Physicochemical, morphological, and rheological characterization of Xanthosoma robustum Lego-like starch

International Journal of Biological Macromolecules 65 (2014) 222–228

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Physicochemical, morphological, and rheological characterization of Xanthosoma robustum Lego-like starch a,b ˜ ˜ a,b , Sandra M. Londono-Restrepo , Natalia Rincón-Londono c,d,∗ Margarita Contreras-Padilla , Andrés A. Acosta-Osorio e , Luis A. Bello-Pérez f , b Juan C. Lucas-Aguirre , Víctor D. Quintero b , Posidia Pineda-Gómez g,h , Alicia del Real-López c , Mario E. Rodríguez-García c a Posgrado en Ciencia e Ingeniería de Materiales, Centro de Física Aplica y Tecnología Avanzada, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro C.P. 76230, M´exico b Universidad del Quindío, Programa de Química, Armenia, Quindío, Colombia c Departamento de Nanotecnología, Centro de Física Aplica y Tecnología Avanzada, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Qro C.P. 76230, M´exico d División de Estudios de Posgrado e Investigación, Facultad de Ingeniería, Universidad Autónoma de Querétaro, Querétaro, Qro, M´exico e División de Tecnología Ambiental, Universidad Tecnológica de Querétaro, Querétaro, Qro, M´exico f Instituto Politécnico Nacional, CEPROBI, Km. 6.5 Carr. Yautepec-Jojutla, Col. San Isidro, Yautepec, Morelos C.P. 62731, M´exico g Universidad de Caldas, Manizales, Caldas A.A. 275, Colombia h Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Manizales, Caldas A.A. 127, Colombia

a r t i c l e

i n f o

Article history: Received 21 November 2013 Received in revised form 9 January 2014 Accepted 17 January 2014 Available online 24 January 2014 Keywords: Mafafa starch Xanthosoma robustum Lego structure Viscosity Physicochemical characterization

a b s t r a c t This work presents the physicochemical and pasting characterization of isolated mafafa starch and mafafa flour (Xanthosoma robustum). According to SEM images of mafafa starches in the tuber, these starches form Lego-like shaped structures with diameters between 8 and 35 ␮m conformed by several starch granules of wedge shape that range from 2 to 7 ␮m. The isolated mafafa starch is characterized by its low contents of protein, fat, and ash. The starch content in isolated starch was found to be 88.58% while the amylose content obtained was 35.43%. X-ray diffraction studies confirm that isolated starch is composed mainly by amylopectin. These results were confirmed by differential scanning calorimetry and thermo gravimetric analysis. This is the first report of the molecular parameters for mafafa starch: molar mass that ranged between 2 × 108 and 4 × 108 g/mol, size (Rg) value between 279 and 295 nm, and molecular density value between 9.2 and 9.7 g/(mol nm3 ). This study indicates that mafafa starch shows long chains of amylopectin this fact contributes to higher viscosity development and higher gel stability. The obtained gel phase is transparent in the UV–vis region. The viscosity, gel stability and optical properties suggest that there is potential for mafafa starch applications in the food industry. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Mafafa (Xanthosoma robustum) contributes with a significant portion of the carbohydrate content of the typical diet in many regions within developing countries such as, Colombia, Panama, and Nicaragua. Although, Mafafa starch is less important in terms of usage than other tropical root crops, such as, cassava and sweet potato, it is still a major staple in some parts of the

∗ Corresponding author at: Departamento de Nanotecnología, Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Querétaro, Qro, México. Tel.: +52 442 2381168; fax: +52 442 2381168. E-mail address: [email protected] (M. Contreras-Padilla). 0141-8130/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijbiomac.2014.01.035

tropics and subtropics. The common names for Xanthosoma are: mafafa, tannia, tannier, yautia, malanga, new cocoyam, ocumo, rascadera, tiquisque, quequexque, calusa, mangarito, tayobe, taye, and macabo, among others. The main problem associated with mafafa roots, is that they have a short shelf life due to their high moisture content. One of the best ways to preserve mafafa roots is processing them to obtain flour and/or starch [1]. Starch obtained from these tubers has never been commercialized because its properties are unknown. New starch sources with different physicochemical properties are demanded by new applications that require specific properties, such as high viscosity and transparent gels. For example, a starch that develops high viscosity values has potential applications as a thickener. The importance of studies of non-traditional starch sources has

