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a Univ. of Idaho Research and Extension Center, P.O. Box 870, Aberdeen, ID 83210
b Pendelton Flour Mills, 463 W. Hwy 26, Blackfoot, ID 83221
* Corresponding author (esouza{at}uidaho.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Both protein quantity and quality are required for optimum bread performance. Nitrogen fertilization strongly influences the quantity of protein in wheat flour (Dubetz et al., 1979; Gauer et al., 1992). Studies have demonstrated the importance of N application timing for optimal wheat yield, increased grain protein concentration, and reductions in N loss from the soil-plant system (Fowler et al., 1989; Hucklesby et al., 1971; Altman et al., 1983; Miezan et al., 1977). Nitrogen applications later in the season, near anthesis, when coupled with irrigation, increased grain protein concentration more than earlier applications (Wuest and Cassman, 1992; Strong, 1982). Bread loaf volume is positively and directly correlated with flour protein concentration (Bushuk, 1985; Finney and Barmore, 1948). Therefore, protein quantity and quality have received considerable attention in wheat improvement programs. However, simultaneously increasing both grain yield and grain protein content has been difficult because of the widely documented negative association between these two traits (Terman et al., 1969; Cox et al., 1985).
Water deficits also are associated with increased grain protein content (Terman et al., 1969; Entz and Fowler, 1989). Irrigation, or any cultural practice that enhances yield potential, can decrease grain protein content because of dilution with carbohydrates if nitrogen availability is not increased commensurately (Bole and Dubetz, 1986; Eck, 1988). Excess irrigation, or irrigation in the absence of a yield increase, decreased grain protein (Robinson et al., 1979), apparently by leaching nitrogen below the root zone. In contrast, irrigation increased grain protein content in other cases (Yamada et al., 1972; Rajeswara Rao and Prasad, 1987; Puri et al., 1989), and irrigation can mobilize surface-applied fertilizer (Slukhai and Zhabitskii, 1970).
Although flour protein composition depends primarily on genotype, environmental factors (e.g., nitrogen, water stress, and temperature conditions) also influence flour protein composition (Sosulski et al., 1963; Benzian et al., 1983; Stapper and Fischer, 1990; McDonald, 1992). Moreover, there is potential for considerable interaction between genotypic and environmental factors (Panozzo and Eagles, 2000).
Starch characteristics also may contribute to the bread baking performance of wheat flours. For example, small starch granules had a lower baking potential than the corresponding normal starch (Kulp, 1973). Soulaka and Morrison (1985) performed baking experiments with mixtures of A- and B-granules, and reported an optimum proportion of B-granules in the blend (25–35% by weight), beyond which loaf volume decreases. Environmental conditions such as shading and nutrition or drought and disease during grain fill affected the size and number of starch granules deposited in the wheat kernel (Caley et al., 1990). Shi et al. (1994) concluded that heat stress during grain filling reduced starch accumulation, starch granule size, and the number of B-type granules and increased starch-swelling power.
Starch paste viscosity is highly correlated with noodle sensory quality, and flours with low starch viscosities do not make satisfactory alkali (Chinese-style) noodles (Ross et al., 1997). Panozzo and McCormick (1993) determined that flour viscosity (high hot paste viscosity) is an indicator of Japanese (Udon) noodle quality. Starch viscosity relates to noodle firmness, elasticity, and physical integrity after boiling (Miura and Tanii, 1994). The ratio of amylose to amylopectin is strongly correlated to hot paste peak viscosity (Toyokawa et al., 1989) and is a primary source of pasting variation for flour/water slurries. Normal amylose flours have less water holding capacity than reduced amylose (partial waxy) flours (Toyokawa et al., 1989) and, consequently, a lower peak viscosity. Peak paste viscosity was significantly correlated with apparent amylose (Miskelly and Moss, 1985). Although mutations to the Granule Bound Starch Synthase (GBSS) gene significantly reduce grain amylose content, the relative magnitude of environmental influences on amylose content compared with GBSS mutations is not well understood.
Color defines noodle class and acceptability: a bright product, free from specks or other discoloration is preferred. Raw noodles must maintain color during short-term storage. Color stability is largely a function of polyphenol oxidase (PPO) activity and growing environment. PPO activity increases gray tones in noodles, and the level of PPO activity varies among cultivars (Kruger et al., 1994). The whiteness or brightness of the noodle may decrease with increasing protein concentration (Souza et al., 2004). Guttieri et al. (2001a) found that moisture stress during the growing season significantly increased the yellowness of noodles prepared from flours.
