Research Article Received: 13 February 2015
Revised: 18 May 2015
Accepted article published: 8 June 2015
Published online in Wiley Online Library:
(wileyonlinelibrary.com) DOI 10.1002/jsfa.7295
Physico-chemical properties of starches isolated from potato cultivars grown in soils with different phosphorus availability Magali Leonel,a* Ezequiel L Carmo,a Adalton M Fernandes,a Célia ML Francoa,b and Rogério P Sorattoa,c Abstract BACKGROUND: Starch is the major component of potato tubers, amounting approximately to 150-200 g kg −1 of the tuber weight. Starch is considered to be a major factor for the functionality of the potato in food applications. This study evaluated the physical characteristics of potato starches isolated from tubers of different potato cultivars grown in soil with three levels of phosphorus (P) availability. All potatoes were growing according the same method. The starches were isolated by physical methods and the samples were analyzed for the amylose, P content, paste properties (RVA) and thermal properties of gelatinization and retrogradation (DSC). Experimental data were analyzed considering the potato cultivars and the three soil P availability. RESULTS: For all measured parameters significant impact of cultivar and soil P availability was determined. Phosphorus contents in potato starches ranged from 0.252 to 0.647 g kg−1 and amylose from 27.18 to 30.8%. Starches from different potato cultivars independent of soil showed a small range of gelatinization temperature. All starches showed low resistance heating and shear stress. CONCLUSION: The results showed the influence of growing conditions (soil P availability) and also of the differences between the potato cultivars on important characteristics of applicability of starches. © 2015 Society of Chemical Industry Keywords: amylose; Solanum tuberosum; starch; phosphorus; thermal properties; viscosity
INTRODUCTION Potato (Solanum tuberosum L.) is one of the most important crops for feeding the world’s population. With nearly 367 million tons harvested in 2013, it ranks fourth in world production after rice, wheat and maize. In the same year, according to the Food and Agriculture Organization of the United Nations,1 3.57 million tons of potato were harvest in Brazil. However, it is estimated that less than 50% of potatoes grown worldwide are consumed fresh. Industrial uses of potatoes include products such as frozen fries, flakes, snacks, flour and starch.2 Phosphorus (P) participates in many metabolic processes in plants, such as energy transfer, synthesis of nucleic acids, starch synthesis, respiration, synthesis and stability of membranes, activation and deactivation of enzymes, redox reactions and carbohydrate metabolism.3 Phosphorus deficiency has been shown to reduce growth of primary roots and enhance length and density of root hairs and lateral roots in many plant species.4,5 Starch is the main reserve carbohydrate in higher plants, the second most abundant biopolymer on earth and the most important carbohydrate for food, representing the main feature of the human diet and the raw material for various industrial applications.6 An increase in processed and pre-prepared food products has created a demand for the development of starches with certain qualities required for these applications. These starches can be found by J Sci Food Agric (2015)
searching for other plant varieties or species as well as by studying of genetically modify plants or the conditions of growth. Starch is composed exclusively of glucose residues linked by only two types of bonds: 𝛼-1,4 and 𝛼-1,6 glucosidic linkages. The main constituents of starch granules are amylopectin and amylose. Amylopectin (75% by weight) is a semi-crystalline, highly branched polysaccharide with an 𝛼-1,4 backbone and 4–5% 𝛼-1,6 branch points. Amylose (25%) is amorphous in the native starch granule and is essentially composed of linear chains of 𝛼-1,4-linked glucose units. As a minor component, tuberous starches, e.g. those prepared from potatoes, are rich in covalently bound phosphate. This natural substitution is restricted to the amylopectin fraction
∗
Correspondence to: Magali Leonel, Center for Tropical Roots and Starches (CERAT), São Paulo State University (UNESP), Botucatu, São Paulo 18610-307, Brazil. E-mail: [email protected]
a Center for Tropical Roots and Starches (CERAT), São Paulo State University (UNESP), Botucatu, São Paulo, Brazil b Department of Food Engineering and Technology, Institute of Biosciences, Language, and Physical Sciences, São Paulo State University (UNESP), São José do Rio Preto, São Paulo, Brazil c Department of Crop Science, College of Agricultural Sciences, São Paulo State University (UNESP), Botucatu, São Paulo, Brazil
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Table 1. Basic characteristics of experimental conditions Characteristic GPS coordinates Hieght above sea level (m) Soil classification Clay soil characteristics (0–0.2 m of depth) pH (1:2.5 soil/CaCl2 suspension 0.01 mol L−1 ) Organic matter (g dm−3 ) Presin-extractable (mg dm−3 ) K (mmolc dm−3 ) Ca (mmolc dm−3 ) Mg (mmolc dm−3 ) H + Al (mmolc dm−3 ) Cation exchange capacity (mmolc dm−3 ) Base saturation (%) Sand (g kg−1 ) Silt (g kg−1 ) Clay (g kg−1 )
Low P
High P
23∘ 02′ 27′′ S, 48∘ 47′ 57′′ W 744 Oxisol clayey loam
23∘ 28′ 48′′ S, 49∘ 01′ 28′′ W 649 Oxisol clayey
23∘ 07′ 69′′ S, 49∘ 12′ 30′′ W 737 Oxisol clayey
5.7 47.6 14 2.3 59.7 19.3 26.9 108.2 75 311 289 400
4.8 26.7 36 2.3 31.5 10.7 45.7 90.2 49 292 184 524
4.8 27.8 70 3.3 30.9 9.0 50.8 94.0 46 153 245 602
and is found at the C-2, C-3 and C-6 positions of the glucose residues.7 Starch biosynthesis and granule formation are complex processes. Biosynthesis requires the concerted action of a range of enzyme activities. Starch phosphorylation constitutes an integral part of the starch-biosynthetic pathway. Starch phosphorylation is also an important aspect of plant metabolism because of its role in starch degradation. Reducing the extent of starch phosphorylation has been shown to impair the degradation of starch, whereas an increase in starch phosphorylation was shown to stimulate the activity of the starch-degrading amylase enzyme.7 – 10 Native starches generally contain small amounts of P. In root and tuber starches, P is covalently linked to the starch in the form of P esters, whereas in cereal starches it occurs mostly as contaminating phospholipids. Inorganic phosphate may also be present.11 The degree of phosphorylation has a profound effect on the physical and chemical properties of the starch. Because the degree of phosphorylation influences the qualitative properties of starch there is interest in the effect of environmental parameters; specifically, to what extent starch phosphorylation can be manipulated by controlling phosphate supply to the plants.12 Noda et al.13 studied the starch P content in potato cultivars and its effect on starch properties and their results indicated that enhancing the starch phosphate resulted in significant increases in the swelling power, peak viscosity, and breakdown and significant but small increases in the onset and peak temperatures of gelatinization. Other starch quality parameters, such as the amylose content, granule median size, and the gelatinization enthalpy, did not significantly change due to the degree of phosphate substitution of starch. Lu et al.,14 studying the correlation between physicochemical and nutritional properties of dry matter and starch in potatoes grown in different locations, observed that P content of starch was a key factor affecting physico-chemical and nutritional properties of dry matter and starch in potatoes. Considering that starch properties depend on its physical and chemical characteristics and that it has been reported that starch is significantly influenced by the cultivars and environmental factors,15,16 this work was undertaken to study and compare P content, amylose, thermal and pasting properties of potato starches
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Medium P
from different cultivars grown in soils with different levels of P availability.