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increased because traditional raw materials as maize have raised their market cost as the demand for food and industrial usage have intensified [2]. Therefore, it is very important to study alternative starch sources to obtain products exhibiting better physicochemical, nutrimental and functional properties or to develop a mixture of conventional and unconventional starch products [3]. Lu et al. [4] found that the content of starch as well as some physical properties in mafafa depend on seasonal conditions. Nevertheless, the performance of a given starch in any application is governed by its physicochemical properties. Starches from different sources are known to differ in their physical and chemical properties. These differences are believed to arise from differences in the amylose/amylopectin ratio in the starch granule, the characteristics of each fraction in terms of molecular weight, length/degree of branching, the physical manner in which these constituents are arranged within the starch granules and the presence of naturally occurring non-carbohydrate impurities [5]. Bello-Pérez and Paredes-López [2] studied the potential nutrimental characteristics of starchy products. They describe the physicochemical and digestibility characteristics of starch present in diverse food crops, namely; maize, beans, and unconventional starch sources such as banana (Musa paradisiaca L.), mango (Mangifera indica L.), amaranth (Amaranthus hypochondriacus), and barley (Hordeum vulgare), among others. The work presented in this paper focuses on the analysis of the physicochemical, microstructural, molecular, structural, optical, and pasting properties of isolated starch and flours from mafafa. This investigation supports the potential of this starch for industrial applications.

2. Materials and methods Mafafa samples were obtained from an experimental field from Universidad del Quindio, located in Armenia, Quindío (Central region of Colombia) and were harvested on July 2012. Mafafa plants (Fig. 1a) have between 1.2 and 2.5 m of height, the main stem is a starch-rich underground structure called corm. The sagittate-ovate leaves are between 0.8 and 1.2 m long and arise directly from the corm, Fig. 1b shows a characteristic mafafa cormels, measuring from 8 cm to 15 cm in diameter (Fig. 1c). These cormels can reach around 20–40 cm of length. Fig. 1c shows the internal part of the mafafa cormel.

2.1. Starch sample preparation and commercial standards Mafafa flour was obtained using a transversal cutting of the tubers, drying them and milling of the drying pulp slides. The isolate starch was obtained using the method proposed by Pineda-Gómez et al. [6], but including a modification in the drying process, in which a vacuum drying process was used. The mafafa flour was stirred and washed with distiller water in order to obtain isolated starches. An amount of 200 g of pulp and 800 mL of distilled water were ground in a blender for 1 min, then the slurry was passed through a sieve mesh 100 (147 ␮m). The liquid that passed through the mesh was allowed to stand for 12 h, then it was decanted. The starch was then dried in a vacuum furnace for 12 h using 1.33 Pa and 40 ◦ C to avoid starch damage. Dry sample was milled again in a coffee grinder ´ (Krups, Mexico) in intervals of time of 10 s in order to prevent over heating of the equipment, this operation was carry out 3 times, then the milled product was sieved in a mesh 100. Commercial standards of amylose (Sigma Aldrich A-7043, 70% purity, USA), amylopectin (Sigma Aldrich 101220, 75% purity, USA) as well as corn starch (Newport, USA) were used as reference.

Fig. 1. (a) Mafafa plant, (b) characteristic mafafa cormel, and (c) shows a transversal cut of a cormel.

2.2. Chemical proximate analysis Both mafafa flour, and isolated mafafa starch were studied. The crude protein (N × 6.25) was measured by the micro-Kjeldahl (Method 46-13, AACC [7]), moisture was determined according with Method 925.10, AOAC [8], total ether extract measurement was carried out following the Method 30-25, AACC [9] and ashes content was done according to Method 08-01, AACC [9]. Each measurement was carried out three times. 2.3. Amylose and starch content The starch and amylose content from isolate starch were determined utilizing the commercial kit Megazyme, assays K-TSTA and K-AMYL, respectively (Ireland International, Ltd., Bray, Ireland) according to the manufacturer’s procedure [10,11]. 2.4. Starch granule solubilization for structural analysis The solubilization of the starch was performed following the procedure described by Bello-Perez et al. [12], briefly; 20 mg of starch were added into a Teflon cup containing 10 mL of deionized water, the cup was introduced in a polycarbonate vessel (Parr Instrument Co., Moline, IL, USA) and centered inside a microwave

