2018 Volume 24 Issue 3 Pages 559-565
Starch isolated from cv. Toyoshiro potatoes cultivated with/without calcium fertilizer application in two locations, Kamikawa and Tokachi, was evaluated for total starch, resistant starch, amylose, phosphorous and calcium contents, average granule size, pasting properties and thermal properties. Total starch and resistant starch contents were similar between the control and the calcium treatment in both locations. Average granule size, amylose and calcium contents were significantly higher in the calcium treatment in both locations (p < 0.05). Peak and breakdown viscosities did not significantly differ between the control and the calcium treatment in the two locations. Calcium treatment significantly reduced initiation (T0), peak (TP) and conclusion (TC) temperatures of gelatinization in Kamikawa, and significantly increased T0 and TP in Tokachi, while the enthalpy of gelatinization (ΔH) was similar (p < 0.05).
Starches with specific physicochemical properties are necessary to impart desirable characteristics, such as cooking, textural, nutritional and sensory, to food products (Yousif et al., 2012; Chung et al., 2014). Potato (Solanum tuberosum L.) starch is a popular and multifunctional material used in the food industry, due to its many desirable properties, such as clear, thick viscoelastic gel forming ability, high swelling power, peak and breakdown viscosities, which are mostly attributed to its very high phosphorous content (Wiesenborn et al., 1994; Hoover, 2001). In potato starch, phosphorous is mainly found as phosphate monoesters esterified to long chain amylopectin chains, either at C-6 or C-3 positions in glucose residues (Leszcsński, 2004).
Some of the phosphate esters on adjacent amylopectin chains are naturally found cross-linked with various cations, such as calcium and magnesium, by ionic forces, which resemble industrially prepared, chemically modified starch by covalent cross-linking (De Willigen et al., 1976; Ciesielski and Tomasik, 2004; Zaidul et al., 2007a). The capacity of starch to react with metal ions and the subsequent metal ion absorption result in markedly altered physicochemical properties compared to native counterparts and provide important mineral elements to the human body via starchy foods (Fortuna et al., 2013). Thus, characterization of the nature of starch interactions with metal ions is important in designing novel foods with nutritional claims and in other industrial applications, such as in the textile, paper, pharmaceutical and cosmetic industries, where starch is used as a colloidal stabilizer, thickener, water holding agent, filler and many other (Sing et al., 2006).
Mineral fortification of starch results in altered and improved physicochemical properties that tailor the native starch for specific food applications (Hermansson and Svegmark, 1996). Noda et al. (2014) reported a successful method to increase the calcium and magnesium contents in industrially prepared potato starch by immersion in calcium and magnesium mineral solutions, resulting in good viscosity stability of the resultant starch with lower peak and breakdown viscosities. Slightly higher specific loaf volumes and appearance scores obtained for bread made by incorporating calcium fortified potato starch provide evidence for its utilization in the manufacture of food products with desirable characteristics (Noda et al., 2015).
Calcium fertilizer application in potato cultivation has been practiced as a reliable method to combat physiological disorders associated with significant profit losses (Gunter and Palta, 2008). In-season calcium application was found to increase tuber calcium content as much as eight-fold according to Kratzke and Palta (1986). Since mineral fortification of starch resulted in altered physicochemical properties, it was hypothesized that increased tuber calcium content by fertilizer application might cause similar alterations in starch properties. Thus, the aim of this study was to determine the effects of calcium fertilizer application on the calcium content and physicochemical properties of starch. Also, we aimed to determine the differences or similarities of the aforementioned effects between two locations, as significantly different starch physicochemical properties were observed between these two locations in our previous study.
Materials A common processing type potato variety, cv. Toyoshiro, was cultivated in two locations, Tokachi and Kamikawa, two of the major potato producing districts in Hokkaido Prefecture, Japan in 2015. Cultivation was conducted under control conditions (only the basal fertilizer application according to Hokkaido Fertilizer Recommendation Guidelines) and with application of calcium fertilizer (CaSO4) at a rate of 50 kg per 10 acres along with the basal fertilizer at the time of planting.