MATERIALS AND METHODS Growing of potatoes Three experiments were conducted under field conditions in areas of commercial production of potato. Prior to the experiments soil samples consisting of 20 sub-samples was taken in the 0–0.2 m layer depth to determine the soil chemical properties (Table 1). The experiments were conducted in soils with different levels of P available: low (14 mg dm−3 ), medium (36 mg dm−3 ) and high (70 mg dm−3 ). The P available was extracted using ion exchange resin and measured by colorimetry, according van Raij et al.17 Table 1 shows basic characteristics of the experimental conditions. The three experiments were conducted in a randomized block design with four replications. The treatments consisted of five potato cultivars and each plot consisted of five rows of 5 m. For the evaluations were considered central rows disregarding 0.5 m at the end of each row of plants and a row on each side of the plot. The potato cultivars used in all the experiments were: Agata, Asterix, Atlantic, Markies and Mondial. Cultivar Agata is the most planted in Brazil, occupying about 60% of the planted area. The cultivar Asterix is the most industrially used for the production of frozen fried potatoes. The cultivar Atlantic is the main cultivar suitable for the production of chips. The cultivar Markies is suitable for preparation for cooking as well as to fry. The cultivar Mondial presents high yield of tubers with low dry matter content characteristic that cater to the in natura market of potato. All potatoes were growing according the same method. For planting, the furrows were opened mechanically at a row spacing of 0.80 m. In all experiments, it was applied in the furrow insecticide thiamethoxam (155 g of i.a. ha−1 ) and chlorpyrifos (557 g of i.a. ha−1 ), fungicides pencycuron (280 g of i.a. ha−1 ), metiram (77 g of i.a. ha−1 ) and fluazinam (1155 g of i.a. ha−1 ) and the fungicide/bactericide streptomycin (17 g of i.a. ha−1 ). Mineral fertilization at planting of all experiments consisted of the application of 62 kg ha−1 N and 124 kg ha−1 K2 O for all cultivars in the form of ammonium sulfate and potassium chloride,
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Properties of potato starches
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respectively. Phosphate fertilizer was not applied to evaluate only the P already available in the soil. Top-dressing fertilization in areas with low, medium and high P availability was performed at 22, 24 and 28 days after planting (DAP), respectively. In the area with low, medium and high P avaliability 43, 64 and 41 kg ha−1 N, respectively, was applied. The insecticide thiamethoxam (198 g i.a. ha−1 ) and the fungicide fluazinam (1035 g i.a. ha−1 ) were used in the experiments simultaneously with the operation of hilling. The irrigation of the fields was carried out by sprinkler system center pivot. In all experiments pest control was performed according to technical recommendations for the potato crop. The plants of all areas were desiccated with diquat (331 g i.a. ha−1 ) around 100 DAP, and 21 days after the tubers were harvested for the evaluations. Starch isolation Uniform-size potatoes were selected from each cultivar before starch isolation. The tubers were peeled, sliced, and ground at high speed in a blender with distilled water (1:1 v/v) at 8∘ C for 2 min. The homogenate was passed through sieves (0.250 and 0.180 mm screen), and the solids retained were washed three times on the sieve. The filtrate was left to stand overnight at 5∘ C for decantation. The starch sediment was washed with distilled water and ethanol, recovered by centrifugation, and dried at 38∘ C in an air circulation oven. Analysis of starches The amylose content of starch was determined using the method of Williams et al.18 This analysis was carried out in triplicate. The content of P in potato starches was analyzed according to the methodology described by Malavolta et al.19 This analysis was carried out in triplicate. The thermal properties of potato starches were analyzed using a differential scanning calorimeter (DSC) Pyris 1 (Perkin Elmer, Norwalk, CT, USA). Starch samples (2.0 mg, dry basis) were weighed into aluminium pans, mixed with deionized water (6 μL) and sealed. The sealed pans were kept at room temperature for 2 h for balance and heated at a rate of 10∘ C min−1 from 25∘ C to 100∘ C. An empty pan was used as reference. After running the samples in DSC, they were refrigerated at 5∘ C for 14 days and analyzed again under the same conditions to determine the thermal properties of retrograded starches. The gelatinization temperature (initial, peak and final) and the enthalpy change of native and retrograded starches were determined using the Pyris 1 software from Perkin Elmer. This analysis was carried out in triplicate. For the analysis of the pasting properties the Rapid Visco Analyser (RVA; Warriewood, Australia) was used. The starch suspensions (2.5 g of starch in 25 mL of water), corrected for the basis of 14% of moisture, passed by the programming: 50∘ C for 1 min, heating from 50∘ C to 95∘ C at a rate of 6∘ C min−1 , maintaining the paste at 95∘ C for 5 min, cooling from 95∘ C to 50∘ C at a rate of 6∘ C min−1 . The viscosity was expressed as rapid visco unit (RVU) (1RVU = 12cP).20 From the graph obtained were evaluated: pasting temperature, maximum viscosity (peak), breakdown, final viscosity and setback. This analysis was carried out in triplicate. Statistical analysis Experimental data were analyzed together considering the potato cultivars and the three soil P availabilities. Data were subjected to analysis of variance using the SAS statistical software. The blocks J Sci Food Agric (2015)
Table 2. Phosphorus and amylose contents in starches of potato cultivars as affected by the soil P availability Soil P availability (mg dm−3 ) Cultivar Phosphorus (g kg−1 ) Agata Asterix Atlantic Markies Mondial Amylose (%) Agata Asterix Atlantic Markies Mondial
14
36
0.646Aa 0.252Cd 0.383Cb 0.372Cb 0.325Cc
0.533Bb 0.413Bc 0.564Ba 0.422Bc 0.436Bc
30.8Aa 29.3Bbc 29.1Ac 29.8Bb 27.2Bd
29.8Ba 29.6Ba 27.1Bb 29.6Ba 27.5Bb
70
0.550Ba 0.454Ab 0.622Aa 0.557Aa 0.466Ab 29.8Bb 30.8Aa 27.4Bc 30.7Aab 30.8Aa
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
and all the block interactions were considered to be random effects. The cultivars and P availability were considered to be fixed effects. The means were separated using Tukey’s test at the 0.05 probability level.
RESULTS AND DISCUSSION Results of P contents in potato starches showed a range of 0.252 to 0.647 g kg−1 , with significant differences between cultivars and soils (Table 2). Noda et al.13 also observed a variation in the P content in starch of potato cultivars reporting a variation of 0.308 to 1.24 g kg−1 . The comparison of the starch P content from different potato cultivars and soils showed that with the exception of cultivar Agata, higher contents of P in starch are observed when potatoes were grown in soils with a higher P availability (Table 2). The P uptake by plant roots is the result of interactions of morphological and physiological characteristics of roots, which can vary among potato cultivars,21 the rhizosphere immediately adjacent to the root system and soil characteristics that determine the flow of nutrients to the soil–root interface. The soils where experiments were conducted were acids and with medium and high P availability had lower contents of calcium and magnesium (Table 1), which may have interfered with the P uptake.22 Wekesa et al.,22 studying the effect of soil characteristics on potato tuber minerals composition, observed a positive correlation between potato tuber minerals levels and the soil mineral contents and the difference in behavior of the cultivar Agata (Table 2) may be related to differences in physiological parameters of root system affecting P uptake21 and allocation of P to the tubers.23 Fernandes et al.23 found that the availability of P in the soil affects the variable way in the allocation of P for potato cultivars tubers. The potato has been considered as a plant with low efficiency of P utilization and with little ability to uptake P in soils with low availability, which has often been attributed to its low density of roots, which develop mostly concentrated in the first 30 cm deep, below the seed tubers.24,25 The contents of amylose of different cultivars and soils ranged from 27.18 to 30.8% (Table 2). It was observed differences between