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oven at maximum power during 1 min (1100 W). The cooling step was carried out by immersion in an ice bath for 30 min. The solution was filtered through a 5 ␮m nylon membrane (Millipore, Bedford, MA, USA) and immediately injected onto the high-performance size exclusion chromatographic system (HPSEC). 2.5. Amylopectin molecular weight and gyration radii HPSEC analysis combined with multi-angle laser-light scattering (MALLS) (Dawn 8+ Heleos, Wyatt Technology Corporation, CA, USA) and refractive index detectors (Agilent 1100, model G1362A, Agilent Technologies, UK) were used to calculate the molecular weight (Mw), gyration radii (Rg) and molecular density () of the starch. A Shodex OH PAK SB-807 HQ analytical column (Showa Denko K.K., Tokyo, Japan) was used to separate starch molecules. The mobile phase used was distilled-deionized water with 0.02% sodium azide, flow rate was 0.3 mL/min. Data obtained from MALLS and RI detectors was analyzed using Astra software to obtain the amylopectin (AP) molecular weight distribution (version 5.3.4.14, Wyatt Technology Corporation, CA, USA). 2.6. Amylopectin chain length distribution The branch-chain-length distribution of amylopectin was determined following the procedure described by Jane and Chen [13] and Wong and Jane [14]. Starch was debranched using isoamylase (Megazyme, Wicklow, Ireland) and the branch chain length distribution was determined using an ICS-5000 high-performance anion-exchange chromatograph (HPAEC) equipped with a pulsed amperometric detector (PAD) (Dionex, Sunnyvale, CA, USA). A CarboPac PA 200 anion-exchange analytical column (250 mm × 3 mm) was used for sample separation. The mobile phase used for separation consisted of eluent A (deionized water), eluent B (100 mM NaOH), eluent C (100 mM NaOH) and eluent D (150 mM NaOH and 500 mM NaAc) with a flow rate of 0.5 mL/min. The separation gradient was as follows: for eluent C (0–5 min, 95%; 5–18 min, 60%; 18–55 min, 15%; and 55–75 min, 95%) and for eluent D (0–5 min, 5%; 5–18 min, 40%; 18– 55 min, 85%; and 55–75 min, 5%). The chains were categorized as (short to long) A, B1, B2, and B3 and longer chains according to the protocol of Hanashiro et al. [15]. 2.7. SEM analysis The morphology of the mafafa starches from a longitudinal cut of a cormel, as well as isolates mafafa starch samples was analyzed with a high vacuum scanning electron microscope (JEOL, JSM-6060LV) with a resolution of between 1500× and 5000×. The analysis conditions used were 20 kV electron acceleration voltage and in high vacuum (HV) mode with 12-20 Pa of pressure. The samples were fixed to the bronze specimen holder with a carbon tape and mounted. Then they were subject to gold sputtering to improve the electrical contact. 2.8. X-ray diffraction characterization The X-ray diffraction patterns of amylose (Sigma Aldrich A7043, 70% purity, USA), amylopectin (Sigma Aldrich 101220, 75% purity, USA) as well as the mafafa isolated starch were studied. The samples were ground into a fine powder and passed through a 260-␮m screen. The X-ray diffraction patterns of the samples were obtained on a diffractometer (Rigaku, miniflex) operating at 35 kV and 15 mA, with a Cu K␣ radiation wavelength of  = 0.15406 nm, and from 5◦ to 50◦ on a 2 scale with a step size of 0.02◦ . The measurements were performed at room temperature.

