Release of exchangeable and non-exchangeable magnesium from nigerian soils on cropping with maize or chemical extraction

A greenhouse experiment with maize (Zea Mays L.) using 12 representative soils of Western Nigeria indicated that the rate of release of non-exchangeable Mg was too slow to meet crop requirements. Total Mg removed by four successive crops of maize (y) was well correlated with initial exchangeable Mg (x) (y = 6.34 + 1.06 x, r = 0.996***) suggesting that neutral N NH₄OA c-extractable Mg is the best measure of available Mg in these soils even under intensive cropping. The slow release of non-exchangeable-extractable Mg in the soils may be due to low percentages of silt and clay and their mineralogy. Total and non-exchangeable Mg extracted by acidified N NH₄OA c (pH 1.0) in 15 min at a soil extractant ratio of 1:5 correlated best with the total and non-exchangeable Mg removed by cropping (r = 0.944*** and 0.734*** respectively). The use of such an acid extractant on these soils is, however, open to question in view of the relatively large amounts of non-exchangeable Mg extracted by it compared with that extracted by cropping. Incipient Mg deficiency symptoms appeared in two-week-old plants when they contained 0.11–0.15% Mg. Persistent deficiency symptoms were associated with 0.1% Mg in the plants, 21–22 parts/10⁶ exchangeable Mg and 5% (or less) Mg saturation of CEC.     

Aqua regia extractable selenium concentrations of some Scottish topsoils measured by ICP‐MS and the relationship with mineral and organic soil components

BACKGROUND: To provide information concerning the geographical distribution of selenium (Se) in the soils of Scotland, we analysed 47 arable soils selected on the basis of their parent rock, which were expected to have relatively high, low or unclassified Se concentrations. To investigate relationships between the actual minerals in the soils and the aqua regia extractable Se concentration of the soil, soil minerals were quantified by X‐ray diffraction. RESULTS: The aqua regia extractable Se concentrations of the soils were between 0.19 and 1.46 mg kg^?1. No simple correlation between the aqua regia extractable Se concentrations of the soil and the parent rock classification estimated by soil survey was evident. Partial least squares analysis revealed that the aqua regia extractable Se concentration of the soils was positively related to loss on ignition (LOI) or C concentration and negatively related to the K‐feldspar concentration, with other minerals being less important. CONCLUSION: The Se concentration of arable topsoils from Scotland is more related to LOI or carbon concentration, with parent material being less important. Copyright © 2010 Society of Chemical Industry     

Laboratory measurements of dry deposition of sulphur dioxide on to several soils from England and Wales

A laboratory method for measuring the dry deposition of sulphur dioxide (SO₂) on to soils is described. The effect of soil type on deposition velocity (v_g) was examined using samples of soils collected from 16 sites in England and Wales. Although the values of v_g measured for soils at field capacity did not differ significantly they were related to soil pH; thus they ranged from 0.422 cm s^?1 at pH 4.5 to 0.648 cm s^?1 at pH 7.5. Oven drying reduced v_g from an average value of 0.535 cm s^?1 for soils at field capacity to 0.264 cm s^?1. A large proportion of deposited SO₂ was recovered from the soil as sulphate S. At an atmospheric concentration of 36 μg SO₂ m^?3, about the mean for Great Britain, the input of sulphur through this process would be 10 kg ha^?1 in a 4-month fallow period.     

Estimation of Contributions of Hydration and Glass Transition to Heat Capacity Changes During Melting of Native Starches in Excess Wate

Contributions of the heat capacity changes by hydration (Δ_mC_p^hydr) and by glass transition (Δ_mC_p^gtr) to the heat capacity changes (Δ_mC_p^exp) measured during melting of various native starches in excess water were estimated. Whereas Δ_mC_p^gtr was independent of the origin and polymorphous structure of the starches, Δ_mC_p^hydr depended on the origin of starch. It is shown that Δ_mC_p^exp of native starches can be calculated as the sum Δ_mC_p^gtr and Δ_mC_p^hydr. Calculated values of Δ_mC_p^gtr (12.5 ± 2.8 Jmol⁻¹ K⁻¹) were similar to those of synthetic polymers. The values of Δ_mC_p^hydr of all investigated starches varied from 10.7 to 18.5 Jmol⁻¹ K⁻¹ except for maize starch (56.1 Jmol⁻¹ K⁻¹). It is suggested that this difference is due to special structural features of maize starch.     