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www.soci.org cultivars in same soil as well as into same cultivar in different availability of P in the soil. For cultivars Asterix, Markies and Mondial higher amylose contents were observed in soil with higher P availability. However, ‘Agata’ and ‘Atlantic’ had higher contents of amylose in soil with low P available. For food processing purposes potatoes with higher amylose content are appreciated, unlike potatoes used for non-food industry containing higher amylopectin levels in starch.26 The influence of grow conditions on the physicochemical characteristics of starches has been reported. Šimková et al.,26 studying the effect of cultivar, location and year on total starch, amylose, P contents, and starch grain size of potato cultivars, observed that the amylose and P contents showed a clear negative correlation. For all measured parameters (starch, amylose, P and starch granule size) significant impact of cultivar was determined. Location and year had lower but significant impact. No statistically significant effect of year on amylose was found by these authors. When starch is heated in the presence of enough water its crystalline organization decomposes to form amorphous regions. This molecular disordering is called gelatinization. Differential scanning calorimetry (DSC) identifies melting and crystallization events as well as glass transition temperatures. The data of DSC showed differences between potato cultivars and into same cultivars grown in soils with different P availability for all parameters of thermal properties (Table 3). Onset temperature ranged from 58.17 to 62.76∘ C in soil with low P availability, 60.43 to 62.20∘ C in soil with medium P availability and 61.80 to 63.80∘ C in soil with higher level of P available (Table 3). The temperature of peak ranged from 61.00 to 65.57∘ C, 63.33 to 65.10∘ C and 64.40 to 65.23 for soils with low, medium and high level of P available, respectively. For the final temperature variations from 64.5 to 69.7∘ C (low P in soil), 66.7 to 68.7∘ C (medium P) and 67.4 to 70.63∘ C (high P) were observed. The results of the transition temperatures in gelatinization of starches were similar to those reported by Kaur et al.27 who, evaluating some properties of potatoes starches, observed that the endothermic peaks for different potato cultivars were between 59.96 and 68.89∘ C, the temperature of the peak ranged from 63.37 to 64.58∘ C and the final temperature ranged from 67.4 to 68.9∘ C. But the range of enthalpy of gelatinization observed by these authors was lower than that obtained in this work (Table 3). The cultivars Agata, Asterix and Atlantic showed lower transition temperatures (T 0 , T p and T c ) in soil with lower availability of P (Table 3). This was not observed for the starches isolated from Markies and Mondial cultivars that showed higher values for onset, peak and conclusion temperatures of gelatinization in soil with lower level of P available, which may be due to the effect of monoester phosphate groups linked to amylopectin.28 According to Tester et al.,29 the extension of crystalline perfection is reflected at the gelatinization temperature range and the change of enthalpy obtained by DSC. Starches from different potato cultivars independent of soil showed small range of gelatinization temperature and also showed low variation of enthalpy (ΔH). The starch of cultivar Agata showed high temperatures of gelatinization which can indicate long chain branched of amylopectin (Table 3). The starch crystallinity can be estimated by the enthalpy (ΔH), energy required to melt the duplexes segments. The gelatinization temperature (initial and peak) can be used as a measure of stability or completeness of crystalline regions and the width of endothermic peak as an estimative of the heterogeneity of the crystalline structure.30
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Table 3. Thermal properties of gelatinization of the starches of potato cultivars as affected by the soil P availability Soil P availability (mg dm−3 ) Cultivar Onset temperature, T 0 (∘ C) Agata Asterix Atlantic Markies Mondial Peak temperature, T p (∘ C) Agata Asterix Atlantic Markies Mondial Final temperature, T c (∘ C) Agata Asterix Atlantic Markies Mondial T c − T 0 = 𝚫T (∘ C) Agata Asterix Atlantic Markies Mondial Enthalpy change, 𝚫H (J g−1 ) Agata Asterix Atlantic Markies Mondial
14
36
70
62.47Bb 58.17Ce 60.53Cd 62.76Aa 62.13Ac
62.20Ca 60.43Bd 61.70Bb 61.90Bb 60.43Cc
63.80Aa 61.9Ac 62.50Ab 62.57Ab 61.80Bc
65.43Ba 61.00Cd 63.60Cc 65.57Aa 65.10Ab
65.10Ca 63.33Be 64.27Bc 64.77Cb 63.77Cd
66.6Aa 64.4Ac 65.23Ab 65.13Bb 64.4Bc
69.7Ba 64.5Cd 67.5Bc 69.47Aa 68.57Ab
68.7Ca 66.7Bc 67.7Bb 68.53Ba 66.9Cc
70.63Aa 67.6Ac 68.8Ab 68.7Bb 67.4Bc
7.24Aa 6.35Ac 7.00Aab 6.67Abc 6.41Ac 15.8Aa 13.6Ac 14.3Ab 16.1Aa 13.7Bc
6.49Ca 6.32Aab 6.00Cb 6.65Aa 5.97Bb 11.7Cd 12.8Bc 14.17Ab 13.9Cb 17.3Aa
6.86Ba 5.69Bc 6.38Bb 6.14Bb 5.57Cc 13.8Bb 12.3Cc 14.03Ab 14.6Ba 13.8Bb
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
The properties of gelatinization and swelling are, in part, controlled by the structure of amylopectin. As the crystalline regions of the starch granule are mainly composed by amylopectin, starches with high amylose content have low gelatinization temperatures and enthalpy.31 Nevertheless it was not possible to observe this relation in this experiment (Tables 2 and 3). As expected the retrograded starches showed lower thermal properties than gelatinized starches (Table 4). When analyzing the relationship between enthalpy of retrogradation and enthalpy of gelatinization generally we observed a negative ratio of P available in soil and retrogradation in starches of potato cultivars. The observation of relationship of P content and retrogradation in potato starches is in agree with related by Lu et al.;14 however, a few investigators have reported that P in potato starch granules was positively correlated with degree of retrogradation and tends to increase the retrogradation enthalpy.32,33 This contradiction might be largely attributed to the different materials used in their studies, the levels of amylose and P contents as well as amylopectin chain length distribution of the starches. During the retrogradation the amylose molecules form double helices of 40 to 70 glucose units and amylopectin form smaller double helices, due
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Properties of potato starches
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Table 4. Thermal properties of retrogradation of the starches of potato cultivars as affected by the soil P availability
Table 5. Pasting properties of the starches of potato cultivars as affected by the soil P availability
Soil P availability (mg dm−3 ) Cultivar Onset temperature, T 0 (∘ C) Agata Asterix Atlantic Markies Mondial Peak temperature, T p (∘ C) Agata Asterix Atlantic Markies Mondial Final temperature, T c (∘ C) Agata Asterix Atlantic Markies Mondial T c − T 0 = 𝚫T (∘ C) Agata Asterix Atlantic Markies Mondial Enthalpy change, 𝚫H (J g−1 ) Agata Asterix Atlantic Markies Mondial
14
36
70
44.8Bd 43.0Be 50.7Ba 46.4Bc 49.09Ab
45.8Ad 41.3Ce 51.3Aa 49.9Ab 48.3Bc
40.5Ce 43.6Ab 45.1Ca 41.7Cd 42.5Cc
59.8Aa 53.7Bb 59.96Aa 59.7Aa 59.9Aa
