O-STARCH-6. Physico-Chemical and Functional Properties of Under-Utilized Starches in South-East Asia. 1. Introduction. 2. Materials and methods

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1 O-STARCH-6 Physico-Chemical and Functional Properties of Under-Utilized Starches in South-East Asia Thierry Tran 1,4,*, Juan Bautista Sanz Hernández 1, Béatrice Bellassee 1, Guillaume Da 2,3, Hong Luong Nga 2, Rungtiva Wansuksri 1, Sunee Chotineeranat 1, Kuakoon Piyachomkwan 1, Le Thanh Mai 2, Klanarong Sriroth 1, Dominique Dufour 4,5 1 Cassava and Starch Technology Research Unit (CSTRU/BIOTEC), Kasetsart University, Jatujak, Bangkok 10900, Thailand 2 Hanoi University of Technology (HUT), IBFT, Hanoi, Vietnam 3 Laboratoire GPMA-ENSBANA (EA4181), 1 esplanade Erasme, Dijon, France 4 Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), 73 rue Jean-François Breton, TA B-95/16, Montpellier Cedex 5, France 5 Centro Internacional de Agricultura Tropical (CIAT), Apdo Aéreo 6713, Cali, Colombia * Corresponding author: Tel ; thierry.tran@cirad.fr 1. Introduction Roots and tubers in South-East Asia represent a highly diverse source of starch but many crops remain underutilized in agro-industrial processes, with production limited to small scale extraction for local use. Hence few studies are available on the systematic characterization of a large array of starches, using the same set of analytical techniques and experimental conditions. The objectives of this paper were to identify physicochemical and functional properties relevant for food applications and specific to some of these starches, in order to demonstrate their potential as food ingredients and thereby encourage the development of economic activities related to their production and use. 2. Materials and methods 2.1 Starches The starches used in this study included canna (two samples), mungbean (two samples), sago, kudzu, taro (two samples), yam bean and sweet potato, and were sourced from Vietnam and Thailand, either from commercial suppliers or by extraction from the fresh roots at laboratory scale. Cassava starch from commercial sources in Vietnam and Thailand, and analytical grade rice and maize starches from Sigma-Aldrich were also included as references. 2.2 Characterization of starch samples composition and morphology Lipid, nitrogen and ash contents were determined following standard analytical methods in order to check the starch purity of the samples. Amylose content was determined by different methods based on iodine blue value reading at 680nm (Takeda et al., 1983), iodine affinity measurement by amperometric titration, amylose/amylopectin separation by size exclusion chromatography (HP-SEC), and enthalpy measurement of amylose-lipid complexes melting by differential scanning calorimetry (Mestres et al., 1996). The morphological properties of the starch granules were analyzed using optical microscopy, scanning electronic microscopy, and size distribution by laser diffraction technique. The type of crystallinity of the native starch samples was determined using wide angle X-rays diffraction. 85

