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Oil and fatty acid distribution in different circles of sunflower head
Food Chemistry 128 (2011) 590–595
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Oil and fatty acid distribution in different circles of sunflower head Fayyaz-ul- Hassan, Shuaib Kaleem, Mukhtar Ahmad ⇑ Pir Mehr Ali Shah, Arid Agriculture University Rawalpindi, Pakistan
a r t i c l e
i n f o
Article history: Received 23 April 2010 Received in revised form 13 November 2010 Accepted 1 February 2011 Available online 13 April 2011 Keywords: Oil Fatty acid Distribution Circles
a b s t r a c t Prevailing temperature at anthesis influences pollen health, fertilisation, seed filling, oil and fatty acid accumulation in different circles of sunflower head. Field experiments were conducted, during 2007 and 2008, at Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi, Pakistan, to document oil and fatty acid distributions in different circles of sunflower head. Hybrid S-278 was planted in randomised complete block design with a two factors factorial experiment, with four replications. At maturity, heads were divided into three equal circles (outer, middle and central); thereafter, oil and fatty acid distributions were separately determined in each circle. Oil and fatty acid concentrations in three circles differed significantly. The outer circle accumulated high oil and oleic contents which decreased to a minimum in the central circle; however, linoleic acid consistently increased, from outer to central circle, during both the years. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Sunflower oil extracted from achenes is commonly used in food, as a frying medium, and in cosmetic formulations, as an emollient. Oil is light in taste and appearance. It is a combination of monounsaturated and polyunsaturated fats with low saturated fat levels. Oil is liquid at room temperature. Fatty acid composition is a major determinant of oil quality, mainly with good percentages of oleic and linoleic acid. Fatty acid composition is mainly affected by genotypes and environmental conditions, temperature having a major influence on oil quality (Izquierado, Aguirrezabal, Andrade, & Pereyra, 2002). Sunflower is a temperate crop but it can perform well under various climatic and soil conditions. It is a short duration crop maturing in 100–120 days. Temperature is a major environmental factor that determines the rate of plant development. Fluctuations in temperature and moisture availability affect the quantity and quality of oil accumulation (Hassan, Manaf, & Ejaz, 2005). Variation in unsaturated fatty acids profile is strongly influenced by both genetics and climate. Demurin, Skoric, Veresbaranji, and Jocic (2000) concluded that oleic acid content is essentially influenced by temperature during seed development; each 1 °C increase of temperature leads to about 2% increase of oleic acid. Oil and fatty acid composition in seeds are important targets in sunflower breeding. A completely developed head usually has a small circular depression in the centre while middle and outer whorls are flat. Anthesis (pollen shedding) begins at the periphery and proceeds ⇑ Corresponding author. Fax: +92 51 9290160. E-mail address: [email protected] (M. Ahmad). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.02.002
to the centre of the head (Putnam et al., 1990). Similarly, maturation of sunflower seeds takes place from the perimeter to the centre of sunflower head and seeds maturing at higher temperature would accumulate higher oil content (Weiss, 2000). Different whorls within a head fertilise and mature differently (Alkio, Diepenbrock, & Grimm, 2002); thus, growth of achenes mainly depends on phloem transport from upper fully expanded green leaves to the capitulum. Improved assimilate supply to growing achenes is regarded as the main factor for increase in yield of modern sunflower hybrids (Lopez Pereira, Trapani, & Sadras, 1999). Munshi, Kaushal, and Bajaj (2003) studied the physiochemical properties of seeds located in different whorls of sunflower head and concluded that the proportion of filled seeds decreased from outer to central whorl. A 10-fold decrease in filled to un-filled seed ratio was observed, due to which oil content was higher in the outer than in the middle and central whorls. The higher oil content in the outer whorl was concluded to be the effect of environmental conditions and the span of seed development. The accumulation of oil during seed filling was considered to be dependent upon an unhampered supply of photo-assimilates from the source to the sink. Similarly, Alkio and Grimm (2003) observed poorly developed or un-filled achenes in the central part of the sunflower head. They further concluded that, before fertilisation and seed filling, assimilates and nutrients are required for floret development and flowering. Following anthesis, if no fertilisation occurs or the embryo is aborted due to environment, the assimilate demand is reduced, ultimately causing the vascular tissues of this head region to degenerate, leading to empty achenes, influencing oil and oil quality. Vascular bundles originating from the stem run radially toward the periphery of the capitulum and from there toward the centre of the capitulum. The occurrence of empty achenes is
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highest in the centre of the capitulum and poor seed filling is related to poor vascularisation of receptacle; thus, oil and oil quality are affected more in this portion of the head (Goffner, Cazalis, Percie du sert, Calmes, & Cavalie, 1988). At the time of achene maturity, heavier seeds were observed in the outer region, probably due to the early maturation and production of more filled seeds in the peripheral zones (Baydar & Erbas, 2005). Although quite abundant literature is available on breeding, agronomic, physiological and quality aspects of different hybrids grown in different parts of the world, information related to distribution of oil and fatty acids in different circles of sunflower head is scarce. The present study was designed to document how seed position affects oil and fatty acid accumulation in different circles of sunflower head. 2. Materials and methods 2.1. Field experimentation and soil status Fig. 1. Circles of sunflower head.
Field experiments were conducted at Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi, Pakistan, located at 33° and 38° N and 73° and 04° E, during 2007 and 2008. The soil of the experimental site was loam-type in texture with class typic camborthids having sand 43%, silt 46% and clay 11%, pH 7.4 and EC 0.66 m S cm 1. Available NPK concentrations in the soil before sowing were 300, 5.00 and 140 mg kg 1, respectively. 2.2. Soil preparation and sowing methodology Prior to sowing, the particular site was fallow during the winter and was prepared for sowing by giving one soil-inverting plough and, thereafter, ploughed thrice with a tractor-mounted cultivator and planked with the last ploughing. The recommended dose of fertiliser of 80 kg nitrogen and 60 kg P2 O5 per hectare was applied in the form of urea and DAP at the time of last ploughing. Crop was sown on 18th March, 2007, and 20th March, 2008. Sowing was done with a dibbler, by putting two seeds at each pre-marked spot. Plant to plant distance was maintained 25 cm, and row to row 75 cm, in a net plot size of 5 3 m2. The sunflower hybrid S-278 was sown by using seed at 5 k/ha. After complete emergence, one plant was maintained per hill. Weeds were kept under control by hand-weeding throughout crop life cycle.