2.9. DSC analysis The DSC curves of mafafa isolated starch were measured using the Differential Scanning Calorimeter DSC Q100, TA Instrument. Calibrations were performed using pure indium with a heat of fusion of 28.4 J/g and a melting temperature of 56.66 ◦ C. Samples of 6.0 ± 0.1 mg were prepared by adding deionized water to the mafafa starch into the pan until they reach a moisture of 85% (w/w). The pans were hermetically sealed and kept at room temperature for 12 h and then, the samples were scanned from 30 ◦ C to 110 ◦ C at 7.5 ◦ C/min. An empty aluminum pan was used as reference. During the scans, the space surrounding the sample chamber was filled with dry nitrogen. For each thermogram, the gelatinization transition parameters were measured using a DSC software (Universal Analysis 2000 TA Instruments). These values were referred as onset (T0 ), mid-point (Tp ), and end (Te ) temperatures and enthalpy of gelatinization (H). Each experiment was conducted in duplicates. 2.10. Thermogravimetry analysis (TGA) A TGA Q500 (TA Instruments USA) thermobalance was used for the TG analysis, the samples of 8.0 ± 1.0 mg were placed in the platinum crucible of thermobalance. A Heating rate of 7.5 ◦ C/min was applied in each ramp for mafafa starch, amylose and amylopectin samples. The experiments were carried out in a N2 atmosphere, using a flow maintained at 70 mL/min. The TG data were processed using the Universal Analysis 2000 TA software. The maximum rate of the reaction was determined through the peak temperature in the DTG curve. Duplicate runs were performed to the aforementioned samples. 2.11. Analysis of the apparent viscosity The apparent viscosities of the isolate mafafa starch water suspensions were determined using a rheometer (Anton Paar MCR102; Austria) with 3 g of starch or flour and 18 mL of water (85.7% moisture). For comparison, a corn starch was used as reference (Newport for RVA system). The test was carried out under the same conditions. The following thermal profile was used: initially, the temperature of the system was 50 ◦ C, and it remained constant for 1 min, then the sample was heated for 5.3 min from 50 ◦ C to 90 ◦ C, next, it was held at a constant temperature of 90 ◦ C for 5.3 min, after that, the sample was cooled down to 50 ◦ C in 5.3 min and finally, this temperature was kept constant for 1 min. Three different measurements were performed. The geometrical characteristics of the set up were: a vessel with a 0.026 m diameter, 0.054 m high; an impeller of 0.024 m diameter, 0.030 m high. The frequency of the system was set to 194 rpm according to the methodology proposed by Acosta-Osorio et al. [16]. 2.12. Optical properties The optical properties in the UV–vis region were measured in order to study the absorption bands present in the mafafa gel. A Lambda 25 spectrometer (Perkin Elmer, USA) in transmittance mode from 200 to 1100 nm was used. 3. Results and discussion 3.1. Chemical proximate analysis and yield extraction of mafafa starch The chemical composition of mafafa flour and isolated starch were determined, the results are shown in Table 1. As it can be seen, the isolated starch shows low content of protein, fat, and ash compared to the mafafa flour, which is due to the isolation starch process. The moisture content of mafafa flour and starch was around

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Table 1 Chemical composition (w/w; dry basis) of Xanthosoma Mafafa starch and flour. Sample Flour Isolate starch

% moisture 10.05 ± 0.11 10.09 ± 0.11

% fatty material

% ash

% crude protein

% crude fiber

1.30 ± 0.04 1.22 ± 0.04

0.33 ± 0.01 0.18 ± 0.01

6.81 ± 0.34 1.21 ± 0.01

1.39 ± 0.04 ND

ND, not detected by the method used. Data are average of three repetition ± standard deviation.

10% that is an accepted value according to the range that has been established for dry products in order to prolong their useful life. The yield obtained of mafafa starch was 6.92 g/100 g of tuber. This result agrees with Brito et al. [17] who reported values of yields of extraction of starch from tubers and roots between 4.61 and 16.22 g/100 g of raw matter.

Table 2 Molar mass (Mw), gyration radii (Rg), and molecular density () of mafafa isolate starch.*. Sample Isolate starch

Mw (×108 g/mol) 3.0±1.2

Rg (nm) 287±11.31

 (g/(mol nm3 )) 9.45±0.35

*Data reported are the average of duplicate analysis.

