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1 This is not a peer-reviewed article. Paper Number: 0611 An ASAE Meeting Presentation Determination of Specific Heat and Gelatinization Temperature of Rice using Differential Scanning Calorimetry Author's Name, optional title or degree: Debabandya Mohapatra Research Scholar, Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur, India Next Author (repeat for each author): Satish Bal Professor, Agricultural and Food Engineering Department Indian Institute of Technology, Kharagpur, India Written for presentation at the 00 ASAE Annual International Meeting Sponsored by ASAE Riviera Hotel and Convention Center Las Vegas, Nevada, USA 7-0 July 00 Abstract. Specific heat and gelatinization temperature of long-grain basmati rice were measured using differential scanning calorimetry (DSC). The value of specific heat of brown rice sample ranged between 1.7 to.8 kj/kg K, with temperature varying from -10 to 10 C range, whereas the same varied from 1. to. kj/kg-k for paddy for moisture content of 1 % and 1. % (wb), respectively. The gelatinization temperature range of has been found to be between 7-77 C for the powdered milled rice sample. Keywords. DSC, Rice, specific heat, gelatinization temperature, physical properties (The ASAE disclaimer is on a footer on this page, and will show in Print Preview or Page Layout view.) The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of the American Society of Agricultural Engineers (ASAE), and its printing and distribution does not constitute an endorsement of views which may be expressed. Technical presentations are not subject to the formal peer review process by ASAE editorial committees; therefore, they are not to be presented as refereed publications. Citation of this work should state that it is from an ASAE meeting paper EXAMPLE: Author's Last Name, Initials. 00. Title of Presentation. ASAE Paper No. 0xxxx. St. Joseph, Mich.: ASAE. For information about securing permission to reprint or reproduce a technical presentation, please contact ASAE at hq@asae.org or (90 Niles Road, St. Joseph, MI USA).

2 Introduction Thermal properties of biological materials are useful not only for quantifying thermal process, but also for designing processing system. Various research towards a better understanding of drying, parboiling and storage of the cereal crops like rough rice needs a knowledge of thermal properties such as specific heat and gelatinization temperature of the grain. Values of specific heat determination of many food materials, using DSC have been reported for various researchers. Gelatinization temperature has long been associated with the inherent starch property of the cereal grains. Starch consists of a branched fraction, amylopectin, and a linear fraction, amylose. Waxy rice starch has an apparent amylose content of %, non waxy rice may have 7-% amylose, equivalent to 8-7% amylose in starch. The amylose content of the milled rice may be classified as waxy (1- %); low (7-0 %); intermediate (0-%); and high (> %). The gelatinization temperature is measured by he degree of disintegration of milled rice in 1.7 % KOH for h at 0 C using a 1-7 scale proportionate to degree of spreading. High gelatinization temperature has so far been associated with waxy and low amylose-starch, but the gelatinization temperature of the intermediate amylose variety are difficult to find in this method (Juliano, 1996). Since the gel spreading method is qualitative and purely based on the judgment of the researcher, the results cannot be fool proof and has less accurate reproducibility. The gel consistency also has been the indicator of gelatinization temperature. This is a measure of viscosity of the material. This method also did not always provide a good correlation of gel viscosity with gelatinization temperature (Merca and Juliano, 1981). Hence the method of DSC is useful in accurate measurement of the starch property. This method enables the researcher to accurately monitor the phase transition of the starch material during dynamic heating. Moisture content has profound effect on the various physical and thermal properties of agricultural material. Specific heat is often expressed as function of moisture content using linear relations (Mohsenin, 1980). Temperature also has an effect on specific heat of the organic material and long has been ignored. Muir and Viravanichai (197) observed that specific heat of wheat increased almost linearly with temperature of 0 to 0 C for a seed moisture content up to 0 % (w.b.). Dutta et al. (1988) related the specific heat of peanuts to temperature in linear and second-degree polynomial relations. Several methods of specific heat measurement of food and agricultural material were method of mixtures, empirical equations, method of comparison calorimeter, method of guarded plate, method of calculated specific heat, adiabatic calorimeters, and differential scanning calorimetry (Mohsenin, 1980). The method of mixture has been the most common method reported in the literature for measurement of specific heat of biological material (Mohsenin, 1980). But the heat of hydration released when the material absorb from the calorimeter water can introduce errors in the measurement. Hence, the effect of temperature on specific heat is also difficult to observe with this method. The specific heat values of undried material is always greater than that of the calculated values obtained from the specific heat values of the dry material due to presence of moisture (Mohesenin, 1980). The major

