Physicochemical properties of starch obtained from Dioscorea nipponica Makino comparison with other tuber starches

Physicochemical properties of starch obtained from Dioscorea nipponica Makino comparison with other tuber starches

Journal of Food Engineering 82 (2007) 436–442 www.elsevier.com/locate/jfoodeng Physicochemical properties of starch obtained from Dioscorea nipponica...

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Journal of Food Engineering 82 (2007) 436–442 www.elsevier.com/locate/jfoodeng

Physicochemical properties of starch obtained from Dioscorea nipponica Makino comparison with other tuber starches Yi Yuan a, Liming Zhang a,*, Yujie Dai a, Jiugao Yu b a

Tianjin Key Laboratory of Industrial Microbiology, College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300222, China b School of Science, Tianjin University, Tianjin 300072, China Received 4 July 2006; received in revised form 3 December 2006; accepted 21 February 2007 Available online 12 March 2007

Abstract In the development of food and medicine industry, more and more attentions have been paid on new starches with different properties. Dioscorea nipponica Makino, which is a widely used medicinal plant in the pharmaceutical industry, contains plenty of starches in its tubers. These starches are usually ignored and wasted during the isolation and separation of the small-molecule bioactive ingredients. In this paper, D. nipponica Makino starch was separated and characterized by scanning electron microscope (SEM), X-ray diffraction and granule size analysis. Compared with tapioca and potato starches, the morphology of D. nipponica Makino starch showed smaller particles, oval shaped and dissimilar granules in size. The crystal type of D. nipponica Makino starch was C-type pattern. The amylose content in D. nipponica Makino starch was 26.3%. Significant differences from D. nipponica Makino and other tuber starches in thermal properties were obtained by differential scanning calorimetry (DSC). The starch separated from D. nipponica Makino showed the highest transition temperature (67.4–76.0–81.1 °C) and intermediate enthalpy (18.6 J/g) of gelatinization. According to the viscosity measurement with Brabender viscograph, D. nipponica Makino starch exhibited lower peak viscosity, higher setback and lower breakdown viscosity. Its less swelling power corresponded with its lower breakdown viscosity. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Dioscorea nipponica Makino starch; Morphology; Amylose; Pasting properties

1. Introduction Dioscorea nipponica Makino is a unique Dioscorea L. botanical in China. There is abundant dioscin in its tuber. It is one of the most important pharmaceutical raw materials for D. nipponica Makino diosgenin in industry. Because diosgenin is an ideal parental drug to synthesize variety steroidal hormones and steroidal contraceptives, D. nipponica Makino investigation is becoming popular. In the process of diosgenin isolation from D. nipponica Makino tuber in Chinese industry, starch and its homogeneous carbohydrates are let into the environment directly and water source is contaminated. Every year, there are 1000 tons of diosgenin produced in China, meanwhile *

Corresponding author. Tel.: +86 22 60601265. E-mail address: ga[email protected] (L. Zhang).

0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.02.055

16,000 tons of dioscorea starch are decomposed or disrupted in technologic processing and then drained into river with sewerage (Zhou & Feng, 1995). To fully use the source of medicinal plant and protect environment, the ideal method is to collect and make use of the dioscorea starch. In recent years, native starch processing and flour applications in Chinese food industry have been widely investigated. In Chinese market, native starch is considered as health food because of its coming from green botanical source and its undefiled property. Meanwhile, as a good source of carbohydrate polymers, botanical starch is becoming an essential part of people diet. The main application claimed for tuber flour has been in bread products and snacks (Alves et al., 2002). Now, because the single cereal starch source is insufficient to supply, the starch industry pays attention to other alternatives could satisfy people’s demands (Manek et al., 2005). From a pharmaceutical

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standpoint, starch finds its value in solid oral dosage forms, where it has been used as a binder, diluent and disintegrant (Patel & Hopponen, 1966). Also tuber starch has been applied in textile, papermaking, feedstuff and paint industry as thickening and gelling agent (Zhao, Yue, & Mao, 2005). Therefore, D. nipponica Makino having considerable starch content may be considered as new starch sources for the food and medicine industry like other medicinal plants. Although, the dioscin was studied widely in the world, D. nipponica Makino starch isolation has not yet been released or studied. This study was to obtain the physicochemical properties of D. nipponica Makino starch and compare them from that of other tuber starches in order to evaluate D. nipponica Makino starch’s potential use as food ingredients. The granule size and morphology (carried out by scanning electron microscopy, SEM), crystallinity structures (characterized by X-ray powder diffraction), thermal and pasting properties of D. nipponica Makino starch were to be elucidated in this study.