in 4 ml of 1 M KOH for one hour at room temperature. The resultant fatty acid methyl esters (FAME) were extracted with high performance liquid chromatography-grade hexane and analysed by GC using a fused capillary column (WCOT fused silica 30 m 0.25 mm coating CPWAX 52 CBDF = 0.25 lM, CP8713), a flame ionisation detector (FID) and nitrogen gas as carrier (3.5 ml/min). FAMEs were injected manually. Fatty acids were detected by chromatographic retention time and by comparison with authentic standards (Paquot, 1988). 2.5. Statistical analysis The collected data were subjected to statistical analysis by using analysis of variance with the help of MSTATC, separately for both the years (Freed & Eisensmith, 1986). Least significant difference (at 5% probability) was used to compare the means (Montgomery, 2001). Multiple regression analysis was performed by using STATGRAPHICS software while Box-and-Whisker plots were generated by using original recorded data (StatPoint Technologies Inc., 2009). 3. Results
2.3. Data recording and treatments
3.1. Oil content
Ten randomly selected heads from central rows in each plot and three replications were harvested on the 8th of July, 2007 and the 11th of July, 2008 and sun-dried for five days. Heads were equally divided (Fig. 1) into three circles Outer (O), middle (M) and central (C). The two years (2007 and 2008) were considered as factor A and three equal circles (outer, middle and central), thus making three treatments, as factor B. Meteorological data during the course of the experiment were also recorded (Table 1).
Oil content consistently decreased from outer to central circle during both the years. Statistical differences for oil content were recorded among circles for both the years, 2007 and 2008 (Table 2). The maximum oil content (48.87%) was obtained from the outer circle which was statistically (p < 0.05) similar to the middle circle (47.55%) but statistically (p < 0.05) different from the central circle (45.19%). Comparison of the years showed statistically non-significant differences for oil content. Interactions of years circles were statistically significant. The outer circle accumulated the maximum (48.85%, 47.70%) oil contents during both years of experimentation, respectively, while the central circle gave the minimum (44.26%, 46.12%) values during the two years, respectively. Similarly, the output of the multiple linear regression model to describe the relationship between oil contents and two independent variables, i.e. years (Y) and sunflower head circles (C), depicted a negative relationship (Oil content = 50.285 0.13 Y 1.5425 C). Since the p-value was less than 0.05, a statistically significant relationship existed between the variables. The R-Squared and adjusted R-squared statistics indicated 51.08% and 44.56% variability in oil content, respectively, with standard error
2.4. Oil extraction and fatty acid determination Achenes from each circle were separated by hand. Achenes from each circle were separately analysed for oil content by NMR, Model MQA-7005, Oxford Institute, USA, by standardising the equipment with six different oil contents (samples previously analysed). Thus oil contents in each circle were recorded (Warnsely, 1998). The fatty acids in oil were analysed by a gas chromatograph (AIML-NUCON) after intersterilification with methanolic KOH. In this method, fatty acids were converted to methyl esters prior to analysis by gas chromatography (GC). Oil samples (50 ll) were methylated
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Table 1 Meteorological data for crop duration (2007 and 2008). Month
2007
2008
Temperature (°C)
March April May June July
Rainfall (mm)
Max (mean)
Min (mean)
23.10 34.00 37.30 37.60 35.20
9.00 15.90 19.80 23.00 21.50
143.20 18.00 80.60 22.30 95.50
RH (%) (mean)
47.00 44.00 42.00 51.00 68.00
Sunshine (mean h)
Temperature (°C) Max (mean h)
Min (mean)
7.40 10.70 10.00 9.50 9.30
29.67 29.70 37.16 35.57 35.01
11.78 15.77 20.76 22.29 22.75
Rainfall (mm)
RH (%) (mean)
Sunshine (mean h)
19.10 92.90 10.10 225.00 240.00
57.00 59.33 40.00 62.43 69.61
7.90 7.71 9.92 7.47 7.38
Table 2 Oil and fatty acid distribution in different circles of sunflower head during 2007 and 2008.
O M C LSD (5% probability)
Oil content (%)
Palmitic acid
Stearic acid (%)
Oleic acid (%)
2007
2008
2007
2008
2007
2008
2007
2008
Linoleic acid (%) 2007
2008
48.85a 48.10a 44.26c 1.034
47.7ab 47.00ab 46.12b
5.56ab 5.77ab 6.10a 0.972
5.06b 5.00b 5.69ab
2.60 2.82 2.53 –
3.24NS 2.89 2.87
52.4a 51.4b 51.0b 1.013
54.1c 52.3d 45.1d
35.3e 36.1d 36.4d 0.359
32.3c 35.0b 41.0a
Any two means not sharing a letter in common differ significantly. O = outer, M = middle, C = central.
of 1.35. Similarly, distribution of oil among different circles, with median, was elaborated by Box-and-Whisker Plot, which showed that oil contents were greater in the outer circle and decreased significantly to middle and inner circles (Fig. 2).
Outer circle
Middle circle 3.2. Palmitic acid Palmitic acid accumulation in different circles showed a small increase from outer to central circle during 2007; however, no consistent pattern was visible during 2008. Statistically (p < 0.05) similar results were exhibited, among circles, for palmitic acid (Table 2). Comparison of the years showed statistical (p < 0.05) differences for palmitic acid. Comparatively higher (5.81%) palmitic acid was accumulated during 2007 as compared to 2008 (5.61%). The interaction (years circles) were also statistically (p < 0.05) nonsignificant. The regression analysis for palmitic acid, among different sunflower circles and years, revealed that it increased from outer to inner circle but decreased during the second year (palmitic acid = 5.875 0.2 Y + 0.0675 C). However, the p-value was greater or equal to 0.05, and hence depicted a statistically non-significant relationship, with standard error of 0.66. The trend of palmitic acid was further elucidated by Box-and-Whisker Plot (Fig. 3). 3.3. Stearic acid Statistically (p < 0.05) similar results were exhibited among circles regarding stearic acid for both the years (Table 2). Comparison
Outer circle
Middle circle
Inner circle 4.6
5
5.4
5.8
6.2
6.6
7
Palmitic acid (%)
Fig. 3. Multiple Box-and-Whisker plot showing relationship between palmitic acid and head circles with median vertical line.
of the years showed statistical differences for stearic acid. A comparatively higher (3.52%) value was obtained during 2008 than 2007 (2.65%). The interaction (years circles) was statistically (p < 0.05) significant with regard to stearic acid. The maximum (2.82%, 3.24%) stearic acid was recorded for the middle circle during 2007 and for the outer circle during 2008, respectively, while the minimum (2.53%, 2.87%) value was obtained for the central circle during 2007 and 2008, respectively. The output of regression analysis showed that stearic acid increased significantly during the second year; on moving from outer to middle circle, it decreased (stearic acid = 1.885 + 0.87 Y 0.0525 C). Since the p-value for the regression model was less than 0.05, a statistically significant relationship existed between the variables. The R-squared statistic indicated 40.44% of variability in stearic acid due to variables while the adjusted R-squared statistic showed a variability of 32.49% with standard error of 0.58. The Box-andWhisker plot (Fig. 4) further explained the trend of stearic acid among sunflower circles with deviation from mean.
