Effect of Pre-Gelatinization on the Physicochemical Properties of Dry Flours Produced from 5 Cassava Varieties of the Philippines

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1 Food Science and Technology Research, 20 (6), 1131 _ 1140, 2014 Copyright 2014, Japanese Society for Food Science and Technology doi: /fstr Original paper Effect of Pre-Gelatinization on the Physicochemical Properties of Dry Flours Produced from 5 Cassava Varieties of the Philippines Daiki Murayama 1, Miki Kasano 1, Dennis Marvin Santiago 2, 3, Hiroaki Yamauchi 1 and Hiroshi Koaze 1* 1 Department of Food Science, Obihiro University of Agriculture and Veterinary Medicine, West 2-11, Inada, Obihiro, Hokkaido , Japan 2 The United Graduate School of Agricultural Science, Iwate University, Ueda, Morioka, Iwate , Japan 3 Food Science Cluster, College of Agriculture, University of the Philippines Los Baños, College, Laguna, Philippines 4031 Received June 3, 2014 ; Accepted July 24, 2014 The objectives of this study were to characterize the physicochemical properties of 5 different cassava varieties developed in the Philippines and to investigate the effect of pre-gelatinization on flour properties. The physicochemical properties were assessed by proximate, mineral and soluble sugar composition, starch, pasting and thermal properties, solubility, swelling power and particle size distribution. All dry flours showed significantly higher values for peak viscosity, hot paste viscosity and final viscosity, breakdown, pasting temperature and α-amylase activity than the corresponding pre-gelatinized flours ( p < 0.05). Complete amorphization of starch contained in pre-gelatinized flours was confirmed by DSC, and it was found that pre-gelatinization caused significant increases in the content of fructose, glucose, amylose, damaged starch and mean particle size, compared to the corresponding dry flours ( p < 0.05). Principal component analysis was carried out to assess the overall flour quality and the suitability of particular varieties for pre-gelatinization by steam treatment. Keywords: cassava, dry flour, pre-gelatinization, physicochemical properties, pasting properties, swelling power, solubility Introduction Cassava (Manihot esculenta Crantz) is widely cultivated and consumed in tropical regions such as Southeast Asia, Africa and South America. In 2012, total world cassava root production was 260 million tons, of which 2.2 million tons were produced in the Philippines. Cassava production in the Philippines is increasing, with production in 2012 approximately 1.5 times greater than in 2002 (FAO i) ). Cassava contains the largest amount of carbohydrate of any food crop other than sugarcane (Okigbo, 1980). Hence, cassava is an important source of carbohydrates for people in the tropics. Cassava root, flour and starch are consumed in the Philippines in various kinds of food, while breeding of cassava varieties is targeted at improving particular properties, for example, to achieve higher yield, better disease resistance, higher starch content and lower cyanide content (Mariscal et al., 2002). However, fresh cassava root that is not kept under suitable storage conditions deteriorates rapidly due to physiological changes and microbial activity, and cassava root has a very short shelf-life, usually less than 2 days (Abera and Rakshit, 2003; Isamah, 2004). Therefore, cassava root must be processed into products such as flour and starch soon after harvesting. Cassava varieties that can be used for preparing flour have been bred in the Philippines. One of the newest varieties, developed for higher fresh root yield, is Cv-46 (Philippine Root Crop Research and Training Center ii) ). It has been reported that the Lakan 1 variety has better agronomic characteristics, such as water deficit resistance and high yield (Bergantin et al., 2004; Taguiam et al., *To whom correspondence should be addressed. koaze@obihiro.ac.jp

2 ). In addition, it is recognized that the physicochemical properties of flour vary depending on the variety of cassava used. For example, Niba et al. (2002) and Charoenkul et al. (2011) determined the physicochemical properties of flours and starches from different cassava varieties grown in Nigeria and Thailand, respectively, and reported that the use of different varieties resulted in changes in chemical composition, pasting properties and thermal properties. Furthermore, cassava flours may be prepared by different methods, including milling dried roots directly into flour, pre-gelatinization prior to drying and milling, fermentation and water soaking. Pre-gelatinized cassava flour is commonly used for cooking traditional products such as cassava cake in the Philippines. In addition, different preparation methods lead to differences in the physicochemical properties of flours. For example, Adebowale et al. (2008) reported that cassava flours prepared by different roasting methods have different physicochemical properties such as sugar content and peak viscosity. A