2 2.3 Starch gelatinization and retrogradation Gelatinization and retrogradation characteristics were determined by differential scanning calorimetry (DSC) using a Perkin-Elmer DSC7 (Wellesley, Massachusetts, USA) calibrated with indium. Each starch sample was weighed in an aluminium DSC pan (typically mg), and mixed with distilled water before sealing the pan, so that the starch:water ratio was approximately 1:3. The DSC pan was equilibrated at room temperature for at least one hour, then transferred to the DSC and equilibrated for 3 minutes at the experiment starting temperature (25 C) before heating up to 105 C at 10 C.min -1. The gelatinization peak was analyzed using the Perkin-Elmer Pyris software. Parameters recorded were the onset temperature, peak temperature, end temperature, and peak area (in mj). The gelatinization enthalpy H was calculated on a dry basis (J/g of dry starch), using the peak area, the sample weight and sample moisture content. Measurements were done in three replicates for each sample. Following the gelatinization experiments, the aluminium pans containing the samples were stored at 4 C for 15 days to let the samples reach maximum retrogradation. Each sample was then characterized by DSC, using the same protocol as gelatinization measurements. The retrogradation peak was analyzed in the same way as the gelatinization peak. 2.4 Viscosity and shear resistance The viscosity profile of starch during controlled cooking was recorded by RVA using the standard method as follows: Holding at 50 C for 1 ; heating to 95 C at 12 C/min; heating at 95 C for 2 30 ; cooling to 50 C at 12 C/min; holding at 50 C for 2. Stirring was constant at 160rpm during the whole measurement, except for the first 10 during which the sample was mixed at 960rpm to ensure full dispersion. Key parameters recorded from the RVA profile to describe viscosity development during gelatinization were the Pasting temperature, the Peak viscosity, the Breakdown/Peak viscosity ratio, and the final viscosity. The shear resistance of starches was assessed using the RVA method described above, modified to stir the sample at high speed (960 rpm) during the 2 30 holding step at 95 C. The shear resistance was calculated as the ratio between the final viscosity at the end of the shear treatment and the final viscosity at the end of the standard RVA viscosity measurement. 2.5 Gel clarity and texture Gel clarity was determined by measuring the transmittance at 650nm of 1% starch pastes gelatinized at 95 C for 10 minutes (Craig et al., 1989). Gel texture was measured by compressing 10.3% starch gels prepared using the RVA gelatinization protocol described in section 2.4 and stored at 4 C for 13 days. The gel dimensions were 36mm diameter and 20.5mm height. The compression was uniaxial at 2mm/s to a target strain of 50% of the gel initial height. Measurements were done in triplicates. The parameters recorded were the peak force and the deformation at peak force, which were normalized to compression strength (kg/m 2 ) and strain at peak force. 2.6 Texture of noodles prepared with pure starches and starch blends Noodles were prepared by working a mix of starch and water into a dough. Part of the starch was gelatinized by microwave heating with water before mixing, so that a suitable dough could be obtained. The dough was then fed into a Marcato 150 pasta machine to obtain flat noodles. After cooking in boiling water for 3-5 minutes, the noodles had a cross-section of 9x2mm, and were cut in strips 150mm long. Two series of noodles were prepared: Firstly pure noodles of each type of starch were made; secondly some starches (mungbean, canna, 86

3 kudzu and sago) were blended to cassava starch in proportions of 20, 40, 60 and 80% in order to assess how these starches would modify the properties of pure cassava noodles. Noodle texture was assessed with a Texture Analyzer working in extension mode. The noodles were extended from an initial length of 50mm at 2mm/s until break, which occurred typically after mm extension. 15 to 20 replications were done for each sample. The parameters recorded were the peak force and the deformation at peak force, which were normalized to tensile strength (kg/m 2 ) and strain at peak force. 3. Results and discussion 3.1 Physicochemical and morphological properties of starches The results of the proximate analysis confirmed that all the starches included in the study were of suitable purity, with the highest lipid, nitrogen and ash contents at 0.45% in cassava sample, 0.023% in kudzu sample and 0.44% in potato sample. The amylose contents determined by four different techniques are summarized in table 1. Although absolute values varied, overall the four techniques gave similar rankings for the various samples, with mungbean, canna and sago showing the highest amylose contents (24-40%), followed by kudzu, cassava, sweet potato in the range 17-22%, then by yam bean (14-18%) and taro (7-10%). Microscopic observations evidenced the diversity in size and shape of starch granules from different varieties. The granule size distribution date identified taro and rice as starches with the smallest granules (2.6 and 5.6m respectively), and canna and potato as starches with the largest granules (55.5 and 42.6m respectively). Small granules starches such as taro stay in suspension much more readily than other starches (making the use of centrifugation necessary during taro starch extraction, whereas sedimentation is sufficient for most other starches), and hence may find applications for the manufacture of pharmaceutical pills which do not form deposits once dispersed in water prior to consumption. The analysis of native starch crystallinity by X-rays diffraction indicated that most starches in the study had a A- type pattern (yam bean, taro, sago, cassava, sweet potato, swamp taro), while canna and kudzu had a B-type pattern and mungbean a C-type pattern. Other studies (Zobel, 1988; Hung et al., 2005) found that the same starches can have different types of crystallinity, indicating that crystallinity type may be determined both by genetic factors and environmental factors during starch biosynthesis. The characteristics of gelatinization and retrogradation of the various starches determined by DSC are summarized on figure 1. The ranges of gelatinization onset temperatures and enthalpies for the different starches were C and 9-19J/g respectively, while the corresponding data for retrogradation were C and 4-10J/g, respectively. Hence the melting of retrograded starches took place over a narrower range of conditions compared to gelatinization, indicating that the crystallites formed during retrogradation were more homogeneous than the native crystallites. In other words, some of the differences typically observed between starches in their native state are lost after gelatinization. The retrogradation tendency, calculated as the ratio between retrogradation and gelatinization enthalpies, confirmed that cassava has the lowest retrogradation tendency (25-37%) followed by kudzu and canna (43-51%), whereas starches such as sweet potato and mungbean showed a high tendency in the range 62-66%. In comparison, cereal starches have a still higher retrogradation tendency with 75% for maize and 88% for rice. 87