3.4. Oleic acid
Inner circle 43
45
47
49
51
Oil contents (%)
Fig. 2. Multiple Box-and-Whisker plot showing relationship between oil contents and head circles with median vertical line.
Oleic acid consistently decreased from outer to central circle during both the years. Statistical differences for oleic acid were recorded among circles during 2007 and 2008 (Table 2). The maximum oleic acid (53.3%) was accumulated in the outer circle which was statistically (p < 0.05) different from rest of the circles,
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oleic acid while the adjusted R-squared statistic showed a value of 49.8% with standard error of 1.95. Similarly, distribution of linoleic acid among different circles with median was elaborated by Boxand-Whisker plot, which showed more linoleic acid recorded for the central circle (Fig. 6).
Outer circle
Middle circle
4. Discussion
Inner circle 2
2.4
2.8
3.2
3.6
4
Stearic acid (%)
Fig. 4. Multiple Box-and-Whisker plot showing relationship between stearic acid and head circles with median vertical line.
while the minimum (48.1%) value was obtained for the central circle. Comparison of the years showed statistical differences for oleic acid. Comparatively higher values were obtained during 2007 than during 2008. Interactions of years x circles were statistically (p < 0.05) significant. The maximum (52.4%, 54.1%) oleic acid was recorded for the outer circle during 2007 and 2008, respectively, and the minimum (51.0%, 45.2%) value for the central circle during 2007 and 2008, respectively. The regression analysis revealed that oleic acid contents decreased during 2008 and from outer to central circle (oleic acid = 57.86 1.07 Y 2.595 C). Similarly, pvalue regression analysis was less than 0.05; therefore statistically significant relationships exited between variables. The R-squared and adjusted R-squared statistics indicated 55.2% and 49.3% variability in oleic acid, respectively, with a standard error of 2.15. Similarly, the trend of oleic acid among sunflower head circles was further elaborated by a Box-and-Whisker plot (Fig. 5). 3.5. Linoleic acid Contrary to oleic acid, linoleic acid consistently increased from outer to central circle for both the years (Table 2). The maximum linoleic acid (38.7%) accumulated in the central circle was statistically (p < 0.05) different from the rest of the circles, while the minimum (33.8%) value was observed for the outer circle. Comparison of the years showed statistically non-significant differences for linoleic acid. However, the interaction of years circles was statistically (p < 0.05) significant. The maximum (36.4%, 41.0%) linoleic acid was recorded for the central circle during 2007 and 2008, respectively, while the minimum (35.3%, 32.3%) accumulated in the outer circle during 2007 and 2008, respectively. The output of regression analysis showed that linoleic acid contents increased among years and head circles (linoleic acid = 30.88 + 0.16 Y + 2.44 C). Since the p-value of regression analysis was less than 0.05, a statistically significant relationship existed between the variables. The R-squared statistic indicated 55.7% variability in lin-
In temperate regions, sunflower requires approximately 11 days from planting to emergence, 33 days from emergence to head visible, 27 days from head visible to first anther, 8 days from first to last anther, and 30 days from last anther to maturity (Putnam et al., 1990). The difference (of eight to ten days from first to last anther) indicates that temperature/environmental conditions varied for anther shedding on different days, thus creating a basis for difference in seed setting, development and oil accumulation. Increase of 1 °C in temperature, during flowering to maturity, of sunflower, caused increase of 1% in oil content of sunflower (Demurin et al., 2000). Similarly, high oleic sunflower oil had greater thermal stability than did normal sunflower oil (Smith, Robert & Min, 2007). In the present investigations, progressive reduction of oil content, from outer to central circle of the crop, is in line with the findings of Munshi et al. (2003) who concluded that seeds in the outer region grew at a slow rate than those in the central region; thus, time available to outer region seeds was more than that available to seeds in the central region. Slow accumulation, for a longer period of time, would increase the total oil content. The opposite relationship (Fig. 7) between head circles and oil content, for both the years, is supportive of the above assumption. An overall higher percentage of oil was found from the 2007 crop than that for 2008 crop. Lower achene oil content during 2008 may be due to comparatively lower temperature during seed development and maturation as compared with the high temperature prevailing during 2007 (Table 1). Thus, results of the present study are consistent with the findings of Weiss (2000) who concluded that crops maturing at higher temperature would accumulate higher oil contents. Inconsistent patterns for palmitic acid accumulation were observed among circles in the present study. Comparison of the years regarding palmitic acid revealed less accumulation during 2008 than 2007. The smaller palmitic acid values during 2008 might be due to the low temperature prevailing during seed development and maturation (Table 1) which accords with the findings of Rehmatalla, Babiker, Krishna, and Tiny (2001) who concluded that fatty acid compositions of oilseeds are modified by the duration of seed development and prevailing environmental conditions. Similarly, inconsistent patterns of stearic acid accumulation in the present investigation are similar to the findings of Baydar and Erbas (2005) who found that the accumulation pattern for saturated fatty acid was similar, with slight fluctuations. Similar to our findings (Roche et al., 2010) reported that higher temperature prevailing
Outer circle
Outer circle
Middle circle
Middle circle
Inner circle
Inner circle 45
47
49
51
53
55
Oleic acid (%)
Fig. 5. Multiple Box-and-Whisker plot showing relationship between oleic acid and head circles with median vertical line.
32
34
36 38 Linoleic acid (%)
40
42
Fig. 6. Multiple Box-and-Whisker plot showing relationship between linoleic acid and head circles with median vertical line.
Fayyaz-ul- Hassan et al. / Food Chemistry 128 (2011) 590–595 51
57 Oleic acid (%)
Oil content (%)
50 49 48 y = -1.54x + 50.083 R² = 0.9137
47 46
y = -2.595x + 58.848 R² = 0.9401
44 y = 2.45x + 28.67 R² = 0.9742
55 53
42 40
51
38
49
36
47
34
45
32
43 45
Linoleic acid (%)
594
30 0
1
2
3
4
Head circles
44 0
1
2
3
4
Oleic acid
Linoleic acid
Head circles
Fig. 8. Relationship between oleic and linoleic acid.