Phase Transitions and Unfreezable Water Content of Carrots, Reindeer Meat and White Bread Studied using Differential Scanning Calorimetry

Differential scanning calorimetry was used to measure the phase transitions and unfreezable water of carrots, reindeer meat, and white bread. The incipient melting point (T_im), incipient intensive melting point (T′_im), the onset temperature of melting (T_m), latent heat of melting (ΔH_m), specific heat (C_p) and enthalpy (ΔH) were determined from the melting curves. T′_im, T_mΔH_m and ΔH and the unfreezable water were found to be functions of moisture. The T_im, temperatures were ? 39°C, ?33°C, ?40°C; T′_im, ?11.8°C, ?13.3°C ?17.3°C T_m, ? 3.4°C, ? 3.1°C, ? 12.2°C for carrot, reindeer meat, and white bread, respectively. The unfreezable water was 8.3% for carrots, 15.1% for reindeer meat, and 22.5% for white bread, determined from ΔH_m and 3.4%, 6.4% and 2.9%, determined from ΔH. The lowest water detectable from ΔH_m was 26.4% and from ΔH 3.6%.     

Sorption of three tetracyclines by several soils: assessing the role of pH and cation exchange

Tetracyclines (TCs) are widely used in veterinary medicine for treatment and prevention of disease and are present in animal waste products. Detection of TCs in soil, sediments, and water, and the growing concern of their potentially adverse effect on natural ecosystems have resulted in a need to understand their behavior in aqueous soil systems. TCs have multiple ionizable functional groups such that at environmentally relevant pH values, they may exist as a cation (+ 0 0), zwitterion (+ - 0), or a net negatively charged ion (+ - -), which complicates predicting their sorption, availability, and transport. We investigated the sorption of oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) by several soils varying in pH, clay amount and type, cation exchange capacity (CEC), anion exchange capacity (AEC), and soil organic carbon in 0.01 N CaCl2, 0.001 N CaCl2, and 0.01 N KCI. All three TCs are highly sorbed, especially in acidic and high clay soils. When normalized to CEC, sorption tends to decrease with increasing pH. A sorption model in which species-specific sorption coefficients normalized to pH-dependent CEC (Kd+00, kd+-0, and kd+--) and weighted by the pH-dependent fraction of each species fit the data well across all soils except for a soil rich in gibbsite and high in AEC. Resulting kd+00 values were more than an order of magnitude larger than values for either kd+0 and kd+--values such that kd+00 alone described most of the sorption observed as a function of pH for eight soils that varied in their mineralogy and pH (pH ranged from 4 to 8).     

Leaching losses of nutrients and yield and nutrient uptake by container-grown begonia as affected by lime and fertiliser applications to a peat medium

The effect of increased lime applications and one rate of soluble basal fertiliser on leaching losses of NH₄-N, NO₃-N, P, Ca, Mg and K from peat in containers was studied in the presence or absence of Begonia semperflorens plants in a greenhouse pot experiment. Percentage recoveries (leached, plus extractable nutrient remaining in the peat, plus plant uptake) of mineral N and P were in the range of 60–80% while those for Ca, Mg and K ranged from 95 to 111%. Percentage leaching losses in the absence of plants were: mineral N, 75–76%; P, 59–74%; Ca, 5–7%; Mg, 14–19%; and K, 17–31%. In the presence of plants, the average decrease in the percentage loss of nutrients by leaching was: N, 9.3%; P, 4.4%; Ca, 0.5%; Mg, 0.3%; and K, 1.3% Liming tended to decrease leaching losses of NH₄-N, P, Ca and Mg but increase those of K and NO₃-N. The phosphate adsorption capacity of the peat was not measurable but significant ammonia fixation from added (NH₄)2SO₄ was demonstrated at high pH (>6.5) concomitant with high N rates (> 300 g N m^?3). Effective cation-exchange capacity (CEC) and CEC measured with unbuffered 1m NH₄CI were both more than doubled with increased lime additions as the pH of the peat increased from 4.3 to 5.6. The conventional CEC measurement (NH₄OAc, pH 7.0) and BaCl₂-TEA (pH 8.2) CEC both remained unaffected by the initial lime rates, and both greatly overestimated the CEC of the peat at its unbuffered pH.     

