Classification of rice cultivars based on cluster analysis of hydration ...

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Setback values indicate the hardness <strong>of</strong> gel paste upon cooling. Setback values <strong>of</strong> high amylose starches from <strong>cultivars</strong> A and B were higher than that <strong>of</strong> others. Strangely, high setback value was observed in the starch <strong>of</strong> cultivar J which was categorized under a low amylose starch group or variety, <strong>based</strong> on amylose content. These results provide another example that actual pasting property is more important than amylose content for industry considerations. The starch from cultivar L showed the lowest setback value indicating a lower tendency to retrograde and is correspondingly more viscosity-stable. It is known that setback value is an important parameter for presumption <strong>of</strong> starch retrogradation which occurs severely in case <strong>of</strong> high amylose starches (Karim et al., 2000; Miles, Morris, Orford, & Ring, 1985). 3.4. <strong>Classification</strong> <strong>of</strong> <strong>rice</strong> starches Rice <strong>cultivars</strong> are classified according to previously determined amylose content <strong>of</strong> their starches, as shown in Table 3, into 3 groups. The present categorization is different from the conventional system <strong>of</strong> categorization <strong>based</strong> on amylose content <strong>of</strong> starch. As aforementioned, <strong>based</strong> on processability characteristics the <strong>rice</strong> <strong>cultivars</strong> are categorized into four groups (Table 4). As a result, medium and low amylose groups are merged into single Group ii since statistical difference was not significant. Clustering analysis <strong>of</strong> pasting parameters, hydration parameters, and a combination <strong>of</strong> both parameters (the combined parameters) <strong>of</strong> the starches was performed to classify <strong>rice</strong> <strong>cultivars</strong>. The <strong>rice</strong> <strong>cultivars</strong> classification <strong>based</strong> on pasting parameters listed in Table 3. Interestingly, cultivar J was grouped with A in spite <strong>of</strong> huge difference in amylose content where J possess concentration similar to that <strong>of</strong> the levels present in <strong>cultivars</strong> H and I. The peculiarity <strong>of</strong> cultivar J regarding the pasting properties is an example that the amylose content is <strong>of</strong>ten not disparate from the pasting properties. The seven studied <strong>cultivars</strong> having medium and low amylose starches were distributed in Groups iii and iv; they are not in order with respect to amylose content and correspondingly <strong>cultivars</strong> E and F, <strong>rice</strong> <strong>cultivars</strong> with medium amylose starch content, were swapped with <strong>cultivars</strong> G and I but grouped with cultivar H. Cultivars C and D were categorically placed under Group iii, separated from <strong>cultivars</strong> E and F despite having a similar amount <strong>of</strong> amylose (about 21 g/100 g). On the other hand, cultivar G was clustered with <strong>cultivars</strong> C and D due to similar pasting characteristics though there is a difference in their amylose contents. We assumed that proccesability <strong>of</strong> <strong>rice</strong> starches was affected not only amylose content but other factors such as soluble amylose content, amylopectin chain length, crystallinity, residue protein content, and amyloseelipid complex. Rice <strong>cultivars</strong> were classified <strong>based</strong> on hydration parameters <strong>of</strong> their starches into 4 groups. Interestingly, <strong>cultivars</strong> A and J were classified into one group and <strong>cultivars</strong> C and D were separated from <strong>cultivars</strong> E and F; these results are in good agreement with the classification <strong>based</strong> on the pasting property parameters. Cultivars A and B were distributed between two different groups. The classification <strong>of</strong> cultivar I <strong>based</strong> on the hydration parameters was not in agreement with the previous classification; cultivar I was grouped Table 3 Cluster analysis classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on processability parameters. with <strong>cultivars</strong> C, D, and G in the cluster analysis <strong>based</strong> on the pasting parameters. Cultivar I showed relatively higher values <strong>of</strong> WAI and SP similar to <strong>cultivars</strong> B, E, F, and H. Cultivars K and L, the glutinous <strong>rice</strong> <strong>cultivars</strong>, are classified into two different groups. Both <strong>cultivars</strong> showed excessively high values <strong>of</strong> WS and SP compared to those <strong>of</strong> non-glutinous <strong>cultivars</strong>, but they are considered statistically as different categories due to significant difference in the hydration properties. This result indicates that the hydration properties <strong>of</strong> the <strong>rice</strong> starches are different even if their amylose contents are similar. The classification <strong>based</strong> on combined parameters was different from the cluster analysis <strong>based</strong> classification which, in turn, <strong>based</strong> on pasting property parameters; but was similar to the results obtained by the cluster analysis using the hydration parameter. 