Starch isolation All samples were subjected to starch extraction immediately after their respective harvest dates. One kilogram of peeled potatoes was ground using a laboratory scale blender in 10 L of deionized water. The starch slurry was sieved using a series of parallel sieves with mesh sizes of 710, 106 and 75 µm and allowed to stand undisturbed for 2 h. After filtering using a glass filter (26G2, Asahi Glass Co. Ltd., Tokyo, Japan), approximately 3 L of deionized water was added to the residue and allowed to stand for 6 h while stirring using a magnetic stirrer. After filtering, 3 L of deionized water was added and stirred for another 2 h. This was repeated twice before the crude starch was separated. The isolated starch was oven-dried at 55°C for 4.5 h. The dried starch was ground, sieved through a sieve with a mesh size of 106 µm and stored in air-tight plastic containers at 4°C until further analysis. Prior to further analysis, the moisture content was measured according to the AOAC method at 135°C (AOAC, 2000).
Amylose content Amylose content of the isolated starch samples was measured according to the procedure by Yun and Matheson (1990), with modifications as described in the Megazyme Amylose/Amylopectin Assay procedure (K-AMYL 07/11). Amyloglucosidase (EC 3.2.1.3., 3300 U/mL) and a glucose oxidase–peroxidase assay kit (cat. No. K-GLUC) were purchased from Megazyme (Megazyme International Ireland Ltd., Wicklow, Ireland).
Resistant starch and total starch contents Resistant starch and total starch contents of the isolated starch were measured according to the AOAC method 2002.02 and the AOAC method 996.11, respectively.
Phosphorous and calcium contents Mineral contents (P and Ca) of the starches were determined by an inductively coupled plasma-sequential plasma spectrometer (ICPS-8100, Shimadzu Co. Ltd., Kyoto, Japan). One hundred milligrams of each sample was wet digested with H2SO4-H2O2 and the resultant clear solution was quantitatively transferred to a 25 mL volumetric flask with 2N HCl. Well mixed samples were analyzed along with a standard series of 0.0, 1.0, 2.0, 3.0 and 4.0 ppm of P and 0.0, 0.25, 0.5, 0.75 and 1.0 ppm of Ca in 0.2N HCl.
Particle size and particle size distribution Starch particle size and particle size distribution were determined using a compact laser diffraction particle size analyzer (LA-300, Horiba Instruments Co. Ltd., Kyoto, Japan).
Swelling power and solubility Swelling power and solubility of the isolated starches were determined using an 0.4% aqueous suspension of starch and employing the method of Yousif et al. (2012) with slight modifications. Starch solutions were heated at 70, 80 and 90°C for 30 min in a water bath and cooled at 10°C for 20 min, before being centrifuged at 3000 g and subjected to gravimetric measurement.
Pasting properties Pasting properties of the starch samples were measured using a rapid visco analyzer (RVA-4, Newport Scientific Pvt. Ltd., Warriewood, Australia). A 6% aqueous suspension of starch was analyzed in triplicate for peak, breakdown, final, and setback viscosities as well as pasting temperature (as defined in Figure 1) using the method described by Singh et al. (2006).
Pasting parameters
Thermal properties A differential scanning calorimeter (Micro DSC II, Setaram Inc., Caluire, France) was used to determine the thermal properties of the starch. A 30% aqueous starch solution was prepared in a metal canister, then hermetically sealed and kept overnight at room temperature. Samples were analyzed in the scanning temperature range from 30 to 95°C and a scanning rate of 0.8°C/min, using distilled water as the reference. Enthalpy of gelatinization (ΔH), onset (T0), peak (TP) and conclusion (TC) temperatures of gelatinization were measured in triplicate.
Statistical analysis Analysis of variance (ANOVA) was used to analyze the data using SPSS statistical software version 17.0 (SPSS Inc., Chicago, USA). When significant differences were revealed (p < 0.05), mean scores were subjected to multiple comparisons using Duncan's multiple range test (p < 0.05).