Fig. 7. Relationship between head circles and oil content (means of two years).
during seed formation had affected oil contents of sunflower significantly. Our results reveal that outer circles accumulated higher oleic acid during both years, which progressively decreased from outer to central circles. Pollination, seed development and seed maturation take place from the peripheral toward the central whorl on a single head. These processes take place at different intervals of time at different temperatures. Progressive reduction of oleic acid from outer to central circle is in accordance with results of Munshi et al. (2003) who concluded that peripheral seeds mature earlier at higher temperatures, then middle and centre last; thus, all three whorls, maturing on different days, with varying maturing temperature, accumulated various oleic contents. Similarly, Hernandez and Palmer (1992) concluded that, at the time of photo-assimilate distribution in capitulum during anthesis and seed filling, generally, peripheral florets start to import earlier and they incorporate higher amounts of carbohydrates, oil and oleic contents than do the central ones. In our investigations, relatively higher oleic acid was observed during the 1st year than during the 2nd year. Lower oleic acid during the 2nd year may be attributed to low temperature prevailing at the time of achene development, in addition to other environmental factors (e.g. sunshine hours). Our findings are in line with the earlier findings of Izquierado, Aguirrezabal, Andrade, and Cantarero (2006) who observed a linear relationship between oleic acid concentration and temperature and recorded a higher concentration of oleic acid at warmer temperature in the spring season due to reduced or limited activity of de-saturase enzyme, responsible for the conversion of oleic acid to linoleic acid. Increased concentration of oleic acid, because of rising temperature during 2007 (Table 1), may improve oil quality in the form of oxidative stability during storage and frying (Smith et al., 2007). The results for linoleic acid in different circles of sunflower hybrids were contrary to those observed for oleic acid. Results in Table 2 revealed that the central circle accumulated more linoleic acid this progressively increased from outer to central circles for both the years of experimentation. Results of the present study are in line with the findings of Baydar and Erbas (2005) who concluded that position of seeds on sunflower head had a strong effect on fatty acid contents. As peripheral seeds mature earlier at higher temperatures than middle and centre last, outer seeds accumulate lower linoleic contents than do central seeds (being matured at relatively low temperature). Relatively higher linoleic acid was observed during the 2nd than during the 1st year of study. Higher linoleic acid content during the 2nd year may be attributed to low temperature conditions prevailing at the time of achene development (Table 1). At low temperature, the enzyme de-saturase becomes active, which is responsible for the conversion of oleic to linoleic acid (Baux, Hebeisen, & Pellet, 2008). Similarly, Demurin et al. (2000) reported a negative correlation between oleic and linoleic acid percentages (which are essentially influenced by temperature). An inverse relationship between oleic acid, and linoleic acid,
for circles in the present study, is supportive of the above conclusions (Fig. 8). 5. Conclusion Distribution of oil and fatty acids in different head circles is a combined function of growth, development and overall plant structure, affected by environmental conditions. At present, all the hybrids under cultivation have heads with different maturity times, which ultimately affect oil quality and quantity. Therefore, a broader, comprehensive, meaningful breeding and hybridisation, agronomic and physiological strategy, for the development of new hybrids with enhanced vascular connections, is needed, so that assimilates may partition actively and equally in all the regions/ circles of the head. This equal distribution of assimilates and maturity at one time may enhance the proportion of fully filled seed, improving oil and fatty acid accumulation percentage down to the centre of the capitulum. References Alkio, M., Diepenbrock, W., & Grimm, E. (2002). Evidence for sectorial photoassimilate supply in the capitulum of sunflower (Helianthus annuus L). New Phytologist, 156, 445–456. Alkio, M., & Grimm, E. (2003). Vascular connections between receptacle and empty achenes in sunflower (Helianthus annuus L). Journal of Experimental Botany, 54, 345–348. Baux, A., Hebeisen, T., & Pellet, D. (2008). Effects of minimal temperatures on low linolenic rapeseed oil fatty acid composition. European Journal of Agronomy, 29, 102–107. Baydar, H., & Erbas, S. (2005). Influence of seed development and seed position on oil, fatty acids and total tocopherol contents in sunflower (Helianthus annuus L.). Turk Journal of Agriculture, 29, 179–186. Demurin, Y., Skoric, D., Veresbaranji, I., & Jocic, S. (2000). Inheritance of increased oleic acid content in sunflower seed oil. Helia, 23, 87–92. Freed, R. D., & Eisensmith, S. P. (1986). MSTAT Microcomputer Statistical Program. Michigan, USA: Michigan State University of Agriculture and Applied Science. Goffner, D., Cazalis, R., Percie du sert, C., Calmes, J., & Cavalie, G. (1988). 14C photo assimilate interception and seed production in sunflower as influenced by temperature and radiation. Australian Journal of Plant Physiology, 11, 255–265. Hassan, F. U., Manaf, A., & Ejaz, M. (2005). Determinants of oil and fatty acid in peanut. International Journal of Agriculture and Biology, 7, 895–899. Hernandez, L. F., & Palmer, J. H. (1992). Incorporation of 14C labelled metabolites into the developing sunflower capitulum. Proceedings of 13th international sunflower conference. Pisa, Italy, Toowoomba, Australia: International Sunflower Association. http://www.statgraphics.com/statpoint.htm. Izquierado, N., Aguirrezabal, L., Andrade, F., & Cantarero, M. (2006). Modelling the response of fatty acid composition to temperature in a traditional sunflower hybrid. Agronomy Journal, 98, 451–461. Izquierado, N., Aguirrezabal, L., Andrade, F., & Pereyra, V. (2002). Night temperature affects fatty acid composition in sunflower oil depending on the hybrid and the phenological stage. Field Crop Research, 77, 115–126. Lopez Pereira, M., Trapani, N., & Sadras, V. O. (1999). Genetic improvement of sunflower in Argentina between 1930 and 1995. II. Phenological development, growth and source-sink relationship. Field Crop Research, 6, 247–254. Montgomery, D. C. (2001). Design and Analysis of Experiments (5th Ed.). New York: John Willy and Sons. pp. 64–65. Munshi, S. K., Kaushal, B., & Bajaj, R. K. (2003). Compositional changes in seeds influenced by their positions in different whorls of mature sunflower head. Journal of Science Food and Agriculture, 83(15), 1622–1626.