Differential scanning calorimetric studies of Philippines natural grade κ-carrageenan

Using differential scanning calorimetry, the gel-sol transition temperatures were compared for KCl-precipitated κ-carrageenan and Philippines natural grade (PNG) κ-carrageenan. The latter contains cellulose, which is associated with the carrageenan in seaweed. This leads to lower gel-sol transition temperatures. More heat absorption (-ΔH_m = 79 kJ/mol) is required for the formation of junction zones for the PNG κ-carrageenan than the KCl-precipitated κ-carrageenan (-ΔH_m = 40 kJ/mol). This behaviour can be attributed to the cellulose interspersing between κ-carrageenan aggregates in the PNG κ-carrageenan gels.     

Possibilities of enhancing the colour of egg yolk

BACKGROUND: This study attempts to compare two possibilities of enhancing the colour of egg yolk. One of them is based on the ecological rearing of laying hens on natural green grass whereas the other uses a feeding dose supplemented with natural pigments in laying hens reared in individual cages. Is it possible to distinguish these two technologies using yolk colour determination in the CIELAB system? RESULTS: Yolk colour parameters such as L*, a*, and b* in the group of grazed hens are significantly different (α = 0.001) from those observed in hens reared in cages. The yolk colour shows a darker, redder and more yellow colour. The greatest difference was seen in the red colour parameter, a*, that increased more than twice. Visually, this means a shift towards a more orange colour. Compared to grazing in the meadow (ΔE* = 13.257), the addition of artificial pigments in the feed resulted in a more significant increase in the parameter ΔE* (CIE total colour difference), with the greatest value of ΔE* being observed with the use of both pigments (ΔE* = 24.265). CONCLUSION: Grazing increases the parameter a* whereas the values of the parameter C*_ab remain relatively low. The parameter ΔE* is significantly lower in the case of grazing as compared to the supplementation of the feed with pigments. However, colourity parameters cannot be used as a specific standard to identify a particular grazing technology as their values vary during the laying period. Copyright © 2011 Society of Chemical Industry     

Thermal and Molecular Characterization of Aspergillus awamori Glucoamylase Catalytic and Starch‐Binding Domains

Aspergillus awamori glucoamylase catalytic domain, linker, and starch‐binding domain, the first and third expressed from yeast, have molecular masses of 56.2, 12.6 and 12.9 kDa, respectively, as determined by MALDI‐TOF mass spectroscopy, and have 10.2, 73.2 and 7.0 % (w/w) carbohydrate, respectively, showing overglycosylation by yeast. Unfolding of the starch‐binding domain monitored by circular dichroism is reversible at pH 6.0—8.0, with the unfolding T_m and ΔH increasing from 49.7 to 58.5 °C and from 284 to 351 kJ/mol, respectively, as pH decreases from 8.0 to 6.0. The catalytic domain unfolds irreversibly at pH 7.5, producing a single asymmetric endotherm by differential scanning calorimetry, with T_m and ΔH at a 1 °C/min heating rate being 60.9 °C and 1720 kJ/mol, but with both increasing as the heating rate increases. This suggests that unfolding is partially under kinetic control, while various tests show that it does not follow a simple two‐state irreversible model. Values of ΔH from calculated solvent‐accessible surface areas of unglycosylated catalytic and starch‐binding domains are about 100 kJ/mol lower than experimentally determined ΔH values of the corresponding glycosylated domains, showing the effect of glycosylation on unfolding enthalpies.     

Kinetics of colour development in aqueous fructose systems at high temperatures

Non‐enzymatic browning was studied in aqueous model systems containing fructose and aspartic acid, glutamic acid or asparagine at three different soluble solid concentrations (150, 300 and 450 g kg⁻¹), which were heat treated for different times at four temperatures (85, 90, 95 and 100 °C). Various indicators were used to evaluate the extent of the Maillard reaction: spectrophotometric measurements at 280 and 420 nm (A₂₈₀ and A₄₂₀) and CIE (Commission Internationale de l'Eclairage) parameters L* (lightness), a* (redness), b* (yellowness) and ΔE* (colour difference, which is expressed as [(Δa*)² + (Δb*)² + (ΔL*)²]^1/2). The pH and the formol index were also determined. The indicator for colourless intermediate formation, A₂₈₀, showed that the kinetic constant values increased with increasing heat treatment temperature, while the influence of soluble solid concentration was not clear. After a short induction period the data were well described by assuming zero‐order kinetics. Glutamic acid turned out to be the most reactive amino acid, while asparagine was the least reactive. With reference to brown pigment formation, A₄₂₀ and ΔE*, glutamic acid was the least reactive amino acid. In all the experiments assayed, except for glutamic solutions with fructose concentrations of 150 and 300 g kg⁻¹, the data were best correlated with combined kinetics. © 2000 Society of Chemical Industry     

