Structural Modification of Gluten Proteins in Strong and Weak Wheat Dough as Affected by Mixing Temperature

The effects of temperature (≥25°C) on dough rheological properties and gluten functionality have been investigated for decades, but no study has addressed the effect of low temperature (<30°C) on gluten network attributes in flours with strong and weak dough characteristics. This study monitored changes in protein extractability in the presence and absence of reducing agents, the contents of readily accessible and SDS‐accessible thiols, and the secondary structural features of proteins in doughs from commercial hard wheat flour (HWF) and soft wheat flour (SWF) mixed at 4, 15, and 30°C. SWF mixed at 4 and 15°C showed similar mixing properties as HWF mixed at 30°C (which is the standard temperature). The effect of mixing temperature is different at the molecular level between the two flours studied. Protein features of HWF did not change as mixing temperature decreased, with the only exception being an increase in SDS‐accessible thiols. Decreasing mixing temperature for SWF caused an increase in SDS protein solubility and SDS‐accessible thiols as well as an increase in β‐turn structures at the expense of β‐sheet structures. Thus, noncovalent interactions appear to drive protein network at low temperatures (4 and 15°C), whereas covalent interactions dominate at standard mixing temperature (30°C) in doughs from both flours.     

Effect of Exogenous Lipase on Dough Lipids During Mixing of Wheat Flours

In control dough, endogenous wheat lipase was inactive, because the triacylglycerol (TAG), 1,2-diacylglycerol (DAG_1,2), and 1,3-diacylglycerol (DAG_1,3) fractions of nonpolar lipids were not affected by mixing. Conversely, the free fatty acid (FFA) and monoacylglycerol (MAG) fractions decreased, mainly due to the oxidation of polyunsaturated fatty acids (PUFA) catalyzed by wheat lipoxygenase. Addition of exogenous lipase to flour (15 lipase units [LU] per gram of dry matter) resulted in substantial modification of nonpolar lipids during dough mixing. Due to the 1,3 specificity of the lipase used in this experiment, the TAG and DAG_1,3 fractions decreased, whereas the MAG and FFA fractions increased. The DAG_1,2 fraction increased at the beginning of mixing and decreased after 40 min of mixing. Moreover, part of the PUFA released by lipase activity was oxidized by wheat lipoxygenase, resulting in major losses of PUFA. Conversely, the net content of the saturated and monounsaturated fatty acids (SMUFA) remained constant, because the free SMUFA content increased primarily at the expense of the esterified forms. For a constant mixing time of 20 min, increasing the amount of lipase added to dough (from 2.5 to 25 LU/g of dry matter) resulted in a linear decrease in the TAG fraction and a linear increase in the SMUFA content in the FFA fraction. At the same time, the PUFA content of the FFA fraction increased only for additions of lipase to flour of >5 LU/g of dry matter, due to partial oxidation by wheat lipoxygenase.     

Stress Relaxation Behavior of Wheat Dough,Gluten, and Gluten Protein Fractions

Relaxation behavior was measured for dough, gluten and gluten protein fractions obtained from the U.K. biscuitmaking flour, Riband, and the U.K. breadmaking flour, Hereward. The relaxation spectrum, in which relaxation times (τ) are related to polymer molecular size, for dough showed a broad molecular size distribution, with two relaxation processes: a major peak at short times and a second peak at times longer than 10 sec, which is thought to correspond to network structure, and which may be attributed to entanglements and physical cross‐links of polymers. Relaxation spectra of glutens were similar to those for the corresponding doughs from both flours. Hereward gluten clearly showed a much more pronounced second peak in relaxation spectrum and higher relaxation modulus than Riband gluten at the same water content. In the gluten protein fractions, gliadin and acetic acid soluble glutenin only showed the first relaxation process, but gel protein clearly showed both the first and second relaxation processes. The results show that the relaxation properties of dough depend on its gluten protein and that gel protein is responsible for the network structure for dough and gluten.     

