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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
Journal of Integrative Agriculture
September 2013
2013, 12(9): 1560-1567
RESEARCH ARTICLE
Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize LU Da-lei, SUN Xu-li, WANG Xin, YAN Fa-bao and LU Wei-ping Key Laboratory of Crop Genetics and Physiology of Jiangsu Province/Key Laboratory of Crop Physiology, Ecology and Cultivation in Middle and Lower Reaches of Yangtse River, Ministry of Agriculture/College of Agriculture, Yangzhou University, Yangzhou 225009, P.R.China
Abstract Grain physicochemical properties determine the table quality of fresh waxy maize. Two waxy maize varieties, Suyunuo 5 (shading tolerant) and FHN003 (shading sensitive), were used to estimate the effect of shading (plants received 30% less radiation than control) during grain filling (from 0 d to 23 d after pollination) on physicochemical properties of fresh waxy maize grain. Shading decreased the grain fresh weight of Suyunuo 5 and FHN003 by 8.4 and 19.1%, respectively. Shading increased the grain water content of FHN003, whereas that of Suyunuo 5 was not affected. In both varieties for shading treatment, soluble sugar, starch and protein contents were decreased, whereas zein content was increased. The changes in globulin, albumin and glutenin contents under shading were variety dependent. In both varieties, shading decreased λmax, iodine binding capacity and the percentage of large starch granules (diameter >17 m) but increased crystallinity. The results of rapid visco analysis showed that the viscosity characteristics (except for pasting temperature) of both varieties were decreased by shading; however, FHN003 was more severely affected than Suyunuo 5. Under shading, ΔHret and %R were decreased in both varieties, whereas the changes in ΔH gel and transition temperatures were variety dependent. Hardness, cohesiveness and chewiness were decreased in both varieties. Significant differences in physicochemical characteristics were observed between the two varieties. Key words: fresh waxy maize, shading, grain quality, physicochemical property
INTRODUCTION Waxy maize endosperm starch is composed of nearly 100% amylopectin, which endows its better viscous taste and easy digestion compared with other maize types such as normal or sweet maize (Singh et al. 2006). Waxy maize is mainly produced for fresh eating in China. With the improvement of national living standards, there is a promising trend for fresh waxy maize market expansion both domestically and internationally. Physicochemical properties of grain are important
in determining the table quality of waxy maize (Simla et al. 2010). Physicochemical characteristics of maize are different among various genotypes and controlled by the interaction between environment and cultivation measures (Earle 1977). Therefore, with the advancements in germplasm and cultivation measures, environment plays an important role in maize grain quality improvement. As a major environmental factor of crop growth, light intensity influences both the yield and quality of maize (Earley et al. 1966; Chan and Mackenzie 1972; Earle 1977; Setter et al. 2001). The effect of shading
Received 30 July, 2012 Accepted 22 November, 2012 LU Da-lei, E-mail: [email protected]; Correspondence LU Wei-ping, Tel: +86-514-87979377, Fax: +86-514-87976817, E-mail: [email protected]
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S2095-3119(13)60560-2
Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
on grain formation at grain filling stage is larger than other stages (Kiniry and Ritchie 1985). Low light intensity after pollination reduces grain yield and starch content, whereas protein content is variety dependent (Earley et al. 1966; Jia et al. 2007, 2011). Shading also decreases the activities of enzymes involved in starch and protein syntheses (Jia et al. 2007; Zhang et al. 2008). However, little is known about the effect of shading on the physicochemical properties (e.g., pasting, thermal, and textural characteristics) of maize during grain filling, all of which determine its final product quality (Jia et al. 2007). Field microclimates after pollination play important roles in determining waxy maize grain yield and quality formation. In waxy maize production, the sowing period is from middle March to middle August in Jiangsu Province, China. The weak light during grain filling due to late sowing dates is an important environmental factor that affects plant growth. However, little is known about the effect of weak light on the quality of waxy maize. Thus, plants were subjected to shading during grain filling under field conditions to determine the effect of low radiation on the grain composition and physicochemical properties of fresh waxy maize. The generated results may serve as a basis for improving the quality of fresh waxy maize.
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shading (67.1%) was significantly higher than that under control (61.4%), indicated that grain filling rate was delayed when light intensity was insufficient.
Proximate compositions Compared with control, shading decreased the soluble sugar, starch and protein contents for both varieties (Table 1). Suyunuo 5 had higher starch content and lower sugar content than FHN003. Under shading, zein content was increased, whereas the changes in globulin, albumin and glutenin contents were variety dependent. In addition, the albumin and globulin contents of FHN003 were decreased, whereas those of Suyunuo 5 were not affected. The glutenin content of FHN003 under control and shading was similar, whereas that of Suyunuo 5 under shading was significantly decreased.
Granule size distribution Shading during grain filling had significant effects on starch granule size distribution (Table 2). It increased the percentage of medium starch granules (diameter between 9 and 17 m) and decreased the percentage of large starch granules (diameter >17 m), whereas the percentage of small starch granules (<9 m) in response
RESULTS Grain weight and water content Grain fresh weight of Suyunuo 5 and FHN003 were decreased by 8.4 and 19.1%, respectively. The serious decrement of yield in FHN003 indicated that this variety was more sensitive to weak light (Fig. 1). In Suyunuo 5, water content under control and shading were 61.1 and 60.7%, respectively, indicated the variety was not affected by shading. In FHN003, the water content under
Fig. 1 Effect of shading on grain fresh weight and water content in fresh waxy maize.
Table 1 Effect of shading on the proximate composition of flour for fresh waxy maize Variety
Treatment
Soluble sugar (%)
Starch (%)
Protein (%)
Albumin (%)
Suyunuo 5
Control Shading Control Shading
7.71±0.38 c 5.93±0.74 d 12.5±0.14 a 10.8±0.81 b
68.3±1.6 a 66.5±0.9 b 59.2±0.7 c 56.5±0.3 d
10.4±0.12 b 10.1±0.01 c 10.9±0.02 a 9.7±0.21 d
2.4±0.12 b 2.5±0.05 b 3.5±0.09 a 2.4±0.07 b
FHN003
Globulin (%) 0.62±0.06 a 0.54±0.03 ab 0.48±0.03 b 0.36±0.11 c
Zein (%) 2.8±0.09 c 3.1±0.14 ab 2.9±0.08 bc 3.2±0.13 a
Glutenin (%) 3.2±0.08 a 2.7±0.36 b 2.5±0.11 b 2.4±0.55 b
Values in the same column with the same letters do not differ significantly (P<0.05). The same as below.
