Cluster analysis of rice starch varieties based on processability

Transcription

1 Cluster analysis of rice starch varieties based on processability Inae Lee a, Kyoung Jin We a, Junho Jung a, Seung-Won Kim a, Sanghoon Ko a a Sejong University, Department of Food Science and Technology, Seoul, Republic of Korea (sanghoonko@sejong.ac.kr) ABSTRACT Rice starch as a food additive affects nutritional, process, and texture properties in foods. The processability of starch is different depending on variety of rice cultivars. At present, rice starches are categorized by the amylose content which is dependent on the cultivar. However, the processabilities of rice starches are similar or different regardless of amylose content. Thus, it is important to classify cultivars of rice starches based on physical behaviors during processing. However, it is difficult to categorize the rice starches since there are so many rice cultivars all over the world. For this reason, qualities and functionalities of rice starches have been controlled poorly due to lack of a proper classification method. The purposes of this study are to classify starches of different rice cultivars based on processability such as water solubility and pasting properties and to simplify categorization the varieties of rice cultivars into based on their similarity based characteristics. In this study, rice starches were analysed in 12 different cultivars (A to L). Water solubility analysis and rapid visco analysis (RVA) were performed to characterize the physical properties of the starches, and corresponding parameters of the analyses were used to classify the cultivars by hierarchical cluster analysis. For comparison, the rice cultivars were categorized based on their amylose content. The cluster analysis based on the water solubility parameters categorized 12 rice cultivars into five groups as A, C, D, G, H / B, E, I / F, J / K / L. The classification based on the pasting parameters was 5 groups, A/ B / C, D, F, G, H / E, I, J / K, L. The classification of the rice starches were based on amylose content, water-related and pasting parameters. The classification based on the amylose content was slightly different from that base on water solubility or pasting characteristics. Especially, cultivar E was not within the same group of cultivars F, G, and H although cultivars E, F, G, and H contained similar amount of amylose. The cultivar E showed different water solubility and pasting property from the cultivars with similar amylose content. Thus, the classification of rice cultivars based on the practical processability is more appropriates useful than that based on the classical amylose content. Rice cultivars within the category of the classification based on practical processability can be assumed as a similar ingredient. Thus, mixture of the starches from the same category can be used as an ingredient for rice processing including starch production. In conclusion, rice starches categorization can be simplified and standardized by using processibility parameters despite a variety of rice cultivars. The simplified classification of rice ingredients makes industrial utilization easy including rice starch industries. Keywords: rice starch; cultivars; pasting property; cluster analysis; grouping INTRODUCTION Rice starch as a food additive affects nutritional, processing, and texture properties in foods. The processability of starches is different depending on variety of rice cultivars. At present, the processability of rice starches is categorized by taking into account the amylose content which is dependent on the cultivar. However, the processability of rice starches is affected by grain length, amylose and amylopectin structure shape, size, and molecular weight [1][2][3] in addition to amylose content. For instance, long-grain and short-grain rice show large difference in their chemical compositions and processibility. For these reasons, rice starch industry has been suffered from inability in securing the uniform quality ingredient since rice commodity that is traded originates from a wide variety of cultivars. Each rice variety possesses unique processibility; it is hard to control the quality of rice starch made of the commodities obtained seasonally and regionally. Thus, it is necessary to classify rice based on physical behaviour of their starches during processing. The expand RVA parameters have been extensively used for physical properties comparison studies in starch applications [4]. The RVA profile shows viscosity changes of starch during a time/ temperature schedule in a