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2.3. SEM The dried starch samples were mounted on a glass board covered with double-side tape and gilded with gold in a Polaron E-5200 coating unit (Polaron equipment, Watford, England). Then the prepared starch granule morphology was received using Philips XL-30 ESEM scanning electron microscope (Philips, Eindhoven, Holland). These images of samples were received at 20.0 kV accelerating voltage and magnified 1000 times. 2.4. Granule size analysis The particle size analysis of starch samples was obtained using a Omec LS-POP(III) laser particle sizer (Omec, Guangdong, China). Samples were dissolved with 5% sodium metaphosphate solution at room temperature before testing. Sampling was done with triplicate samples. 2.5. X-ray powder diffraction

2. Materials and methods 2.1. Materials Tubers of D. nipponica Makino were obtained from Lishi medicine Co., Shanxi, China (February, 2006). These tubers were cultivated (under soil conditions) in the province of Shanxi, China for two years cultivation period. Comparative experiments were carried out using commercial native starches. Native tapioca starch and native potato starch were received from Kebayoran Lama, Jakarta, Indonesia and Feima food Co., Ltd. (Inner Mongolia, China), respectively. 2.2. Starch extraction In the D. nipponica Makino starch isolation, the tubers were trimmed to get rid of defective parts and washed with water, then the tubers were sliced into pieces with the thickness between 3 and 5 mm and dried in an oven until weight constancy. The small slices were incubated in 0.2 % (w/v) NaOH solution (pH 10–11) for 24 h. In order to macerate the botanical cell wall and to reduce activities of microbes and enzymes that may decompose starches. After the tubers were milled, the slurry was filtered through 150 lm screen. The supernatant was milled for several times and the slurry refiltered through 150 lm screen to keep the cell wall off the starch slurry. Then the residue was amassed and deposited quietly for 6 h. The liquid layer was discarded and the superficial impurity of starch was eradicated. Ethanol (95%) was added in order to remove the scanty dioscin. Subsequently, the starch fraction was raised several times with distilled water until a neutral pH was reached. The slurry was sieved with 75 lm mesh size several times. The starch suspension obtained was dried in a convection oven at 50 °C until weight constancy. The dried material was milled and sieved with 75 lm screen to get the starch flour.

The structures of native starch were carried out using wide-angle X-ray diffraction. They were recorded with a Rigaku D/max 2500 X-ray powder diffractometer (Rigaku, Tokyo, Japan). These powder samples were scanned using ˚ ) at 40 kV and 150 mA. Cu Ka radiation (k = 1.54056 A The scanning region of the angles (2h) was from 3° to 50° at a scanning speed of 6°/min. The scan steps size of 0.02 were used with a dwell time of 0.2 s. The degree of crystallinity of samples was quantitatively estimated following the method of Nara and Komiya (1983). 2.6. Determination of amylose content The apparent amylose contents were determined by the amylose–iodine complex procedure (Fathat, Tunde, & Roger, 1999) with modification. The results were obtained using the spectrophotometer (Shimadzu UV-1700, Tokyo, Japan). The sample starch of 0.1000 g was suspended in the solution contains 1 ml 99% (v/v) ethanol and 9 ml 1 M NaOH and heated in a water bath of 95 °C for 10 min. Then the starch suspensions were diluted with deionized water to 100 ml. Five milliliter suspension was transferred into 100 ml flask, 50 ml deionized water and 1 ml iodine solution were transferred at the same time. After that the volume was made up to 100 ml with deionized water. Five milliliter 0.09 M NaOH solution was transferred into another flask as a blank. Then the value of absorbance density was obtained at 620 nm. The experiments were performed in triplicates. 2.7. Determination of swelling power and solubility The value of swelling power and solubility were determined according to the modified method described by Schoch (1964). Fifty milliliter of 2% (w/w) starch (dry basis) suspension was prepared and measured exactly.