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Oil and fatty acid distribution in different circles of sunflower head Fayyaz-ul- Hassan, Shuaib Kaleem, Mukhtar Ahmad ⇑ Pir Mehr Ali Shah, Arid Agriculture University Rawalpindi, Pakistan
a r t i c l e
i n f o
Article history: Received 23 April 2010 Received in revised form 13 November 2010 Accepted 1 February 2011 Available online 13 April 2011 Keywords: Oil Fatty acid Distribution Circles
a b s t r a c t Prevailing temperature at anthesis influences pollen health, fertilisation, seed filling, oil and fatty acid accumulation in different circles of sunflower head. Field experiments were conducted, during 2007 and 2008, at Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi, Pakistan, to document oil and fatty acid distributions in different circles of sunflower head. Hybrid S-278 was planted in randomised complete block design with a two factors factorial experiment, with four replications. At maturity, heads were divided into three equal circles (outer, middle and central); thereafter, oil and fatty acid distributions were separately determined in each circle. Oil and fatty acid concentrations in three circles differed significantly. The outer circle accumulated high oil and oleic contents which decreased to a minimum in the central circle; however, linoleic acid consistently increased, from outer to central circle, during both the years. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Sunflower oil extracted from achenes is commonly used in food, as a frying medium, and in cosmetic formulations, as an emollient. Oil is light in taste and appearance. It is a combination of monounsaturated and polyunsaturated fats with low saturated fat levels. Oil is liquid at room temperature. Fatty acid composition is a major determinant of oil quality, mainly with good percentages of oleic and linoleic acid. Fatty acid composition is mainly affected by genotypes and environmental conditions, temperature having a major influence on oil quality (Izquierado, Aguirrezabal, Andrade, & Pereyra, 2002). Sunflower is a temperate crop but it can perform well under various climatic and soil conditions. It is a short duration crop maturing in 100–120 days. Temperature is a major environmental factor that determines the rate of plant development. Fluctuations in temperature and moisture availability affect the quantity and quality of oil accumulation (Hassan, Manaf, & Ejaz, 2005). Variation in unsaturated fatty acids profile is strongly influenced by both genetics and climate. Demurin, Skoric, Veresbaranji, and Jocic (2000) concluded that oleic acid content is essentially influenced by temperature during seed development; each 1 °C increase of temperature leads to about 2% increase of oleic acid. Oil and fatty acid composition in seeds are important targets in sunflower breeding. A completely developed head usually has a small circular depression in the centre while middle and outer whorls are flat. Anthesis (pollen shedding) begins at the periphery and proceeds ⇑ Corresponding author. Fax: +92 51 9290160. E-mail address: [email protected] (M. Ahmad). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.02.002
to the centre of the head (Putnam et al., 1990). Similarly, maturation of sunflower seeds takes place from the perimeter to the centre of sunflower head and seeds maturing at higher temperature would accumulate higher oil content (Weiss, 2000). Different whorls within a head fertilise and mature differently (Alkio, Diepenbrock, & Grimm, 2002); thus, growth of achenes mainly depends on phloem transport from upper fully expanded green leaves to the capitulum. Improved assimilate supply to growing achenes is regarded as the main factor for increase in yield of modern sunflower hybrids (Lopez Pereira, Trapani, & Sadras, 1999). Munshi, Kaushal, and Bajaj (2003) studied the physiochemical properties of seeds located in different whorls of sunflower head and concluded that the proportion of filled seeds decreased from outer to central whorl. A 10-fold decrease in filled to un-filled seed ratio was observed, due to which oil content was higher in the outer than in the middle and central whorls. The higher oil content in the outer whorl was concluded to be the effect of environmental conditions and the span of seed development. The accumulation of oil during seed filling was considered to be dependent upon an unhampered supply of photo-assimilates from the source to the sink. Similarly, Alkio and Grimm (2003) observed poorly developed or un-filled achenes in the central part of the sunflower head. They further concluded that, before fertilisation and seed filling, assimilates and nutrients are required for floret development and flowering. Following anthesis, if no fertilisation occurs or the embryo is aborted due to environment, the assimilate demand is reduced, ultimately causing the vascular tissues of this head region to degenerate, leading to empty achenes, influencing oil and oil quality. Vascular bundles originating from the stem run radially toward the periphery of the capitulum and from there toward the centre of the capitulum. The occurrence of empty achenes is
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highest in the centre of the capitulum and poor seed filling is related to poor vascularisation of receptacle; thus, oil and oil quality are affected more in this portion of the head (Goffner, Cazalis, Percie du sert, Calmes, & Cavalie, 1988). At the time of achene maturity, heavier seeds were observed in the outer region, probably due to the early maturation and production of more filled seeds in the peripheral zones (Baydar & Erbas, 2005). Although quite abundant literature is available on breeding, agronomic, physiological and quality aspects of different hybrids grown in different parts of the world, information related to distribution of oil and fatty acids in different circles of sunflower head is scarce. The present study was designed to document how seed position affects oil and fatty acid accumulation in different circles of sunflower head. 2. Materials and methods 2.1. Field experimentation and soil status Fig. 1. Circles of sunflower head.
Field experiments were conducted at Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi, Pakistan, located at 33° and 38° N and 73° and 04° E, during 2007 and 2008. The soil of the experimental site was loam-type in texture with class typic camborthids having sand 43%, silt 46% and clay 11%, pH 7.4 and EC 0.66 m S cm 1. Available NPK concentrations in the soil before sowing were 300, 5.00 and 140 mg kg 1, respectively. 2.2. Soil preparation and sowing methodology Prior to sowing, the particular site was fallow during the winter and was prepared for sowing by giving one soil-inverting plough and, thereafter, ploughed thrice with a tractor-mounted cultivator and planked with the last ploughing. The recommended dose of fertiliser of 80 kg nitrogen and 60 kg P2 O5 per hectare was applied in the form of urea and DAP at the time of last ploughing. Crop was sown on 18th March, 2007, and 20th March, 2008. Sowing was done with a dibbler, by putting two seeds at each pre-marked spot. Plant to plant distance was maintained 25 cm, and row to row 75 cm, in a net plot size of 5 3 m2. The sunflower hybrid S-278 was sown by using seed at 5 k/ha. After complete emergence, one plant was maintained per hill. Weeds were kept under control by hand-weeding throughout crop life cycle.