Desorption isotherms and thermodynamic properties of sweet corn cultivars (Zea mays L.)

The desorption isotherms and thermodynamic properties of two cultivars of sweet corn were obtained during the drying process of these products. The isotherms were determined by a dynamic method for various temperature and humidity conditions. Equilibrium moisture content (X_eq) data were correlated by the Guggenheim–Anderson–de Boer model and an artificial neural network (ANN) model. These models were fitted to the experimental data. The X_eq for corn grain increased with an increase in the relative humidity at fixed temperature and decreased with an increase in temperature at a constant relative humidity. The experimental data were analysed by a thermodynamic approach to obtain the isosteric heat of desorption (ΔH), differential entropy (ΔS), activation energy (E_a) and Gibbs free energy (ΔG). The ΔH and ΔS increased with a decrease in moisture content, while ΔG decreased exponentially with an increase in X_eq. The Arrhenius equation was used to obtain E_a values, with Supersweet corn having higher E_a.     

Influence of the season on the relationships between NMR transverse relaxation data and water‐holding capacity of turkey breast meat

In the last few years the poultry industry has seen a significant deterioration in meat quality properties during the summer season. The objective of this study was to evaluate the seasonal effect (summer and winter) on turkey meat quality assessed by both conventional and low‐resolution nuclear magnetic resonance (LR‐NMR) analysis. Eighty‐eight breast muscle samples (35 winter and 53 summer) from BUT‐Big 6 turkeys belonging to 16 different flocks, were randomly collected from a commercial processing plant. The samples were analysed for transverse relaxation times (T₂) by LR‐NMR and for initial pH (15 min post mortem), ultimate pH (24 h post mortem) and pH after cooking, temperature at 15 min post mortem, water‐holding capacity (WHC, drip loss, filter paper press wetness and cooking loss) at 24 h post mortem, colour of raw and cooked meat and chemical composition (moisture, lipids and proteins). The results indicate that, during the summer season, turkey breast meat undergoes a relevant WHC decrease. Cluster analysis of the raw LR‐NMR data evidenced the presence of two groups corresponding to samples harvested in each different season. Correlations between the LR‐NMR signal and the conventional parameters measuring WHC were obtained by a recently proposed type of principal component regression (PCR) termed relative standard deviation PCR. Copyright © 2004 Society of Chemical Industry     

Effects of methylcellulose,xanthan gum and carboxymethylcellulose on thermal properties of batter systems formulated with different flour combinations

The functionalities of hydrocolloid–flour mixtures in terms of the thermal properties of their resulting batter systems were investigated, and the effects of different thermal processes such as cooking–freezing–thawing (CFT) and freezing–cooking (FC) on thermal properties of the various batter systems were determined in this study. Differential scanning calorimetry (DSC) was used to determine thermal property parameters including gelatinization temperature (T_G), total enthalpies of gelatinization (ΔH_G), glass transition temperature (T_g), melting peak temperature (T_m), and total melting enthalpies (ΔH_m). The different thermal processes did not significantly affect either T_G or ΔH_G of batter systems, but they influenced the glass transition behavior and the ΔH_m of batter systems. The thermal processes also showed different effects on the batter systems containing different hydrocolloids such as methylcellulose (MC), carboxymethylcellulose (CMC), and xanthan gum (XG). The hydrocolloids shifted T_G upwards, depressed T_g, and increased T_m of batters. The effect of these hydrocolloids on glass transition temperature was more pronounced in raw samples (FC process) than in cooked samples and increased with increasing levels of CMC and MC used in the formulations. Batters with MC showed increased ΔH_m for all the thermal processes. CMC only showed significant effect on ΔH_m for cooked samples (CFT process). MC and CMC showed more pronounced effects on T_g for raw uncooked rice- and corn flour-based batters than on raw uncooked wheat flour-based batters. However, this special effect was not obvious in the batters containing 0.2% XG.     