3.2. The morphologic analysis of mafafa Fig. 2(a–d) shows SEM images of a longitudinal cut of mafafa tuber taken at 1500×, 2500×, 2500x (different zone), and 4000×, respectively. It is clear that, in this case, the starch granules are forming a Lego-like macro particle. The single starch grains vary in shape and size. The Lego-like particles have dimensions between 8 and 35 ␮m. The number of starch granules that formed a Lego-like mafafa particle varied from 6 to 30. This morphology is interesting because the starch exhibits irregular shapes as wedges that are densely packed. Fig. 3 shows the mafafa isolated starch taken at 2000×, 3500×, 5000×, and 5000× (different zone). These images show that the micro particles were disaggregated after the isolation process and now they appear as starch wedges, with dimensions from 2 to 7 ␮m. It is well known that the size, as well as, the physicochemical properties of a given starch depend on agronomic farming practices, harvest season and plant species. Asaoka et al. [18] studied the starch extracted from four varieties of cassava roots, which were harvested on four different occasions. They showed different granule sizes depending on the harvest seasons and minor differences in the X-ray crystallinity were observed. 3.3. Amylose and starch content The starch content in isolated starch granules was found to be 88.58 ± 1.59% while the amylose content was 35.43 ± 1.22%; this means that the mafafa isolated starch is rich in amylopectin.

3.4. Amylopectin molecular parameters and chain length distribution The molar mass (Mw), gyration radii (Rg), and molecular density () of the mafafa isolated starch (X. robustum) were obtained for the first time. Results are shown in Table 2. Mafafa starch showed Mw that ranged between 2 × 108 and 4 × 108 g/mol, size (Rg) value between 279 and 295 nm, and  value between 9.2 and 9.7 g/(mol nm3 ). Other study of a similar tuber (Colocasia esculenta L.) reported a higher value of Mw (1.2 × 109 g/mol) and Rg (424 nm) [19]. Also, in a Mexican tuber (chayote starch), Mw and Rg values were found to be higher [20] than those found for mafafa starches. The chain-length distributions of amylopectin (AP) from mafafa starches are shown in Table 3. The mafafa starch presented the highest proportion of chains with DP 13-31, classified as B shortchains [21] followed by chains with DP 6-12 (short chains or A chains). An important amount of very short (DP ≤ 6) and long (DP ≥ 32) chains were found in mafafa starch. These structural characteristics of mafafa starch can influence its physicochemical and functional properties. It is important to highlight that an important amount of long chains (B chains) is present in mafafa starch, around 50% and up of the total amylopectin chains are in this group. This pattern may contribute to the formation of more and longer double helices of AP, and influence their physicochemical and functional characteristics [21]. It was reported that starches with long chains

Fig. 2. SEM images corresponding to the mafafa starches from a longitudinal cut of the mafafa cormel: (a) 1500×, (b) 2500×, (c) 2500× (different zone), and (d) 4000×.

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Fig. 3. SEM images of isolated starches from mafafa: (a) 2000×, (b) 3500×, (c) 5000×, and (d) 5000x (different zone).

Table 3 Chain-length distribution of amylopectin from mafafa starch.*. Sample

AP

Chain-length distribution (%) ≤6

6–12

13–31

≥32

L.C. average

Max detectable

19.2 ± 0.2

31.3 ± 0.7

36.7 ± 0.1

12.8 ± 0.1

26.9 ± 0.6

109

AP, amylopectin. ∗ Data reported are the average of duplicate analysis.

show a higher viscosity value and gel stability than starches with short chains [22]. Starches with a higher amount of long chains are more stable during the pasting phenomenon than those with a higher amount of short chains [23].

3.6. Thermal properties of mafafa starch Fig. 5 shows the DSC thermogram of a mafafa starch–water system using a moisture content of 85% and a heating rate of 7.5 ◦ C/min, which corresponds to the same heat rate used in the pasting profile experiments. For the complete gelatinization event

3.5. X-ray diffraction Starch is formed by two biopolymeric molecules: amylose and amylopectin, the structure of these molecules can be studied using X-ray diffraction. So far, only the structure of amylose has been reported (␣-amylose 43-1858) (JCPDS-International Centre for Diffraction Data 1997) [24], while the structure of amylopectin is still under study. The intensity of each of the peaks that form a pattern composed by the mixture of different phases is proportional to the concentration of each of the crystalline components. A phase can be identified by inspecting directly the well-established powder diffraction files (PDF) database that identifies crystalline structures. From a physics point of view, the non-identified peaks can be the result of new phases or non-identified structures, such as, amylopectin in starch. Fig. 4 shows the X-ray diffraction patterns of amylopectin (Sigma Aldrich), amylose (Sigma Aldrich), and isolated mafafa starch. The continuous lines in this figure represent the diffraction planes of amylose. According to this figure, starch from mafafa does not exhibit the characteristic peaks of amylose located at 19.70◦ (0 0 4), 22.25◦ (2 2 0) and 24.03◦ (1 3 0). On the other hand, the peak located around 23.106◦ is present only in mafafa starch and amylopectin standard; this is an indication that the starch from mafafa is formed mainly by amylopectin. This result agrees with the determination of amylose test in which it is clear that starch from mafafa is rich in amylopectin.