study on the effects of cooking method and storage temperature on the retrogradation of starch in cassava flours was carried out by Rodríguez-Sandoval et al. (2008). Since few studies are available on cassava flours processed in the Philippines, more technical information on the properties of cassava flours is needed for a better understanding of this ingredient. Thus, the objectives of this study were to characterize the physicochemical properties of 5 different cassava varieties developed in the Philippines and to investigate the effect of pre-gelatinization on flour properties. Materials and Methods Raw materials Six cassava varieties, namely Lakan 1, Sultan 6, Sultan 7, Rajah 2 and Rajah 4, were harvested from field plots at the Institute of Plant Breeding, University of the Philippines in Los Baños. Freshly harvested cassava roots were used for preparation of dry and pre-gelatinized flours within 2 days after harvesting. Preparation of dry flours Cassava roots were peeled, washed, chipped and dried in a hot air oven at 40. The dried chips were milled by a blender and sifted through a sieve with an aperture of 180 μm. The samples were stored at 4 before analysis. Preparation of pre-gelatinized flours Cassava roots were peeled, washed and steamed in a home steamer. Steamed cassava roots were chipped and dried in a hot air oven at 40. The dried pre-gelatinized chips were milled in a blender and sifted through a sieve. The samples were stored at 4 before analysis. Analytical methods of chemical composition Moisture, crude protein, crude fat and ash content were determined by standard AOAC methods (2000). Total starch, amylose, damaged starch content and α-amylase activity were determined by Megazyme assay kits based on the methods of McCleary et al. (1997), Yun and Matheson (1990), Gibson et al. (1991) and McCleary and Sheehan (1987) (Megazyme International Co. Ltd.). Glucose, fructose and sucrose contents were determined by HPLC after extraction with 80% (v/v) ethanol. Mineral contents of magnesium, D. Murayama et al. phosphorus, potassium and calcium were determined by inductively coupled plasma mass spectrometry (ICPS-8100, Shimadzu Co. Ltd.). After ashing of a 2 g sample, the resulting ash was dissolved in 2N-HCl and the solution was subjected to mineral analysis. Analytical methods for physical properties Particle size distribution was determined using a compact laser diffraction particle size analyzer (LA-300, HORIBA Co. Ltd.). To determine the pasting properties of the flour, a 10% dry weight basis (dwb) slurry was subjected to analysis using a Rapid Visco Analyzer (RVA) (RVA-4, Newport Scientific, Inc.) with a paddle rotating at 960 rpm for the first 10 sec and then at a fixed speed of 160 rpm. The slurry was heated from 50 to 95 at a rate of 12 /min, held at 95 for 2.5 min, cooled to 50 at a rate of 12 /min, and then kept at 50 for 2 min. The pasting properties determined included peak viscosity (the highest viscosity observed during heating), hot paste viscosity (the viscosity at the end of the 95 period), final viscosity (the viscosity at the end of the period at 50, breakdown (peak viscosity minus hot paste viscosity), setback (final viscosity minus hot paste viscosity) and pasting temperature (Limpisut and Jindal, 2002; Yadav et al., 2006). Thermal properties were determined using a differential scanning calorimeter (DSC) (Micro DSC II, Setaram, Inc.). A sample of 300 mg dwb was weighed in a DSC pan and distilled water was added to give a suspension of 30% dwb. The pan was sealed and allowed to stand overnight at 20. The scanning temperature range was set at 30 to 95 and the heating rate was 1.5 /min. 700 mg of water was used as a reference. Solubility and swelling power were determined using a method described by Sa nchez et al. (2010) with slight modification. A 1% dwb flour suspension was heated from 35 to 50, 60, 70, 80, 90 and 95 at a rate of 6 /min using a RVA. After holding at the set temperature for 2.5 min, the suspension was centrifuged at 3000 rpm for 15 min and both supernatant and sediment were collected. The sediment was used for analysis of swelling power and the supernatant was used for solubility analysis after drying at 105 for 24 hrs. Statistical analysis The physicochemical properties of dry and pre-gelatinized flours were statistically analyzed using SPSS for Windows (ver. 17.0). One-way analysis of variance and Duncan s multiple-range test were carried out for comparison of the physicochemical properties of dry and pre-gelatinized flours between 5 varieties at a 5% significance level. The effect of pregelatinization on flour properties for each variety was examined using t-test at 5% significance level. Multiple correlation analysis was performed to evaluate the correlationship between the chemical and physical properties of dry and pre-gelatinized flours, while principal component analysis was applied to assess overall flour quality and to evaluate the effect of pre-gelatinization on flour properties.