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to shading was variety dependent. In Suyunuo 5, shading decreased the percentage of starch granules that diameter was <5 m, whereas percentage of starch granules that diameter between 5 and 9 m was increased. A contrary changing trend was observed in FHN003.
Iodine binding capacity Compared with control, shading decreased the blue value, max, and iodine binding capacity of both varieties (Table 3). However, both max and iodine binding capacity presented a typical waxy character, and no differences were observed between the two varieties.
Crystalline property Shading during grain filling did not affect the crystalline types, all samples showed peaks at 2θ=15, 23, 17, 18°, indicating a typical A-type diffraction pattern (Fig. 2). Shading increased the peak intensities of both varieties, results in their higher crystallinities (20.5 vs. 18.3% in FHN003 and 23.1 vs. 17.9% in Suyunuo 5).
Pasting property Pasting characteristics, except for pasting temperature, were significantly affected by shading (Table 4). Characteristics, including peak, trough, breakdown, final, and setback viscosities, were decreased by shading in both varieties; however, the decrement was more serious in FHN003 than in Suyunuo 5. Compared with FHN003, Suyunuo 5 under both treatments presented higher peak and breakdown viscosities, indicated its
better processing quality.
Thermal property Thermal characteristics observed via differential scanning calorimetry showed that ΔHgel and transition temperatures (To, Tp and Tc) of Suyunuo 5 were not affected by shading (Table 5). However, ΔHgel was increased and transition temperatures were decreased by shading for FHN003. Shading decreased %R in both varieties; and a lower %R was found in Suyunuo 5 than in FHN003, indicated the lower retrogradation tendency of Suyunuo 5 than FHN003, which endowed its advantage on quickly iced cobs. The change in ΔHret under shading was variety dependent. It was decreased in Suyunuo 5 but was not affected in FHN003.
Textural property Shading during grain filling decreased the hardness, cohesiveness and chewiness in both varieties (Table 6). The adhesiveness of FNH003 was decreased by shading, whereas that of Suyunuo 5 was not affected by it. In addition, shading decreased the resilience of Suyunuo 5 but did not affect that of FNH003. The average values of hardness, cohesiveness, chewiness, resilience, and adhesiveness obtained from Suyunuo 5 were lower than those obtained from FHN003.
DISCUSSION Shading among different stages of maize growth decreases grain yield because maize is a C4 plant that
Table 2 Effect of shading on the starch granule volume size distribution in fresh waxy maize Variety
Treatment
<5 m (%)
5-9 m (%)
9-13 m (%)
13-17 m (%)
>17 m (%)
Suyunuo 5
Control Shading Control Shading
3.5±0.2 a 1.0±0.1 b 1.5±0.0 b 3.6±1.5 a
17.0±0.8 c 25.2±0.3 a 21.3±1.0 b 16.3±1.9 d
19.0±1.4 c 26.9±0.9 a 20.8±1.0 b 26.4±0.2 a
11.8±2.1 c 14.0±0.7 b 11.1±1.2 c 19.1±0.5 a
48.7±1.4 a 32.9±1.9 b 45.3±3.2 a 34.6±0.1 b
FHN003
Table 3 Effect of shading on the iodine binding capacity of flour for fresh waxy maize Variety
Treatment
Blue value
Suyunuo 5
Control Shading Control Shading
0.158±0.009 a 0.131±0.007 b 0.154±0.005 a 0.133±0.005 b
FHN003
λmax (nm) 533.2±2.9 a 528.5±0.0 b 537.7±2.8 a 530.9±0.7 b
Iodine binding capacity 0.557±0.012 a 0.511±0.003 b 0.579±0.013 a 0.523±0.014 b
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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
Fig. 2 Effect of shading on crystalline pattern of fresh waxy maize.
needs high light radiation intensity (Earley et al. 1966; Chan and Mackenzie 1972; Earle 1977; Setter et al. 2001; Jia et al. 2007, 2011). At present study, shading decreased the grain fresh weight of both varieties; FHN003, which was sensitive to light stress, was more seriously affected than Suyunuo 5. Shading increased the water content of FHN003 but did not affect that of Suyunuo 5. Jia et al. (2007) demonstrated the same result in mature normal maize grains. This finding may be attributed to delayed grain filling rate and prolonged grain filling stage when light intensity was insufficient. Shading during grain filling significantly decreased
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starch and soluble sugar content in grains. Similar results were observed on normal and high-starch maize (Setter et al. 2001; Jia et al. 2007, 2011). Shading could also decrease starch and sucrose content of sunflower leaves (Correia et al. 2006). The lower starch content under shading may be due to the decreased activities of key starch synthesis enzymes (Jia et al. 2007; Zhang et al. 2008). Shading also decreases the activities of protein synthesis enzymes in maize (Earley et al. 1966, 1967; Jia et al. 2007; Zhang et al. 2008), which could retard protein accumulation and decrease protein content. A similar observation was found in oat (Doehlert et al. 2001). According to Li et al. (2012), moderate low light intensities decrease protein content, whereas severe shading increases protein content. The increase in protein content for severe shaded grains is mostly a result of the concentration effects (Li et al. 2012) because the reduction in grain protein is not proportionally as great as the reduction in grain yield (Early et al. 1967). Shading increased zein content, whereas the changes in globulin, albumin and glutenin contents were variety dependent. The variety-dependent effects of shading on protein fractions were also observed in wheat except gliadin (zein), which gradually increased with increasing shading intensity (Li et al. 2012).