55.2Bc 51.9Cd 57.9Bb 59.5Aa 55.3Bc
48.1Cd 54.7Aa 53.9Cb 49.8Bc 53.9Cd
68.67Ab 60.23Bc 68.9Ab 69.07Ab 69.6Aa
62.23Bc 58.8Cd 65.93Ba 65.88Ba 63.20Bb
56.8Cc 61.46Aa 59.7Cb 59.2Cb 61.0Ca
23.87Aa 17.25Be 18.22Ad 22.68Ab 20.49Ac
16.46Bb 17.49ABa 14.65Bc 15.97Cb 14.89Cc
16.29Bc 17.82Ab 14.64Bd 17.64Bb 18.51Ba
5.23Ad 2.80Ce 6.20Ab 7.27Aa 5.70Bc
1.57Ce 5.50Ab 4.40Bc 3.17Bd 6.67Aa
1.97Bd 4.7Ba 2.03Cd 3.0Cc 4.5Cb
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
to restrictions imposed by the branched structure of the molecules and the length of the branches. This re-association occurs in the form molecular and structural more weakly than that found in the native molecule. Therefore, less energy is required to melt the restructured crystals.34 Gelatinization occurs when native starch is heated in the presence of sufficient moisture. The granules absorb water and swell, and the crystalline organization is irreversibly disrupted. Pasting encompasses the changes that occur after gelatinization upon further heating and these include further swelling of granules, leaching of molecular components from the granules and eventual disruption of granules especially with the application of shear forces. Results of pasting properties of potato starches showed differences in all parameters between cultivars and for the same cultivar grown in soils with different levels of P availability (Table 5). The peak of viscosity of starches ranged from 714.25 to 924.77 RVU in soil with low P, from 872.38 to 1014.09 RVU and from 921.94 to 1088.37 for soils with medium and higher availability of P, respectively (Table 5). The cultivars Asterix, Markies and Mondial showed higher P content, amylose and peaks of viscosity in soil with high P availability and these cultivars showed starches with J Sci Food Agric (2015)
Soil P availability (mg dm−3 ) Cultivar Peak (RVU) Agata Asterix Atlantic Markies Mondial Breakdown (RVU) Agata Asterix Atlantic Markies Mondial Final viscosity (RVU) Agata Asterix Atlantic Markies Mondial Setback (RVU) Agata Asterix Atlantic Markies Mondial
14
36
70
870.77Bb 714.25Cd 859.50Cb 781.59Cc 924.77Ca
872.38Bd 887.39Bc 1014.09Ba 892.79Bc 973.46Bb
918.57Ad 992.77Ac 1088.37Aa 921.94Ad 1046.08Ab
642.98Cb 484.50Cd 645.29Bb 574.63Cc 828.58Ca
760.31Bc 797.52Bb 927.15Aa 799.18Ab 914.84Ba
824.84Ad 881.36Ac 922.20Ab 710.84Bd 949.84Aa
277.71Ab 264.96Ac 259.87Bc 260.88Cc 291.00Aa
284.67Aa 255.56Bc 254.21Bc 269.55Bb 271.71Bb
279.13Ab 254.38Bc 338.21Aa 278.96Ab 275.13Bb
49.92Bb 35.21Cb 45.67Bb 53.92Bb 194.82Ba
172.60Ab 165.69Ab 167.27Ab 175.93Ab 213.08Aa
185.40Aa 142.96Bb 172.07Aa 67.59Bc 178.88Ba
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
lower P content and amylose in soils with low P (Tables 2 and 5), showing a positive relationship between the level of P available in the soil and these starch characteristics. The peak of viscosity is indicative of the water-binding capacity of the starch and the ease with which the starch granules are disintegrated.35 The cultivar Mondial showed higher peak of viscosity in soil with low P availability and ‘Atlantic’ in soils with medium and high P (Table 5). If we analyze the percentage of amylose of these cultivars it is possible to observe a negative relationship between the amylose content of starch and the peak viscosity. This observation agrees with Lu et al.14 which analyzing starch potatoes reported that a higher level of amylose resulted in a lower peak viscosity. Starch-bound phosphate is an important factor for determining the starch viscosity characteristics. Several results have been obtained that demonstrate that higher starch P content is closely associated with higher viscosity in potato.36 When we analyzed the results of P in potato starch it was possible observe higher viscosity peak to ‘Atlantic’ starch in soils with medium and high availability of P, and this cultivar also showed higher viscosity peak in these soils when compared with other cultivars (Table 5). When potato starch is pasted, its phosphate groups ionize, leaving the starch with a negative charge. The resulting slight coulombic repulsion greatly opens up the branched amylopectin molecules and increases their salvation.14 This might explain the observation of relationship of P and peak viscosity (Tables 1, 2 and 5).
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www.soci.org Regarding breakdown all starches showed low resistance heating and shear stress during cooking with the highest values observed for all cultivars in soil with high P content (Table 5). Setback is a measure of recrystallization of gelatinized starch during cooling. All starches showed increase of viscosity with cooling and tendency to retrogradation. Results showed that setback of starches ranged from 35.21 to 194.82 RVU, soil with low P, 165.69 to 213.08 RVU, soil with medium P, and 67.59 to 185.4 RVU in soil with high P (Table 5). In soils with low and medium P availability the cultivar Mondial showed higher retrogradation tendency when compared with other cultivars. The retrogradation of amylose in processed foods is considered to be important for properties relating to stickiness, ability to absorb water, and digestibility, whereas retrogradation of amylopectin is probably a more important determinant in the staling of bread and cakes.35
CONCLUSION The physical properties of potato starches ranged among cultivars and the P available in the soil had interference on these properties independent of the cultivar. The identification of these effects on determinants properties for the applicability of starches provide useful and important information for potato producer, researchers and industrial sector because it opens possibilities of control of culture conditions aiming to get native starches with special properties.
ACKNOWLEDGEMENTS The authors are grateful to CNPq for financial support.
REFERENCES 1 Food and Agriculture Organization of the United Nations, FAOSTAT Database. Available: http://faostat.fao.org [13 January 2014]. 2 Gómez-Castillo D, Cruz E, Iguaz A, Arroqui C and Vírseda P, Effects of essential oils on sprout suppression and quality of potato cultivars. Postharvest Biol Technol 82:15–21 (2013). 3 Vance CP, Uhde-Stone C and Allan DL, Phosphorus acquisition and use: Critical adaptations by plants for securing a nonrenewable resource. New Phytol 157:423–447 (2003). 4 López-Bucio J, Cruz-Ramírez A and Herrera-Estrella L, The role of nutrient availability in regulating root architecture. Curr Opin Plant Biol 6:280–287 (2003). 5 Desnos T, Root branching responses to phosphate and nitrate. Curr Opin Plant Biol 11:82–87 (2008). 6 Geigenberger P, Regulation of starch biosynthesis in response to a fluctuating environment. Plant Physiol 155:1566–1577 (2011). 7 Blennow A, Engelsen SB, Nielsen TH, Baunsgaard L and Mikkelsen R, Starch phosphorylation: A new front line in starch research. Trends Plant Sci 17:445–450 (2002). 8 Baunsgaard L, Lutken H, Mikkelsen R, Glaring MA, Pham TT and Blennow A, A novel isoform of glucan, water dikinase phosphorylates pre-phosphorylates alpha-glucans and is involved in starch degradation in Arabidopsis. Plant J 41:595–605 (2005). 9 Edner C, Li J, Albrecht T, Mahlow S, Hejazi M, Hussain H et al., Glucan, water dikinase activity stimulates breakdown of starch granules by plastidial beta-amylases. Plant Physiol 145:17–28 (2007). 10 Carpenter M, Joyce N, Butler R, Genet R and Timmerman-Vaughan G, A mass spectrometric method for quantifying C3 and C6 phosphorylation of starch. Anal Biochem 431:115–119 (2012). 11 Yoneya T, Ishibashi K, Hironaka K and Yamamoto K, Influence of cross-linked potato starch treated with POCl3 on DSC, rheological properties and granule size. Carbohydr Polym 53:447–457 (2003). 12 Jacobsen HB, Madsen MH, Christiansen J and Nielsen TH, The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants. Potato Res 41:109–116 (1998).