3 Pre-gelatinization of Cassava Flours of the Philippines 1133 Table 1. Proximate composition of dry and pre-gelatinized flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). Table 2. Mineral composition of dry and pre-gelatinized flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). Results and Discussion Proximate composition Table 1 presents the proximate compositions of dry and pre-gelatinized flours. The crude protein, crude fat, ash and total starch contents of the dry flours used were 1.31 _ 1.98, 0.48 _ 1.03, 2.13 _ 3.36 and _ 78.76% dwb, respectively. These values were comparable to those reported by Moorthy et al. (1996), Aryee et al. (2006), Rodríguez-Sandoval et al. (2008) and Charoenkul et al. (2011). Aryee et al. reported that moisture is an important parameter in the storage of cassava flour, with a highest allowable moisture content of 12% for prevention of microbial growth and a longer shelf life. In the present study, all flours had a moisture content of less than 12%; therefore, they all had a relatively safe and long shelf life. Dry and pre-gelatinized flour from the variety Sultan 7 had significantly higher crude protein and ash contents than the other varieties ( p < 0.05). In a comparison of the crude protein content of dry and pre-gelatinized flours, dry flours of 3 varieties had significantly higher values than pre-gelatinized flours ( p < 0.05). The major cause of this significant decrease in the crude protein content may be the pre-gelatinization process, which allows elution and dissolution of water-soluble proteins during steam treatment. The total starch contents of the dry flours were similar to those observed by Niba et al. (2002). Pre-gelatinization also led to a significant decrease in the total starch content ( p < 0.05), which may have been caused by enzymatic digestion of gelatinized starch, as reported by Sagum and Arcot (2000) in their study on the effect of heat processing on the starch content of rice. Mineral composition The major mineral components of dry and pre-gelatinized flours such as magnesium, phosphorus, potassium and calcium are shown in Table 2. The most dominant mineral in all flours was potassium, at _ mg/100 g dwb. Charles et al. (2005) reported that the mean Mg, P, K and Ca

4 1134 Table 3. Soluble sugar composition of dry and pre-gelatinized flours. D. Murayama et al. Table 4. Starch properties of dry and pre-gelatinized flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). contents of peeled and oven-dried cassava flours of 5 varieties from Thailand were 35.5, 134.1, and mg/100 g dwb, respectively. In comparison, we observed higher mean contents of Mg, P and K, but lower mean Ca contents, in flours from the Philippines. Such differences may be mainly caused by differences in genotype and in the cultivation conditions. Soluble sugar composition Table 3 indicates the soluble sugar composition of dry and pre-gelatinized flours. The major soluble sugar was sucrose, ranging between and mg/g dwb. Flours processed from the Lakan 1 variety contained significantly lower amounts of soluble sugar than those from other varieties ( p < 0.05). The glucose and sucrose contents were similar to those reported by Carvalho et al. (2004) on peeled cassava root from Brazil, except for the dry flour from Lakan 1. Although Carvalho et al. also reported that cassava varieties used for starch production have a relatively lower soluble sugar content, the cassava varieties used in the present study are recommended for starch production, flour, food and feeds, regardless of soluble sugar content, by the Philippine Root Crop Research and Training Center ii). In a comparison of soluble sugar content in flours obtained by two different treatments, all pre-gelatinized flours showed significantly higher fructose and glucose contents. This may be caused by enzymatic hydrolysis of starch and sucrose during steam treatment in the pre-gelatinization process. Starch properties Table 4 shows the amylose and damaged starch contents and the α-amylase activities of dry and pregelatinized flours as starch properties. These results were similar to those reported by Aryee et al. (2006), Shittu et al. (2008) and Charoenkul et al. (2011). The