Mixing Properties,Baking Potential,and Functionality Changes in Storage Proteins During Dough Development of Triticale‐Wheat Flour Blends

Flours from advanced lines or cultivars of six triticales and two prime hard wheats, along with triticale‐wheat blends, were investigated for mixing, extension (excluding blends), and baking properties using microscale testing. Percentage total polymeric protein (PPP) and percentage unextractable polymeric protein (UPP) of flours and doughs, including blends, mixed to optimal dough development were estimated using size‐exclusion HPLC to determine the changes in protein solubility and association with blend composition (BC), mixing properties, and loaf height. Each triticale was blended with flours of each of the two wheat cultivars (Hartog and Sunco) at 0, 30, 40, 50, 60, 70, and 100% of wheat flour. Nonlinear relationships between BC and mixograph parameters (mixing time [MT], bandwidth at peak resistance [BWPR], and resistance breakdown [RBD]) were observed. A linear relationship between BC and peak resistance (PR) was predominant. PPP of triticale flours was mostly higher than PPP of wheat cultivars. UPP of all triticales was significantly lower than wheat cultivars. PPP of freeze‐dried doughs was mostly nonsignificant across the blends and showed a curvilinear relationship with BC. The deviations from linearity of MT and PPP were higher in triticale‐Sunco blends than in triticale‐Hartog blends. UPP of blends was closer to or lower than the lower component in the blend. The deviations from linearity for MT and UPP were greater in triticale‐Hartog blends than triticale‐Sunco blends. A highly significant correlation (P < 0.001) was observed between BWPR and loaf height. This suggested that BWPR in triticale‐wheat flour blends could be successfully used for the prediction of loaf height. Triticale flour could be substituted for wheat flour up to 50% in the blend without drastically affecting bread quality. Dough properties of triticale‐wheat flour blends were highly cultivar specific and dependent on blend composition. This strongly suggested that any flour blend must be tested at the desired blend composition.     

Gluten Structural Evolution During Pasta Processing of Refined and Whole Wheat Pasta from Hard White Winter Wheat: The Influence of Mixing,Drying, and Cooking

An attempt was made to evaluate gluten structural changes in refined and whole wheat pasta from hard white winter wheat to elucidate the impact of whole wheat components on the formation and structure of the gluten network in pasta. Attenuated total reflectance–FTIR spectroscopy was used to track gluten secondary structure through most of the major steps in pasta processing: raw material, mixing, drying, and cooking. Protein solubility, accessible thiols, and SDS‐PAGE data were also collected to provide additional information on the nature of protein interactions and network composition. Few secondary structural differences were observed between refined and whole wheat flours from hard white wheat. However, mixing induced a significant shift to β‐sheet structures in refined dough that was not equally matched by whole wheat dough. Drying under both high temperature, short time (HT) and low temperature, long time (LT) conditions resulted in a reversion to structural distributions similar to those for flour in both pastas. However, greater protein denaturation in HT samples was indicated by lower protein solubility also in the presence of denaturants and disulfide reducing agents. Cooking generated a substantial increase in β‐sheet structures for both pasta systems. This structure was greatest in refined and LT samples. Thiol accessibility data indicate the presence of a highly aggregated, compact gluten network in refined pasta, mostly driven by hydrophobic association. Conversely, the network in whole wheat pasta was more loosely associated and dependent on disulfide bonding, both of which fit well with the secondary structural data.     

弱筋小麦品质评价指标研究

为了确定评价弱筋小麦品质的核心指标,建立弱筋小麦品质评价体系,本研究以长江中下游麦区推广的9个弱筋品种为试验材料,连续进行4年种植试验,测定其籽粒蛋白质含量、籽粒硬度,湿面筋含量、面筋指数、沉淀值和溶剂保持力(SRC)等面粉理化指标,粉质仪和吹泡仪等面团流变学特性参数并制作曲奇饼干测试饼干直径、厚度等品质参数。结果表明,弱筋小麦多数品质性状受基因型和环境共同影响,其中蛋白质含量、硬度、沉淀值、水SRC、碳酸钠SRC、乳酸SRC、吹泡仪参数、粉质仪弱化度以及曲奇饼干直径、厚度均表现为基因效应大于环境效应;弱筋小麦的籽粒蛋白质含量、湿面筋含量、粉质仪吸水率、粉质仪形成时间、粉质仪稳定时间、粉质仪粉质质量指数在各品种间无显著差异;弱筋小麦的硬度、面筋指数、水SRC、碳酸钠SRC、吹泡仪弹性(P值)、吹泡仪弹性/延伸性(P/L值)、粉质仪弱化度在各小麦品种间差异显著(P<0.05),上述指标与曲奇品质呈显著或极显著相关性,可作为评价弱筋小麦品质的重要指标。优质弱筋小麦品质评价标准推荐为:硬度≤25,面筋指数≥80%,水SRC≤60%,碳酸钠SRC≤75%,吹泡仪P值≤40 mm、延伸性(L值)≥95 mm、P/L值≤0.45,75≤弱化度≤95。对连续种植4年的不同弱筋小麦品质性状进行聚类分析,发现扬麦13、扬麦9号、扬麦19为优质弱筋小麦。本研究结果为弱筋小麦品种选育提供了支撑。     