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13 Noda T, Kottearachchi NS, Tsuda S, Mori M, Takigawa S, Matsuura-Endo C et al., Starch phosphorus content in potato (Solanum tuberosum L.) cultivars and its effect on other starch properties. Carbohydr Polym 68:793–796 (2007). 14 Lu Z-L, Yada RY, Liu Q, Bizimungu B, Murphy A, De Koeyer D et al., Correlation of physicochemical and nutritional properties of dry matter and starch in potatoes grown in different locations. Food Chem 126:1246–1253 (2011). 15 Kaur A, Singh N, Ezekiel R and Guraya HS, Physicochemical, thermal and pasting properties of starches separated from different potato cultivars grown at different locations. Food Chem 101:643–651 (2007). 16 Opabode JT, Akinkunmi JA and Akinyemiju OA, Influence of marker genes physicochemical properties of starch produced by transgenic cassava (Manihot esculenta Crantz) plants. JAS 5:201–209 (2013). 17 van Raij B, Andrade JC, Cantarella H and Quaggio JA, Análise Química para Avaliação da Fertilidade de Solos Tropicais. Instituto Agronômico, Campinas (2001). 18 Williams PC, Kuzina FD and Hlynka L, A rapid calorimetric procedure for estimating the amylose content of starches and flour. Cereal Chem 47:411 (1970). 19 Malavolta E, Vitti GC and Oliveira AS, Avaliação do Estado Nutricional das Plantas: Princípios e Aplicações, 2nd edition. Associação Brasileira da Potassa e do Fosfato, Piracicaba (1997). 20 Leonel M, Freitas TS and Mischan MM, Physical characteristics of extruded cassava starch. Sci Agric 66:486–493 (2009). 21 Fernandes AM, Soratto RP and Gonsales JR, Root morphology and phosphorus uptake by potato cultivars grown under deficient and sufficient phosphorus supply. Sci Hort 180:190–198 (2014). 22 Wekesa MN, Okoth MW, Abong’ GO, Muthoni J and Kabira JN, Effect of soil characteristics on potato tuber minerals composition of selected Kenyan varieties. JAS 6:163–171 (2014). 23 Fernandes AM, Soratto RP and Pilon C, Soil phosphorus increases dry matter and nutrient accumulation and allocation in potato cultivars. Am J Potato Res 92:117–127 (2015). 24 Dechassa N, Schenk MK, Claassen N and Steingrobe B, Phosphorus efficiency of cabbage (Brassica oleraceae L. var. capitata), carrot (Daucus carota L.), and potato (Solanum tuberosum L.). Plant Soil 250:215–224 (2003). 25 Iwama K, Physiology of the potato: new insights into root system and repercussions for crop management. Potato Res 51:333–353 (2008). 26 Šimkova, D, Lachman J, Hamouz K and Vokal B, Effect of cultivar, location and year on total starch, amylose, phosphorus content and starch grain size of high starch potato cultivars for food and industrial processing. Food Chem 141:3872–3880 (2013). 27 Kaur L, Singh N and Sodhi NS, Some properties of potatoes and rheological properties of starches. Food Chem 79:183–192 (2002). 28 McPherson AE and Jane J, Comparison of waxy potato with other root and tuber starches. Carbohydr Polym 40:57–70 (1999). 29 Tester RF, Debon SJJ, Davies HV and Gidley MJ, Effect of temperature on synthesis, composition and physical properties of potato starch. J Sci Food Agric 79:2045–2051 (1999). 30 Blennow A, Bay-Smidt AM, Olsen CE and Møller BL, The distribution of covalently bound phosphate in the starch granule in relation to starch crystallinity. Int J Biol Macromol 27:211–218 (2000). 31 Noda T, Takahata Y, Sato T, Suda I, Morishita T, Ishiguro K et al., Relationships between chain length distribution of amylopectin and gelatinization properties within the same botanical origin for sweet potato and buck wheat. Carbohydr Polym 37:153–158 (1998). 32 Hopkins S and Gormley R, Rheological properties of pastes and gels made from starch separated from different potato cultivars. LWT – Food Sci Technol 33:388–396 (2000). 33 Muhrbeck P and Eliasson AC, Influence of the naturally occurring phosphate esters on the crystallinity of potato starch. J Sci Food Agric 55:13–18 (1991). 34 Sasaki T, Yasui T and Matsuki J, Effect of amylose content on gelatinization, retrogradation, and pasting properties of starch from waxy and non-waxy wheat and their F1 seeds. Cereal Chem 77:58–63 (2000). 35 Copeland L, Blazek J, Slaman H and Tang MC, Form and functionality of starch. Food Hydrocolloids 23:1527–1534 (2009). 36 Blennow A, Bay-Smidt AM, Leonhardt P, Bandsholm O and Madsen MH, Starch paste stickiness is a relevant native starch selection criterion for wet-end paper manufacturing. Starch 55:381–389 (2003).
© 2015 Society of Chemical Industry
J Sci Food Agric (2015)
Revised: 18 May 2015
Accepted article published: 8 June 2015
Published online in Wiley Online Library:
(wileyonlinelibrary.com) DOI 10.1002/jsfa.7295
Physico-chemical properties of starches isolated from potato cultivars grown in soils with different phosphorus availability Magali Leonel,a* Ezequiel L Carmo,a Adalton M Fernandes,a Célia ML Francoa,b and Rogério P Sorattoa,c Abstract BACKGROUND: Starch is the major component of potato tubers, amounting approximately to 150-200 g kg −1 of the tuber weight. Starch is considered to be a major factor for the functionality of the potato in food applications. This study evaluated the physical characteristics of potato starches isolated from tubers of different potato cultivars grown in soil with three levels of phosphorus (P) availability. All potatoes were growing according the same method. The starches were isolated by physical methods and the samples were analyzed for the amylose, P content, paste properties (RVA) and thermal properties of gelatinization and retrogradation (DSC). Experimental data were analyzed considering the potato cultivars and the three soil P availability. RESULTS: For all measured parameters significant impact of cultivar and soil P availability was determined. Phosphorus contents in potato starches ranged from 0.252 to 0.647 g kg−1 and amylose from 27.18 to 30.8%. Starches from different potato cultivars independent of soil showed a small range of gelatinization temperature. All starches showed low resistance heating and shear stress. CONCLUSION: The results showed the influence of growing conditions (soil P availability) and also of the differences between the potato cultivars on important characteristics of applicability of starches. © 2015 Society of Chemical Industry Keywords: amylose; Solanum tuberosum; starch; phosphorus; thermal properties; viscosity
INTRODUCTION Potato (Solanum tuberosum L.) is one of the most important crops for feeding the world’s population. With nearly 367 million tons harvested in 2013, it ranks fourth in world production after rice, wheat and maize. In the same year, according to the Food and Agriculture Organization of the United Nations,1 3.57 million tons of potato were harvest in Brazil. However, it is estimated that less than 50% of potatoes grown worldwide are consumed fresh. Industrial uses of potatoes include products such as frozen fries, flakes, snacks, flour and starch.2 Phosphorus (P) participates in many metabolic processes in plants, such as energy transfer, synthesis of nucleic acids, starch synthesis, respiration, synthesis and stability of membranes, activation and deactivation of enzymes, redox reactions and carbohydrate metabolism.3 Phosphorus deficiency has been shown to reduce growth of primary roots and enhance length and density of root hairs and lateral roots in many plant species.4,5 Starch is the main reserve carbohydrate in higher plants, the second most abundant biopolymer on earth and the most important carbohydrate for food, representing the main feature of the human diet and the raw material for various industrial applications.6 An increase in processed and pre-prepared food products has created a demand for the development of starches with certain qualities required for these applications. These starches can be found by J Sci Food Agric (2015)
searching for other plant varieties or species as well as by studying of genetically modify plants or the conditions of growth. Starch is composed exclusively of glucose residues linked by only two types of bonds: 𝛼-1,4 and 𝛼-1,6 glucosidic linkages. The main constituents of starch granules are amylopectin and amylose. Amylopectin (75% by weight) is a semi-crystalline, highly branched polysaccharide with an 𝛼-1,4 backbone and 4–5% 𝛼-1,6 branch points. Amylose (25%) is amorphous in the native starch granule and is essentially composed of linear chains of 𝛼-1,4-linked glucose units. As a minor component, tuberous starches, e.g. those prepared from potatoes, are rich in covalently bound phosphate. This natural substitution is restricted to the amylopectin fraction
∗
Correspondence to: Magali Leonel, Center for Tropical Roots and Starches (CERAT), São Paulo State University (UNESP), Botucatu, São Paulo 18610-307, Brazil. E-mail: [email protected]
a Center for Tropical Roots and Starches (CERAT), São Paulo State University (UNESP), Botucatu, São Paulo, Brazil b Department of Food Engineering and Technology, Institute of Biosciences, Language, and Physical Sciences, São Paulo State University (UNESP), São José do Rio Preto, São Paulo, Brazil c Department of Crop Science, College of Agricultural Sciences, São Paulo State University (UNESP), Botucatu, São Paulo, Brazil
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Table 1. Basic characteristics of experimental conditions Characteristic GPS coordinates Hieght above sea level (m) Soil classification Clay soil characteristics (0–0.2 m of depth) pH (1:2.5 soil/CaCl2 suspension 0.01 mol L−1 ) Organic matter (g dm−3 ) Presin-extractable (mg dm−3 ) K (mmolc dm−3 ) Ca (mmolc dm−3 ) Mg (mmolc dm−3 ) H + Al (mmolc dm−3 ) Cation exchange capacity (mmolc dm−3 ) Base saturation (%) Sand (g kg−1 ) Silt (g kg−1 ) Clay (g kg−1 )