in 4 ml of 1 M KOH for one hour at room temperature. The resultant fatty acid methyl esters (FAME) were extracted with high performance liquid chromatography-grade hexane and analysed by GC using a fused capillary column (WCOT fused silica 30 m 0.25 mm coating CPWAX 52 CBDF = 0.25 lM, CP8713), a flame ionisation detector (FID) and nitrogen gas as carrier (3.5 ml/min). FAMEs were injected manually. Fatty acids were detected by chromatographic retention time and by comparison with authentic standards (Paquot, 1988). 2.5. Statistical analysis The collected data were subjected to statistical analysis by using analysis of variance with the help of MSTATC, separately for both the years (Freed & Eisensmith, 1986). Least significant difference (at 5% probability) was used to compare the means (Montgomery, 2001). Multiple regression analysis was performed by using STATGRAPHICS software while Box-and-Whisker plots were generated by using original recorded data (StatPoint Technologies Inc., 2009). 3. Results
2.3. Data recording and treatments
3.1. Oil content
Ten randomly selected heads from central rows in each plot and three replications were harvested on the 8th of July, 2007 and the 11th of July, 2008 and sun-dried for five days. Heads were equally divided (Fig. 1) into three circles Outer (O), middle (M) and central (C). The two years (2007 and 2008) were considered as factor A and three equal circles (outer, middle and central), thus making three treatments, as factor B. Meteorological data during the course of the experiment were also recorded (Table 1).
Oil content consistently decreased from outer to central circle during both the years. Statistical differences for oil content were recorded among circles for both the years, 2007 and 2008 (Table 2). The maximum oil content (48.87%) was obtained from the outer circle which was statistically (p < 0.05) similar to the middle circle (47.55%) but statistically (p < 0.05) different from the central circle (45.19%). Comparison of the years showed statistically non-significant differences for oil content. Interactions of years circles were statistically significant. The outer circle accumulated the maximum (48.85%, 47.70%) oil contents during both years of experimentation, respectively, while the central circle gave the minimum (44.26%, 46.12%) values during the two years, respectively. Similarly, the output of the multiple linear regression model to describe the relationship between oil contents and two independent variables, i.e. years (Y) and sunflower head circles (C), depicted a negative relationship (Oil content = 50.285 0.13 Y 1.5425 C). Since the p-value was less than 0.05, a statistically significant relationship existed between the variables. The R-Squared and adjusted R-squared statistics indicated 51.08% and 44.56% variability in oil content, respectively, with standard error
2.4. Oil extraction and fatty acid determination Achenes from each circle were separated by hand. Achenes from each circle were separately analysed for oil content by NMR, Model MQA-7005, Oxford Institute, USA, by standardising the equipment with six different oil contents (samples previously analysed). Thus oil contents in each circle were recorded (Warnsely, 1998). The fatty acids in oil were analysed by a gas chromatograph (AIML-NUCON) after intersterilification with methanolic KOH. In this method, fatty acids were converted to methyl esters prior to analysis by gas chromatography (GC). Oil samples (50 ll) were methylated
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Table 1 Meteorological data for crop duration (2007 and 2008). Month
2007
2008
Temperature (°C)
March April May June July
Rainfall (mm)
Max (mean)
Min (mean)
23.10 34.00 37.30 37.60 35.20
9.00 15.90 19.80 23.00 21.50
143.20 18.00 80.60 22.30 95.50
RH (%) (mean)
47.00 44.00 42.00 51.00 68.00
Sunshine (mean h)
Temperature (°C) Max (mean h)
Min (mean)
7.40 10.70 10.00 9.50 9.30
29.67 29.70 37.16 35.57 35.01
11.78 15.77 20.76 22.29 22.75
Rainfall (mm)
RH (%) (mean)
Sunshine (mean h)
19.10 92.90 10.10 225.00 240.00
57.00 59.33 40.00 62.43 69.61
7.90 7.71 9.92 7.47 7.38
Table 2 Oil and fatty acid distribution in different circles of sunflower head during 2007 and 2008.
O M C LSD (5% probability)
Oil content (%)
Palmitic acid
Stearic acid (%)
Oleic acid (%)
2007
2008
2007
2008
2007
2008
2007
2008
Linoleic acid (%) 2007
2008
48.85a 48.10a 44.26c 1.034
47.7ab 47.00ab 46.12b
5.56ab 5.77ab 6.10a 0.972
5.06b 5.00b 5.69ab
2.60 2.82 2.53 –
3.24NS 2.89 2.87
52.4a 51.4b 51.0b 1.013
54.1c 52.3d 45.1d
35.3e 36.1d 36.4d 0.359
32.3c 35.0b 41.0a
Any two means not sharing a letter in common differ significantly. O = outer, M = middle, C = central.
of 1.35. Similarly, distribution of oil among different circles, with median, was elaborated by Box-and-Whisker Plot, which showed that oil contents were greater in the outer circle and decreased significantly to middle and inner circles (Fig. 2).
Outer circle
Middle circle 3.2. Palmitic acid Palmitic acid accumulation in different circles showed a small increase from outer to central circle during 2007; however, no consistent pattern was visible during 2008. Statistically (p < 0.05) similar results were exhibited, among circles, for palmitic acid (Table 2). Comparison of the years showed statistical (p < 0.05) differences for palmitic acid. Comparatively higher (5.81%) palmitic acid was accumulated during 2007 as compared to 2008 (5.61%). The interaction (years circles) were also statistically (p < 0.05) nonsignificant. The regression analysis for palmitic acid, among different sunflower circles and years, revealed that it increased from outer to inner circle but decreased during the second year (palmitic acid = 5.875 0.2 Y + 0.0675 C). However, the p-value was greater or equal to 0.05, and hence depicted a statistically non-significant relationship, with standard error of 0.66. The trend of palmitic acid was further elucidated by Box-and-Whisker Plot (Fig. 3). 3.3. Stearic acid Statistically (p < 0.05) similar results were exhibited among circles regarding stearic acid for both the years (Table 2). Comparison
Outer circle
Middle circle
Inner circle 4.6
5
5.4
5.8
6.2
6.6
7
Palmitic acid (%)
Fig. 3. Multiple Box-and-Whisker plot showing relationship between palmitic acid and head circles with median vertical line.
of the years showed statistical differences for stearic acid. A comparatively higher (3.52%) value was obtained during 2008 than 2007 (2.65%). The interaction (years circles) was statistically (p < 0.05) significant with regard to stearic acid. The maximum (2.82%, 3.24%) stearic acid was recorded for the middle circle during 2007 and for the outer circle during 2008, respectively, while the minimum (2.53%, 2.87%) value was obtained for the central circle during 2007 and 2008, respectively. The output of regression analysis showed that stearic acid increased significantly during the second year; on moving from outer to middle circle, it decreased (stearic acid = 1.885 + 0.87 Y 0.0525 C). Since the p-value for the regression model was less than 0.05, a statistically significant relationship existed between the variables. The R-squared statistic indicated 40.44% of variability in stearic acid due to variables while the adjusted R-squared statistic showed a variability of 32.49% with standard error of 0.58. The Box-andWhisker plot (Fig. 4) further explained the trend of stearic acid among sunflower circles with deviation from mean.