3.5. Validation <strong>of</strong> cluster analysis classification <strong>of</strong> <strong>rice</strong> starches Texture pr<strong>of</strong>ile analysis parameters <strong>of</strong> <strong>rice</strong> starch gels are listed in Table 4. The gel texture pr<strong>of</strong>iles are indicated by hardness, cohesiveness, and gumminess dependent on physicochemical properties <strong>of</strong> individual starches used. The overall, hardness and gumminess increased but cohesiveness decreased as amylose content increases. However, hardness and gumminess <strong>of</strong> <strong>cultivars</strong> D and E were exceptional compared to other <strong>cultivars</strong> having similar amylose starches. This result shows that the texture pr<strong>of</strong>iles <strong>of</strong> the starch gels could be different even if their amylose contents are similar as observed with hydration and pasting properties studied previously. It is an example to show that the amylose content is not disparate from starch texture pr<strong>of</strong>iles which are important parameters to determine functionality and sensory properties <strong>of</strong> the starch-<strong>based</strong> foods. The classification <strong>of</strong> the <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on the texture pr<strong>of</strong>iles <strong>of</strong> the prepared gels is shown in Table 5. It has been performed to validate the cluster analysis classification established by the hydration and pasting parameters. Cultivars A and B containing high amylose were placed into two separate groups; they are categorically placed into different groups by the clustering analyses <strong>based</strong> on pasting properties, hydration, and their combination, but Based on Group i Group ii Group iii Group iv Group v Group vi amylose content A, B C, D, E, F, G, H, I, J K, L pasting viscosity A, J B C, D, G, I E, F, H K L hydration A, C, D, G, J B, E, F, H, I K L combined a A, C, D, G, J B, E, F, H, I K L a Combined with hydration and pasting parameters. I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168 167 Table 4 Texture pr<strong>of</strong>ile analysis <strong>of</strong> <strong>rice</strong> starch gels. Hardness (N) Cohesiveness Gumminess A 1.64 a 0.63 e 1.04 a B 1.15 b 0.76 d 0.88 ba C 0.79 c 0.79 dc 0.63 bcd D 0.91 cb 0.81 bdc 0.74 bc E 0.48 ed 0.86 bdac 0.41 efd F 0.50 ed 0.77 d 0.38 efd G 0.65 cd 0.89 bdac 0.57 ecd H 0.51 ed 0.92 bac 0.46 efcd I 0.42 edf 0.88 bdac 0.37 efd J 0.36 ef 0.93 ba 0.33 ef K 0.18 f 0.98 a 0.17 f L 0.19 f 0.99 a 0.19 f Means with the different letters in the same column are significantly different at the 5% level.
168 Table 5 Cluster analysis classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> <strong>based</strong> on textural parameters. Group i Group ii Group iii Group iv Group v A B C E K D F L G H I J not by the classification <strong>based</strong> on amylose contents (Table 3). The most important advantage with the new classification system is that <strong>cultivars</strong> C, D, and G and <strong>cultivars</strong> E, F, and H have been categorically placed under two different groups, which belong to a single group in the case <strong>of</strong> amylose-<strong>based</strong> classification (Table 3). In the classification <strong>based</strong> on pasting parameters, Group iv (<strong>cultivars</strong> E, F, and H) showed higher values <strong>of</strong> peak, trough, final, breakdown, and setback viscosities than Group iii (<strong>cultivars</strong> C, D, and G). In the proposed classification <strong>based</strong> on the hydration parameters and their combination with pasting properties data, Group i (<strong>cultivars</strong> C, D, and G) showed lower values <strong>of</strong> WAI and SP than Group ii (<strong>cultivars</strong> E, F, and H). This cluster analysis was successful to classify the <strong>cultivars</strong> C, D, and G and the <strong>cultivars</strong> E, F, and, H which differ in terms <strong>of</strong> processability. In our previous study (unpublished report), the protein content in <strong>rice</strong> flour <strong>of</strong> cultivar E, F (6.64 g/100 g), and H (6.12 g/100 g) was found lower than cultivar C (6.38 g/100 g), D (6.68 g/100 g), and G (6.77 g/100 g). Protein content can be correlated with pasting properties. Therefore, there are differences in physical characteristics because residue protein content may be lower in starch isolated from <strong>cultivars</strong> E, F, and H than one <strong>of</strong> <strong>cultivars</strong> G, C, and D. In conclusion, the classification system <strong>based</strong> on pasting and hydration parameters representing practical processability is better compared to the conventional method <strong>based</strong> on amylose content. 4. Conclusions In this study, classification <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong> was performed <strong>based</strong> on the hydration and the pasting properties <strong>of</strong> their starches. The <strong>cultivars</strong> having similar amylose content are categorized into different groups under proposed new classification because their starches showed different hydration and pasting properties. However, some <strong>cultivars</strong> with different amylose contents are grouped together into a single category due to the similarity <strong>of</strong> hydration and pasting properties <strong>of</strong> their starches. Thus, the classification <strong>of</strong> <strong>rice</strong> starches, in turn, <strong>cultivars</strong> <strong>based</strong> on the practical processability is more appropriate and useful system than the classical classification considering the amylose content only. This study provides a resolution to standardize purpose-specific classification <strong>of</strong> starches from a variety <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>. Rice <strong>cultivars</strong> classified within a category <strong>based</strong> on practical processability can be considered as uniform even if their chemical compositions including amylose content are different. Thus, mixture <strong>of</strong> the starches from different <strong>rice</strong> <strong>cultivars</strong> but possessing similar processing characteristics can be used for different food applications. In conclusion, <strong>rice</strong> starches categorization can be simplified and standardized by using processability parameters despite a variety <strong>of</strong> <strong>rice</strong> <strong>cultivars</strong>. This classification strategy can be expanded to categorize <strong>rice</strong> <strong>cultivars</strong> suited for properties <strong>of</strong> precooked dried <strong>rice</strong>, <strong>rice</strong> noodle, and bakery products when the classification is I. Lee et al. / LWT - Food Science and Technology 48 (2012) 164e168 carried out <strong>based</strong> on the parameters that represent practical processabilities. 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