Fig. 4. X-ray diffraction patterns of amylopectin (Sigma Aldrich), amylose (Sigma Aldrich), and mafafa isolated starch.

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Fig. 5. DSC thermogram corresponding to the gelatinization process of the mafafa.

Fig. 7. (a) Pasting profile of mafafa isolated starches, and corn starch and (b) the UV–vis spectra of the dry gel 198 ␮m of thick of mafafa starch.

Fig. 6. (a) TGA curves corresponding to the decomposition process for all the samples at 7.5 ◦ C/min. (b) DTGA curves corresponding to the principal stage of decomposition process for all the samples at 7.5 ◦ C/min.

Te − T0 was 9.34 ◦ C. In this temperature window, the molecular and structural order of the starch granules gets disrupted. The required energy for gelatinization is the enthalpy whose value was 14.08 J/g. The peak temperature of the gelatinization Tp was 73.12 ◦ C. Finally, for temperatures up to gelatinization range, which are those above 77.66 ◦ C, no thermal transitions in the system were found. These conditions indicate that the whole system is now gelatinized, forming a new phase composed by gelatinized starch granules, amylose and water. Additionally, the thermal behavior of the mafafa starch was investigated with thermogravimetric analysis (TGA). Fig. 6 presents the thermal degradation of mafafa starch, amylose and amylopectin; as well as the analysis of their first derivate (right axis). For all the samples, the thermal decomposition process was developed in three steps. The first step, corresponding to a reduction in mass at temperatures below 120 ◦ C, can be associated to the loss of water of the samples, this value is approximately 8% of the weight, while in amylose and amylopectin samples, it reaches up to 12%. In the second stage (250 ± 10 ◦ C ≤ T ≤ 360 ± 10 ◦ C), mass loss is due to the main decomposition processes of starch macromolecules. Both mafafa and amylopectin showed the biggest temperature decomposition. This indicates that mafafa shows greater similarity with amylopectin, this finding is consistent with the X-ray diffraction analysis and amylose determination. The first derivate showed a shift to high temperature, which indicated that amylopectin exhibits a more complex structure than amylose. In the

third stage (T > 400 ◦ C), inert carbonaceous residues were formed; mass loss became stabilized. Fig. 6 also shows the first derivative DTGA curves of the main stage corresponding to the degradation of the three samples. The well-defined peak in these curves permits to identify the beginning and end of the event corresponding to thermal degradation. This stage begins with a rapid dehydration and decomposition of hydroxyl groups in glucose rings to form water molecules. According to Liu et al. [25] during this stage the main chain breaking occurs when C C H, C O, and C C bounds break. The gaseous decomposition products consist primarily of H2 O, CO, and CO2 . As can be seen in Fig. 6, the DTGA curves exhibited only one peak, indicating the possibility of a simple mechanism of reaction involving degradation of the starch polymers (amylose and amylopectin) [25]. A narrow and high peak from amylose indicates a rapid degradation process in a low temperature range (T = 50 ◦ C). In contrast, the widening of the peak with less height from amylopectin and mafafa, indicates a slower degradation process that occurs at 70 ◦ C < T < 80 ◦ C. Liu et al. [25] studied the kinetics and mechanism of thermal decomposition of corn starches with different amylose/amylopectin ratios. They found that higher activation energy is necessary for high amylopectin corn starch, which could be explained by the higher molecular weight and its higher content of ␣-1,6 bonds. Once more, there is a greater similarity between amylopectin and mafafa in the peak shape for thermal degradation, which confirms that mafafa is an amylopectin-rich starch, in agreement with the results obtained from the amylose determination test. 3.7. Pasting properties of mafafa starch Fig. 7a shows the characteristic pasting profile of isolated mafafa starch, and corn starch (Newport) aqueous suspensions, as well as the thermal profile (right axis). In Fig. 7a, the isolated mafafa starch

Table 4 Pasting properties of mafafa isolated starch and corn starch. Samples

Peak temperature (◦ C)