Table 4 Effect of shading on the pasting property of flour for fresh waxy maize Variety Suyunuo 5 FHN003
Treatment
PV (cP)
Control Shading Control Shading
1 240.0±50.9 a 1 089.5±13.4 b 1 028.5±44.5 b 596.5±24.7 c
TV (cP) 534.0±18.4 b 445.5±13.4 c 717.5±30.4 a 354.5±19.1 d
BD (cP) 706.0±32.5 a 644.0±0.0 b 311.0±14.1 c 242.0±5.7 d
FV (cP)
SB (cP)
Ptemp (°C)
677.5±14.8 b 539.5±9.2 c 874.5±43.1 a 443.0±5.7 d
143.5±3.5 a 94.0±4.2 b 157.0±12.7 a 88.5±13.4 b
70.3±0.6 a 70.3±0.7 a 68.7±0.5 a 69.5±0.6 a
PV, peak viscosity; TV, trough viscosity; BD, breakdown viscosity; FV, final viscosity; SB, setback viscosity; Ptemp, pasting temperature.
Table 5 Effect of shading on the pasting properties of flour for fresh waxy maize Variety Suyunuo 5 FHN003
Treatment
ΔHgel (J g-1)
To (°C)
Tp (°C)
Tc (°C)
ΔHret (J g-1)
%R
Control Shading Control Shading
7.2±0.2 ab 6.9±0.1 ab 6.5±0.7 b 7.8±0.9 a
66.8±0.2 a 67.2±0.0 a 67.0±0.1 a 66.3±0.0 b
72.7±0.0 a 72.8±0.0 a 72.8±0.1 a 72.1±0.1 b
79.9±0.3 a 80.0±0.1 a 79.3±0.1 b 78.9±0.1 c
0.9±0.2 b 0.3±0.0 c 1.7±0.0 a 1.6±0.1 a
12.5±2.2 c 3.8±0.1 d 26.3±1.0 a 20.9±0.6 b
ΔHgel, gelatinization enthalpy; To, onset temperature; Tp, peak gelatinization temperature; Tc, conclusion temperature; ΔHret, retrogradation enthalpy; %R, retrogradation percentage.
Table 6 Effect of shading on the textural property of flour for fresh waxy maize Variety
Treatment
Hardness (g)
Adhesiveness
Cohesiveness
Chewiness
Suyunuo 5
Control Shading Control Shading
10 782.8±1 103.8 c 10 294.7±1 315.8 d 13 617.7±1 080.0 a 12 358.1±988.6 b
-16.7±6.9 b -18.3±5.2 b -10.9±4.6 a -17.9±6.3 b
0.296±0.029 b 0.258±0.043 c 0.328±0.029 a 0.295±0.047 b
1 349.0±411.5 bc 1 008.6±395.1 c 1 904.7±373.6 a 1 483.2±467.3 b
FHN003
Resilience 0.241±0.024 a 0.210±0.041 b 0.258±0.024 a 0.250±0.045 a
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In both varieties, shading during grain filling significantly decreased the percentage of starch granules >17 m in diameter. Similar results were reported in spring barley (Grashoff and Antuono 1997), wheat (Cai et al. 2008) and cassava (Min et al. 2010). Jia et al. (2011) also reported that endosperm cells were decreased under shading in normal maize by scanning electron microscopy. This finding may be because the shading after pollination delayed grain filling and inhibited endosperm cell enlargement. In amylopectin, max and iodine binding capacity, which depend on the length of glucan helices, were found to be approximately 540 nm and 0.55, respectively (Fiedorowicz and Rebilas 2002). All samples measured by max and crystalline diffraction pattern presented a typical waxy character (Chang et al. 2006). Compared with control, shading decreased blue value, max and iodine binding capacity, indicating that starch without shading had a higher ratio of long chain branch (Fiedorowicz and Rebilas 2002). The crystallinity of both varieties was increased because the sample under shading processed small starch granules that can easily form gels (Ji et al. 2003). The pasting characteristics, including peak, trough, breakdown, final, and setback viscosities, were decreased by shading in both varieties. The sample without shading had higher starch content and larger granules. Compared with Suyunuo 5, the pasting characteristics of FHN003 were more seriously affected by shading because of its sensitivity to weak light. Jia et al. (2007) also reported that peak and breakdown viscosities were decreased by shading in normal and high-starch maize. Bao et al. (2004) observed that rice starch presents higher peak and breakdown viscosities when the growth season has higher light intensity. Under both treatments, the peak and breakdown viscosities of Suyunuo 5 were higher than those of FHN003, indicating its better viscous taste. Significant differences in pasting characteristics were also observed among different varieties (Sandhu et al. 2005; Chang et al. 2006; Singh et al. 2006; Sandhu and Singh 2007). The transition temperatures (To, Tp and Tc) and %R of rice starch under the growth seasons have higher temperature, higher light intensity and less rainfall (Xu et al. 2004). At present study, ΔH gel and transition temperatures of Suyunuo 5 were not affected by shading. By contrast, shading increased the ΔHgel and
decreased the transition temperatures of FHN003. Shading decreased the %R of both varieties. This parameter was found higher in rice starch when the growth seasons have high light intensities (Xu et al. 2004). ΔHret and %R of Suyunuo 5 under both treatments were lower than those of FNH003, indicated the lower retrogradation tendency of Suyunuo 5, which endowed its advantage in chilled foodstuffs. Bao et al. (2004) observed that rice starch under growth seasons with less light intensities presents higher hardness. By contrast, adhesiveness and cohesiveness were not affected by growth environment. In the present study, the grains under control presented higher grain weight, lower water content and higher proximate (sugar, starch and protein) content. As a result, the grains of both varieties under control had higher hardness, cohesiveness and chewiness. Adhesiveness and resilience in response to shading were variety dependent. The average values of hardness, cohesiveness, chewiness, resilience, and adhesiveness obtained from Suyunuo 5 were lower than those obtained from FHN003, indicating its better eating quality (i.e., viscous and soft taste).
CONCLUSION Shading after pollination decreased grain fresh weight of both varieties, and the decrement was more seriously for FHN003. Under shading, grain water content of FHN003 was higher than that of Suyunuo 5, indicating its slowly filling rate. In both varieties, shading decreased the content of grain starch, soluble sugar and protein, iodine binding capacity, and the percentage of large starch granule (diameter >17 m) but increased crystallinity, which results in the lower peak and breakdown viscosities, %R, hardness, cohesiveness, and chewiness. Compared with FHN003, Suyunuo 5 under both treatments presented higher peak and breakdown viscosities and lower %R, hardness, adhesiveness, and chewiness, indicating its better eating and processing quality.