Understanding hard wheat responses to environmental and management variables will improve recommendations made to growers in the Pacific Northwest for specific end-uses. This study measures the nitrogen and irrigation management effects on the relative quality of noodles and bread produced by hard spring wheat cultivars that were developed for either bread or noodle applications.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The experimental design was a split-split plot design with four replications. Main plots (12.2 x 36.6 m) were irrigation treatments (3): early irrigation (Ie), moderate irrigation (Im), and optimal irrigation (Io). Main plots were spaced appropriately to provide for differential irrigation from the solid-set overhead sprinkler irrigation system. Subplots (3 m x 36.6 m) were cultivars (4): Idaho 377s hard white spring (HWS, Souza et al., 1997), Lolo HWS (Souza et al., 2003), IDO523 (‘Winsome’/Idaho 377s) HWS, and Westbred 936 hard red spring (HRS). Sub-subplots (3 x 9.1 m) were nitrogen levels (4). Nitrogen treatment rates ranged from deficient to excessive (Table 1).
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Wheat was planted 16 April 1999 and 10 April 2000. Wheat was seeded at 106 kg ha–1 with a double disk drill set at 18-cm row spacing. Broadleaf and grass weeds were controlled with application of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and diclofop {(RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid} herbicides.
Overhead sprinkler irrigation, placed lengthwise along the borders of each main plot, was used to irrigate the experimental area. Differential irrigation was achieved by blocking sprinkler nozzles in specific plots. The optimal irrigation treatment was irrigated weekly to replace 100% estimated crop evapotranspiration (ET) (modified Penman method) until the final irrigation on 3 Aug. 1999 and 27 July 2000 at Zadoks 86 (Table 2). The early and moderate irrigation treatments were irrigated weekly at 100% ET replacement through jointing (Zadoks 37). Beginning 10 June 1999 and 30 May 2000, the early and moderate irrigation treatments were irrigated weekly to 50% ET replacement. On 30 June 1999 and 19 June 2000 (Zadoks 58), the early irrigation treatment received only 25% ET replacement through the final irrigation on 8 July 1999 and 3 July 2000 at Zadoks 75. The moderate irrigation treatment was irrigated to 50% ET replacement until the final irrigation on 22 July 1999 and 12 July 2000 at Zadoks 83. Crop ET estimates were obtained from the United States Bureau of Reclamation Pacific Northwest Region Agrimet System, which maintains a weather station at the University of Idaho Aberdeen Research and Extension Center. Irrigation amounts were measured with rain gauges placed in the crop. Average cumulative rainfall plus irrigation amounts in 1999 and 2000 for the early, moderate, and optimal irrigation treatments were equivalent to 38, 46, and 88%, respectively, of estimated crop ET (Fig. 1). The 88% treatment was considered a full irrigation treatment as ET was replaced with irrigation after an initial period at the seedling stage when irrigation was unavailable and soil moisture was sufficient for the crop.
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Quality Analyses
Flour quality analyses were conducted at the University of Idaho's Aberdeen Wheat Quality Laboratory. Milling, baking, and noodle analyses were conducted on one sample per sub-subplot in each of four replications of the experiment in each year. Methods for tempering (AACC 2000; methods 44-11 and 26-10), milling (method 26-21), mixograph analyses (method 54-40), and baking were as Souza et al. (1993) described and were in accordance with those described by the AACC (2000).
Alkaline noodles were prepared as described previously (Guttieri et al., 2001a) from 25 g of flour mixed to a crumbly consistency with 9 mL of an alkaline salt solution (0.25% w/v Na2Co3, 1% NaCl). Noodle sheet color was measured in Commission Internationale de l‘Eclairage (CIE) tristimulus color space (L*, a*, b*) with a Minolta CM-2002 spectrophotometer (Minolta Camera, Chuo-Ku, Osaka, Japan) with a 50-mm measurement aperture. CIE-L* measures noodle lightness, CIE-a* measures the red-green color axis, and CIE-b* measures the yellow-blue color axis. Noodle dough color was measured after sheeting (0 h) and after 24-h incubation in a resealable plastic bag at room temperature. Average readings of stacks of three noodle sheets were recorded.
Flour pasting viscosity of each sample was determined using the Rapid Visco-analyser (Newport Scientific, Australia). A slurry consisting of 3-g flour and 25 mL of water solution was mixed and heated at a constant rate, and viscosity was recorded as described by Guttieri et al. (2001b).