Proteins Extracted by Water or Aqueous Ethanol During Refining of Developed Wheat Dough to Vital Wheat Gluten and Crude Starch as Determined by Capillary‐Zone Electrophoresis (CZE)

Fluids applied to large‐sale, technical separation of wheat starch and protein also extract soluble proteins. The degree and rate of extraction and the specific components extracted depend on the flour, the flour hydration and development, the starch‐displacing fluid composition, the temperature, and the mechanical processing method. This study sought to identify major extracted protein groups using high‐performance capillary zone electrophoresis (CZE) applied directly to fluids obtained during laboratory‐scale technical separations. A dough‐ball or compression separation method was applied using a Glutomatic system and a batter or dispersion method was applied using a a McDuffie mixer and Pharmasep vibratory separator. Process fluids were water at 22°C to model commercial practice and 70 vol% ethanol in water at ‐13°C to model the cold ethanol process being developed here. Data were referenced to use of 70 vol% ethanol in water at 22°C in the Glutomatic compression method. The dough processed by each method was developed by mixing to a separable state. When flooded with excess water, this dough immediately released starch and water‐soluble or albumin proteins. When flooded with excess cold aqueous ethanol, neither the albumin nor gliadin proteins appeared in significant amounts until the bulk of the starch had been displaced, regardless of the mechanical method. Even with extraction and manipulation well beyond that necessary for starch displacement, the net amount of gliadin proteins dissolved was only ≈10% of that available from wet developed dough using 70 vol% ethanol at 22°C. There was more gliadin protein in the fluids at earlier stages of processing when the batter dispersion method was applied using cold ethanol. The most common soluble proteins revealed in the electrophoresis patterns for the batter compression method using cold aqueous ethanol were initially albumins and later γ‐gliadins. Albumins not appearing as soluble in cold 70 vol% ethanol were found in the insoluble crude starch, suggesting their precipitation in the dough fluids during the change from free water to cold aqueous ethanol. These results establish that some protein is dissolved during starch displacement by cold aqueous ethanol, but that the amounts may be limited by control of the mechanical working of the dough in the presence of the displacing fluids.     

Demixing in Wheat Doughs—Its Influence on Dough and Gluten Rheology

Reshaping of relaxed wheat doughs leads to an increase in firmness that significantly changes the results of rheological measurements involving large uniaxial deformations of the dough, whereas the gluten properties remain unaffected. Microscopic investigations reveal that directly after kneading, starch and gluten are thoroughly mixed. However, the shaping procedure of a relaxed dough or shear-flow during rheological measurements cause a separation of gluten and starch. The dilatant behavior of the starch granules and the capacity of gluten to aggregate account for the observed dough-hardening.     

Comparison of Small and Large Deformation Rheological Properties of Wheat Dough and Gluten

The rheological properties of dough and gluten are important for end‐use quality of flour but there is a lack of knowledge of the relationships between fundamental and empirical tests and how they relate to flour composition and gluten quality. Dough and gluten from six breadmaking wheat qualities were subjected to a range of rheological tests. Fundamental (small‐deformation) rheological characterizations (dynamic oscillatory shear and creep recovery) were performed on gluten to avoid the nonlinear influence of the starch component, whereas large deformation tests were conducted on both dough and gluten. A number of variables from the various curves were considered and subjected to a principal component analysis (PCA) to get an overview of relationships between the various variables. The first component represented variability in protein quality, associated with elasticity and tenacity in large deformation (large positive loadings for resistance to extension and initial slope of dough and gluten extension curves recorded by the SMS/Kieffer dough and gluten extensibility rig, and the tenacity and strain hardening index of dough measured by the Dobraszczyk/Roberts dough inflation system), the elastic character of the hydrated gluten proteins (large positive loading for elastic modulus [G′], large negative loadings for tan δ and steady state compliance [J_e⁰]), the presence of high molecular weight glutenin subunits (HMW‐GS) 5+10 vs. 2+12, and a size distribution of glutenin polymers shifted toward the high‐end range. The second principal component was associated with flour protein content. Certain rheological data were influenced by protein content in addition to protein quality (area under dough extension curves and dough inflation curves [W]). The approach made it possible to bridge the gap between fundamental rheological properties, empirical measurements of physical properties, protein composition, and size distribution. The interpretation of this study gave indications of the molecular basis for differences in breadmaking performance.     