MATERIALS AND METHODS Experimental design The experiment was conducted at the Experimental Farm of
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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
Yangzhou University, China (32°24´N, 119°26´E) in 2011. The soil is sandy loam containing 0.88 g kg-1 total N, 37.2 mg kg-1 available N, 20.1 mg kg-1 available P, and 86.2 mg kg-1 available K at 0-20 cm soil layer. Two waxy maize varieties, Suyunuo 5 (shading tolerant) and FHN003 (shading sensitive), were used. The sowing date was 1 July 2011; the optimum sowing date was between 25 June 2011 and 5 July 2011. At the jointing stage, the plants were given approximately 500 kg ha-1 of basal fertilizer (commercial fertilizer, N/P2O5/K2O=15%:15%:15%) before sowing and 326 kg ha -1 of top dressing (commercial urea, N content =46%). The experimental design was a split-plot with two replicates, with shading in the main plots and cultivars in the sub-plots. Other crop management methods were conducted following the same procedure as that for conventional high-yielding cultivation. The plants were covered with a layer of black polyethylene nets, which blocked approximately 30% of the solar radiation above the canopy in clear days during grain filling (0 to 23 d after pollination). Plants without shading were set as control. Nets were placed more than 450 cm higher above the ground to allow a good ventilation condition. The microclimate (CO 2 and temperature) was similar except for light intensity, which at 1, 6 and 13 Sep. was 1 635 and 1 260, 1 428 and 1 028 and 1 150 and 810 mol m-2 s-1 for the control and shading, respectively.
Grain fresh weight and water content Grains were picked off from the cob, and the weight of 100 grains was determined. The dry weight was weighed after the grains were dried at 40°C to constant weight. Water content (%)=(1-Dry weight/Fresh weight)×100
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Protein extraction The protein fractions albumin, globulin, zein, and glutenin were sequentially extracted from 1 g of flour (Luthe 1983). During each extraction step, the samples were continuously stirred for 20 min in a magnetic stirrer. Soluble and insoluble fractions were separated by centrifugation at 5 000×g for 10 min. Albumin was extracted at 20°C with 10 mL of pure water. Globulin, zein and glutenin were extracted at 20, 85 and 20°C from the previous pellet with 10 mL of 0.1 mol L-1 NaCl, 75% (v/v) ethanol and 0.02 mol L-1 NaOH, respectively. Each extraction step was repeated four times for all protein fractions.
Proximate analysis Soluble sugar and starch content in flour were determined according to ICC Method No. 123/1 (ICC 1994). Nitrogen content was determined using the Kjeldahl method (AACC 1990), and protein content was evaluated by measuring the nitrogen content (Protein content=Nitrogen content×6.25).
Granule size distribution Particle size characteristics of starch were analyzed using a laser diffraction particle size analyzer (Mastersizer 2000, Malvern, England). The accuracy of the instrument was checked with Malvern standard glass particles. The instrument, which is based on the principle of laser light scattering, can measure sizes between 0.1 and 2 000 m. The size distribution is expressed in terms of the volumes of equivalent spheres. The criteria selected are the percentage volume (% vol.) of granules following the standard proposed by Ji et al. (2003).
Processing of flour X-ray diffraction pattern Grains were ground in a grinder, passed through a 100mesh (0.149 mm) sieve, and then oven dried at 40°C.
Starch isolation Starch was isolated from the grains following the methods described by Sandhu et al. (2005) with minor modifications following Lu and Lu (2012).
Blue value, λmax and iodine binding capacity The λmax and blue values of flour were measured according to the method described by Chang et al. (2006). The iodine binding capacity is equal to the blue value at 635 nm/520 nm.
X-ray diffraction patterns were obtained using an X-ray diffractometer (D8 Advance, Bruker-AXS, Germany) operated at 200 mA and 40 kV. The scanning region of the diffraction angle (2θ) ranged from 3 to 40° at 0.04° step size with a count time of 0.6 s. The degree of crystallinity was calculated based on the methods of Hayakawa et al. (1997).
Textural properties Fresh waxy maize cobs were boiled in an electric cooker for 30 min, and the textural properties of fully cooked grains cut off from the mid of the cob were immediately measured using a TA-XT2i texture analyzer (Stable Micro Systems, England) coupled with an aluminum plate probe (35.0 mm
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in diameter). Some parameters of the compression mode were set as follows: pretest speed, 1.0 mm s-1; test speed, 2.0 mm s-1; posttest speed, 2.0 mm s-1; trigger force, 15 g; and distance, 70% of the initial sample height. A force-time curve was obtained from the test, and the textural results discussed in the following subsections were determined.
Thermal properties The thermal characteristics of flour were studied using a differential scanning calorimeter (Model 200 F3 Maia, NETZSCH, Germany) according to the method described by Sandhu and Singh (2007).
Pasting properties The pasting properties of flour were evaluated with a rapid visco analyzer (Model 3D, Newport Scientific, Australia). The sample suspension (28 g total weight, 10%, w/w, dry basis for flour) was equilibrated at 50°C for 1 min, heated to 95°C at a rate of 12°C min-1, maintained at 95°C for 2.5 min, cooled to 50°C at 12°C min-1, and then maintained at 50°C for 1 min. Paddle speed was set to 960 r min-1 for the first 10 s and then to 160 r min-1 for the rest of the analysis.
Statistical analysis The data were subjected to analysis of variance using the least significant difference test at the 5% probability level using the data processing system (DPS 7.05) proposed by Tang and Feng (2007). The figures were obtained from Microsoft Excel 2003.
Acknowledgements The study was financially supported by the National Natural Science Foundation of China (30971731, 31000684 and 31271640) and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.