Physicochemical composition Table 1 summarizes total starch, amylose and resistant starch contents of starch isolated from the two locations. Total starch content varied between 87.4 and 90.4% on a dry weight basis (dwb), and did not differ significantly between the control and calcium treatments or between the two locations. A previous study by Sulaiman (2005) reported increased total starch content following calcium fertilizer application, which is in contrast to the findings of this study. The amylose content varied between 21.2 and 34.0% dwb. Significantly higher amylose content was observed in calcium applied starch samples in both locations (p < 0.05), which is in contrast to the findings of Sulaiman (2005). Resistant starch content varied between 76.7 and 78.7% dwb and was similar between the test samples in both locations, which is consistent with the findings of Noda et al. (2014). In previous studies, modified starches by cross-linking have exhibited increased digestibility with increased calcium content when digested with pancreatic α-amylase, while the opposite was observed for amyloglucosidase (Islam and Azemi, 1998). An increased susceptibility in digestibility with pancreatic α-amylase observed for calcium-treated starches can be attributed to the requirement for calcium in the mode of action of α-amylase, while calcium is known to inhibit amyloglucosidase activity (Moran, 1982; Stauffer, 1987; Islam and Azemi, 1998). The Megazyme assay procedure used in this study employs both of the enzymes mentioned above, and thus the enhancing or inhibiting activity might have neutralized the result to obtain statistically similar resistant starch contents between the control and calcium applied samples.
| Tokachi | Kamikawa | |||||
|---|---|---|---|---|---|---|
| Ca treatment | AM (% dwb) | TS (% dwb) | RS (% dwb) | AM (% dwb) | TS (% dwb) | RS (% dwb) |
| Ca− | 26.1 ± 0.5 a * | 88.5 ± 1.5 a | 76.7 ± 1.2 a | 21.2 ± 0.5 a | 90.4 ± 2.5 a | 76.7 ± 1.2 a |
| Ca+ | 34.0 ± 1.5 b | 87.4 ± 1.5 a | 78.5 ± 1.3 a | 32.4 ± 1.3 b | 89.9 ± 2.2 a | 78.7 ± 1.7 a |
Abbreviations: AM, amylose content; TS, total starch content; RS, resistant starch content; Values within each column with different letters are significantly different between Ca treatments at p<0.05. Values with * superscript are significantly higher than the other location at p<0.05.
The calcium content of the starch samples varied between 4.2 and 4.9 mg/100 g dwb as shown in Table 2. The calcium fertilizer applied starch samples reported significantly higher calcium contents compared to their control counterparts in each location (p < 0.05). The observed calcium contents in the test samples were slightly lower than that previously reported, 5–20 mg/100 g, in factory-made potato starch (Kainuma et al., 1976; Zaidul et al., 2007a). This observation can be attributed to the method of preparation or extraction of starch, which involves rinsing with distilled water, resulting in a loss of the initial amount of metal ions (Fortuna et al., 2013). The starch extraction method employed in this study was also a rinsing method, where the homogenized potato tuber pulp was rinsed with deionized water several times, which might have resulted in the loss of a significant amount of calcium, where 90% of calcium compounds in potato tuber are found as either water-or salt-soluble forms (Subramanian et al., 2011).
| Tokachi | Kamikawa | |||||
|---|---|---|---|---|---|---|
| Ca treatment | Ca (mg/100g dwb) | P (mg/100g dwb) | A VG(µm) | Ca (mg/100g dwb) | P (mg/100g dwb) | A VG(µm) |
| Ca− | 4.6 ± 0.0 a * | 56.1 ± 0.6 a | 40.5 ± 0.3 a * | 4.2 ± 0.1 a | 71.5 ±0.8 b* | 35.9 ± 0.0 a |
| Ca+ | 4.8 ± 0.1 b | 56.1 ± 1.1 a | 42.5 ± 1.0 b * | 4.9 ± 0.2 b | 66.1 ±0.2 a* | 40.4 ± 0.2b |
Abbreviations: A VG, average granule size; Values within each column with different letters are significantly different between Ca treatments at p<0.05. Values with * superscript are significantly higher than the other location at p<0.05.
The phosphorous content was between 56.1 and 71.5 mg/100 g dwb, which is comparable with the phosphorous content of factory-made potato starch in local factories in Hokkaido (Zaidul et al., 2007a; Zaidul et al., 2007b). Starches from Kamikawa had significantly higher phosphorus content for both the control and calcium applied samples compared to Tokachi, which is in accordance with the results of the author's previous study (Pelpolage et al., 2016). As cations, such as calcium and magnesium, are able to cross-link with phosphate ester groups on adjacent amylopectin chains, their contents were found to be higher in starches with higher phosphorous content, as reported by Zaidul et al. (2007a) and Chen et al. (2003). However, this trend was not observed in the present study. In this study, the two locations showed two different trends. In Tokachi, the phosphorous content in the two treatments was similar, but the calcium content was significantly higher in the calcium applied starch sample (p < 0.05). In Kamikawa, the phosphorous content was significantly higher in the control sample and the calcium content was significantly higher in the calcium applied starch sample (p < 0.05).