Low P
High P
23∘ 02′ 27′′ S, 48∘ 47′ 57′′ W 744 Oxisol clayey loam
23∘ 28′ 48′′ S, 49∘ 01′ 28′′ W 649 Oxisol clayey
23∘ 07′ 69′′ S, 49∘ 12′ 30′′ W 737 Oxisol clayey
5.7 47.6 14 2.3 59.7 19.3 26.9 108.2 75 311 289 400
4.8 26.7 36 2.3 31.5 10.7 45.7 90.2 49 292 184 524
4.8 27.8 70 3.3 30.9 9.0 50.8 94.0 46 153 245 602
and is found at the C-2, C-3 and C-6 positions of the glucose residues.7 Starch biosynthesis and granule formation are complex processes. Biosynthesis requires the concerted action of a range of enzyme activities. Starch phosphorylation constitutes an integral part of the starch-biosynthetic pathway. Starch phosphorylation is also an important aspect of plant metabolism because of its role in starch degradation. Reducing the extent of starch phosphorylation has been shown to impair the degradation of starch, whereas an increase in starch phosphorylation was shown to stimulate the activity of the starch-degrading amylase enzyme.7 – 10 Native starches generally contain small amounts of P. In root and tuber starches, P is covalently linked to the starch in the form of P esters, whereas in cereal starches it occurs mostly as contaminating phospholipids. Inorganic phosphate may also be present.11 The degree of phosphorylation has a profound effect on the physical and chemical properties of the starch. Because the degree of phosphorylation influences the qualitative properties of starch there is interest in the effect of environmental parameters; specifically, to what extent starch phosphorylation can be manipulated by controlling phosphate supply to the plants.12 Noda et al.13 studied the starch P content in potato cultivars and its effect on starch properties and their results indicated that enhancing the starch phosphate resulted in significant increases in the swelling power, peak viscosity, and breakdown and significant but small increases in the onset and peak temperatures of gelatinization. Other starch quality parameters, such as the amylose content, granule median size, and the gelatinization enthalpy, did not significantly change due to the degree of phosphate substitution of starch. Lu et al.,14 studying the correlation between physicochemical and nutritional properties of dry matter and starch in potatoes grown in different locations, observed that P content of starch was a key factor affecting physico-chemical and nutritional properties of dry matter and starch in potatoes. Considering that starch properties depend on its physical and chemical characteristics and that it has been reported that starch is significantly influenced by the cultivars and environmental factors,15,16 this work was undertaken to study and compare P content, amylose, thermal and pasting properties of potato starches
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Medium P
from different cultivars grown in soils with different levels of P availability.
MATERIALS AND METHODS Growing of potatoes Three experiments were conducted under field conditions in areas of commercial production of potato. Prior to the experiments soil samples consisting of 20 sub-samples was taken in the 0–0.2 m layer depth to determine the soil chemical properties (Table 1). The experiments were conducted in soils with different levels of P available: low (14 mg dm−3 ), medium (36 mg dm−3 ) and high (70 mg dm−3 ). The P available was extracted using ion exchange resin and measured by colorimetry, according van Raij et al.17 Table 1 shows basic characteristics of the experimental conditions. The three experiments were conducted in a randomized block design with four replications. The treatments consisted of five potato cultivars and each plot consisted of five rows of 5 m. For the evaluations were considered central rows disregarding 0.5 m at the end of each row of plants and a row on each side of the plot. The potato cultivars used in all the experiments were: Agata, Asterix, Atlantic, Markies and Mondial. Cultivar Agata is the most planted in Brazil, occupying about 60% of the planted area. The cultivar Asterix is the most industrially used for the production of frozen fried potatoes. The cultivar Atlantic is the main cultivar suitable for the production of chips. The cultivar Markies is suitable for preparation for cooking as well as to fry. The cultivar Mondial presents high yield of tubers with low dry matter content characteristic that cater to the in natura market of potato. All potatoes were growing according the same method. For planting, the furrows were opened mechanically at a row spacing of 0.80 m. In all experiments, it was applied in the furrow insecticide thiamethoxam (155 g of i.a. ha−1 ) and chlorpyrifos (557 g of i.a. ha−1 ), fungicides pencycuron (280 g of i.a. ha−1 ), metiram (77 g of i.a. ha−1 ) and fluazinam (1155 g of i.a. ha−1 ) and the fungicide/bactericide streptomycin (17 g of i.a. ha−1 ). Mineral fertilization at planting of all experiments consisted of the application of 62 kg ha−1 N and 124 kg ha−1 K2 O for all cultivars in the form of ammonium sulfate and potassium chloride,
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Properties of potato starches
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respectively. Phosphate fertilizer was not applied to evaluate only the P already available in the soil. Top-dressing fertilization in areas with low, medium and high P availability was performed at 22, 24 and 28 days after planting (DAP), respectively. In the area with low, medium and high P avaliability 43, 64 and 41 kg ha−1 N, respectively, was applied. The insecticide thiamethoxam (198 g i.a. ha−1 ) and the fungicide fluazinam (1035 g i.a. ha−1 ) were used in the experiments simultaneously with the operation of hilling. The irrigation of the fields was carried out by sprinkler system center pivot. In all experiments pest control was performed according to technical recommendations for the potato crop. The plants of all areas were desiccated with diquat (331 g i.a. ha−1 ) around 100 DAP, and 21 days after the tubers were harvested for the evaluations. Starch isolation Uniform-size potatoes were selected from each cultivar before starch isolation. The tubers were peeled, sliced, and ground at high speed in a blender with distilled water (1:1 v/v) at 8∘ C for 2 min. The homogenate was passed through sieves (0.250 and 0.180 mm screen), and the solids retained were washed three times on the sieve. The filtrate was left to stand overnight at 5∘ C for decantation. The starch sediment was washed with distilled water and ethanol, recovered by centrifugation, and dried at 38∘ C in an air circulation oven. Analysis of starches The amylose content of starch was determined using the method of Williams et al.18 This analysis was carried out in triplicate. The content of P in potato starches was analyzed according to the methodology described by Malavolta et al.19 This analysis was carried out in triplicate. The thermal properties of potato starches were analyzed using a differential scanning calorimeter (DSC) Pyris 1 (Perkin Elmer, Norwalk, CT, USA). Starch samples (2.0 mg, dry basis) were weighed into aluminium pans, mixed with deionized water (6 μL) and sealed. The sealed pans were kept at room temperature for 2 h for balance and heated at a rate of 10∘ C min−1 from 25∘ C to 100∘ C. An empty pan was used as reference. After running the samples in DSC, they were refrigerated at 5∘ C for 14 days and analyzed again under the same conditions to determine the thermal properties of retrograded starches. The gelatinization temperature (initial, peak and final) and the enthalpy change of native and retrograded starches were determined using the Pyris 1 software from Perkin Elmer. This analysis was carried out in triplicate. For the analysis of the pasting properties the Rapid Visco Analyser (RVA; Warriewood, Australia) was used. The starch suspensions (2.5 g of starch in 25 mL of water), corrected for the basis of 14% of moisture, passed by the programming: 50∘ C for 1 min, heating from 50∘ C to 95∘ C at a rate of 6∘ C min−1 , maintaining the paste at 95∘ C for 5 min, cooling from 95∘ C to 50∘ C at a rate of 6∘ C min−1 . The viscosity was expressed as rapid visco unit (RVU) (1RVU = 12cP).20 From the graph obtained were evaluated: pasting temperature, maximum viscosity (peak), breakdown, final viscosity and setback. This analysis was carried out in triplicate. Statistical analysis Experimental data were analyzed together considering the potato cultivars and the three soil P availabilities. Data were subjected to analysis of variance using the SAS statistical software. The blocks J Sci Food Agric (2015)
Table 2. Phosphorus and amylose contents in starches of potato cultivars as affected by the soil P availability Soil P availability (mg dm−3 ) Cultivar Phosphorus (g kg−1 ) Agata Asterix Atlantic Markies Mondial Amylose (%) Agata Asterix Atlantic Markies Mondial
14
36
0.646Aa 0.252Cd 0.383Cb 0.372Cb 0.325Cc
0.533Bb 0.413Bc 0.564Ba 0.422Bc 0.436Bc
30.8Aa 29.3Bbc 29.1Ac 29.8Bb 27.2Bd
29.8Ba 29.6Ba 27.1Bb 29.6Ba 27.5Bb
70
0.550Ba 0.454Ab 0.622Aa 0.557Aa 0.466Ab 29.8Bb 30.8Aa 27.4Bc 30.7Aab 30.8Aa
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
and all the block interactions were considered to be random effects. The cultivars and P availability were considered to be fixed effects. The means were separated using Tukey’s test at the 0.05 probability level.
