁺, Fe³⁺ and NBS are strong inhibitors of the enzyme. DTT and Na⁺ activate xylanase K II by 24 and 13%, respectively. Enzyme K II used as additive to flour improves dough properties, increases the volume of wheat–rye and whole meal bread, and increases the porosity of crumb and the moisture of the final product, consequently extending the shelf life of bread.     

Physical characteristics of olive stone wooden residues: possible bulking material for composting process

The present work focuses on the study of the physical characteristics of olive stone wooden residues at the prospect of its use as a bulking material in compost process. The physical characteristics that were studied according to particle mesh classification, were the apparent density, porosity, water holding capacity, air free space and air pressure drop. From the experimental results, it was proved that only the fraction of 6.8–12.5 mesh, which is 29.40% of the substrate, could maintain the moisture in the optimum range 40–60%. The fraction of the particles of 2.6–23.6 mesh, which was 74.68% of the substrate, had appropriate porosity for composting. It was also proved that for dried substrate and air velocity 300 m h⁻¹, acceptable pressure drop (10 cm H₂O m⁻¹) was observed for the fraction of the particles of 2.6–27.5 mesh, which was 80.08% of the substrate, while for dried substrate and air velocity 150 m h⁻¹, the respective fraction was particles of 2.6–37.9 mesh which accounted for the 89.48% of the substrate. Conclusively, olive oil processing solid residues have the physical characteristics, so as to be used for composting or as a substrate for co-composting with high strength wastewater.     

Improvement of tolerance to freeze-thaw stress of baker's yeast by cultivation with soy peptides

The tolerance to freeze–thaw stress of yeast cells is critical for frozen-dough technology in the baking industry. In this study, we examined the effects of soy peptides on the freeze–thaw stress tolerance of yeast cells. We found that the cells cultured with soy peptides acquired improved tolerance to freeze–thaw stress and retained high leavening ability in dough after frozen storage for 7 days. The final quality of bread regarding its volume and texture was also improved by using yeast cells cultured with soy peptides. These findings promote the utilization of soy peptides as ingredients of culture media to improve the quality of baker’s yeast.     

What effect will a few degrees of climate change have on human heat balance? Implications for human activity

While many factors affecting human health that will alter with climate change are being discussed, there has been no discussion about how a warmer future will affect man’s thermoregulation. Using historical climate data for an Australian city and projections for Australia’s climate in 2070, we address the issue using heat balance modelling for humans engaged in various levels of activity from rest to manual labour. We first validate two heat balance models against empirical data and then use the models to predict the number of days at present and in 2070 that (1) sweating will be required to attain heat balance, (2) heat balance will not be possible and hyperthermia will develop, and (3) body temperature will increase by 2.5°C in less than 2 h, which we term “dangerous days”. The modelling is applied to people in an unacclimatised and an acclimatised state. The modelling shows that, for unacclimatised people, outdoor activity will not be possible on 33–45 days per year, compared to 4–6 days per year at present. For acclimatised people the situation is less dire but leisure activity like golf will be not be possible on 5–14 days per year compared to 1 day in 5 years at present, and manual labour will be dangerous to perform on 15–26 days per year compared to 1 day per year at present. It is obvious that climate change will have important consequences for leisure, economic activity, and health in Australia.     

Drying of Pomegranate Arils and Selection of a Suitable Drying Model

The drying characteristics of pomegranate arils were investigated in temperature range of 50–70 °C. The increase in drying air temperature resulted in a decrease in drying time. The drying rate was found to increase with temperature, thereby reducing the total drying time. Thirteen drying models were evaluated in the kinetics research. The goodness of fit of the proposed models was evaluated by using the determination of coefficient (R ² ), mean relative percent error (P), reduced chi-square (χ ²), and root means square error (RMSE). The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivity (D _eff) ranged from 9.447 × 10⁻¹¹ to 3.481 × 10⁻¹⁰ m²/s as calculated by the Fick’s second law of diffusion. The temperature dependence of the value of effective moisture diffusivity followed an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined to be 60.34 kJ/mol.     