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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
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Setter T L, Flannigan B A, Melkonian J. 2001. Loss of kernel set due to water deficit and shade in maize: carbohydrate supplies, abscisic acid, and cytokinins. Crop Science, 41, 1530-1540. Simla S, Lertrat K, Suriharn B. 2010. Carbohydrate characters of six vegetable waxy corn varieties as affected by harvest time and storage duration. Asian Journal of Plant Science, 9, 463-470. Singh N, Inouchi N, Nishinari K. 2006. Structure, thermal and viscoelastic characteristics of starches separated from normal, sugary and waxy maize. Food Hydrocolloids, 20, 923-935. Tang Q Y, Feng M G. 2007. DPS Data Processing System: Experimental Design, Statistical Analysis and Data Mining. Science Press, Beijing, China. (in Chinese) Xu L J, Xie J K, Kong X L, Bao J S. 2004. Analysis of genotypic and environmental effects on rice starch. 2: thermal and retrogradation properties. Journal of Agriculture and Food Chemistry, 52, 6017-6022. Zhang J W, Dong S T, Wang K J, Hu C H, Liu P. 2008. Effects of shading in field on key enzymes involved in starch synthesis of summer maize. Acta Agronomica Sinica, 34, 1470-1474. (in Chinese) (Managing editor WANG Ning)
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2013, 12(9): 1560-1567
RESEARCH ARTICLE
Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize LU Da-lei, SUN Xu-li, WANG Xin, YAN Fa-bao and LU Wei-ping Key Laboratory of Crop Genetics and Physiology of Jiangsu Province/Key Laboratory of Crop Physiology, Ecology and Cultivation in Middle and Lower Reaches of Yangtse River, Ministry of Agriculture/College of Agriculture, Yangzhou University, Yangzhou 225009, P.R.China
Abstract Grain physicochemical properties determine the table quality of fresh waxy maize. Two waxy maize varieties, Suyunuo 5 (shading tolerant) and FHN003 (shading sensitive), were used to estimate the effect of shading (plants received 30% less radiation than control) during grain filling (from 0 d to 23 d after pollination) on physicochemical properties of fresh waxy maize grain. Shading decreased the grain fresh weight of Suyunuo 5 and FHN003 by 8.4 and 19.1%, respectively. Shading increased the grain water content of FHN003, whereas that of Suyunuo 5 was not affected. In both varieties for shading treatment, soluble sugar, starch and protein contents were decreased, whereas zein content was increased. The changes in globulin, albumin and glutenin contents under shading were variety dependent. In both varieties, shading decreased λmax, iodine binding capacity and the percentage of large starch granules (diameter >17 m) but increased crystallinity. The results of rapid visco analysis showed that the viscosity characteristics (except for pasting temperature) of both varieties were decreased by shading; however, FHN003 was more severely affected than Suyunuo 5. Under shading, ΔHret and %R were decreased in both varieties, whereas the changes in ΔH gel and transition temperatures were variety dependent. Hardness, cohesiveness and chewiness were decreased in both varieties. Significant differences in physicochemical characteristics were observed between the two varieties. Key words: fresh waxy maize, shading, grain quality, physicochemical property
INTRODUCTION Waxy maize endosperm starch is composed of nearly 100% amylopectin, which endows its better viscous taste and easy digestion compared with other maize types such as normal or sweet maize (Singh et al. 2006). Waxy maize is mainly produced for fresh eating in China. With the improvement of national living standards, there is a promising trend for fresh waxy maize market expansion both domestically and internationally. Physicochemical properties of grain are important
in determining the table quality of waxy maize (Simla et al. 2010). Physicochemical characteristics of maize are different among various genotypes and controlled by the interaction between environment and cultivation measures (Earle 1977). Therefore, with the advancements in germplasm and cultivation measures, environment plays an important role in maize grain quality improvement. As a major environmental factor of crop growth, light intensity influences both the yield and quality of maize (Earley et al. 1966; Chan and Mackenzie 1972; Earle 1977; Setter et al. 2001). The effect of shading
Received 30 July, 2012 Accepted 22 November, 2012 LU Da-lei, E-mail: [email protected]; Correspondence LU Wei-ping, Tel: +86-514-87979377, Fax: +86-514-87976817, E-mail: [email protected]
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S2095-3119(13)60560-2
Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
on grain formation at grain filling stage is larger than other stages (Kiniry and Ritchie 1985). Low light intensity after pollination reduces grain yield and starch content, whereas protein content is variety dependent (Earley et al. 1966; Jia et al. 2007, 2011). Shading also decreases the activities of enzymes involved in starch and protein syntheses (Jia et al. 2007; Zhang et al. 2008). However, little is known about the effect of shading on the physicochemical properties (e.g., pasting, thermal, and textural characteristics) of maize during grain filling, all of which determine its final product quality (Jia et al. 2007). Field microclimates after pollination play important roles in determining waxy maize grain yield and quality formation. In waxy maize production, the sowing period is from middle March to middle August in Jiangsu Province, China. The weak light during grain filling due to late sowing dates is an important environmental factor that affects plant growth. However, little is known about the effect of weak light on the quality of waxy maize. Thus, plants were subjected to shading during grain filling under field conditions to determine the effect of low radiation on the grain composition and physicochemical properties of fresh waxy maize. The generated results may serve as a basis for improving the quality of fresh waxy maize.
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shading (67.1%) was significantly higher than that under control (61.4%), indicated that grain filling rate was delayed when light intensity was insufficient.
Proximate compositions Compared with control, shading decreased the soluble sugar, starch and protein contents for both varieties (Table 1). Suyunuo 5 had higher starch content and lower sugar content than FHN003. Under shading, zein content was increased, whereas the changes in globulin, albumin and glutenin contents were variety dependent. In addition, the albumin and globulin contents of FHN003 were decreased, whereas those of Suyunuo 5 were not affected. The glutenin content of FHN003 under control and shading was similar, whereas that of Suyunuo 5 under shading was significantly decreased.
Granule size distribution Shading during grain filling had significant effects on starch granule size distribution (Table 2). It increased the percentage of medium starch granules (diameter between 9 and 17 m) and decreased the percentage of large starch granules (diameter >17 m), whereas the percentage of small starch granules (<9 m) in response
RESULTS Grain weight and water content Grain fresh weight of Suyunuo 5 and FHN003 were decreased by 8.4 and 19.1%, respectively. The serious decrement of yield in FHN003 indicated that this variety was more sensitive to weak light (Fig. 1). In Suyunuo 5, water content under control and shading were 61.1 and 60.7%, respectively, indicated the variety was not affected by shading. In FHN003, the water content under
Fig. 1 Effect of shading on grain fresh weight and water content in fresh waxy maize.