RESULTS AND DISCUSSION Results of P contents in potato starches showed a range of 0.252 to 0.647 g kg−1 , with significant differences between cultivars and soils (Table 2). Noda et al.13 also observed a variation in the P content in starch of potato cultivars reporting a variation of 0.308 to 1.24 g kg−1 . The comparison of the starch P content from different potato cultivars and soils showed that with the exception of cultivar Agata, higher contents of P in starch are observed when potatoes were grown in soils with a higher P availability (Table 2). The P uptake by plant roots is the result of interactions of morphological and physiological characteristics of roots, which can vary among potato cultivars,21 the rhizosphere immediately adjacent to the root system and soil characteristics that determine the flow of nutrients to the soil–root interface. The soils where experiments were conducted were acids and with medium and high P availability had lower contents of calcium and magnesium (Table 1), which may have interfered with the P uptake.22 Wekesa et al.,22 studying the effect of soil characteristics on potato tuber minerals composition, observed a positive correlation between potato tuber minerals levels and the soil mineral contents and the difference in behavior of the cultivar Agata (Table 2) may be related to differences in physiological parameters of root system affecting P uptake21 and allocation of P to the tubers.23 Fernandes et al.23 found that the availability of P in the soil affects the variable way in the allocation of P for potato cultivars tubers. The potato has been considered as a plant with low efficiency of P utilization and with little ability to uptake P in soils with low availability, which has often been attributed to its low density of roots, which develop mostly concentrated in the first 30 cm deep, below the seed tubers.24,25 The contents of amylose of different cultivars and soils ranged from 27.18 to 30.8% (Table 2). It was observed differences between
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www.soci.org cultivars in same soil as well as into same cultivar in different availability of P in the soil. For cultivars Asterix, Markies and Mondial higher amylose contents were observed in soil with higher P availability. However, ‘Agata’ and ‘Atlantic’ had higher contents of amylose in soil with low P available. For food processing purposes potatoes with higher amylose content are appreciated, unlike potatoes used for non-food industry containing higher amylopectin levels in starch.26 The influence of grow conditions on the physicochemical characteristics of starches has been reported. Šimková et al.,26 studying the effect of cultivar, location and year on total starch, amylose, P contents, and starch grain size of potato cultivars, observed that the amylose and P contents showed a clear negative correlation. For all measured parameters (starch, amylose, P and starch granule size) significant impact of cultivar was determined. Location and year had lower but significant impact. No statistically significant effect of year on amylose was found by these authors. When starch is heated in the presence of enough water its crystalline organization decomposes to form amorphous regions. This molecular disordering is called gelatinization. Differential scanning calorimetry (DSC) identifies melting and crystallization events as well as glass transition temperatures. The data of DSC showed differences between potato cultivars and into same cultivars grown in soils with different P availability for all parameters of thermal properties (Table 3). Onset temperature ranged from 58.17 to 62.76∘ C in soil with low P availability, 60.43 to 62.20∘ C in soil with medium P availability and 61.80 to 63.80∘ C in soil with higher level of P available (Table 3). The temperature of peak ranged from 61.00 to 65.57∘ C, 63.33 to 65.10∘ C and 64.40 to 65.23 for soils with low, medium and high level of P available, respectively. For the final temperature variations from 64.5 to 69.7∘ C (low P in soil), 66.7 to 68.7∘ C (medium P) and 67.4 to 70.63∘ C (high P) were observed. The results of the transition temperatures in gelatinization of starches were similar to those reported by Kaur et al.27 who, evaluating some properties of potatoes starches, observed that the endothermic peaks for different potato cultivars were between 59.96 and 68.89∘ C, the temperature of the peak ranged from 63.37 to 64.58∘ C and the final temperature ranged from 67.4 to 68.9∘ C. But the range of enthalpy of gelatinization observed by these authors was lower than that obtained in this work (Table 3). The cultivars Agata, Asterix and Atlantic showed lower transition temperatures (T 0 , T p and T c ) in soil with lower availability of P (Table 3). This was not observed for the starches isolated from Markies and Mondial cultivars that showed higher values for onset, peak and conclusion temperatures of gelatinization in soil with lower level of P available, which may be due to the effect of monoester phosphate groups linked to amylopectin.28 According to Tester et al.,29 the extension of crystalline perfection is reflected at the gelatinization temperature range and the change of enthalpy obtained by DSC. Starches from different potato cultivars independent of soil showed small range of gelatinization temperature and also showed low variation of enthalpy (ΔH). The starch of cultivar Agata showed high temperatures of gelatinization which can indicate long chain branched of amylopectin (Table 3). The starch crystallinity can be estimated by the enthalpy (ΔH), energy required to melt the duplexes segments. The gelatinization temperature (initial and peak) can be used as a measure of stability or completeness of crystalline regions and the width of endothermic peak as an estimative of the heterogeneity of the crystalline structure.30
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Table 3. Thermal properties of gelatinization of the starches of potato cultivars as affected by the soil P availability Soil P availability (mg dm−3 ) Cultivar Onset temperature, T 0 (∘ C) Agata Asterix Atlantic Markies Mondial Peak temperature, T p (∘ C) Agata Asterix Atlantic Markies Mondial Final temperature, T c (∘ C) Agata Asterix Atlantic Markies Mondial T c − T 0 = 𝚫T (∘ C) Agata Asterix Atlantic Markies Mondial Enthalpy change, 𝚫H (J g−1 ) Agata Asterix Atlantic Markies Mondial
14
36
70
62.47Bb 58.17Ce 60.53Cd 62.76Aa 62.13Ac
62.20Ca 60.43Bd 61.70Bb 61.90Bb 60.43Cc
63.80Aa 61.9Ac 62.50Ab 62.57Ab 61.80Bc
65.43Ba 61.00Cd 63.60Cc 65.57Aa 65.10Ab
65.10Ca 63.33Be 64.27Bc 64.77Cb 63.77Cd
66.6Aa 64.4Ac 65.23Ab 65.13Bb 64.4Bc
69.7Ba 64.5Cd 67.5Bc 69.47Aa 68.57Ab
68.7Ca 66.7Bc 67.7Bb 68.53Ba 66.9Cc
70.63Aa 67.6Ac 68.8Ab 68.7Bb 67.4Bc
7.24Aa 6.35Ac 7.00Aab 6.67Abc 6.41Ac 15.8Aa 13.6Ac 14.3Ab 16.1Aa 13.7Bc
6.49Ca 6.32Aab 6.00Cb 6.65Aa 5.97Bb 11.7Cd 12.8Bc 14.17Ab 13.9Cb 17.3Aa
6.86Ba 5.69Bc 6.38Bb 6.14Bb 5.57Cc 13.8Bb 12.3Cc 14.03Ab 14.6Ba 13.8Bb
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