highest amylose content was observed in the dry and pregelatinized flours of Sultan 7 variety. Compared to the dry flours, all pre-gelatinized flours showed a significant increase in amylose content ( p < 0.05). This observation is in agreement with those of Yadav et al. (2006), who reported an increase in the amylose content of potato flours resulting from molecular degradation of starch granules under hydrothermal treatment. The dry flour from Sultan 7 had the highest degree of damaged starch, and it was found that pre-gelatinization caused a significant increase in damaged starch content ( p < 0.05). Steam treatment during pre-gelatinization resulted in degradation of the crystalline regions, and the subsequent drying and milling processes may have caused greater mechanical damage to the pre-gelatinized starch. The α-amylase activity ranged from to for dry flour and to for pre-gelatinized flour. All pregelatinized flours showed significantly lower enzymatic activity than dry flours ( p < 0.05), which may be due to inactivation of enzymes during steam treatment in pre-gelatinization. Particle size distribution The mean particle size of the dry and pre-gelatinized flours ranged from to μm and to μm, respectively, as shown in Table 5. The mean particle sizes of the dry flours were greater than those observed by Charoenkul et al. (2011), who reported that the mean particle size of hot-air-oven-dried cassava flours from 12 varieties ranged between and μm. The mean particle sizes of all pregelatinized flours were significantly greater than those of the dry flours ( p < 0.05) and this was attributed to swelling of the starch during pre-gelatinization. Pasting properties The pasting properties of dry and pregelatinized flours are shown in Table 6, and the pasting profile of Rajah 4 is shown in Fig. 1 as an example. The peak viscosities of the dry flours ranged between and cp, and the flour from the Rajah 4 variety had the highest peak viscosity among the 5 varieties examined. Rajah 4 also showed the greatest breakdown, indicating a low ability to withstand heating and shear stress, and the highest setback, indicating the highest potential for retrogradation (Newport Scientific, 1998). Pre-gelatinization by steam treatment led to a decrease in viscosity; thus, all pre-gelatinized flours showed significantly lower

5 Pre-gelatinization of Cassava Flours of the Philippines 1135 Table 5. Particle size distribution of dry and pre-gelatinized flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). Table 6. Pasting properties of dry and pre-gelatinized flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Mean values in the same column with * are significantly higher than that of the corresponding flour of the same variety ( p < 0.05). Fig. 1. Pasting profile of dry and pre-gelatinized flours from Rajah 4.

6 1136 D. Murayama et al. Table 7. Thermal properties of dry flours. Mean values in the same column with different letters are significantly different within the same treatment ( p < 0.05). Fig. 2. Solubility of (A) dry flours and (B) pre-gelatinized flours. values of peak viscosity, hot paste viscosity and breakdown than the corresponding dry flours ( p < 0.05). In addition, the pregelatinized flours did not show distinct peak viscosity or breakdown, due to complete gelatinization and damage of starch during steaming and milling operations. These results agreed with reports by Hagenimana et al. (2006), Yadav et al. (2006) and Soison et al. (2014). The value of final viscosity indicates the ability of materials to form a viscous paste or gel after cooking and cooling (Newport Scientific, 1998). Higher final viscosity was observed in the dry flours from Lakan 1, Sultan 7 and Rajah 2, while Lakan 1 showed the highest final viscosity among pre-gelatinized flours. The high final viscosities of these flours may be influenced by the low soluble sugar content and high amylose content. Thermal properties Table 7 shows the thermal properties of the dry flours. The onset temperature (To), peak temperature (Tp), conclusion temperature (Tc) and enthalpy (ΔH) for gelatinization of dry flours ranged from 63.3 to 65.4, 68.7 to 70.7, 76.6 to 79.4 and 12.2 to 13.4 J/g dwb, respectively. Charoenkul et al. (2011) reported higher To, Tp and Tc values than those observed