Study of Thermal Properties of Oat Globulin by Differential Scanning Calorimetry

The thermal behavior of oat globulin was studied by differential scanning calorimetry (DSC). The effects of pH, salts, and of various structure perturbants upon thermal characteristics were determined. Raising or lowering pH from near neutrality reduced denaturation temperature. (T_d), enthalpy (ΔH) and cooperativity indicated by increase in width at half height (ΔT_1/2). The effect of salts on thermal stability was related to their position in the lyotrophic series and suggests involvement of hydrophobic interaction in the thermal stability of oat globulin. Increasing concentrations of urea progressively lowered T_d and ΔH and increased ΔT_1/2; sodium dodecyl sulfate (SDS) lowered ΔH without affecting T_d; ethylene glycol (EC) lowered T_d without changing ΔH. Dithiothreitol did not affect DSC characteristics suggesting that disulfide bonds do not contribute to the thermal response of oat globulin.     

Effect of lime on the dissolution of two phosphate rocks in acid soils

The effect of pH and calcium (Ca) on the dissolution of Gafsa (GPR) and Christmas Island A (CIPR) phosphate rocks (PR) was examined in closedincubation and open-leaching systems in six acid, Malaysian soils. The pH of the soils was increased to between 4.5 and 6.1 by incubating with calcium carbonate (CaCO₃); soil was also incubated with calcium chloride (CaCl₂) to provide equivalent amounts of Ca without causing any marked change in pH. In the closed-incubation system, dissolution of reactive GPR was overall higher (11–70%) than for the less reactive CIPR (12–43%) after 60 days of incubation. Dissolution of PR decreased with increasing levels of CaCO₃ or CaCl₂, but the decrease was more pronounced in CaCO₃-treated than in CaCl₂-treated soils. Increasing additions of CaCl₂ decreased the size of the available sink for Ca from 84.0 to 0 mmol (+) kg^–1 soil. Although the addition of CaCO₃ increased the cation-exchange capacity (CEC) of these variable-charge soils (from 23.0 to 199.0 mmol (+) kg^–1 soil), most of the newly-created exchange sites were occupied by Ca added through CaCO₃. This was responsible for the decrease in size of the sink for Ca. Addition of CaCO₃ also decreased the proton supply from 260.7 to 0 mmol (+) kg^–1 soil, which in conjunction with the decrease in size of the Ca sink decreased the dissolution of PR. The effect of CaCO₃ and CaCl₂ on PR dissolution varied between soils and was related to pH-buffering and the Ca-sink size. In an open-leaching system, large amounts of Ca (8–40%) added as CaCO₃ were removed in the leachate and hence the decrease in GPR dissolution with CaCO₃ addition was less in the open-leaching than in the closed-incubation system.     