3.4. Oleic acid
Inner circle 43
45
47
49
51
Oil contents (%)
Fig. 2. Multiple Box-and-Whisker plot showing relationship between oil contents and head circles with median vertical line.
Oleic acid consistently decreased from outer to central circle during both the years. Statistical differences for oleic acid were recorded among circles during 2007 and 2008 (Table 2). The maximum oleic acid (53.3%) was accumulated in the outer circle which was statistically (p < 0.05) different from rest of the circles,
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oleic acid while the adjusted R-squared statistic showed a value of 49.8% with standard error of 1.95. Similarly, distribution of linoleic acid among different circles with median was elaborated by Boxand-Whisker plot, which showed more linoleic acid recorded for the central circle (Fig. 6).
Outer circle
Middle circle
4. Discussion
Inner circle 2
2.4
2.8
3.2
3.6
4
Stearic acid (%)
Fig. 4. Multiple Box-and-Whisker plot showing relationship between stearic acid and head circles with median vertical line.
while the minimum (48.1%) value was obtained for the central circle. Comparison of the years showed statistical differences for oleic acid. Comparatively higher values were obtained during 2007 than during 2008. Interactions of years x circles were statistically (p < 0.05) significant. The maximum (52.4%, 54.1%) oleic acid was recorded for the outer circle during 2007 and 2008, respectively, and the minimum (51.0%, 45.2%) value for the central circle during 2007 and 2008, respectively. The regression analysis revealed that oleic acid contents decreased during 2008 and from outer to central circle (oleic acid = 57.86 1.07 Y 2.595 C). Similarly, pvalue regression analysis was less than 0.05; therefore statistically significant relationships exited between variables. The R-squared and adjusted R-squared statistics indicated 55.2% and 49.3% variability in oleic acid, respectively, with a standard error of 2.15. Similarly, the trend of oleic acid among sunflower head circles was further elaborated by a Box-and-Whisker plot (Fig. 5). 3.5. Linoleic acid Contrary to oleic acid, linoleic acid consistently increased from outer to central circle for both the years (Table 2). The maximum linoleic acid (38.7%) accumulated in the central circle was statistically (p < 0.05) different from the rest of the circles, while the minimum (33.8%) value was observed for the outer circle. Comparison of the years showed statistically non-significant differences for linoleic acid. However, the interaction of years circles was statistically (p < 0.05) significant. The maximum (36.4%, 41.0%) linoleic acid was recorded for the central circle during 2007 and 2008, respectively, while the minimum (35.3%, 32.3%) accumulated in the outer circle during 2007 and 2008, respectively. The output of regression analysis showed that linoleic acid contents increased among years and head circles (linoleic acid = 30.88 + 0.16 Y + 2.44 C). Since the p-value of regression analysis was less than 0.05, a statistically significant relationship existed between the variables. The R-squared statistic indicated 55.7% variability in lin-
In temperate regions, sunflower requires approximately 11 days from planting to emergence, 33 days from emergence to head visible, 27 days from head visible to first anther, 8 days from first to last anther, and 30 days from last anther to maturity (Putnam et al., 1990). The difference (of eight to ten days from first to last anther) indicates that temperature/environmental conditions varied for anther shedding on different days, thus creating a basis for difference in seed setting, development and oil accumulation. Increase of 1 °C in temperature, during flowering to maturity, of sunflower, caused increase of 1% in oil content of sunflower (Demurin et al., 2000). Similarly, high oleic sunflower oil had greater thermal stability than did normal sunflower oil (Smith, Robert & Min, 2007). In the present investigations, progressive reduction of oil content, from outer to central circle of the crop, is in line with the findings of Munshi et al. (2003) who concluded that seeds in the outer region grew at a slow rate than those in the central region; thus, time available to outer region seeds was more than that available to seeds in the central region. Slow accumulation, for a longer period of time, would increase the total oil content. The opposite relationship (Fig. 7) between head circles and oil content, for both the years, is supportive of the above assumption. An overall higher percentage of oil was found from the 2007 crop than that for 2008 crop. Lower achene oil content during 2008 may be due to comparatively lower temperature during seed development and maturation as compared with the high temperature prevailing during 2007 (Table 1). Thus, results of the present study are consistent with the findings of Weiss (2000) who concluded that crops maturing at higher temperature would accumulate higher oil contents. Inconsistent patterns for palmitic acid accumulation were observed among circles in the present study. Comparison of the years regarding palmitic acid revealed less accumulation during 2008 than 2007. The smaller palmitic acid values during 2008 might be due to the low temperature prevailing during seed development and maturation (Table 1) which accords with the findings of Rehmatalla, Babiker, Krishna, and Tiny (2001) who concluded that fatty acid compositions of oilseeds are modified by the duration of seed development and prevailing environmental conditions. Similarly, inconsistent patterns of stearic acid accumulation in the present investigation are similar to the findings of Baydar and Erbas (2005) who found that the accumulation pattern for saturated fatty acid was similar, with slight fluctuations. Similar to our findings (Roche et al., 2010) reported that higher temperature prevailing
Outer circle
Outer circle
Middle circle
Middle circle
Inner circle
Inner circle 45
47
49
51
53
55
Oleic acid (%)
Fig. 5. Multiple Box-and-Whisker plot showing relationship between oleic acid and head circles with median vertical line.
32
34
36 38 Linoleic acid (%)
40
42
Fig. 6. Multiple Box-and-Whisker plot showing relationship between linoleic acid and head circles with median vertical line.
Fayyaz-ul- Hassan et al. / Food Chemistry 128 (2011) 590–595 51
57 Oleic acid (%)
Oil content (%)
50 49 48 y = -1.54x + 50.083 R² = 0.9137
47 46
y = -2.595x + 58.848 R² = 0.9401
44 y = 2.45x + 28.67 R² = 0.9742
55 53
42 40
51
38
49
36
47
34
45
32
43 45
Linoleic acid (%)
594
30 0
1
2
3
4
Head circles
44 0
1
2
3
4
Oleic acid
Linoleic acid
Head circles
Fig. 8. Relationship between oleic and linoleic acid.