4 3.2 Functional properties of starches: Viscosity and gel clarity The main parameters of RVA viscosity profiles are summarized on figure 2. Some starches showed interesting cooking characteristics, notably different from common starches such as rice, maize and potato: Mungbean starch combined high peak viscosity ( cP) and stable viscosity (breakdown 28% of peak viscosity); canna starch combined high peak viscosity ( cP) and short cooking time (60-68s from pasting onset to peak viscosity); sago starch showed a short cooking time (38s from pasting onset to peak viscosity) and good shear resistance (73% recovery after high-speed stirring); and sweet potato starch combined low pasting onset (71 C), high peak viscosity (6073cP) and good shear resistance (75% recovery after high-speed stirring). Hence RVA pasting characteristics evidenced different cooking behaviours between starches, and thus the possibility to match the type of starch with cooking requirements. The different starches in the study exhibited wide variations in shear resistance, from for canna, mungbean and kudzu, up to for cassava, sweet potato and sago. Gel clarity measurements indicated that canna, sago and cassava had a markedly higher gel clarity (32-40% transmittance at 650nm), while other samples were in the range 14-20% transmittance. Taro had the lowest clarity with only 8% transmittance, possibly due to its small granule size and hence the presence of a large number of granule remnants after gelatinization. 3.3 Starch gel texture The characteristics of gel texture for the various starches are summarized on figure 3. Mungbean and canna starches gave hard gels with high compressive strengths ( kg/m 2 ), whereas taro, yam bean, kudzu, rice and maize gave much softer gels with compressive strengths below 6000kg/m 2. Compressive strains at peak force evidenced further differences between starches, with mungbean and taro able to undergo large ( ), sago, canna and yam bean intermediate ( ), and kudzu only small (0.20) deformations. Hence different types of starches generated a variety of gel textures, from soft to hard and from fairly brittle to more cohesive. In particular, canna and mungbean starches formed unusually hard gels, compared to commonly used starches such as rice and maize. Mungbean was particularly noteworthy because of the combination of high gel strength and good ability for deformation. Gels made with sago starch had good mechanical properties as well with a fairly high compression strength (11000kg/m 2 ) and a strain at peak force of 0.42, intermediate between that of canna and mungbean. 3.4 Noodles texture The characteristics of noodles texture are summarized on figure 4. Noodles prepared from canna and mungbean were rigid with high tensile strengths ( kg/m 2 ) and low strains at break ( ), while noodles from kudzu, sago and cassava were soft and extensible with low tensile strengths (1340, 1590, 430 kg/m 2, respectively) and fairly high strains at break (0.63, 0.94, 1.21, respectively). Noodles prepared using blends of cassava with other starches exhibited different mechanical behaviors depending on the types of starch used. When the proportion of the additional starch was below 40%, the tensile strength was determined mainly by the cassava fraction; above 40% the tensile strength increased with the proportion of additional starch. The strain at break remained equal to that of pure cassava noodles (~1.2) in the case of kudzu/cassava blends up to 80% kudzu, whereas it remained equal to that of pure sago noodles (~0.9) in the case of sago/cassava blends up to 80% 88