灌浆期高温胁迫对不同品种小麦蛋白组分及面团揉混特性的影响

为研究灌浆期高温胁迫对不同品种小麦蛋白组分及面团揉混特性的影响,以济麦22(JM22)和新麦26(XM26)为材料,通过灌浆初期(S1)和灌浆中期(S2)在田间搭棚进行高温胁迫处理,以未进行高温胁迫的大田小麦作对照(CK),收获后对小麦淀粉黏滞谱、蛋白质组分含量和揉混参数等进行分析。结果表明,与各自CK相比,JM22的黏滞谱参数除回复值和糊化温度降低外,其余参数均升高,XM26的黏滞谱参数除峰值时间外均降低。S1和S2使JM22的峰值黏度、低谷黏度、崩解值、最终黏度、峰值时间分别较CK提高2.81%和18.63%、7.71%和19.51%、11.88%和21.15%、1.88%和12.22%、2.45%和4.08%,且S2均大于CK和S1,S1与CK差异不显著;S1和S2使XM26的峰值黏度、低谷黏度、最终黏度、回复值分别较CK降低12.95%和31.21%、1.81%和27.18%、2.50%和22.22%、3.57%和14.39%,其中,S2、S1与CK三者之间的峰值黏度均达显著水平。与CK相比,高温胁迫后JM22的蛋白质含量降低,而XM26升高。两品种各组分蛋白含量均发生改变,S...     

Changes in SDS Solubility of Glutenin Polymers During Dough Mixing and Resting

An online coupling of high‐performance size‐exclusion chromatography (HPSEC) combined with multiangle laser‐light scattering (MALLS) and a reverse‐phase HPLC procedure were used to characterize and reveal the polydispersity of the glutenin polymers of doughs during mixing and resting. Experiments involved doughs prepared from several samples of a common French wheat cultivar (Soissons) differing in total amount of SDS‐unextractable glutenin polymers. During dough mixing, the amounts, size distribution of protein, and glutenin subunit composition within the SDS‐unextractable polymers changed. However, the major changes in SDS‐unextractable glutenin content and size distribution occurred before the peak mixing time (MT) was reached, whereas detectable changes in subunit composition also occurred after the peak MT. Even if sonication, which was used to solubilize the total wheat glutenin, can narrow the glutenin size distribution, HPSEC‐MALLS revealed a close relationship between the SDS solubility of the glutenin polymers and size distribution, confirming a depolymerization and repolymerization hypothesis. During the depolymerization of the SDS‐unextractable polymers, glutenin subunits were released in nonrandom order, which indicated that the polymers have a hierarchical structure. Some HMW glutenin subunits (HMW‐GS), especially 1D×5, were particularly resistant to the depolymerization mechanism. This suggested that the subunit plays a major role in forming the backbone of the SDS‐unextractable polymers, consistent with the potential to form branched structure. These studies suggest that the SDS‐unextrac‐table polymers in flours have a well‐ordered structure that can be modified by dough mixing and resting.     

Effects of Cultivar and Temperature During Grain Filling on Wheat Protein Content,Composition, and Dough Mixing Properties

Three wheat cultivars, Bastian, Polkka, and Tjalve, were grown in growth chambers at 9, 12, 15, 18, and 21°C during grain filling in 1994, 1995, and 1996. The wheat samples were analyzed for protein content and sodium dodecyl sulfate (SDS) sedimentation volume. The mixing properties of sifted flours were determined by mixograph, and the flour protein composition was determined by size-exclusion fast protein liquid chromatography (SE-FPLC). The protein content, sedimentation volume, and mixogram parameters were affected by the temperature during grain filling. The protein content increased as the temperature increased. The sedimentation volumes and the mixograph data showed temperature effects that could not be explained by variation in protein content. The proportion of the polymeric flour proteins increased with increasing temperature. Positive correlations were found between the proportion of polymeric proteins and SDS sedimentation volume and, within each year, between the proportion of polymeric proteins and mixograph peak time. Negative correlations were found between the proportion of low molecular weight flour proteins (proportion of fraction IV) and sedimentation volume. The differences in these quality parameters among cultivars exceeded the effect of temperature during grain filling.     