Table 1 Effect of shading on the proximate composition of flour for fresh waxy maize Variety
Treatment
Soluble sugar (%)
Starch (%)
Protein (%)
Albumin (%)
Suyunuo 5
Control Shading Control Shading
7.71±0.38 c 5.93±0.74 d 12.5±0.14 a 10.8±0.81 b
68.3±1.6 a 66.5±0.9 b 59.2±0.7 c 56.5±0.3 d
10.4±0.12 b 10.1±0.01 c 10.9±0.02 a 9.7±0.21 d
2.4±0.12 b 2.5±0.05 b 3.5±0.09 a 2.4±0.07 b
FHN003
Globulin (%) 0.62±0.06 a 0.54±0.03 ab 0.48±0.03 b 0.36±0.11 c
Zein (%) 2.8±0.09 c 3.1±0.14 ab 2.9±0.08 bc 3.2±0.13 a
Glutenin (%) 3.2±0.08 a 2.7±0.36 b 2.5±0.11 b 2.4±0.55 b
Values in the same column with the same letters do not differ significantly (P<0.05). The same as below.
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to shading was variety dependent. In Suyunuo 5, shading decreased the percentage of starch granules that diameter was <5 m, whereas percentage of starch granules that diameter between 5 and 9 m was increased. A contrary changing trend was observed in FHN003.
Iodine binding capacity Compared with control, shading decreased the blue value, max, and iodine binding capacity of both varieties (Table 3). However, both max and iodine binding capacity presented a typical waxy character, and no differences were observed between the two varieties.
Crystalline property Shading during grain filling did not affect the crystalline types, all samples showed peaks at 2θ=15, 23, 17, 18°, indicating a typical A-type diffraction pattern (Fig. 2). Shading increased the peak intensities of both varieties, results in their higher crystallinities (20.5 vs. 18.3% in FHN003 and 23.1 vs. 17.9% in Suyunuo 5).
Pasting property Pasting characteristics, except for pasting temperature, were significantly affected by shading (Table 4). Characteristics, including peak, trough, breakdown, final, and setback viscosities, were decreased by shading in both varieties; however, the decrement was more serious in FHN003 than in Suyunuo 5. Compared with FHN003, Suyunuo 5 under both treatments presented higher peak and breakdown viscosities, indicated its
better processing quality.
Thermal property Thermal characteristics observed via differential scanning calorimetry showed that ΔHgel and transition temperatures (To, Tp and Tc) of Suyunuo 5 were not affected by shading (Table 5). However, ΔHgel was increased and transition temperatures were decreased by shading for FHN003. Shading decreased %R in both varieties; and a lower %R was found in Suyunuo 5 than in FHN003, indicated the lower retrogradation tendency of Suyunuo 5 than FHN003, which endowed its advantage on quickly iced cobs. The change in ΔHret under shading was variety dependent. It was decreased in Suyunuo 5 but was not affected in FHN003.
Textural property Shading during grain filling decreased the hardness, cohesiveness and chewiness in both varieties (Table 6). The adhesiveness of FNH003 was decreased by shading, whereas that of Suyunuo 5 was not affected by it. In addition, shading decreased the resilience of Suyunuo 5 but did not affect that of FNH003. The average values of hardness, cohesiveness, chewiness, resilience, and adhesiveness obtained from Suyunuo 5 were lower than those obtained from FHN003.
DISCUSSION Shading among different stages of maize growth decreases grain yield because maize is a C4 plant that
Table 2 Effect of shading on the starch granule volume size distribution in fresh waxy maize Variety
Treatment
<5 m (%)
5-9 m (%)
9-13 m (%)
13-17 m (%)
>17 m (%)
Suyunuo 5
Control Shading Control Shading
3.5±0.2 a 1.0±0.1 b 1.5±0.0 b 3.6±1.5 a
17.0±0.8 c 25.2±0.3 a 21.3±1.0 b 16.3±1.9 d
19.0±1.4 c 26.9±0.9 a 20.8±1.0 b 26.4±0.2 a
11.8±2.1 c 14.0±0.7 b 11.1±1.2 c 19.1±0.5 a
48.7±1.4 a 32.9±1.9 b 45.3±3.2 a 34.6±0.1 b
FHN003
Table 3 Effect of shading on the iodine binding capacity of flour for fresh waxy maize Variety
Treatment
Blue value
Suyunuo 5
Control Shading Control Shading
0.158±0.009 a 0.131±0.007 b 0.154±0.005 a 0.133±0.005 b
FHN003
λmax (nm) 533.2±2.9 a 528.5±0.0 b 537.7±2.8 a 530.9±0.7 b
Iodine binding capacity 0.557±0.012 a 0.511±0.003 b 0.579±0.013 a 0.523±0.014 b
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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
Fig. 2 Effect of shading on crystalline pattern of fresh waxy maize.
needs high light radiation intensity (Earley et al. 1966; Chan and Mackenzie 1972; Earle 1977; Setter et al. 2001; Jia et al. 2007, 2011). At present study, shading decreased the grain fresh weight of both varieties; FHN003, which was sensitive to light stress, was more seriously affected than Suyunuo 5. Shading increased the water content of FHN003 but did not affect that of Suyunuo 5. Jia et al. (2007) demonstrated the same result in mature normal maize grains. This finding may be attributed to delayed grain filling rate and prolonged grain filling stage when light intensity was insufficient. Shading during grain filling significantly decreased
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starch and soluble sugar content in grains. Similar results were observed on normal and high-starch maize (Setter et al. 2001; Jia et al. 2007, 2011). Shading could also decrease starch and sucrose content of sunflower leaves (Correia et al. 2006). The lower starch content under shading may be due to the decreased activities of key starch synthesis enzymes (Jia et al. 2007; Zhang et al. 2008). Shading also decreases the activities of protein synthesis enzymes in maize (Earley et al. 1966, 1967; Jia et al. 2007; Zhang et al. 2008), which could retard protein accumulation and decrease protein content. A similar observation was found in oat (Doehlert et al. 2001). According to Li et al. (2012), moderate low light intensities decrease protein content, whereas severe shading increases protein content. The increase in protein content for severe shaded grains is mostly a result of the concentration effects (Li et al. 2012) because the reduction in grain protein is not proportionally as great as the reduction in grain yield (Early et al. 1967). Shading increased zein content, whereas the changes in globulin, albumin and glutenin contents were variety dependent. The variety-dependent effects of shading on protein fractions were also observed in wheat except gliadin (zein), which gradually increased with increasing shading intensity (Li et al. 2012).