5 cassava. In the case of canna/cassava and mungbean/cassava blends, the strain at break varied regularly as the proportions of the two components of the blends varied. These observations raised the hypothesis that different starches may have different levels of compatibility when blended together, resulting either in a fairly homogeneous blend when the compatibility is good, or on the contrary in a phase separation between the two starch fractions. In the first scenario, the mechanical properties would be determined by both starches together, as could be the case for the canna/cassava and mungbean/cassava blends, while in the second scenario the mechanical properties would be determined mainly by one of the two starches, as could be the case for the kudzu/cassava and sago/cassava blends. 3.5 Syneresis after refrigerated and frozen storage Syneresis studies indicated that sago starch gels had the best stability under refrigerated conditions (syneresis below 2%), while the other starches had syneresis in the range 22-44%. Mungbean and canna starch gels were more efficient for retaining water after five freezethaw cycles: 7-9% and 22-25% syneresis respectively, while the other starches had syneresis in the range 33-44%. The better water retention observed in mungbean and canna gels after freeze-thaw cycles may be due simply to their higher gel strength, which resulted in less gel deformation under the compression conditions used and therefore in less water being extracted from the gel matrix. Indeed, when the starch gels after freezing were compressed harder to extract as much water as possible without breaking the gel matrix, the differences observed between starches were reduced so that all starches showed levels of syneresis in the range 46-66%. 4. Conclusion Overall, this study demonstrates that underutilized starches have characteristics exceeding those of commonly used starches (corn, rice, potato, cassava), and thus can find applications where traditional starches are not suitable or would require physico-chemical modifications. Particularly useful characteristics include small granules (taro), large granules (canna), high viscosity development (canna, mungbean), stable viscosity (sago), high gel strength and strain at break (mungbean); high gel clarity (canna, cassava, sago), low syneresis after refrigerated storage (sago). Acknowledgements This work was supported by a grant from the Agence Universitaire pour la Francophonie (AUF), as well as by the National Center for Genetic Engineering and Biotechnology (BIOTEC) and the National Science and Technology Development Agency of Thailand (NSTDA). References 1. Craig S.A.S., Maningat C.C., Seib P.A. and Hoseney R.C. (1989). Starch paste clarity. Cereal Chemistry 66 (3): Mestres C., Matencio F., Pons B., Yajid M. and Fliedel G. (1996). A rapid method for the determination of amylose content by using differential scanning calorimetry. Starch/Stärke 48 (1): Pham V.H. and Morita N. (2005). Physicochemical properties and enzymatic digestibility of starch from edible canna (Canna edulis) grown in Vietnam. Carbohydrate Polymers 61: Takeda C., Takeda Y. and Hizukuri S. (1983). Physicochemical properties of lily starch. Cereal Chemistry 60 (3):

6 5. Zobel H.F. (1988). Starch crystal transformations and their industrial importance. Starch/Stärke 40 (1):1-7. Table 1: Amylose contents (%) of the starches determined by different techniques Sample DSC HP- SEC Amperometric titration Blue Value Mungbean Thai Sago 1 Thai Canna purified Viet Canna non-bleached Viet Swamp taro Viet Kudzu purified Viet Sweet potato Viet (1017) Cassava purified Viet Figure 1: Gelatinization and retrogradation onset temperatures and enthalpies of the starches determined by DSC. The vertical and horizontal lines indicate two times the standard deviation Temperature ( C) Sweet potato Canna pur. Sweet potato Cassava pur. Potato Cassava non-bleach Kudzu Canna non-bleach Cassava bleach Canna bleach Cassava Mungbean Thai Viet Cannas Kudzu Cassava bleach Cassava Potato Viet pur. Cassava non-bleach G-Onset (ºC) R-Onset (ºC) Enthalpy (J/g) 90

7 Figure 2: RVA gelatinization parameters for the various starches studied. The horizontal lines indicate two times the standard deviation. Swamp taro Viet Mungbean Thai Kudzu purified Canna bleached Canna purified Canna non-bleached Cassava bleached Sweet potato Cassava non-bleached Cassava purified Potato Viet Pasting temperature ( C) 80 Potato Viet Canna purified Sweet potato Canna bleached Mungbean Thai 4425 Cassava purified 4196 Cassava bleached Kudzu purified 3775 Canna non-bleached Cassava non-bleached 3198 Swamp taro Viet Peak viscosity (cp) 9857 Figure 2 (continued): RVA gelatinization parameters for the various starches studied. The horizontal lines indicate two times the standard deviation. Cassava bleached Potato Viet Cassava purified Cassava non-bleached Canna bleached Sweet potato Canna non-bleached Canna purified Swamp taro Viet Mungbean Thai Kudzu purified Mungbean Thai Canna purified Potato Viet Kudzu purified Canna bleached Sweet potato Canna non-bleached Cassava purified Swamp taro Viet Cassava non-bleached Cassava bleached Breakdown/Peak viscosity (%) Final viscosity (cp) Figure 3: Compression strength and strain at peak force of starch gels. The vertical and horizontal lines indicate two times the standard deviation Mungbean Thai Compression strength (kg/m2) Canna non-bleach Canna bleach Canna pur Kudzu pur Strain at break 91 91

8 Figure 4: Tensile strength and strain at peak force of noodles in function of the proportions of starches in the blends. 92

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