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Then the starch suspension was incubated in a water bath at different temperatures from 65 °C to 95 °C with a working churn and kept at constant temperature for 30 min. Subsequently, the sample was cooled to room temperature and put into centrifuge tubes with cap. Then these tubes were centrifuged at 3000 r/min for 20 min. The swelling power and the solubility were determined by measuring the sediment weight and the solid content of the supernatant in the centrifuge tubes respectively. 2.8. Differential scanning calorimetry The thermal analyses of starch samples were obtained using differential scanning calorimetry (DSC 204 HP, Netzsch, Germany). The starch samples were adjusted to 1:3 flour-to-water ratios and each starch slurry (4.0 mg starch in 12 ll distilled water) was transferred to an aluminum pan (Mettler, ME-27331). And these pans were hermetically sealed, equilibrated at room temperature for 1-2 h and heated from 20 °C to 120 °C at a heating rate of 10 °C/min. The melting enthalpy and the temperature axis were calibrated with indium. Each test was carried out with an empty pan as a reference and the onset of gelatinization (To), the peak temperature (Tp), the gelatinization temperature at conclusion (Tc), and melting enthalpy (DH) were recorded. The range of gelatinization temperature (R) was computed as (Tc To) and the peak height index (PHI) was calculated as the ratio DH/(Tp To) (Krueger, Knutson, Inglett, & Walker, 1987; Vasanthan & Bhatty, 1996). Each test was performed in triplicates. 2.9. Determination of pasting properties The pasting properties of the samples were measured using Brabender Viscograph-E Measurement & Control Systems (Brabender OHG, Duisburg, Germany). Thirty grams (dry basis) of starch sample and 470 ml of distilled water (6%, w/w) were mixed and transferred into the cup of Brabender viscograph. The starch suspension was heated from 35 °C to 95 °C at 1.5 °C/min and kept for 30 min at 95 °C, then it was cooled down to 50 °C at a rate of 1.5 °C/min and held at 50 °C for 30 min too. Parameters recorded from the pasting cures, which included the peak viscosity (PV), final viscosity at 95 °C (HPV), viscosity at 50 °C (CPV), breakdown viscosity (BV) and setback viscosity (SV). 3. Results and discussion 3.1. Starch granule morphology The granule shape, size and morphology of samples are shown in Fig. 1. The granule morphology is significantly different from that of tapioca and potato starch. The starch granules with spherical, ellipsoidal and irregular shaped had been reported by Jane et al. (1994). D. nipponica Makino starch granule is dissimilar in size and loosely packed.

Fig. 1. Scanning electron micrographs of (i) D. nipponica Makino starch, (ii) tapioca starch, and (iii) potato starch.

And it shows oval shaped like potato starch micrograph with some granules sausage shaped. It exhibits smooth surface as potato starch granules. The micrograph indicates the starch passive activity of enzymes because of the high pH value kept in processing. And it keeps the granules away from exhibiting cracks (Lorenz & Dilsaver, 1982). However, the tapioca starch shows incomplete hemisphere granules with fissures, similar in size and tightly packed. The results are not consistent with the literature written by Soni, Sharma, and Dobhal (1985).

Y. Yuan et al. / Journal of Food Engineering 82 (2007) 436–442 Table 1 Granule size data of D. nipponica Makino, tapioca and potato starches Sample

Range of granule size (lm)

Average value of granule sizea (lm)

D. nipponica Makino Tapioca Potato

3–22 6–31 10–65

9.5 ± 0.2 14.7 ± 0.3 30.5 ± 0.5

a

Data were reported in means ± standard deviation, (n = 3).

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starch showed medium peaks at 5.5° and 23.4°of 2h, and strong peaks at 15.1°, 17.2°, 22.8° and 26.5° of 2h angles. Therefore, the diffractograms have an intermediate crystallite form (type-C) different from type A and type B. And the degrees of crystallinity of three kinds of starches (Table 3) were calculated from Fig. 2. 3.3. Amylose content

The granule size of D. nipponica Makino starch was smaller than that of tapioca and potato starch (Table 1). The smaller granule sizes improve the digestibility because smaller granules have a greater surface area and are more rapidly digested by amylases. The relationship between granule size and digestibility was previously reported (Cone & Wolters, 1990; Franco, Preto, & Ciacco, 1992; Riley, 2004). 3.2. X-ray power diffraction The crystal characterizations of native starch granules were often carried out using X-ray diffraction patterns, which had been classified as A, B or C pattern. According to current models of starch granule, parallel double amylopectin molecules result in the formation of crystalline regions, while amylose molecules result in the formation of amorphous regions in the starch structure (Cheetham & Tao, 1998). The relative intensity of the peaks of all samples is shown in Table 2. The d-spacing was calculated with ˚. Bragg’s equation as nk = 2d sin h, where k is 1.54056 A Tapioca starch showed strong diffraction peaks at 15.2°, 17.4°, 22.8° and 23.4° of 2h. This was consistent with expected A-type pattern. Potato starch showed characteristic peaks at 5.8°, 17.2°, 22.1° and 24.2° of 2h, which are usually expected as B-type pattern. D. nipponica Makino