Effect of Mechanical Dough Development on the Extractability of Wheat Storage Proteins from Bread Dough

Six wheat cultivars covering a range of quality parameters were mixed to various proportions of their optimum work input using mechanical dough development (MDD) mixers. Mixing and baking characteristics were determined and each dough was subsampled. The proteins were extracted for analysis by reversed-phase HPLC. Considerable protein mobilization appeared to occur during the MDD process, but the changes appeared to be cultivar-specific and did not indicate how mixing or baking behavior could be predicted. Protein content in extracted fractions was lowest for the weakest, poorest quality wheat but failed to consistently rank the stronger samples. Acetic acid insoluble protein level decreased with mixing as did extractable high molecular weight glutenin subunits. Gliadin protein level initially decreased with mixing before rising sharply with overmixing, while low molecular weight glutenin subunits displayed the reverse pattern. The rate of change of the extractability of the protein fractions with work input was greatest for the weakest samples and least for the stronger samples. However, when the protein quantity in the extractable fractions was plotted against relative work input, the rate of change of protein extractability did not appear to vary significantly between cultivars of different strengths.     

不同施氮量对弱筋小麦产量与品质的影响

通过对3个弱筋小麦品种的5个不同施氮量的研究,探索出弱筋小麦对氮肥量的需求。研究结果表明,弱筋小麦产量与施氮量呈正相关关系,但品质与施氮量呈负相关关系。综合分析,在磷、钾肥确定的条件下,施纯氮量120kg hm-2的处理,既兼顾了产量又确保了弱筋粉小麦的优良品质。     

Effect of Adding Exogenous Oxidative Enzymes on the Activity of Three Endogenous Oxidoreductases During Mixing of Wheat Flour Dough

The behavior of different exogenous enzymes (soybean lipoxygenase [SLOX], horseradish peroxidase [HPOD], catalase from bovine liver [BCAT], and glucose oxidase [GOX] from Aspergillus niger) added to dough was studied during mixing. The effect of adding these exogenous oxidoreductases on the activity of three oxidative enzymes present in wheat flour (lipoxygenase [WLOX], peroxidase [WPOD], and catalase [WCAT]) was examined. Proper assay conditions were established to differentiate between added WLOX, WPOD, and WCAT and the corresponding activities present in wheat flour. For doughs with added SLOX, an immediate loss of extractable SLOX (≈40%) was observed which remained constant during further mixing. When compared with the control dough, addition of SLOX decreased the losses in WLOX and WCAT activities, whereas WPOD activity was unaffected. With doughs supplemented by HPOD, an immediate loss of 20% in the HPOD activity was observed which did not change after 20 min of mixing. Compared with control dough, addition of HPOD did not affect the behavior of WLOX and WPOD, whereas a slight decrease in the WCAT losses was observed. Addition of BCAT to the dough did not change the behavior of WLOX and WPOD, whereas the losses in WCAT were less rapid. Half of the extractable activity of BCAT was lost at the beginning of mixing with no change during further mixing. For doughs supplemented with GOX, 25% of the GOX activity was lost in the first 5 min of mixing and an additional loss of 20% was observed after 20 min of mixing. Compared with dough without GOX, addition of GOX decreased the losses in WLOX, whereas losses in WCAT and WPOD increased. Glucose and ferulic acid were also added to doughs supplemented with GOX. Added glucose decreased the losses in GOX and WLOX and did not change the behavior of WPOD and WCAT during mixing. Addition of ferulic acid promoted a slight increase of the losses in WLOX and WCAT and almost no change for GOX and WPOD.     

