CLASSIFICATION OF RICE CULTIVARS BY USING PHYSICOCHEMICAL, THERMAL, HYDRATION PROPERTIES, AND COOKING QUALITY 1 JITNAPA BOONMEEJOY, 2JETSADA WICHAPHON, 3SUDARAT JIAMYANGYUEN 1,2, 3 Department of Agro-Industry, Faculty of Agriculture, Natural Resources and Environment, Naresuan University, MuangPhitsanulok, THAILAND 65000 E-mail: [email protected], [email protected], [email protected] Abstract— The classification of eight different rice cultivar was conducted to classify high amylose content rice (HM 105, RD15 and PTT1), medium amylose content rice (KTH17) and low amylose content rice (PL2, RD31, SP1 and CN1). Physicochemical, thermal, hydration, cooking quality and effect of storage time were studied in order to classify rice cultivar by principal component analysis. The results showed that amylose content of high amylose rice increased during storage time but amylose content of low and medium amylose rice were consistent. Hardness value increased during storage time. High amylose rice showed higher hardness compared to medium and low amylose. The highest and lowest hardness value was found in SP1 (901 N) and PTT1 (431 N), respectively. This indicated that amylose content affected hardness. The result of thermal properties showed that the gelatinization temperature positively correlated with amylose content. The highest onset, peak and conclusion temperature showed in RD31 (72.67ºC, 77.08 ºC and 84.03 ºC, respectively). The storage time had no effect on thermal properties. The results showed that optimum cooking time positively correlated with amylose content. The highest optimum cooking time showed in CN1 (33.0 min) and lowest cooking time showed in HM105 (12.33 min). Hydration properties of different rice cultivar showed that high amylose content rice have capacity to absorb water more than low and medium amylose rice. The classification of rice cultivars resected in two groups by using principal component analysis. PC1 and PC2 contributed for 53.4% and 21.8% variance, respectively. The low and medium amylose were classified in one group and separate from high amylose content rice. The results suggested that amylose content alone cannot be used to classify rice cultivars. The physicochemical, thermal, hydration, and cooking quality can difference classify rice cultivar with amylose content. This results can be a useful alternative for the food industry, especially for rice noodle industry. Keywords- Rice Flour, Cooking Quality, Amylose Content, Principal Component Analysis species after selecting those by its food applicable properties for appropriate management of rice starch quality. Especially, there exists a significant difference in physicochemical properties even among the starch obtained from rice cultivars with similar amylose content [6]-[7]. So, amylose content have been used to distinguish the rice starch characteristics. Champagne et al. [8] predicted cooked rice texture which results showed that rice with similar amylose and protein content still had different texture quality. Factor that affect the textural quality of cooked rice include rice variety, amylose content, pasting properties, protein content, postharvest practice, moisture content, temperature, and storage period [9][11]. Another important parameters to represent starch characteristics are water hydration properties including water absorption index (WAI), water solubility (WS), and swelling power (SP). The hydration properties of starch can be correlated with its pasting properties and physicochemical properties which are important for the application of starch in industry. Principal component analysis (PCA) is a classical statistical method to extracts relevant information from a large data set. The purpose of this study are to classify different rice cultivars based on physicochemical properties such as texture properties and thermal properties, rice cooking quality and hydration properties compare with amylose content. I. INTRODUCTION Rice is one of the major staple food in the world since centuries. Rice is the most important cereal for human consumption. Rice industry is suffering from inefficiency in securing the uniform quality ingredient since rice commodities that are traded involve a wide variety of cultivars. The physicochemical properties of freshly harvested rice change during aging of rice [1]-[3].The most important change that occur during the aging process involves rheological properties, which contribute significantly to cooking and eating properties. Rice grain exhibits distinct physicochemical properties, depending upon the variety, and quality of starch especially influences its cooking properties [4]. In rice, amylose content of starch is one of the important characteristics determining eating and cooking qualities [5].The changes in rice properties during aging have been reported to depend upon variety, storage conditions, and amylose content. Amylose content has been long used as a parameter to predict the texture of cooked rice. Juliano has suggested classification of amylose content as waxy (0-5%), very low (5-12%), low (12-20%), intermediate (2025%), and high (25-33%). The industrial standpoint, it is approach to simplify rice cultivars categorization. Thus it is plausible to classify the rice starch categorized by similarity on the processability of their Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2 66 Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality Brookfield viscometers Ltd., USA). The rice samples were prepared by the modified method of Juliano et al. [13]. Rice samples 10 g cooked in 100 ml distilled water at 95±1°C till white core disappeared. The cooked rice was drained of water completely using a strainer and surface moisture of the samples was blotted out. A 250 mm diameter probe was used to compress sample, with pre-test and post-test speeds of 1 mm/s and test speed of 0.5 mm/s. Parameters recorded from the test curves was hardness II. MATERIALS AND METHODS 2.1. Materials Eight different cultivars of rice were used in the study. The cultivars of HM105, RD15, and PTT1were low amylose content rice. The KTH17 was medium amylose rice and CN1, RD31, SP1, and PL2 were high amylose content rice. The moisture content of all milled rice was 10-13%. All the sample were stored at room temperature (27-37ºC) in wood box for six months. 