Isolate starch Corn starch

84.02 86.61

Peak viscosity (mPa s) 20,870 12,360

Breakdown (mPa s)

Setback (mPa s)

6987 6778

5573 4932

Final viscosity (mPa s) 12,560 11,710

Peak time (s) 337 394

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exhibits a higher peak viscosity than corn starch; it is remarkable that mafafa starch reaches a value of peak viscosity that is 90% higher than the corn starch value. Table 4 shows the pasting characteristics of isolated starch, and corn starch. The peak temperature varies significantly and ranged from 84 ◦ C to 90 ◦ C. The fact that the viscosity of mafafa isolated starch reaches is maximum for a lower temperature when compared to corn starch, may be attributed to its lower resistance toward swelling. Peak viscosity reflects the capacity of starch granules to swell freely before their physical breakdown due to the increasing temperature and mechanical agitation during the experiment. Shibanuma et al. [26] reported that the properties of starch dispersion were more affected by the chain-length distribution of amylopectin than by the molar mass. Additionally, viscosities during pasting are greatly affected by the Amylose/amylopectin ratio, and in this case, mafafa starch is rich in amylopectin [27]. On the other hand, the particle size distribution of mafafa starch ranged from 2 to 7 ␮m, while the average value for corn starch was 12.33 ± 2.23 ␮m. This suggests that particle size may also influence the pasting profile and the peak viscosity. It was found that when the particle size decreases the peak viscosity increases [16]. The breakdown viscosity in the case of isolated starch and isolated corn starch was similar. The setback is a measure of reorganization of the exuded amylose–amylopectin from the gelatinized starch with water during the cooling stage in which a gel is formed. The setback can be defined as the recovery of viscosity during cooling of the heated starch suspension. According to the setback values showed in Table 4, the amylose–amylopectin–water gel of mafafa starch is more stable than the gel formed in the case of corn starch. Final viscosity is an indication of the ability of the starch to maintain a viscous paste at the end of the cooling process. In the case of mafafa starch this paste is more stable than the paste obtained from corn starch. 3.8. Optical properties UV–vis Fig. 7b shows the UV–vis spectra of dry gel for a 198 ␮m thickness. In this figure, it is clear that this thin film is transparent in this spectral region and thus, it opens a potential application for the development of thin films based in this mafafa starch. 4. Conclusions According to the SEM images, mafafa starch exhibits macro Lego-like starch grains formed by starch wedges; these wedges present irregular shapes and sizes. The isolation process used, reduces the protein and fat contents. Mafafa starch granules exhibit 88.58% of starch and 63.15% of amylopectin, these results indicate a major content of amylopectin. These findings agree with the X-ray diffraction pattern. The TGA analysis also showed that mafafa starch is formed mainly by amylopectin. The DSC analysis showed a gelatinization temperature of 73.12 ◦ C that is characteristic of more complex and ordered structures. We have performed the first report of the molecular parameters for mafafa starch (X. robustum). Mafafa starch Mw was measured to be between 2 × 108 and 4 × 108 g/mol, size (Rg) value between 279 and 295 nm, and  value between 9.2 and 9.7 g/(mol nm3 ). Pasting profiles of mafafa starch are characterized by a high peak viscosity in comparison with those of corn starch. Mafafa starch exhibits a transparent thin film that was verified using UV–vis spectrometry. These results suggest