Diversity of Novel Glutenin Subunits in Bread Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Glutenin is a major determinant of baking performance and viscoelasticity, which are responsible for high-quality bread with a light porous crumb structure of a well-leavened loaf. We analyzed the diversity of glutenin genes from six wheat cultivars (Korean cvs. Keumgang and Jinpum, Chinese cvs. China-108 and Yeonnon-78, and Japanese cvs. Norin-61 and Kantou-107). Glutenins contain two types of isoforms such as high molecular weight glutenin subunit (HMW-GS) and low molecular weight glutenin subunit (LMW-GS). Glutenin fractions were extracted from wheat endosperm using Osborne solubility method. A total of 217 protein spots were separated on two-dimensional gel electrophoresis with isoelectric focusing (wide range of pH 3–10). The proteins spots were subjected to tryptic digestion and identified by matrix assisted laser desorption/ionization–time of flight mass spectrometry. HMW-GS (43 isoforms) and LMW-GS (seven isoforms) are directly responsible for producing high-quality bread and noodles. Likewise, all the seed storage proteins are digested to provide nutrients for the embryo during seed germination and seedling growth. We identified the diverse glutenin subunits in wheat cultivars and compared the gluten isoforms among different wheat cultivars according to quality. This work gives an insight on the quality improvement in wheat crop.     

Heat and mass exchange processes between the surface of the human body and ambient air at various altitudes

 The rates of convection and evaporation at the interface between the human body and the surrounding air are expressed by the parameters convective heat transfer coefficient h _c, in W m^–2°C^–1 and evaporative heat transfer coefficient h _e, W m^–2 hPa^–1. These parameters are determined by heat transfer equations, which also depend on the velocity of the airstream around the body, that is still air (free convection) and moving air (forced convection). The altitude dependence of the parameters is represented as an exponential function of the atmospheric pressure p: h _c∼p ⁿ and h _e∼p ^1–n, where n is the exponent in the heat transfer equation. The numerical values of n are related to airspeed: n=0.5 for free convection, n=0.618 when airspeed is below 2.0 ms^–1 and n=0.805 when airspeed is above 2.0 ms^–1. This study considers the coefficients h _c and h _e with respect to the similarity of the two processes, convection and evaporation. A framework to explain the basis of established relationships is proposed. It is shown that the thickness of the boundary layer over the body surface increases with altitude. As a medium of the transfer processes, the boundary layer is assumed to be a layer of still air with fixed insulation which causes a reduction in the intensity of heat and mass flux propagating from the human body surface to its surroundings. The degree of reduction is more significant at a higher altitude because of the greater thickness of the boundary layer there. The rate of convective and evaporative heat losses from the human body surface at various altitudes in otherwise identical conditions depends on the following factors: (1) during convection – the thickness of the boundary layer, plus the decrease in air density, (2) during evaporation (mass transfer) – the thickness of the boundary layer, plus the increase with altitude in the diffusion coefficient of water vapour in the air. The warming rate of the air volume due to convection and evaporation is also considered. Expressions for the calculation of altitude dependences h _c (p) and h _e (p) are suggested. Received: 23 June 1998 / Accepted: 10 February 1999     

Fungal flora of Egyptian baladi bread with special reference to the mutagenic effects of their toxic metabolites

The fungal flora of wheat flour and baladi bread in upper Egypt were investigated. Most of the isolated fungal species belong to the genus Aspergillus. The presence of non heat resistant fungi of the both flat surfaces of baladi bread, came from contamination after baking and from improper handling at homes. Among the heat resistant fungi, A. fumigatus and A. niger, were recorded to inhabit the spongy crumb although the high temperature of baking process which reached approximately 100 ° C in the center of the bread.The mutagenic effects of the fungal metabolites of the extract of mouldy bread was investigated. Several kinds of aberrations were observed in all stages of mitotic division. The most interesting effect of these fungal metabolites were the induction of tripolar and quadripolar spindle. Multinucleate and polyploid cells were also observed under relatively high concentrations. It was noticed that at either higher concentrations or lower concentrations with long exposure, damaged cells were observed. The hazards involved through the consumption of individuals to such mouldy bread, is accumulation of possible deleterious effects from both long and short term exposure to these toxic metabolites.     

Effects of constant and fluctuating soil temperature on growth,development and nutrient uptake of maize seedlings

Summary The effect of constant and fluctuating soil temperature and two soil moisture regimes on the growth, development, transpiration and nutrient uptake by maize seedlings was studied in a greenhouse investigation. The constant root temperatures were maintained at 30, 34, 35, 36, 37, and 38°C for both 250 and 750 cm of soil moisture suctions. The fluctuating root temperature, for 250 cm of soil moisture suction only, of 30–35, 30–39, 30–40, 30–45 and 30–48°C were maintained to simulate the soil temperature regime under field conditions. The constant root temperature of 35°C and fluctuating temperature between 30–40°C significantly decreased the shoot and root growth and transpiration rate. On the average, there was 1.3 and 0.7 g decrease in fresh shoot weight and 0.36 and 0.30 g in fresh root weight per degree increase in root temperature for 250 and 750 soil moisture suction, respectively. In general, the effect of high soil moisture suction on maize seedlings was more severe when at high root temperature. The shoot and root concentration of N, P, and K decreased while that of B increased with increase in root temperature. The root concentration of Zn also decreased with increase in root temperature.     