The average granule size of starch samples ranged from 35.9 to 42.5 µm (Table 2). In both locations, the calcium applied sample had a significantly larger granule size compared to the control. Starch isolated from Tokachi showed significantly larger granule sizes compared to Kamikawa for both the control and calcium treatments. As previously reported by Zaidul et al. (2007a), potato starches with a smaller granule size tended to have higher phosphorous and calcium contents and lower amylose content. In contrast, higher calcium contents were observed in larger granules in this study. However, in Kamikawa, a higher phosphorous content and a lower amylose content were observed for starches with a smaller granule size. The observed deviations in the present study might be attributable to the characteristics specific to the potato cultivar used in this study, since granule size is highly dependent upon the cultivar (Prada and Aguilera, 2012).
Swelling power and solubility Swelling power of all starch samples followed a similar trend in both locations, as shown in Figure 2, where swelling power was increased from 70 to 80°C and reduced from 80 to 90°C, which is in accordance with the results of Noda et al. (2015) and Khan et al. (2014). The increase in swelling power with increasing temperature could be due to the gelatinization of starch, which unfolds the packed starch structure (Khan et al., 2014). The observed decrease in swelling power from 80–90°C might be due to the leaching of amylopectin molecules, which are responsible for starch swelling (Li and Yeh, 2001). Values obtained for swelling power did not differ significantly between the control and calcium applied samples, except at 70°C in Tokachi and 90°C in Kamikawa. At 80 and 90°C, swelling power was comparatively higher in control samples than their calcium applied counterparts in both locations. Noda et al. (2015) also reported significantly low swelling power values for calcium fortified starches at a temperature range of 70 to 85°C.
Swelling power and solubility of potato starch from two locations in Hokkaido
A,B and a,b stand for significant differences between calcium added and control samples at 70, 80 and 90°C from the same location (p < 0.05)
Solubility results did not show a special trend with increasing temperature. Solubility of the control was significantly higher at 70 and 80°C only in Tokachi, while in Kamikawa, solubility between the two treatments did not significantly differ. Generally, cross-linking of starches was found to decrease the swelling power and solubility of starches, by strengthening the bonding between starch chains, resulting in the inhibition of granule swelling (Singh et al., 2007). Thus, similar values observed for swelling power and solubility between the control and calcium applied samples in the present study suggest the presence of bonding forces of similar strength (Kaur et al., 2007).
Pasting properties Peak viscosity did not significantly differ between the control and calcium applied samples in both locations. However, both the control and calcium applied samples from Kamikawa had significantly higher peak viscosities compared to Tokachi, which is attributable to the higher phosphorous contents in the former (Noda et al., 2004). Breakdown viscosity did not significantly differ between the control and calcium treatments or the two locations. The final viscosity did not significantly differ between the control and calcium applied samples, but was significantly higher in Kamikawa compared to Tokachi for both samples. The pasting temperature ranged between 67.1 and 68.8°C. It was significantly higher in the control sample than its calcium applied counterpart in Kamikawa, while in Tokachi it was similar between the control and calcium applied samples. Chemical modification of starch imparts considerable changes to the pasting properties of starch, such as significantly depressed peak and breakdown viscosities (Fortuna et al., 2013; Noda et al., 2015). According to previous reports, the presence of a critical level of divalent cations in potato starch is required to depress the viscosity significantly to obtain better paste stability (De Willigen, 1964; Noda et al., 2015). Thus, a possible reason for the observed similar pasting properties between the control and calcium applied starch samples is that a critical level of calcium content was not found in the tested starch, as suggested by Noda et al. (2015). Although peak and breakdown viscosities only exhibited comparatively lower values with increased calcium content, this might be very useful information for food processors, as calcium fertilizer application tended to change the pasting properties of starch.