The amylose content of D. nipponica Makino starch was obtained by spectrophotometer (Table 3). Significant differences in the amylose content were observed in this study. D. nipponica Makino starch had different amylose content (26.3% dry weight). Starch from potato was found to have the highest apparent amylose content (29.3%), while tapioca starch had the lowest apparent amylose content (23.7%). The amylose contents of potato and tapioca starch determined from the spectrophotometer method were slightly higher than those determined from the iodine potentiometric titration method reported by Chrastil (1987). The difference may be attributed to the different samples and methods. It could be elucidated the interference of intermediate component molecules in the process of spectrophotometer (Gibson, Solah, & McCleary, 1997). 3.4. Swelling power and solubility The solubility is contributed by the content of amylose, and the swelling power is contributed by the content of amylopectin (Tester & Morrison, 1990). The swelling power of starch samples increased as the incubation temperature increased. As been known, starch could not be dissolved in cool water attributed to the starch crystal structure. The starch molecules started to integrate with water as the temperature increased, then the amylose and

Table 2 X-ray powder diffraction data of D. nipponica Makino, tapioca and potato starches ˚) D. nipponica Makino starch d-spacing (A 16.1 5.84 Intensity Medium Strong 2h 5.5 15.2

5.13 Strong 17.3

3.85 Strong 23.1

3.36 Medium 26.5

Tapioca starch

˚) d-spacing (A Intensity 2h

5.82 Strong 15.2

5.09 Strong 17.4

4.43 Weak 20.0

3.81 Strong 23.3

3.40 Weak 26.2

Potato starch

˚) d-spacing (A Intensity 2h

15.2 Medium 5.8

5.82 Weak 15.2

5.13 Strong 17.2

4.03 Medium 22.1

3.42 Weak 26.0

Table 3 X-ray diffraction properties and amylose content of D. nipponica Makino, tapioca and potato starches Sample

Degree of crystallinitya(%)

Type of crystallinity

Amylose contenta (%)

D. nipponica Makino Tapioca Potato

48.5 ± 0.3 48.0 ± 0.2 45.9 ± 0.6

C A B

26.3 ± 0.2 23.7 ± 0.1 29.3 ± 0.2

a

Data were reported in means ± standard deviation, (n = 3).

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Y. Yuan et al. / Journal of Food Engineering 82 (2007) 436–442 100

D. nipponica Makino Tapioca Potato

90 80 70

Solubility [%]

Intensity

Tapioca

Potato

60 50 40 30 20 10

D. nipponica Makino

0 60

3

8

13

18

23

28

33

38

43

65

70

75

80

85

90

95

Temperature [ºC]

2 Theta Fig. 2. Wide-angle X-ray diffractograms of D. nipponica Makino, tapioca and potato starch granules.

100

(Fig. 3). This indicates that the granule structure of D. nipponica Makino starch is more stable (Manek et al., 2005). Meanwhile, the amylose–lipid complexes of D. nipponica Makino starch may restrict granular swelling because the presence of these complexes could decrease the extent of hydration of amylose chains (Hoover, Smith, Zhou, & Ratnayake, 2003).

D. nipponica Makino Tapioca Potato

90 80 70

Swelling power

Fig. 4. Solubility profiles of D. nipponica Makino, tapioca and potato starches.

60 50 40

3.5. DSC thermal properties

30 20 10 0 60

65

70

75

80

85

90

95

Temperature [ºC] Fig. 3. Swelling power profiles of D. nipponica Makino, tapioca and potato starches.

amylopectin were dissociated in suspension, and the solubility of starch was increased. The insoluble starch granules started to swell because of the hydration. It was seen from Fig. 3 that potato starch swelled quickly from 80 to 90 °C, and the higher swelling power of potato starch (at 95 °C) were probably due to the longer chains in amylopectin structure (Sasaki & Matsuki, 1998). Fig. 4 showed that the D. nipponica Makino starch had dissolved well when temperature increased from 65 to 80 °C, whereas the solubility was slightly increased with the increase in temperature from 80 to 95 °C. The solubility of D. nipponica Makino starch (at 95 °C) was much lower than that of potato starch. Although there was a certain similarity with tapioca starch from the column diagram of solubility (Fig. 4), the swelling power of D. nipponica Makino (from 65 to 95 °C) was lower than that of other starch samples