Root effects on soil water and hydraulic properties

Plants can affect soil moisture and the soil hydraulic properties both directly by root water uptake and indirectly by modifying the soil structure. Furthermore, water in plant roots is mostly neglected when studying soil hydraulic properties. In this contribution, we analyze effects of the moisture content inside roots as compared to bulk soil moisture contents and speculate on implications of non-capillary-bound root water for determination of soil moisture and calibration of soil hydraulic properties. In a field crop of maize (Zea mays) of 75 cm row spacing, we sampled the total soil volumes of 0.7 m × 0.4 m and 0.3 m deep plots at the time of tasseling. For each of the 84 soil cubes of 10 cm edge length, root mass and length as well as moisture content and soil bulk density were determined. Roots were separated in 3 size classes for which a mean root porosity of 0.82 was obtained from the relation between root dry mass density and root bulk density using pycnometers. The spatially distributed fractions of root water contents were compared with those of the water in capillary pores of the soil matrix. Water inside roots was mostly below 2–5% of total soil water content; however, locally near the plant rows it was up to 20%. The results suggest that soil moisture in roots should be separately considered. Upon drying, the relation between the soil and root water may change towards water remaining in roots. Relations depend especially on soil water retention properties, growth stages, and root distributions. Gravimetric soil water content measurement could be misleading and TDR probes providing an integrated signal are difficult to interpret. Root effects should be more intensively studied for improved field soil water balance calculations. Presented at the International Conference on Bioclimatology and Natural Hazards, Pol’ana nad Detvou, Slovakia, 17–20 September 2007.     

Effect of psyllium husk and wheat mill bran fractions on the microstructure and mixograph characteristics of Arabic bread

When psyllium husk, wheat bran and germ was added, Incorporation of psyllium and wheat bran may affect the dough structure, dough rheology as well as the final quality of baked Arabic flat bread, which, thus, became important for this study. Scanning Electron Micrographs (SEM) taken on Arabic bread, depicted both intact small and the large starch granules on the outer crust area. This was mainly due to the rapid loss of moisture from the Arabic bread surface during intense baking operation leaving less moisture for gelatinization to take place. With psyllium added to WWF at 0, 3, and 5 % level, the peak time was increased from 3 to 4.5 min. The ascending and descending angle values were more or less identical in all the samples except with wheat germ addition, whereas much lower values (51 to 58°) for these parameters were observed, indicating a faster rate of dough breakdown. With psyllium, fine- and coarse bran addition to WWF, a corresponding increase in peak time was observed. Ascending and descending angles showed similar trends to that of the WWF and psyllium combinations. Use of falling number apparatus is an indirect method of measuring the diastatic enzyme activity in cereal flours. WGF showed lower falling-number values (502 s) than the WWF (607 s). Addition of fine bran to WWF lowered the falling number (607 to 563 s) whereas with coarse wheat bran and germ, these values were increased.     

High-level expression of the <Emphasis Type="Italic">Penicillium notatum</Emphasis> glucose oxidase gene in <Emphasis Type="Italic">Pichia pastoris</Emphasis> using codon optimization

The glucose oxidase (GOD) gene from Penicillium notatum was expressed in Pichia pastoris. The 1,815 bp gene, god-w, encodes 604 amino acids. Recombinant GOD-w had optimal activity at 35–40°C and pH 6.2 and was stable, from pH 3 to 7 maintaining >75% maximum activity after incubation at 50°C for 1 h. GOD-w worked as well as commercial GODs to improve bread making. To achieve high-level expression of recombinant GOD in P. pastoris, 272 nucleotides involving 228 residues were mutated, consistent with the codon bias of P. pastoris. The optimized recombinant GOD-m yielded 615 U ml⁻¹ (2.5 g protein l⁻¹) in a 3 l fermentor—410% higher than GOD-w (148 U ml⁻¹), and thus is a low-cost alternative for the bread baking industry.     