Polyphenol oxidase activity was determined for each sample by a modification of the L-DOPA (3,4-dihydroxyphenylalanine) assay described by Anderson and Morris (2001). Grain was ground in a cyclone mill as described previously (Guttieri et al., 2004). A 1-g sample of whole grain meal was mixed with 5 mL of assay buffer [5 mM L-DOPA in 50 mM 3-(N-morpholino) propane sulfonic acid (MOPS) buffer, pH 6.5], vortexed, and incubated with continuous agitation at room temperature for 30 min. Samples were centrifuged at 4300 x g for 10 min. The absorbance of the supernatant was recorded at 475 nm relative to a durum meal standard.
Statistical Analysis
Data were analyzed by PROC MIXED (SAS Institute Inc., 1996). Year, replication within year, irrigation x replication within year and cultivar x irrigation x replication within year were treated as random effects. Irrigation management and cultivar were considered fixed effects. Least squares means for main effects were determined in PROC MIXED using Satterthwaite's approximation to determine the denominator degrees of freedom for calculation of standard error. Total nitrogen fertility (N) was analyzed as a continuous variable. Quadratic regression models were fitted with the option HTYPE = 1 to sequentially formulate hypotheses. For dependent variables for which the N x N effect was significant, quadratic regression models were developed. Tests for fixed effects and interactions of fixed effects with N were used to determine which models should be used to represent the effects over fertility rates as described in SAS Inst. (1996, p. 103–104). Optimal N fertility rates were derived from quadratic functions by solving for N rate at which the first derivative of the function equaled zero.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Grain yield was reduced 24 and 15% by early (Ie) and moderate (Im) irrigation treatments, respectively, relative to the optimal (Io) irrigation treatment (Table 3, Table 4). Lolo was the highest yielding cultivar. Total N fertility significantly affected grain yield and test weight in a quadratic manner (Table 3). Optimal N rates were 263, 297, and 303 kg ha–1 under early, moderate, and optimal irrigation, respectively. Idaho 377s, IDO523, Lolo, and WPB 936 yields were optimized at 260, 280, 321, and 325 kg ha–1, respectively. Yield depression occurred at high N rates in the absence of lodging (no lodging occurred in either year). Entz and Fowler (1989) and Fowler et al. (1989) and reported similar results and attributed it to a physiological response to high N levels. In this study, the physiological response was manifested as decreased kernel weight with increasing N [Ie: –0.03 g (kg N ha–1)–1, Im: –0.02 g (kg N ha–1)–1, Io: –0.01 g (kg N ha–1)–1].
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Irrigation and cultivar affected flour ash concentration (Table 3). Flour ash from the Ie treatment was 0.16 g kg–1 (Table 4) greater than from the Io treatment. The hard white cultivar, Lolo, had the lowest average flour ash concentration, approximately 0.1 g kg–1 less than the other cultivars (Table 4). Irrigation management affected the response of flour ash concentration to N. Flour ash was reduced by N application only with optimal irrigation management (Table 5). Under optimal irrigation management, flour ash concentration was minimized at 263 kg N ha–1. Cultivars differed in the effect of total N fertility on flour ash (Table 3). Flour ash concentration of Lolo was most affected by N (Table 6). This complexity points to the difficulty of developing generalized models for flour ash as a function of cultivar, fertility, and irrigation management.
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Bread Quality Characteristics
Irrigation, cultivar, and total N fertility significantly affected mixograph peak time (Table 3). Peak time was significantly longer in flours from grain produced under early irrigation (3.8 min), relative to moderate irrigation (3.3 min) and optimal irrigation treatments (3.1 min) (Table 4). WPB 936 had the longest mixograph peak time, 0.2 min longer than Lolo, and 0.3 min longer than Idaho 377s and IDO523 (Table 4). Mixograph peak time increased by 1.91 and 2.00 x 10–3 min per kg N ha–1 in the early and moderate irrigation management treatments, but the response of mixing time to N fertility under the optimal irrigation management treatment was nonsignificant (Table 5).
Cultivar and total N fertility significantly affected mixograph peak height (Table 3). Mixograph peak height of WPB 936 flour was 0.6 cm greater than the average of the three hard white cultivars. Mixograph peak height increased 0.0867 mm for each 1 kg ha–1 increase in total N fertility.
Mixing tolerance of WPB 936 flours was less than the hard white flours (Tables 3 and 4). The interaction of N rate and irrigation management derives from the increased mixograph tolerance with increased N rate under Im, and the insensitivity of mixograph tolerance to N rate under Ie and Io (Table 5).