2.2. Preparation of rice flour The paddy samples were de-husked and polished with Rice polishing machine (NW 1000 TURBO, Natrawee Technology Co., ltd., Chachoengsao, Thailand). Polished rice grains were ground into flour using a blender (MX-900M, Panasonic, Johor, Malaysia) and passed through a 100 mesh sieve screen. The obtained rice flour was kept in a zip-lock plastic bag and stored in freezer at -20oC before analysis. 2.6. Functional properties Water absorption index (WAI) was measured according to the method of Medcalf and Gilles [14]. Starch suspension was heated at 80C. The result were calculated using the following equation Water absorption index = (wet sediment weigh)/ (sample weigh) 2.7. Cooking quality Optimum cooking time was determined by the modified method reported by Juliano [4]. In a 250 ml beaker, about 100 ml-distilled water was boiled (95±1ºC) and 5 g of head rice samples dropped into it. Measurement of cooking duration was started immediately. After 10 min and every minute thereafter, 10 grains of rice were removed and pressed between two clean glass plates. Cooking time was recorded when at least 90% of the grains no longer had opaque core or uncooked centers. The rice was then allowed to simmer for about another 2 min to ensure that the core of all grains had been gelatinized. Optimum cooking time was taken as the established cooking time plus 2 additional minutes. 2.3. Amylose content analysis Amylose content was determined by the modified simplified assay method reported by Juliano [12] using the Starch-iodine blue method. Milled rice flour 0.1 g was weighed in 100 mL volumetric flasks. Then added 1 mL of 95% ethanol and 9 mL of 1 N NaOH. The suspension was heated in a boiling water bath for 10 min. The samples were diluted to 100 mL with distilled water and mixed well. The Samples solution 5 mL of each sample was made up to 100 mL with distilled water, 1 mL of 1 M acetic acid and 2 mL of iodine solution (0.2 g iodine and 2.0 g Potassium iodide in 100 mL distilled water). The test mixture was left for 20 min. Then the intensity of color developed was measured in spectrophotometer (DR 4000U, UV Visible Spectrophotometer, Hach, Loveland, Colorado, USA) at 620 nm against the reagent blank. Amylose content (%) was calculated from a standard curve prepared using amylose standard. 2.8. Statistical analyses Data were analyzed by one way analysis of variance (ANOVA) and Duncan’s multiple range test at 5% probability level (SPSS 17.0). A multivariate analysis software MINITAB version 17 were used to perform principal component analysis (PCA). 2.4. Thermal properties Thermal properties of rice flour were determined by using differential scanning calorimetry (DSC) (DSC 1, METTLER TOLEDO, Columbus, USA). Rice flour samples (10 mg) and distilled water were added to the DSC pan in a 1:2 ratio (w/w). The pan was hermitically sealed and allowed to equilibrate at 25 C for 1 h. The samples were then heated from 10 C to 110 C at 10 C/min. An empty DSC pan was used as a reference. Onset, peak, conclusion temperatures and gelatinization enthalpy were determined. (Shivananda K. GarimellaPurna a, Rebecca A. Miller a, Paul A. Seib a, Robert A. Graybosch b, Yong-Cheng Shi) III. RESULTS AND DISCUSSION 3.1. Chemical analysis 2.5. Texture profiles analysis Textural profile analysis (TPA) of the cooked rice was performed using a texture analyzer (QTS 25, Fig.1. Amylose content of rice flour stored for 6 months Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2 67 Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality They found that cooked rice increased hardness value during storage and Meullenet et al. [18] reported that hardness value of ageing rice was higher than that of freshly rice. From Fig. 2, the hardness of cooked rice shows a positive correlation with amylose content. This suggests that hardness of cooked rice was mainly influenced amylose content. Rice with high amylose content is liable to leach more into the cooking water [19]. The hardness of freshly cooked rice is less than aged cooked rice because amylose and amylopectin reaction occurs contributing to the increase of cooked rice hardness. The long amylopectin chains may crystallize with an amylose molecule, which might extend through several adjacent ‘clusters’, thereby contributing to double helices in several crystallites [20]. 3.3. Functional properties Fig. 3 shows water absorption index (WAI) of different rice cultivars during six months storage. For the first three months, the WAI of highamylose rice was higher than that low and medium amylose rice. The WAI increased during three months of storage and after that it decreased and consistent. The highest and lowest WAI was found in RD31 (14.16) and PL2 (8.02), respectively. This results were different from the previous report [13] showed that the low amylose content rice can absorb water more than high amylose rice, which could be explain that amylose content contains more crystalline region, resulting in the difficulty of water molecules to migrate inside the grains. However, the finding of this study was in accordance with Lee et al. [21], which reported that the WAI of high amylose rice was higher than that of low and medium amylose rice. These disagreed results indicated that amylose content and WAI of aged rice can bedifferently classified depending on rice cultivars. Amylose content of the sample rice cultivars during six months is shown in Fig. 1. The results showed that PL2 rice had the highest amylose content(36.77%) and PTTT1 show the lowest amylose content (18.42%). During storage, amylose content of low and medium amylose rice were consistent but that of high amylose rice increased after 4 months of storage. Villareal [15] and Chrastil [2], [3] and Sermsirisopon [16] reported that amylose content slightly increased during storageshowed that PL2 rice had the highest amylose content(36.77%) and PTTT1 show the lowest amylose content (18.42%). During storage, amylose content of low and medium amylose rice were consistent but that of high amylose rice increased after 4 months of storage. Villareal [15] and Chrastil [2], [3] and Sermsirisopon[16] reported that amylose content slightly increased during storage. 