Fig. 7. Relationship between head circles and oil content (means of two years).
during seed formation had affected oil contents of sunflower significantly. Our results reveal that outer circles accumulated higher oleic acid during both years, which progressively decreased from outer to central circles. Pollination, seed development and seed maturation take place from the peripheral toward the central whorl on a single head. These processes take place at different intervals of time at different temperatures. Progressive reduction of oleic acid from outer to central circle is in accordance with results of Munshi et al. (2003) who concluded that peripheral seeds mature earlier at higher temperatures, then middle and centre last; thus, all three whorls, maturing on different days, with varying maturing temperature, accumulated various oleic contents. Similarly, Hernandez and Palmer (1992) concluded that, at the time of photo-assimilate distribution in capitulum during anthesis and seed filling, generally, peripheral florets start to import earlier and they incorporate higher amounts of carbohydrates, oil and oleic contents than do the central ones. In our investigations, relatively higher oleic acid was observed during the 1st year than during the 2nd year. Lower oleic acid during the 2nd year may be attributed to low temperature prevailing at the time of achene development, in addition to other environmental factors (e.g. sunshine hours). Our findings are in line with the earlier findings of Izquierado, Aguirrezabal, Andrade, and Cantarero (2006) who observed a linear relationship between oleic acid concentration and temperature and recorded a higher concentration of oleic acid at warmer temperature in the spring season due to reduced or limited activity of de-saturase enzyme, responsible for the conversion of oleic acid to linoleic acid. Increased concentration of oleic acid, because of rising temperature during 2007 (Table 1), may improve oil quality in the form of oxidative stability during storage and frying (Smith et al., 2007). The results for linoleic acid in different circles of sunflower hybrids were contrary to those observed for oleic acid. Results in Table 2 revealed that the central circle accumulated more linoleic acid this progressively increased from outer to central circles for both the years of experimentation. Results of the present study are in line with the findings of Baydar and Erbas (2005) who concluded that position of seeds on sunflower head had a strong effect on fatty acid contents. As peripheral seeds mature earlier at higher temperatures than middle and centre last, outer seeds accumulate lower linoleic contents than do central seeds (being matured at relatively low temperature). Relatively higher linoleic acid was observed during the 2nd than during the 1st year of study. Higher linoleic acid content during the 2nd year may be attributed to low temperature conditions prevailing at the time of achene development (Table 1). At low temperature, the enzyme de-saturase becomes active, which is responsible for the conversion of oleic to linoleic acid (Baux, Hebeisen, & Pellet, 2008). Similarly, Demurin et al. (2000) reported a negative correlation between oleic and linoleic acid percentages (which are essentially influenced by temperature). An inverse relationship between oleic acid, and linoleic acid,
for circles in the present study, is supportive of the above conclusions (Fig. 8). 5. Conclusion Distribution of oil and fatty acids in different head circles is a combined function of growth, development and overall plant structure, affected by environmental conditions. At present, all the hybrids under cultivation have heads with different maturity times, which ultimately affect oil quality and quantity. Therefore, a broader, comprehensive, meaningful breeding and hybridisation, agronomic and physiological strategy, for the development of new hybrids with enhanced vascular connections, is needed, so that assimilates may partition actively and equally in all the regions/ circles of the head. This equal distribution of assimilates and maturity at one time may enhance the proportion of fully filled seed, improving oil and fatty acid accumulation percentage down to the centre of the capitulum. References Alkio, M., Diepenbrock, W., & Grimm, E. (2002). Evidence for sectorial photoassimilate supply in the capitulum of sunflower (Helianthus annuus L). New Phytologist, 156, 445–456. Alkio, M., & Grimm, E. (2003). Vascular connections between receptacle and empty achenes in sunflower (Helianthus annuus L). Journal of Experimental Botany, 54, 345–348. Baux, A., Hebeisen, T., & Pellet, D. (2008). Effects of minimal temperatures on low linolenic rapeseed oil fatty acid composition. European Journal of Agronomy, 29, 102–107. Baydar, H., & Erbas, S. (2005). Influence of seed development and seed position on oil, fatty acids and total tocopherol contents in sunflower (Helianthus annuus L.). Turk Journal of Agriculture, 29, 179–186. Demurin, Y., Skoric, D., Veresbaranji, I., & Jocic, S. (2000). Inheritance of increased oleic acid content in sunflower seed oil. Helia, 23, 87–92. Freed, R. D., & Eisensmith, S. P. (1986). MSTAT Microcomputer Statistical Program. Michigan, USA: Michigan State University of Agriculture and Applied Science. Goffner, D., Cazalis, R., Percie du sert, C., Calmes, J., & Cavalie, G. (1988). 14C photo assimilate interception and seed production in sunflower as influenced by temperature and radiation. Australian Journal of Plant Physiology, 11, 255–265. Hassan, F. U., Manaf, A., & Ejaz, M. (2005). Determinants of oil and fatty acid in peanut. International Journal of Agriculture and Biology, 7, 895–899. Hernandez, L. F., & Palmer, J. H. (1992). Incorporation of 14C labelled metabolites into the developing sunflower capitulum. Proceedings of 13th international sunflower conference. Pisa, Italy, Toowoomba, Australia: International Sunflower Association. http://www.statgraphics.com/statpoint.htm. Izquierado, N., Aguirrezabal, L., Andrade, F., & Cantarero, M. (2006). Modelling the response of fatty acid composition to temperature in a traditional sunflower hybrid. Agronomy Journal, 98, 451–461. Izquierado, N., Aguirrezabal, L., Andrade, F., & Pereyra, V. (2002). Night temperature affects fatty acid composition in sunflower oil depending on the hybrid and the phenological stage. Field Crop Research, 77, 115–126. Lopez Pereira, M., Trapani, N., & Sadras, V. O. (1999). Genetic improvement of sunflower in Argentina between 1930 and 1995. II. Phenological development, growth and source-sink relationship. Field Crop Research, 6, 247–254. Montgomery, D. C. (2001). Design and Analysis of Experiments (5th Ed.). New York: John Willy and Sons. pp. 64–65. Munshi, S. K., Kaushal, B., & Bajaj, R. K. (2003). Compositional changes in seeds influenced by their positions in different whorls of mature sunflower head. Journal of Science Food and Agriculture, 83(15), 1622–1626.
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