Influence of Vacuum Mixing on Structural Characteristics and Physical Properties of Noodle Dough

The effects of vacuum mixing on the structural characteristics and physical properties of noodle dough were investigated using three leading Chinese wheat cultivars. Texture profile analysis showed that vacuum mixed doughs when sheeted all gave significantly higher levels of adhesiveness, elasticity, and chewiness than doughs from nonvacuum mixing. The cross section of sheeted dough mixed at 0.06 MPa had a more continuous and compact microstructure with fewer holes and gaps, as well as more even protein distribution at the surface, as evidenced by scanning electron microscopy and Fourier transform infrared microimaging. However, a higher degree of vacuum was detrimental to the developed network for weak dough. Dough mixed at 0.06 MPa had higher glutenin macropolymer content and lower free thiol group concentration compared with nonvacuum mixed doughs, which may largely relate to the improvement of dough texture. The development of the gluten network for weak gluten flour was more sensitive to the degree of vacuum.     

Effect of Amaranthus and Buckwheat Proteins on Wheat Dough Properties and Noodle Quality

Isoelectric protein concentrates (IPC) were prepared from one buckwheat (Fagopyrum esculentum) and five Amaranthus genotypes. Their effect on the mixing properties of a wheat flour was studied. Mixograph and dynamic oscillatory measurements showed significant increases in dough strength with the addition of 2 and 4% IPC, correlated to the water-insoluble fraction level of the IPC. The same IPCs were used at 2% level to supplement a wheat flour in making Chinese dry noodles. Measurable changes in both the raw and cooked noodle color were observed, and the change caused by addition of buckwheat IPC was substantial. Some of the IPCs caused an increase in cooking loss and only one caused an increase in weight, while increase in volume of the cooked noodles was not significantly affected. The changes in the rheological properties of cooked noodles due to addition of IPCs were measured. Overall, their effects were favorable, but the changes were statistically significant in only a few cases. The substantial dough-strengthening effect of the IPCs was hence not effectively translated into improved cooked noodle quality, and possible reasons for this are discussed.     

氮肥运筹方法对强筋小麦产量和品质的调控效应

采用盆栽试验方法研究了氮肥运筹对强筋小麦产量和品质的影响,试验结果表明:合理运筹氮肥能够显著提高强筋小麦籽粒产量。拔节期叶面喷施氮肥显著提高了强筋小麦的株高、穗长、穗数、穗粒数和千粒重,从而促进小麦获得了最高产量;适当增加中、后期氮肥施用比例有利于改善强筋小麦品质,以拔节期和抽穗期分两次追施氮肥效果最佳。综合产量和品质效应,以拔节期喷施氮肥为最佳氮肥运筹方法。     

Controlled Stepwise Reduction of Disulfide Bonds and Heat-Induced Modification of Wheat Dough Proteins

A reducing solution of 2-mercaptoethanol and its oxidized form 2-hydroxyethyl disulfide, whose variable concentrations set variable disulfide reduction potentials, was applied to progressively reduce the disulfide bonds of proteins extracted from doughs made from Meneba and Robin Hood flour. Several dough proteins had disulfide bonds stronger than those of other dough proteins. A SDS-sedimentation method was applied to monitor the baking of dough into bread. Dough proteins susceptible to heat (baking) were studied by SDS-fractionation, extraction with reducing alcoholic solution, SDS-PAGE, and N-terminal protein sequencing. High or low molecular weight glutenins, α, β, and γ-gliadins, α-amylase inhibitor, and α-amylase trypsin inhibitor were identified among the dough proteins modified by heat (as shown by reduced solubility in aqueous-SDS solution). The heat-induced modification of the gliadins and glutenins might contribute to the coagulation of dough proteins, while the heat-induced modification of the amylase or trypsin inhibitors might contribute to the regulation of endogenous or exogenous amylolytic or proteolytic activities in dough or bread.     

氮素供应对强筋小麦产量和品质的影响

选择淮北地区两种土壤类型进行田间试验,研究氮素供应对强筋小麦的产量和品质的影响。结果表明,在一定的施氮范围内,施氮量与产量呈二次曲线关系,与品质呈直线相关关系。在对照产量为6092.15 kg hm-2的砂姜黑土,151kg hm-2的施氮量可获得最高产量7219.6 kg hm-2,蛋白质含量15.504%,湿面筋含量36.077%;174 kg hm-2的施氮量可获得最优品质,产量为7192.94 kg hm-2,蛋白质含量15.721%,湿面筋含量37.125%。对照产量为4457.4 kg hm-2的两合土,施氮量在174 kg hm-2时,可获得最优品质。经效益概算知,兼顾高产、优质、高效的施氮量是最优品质施氮量。