a potential for the development of thin films based on this material. The study indicates that mafafa starch shows long chains of AP, this fact contributes to the development of higher viscosity values and higher gel stability. The high peak viscosity and low content of protein and fat in mafafa starch could promote the use of this product in the food industry. Mafafa starch could replace corn starch by obtaining the same pasting properties in the final product while reducing the total carbohydrate content of the final product. The aforementioned study opens a window for new applications of this kind of starch. Conflict of interest statement For this investigation the authors have no any actual or potential conflict of interest that could inappropriately influence their work. Acknowledgements The authors would like to thank Dra. Beatriz Millan-Malo (UNAM-Juriquilla, México) by their technical support. Margarita Contreras-Padilla would like to thank to CONACYT by her postdoctoral position in CFATA-UNAM. Natalia Rincón and Sandra M. ´ ˜ want to thank CONACYT Mexico for the financial support Londono of their master studies. References [1] E. Pérez, F.S. Schultz, E. Pacheco de Delahay, Carbohydr. Polym. 60 (2005) 139–145. [2] L.A. Bello-Pérez, O. Paredes-López, Food Eng. Rev. 1 (2009) 50–65. [3] V.U. Asumugha, B.C. Uwalaka, Nig. Agric. J. 31 (2000) 78–88. [4] T.J. Lu, J.C. Chen, C.L. Lin, Y.H. Chang, Food Chem. 91 (2005) 69–77. [5] L.M. Nwokocha, N.A. Aviara, C. Senan, P.A. Williams, Carbohydr. Polym. 76 (2009) 362–367. [6] P. Pineda-Gómez, A. Rosales-Rivera, M.E. Rodríguez-García, Starch 64 (2012) 776–785. [7] AACC, Approved Methods, American Association of Cereal Chemists, St. Paul, MN, USA, 2000. [8] AOAC, Official Methods of Analysis, 17th ed., The Association of Official Analytical Chemists, Gaithersburg, MD, USA, 2000. [9] AACC, Approved Methods 08-01 30-25 and 46-13, American Association of Cereal Chemists, St. Paul, MN, USA, 2000. [10] T.S. Gibson, V.A. Solah, B.V. McCleary, J. Cereal Sci. 25 (1997) 111–119. [11] B.V. McCleary, V. Solah, T.S. Gibson, J. Cereal Sci. 20 (1994) 51–58. [12] L.A. Bello-Perez, P. Roger, B. Baud, P. Colonna, J. Cereal Sci. 27 (1998) 267–278. [13] J. Jane, J. Chen, Cereal Chem. 69 (1992) 60–65. [14] K.S. Wong, J. Jane, J. Liq. Chromatogr. Relat. Technol. 20 (1997) 297–310. [15] I. Hanashiro, J.I. Abe, S. Hizukuri, Carbohydr. Res. 283 (1996) 151–159. [16] A.A. Acosta-Osorio, G. Herrera-Ruiz, P. Pineda-Gómez, M.A. Cornejo-Villegas, F. Martínez-Busto, M. Gaytán, M.E. Rodriguez Garcia, Mech. Eng. Res. 1 (2011) 110–121. [17] B. Brito, S. Espín, E. Villacrés, Caracterización Fisico-Química, Nutricional y Funcional de Raíces y Tubérculos Andinos, in: V. Barrera, C. Tapia, A. Monteros (Eds.), Raíces y tubérculos andinos: Alternativas para la conservación y uso sostenible en el Ecuador. Serie: Conservación y uso de la biodiversidad de raíces y tubérculos andinos: Una década de investigación para el desarrollo (1993–2003). No. 4, Instituto Nacional Autónomo de Investigaciones Agropecuarias, Centro Internacional de la Papa, Agencia Suiza para el Desarrollo y la Cooperación, Quito, Ecuador–Lima, Perú, 2004, p. 100, 200. [18] M. Asaoka, J.M.V. Blanshard, J.E. Rickard, Starch 43 (1991) 455–459. [19] E. Agama-Acevedo, F. Garcia-Suarez, F. Gutierrez-Meraz, M. Sanchez-Rivera, E. San Martin, L.A. Bello-Perez, Starch 63 (2011) 139–146. [20] J.P. Hernandez-Uribe, E. Agama-Acevedo, R.A. Gonzalez-Soto, L.A. Bello-Perez, A. Vargas-Torres, Starch 63 (2011) 32–41. [21] S. Hizukuri, Carbohydr. Res. 141 (1985) 295–306. [22] J. Jane, Y.Y. Chen, A.E. McPherson, K.S. Wong, M. Radosavljevic, T. Kasemsuwan, Cereal Chem. 76 (1999) 629–637. [23] D.G. Stevenson, P.A. Domoto, J. Jane, Carbohydr. Polym. 63 (2006) 432–441. [24] A. Imberty, H. Chancy, S. Perez, A. Buleon, J. Mol. Biol. 201 (1988) 365–378. [25] X. Liu, L. Yu, F. Xie, M. Li, Starch 62 (2011) 139–146. [26] Y. Shibanuma, Y. Takeda, S. Hizukuri, Carbohydr. Polym. 29 (1996) 253–261. [27] C.G. Biliaderis, Can. J. Physiol. Pharmacol. 69 (1991) 60–78.