Starch gelatinization was characterized by differential scanning calorimetry because of its accuracy. As known from the literature (Biliaderis, 1980), starch granule was a semi-crystalline entity. It was swollen when treated in the endothermic process. At the same time, the ordering of crystallinity was becoming disordered. The gelatinization properties of starches are summarized in Table 4. Compared with other starches, D. nipponica Makino starch has the highest melting temperature (To, Tp, Tc), which indicates that it has a high level of crystallinity (Tester & Morrison, 1990). The differences in melting temperature among the starches can be attributed to the differences in the compactness of granules, the size of starch molecules and the ratio of amylose and amylopectin (French, 1972). Enthalpy changes for the tapioca, D. nipponica Makino and potato starches were 14.8, 18.6 and 23.4 J/g, respectively (Table 4). Previous study has been postulated that the increasing enthalpy change indicates the decreasing amylose content of the three starches (Iouchi, Glover, Sugimoto, & Fuwa, 1984). The contrary results obtained in the present work can only be elucidated to the biological variation in samples. D. nipponica Makino starch showed a range of gelatinization temperature (13.7 °C) similar to that of potato starch (13.8 °C). The results indicate that the degrees of heterogeneity of crystallites within the granules of the two samples are

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Table 4 Thermal properties of D. nipponica Makino, tapioca and potato starchesa Sample

T o b (°C)

T p c (°C)

T c d (°C)

DHe (J/g)

Rf (°C)

PHIg (J/g/K)

D. nipponica Makino Tapioca Potato

67.4 ± 0.5 64.9 ± 0.2 59.2 ± 0.1

76.0 ± 0.2 69.1 ± 0.3 64.1 ± 0.1

81.0 ± 0.1 75.9 ± 0.1 73.0 ± 0.2

18.6 ± 0.2 14.8 ± 0.2 23.4 ± 0.1

13.7 ± 0. 1 11. 0 ± 0.0 13. 8 ± 0.2

2.2 ± 0.1 3.5 ± 0.2 4.7 ± 0.3

c d e f g

Data were reported in means ± standard deviation, (n = 3). To = onset temperature. Tp = peak temperature. Tc = conclusion temperature. DH = gelatinization enthalpy. R = range of gelatinization temperature. PHI = peak height index.

Table 5 Pasting properties of D. nipponica Makino, tapioca and potato starchesa PTb

PVc

HPVd

(°C) D. nipponica Makino Tapioca Potato a b c d e f g

73 64 64

CPVe

SVf

1800

BVg

362 801 1806

183 250 564

405 426 876

Tapioca

Temperature

1600

(BU) 222 176 312

179 551 1242

Values were means of three determinations (n = 3). PT = pasting temperature. PV = peak viscosity. HPV = hot-paste viscosity. CPV = cool-paste viscosity. SV = setback viscosity. BV = breakdown viscosity.

90 80

Potato

1400

Torque [BU]

Sample

100

2000

D. nipponica Makino

1200

70 60

1000

50

800

40

600

30

400

20

200

10

0 0

13

26

39

52

65

78

91

104

117

Temperature [ºC]

a b

0 130

Time [min] Fig. 5. Brabender viscograms of D. nipponica Makino, tapioca and potato starches.

analogical (Gunaratne & Hoover, 2002). Other properties such as melting enthalpies and peak height indices (PHI) of all starches showed pronounced differences among them. These different thermal properties may be attributed to the differences in the amylopectin content, the degree of crystallinity and the presence of crystalline regions of different strength in the granules of starch samples (Singh & Singh, 2001). 3.6. Pasting properties D. nipponica Makino starch showed a higher pasting temperature (PT) and a lower peak viscosity (PV) compared with tapioca and potato starches (Table 5). Potato starch displayed a larger PV than D. nipponica Makino and tapioca starches. The high initial temperature was attributed to the presence of protein molecules and other polysaccharides (Alves et al., 2002) and the low peak viscosity (PV) indicated low water-holding capacity of the starch (Sekine, 1996). The higher crystallinity of D. nipponica Makino starch (Table 3) is probably responsible for the higher pasting temperature. The viscosity of the potato starch decreased from 1800 to 600 BU during the holding period, whereas D. nipponica Makino starch did not display much shear thinning (Fig. 5). D. nipponica Makino starch paste showed a good shear resistance. This phenomenon may be attributed to its greater amylose and lipid