Characteristic coloring curve for white bread during baking

The effect of heating conditions on the crust color formation was investigated during the baking of white bread. The surface temperatures were monitored with thermocouples attached to the inside surface of the loaf pan cover. The trace of the surface color in the L(*)a(*)b(*) color coordinate system is defined as the characteristic coloring curve. The overall baking process was classified into the following four stages based on the characteristic coloring curve: i) pre-heating (surface temperature < 110 °C), ii) Maillard reaction (110-150 °C), iii) caramelization (150-200 °C), and iv) over-baking (surface temperature>200 °C). A linear relationship was observed between the L(*) decrease and the increase in weight loss of a sample at each oven air temperature. The L(*) value appeared to be suitable as an indicator to control the surface color by baking conditions.     

Characteristic vibration patterns of odor compounds from bread-baking volatiles upon protein binding: density functional and ONIOM study and principal component analysis

As the mechanism underlying the sense of smell is unclear, different models have been used to rationalize structure–odor relationships. To gain insight into odorant molecules from bread baking, binding energies and vibration spectra in the gas phase and in the protein environment [7-transmembrane helices (7TMHs) of rhodopsin] were calculated using density functional theory [B3LYP/6-311++G(d,p)] and ONIOM [B3LYP/6-311++G(d,p):PM3] methods. It was found that acetaldehyde (“acid” category) binds strongly in the large cavity inside the receptor, whereas 2-ethyl-3-methylpyrazine (“roasted”) binds weakly. Lys296, Tyr268, Thr118 and Ala117 were identified as key residues in the binding site. More emphasis was placed on how vibrational frequencies are shifted and intensities modified in the receptor protein environment. Principal component analysis (PCA) suggested that the frequency shifts of C–C stretching, CH₃ umbrella, C = O stretching and CH₃ stretching modes have a significant effect on odor quality. In fact, the frequency shifts of the C–C stretching and C = O stretching modes, as well as CH₃ umbrella and CH₃ symmetric stretching modes, exhibit different behaviors in the PCA loadings plot. A large frequency shift in the CH₃ symmetric stretching mode is associated with the sweet-roasted odor category and separates this from the acid odor category. A large frequency shift of the C–C stretching mode describes the roasted and oily-popcorn odor categories, and separates these from the buttery and acid odor categories.     

Diversity and productivity of plant communities across the Inland Northwest,USA

No definitive explanation for the form of the relationship between species diversity and ecosystem productivity exists nor is there agreement on the mechanisms linking diversity and productivity across scales. Here, we examine changes in the form of the diversity–productivity relationship within and across the plant communities at three observational scales: plots, alliances, and physiognomic vegetation types (PVTs). Vascular plant richness data are from 4,760 20 m² vegetation field plots. Productivity estimates in grams carbon per square meter are from annual net primary productivity (ANPP) models. Analyses with generalized linear models confirm scale dependence in the species diversity–productivity relationship. At the plot focus, the observed diversity–productivity relationship was weak. When plot data were aggregated to a focus of vegetation alliances, a hump-shaped relationship was observed. Species turnover among plots cannot explain the observed hump-shaped relationship at the alliance focus because we used mean plot richness across plots as our index of species richness for alliances and PVTs. The sorting of alliances along the productivity gradient appears to follow regional patterns of moisture availability, with alliances that occupy dry environments occurring within the increasing phase of the hump-shaped pattern, alliances that occupy mesic to hydric environments occurring near the top or in the decreasing phase of the curve, and alliances that occupy the wettest environments having the fewest species and the highest ANPP. This pattern is consistent with the intermediate productivity theory but appears to be inconsistent with the predictions of water–energy theory.     

Effects of High-voltage Electric Field Treatment on the Water Activity of Bread

Treating bread dough by a high-voltage electric field (HVEF) during the first fermentation enabled the bread dough to retain water in the gluten fibers. The microstructure of the gluten fibers was still visible even with an HVEF treatment at 50 kV for 20 min, but could no longer be observed when the gluten was treated for more than 30 min. The crumb temperature of the HVEF treated bread during baking began to rise a few minutes sooner than that of the untreated bread, but the maximum temperature reached was the same in both cases: 99°C. The fact that the water activity of the HVEF-treated bread was 0.987 ± 0.0056, being higher than that of the untreated bread by 0.011, is in good agreement with the growing tests of Rhizopus nigricans. Furthermore, a distinct decrease in the water loss of the baked gluten was observed after the HVEF treatment. These results suggest that the HVEF treatment increased the ability of the gluten fibers, rather than the starch granules, to absorb and retain water; the state of the remaining water is considered to have become immobile, so that migration of moisture to the starch granules in the bread could be minimized.     