Cultivars differed for mixograph water absorption (Table 3): mixograph water absorption was lowest for IDO523 flour (577 g kg–1) and highest for WPB 936 flour (614 g kg–1), (Table 4). There was a significant total N fertility x irrigation treatment interaction for mixograph water absorption (Table 3). Water absorption increased by 0.126 g kg–1 and 0.055 g kg–1 for each 1 kg ha–1 increase in total N fertility under the Ie and Im treatments, respectively (Table 5). However, in the Io treatment, total N fertility did not affect mixograph water absorption. Flour protein concentration is a key determinant of water absorption (Bushuk, 1985). In AACC 54-40 (method for mixograph analysis), flour protein concentration is used to estimate water absorption for conducting the mixograph test [Est. % Absorption = 43.6 + 1.5(% protein), all on 14% moisture flour weight basis]. For some flours, the resulting mixogram may not meet shape parameters (mixograms having relatively wild swings indicate dryness, mixograms with a swayback during hydration and development indicate wetness). In such instances, mixograph absorption is adjusted by ±1% as appropriate, or the mixogram may be repeated with an adjusted volume of water (Finney, 1997). Were flour protein the only determinate of mixograph water absorption, complete correlation between flour protein concentration and mixograph water absorption would be 1.0. In this study, mixograph water absorption was strongly correlated with flour protein concentration (r = 0.83). The pattern of response of mixograph water absorption within irrigation treatments to increasing N is consistent with the strong correlation of mixograph water absorption and flour protein concentration.
Cultivars differed for bread loaf volume (Table 3). Westbred 936 had approximately 13% larger bread loaf volume than the hard white genotypes (Table 4). Loaf volume increased more with N in the Ie and Im treatments [0.66 and 0.45 mL (kg N ha–1)–1], respectively) and least in the Io treatment [0.18 mL (kg N ha–1)–1] (Table 5). Loaf volume was strongly correlated with flour protein (r = 0.85, p < 0.001).
To further evaluate effects of treatments on protein quality, treatment effects were tested on adjusted loaf volume (loaf volume per unit protein). The adjusted loaf volume of the four cultivars differed in responsiveness to N (Table 3). Idaho 377s, Lolo, and WPB 936 adjusted loaf volumes were insensitive to N fertility (Table 6). In contrast, the adjusted loaf volume of IDO523 increased with increasing N fertility.
Polyphenol Oxidase Activity and Alkaline Noodle Color
Polyphenol oxidase (PPO) is a plant enzyme that generates highly reactive quinones from resident phenolic compounds, which react with cellular components and cause browning. Cultivars differed for flour PPO activity (Table 3). Hard white genotypes, as a group, had 45% less PPO activity than Westbred 936 (Table 4). Unlike Westbred 936, all three hard whites were intentionally selected for noodle color (Souza et al., 1997, 2003). Among hard white genotypes, IDO523 had 32% less PPO activity than Idaho 377s and Lolo. Irrigation also affected flour PPO activity (Table 3). PPO activity was significantly greater in grain produced under Ie, the most stressful environmental condition (Table 4).
Cultivars differed for initial noodle brightness (L*) (Table 3). As a group, the hard white genotypes had better (0.7 CIE units) initial noodle brightness than WPB 936 (Table 4). Irrigation and N fertility did not affect initial noodle brightness, and interaction effects of treatments were minor (Table 3). Previous work suggests that protein concentration is less important for determining initial L* in alkaline noodle than for neutral pH Chinese style noodles (Souza et al., 2004). The change in alkaline noodle brightness at 24 h was markedly different for the four cultivars (Table 3). The hard white genotypes had better noodle brightness stability than WPB 936 (Table 4). Change in brightness at 24 h was greatest for flours from grain produced under optimal irrigation management but did not demonstrate a clear trend with changing irrigation treatments from Ie to Io (Table 4). This is also consistent with our earlier findings that genotype is the most significant factor determining noodle brightness and brightness stability, followed by environmental factors that are difficult to model (Souza et al., 2004). In this study as in previous work, limited interactions between cultivar and management or environment were observed for change in noodle brightness (Guttieri et al., 2001a; Souza et al., 2004). This study reinforces the use of noodle brightness as a selection tool for Asian noodle quality because limited genotype x environment interaction provides the ability to select among genotypes with confidence in a limited number of environments.
The initial yellowness (b*) of alkali noodles was significantly affected by cultivar, as well as by irrigation management. Initial noodle yellowness (b*) was greatest in the most stressful irrigation conditions, consistent with our earlier studies (Guttieri et al., 2001a). Idaho 377s and Lolo had approximately 8% greater initial noodle yellowness relative to IDO523 and WPB 936. Initial noodle yellowness increased with N fertility, particularly in the Ie treatment (Table 5).