Table 4 Effect of shading on the pasting property of flour for fresh waxy maize Variety Suyunuo 5 FHN003
Treatment
PV (cP)
Control Shading Control Shading
1 240.0±50.9 a 1 089.5±13.4 b 1 028.5±44.5 b 596.5±24.7 c
TV (cP) 534.0±18.4 b 445.5±13.4 c 717.5±30.4 a 354.5±19.1 d
BD (cP) 706.0±32.5 a 644.0±0.0 b 311.0±14.1 c 242.0±5.7 d
FV (cP)
SB (cP)
Ptemp (°C)
677.5±14.8 b 539.5±9.2 c 874.5±43.1 a 443.0±5.7 d
143.5±3.5 a 94.0±4.2 b 157.0±12.7 a 88.5±13.4 b
70.3±0.6 a 70.3±0.7 a 68.7±0.5 a 69.5±0.6 a
PV, peak viscosity; TV, trough viscosity; BD, breakdown viscosity; FV, final viscosity; SB, setback viscosity; Ptemp, pasting temperature.
Table 5 Effect of shading on the pasting properties of flour for fresh waxy maize Variety Suyunuo 5 FHN003
Treatment
ΔHgel (J g-1)
To (°C)
Tp (°C)
Tc (°C)
ΔHret (J g-1)
%R
Control Shading Control Shading
7.2±0.2 ab 6.9±0.1 ab 6.5±0.7 b 7.8±0.9 a
66.8±0.2 a 67.2±0.0 a 67.0±0.1 a 66.3±0.0 b
72.7±0.0 a 72.8±0.0 a 72.8±0.1 a 72.1±0.1 b
79.9±0.3 a 80.0±0.1 a 79.3±0.1 b 78.9±0.1 c
0.9±0.2 b 0.3±0.0 c 1.7±0.0 a 1.6±0.1 a
12.5±2.2 c 3.8±0.1 d 26.3±1.0 a 20.9±0.6 b
ΔHgel, gelatinization enthalpy; To, onset temperature; Tp, peak gelatinization temperature; Tc, conclusion temperature; ΔHret, retrogradation enthalpy; %R, retrogradation percentage.
Table 6 Effect of shading on the textural property of flour for fresh waxy maize Variety
Treatment
Hardness (g)
Adhesiveness
Cohesiveness
Chewiness
Suyunuo 5
Control Shading Control Shading
10 782.8±1 103.8 c 10 294.7±1 315.8 d 13 617.7±1 080.0 a 12 358.1±988.6 b
-16.7±6.9 b -18.3±5.2 b -10.9±4.6 a -17.9±6.3 b
0.296±0.029 b 0.258±0.043 c 0.328±0.029 a 0.295±0.047 b
1 349.0±411.5 bc 1 008.6±395.1 c 1 904.7±373.6 a 1 483.2±467.3 b
FHN003
Resilience 0.241±0.024 a 0.210±0.041 b 0.258±0.024 a 0.250±0.045 a
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In both varieties, shading during grain filling significantly decreased the percentage of starch granules >17 m in diameter. Similar results were reported in spring barley (Grashoff and Antuono 1997), wheat (Cai et al. 2008) and cassava (Min et al. 2010). Jia et al. (2011) also reported that endosperm cells were decreased under shading in normal maize by scanning electron microscopy. This finding may be because the shading after pollination delayed grain filling and inhibited endosperm cell enlargement. In amylopectin, max and iodine binding capacity, which depend on the length of glucan helices, were found to be approximately 540 nm and 0.55, respectively (Fiedorowicz and Rebilas 2002). All samples measured by max and crystalline diffraction pattern presented a typical waxy character (Chang et al. 2006). Compared with control, shading decreased blue value, max and iodine binding capacity, indicating that starch without shading had a higher ratio of long chain branch (Fiedorowicz and Rebilas 2002). The crystallinity of both varieties was increased because the sample under shading processed small starch granules that can easily form gels (Ji et al. 2003). The pasting characteristics, including peak, trough, breakdown, final, and setback viscosities, were decreased by shading in both varieties. The sample without shading had higher starch content and larger granules. Compared with Suyunuo 5, the pasting characteristics of FHN003 were more seriously affected by shading because of its sensitivity to weak light. Jia et al. (2007) also reported that peak and breakdown viscosities were decreased by shading in normal and high-starch maize. Bao et al. (2004) observed that rice starch presents higher peak and breakdown viscosities when the growth season has higher light intensity. Under both treatments, the peak and breakdown viscosities of Suyunuo 5 were higher than those of FHN003, indicating its better viscous taste. Significant differences in pasting characteristics were also observed among different varieties (Sandhu et al. 2005; Chang et al. 2006; Singh et al. 2006; Sandhu and Singh 2007). The transition temperatures (To, Tp and Tc) and %R of rice starch under the growth seasons have higher temperature, higher light intensity and less rainfall (Xu et al. 2004). At present study, ΔH gel and transition temperatures of Suyunuo 5 were not affected by shading. By contrast, shading increased the ΔHgel and
decreased the transition temperatures of FHN003. Shading decreased the %R of both varieties. This parameter was found higher in rice starch when the growth seasons have high light intensities (Xu et al. 2004). ΔHret and %R of Suyunuo 5 under both treatments were lower than those of FNH003, indicated the lower retrogradation tendency of Suyunuo 5, which endowed its advantage in chilled foodstuffs. Bao et al. (2004) observed that rice starch under growth seasons with less light intensities presents higher hardness. By contrast, adhesiveness and cohesiveness were not affected by growth environment. In the present study, the grains under control presented higher grain weight, lower water content and higher proximate (sugar, starch and protein) content. As a result, the grains of both varieties under control had higher hardness, cohesiveness and chewiness. Adhesiveness and resilience in response to shading were variety dependent. The average values of hardness, cohesiveness, chewiness, resilience, and adhesiveness obtained from Suyunuo 5 were lower than those obtained from FHN003, indicating its better eating quality (i.e., viscous and soft taste).