The fertiliser nitrogen requirement of cereals grown on sandy soils

The responses to fertiliser‐N of winter wheat and winter barley grown on sandy soils were measured in 72 experiments in England from 1990 to 1994. Yield without fertiliser‐N (Y₀) was c 1.1 t ha⁻¹ greater following root crops than following cereals. Following potato crops given organic manures, Y₀ was c 1.2 t ha⁻¹ greater than following unmanured potato crops, but Y₀ was no greater following sugarbeet to which organic manures had been applied. Only after the two driest winters was there sufficient variation in soil N supply in spring (SNS_s) for this to show a relationship with Y₀. However, Y₀ increased with increasing N mineralisation during the growing season (AM) in the three years it was measured. There was no consistent effect of sowing date on Y₀. Following potatoes, yield at optimum fertiliser‐N (Y_opt) decreased as sowing date was delayed, but this was not so after cereals, sugarbeet or overall. There was no increase in Y_opt with SNS_S or AM, but Y_opt decreased with increasing moisture stress (S) in June. The mean yield response to N_opt (Δ_Y) was c 0.4 and 0.8 t ha⁻¹ smaller following potatoes and sugarbeet respectively than following cereals, but not consistently so as there were large interactions between site, year and previous crop. Following root crops, Δ_Y was c 0.6 and 1.4 t ha⁻¹ less after sugarbeet and potatoes respectively that had been given organic manures. Without the addition of organic manures, Δ_Y following potatoes was similar to that following cereals. Regression on SNS_S and AM accounted for 28 and 15% respectively of the variance in Δ_Y. The optimum economic fertiliser‐N application (N_opt) was similar, at c 140 kg ha⁻¹, following cereals and potatoes. Following sugarbeet, cereal N_opt was only c 110 kg ha⁻¹. The differences according to previous crop reported here are consistent with mineralisation of crop residues on sandy soils being more rapid than on other soils; the potato residues were rapidly mineralised in autumn and lost by leaching over winter. Residues from later‐harvested sugarbeet were mineralised during the growing season of the subsequent cereal crop. Fertiliser‐N requirements were, at c 110–140 kg ha⁻¹, smaller than has been found on other soil types, and less than current recommendations for wheat. Requirements were significantly reduced in years of drought stress. No differences were found in N_opt between wheat and barley. These data do not justify the current advice to invariably reduce fertiliser‐N to cereals following potatoes by 20–25 kg ha⁻¹ on these sandy soils. On average a reduction of c 20 kg ha⁻¹ could be made following sugarbeet, with a further reduction of c 40 kg ha⁻¹ N if manures had been applied to the previous sugarbeet crop. A reduction of 40 kg ha⁻¹ N could also be made where cereals followed a potato crop to which manures had been applied. Further refinements on the basis of measurements of soil mineral N could not be justified. Seasonal variation in N response due to drought stress makes recommendations difficult on these soils. Adopting the fertiliser‐N recommendations proposed here would produce N surpluses to the soil of c 37, 10 and 27 kg ha⁻¹ respectively following cereals, sugarbeet and potatoes when cereal grain is removed but straw incorporated. On farms where straw is removed, N surplus would be largely eliminated. Our recommendation that no reduction in fertiliser‐N application to cereal crops grown on sandy soils should be made following potatoes will not increase fertiliser‐N use and is not expected to increase nitrate leaching. Some reduction in nitrate leaching may be achieved if recommendations following cereal crops and sugarbeet are made in accordance with the results reported here. © 2000 Society of Chemical Industry     

Comparison of chemical tests for estimation of the availability of soil zinc

Tests for determining the availability of soil Zn were evaluated by simple and multiple correlation analysis. The soil tests included total Zn, and Zn extractable from soil by 0.2 M MgSO₄, 0.1 N HCl or dithizone. In simple correlation analyses, each of the tests correlated significantly with the uptake of soil Zn by maize (Zea mays L.) plants grown in the glasshouse. The predictions were improved significantly with all tests by the inclusion of one or more of the soil variables, pH and clay and organic matter contents, in multiple correlation analyses. The plant uptake of soil Zn could best be predicted from a multiple regression equation which included soil pH and logarithmic functions of 0.1 N HCl-extractable Zn and soil clay content as the independent variables.     

Prediction of the fertiliser needs of sugar-beet grown on fen peat soils

The fertiliser requirements of sugar-beet grown on fen soils were tested in 52 experiments from 1963 to 1969. In some fields, N.P.K and Na and, especially N and P, greatly increased yields, but the average responses obtained with the four elements were small. To help to predict where and how much fertiliser was needed for sugar-beet, soils were grouped according to soil analysis and classified by loss on ignition. Sugar-beet grown on soils with less than 20 μg/ml P (extracted with sodium bicarbonate) needed 1·20 cwt/acre P₂O₅, with 21–45 μg/ml P, 0·75 cwt/acre P₂O₅, and with more than 45 μg/ml P no fertiliser was required. Most soils contained high concentrations of K; with less than 100 μg/ml K (extracted with ammonium nitrate), 2·00 cwt/acre P₂O was probably justified; with 100–250 μg/ml, 1·00 cwt/acre K₂O was needed. Most of the responses to agricultural salt were by crops on soils with exchangeable sodium concentrations of less than 30 μg/ml Na. Loss on ignition was related to response to N fertiliser; when the loss was 14–25%, N increased yield by 6 cwt/acre sugar and 1·2 cwt/acre N fertiliser was Heeded and when the loss was 26–35%, the yield was increased by 3·5 cwt/acre and 0·6 cwt/acre N was needed. With greater losses there was little response.