7 Pre-gelatinization of Cassava Flours of the Philippines 1137 Fig. 3. Swelling power of (A) dry flours and (B) pre-gelatinized flours. in the present study, but similar ΔH values. Pre-gelatinized flours, in contrast, did not show an endothermic peak. The disappearance of the endothermic peak was explained by Rodríguez-Sandoval et al. (2008) in their studies on steamed and boiled cassava flours, where starch in cooked flour is completely gelatinized, thus losing crystalline region. Solubility and swelling power Fig. 2 shows the solubility transitions of dry and pre-gelatinized flours. The solubility of the dry flours showed slight changes between 50 and 70, and significant increases at 80 and above ( p < 0.05). The solubility of all pre-gelatinized flours increased in a linear fashion with the rise in temperature. In a comparison of solubility between pregelatinized flours, these can be divided into two groups: a highersolubility group consisting of Sultan 6 and Sultan 7, and a lowersolubility group consisting of Lakan 1, Rajah 2 and Rajah 4. Transitions of the swelling power of dry and pre-gelatinized flours are illustrated in Fig. 3. In the dry flours, swelling power increased dramatically from 4.61 _ 6.10 w/w dwb at 60 to _ w/w dwb at 70, followed by a constant increase with rising temperature. In contrast, the swelling power of pregelatinized flours remained constant around 10 w/w dwb and below, due to complete gelatinization of starch during steam treatment in pre-gelatinization and increased starch damage. Pre-gelatinization and heat-moisture treatment have been applied in improvement of bread texture as anti-staling agents (Lorenz and Kulp, 1981; Purhagen et al., 2008), and pre-gelatinized flours obtained by steam treatment, as in this study, may also have potential in texture modification for bakery products. Correlationship between chemical and physical properties Multiple correlation analysis was performed to evaluate the correlationship between the chemical and physical properties of dry and pre-gelatinized flours. In the dry flours, swelling power was highly correlated with total starch content, negatively at 60 and below (r = _ to _ 0.883), and positively at 70 and above (r = to 0.881). At temperatures of 60 and below, water absorption in the dry flours was very low, but this increased drastically at temperatures greater than 70, which is close to the gelatinization temperature, resulting in an increase in swelling power. In addition, the damaged starch content of dry flours showed a significant negative correlation with swelling power at 80 and above (r = _ to _ 0.984, p < 0.05), which clearly indicates that a higher damaged

8 1138 D. Murayama et al. Fig. 4. Loading plots for the first PC and second PC. Mg, P, K, Ca, TS, DS, MPS, PV, HPV, FV, BD, SB, PT, SO and SP stand for magnesium, phosphate, potassium, calcium, total starch, damaged starch content, mean particle size, peak viscosity, hot paste viscosity, final viscosity, breakdown, setback, pasting temperature, solubility and swelling power, respectively. Fig. 5. Principal component score plots for the first PC and second PC. L1, S6, S7, R2 and R4 stand for Lakan 1, Sultan 6, Sultan 7, Rajah 2 and Rajah 4, respectively. starch content leads to lower swelling power, due to the decrease in the crystalline region of starch. In the pre-gelatinized flours, solubility over the temperature range showed a significant positive correlation with damaged starch content (r = to 0.994, p < 0.05). According to Zhang et al. (2013), mechanical damage of starch granules increases the amorphous region of starch, and this allows a subsequent increase in solubility in pre-gelatinized cassava starch. Principal component analysis of flour properties for 5 cassava varieties Principal component (PC) analysis was carried out to assess the overall quality of dry and pre-gelatinized flours produced from 5 cassava varieties based on their physicochemical properties. The proportion of variance of the first PC was 59.0%, and that of the second PC was 18.9%; the accumulated proportion of the first and second PC was 77.9%. Fig. 4 shows a