Flour Pasting Properties
Flour pasting temperature was affected by irrigation and cultivar (Table 3). As a group, the three hard white cultivars pasted at a lower temperature (mean 83.0 C°) than the hard red spring cultivar, WPB 936 (85.3 C°). This likely is due to the effect of the GBSS mutation in two hard white cultivars (Idaho 377s and Lolo), which confer a partial waxy (reduced amylose) characteristic to the starch. Pasting temperature increased with increasing N rate only in the Ie treatment (Table 5). The pasting temperature of flours of the four cultivars also differed in response to increasing N. The pasting temperature of Lolo flour was not responsive to N, while the pasting temperatures of Idaho 377s and IDO523 flours increased with increasing N (Table 6). In contrast, the pasting temperature of WPB 936 decreased with increasing N. Therefore, it is difficult to make general predictions of effects of applied N fertility on pasting temperature across a range of irrigation management systems and cultivars.
Cultivars produced flours with different peak pasting viscosity (Table 3). The partial-waxy, hard white cultivars had greater peak viscosity than the hard red cultivar, and within the hard white cultivars, the wild-type GBSS cultivar IDO523 had a much lower peak viscosity than Lolo or Idaho 377s (Table 4). Irrigation treatment affected the response of flour peak viscosity to N rate. The peak viscosity increase with N rate was greatest under the Io treatment (Table 5). The peak viscosity of Lolo and Idaho 377s flours increased with N fertility, but peak viscosities of IDO523 and WPB 936 flours were insensitive to N (Table 6).
Final viscosities were approximately 250 and 405 cP greater, respectively, for the Im and Ie treatments, than the Io treatment (Table 4). In contrast to the responses observed for peak viscosity, the response of final viscosity to N fertility was nonsignificant under Io, and most significant under Ie (Table 5). But like the response observed for flour peak viscosity, final viscosity response to N fertility was most notable for the cultivar Lolo (Table 6).
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Grain yield was optimized at optimal irrigation by 303 kg N ha–1, yet flour extraction was optimized above this level (314 kg N ha–1), and grain protein, water absorption, loaf volume, and mixograph peak height and time all continued to increase at higher N levels. The linear increase in quality traits with N is in contrast to quadratic yield responses to N. This suggests that genotypes with higher yield optima, such as Lolo and WPB936, should be selected to provide yield responses at the greater nitrogen fertilization rates required to elevate bread quality. Previous work indicates that increased protein concentration and bread loaf volume improves noodle texture (Lang et al., 1998; Souza et al., 2004).
Reduction in irrigation also can increase protein concentration with lower N applications. However, reducing irrigation also lowers the N rates at which cultivars begin to decline in yield. We generally did not observe end-use quality differences between elevation of protein through irrigation management or through N management as strategies to improve grain protein quality, as measured by mixograph or loaf volume. Unlike increased N applications, late-season moisture stress reduced flour extraction rates, increased PPO activity, increased yellowness of noodles (b*), and increased final flour pasting viscosity. The yellow pigmentation may be desirable for some types of Asian noodles, yet, increase of PPO activity and decrease of flour extraction always is undesirable in Asian wheat utilization.
We are unaware of previous reports of available soil N altering flour pasting profiles. The increased response of peak viscosity to N rate with optimal irrigation treatment and the specificity of response of paste viscosity of two cultivars, Lolo and Idaho 377s, to N fertility do not parallel the responses to N fertility observed for flour protein. Therefore, the effects of N fertility on peak viscosity are unlikely to be a consequence of increased flour protein concentration. The greater effect of N fertility on peak viscosity in reduced amylose cultivars, Lolo and Idaho 377s, relative to normal (wild-type) amylose composition cultivars, WPB 936 and IDO523, suggests that effects on peak viscosity may be related to changes in starch composition. We feel this observation warrants further investigation.
In previous work, milling yield of tall genotypes adapted to rain-fed conditions was improved by reduced irrigation, if lodging was reduced (Guttieri et al., 2000). Also milling yield and noodle color of flours from grain produced in low moisture, rain-fed environments may be better than in grain produced in irrigated environments (Souza et al., 2004). Moisture stress reductions in quality observed in this study may relate specifically to irrigated production systems using semidwarf wheat genotypes. Reducing irrigation of semidwarf genotypes may not be the best strategy for increasing protein concentration while maintaining end-use quality for both bread and Asian products. Nitrogen fertilizer management may produce better overall end-use quality in irrigated systems.
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication December 23, 2004.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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