| Tokachi | Kamikawa | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Catreatment | PV(cP) | BDV(cP) | FV(cP) | SBV(cP) | PT(°C) | PV(cP) | BDV(cP) | FV(cP) | SBV(cP) | PT(°C) |
| Ca− | 6035 ± 24 a | 4390± 46 a | 1994 ± 55 a | 348 ±26 a | 67.1 ± 0.5 a | 6455 ± 40 a * | 4396 ± 71 a | 2389 ± 33 a * | 373 ± 8 b | 68.8 ± 0.4 b * |
| Ca+ | 5945 ± 15 a | 4370± 67 a | 1863 ± 73 a | 305 ± 31 a | 68.0 ± 0.5 a | 6441 ± 9 a * | 4374 ± 61 a | 2375 ± 18 a * | 334 ± 10 a | 67.8 ± 0.0 a |
Abbreviations: PV, peak viscosity; BDV, breakdown viscosity; FV, final viscosity; SBV, setback viscosity; PT, pasting temperature; Values within each column with different letters are significantly different between Ca treatments at p<0.05. Values with * superscript are significantly higher than the other location at p <0.05.
Thermal properties Table 4 summarizes the thermal properties of the starch samples. T0 and TP were significantly higher in the calcium applied sample in Tokachi and in the control sample in Kamikawa (p < 0.05). Values obtained for TC did not significantly differ between the control and calcium applied samples in Tokachi, while the control sample showed a significantly higher TC value in Kamikawa (p < 0.05). ΔH varied between 18.3 and 18.8 J/g dwb, but ΔH did not significantly differ between the control and calcium applied samples or between the two locations. Similar observations to Tokachi were reported by Noda et al. (2014) for T0 and TP, which were significantly higher in calcium fortified potato starches. In contrast, Fortuna et al. (2013) reported that the presence of metal ions had no influence on gelatinization temperatures, concluding that the molecular architecture was not significantly affected by the presence of metal ions, such as Mg2+ and K+. However, the introduction of cations, such as calcium, during the chemical modification of starch has long been suggested to modify the starch molecular organization, which in turn was predicted to alter the crystallinity of starch and consequently influence the gelatinization parameters of modified starches (Islam and Azemi, 1998). In the present study, x-ray diffractograms of starches for the control and calcium treatments in each location exhibited only slight differences (data not shown).
| Tokachi | Kamikawa | |||||||
|---|---|---|---|---|---|---|---|---|
| Ca treatment | T0 (°C) | TP (°C) | TC (°C) | ΔH (J/g dwb) | T0 (°C) | TP (°C) | TC (°C) | ΔH (J/g dwb) |
| Ca− | 60.2 ± 0.1 a | 63.2 ± 0.0 a | 69.0 ± 0.1 a | 18.6 ± 0.6 a | 62.1 ± 0.1 b* | 65.4 ± 0.1 b* | 72.1 ± 0.2 b* | 18.8 ± 0.2 a |
| Ca+ | 61.1 ± 0.1 b | 64.1 ± 0.1 b | 69.9 ± 0.0 a | 18.8 ± 0.2 a | 60.8 ±0.1 a* | 63.8 ±0.1 a* | 69.9 ±0.1 a * | 18.3 ± 0.3 a |
Abbreviations: T0, initiation temperature; TP, peak temperature; TC, conclusion temperature; ΔH, enthalpy of gelatinization; Values within each column with different letters are significantly different between Ca treatments at p<0.05. Values with *superscript are significantly higher than the other location at p<0.05.
Results of two-way ANOVA further revealed the presence of significant effects of calcium application on the physicochemical properties of starch. For example, calcium application had significant individual effects on amylose content and average granule size (p < 0.001), while calcium application and location had significant interaction effects on phosphorous and calcium contents, T0, TP and TC (p < 0.001).
Calcium fertilizer application could significantly increase the calcium content in potato starch as hypothesized, though the increase was slightly lower compared to previously reported data. Increased calcium contents had significant effects on several physicochemical properties, such as amylose and phosphorous contents, average granule size and thermal properties. However, there were inconsistent trends between the two locations for the physicochemical properties mentioned above, which might be attributable to the complex nature of interactions among different locations, variety-specific characteristics and agronomic practices. The observed modifications were not as drastic as those previously reported for modified starches produced by immersing in calcium solutions. However, this study sheds some light on the field of starch modification, as it introduces a comparatively low-cost, environmentally-friendly method of calcium enrichment. Thus, we propose further investigation of the relationships between calcium fertilizer application and starch properties, to identify fertilizer application regimes that can improve the starch calcium content and thereby modify starch properties significantly.