2 quantitative manner; the RVA parameters deal with starch physico-chemical characteristics such as hardness, solubility, fracturability, and other texture effects. Other important parameters to represent starch characteristics are water hydration properties which in turn consist of 3 parameters: water absorption index (WAI), water solubility (WS), and swelling power (SP). The hydration properties of starch can be correlated with its pasting behavior and physicochemical properties which are important for the application of starch in industry. However, in many cases, a single-parameter description from different measures rarely reflects whole characteristics of the starch. In addition, it is difficult to classify the rice starches intuitively based on the parameters because of the complexity associated with them. For this reason, qualities and functionalities of rice starches have been controlled poorly due to lack of a proper classification method. To overcome these issues, statistical approach such as cluster analysis can be employed to obtain a categorization pattern from the complex data sets of water hydration and RVA parameters. Cluster analysis is a statistical method to convert various characteristics of objects to quantitative measures (so called similarity distance) and correspondingly to cluster them at relatively close distances into a category. Therefore, a variety of rice cultivars can be categorically divided into several groups based on similarity in processibility of their starches The purposes of this study are to classify starches of different rice cultivars based on processability such as water solubility and pasting properties and to simplify categorization the varieties of rice cultivars into based on their similarity based characteristics. MATERIALS & METHODS Rice starches were analysed in 12 different cultivars (A to L). Water solubility analysis and rapid visco analysis were performed to characterize the physical properties of the starches, and corresponding parameters of the analyses were used to classify the cultivars by hierarchical cluster analysis. Water solubility, pasting property parameters were normalized. For comparison, the rice cultivars were categorized based on their amylose content. RESULTS & DISCUSSION Amylose content and name of rice cultivars shown below Table1. Table 1. Amylose content and name of rice cultivars Cultivars Amylose contents (%) Name A 29.4 Goami B 27.8 Thiland C 19.6 Dongjin 1 D 19.3 Seolgaeng E 18.5 Ilmi F 18.1 Hanmauem G 18.1 Hopyeong H 18. Hiami I 17.7 Deuraechan J 16.9 Hanareum K ~ 1 Boseokchal L ~ 1 Shinseonchal Rice cultivars were classified according to amylose content as shown in Table 2. Rice cultivars were categorized into 3 groups based on their amylose content as A, B / C, D, E, F, G, H, I, J / K, L. In general, Rice cultivars are classified depending on the amylose content of their starches into waxy, low amylose, medium amylose, and high amylose rice starches that usually contain -2, 9-2, 2-25, and over 25% amylose, respectively[5]. Starches of rice cultivars tested in the present study contain different levels of amylose. Therefore, cultivars A and B are categorized into high amylose. Cultivars C, D, E, and F, cultivars G, H, I, and J are categorized into medium amylose and low amylose, respectively. And cultivars K and L are waxy rice starches. However, medium and low amylose groups were merged to Group 2 since difference was not statistically significant.

3 Table 2. Classification of rice starch based on the amylose content Group 1 Group 2 Group 3 A, B C, D, E, F, G, H, I, J K, L Cluster analysis of hydration parameters, and pasting parameters of the starches was performed to classify rice cultivars. The rice cultivars were classified based on WAI, WS, and SP as listed in Table 3. In this kind of classification 12 rice cultivars were categorized into five groups as A, C, D, G, H / B, E, I / F, J / K / L. Interestingly, cultivars A and H were classified into one group and cultivars E and F were separated from cultivars D and G. Cultivars A and B containing high amylose were categorized under two different groups. Cultivar B showed relatively higher values of WAI, WS, and SP than cultivar A; correspondingly the cultivar A was considered differently from cultivar A. Cultivars K and L, glutinous rice cultivars, were classified into different groups. Table 3. Classification of rice starch based on the water hydration parameters A, C, D, G, H B, E, I F, J K L Figure 1. shows water hydration property each group. It could be identified the characteristics of groups by obtained average of parameters value. Group 1 showed lower values of WAI, WS, and SP than Group 2. As aforementioned, cultivars K and L were separated and categorized as group 4 and 5. Both cultivars showed very high values of WS and SP compared with those of non-glutinous cultivars, but they were considered as different categories due to statistically significant difference in the water hydration properties. These results (Table 3. and Figure 1.) show a typical example that the water hydration properties of the rice starches are different even if their amylose content are similar. 1 8 WAI WS SP Figure 1. Comparison of water solubility between goups. Table 4. shows the classification of rice cultivars based on the pasting parameters of their starches into 5 groups, A/ B / C, D, F, G, H / E, I, J / K, L. Interestingly, cultivars E and I were not categorically included within the same group of cultivars F, G, and H although cultivars E, F, G, H, and I contain similar amounts of amylose. The categorization of cultivar F based on the pasting parameters do not allow it to be included under same group as with the previous classification; cultivar F was grouped with cultivars J in the cluster analysis based on the water hydration parameters. But, in classification according to pasting property, they were divided and included in group 3 and 4.