CONCLUSION Shading after pollination decreased grain fresh weight of both varieties, and the decrement was more seriously for FHN003. Under shading, grain water content of FHN003 was higher than that of Suyunuo 5, indicating its slowly filling rate. In both varieties, shading decreased the content of grain starch, soluble sugar and protein, iodine binding capacity, and the percentage of large starch granule (diameter >17 m) but increased crystallinity, which results in the lower peak and breakdown viscosities, %R, hardness, cohesiveness, and chewiness. Compared with FHN003, Suyunuo 5 under both treatments presented higher peak and breakdown viscosities and lower %R, hardness, adhesiveness, and chewiness, indicating its better eating and processing quality.
MATERIALS AND METHODS Experimental design The experiment was conducted at the Experimental Farm of
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Effect of Shading During Grain Filling on the Physicochemical Properties of Fresh Waxy Maize
Yangzhou University, China (32°24´N, 119°26´E) in 2011. The soil is sandy loam containing 0.88 g kg-1 total N, 37.2 mg kg-1 available N, 20.1 mg kg-1 available P, and 86.2 mg kg-1 available K at 0-20 cm soil layer. Two waxy maize varieties, Suyunuo 5 (shading tolerant) and FHN003 (shading sensitive), were used. The sowing date was 1 July 2011; the optimum sowing date was between 25 June 2011 and 5 July 2011. At the jointing stage, the plants were given approximately 500 kg ha-1 of basal fertilizer (commercial fertilizer, N/P2O5/K2O=15%:15%:15%) before sowing and 326 kg ha -1 of top dressing (commercial urea, N content =46%). The experimental design was a split-plot with two replicates, with shading in the main plots and cultivars in the sub-plots. Other crop management methods were conducted following the same procedure as that for conventional high-yielding cultivation. The plants were covered with a layer of black polyethylene nets, which blocked approximately 30% of the solar radiation above the canopy in clear days during grain filling (0 to 23 d after pollination). Plants without shading were set as control. Nets were placed more than 450 cm higher above the ground to allow a good ventilation condition. The microclimate (CO 2 and temperature) was similar except for light intensity, which at 1, 6 and 13 Sep. was 1 635 and 1 260, 1 428 and 1 028 and 1 150 and 810 mol m-2 s-1 for the control and shading, respectively.
Grain fresh weight and water content Grains were picked off from the cob, and the weight of 100 grains was determined. The dry weight was weighed after the grains were dried at 40°C to constant weight. Water content (%)=(1-Dry weight/Fresh weight)×100
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Protein extraction The protein fractions albumin, globulin, zein, and glutenin were sequentially extracted from 1 g of flour (Luthe 1983). During each extraction step, the samples were continuously stirred for 20 min in a magnetic stirrer. Soluble and insoluble fractions were separated by centrifugation at 5 000×g for 10 min. Albumin was extracted at 20°C with 10 mL of pure water. Globulin, zein and glutenin were extracted at 20, 85 and 20°C from the previous pellet with 10 mL of 0.1 mol L-1 NaCl, 75% (v/v) ethanol and 0.02 mol L-1 NaOH, respectively. Each extraction step was repeated four times for all protein fractions.
Proximate analysis Soluble sugar and starch content in flour were determined according to ICC Method No. 123/1 (ICC 1994). Nitrogen content was determined using the Kjeldahl method (AACC 1990), and protein content was evaluated by measuring the nitrogen content (Protein content=Nitrogen content×6.25).
Granule size distribution Particle size characteristics of starch were analyzed using a laser diffraction particle size analyzer (Mastersizer 2000, Malvern, England). The accuracy of the instrument was checked with Malvern standard glass particles. The instrument, which is based on the principle of laser light scattering, can measure sizes between 0.1 and 2 000 m. The size distribution is expressed in terms of the volumes of equivalent spheres. The criteria selected are the percentage volume (% vol.) of granules following the standard proposed by Ji et al. (2003).
Processing of flour X-ray diffraction pattern Grains were ground in a grinder, passed through a 100mesh (0.149 mm) sieve, and then oven dried at 40°C.
Starch isolation Starch was isolated from the grains following the methods described by Sandhu et al. (2005) with minor modifications following Lu and Lu (2012).
Blue value, λmax and iodine binding capacity The λmax and blue values of flour were measured according to the method described by Chang et al. (2006). The iodine binding capacity is equal to the blue value at 635 nm/520 nm.
X-ray diffraction patterns were obtained using an X-ray diffractometer (D8 Advance, Bruker-AXS, Germany) operated at 200 mA and 40 kV. The scanning region of the diffraction angle (2θ) ranged from 3 to 40° at 0.04° step size with a count time of 0.6 s. The degree of crystallinity was calculated based on the methods of Hayakawa et al. (1997).
Textural properties Fresh waxy maize cobs were boiled in an electric cooker for 30 min, and the textural properties of fully cooked grains cut off from the mid of the cob were immediately measured using a TA-XT2i texture analyzer (Stable Micro Systems, England) coupled with an aluminum plate probe (35.0 mm
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in diameter). Some parameters of the compression mode were set as follows: pretest speed, 1.0 mm s-1; test speed, 2.0 mm s-1; posttest speed, 2.0 mm s-1; trigger force, 15 g; and distance, 70% of the initial sample height. A force-time curve was obtained from the test, and the textural results discussed in the following subsections were determined.
Thermal properties The thermal characteristics of flour were studied using a differential scanning calorimeter (Model 200 F3 Maia, NETZSCH, Germany) according to the method described by Sandhu and Singh (2007).
Pasting properties The pasting properties of flour were evaluated with a rapid visco analyzer (Model 3D, Newport Scientific, Australia). The sample suspension (28 g total weight, 10%, w/w, dry basis for flour) was equilibrated at 50°C for 1 min, heated to 95°C at a rate of 12°C min-1, maintained at 95°C for 2.5 min, cooled to 50°C at 12°C min-1, and then maintained at 50°C for 1 min. Paddle speed was set to 960 r min-1 for the first 10 s and then to 160 r min-1 for the rest of the analysis.
Statistical analysis The data were subjected to analysis of variance using the least significant difference test at the 5% probability level using the data processing system (DPS 7.05) proposed by Tang and Feng (2007). The figures were obtained from Microsoft Excel 2003.
Acknowledgements The study was financially supported by the National Natural Science Foundation of China (30971731, 31000684 and 31271640) and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.
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