scattergram of the factor loading plot for the first and second PC. Factor loadings of the first PC showed relatively high positive correlation with damaged starch content, mean particle size and swelling power at 50, while negative correlation was observed from swelling power at 95 and pasting properties. Thus, the first PC can be interpreted as the viscosity and swelling power of starch, which undergoes a drastic change in its granular structure caused by steam treatment during pregelatinization. The factor loading of the second PC was highly correlated with ash, Ca, K, Mg and crude protein contents. Fig. 5 shows a PC score plot for the first and second PC. The dry and pre-gelatinized flours may be divided into two groups based on the first PC scores, with lower scores for the dry flours and higher scores for the pre-gelatinized flours. In the second PC scores, Lakan 1, Sultan 6 and Sultan 7 showed a slight decrease,

9 Pre-gelatinization of Cassava Flours of the Philippines 1139 which indicates low leaching of chemical components such as water-soluble proteins and minerals during steam treatment in pregelatinization. Therefore, these varieties may be suitable for production of pre-gelatinized flours. Conclusion The dry and pre-gelatinized flours from 5 different cassava varieties bred and cultivated in the Philippines had various different physicochemical properties such as proximate composition, mineral and soluble sugar composition, starch properties, pasting and thermal properties, solubility, swelling power and particle size distribution. These properties were assessed by t-test, one-way analysis of variance, multiple correlation analysis and PC analysis for characterization of the 5 cassava varieties and examination of the effect of pre-gelatinization on flour properties. For the dry flours, swelling power increased dramatically from a temperature of 70, which was initiated by gelatinization of starch, whereas constant swelling power and high solubility were observed in the pre-gelatinized flours. These differences were mainly attributed to compositional and structural changes in starch caused by steam treatment during pre-gelatinization. PC component analysis clearly differentiated between the dry and pre-gelatinized flours based on their physicochemical properties, and the Lakan 1, Sultan 6 and Sultan 7 varieties were found to be more suitable for pregelatinization than the others due to their greater retention of chemical components. Pre-gelatinization appears to have high potential for textural and structural improvement by reduction of starch retrogradation in bakery products. Reference Abera, S. and Rakshit, S. K. (2003). Processing technology comparison of physicochemical and functional properties of cassava starch extracted from fresh root and dry chips. Starch-Stärke, 55, Adebowale, A. A., Sanni, L. O., and Onitilo, M. O. (2008). Chemical composition and pasting properties of tapioca grits from different cassava varieties and roasting methods. Afr. J. Food Sci., 2, AOAC (2000). Official methods of analysis, 17th ed., AOAC International, Gaithersburg, MD. Aryee, F. N. A., Oduro, I., Ellis, W. O., and Afuakwa, J. J. (2006). The physicochemical properties of flour samples from the roots of 31 varieties of cassava. Food control, 17, Bergantin, V. R., Yamauchi, A., Pardales Jr, J. R., and Bolatete Jr, D. M. (2004). Screening cassava genotypes for resistance to water deficit during crop establishment. Philipp. J. Crop Sci., 29, Carvalho, L. J. C. B., Souza, C. R. B., Julio Cascardo, C. M., Bloch Junior, B., and Campos, L. (2004). Identification and characterization of a novel cassava (Manihot esculenta Crantz) clone with high free sugar content and novel starch. Plant Mol. Biol., 56, Charles, A. L., Sriroth, K., and Huang, T. C. (2005). Proximate composition, mineral contents, hydrogen cyanide and phytic acid of 5 cassava genotypes. Food Chem., 92, Charoenkul, N., Uttapap, D., Pathipanawat, W., and Takeda, Y. (2011). Physicochemical characteristics of starches and flours from cassava varieties having different cooked root textures. LWT-Food Sci. Technol., 44, Gibson, T. S., Al Qalla, H., and McCleary, B. V. (1991). An improved enzymatic method for the