Responses of nematode communities to different land uses in an aquic brown soil

An analysis of the seasonal and vertical distribution of soil nematode communities under three contrasting land uses, i.e., cropland, abandoned cropland and woodland was conducted in an aquic brown soil. The results showed that different land-use types affected the spatiotemporal distribution of soil nematodes and their dominant genera, and different dominant genera showed different responses to land use. In the abandoned cropland and woodland, most dominant genera were present in the 0–20 cm layers and Chiloplacus was mainly distributed in the 5–30 cm layers, while in the cropland, Pratylenchus exhibited an even distribution from the 0–5 cm to the 40–50 cm depth. Soil environmental parameters under different land use could influence soil nematodes; soil porosity, total organic C, total N and the C/N ratio could positively influence the abundance of some dominant genera. Faunal profiles revealed that environmental stability and the homeostasis in the abandoned cropland and woodland lead to higher levels of community structure, and the soil food web tends to succeed to maturity. Nematode faunal analyses are a useful indicator for interpreting the stress and/or nutrient conditions under different land uses. __________ Translated from Biodiversity Science, 2007, 15(2): 172–179 [译自:生物多样性]     

Modeling the Effect of Glucose Syrup on the Moisture Sorption Isotherm of Figs

Moisture sorption isotherms of figs with and without glucose syrup (at 20% and 40%, w/w) were determined at 5 °C, 25 °C, and 40 °C. A static gravimetric method was used under 0.11–0.84 water activity ranges for the determination of sorption isotherms that were found to be typical type ΙΙΙ for control sample. The inclusion of glucose syrup had significant effects on the sorption isotherms, and the moisture content of samples at each a _w decreased with increasing temperature. The experimental data were fitted well with two-parameter Brunauer–Emmet–Teller, three-parameter Guggenheim–Anderson–de Boer, and four-parameter Peleg models that all had R ² of greater than 0.99. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation from the equilibrium data at different temperatures. It was found that the addition of glucose syrup significantly increased the amount of monolayer water and the isosteric heat of sorption. Both water activity and isosteric heat of sorption increased with glucose syrup level and the shape and status of sorption isotherms tend to change toward the typical sigmoid shape of most food systems.     

Muscle contraction history: modified Hill versus an exponential decay model

In recent years, it has been recognised that improvements to classic models of muscle mechanical behaviour are often necessary for properly modelling co-ordinated multi-joint actions. In this respect, the purpose of the present study was to improve on modelling stretch-induced force enhancement and shortening-induced force depression of muscle contraction. For this purpose, two models were used: a modified Hill model and a model based loosely on mechano-chemistry of the cross-bridge cycle (exponential decay model). The models were compared with a classic Hill model and experimental data. Parameter values were based, as much as possible, on experimental findings in the literature, and tested with new experiments on the gastrocnemius of the rat. Both models describe many features of slow-ramp movements well during short contractions (300–500 ms), but long-duration behaviour is described only partly. The exponential decay model does not incorporate a force–velocity curve. Therefore, its good performance indicates that the status of the classic force–velocity characteristic may have to be reconsidered. Like movement-induced force depression and enhancement, it seems a particular manifestation of time-dependent force behaviour of muscle, rather than a fundamental property of muscle (like the length–tension curve). It is argued that a combination of the exponential decay model (or other models based on the mechano-chemistry of contraction) and structurally based models may be fruitful in explaining this time-dependent contraction behaviour. Furthermore, not in the least because of its relative simplicity, the exponential decay model may prove more suitable for modelling multi-joint movements than the Hill model. Received: 19 March 1999 / Accepted in revised form: 9 June 2000     

Development and validation of computational fluid dynamics models for prediction of heat transfer and thermal microenvironments of corals

We present Computational Fluid Dynamics (CFD) models of the coupled dynamics of water flow, heat transfer and irradiance in and around corals to predict temperatures experienced by corals. These models were validated against controlled laboratory experiments, under constant and transient irradiance, for hemispherical and branching corals. Our CFD models agree very well with experimental studies. A linear relationship between irradiance and coral surface warming was evident in both the simulation and experimental result agreeing with heat transfer theory. However, CFD models for the steady state simulation produced a better fit to the linear relationship than the experimental data, likely due to experimental error in the empirical measurements. The consistency of our modelling results with experimental observations demonstrates the applicability of CFD simulations, such as the models developed here, to coral bleaching studies. A study of the influence of coral skeletal porosity and skeletal bulk density on surface warming was also undertaken, demonstrating boundary layer behaviour, and interstitial flow magnitude and temperature profiles in coral cross sections. Our models compliment recent studies showing systematic changes in these parameters in some coral colonies and have utility in the prediction of coral bleaching.