contents which hold the integrity of the granules and prevent the disrupting (Kasemsuwan, Bailey, & Jane, 1998). The Cold paste viscosities (CPVs) increased after cooling down as shown (Fig. 5) and the increased CPVs indicate that the paste can be more resistant to shearing and can form a more rigid gel (Zhang, Niu, Eckhoff, & Feng, 2005), which suggests a pronounced tendency to retrogradation. High-amylose (linear) starches re-associate more readily than high-amylopectin (branched) starches (Bultosa, Hall, & Taylor, 2002). But in this study, the CPV of D. nipponica Makino starch was lower than other starches (Table 5). Setback is defined as the degree of re-association between the starch molecules involving amylose (Charles, 2004). The highest setback was recorded for potato starch and the SV of D. nipponica Makino starch was higher than that of tapioca starch according to our experiments (Table 5). The highest breakdown viscosity (BV) was recorded for potato starch. The probable reason is the larger granule diameter of potato starch that increases the fragility of the granule in the shear filed. And the BV of tapioca starch was second to potato starch. Higher breakdown viscosity suggests the sample had undergone a higher degree of swelling and subsequent disintegration (Abera & Rakshit, 2003), and the evidence is obtained from the highest swelling power of potato starch (Fig. 3).

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4. Conclusions Starches from medicinal plant are now first researched by commonly used methods. The results of the study suggested that the physical–chemical properties of D. nipponica Makino starch were different from other starches. D. nipponica Makino starch has smaller diameter, oval shaped, higher content of amylose, higher crystallinity and type-C crystalline form. The properties of smaller granules (higher digestibility) and higher amylose contents of D. nipponica Makino starch could be used for the manufacture of food products. It possesses relative higher melting enthalpy and higher peak temperature of DSC. Its lower swelling power displayed the more stable granule structure. Brabender viscosities showed that the peak viscosity and breakdown viscosity of D. nipponica Makino starch were lower than those of potato and tapioca starches. The higher setback viscosity of D. nipponica Makino starch exhibited greater retrogradation tendency, which was an important factor for starch used in food products. Although the property of higher setback viscosity limits the applications of food storage for long duration, this starch may be suitable for food products (e.g. glass noodle) where greater retrogradation tendency is required. The stable granule structure of D. nipponica Makino starch suggests that this starch also can be utilized in food manufactures with minimal modification. Further work will understand the physical–chemical properties and continue to develop insights to the potential applications of D. nipponica Makino starch, although non-food applications have been reported. References Abera, S., & Rakshit, S. K. (2003). Comparison of physicochemical and functional properties Cassava starch extracted from fresh root and dry chips. Starch/Sta¨rke, 55, 287–296. Alves, R. M., Grossmann, M., Ferrero, C., Zaritzky, N. E., Martino, M. E., & Sierakoski, M. R. (2002). Chemical and functional characterization of products obtained from yam tubers. Starch/Sta¨rke, 54, 476–481. Biliaderis, C. G. (1980). Starch gelatinization phenomena studied by differential scanning calorimetry. Journal of Food Science(45). Bultosa, G., Hall, A. N., & Taylor, J. R. N. (2002). Physical–chemical characterization of grain Tef [Eragrostis tef (Zucc) Trotter] starch. Starch/Sta¨rke, 54, 461–468. Charles, A. L. (2004). Some physical and chemical properties of starch isolates of Cassava genotypes. Starch/Sta¨rke, 56, 413–418. Cheetham, N. W. H., & Tao, L. (1998). Solid state NMR studies on the structural and conformational properties of natural maize starches. Carbohydrate Polymers, 36(4), 277–284. Chrastil, J. (1987). Improved colorimetric determination of amylose in starches or flours. Carbohydrate Research, 159, 154–158. Cone, J. W., & Wolters, G. E. (1990). Some properties and degradability of isolated starch granules. Starch/Sta¨rke, 42, 298–301. Fathat, I. A., Tunde, O., & Roger, N. J. (1999). Characterization of starches from West African Yam. Journal of the Science of Food and Agriculture, 79, 2106–2111. Franco, M. L. C., Preto, S. J. R., & Ciacco, C. F. (1992). Factors that affect the enzymatic degradation of natural starch granules-effect of the size of the granule. Starch/Sta¨rke, 44, 113–116. French, D. (1972). Fine structure of starch and its relationship to the organization of starch granules. Journal of Japanese Society for Starch Science(19).

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