The properties of gelatinization and swelling are, in part, controlled by the structure of amylopectin. As the crystalline regions of the starch granule are mainly composed by amylopectin, starches with high amylose content have low gelatinization temperatures and enthalpy.31 Nevertheless it was not possible to observe this relation in this experiment (Tables 2 and 3). As expected the retrograded starches showed lower thermal properties than gelatinized starches (Table 4). When analyzing the relationship between enthalpy of retrogradation and enthalpy of gelatinization generally we observed a negative ratio of P available in soil and retrogradation in starches of potato cultivars. The observation of relationship of P content and retrogradation in potato starches is in agree with related by Lu et al.;14 however, a few investigators have reported that P in potato starch granules was positively correlated with degree of retrogradation and tends to increase the retrogradation enthalpy.32,33 This contradiction might be largely attributed to the different materials used in their studies, the levels of amylose and P contents as well as amylopectin chain length distribution of the starches. During the retrogradation the amylose molecules form double helices of 40 to 70 glucose units and amylopectin form smaller double helices, due
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Properties of potato starches
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Table 4. Thermal properties of retrogradation of the starches of potato cultivars as affected by the soil P availability
Table 5. Pasting properties of the starches of potato cultivars as affected by the soil P availability
Soil P availability (mg dm−3 ) Cultivar Onset temperature, T 0 (∘ C) Agata Asterix Atlantic Markies Mondial Peak temperature, T p (∘ C) Agata Asterix Atlantic Markies Mondial Final temperature, T c (∘ C) Agata Asterix Atlantic Markies Mondial T c − T 0 = 𝚫T (∘ C) Agata Asterix Atlantic Markies Mondial Enthalpy change, 𝚫H (J g−1 ) Agata Asterix Atlantic Markies Mondial
14
36
70
44.8Bd 43.0Be 50.7Ba 46.4Bc 49.09Ab
45.8Ad 41.3Ce 51.3Aa 49.9Ab 48.3Bc
40.5Ce 43.6Ab 45.1Ca 41.7Cd 42.5Cc
59.8Aa 53.7Bb 59.96Aa 59.7Aa 59.9Aa
55.2Bc 51.9Cd 57.9Bb 59.5Aa 55.3Bc
48.1Cd 54.7Aa 53.9Cb 49.8Bc 53.9Cd
68.67Ab 60.23Bc 68.9Ab 69.07Ab 69.6Aa
62.23Bc 58.8Cd 65.93Ba 65.88Ba 63.20Bb
56.8Cc 61.46Aa 59.7Cb 59.2Cb 61.0Ca
23.87Aa 17.25Be 18.22Ad 22.68Ab 20.49Ac
16.46Bb 17.49ABa 14.65Bc 15.97Cb 14.89Cc
16.29Bc 17.82Ab 14.64Bd 17.64Bb 18.51Ba
5.23Ad 2.80Ce 6.20Ab 7.27Aa 5.70Bc
1.57Ce 5.50Ab 4.40Bc 3.17Bd 6.67Aa
1.97Bd 4.7Ba 2.03Cd 3.0Cc 4.5Cb
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
to restrictions imposed by the branched structure of the molecules and the length of the branches. This re-association occurs in the form molecular and structural more weakly than that found in the native molecule. Therefore, less energy is required to melt the restructured crystals.34 Gelatinization occurs when native starch is heated in the presence of sufficient moisture. The granules absorb water and swell, and the crystalline organization is irreversibly disrupted. Pasting encompasses the changes that occur after gelatinization upon further heating and these include further swelling of granules, leaching of molecular components from the granules and eventual disruption of granules especially with the application of shear forces. Results of pasting properties of potato starches showed differences in all parameters between cultivars and for the same cultivar grown in soils with different levels of P availability (Table 5). The peak of viscosity of starches ranged from 714.25 to 924.77 RVU in soil with low P, from 872.38 to 1014.09 RVU and from 921.94 to 1088.37 for soils with medium and higher availability of P, respectively (Table 5). The cultivars Asterix, Markies and Mondial showed higher P content, amylose and peaks of viscosity in soil with high P availability and these cultivars showed starches with J Sci Food Agric (2015)
Soil P availability (mg dm−3 ) Cultivar Peak (RVU) Agata Asterix Atlantic Markies Mondial Breakdown (RVU) Agata Asterix Atlantic Markies Mondial Final viscosity (RVU) Agata Asterix Atlantic Markies Mondial Setback (RVU) Agata Asterix Atlantic Markies Mondial
14
36
70
870.77Bb 714.25Cd 859.50Cb 781.59Cc 924.77Ca
872.38Bd 887.39Bc 1014.09Ba 892.79Bc 973.46Bb
918.57Ad 992.77Ac 1088.37Aa 921.94Ad 1046.08Ab
642.98Cb 484.50Cd 645.29Bb 574.63Cc 828.58Ca
760.31Bc 797.52Bb 927.15Aa 799.18Ab 914.84Ba
824.84Ad 881.36Ac 922.20Ab 710.84Bd 949.84Aa
277.71Ab 264.96Ac 259.87Bc 260.88Cc 291.00Aa
284.67Aa 255.56Bc 254.21Bc 269.55Bb 271.71Bb
279.13Ab 254.38Bc 338.21Aa 278.96Ab 275.13Bb
49.92Bb 35.21Cb 45.67Bb 53.92Bb 194.82Ba
172.60Ab 165.69Ab 167.27Ab 175.93Ab 213.08Aa
185.40Aa 142.96Bb 172.07Aa 67.59Bc 178.88Ba
Means followed by the same upper-case letters in the row or lower-case letters in the column do not differ at 5% level by Tukey’s test.
lower P content and amylose in soils with low P (Tables 2 and 5), showing a positive relationship between the level of P available in the soil and these starch characteristics. The peak of viscosity is indicative of the water-binding capacity of the starch and the ease with which the starch granules are disintegrated.35 The cultivar Mondial showed higher peak of viscosity in soil with low P availability and ‘Atlantic’ in soils with medium and high P (Table 5). If we analyze the percentage of amylose of these cultivars it is possible to observe a negative relationship between the amylose content of starch and the peak viscosity. This observation agrees with Lu et al.14 which analyzing starch potatoes reported that a higher level of amylose resulted in a lower peak viscosity. Starch-bound phosphate is an important factor for determining the starch viscosity characteristics. Several results have been obtained that demonstrate that higher starch P content is closely associated with higher viscosity in potato.36 When we analyzed the results of P in potato starch it was possible observe higher viscosity peak to ‘Atlantic’ starch in soils with medium and high availability of P, and this cultivar also showed higher viscosity peak in these soils when compared with other cultivars (Table 5). When potato starch is pasted, its phosphate groups ionize, leaving the starch with a negative charge. The resulting slight coulombic repulsion greatly opens up the branched amylopectin molecules and increases their salvation.14 This might explain the observation of relationship of P and peak viscosity (Tables 1, 2 and 5).
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www.soci.org Regarding breakdown all starches showed low resistance heating and shear stress during cooking with the highest values observed for all cultivars in soil with high P content (Table 5). Setback is a measure of recrystallization of gelatinized starch during cooling. All starches showed increase of viscosity with cooling and tendency to retrogradation. Results showed that setback of starches ranged from 35.21 to 194.82 RVU, soil with low P, 165.69 to 213.08 RVU, soil with medium P, and 67.59 to 185.4 RVU in soil with high P (Table 5). In soils with low and medium P availability the cultivar Mondial showed higher retrogradation tendency when compared with other cultivars. The retrogradation of amylose in processed foods is considered to be important for properties relating to stickiness, ability to absorb water, and digestibility, whereas retrogradation of amylopectin is probably a more important determinant in the staling of bread and cakes.35
CONCLUSION The physical properties of potato starches ranged among cultivars and the P available in the soil had interference on these properties independent of the cultivar. The identification of these effects on determinants properties for the applicability of starches provide useful and important information for potato producer, researchers and industrial sector because it opens possibilities of control of culture conditions aiming to get native starches with special properties.
ACKNOWLEDGEMENTS The authors are grateful to CNPq for financial support.
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