measurement of starch damage in wheat flour. J. Cereal Sci., 15, Hagenimana, A., Ding, X., and Fang, T. (2006). Evaluation of rice flour modified by extrusion cooking. J. Cereal Sci., 43, Isamah, G. K. (2004). ATPase, peroxidase and lipoxygenase activity during post-harvest deterioration of cassava (Manihot esculenta Crantz) root tubers. Int. Biodeterior. Biodegrad., 54, Limpisut, P. and Jindal, V. K. (2002). Comparison of rice flour pasting properties using Brabender Viscoamylograph and Rapid Visco Analyser for evaluating cooked rice texture. Starch-Stärke, 54, Lorenz, K. and Kulp, K. (1981). Heat-moisture treatment of starches. II. Functional properties and baking potential. Cereal Chem, 58, Mariscal, A. M., Bergantin, R. V., and Troyo, A. D. (2002). Cassava breeding and varietal release in the Philippines. Presented at the seventh regional workshop for Cassava research and development in Asia: Exploring new opportunities for an ancient crop, Bangkok, Oct 28-Nov 1. pp McCleary, B. V., Gibson, T. S., and Mugford, D. C. (1997). Measurement of total starch in cereal products by amyloglucosidase-α-amylase method: Collaborative study. J. AOAC Int., 80, McCleary, B. V. and Sheehan, H. (1987). Measurement of cereal α-amylase: A new assay procedure. J. Cereal Sci., 6, Moorthy, S. N., Wenham, J. E., and Blanshard, J. (1996). Effect of solvent extraction on the gelatinisation properties of flour and starch of five cassava varieties. J. Sci. Food Agric., 72, Newport Scientific (1998). Applications manual for the Rapid Visco TM analyzer. Newport Scientific Pty Ltd., Warriewood. pp Niba, L. L., Bokanga, M. M., Jackson, F. L., Schlimme, D. S., and Li, B. W. (2002). Physicochemical properties and starch granular characteristics of flour from various Manihot esculenta (Cassava) genotypes. J. Food Sci., 67, Okigbo, B. N. (1980). Nutritional implications of projects giving high priority to the production of staples of low nutritive quality: The Case for cassava (Manihot esculenta, Crantz) in the humid tropics of West Africa. Food Nutr. Bull., 2, Purhagen, J. K., Sjöö, M. E., and Eliasson, A. C. (2008). Staling effects when adding low amounts of normal and heat-treated barley flour to a wheat bread. Cereal Chem., 85, Rodríguez-Sandoval, E., Ferna ndez-quintero, A., Cuvelier, G., Relkin, P., and Bello-Pérez, L. A. (2008). Starch retrogradation in cassava flour from cooked parenchyma. Starch-Stärke, 60, Sagum, R. and Arcot, J. (2000). Effect of domestic processing methods on the starch, non-starch polysaccharides and in vitro starch and protein digestibility of three varieties of rice with varying levels of amylose. Food Chem., 70, Sa nchez, T., Dufour, D., Moreno, I. X., and Ceballos, H. (2010).

10 1140 Comparison of pasting and gel stabilities of waxy and normal starches from potato, maize, and rice with those of a novel waxy cassava starch under thermal, chemical, and mechanical stress. J. Agric. Food Chem., 58, Shittu, T. A., Dixon, A., Awonorin, S. O., Sanni, L. O., and Maziya-Dixon, B. (2008). Bread from composite cassava-wheat flour. II: Effect of cassava genotype and nitrogen fertilizer on bread quality. Food Res. Int., 41, Soison, B., Jangchud, K., Jangchud, A., Harnsilawat, T., Piyachomkwan, K., Charunuch, C., and Prinyawiwatkul, W. (2014). Physico-functional and antioxidant properties of purple-flesh sweet potato flours as affected by extrusion and drum-drying treatments. Int. J. Food Sci. Technol. In press. Taguiam, F. C., Bucag, M. T., Tabangin, L. S., and Daoang, E. U. (2010). Yield Evaluation of Cassava as Influenced by Months of Planting in Dry D. Murayama et al. and Wet Season. ISU-Cabagan J. Res., 19, Yadav, A. R., Guha, M., Tharanathan, R. N., and Ramteke, R. S. (2006). Influence of drying conditions on functional properties of potato flour. Eur. Food Res. Technol., 223, Yun, S. H. and Matheson, N. K. (1990). Estimation of amylose content of starches after precipitation of amylopectin by concanavalin-a. Starch- Stärke, 42, Zhang, Y., Huang, Z., Yang, C., Huang, A., Hu, H., Gong, Z., and Huang, K. (2013). Material properties of partially pregelatinized cassava starch prepared by mechanical activation. Starch-Stärke, 65, URL cited i) (April 04, 2014) ii) (May 02, 2014)