3.2. Texture Profiles Analysis (TPA) The hardness of cooked rice is shown in Fig. 2. The highest and lowest hardness belonged toSP1 (901 N) and PTT1 (431 N), respectively. The results show that hardness value of high amylose rice was higher than that of low and medium amylose, except RD31. This indicated that hardness is affected by amylose content of rice. The cooked rice with low amylose exhibited soft texture, while that of high amylose is harder. High amylose rice shows higher hardness value compared to that of low and medium. This is due to the fact that amylose contains more crystalline region, which in turn, shows more compact starch granule and exhibits harder gel trends. In addition, the storage time influenced the texture of cooked rice in which high amylose rice is more affected compared to low and medium amylose rice. This finding was similar to that has been reported by Juliano [4] and Charstil [17]. 3.4. Thermal properties Table 1: Thermal properties of different rice flour during 6 months storage Several concepts have been proposed to explain the gelatinization process. Starch gelatinization is an endothermic process that corresponds to the loss of starch crystalline in the starch granules under particular heat and moisture conditions. Gelatinization describes the range of irreversible changes when starch is heated in excess water [22]. Thermal properties of difference rice flour during six months storage is shown in Table 1. The result Proceedings of The IRES 30th International Conference, Tokyo, Japan, 18th February 2016, ISBN: 978-93-85973-35-2 68 Classification of Rice Cultivars by Using Physicochemical, Thermal, Hydration Properties, and Cooking Quality showed that low and medium amylose rice was not different in terms of onset, peak and conclusion temperatures as well as gelatinization enthalpy during storage. This result indicated that onset, peak and conclusion temperature of rice flour are not affected by storage time. This result was agreeable with the studies of Karlsson and Eliasson [23] who reported that no changes in the onset, peak and conclusion temperatures of starch were observed with storage time. The initiation of gelatinization is called the onset. Peak is the position where theendothermicreaction occurs at the maximum. Conclusion is when all the starch granules are fully gelatinized, and the curve remains stable [24]. high amylose rice also requires more cooking time. From the results of all samples, it was noticed that cooking time increased in accordance with storage time. This finding was agreeable with results of Villareal et al. [15], who reported that the storage time affected gelatinization of rice flour, in which they were positively correlated. This increase was due to the greater mobility and subsequent restructuring of starch and changes in the protein bodies present in the grain. 3.6. Principal component analysis (PCA) The results of physicochemical properties, cooking quality and hydration properties data were used to classify rice cultivar by using principal component analysis as shown as score plot in Fig. 5. From the results showed that amylose content exhibited positive correlation with physicochemical properties, cooking quality and hydration properties (data not shown). The PC1 and PC2 contributed for 53.4% and 21.8% variance, respectively. The results showed distinctive two groups from classification, including (1) low and medium amylose rice and (2) high amylose group. This finding suggested that classification of rice using other parameters (physicochemical, hydration, and cooking quality) can yield different results compared to a conventional method using amylose content. CONCLUSIONS Using solely amylose content may not provide the true results in classifying different rice cultivars. This study suggested alternative way of rice grouping by incorporating physical, thermal, hydration, as well as cooking quality. The results obtained were more appropriate and accurate to apply for rice industry in which combination of these attributes can reflect complete aspects for rice classification. The highest onset, peak and conclusion temperature was found in RD31 (72.67ºC, 77.08 ºC and 84.03 ºC, respectively) and the lowest was found in PL2 (64.41ºC, 67.38 ºC and 73.04 ºC, respectively). Comparing of onset, peak, conclusion and ∆ Hgel among rice varieties with different amylose content, it was found that, in general, high amylose rice showed higher values than those of low and medium amylose rice, which could be affected by starch structure properties. The starch with low amylose contains more amorphous and less crystalline regions, leading to lower gelatinization temperature. The lower gelatinization temperatures for rice flours indicated that less energy is required to starch gelatinization. ACKNOWLEDGMENTS This research was funded by Thailand Research Fund (TRF) under the grant number MSD57I0041. Rice samples and part of financial were provided by the rice milling factory (Rong See Fai Thai Songserm Ltd.) located in NakornSawan Province, Thailand. The authors greatly appreciated REFERENCES [1] 3.5. Cooking quality The cooking time of rice grain of different rice cultivars is shown in Fig. 4. 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