4 Table 4. Classification of rice starch based on the pasting parameters A B C, D, F, G, H E, I, J K, L Figure 2. shows viscosity of rice starches each group. Group 2 contains cultivar B only which exhibit high final viscosity and setback value. There was a difference in the value of peak viscosity and breakdown with cultivar A although cultivar B contains similar amylose content. Cultivar A showed lower peak viscosity and breakdown value than B. These differences were distinct from the pasting properties. Cultivars E, I and J showed higher values of peak, trough, final, breakdown, and setback viscosities than those in cultivars D and H. It is noteworthy to divide into two groups according to pasting properties despite there was no difference amylose content among the cultivars. Cultivar K and L in group 5 were indicated high peak viscosity and low final viscosity and setback value. The starch of cultivar L showed the lowest setback value; it has a lower tendency to retrograde and is correspondingly more viscosity stable. It is known that setback value is an important parameter to expect starch retrogradation which occurs severely in high amylose starches [6]. 6 Viscosity (Pa.s) Peak viscosity Trough Final viscosity Breakdown Setback 1 Figure 2. Comparison of pasting viscosities between goups. Time-to-peak and pasting temperature obtained from RVA data of rice starches each group as shown in Figure 3. Time-to-peak value of group 1 and 3 were longer than other groups, whereas it was the shortest with group 5 cultivars. Cultivar A in group 1 was formed with cultivars in group 3. And Time-to-peak values of them were similar. Because of was highly correlated to WS and SP in a negative manner, pasting temperature value of group 2 was highest whereas that was the lowest group 5.

5 Time (min) 4 2 peak time pasting temperature Temperature ( o C) 5 Figure 3. Comparison of peak time and pasting temperature between goups. CONCLUSION In this study, classification of rice cultivars was performed based on processability of their starches. The properties which determine the peocessability such as water hydration and pasting property have been studied. Certain cultivars were categorized other groups because they starches showed different water solubility and pasting property from a group of cultivars with similar amylose content. On contrary, some cultivars were grouped under one heading a label despite large difference amylose content. Thus, the classification of rice cultivars based on the practical processability is more appropriate and useful than amylose based classical classification. Rice cultivars within a category of the classification based on practical processability can be considered a uniform quality. Thus, mixture of the starches from the same category can be used as an ingredient for rice processing including starch production. In conclusion, rice starches categorization can be simplified and standardized by using processibility parameters despite a variety of rice cultivars. The simplified classification of rice ingredients makes industrial utilization easy including rice starch industries. REFERENCES [1] Tester R.F. & Morrison W.R Swelling and gelatinization of cereal starches. I.Effects of amylopectin, amylose, and lipids. Cereal Chemistry 67(6): [2] Morrison W.R., Tester R.F., Snape C.E., Law R. & Gidley M.J Swelling and gelatinization of cereal starches. IV. Some effects of lipid-complexed amylose and free amylose in waxy and normal barley starches. Cereal Chemistry 7: [3] Tester R.F. & Morrison W.R Swelling and gelatinisation of cereal starches. II. Waxy rice starches. Cereal Chemistry 67: [4] Wiesenborn D.P., Orr P.H., Casper H.H. & Tacke B.K Potato starch paste behavior as related to some physical/chemical properties. Journal of Food Science 59(3): [5] Bemiller J.N. & Whistler R.L. 29. Starch: Chemistry and Technology. In: Cheryl R. Mitchell. (3rd.). Rice starches: Production and properties. Elsevier Inc., Ames, Iowa, USA. [6] Karim A.A., Norziah M.H. & Seow C.C. 2. Methods for the study of starch retrogradation. Food Chemistry 71(1): 9-36.