3 disadvantage of the adiabatic agricultural calorimeter was the introduction of thermal gradient in the sample, which could be the source of error during measurement. The technique of differential scanning calorimetry (DSC) is rapid, direct, dynamic, and required milligram amounts of sample. The dynamic feature allows the determination of specific heat as a function of temperature. McMillin (1969) and Koch (1969) employed DSC to determine the specific heat of wood and dry tree bark, respectively. In both the cases, the specific heats were observed to increase with temperature. Chakrabarti and Johnson (197) used DSC to determine and found that an increase in specific heat of tobacco of up to 16 % with an increase in temperature from 0 to 70 C. Tang et al. (1991) investigated the specific heat of lentil seeds. Wang and Brennan (199) investigated the influence of moisture content and specific heat of potato by DSC. Karunakar et al. (1998) determined the specific heat and thermal conductivity of shrimp meat with respect to temperature. The objectives of the present study were to determine the specific heat of the rice and paddy sample as affected by temperature, and to determine the gelatinization temperature of the milled rice using differential scanning calorimetry (DSC). Materials and Methods: The moisture content and amylose content of the samples were measured according to the approved methods of AACC, prior to the measurement of specific heat and glass transition temperature. The measurement of specific heat was carried out using a NETZSCH Differential Scanning Calorimetry software version.6. (Phonics, Germany), which consisted of a thermal analyzer and cell. Before tests, the equipment was calibrated according to the manufacturers specification. Prior to tests the moisture content of the cleaned brown rice and paddy samples of Basmati variety was determined using standard procedure. Initially the machine was run without any sample, taking only the empty aluminum sample crucible sealed and then it was run using a sapphire disc of 1 mm thickness to prepare the standard line. To prepare the sample for test, a kernel was sliced along the major axis, which was about 1mm in thickness and weighed with a microbalance with a precision of 0.001mg. The thin slice was then placed in an aluminum sample crucible, which was covered with an aluminum lid and sealed to ensure there is no mass loss during heating. The lid was then pressed down to ensure contact between the sample and the container. Tests were done using temperature programme from 0 to 10 C. A heating rate of.0 Kcal/min was used to get better acquisition rate. To determine the glass transition temperature of Basmati rice, milled rice sample was ground in an attrition mill to a mesh size of 0. The powdered sample of rice was then soaked with excess moisture for h before conducting the experiment, so that there is uniform moisture distribution in the sample. Weight of the empty crucible was taken and the sample was placed in the aluminum crucible, which was covered with an aluminum lid and sealed, so as to prevent of

4 spillage of material from the disc. The crucible was then pierced and placed inside the DSC cell. The sample was heated in a dynamic setting at a rate of.0 Kcal/min. Graph was analyzed and the glass transition temperature was found using the thermal analysis software (NETZSCH). Three replications were taken for averaging the result. Statistical modeling procedure Specific heat data were fitted to linear, polynomial nd and rd degree and sigmoidal model using ORIGIN 6.0. Correlation coefficient squared (r ) was used as the criteria for the accuracy of the fit. The average of the relative percent difference between the experimental and predicted values or the mean relative deviation modulus (P) defined by Eq.(1) was used to define model accuracy (Özdemir and Derves, 1999). 100 abs( S i S pre ) P =, () n S i where S i is the observed specific heat and S pre is the predicted specific heat as fitted with the different models and n is the number of observations. Results and Discussions: An initial decrease in the DSC curve (Fig.1) was found before 0 C. It could be due to the excess moisture evaporation of the sample in the initial stage. The graph (Fig.1) analyzed shown that the glass transition temperature of the milled rice powder sample had its peak at 77 C, whereas the onset of the change in phase taken place at about 7.7 C which indicated the onset of starch gelatinization in the sample for which there was a phase change leading into the maximum energy absorption. The curve had a steep decrease, which has its peak at 88 C, showing that there is a phase change in the sample in that temperature range. So it can be concluded that the gelatinization temperature range of the milled rice is between 7-77 C. Fig.1 Glass Transition temperature of the soaked Milled rice powder sample

5 The specific heat values were plotted against temperature for brown rice and paddy (Fig ). It was observed from the specific heat curve of the rice sample that there was increase in the specific heat value with temperature, moisture content of the sample remaining same and it decreased after a certain phase. It was also observed that the specific heat value of the rice sample has its maximum value at a temperature of 8 C, after which the specific heat values decreased to the end of measurement. The maximum value of specific heat corresponds to the dip in the curve as indicated by Fig.1. Hence, it can be concluded that specific heat depends on the starch property. This could be due to the fact that at the onset of gelatinization of the starch material there is rapid absorption of energy due to hydrogen bonding, in the presence of moisture showing a deep in the energy level (Fig, and ). Hence there is an increase in the specific heat value in the material at that point of phase transition, which again decreased as the temperature increased. But there was a shift in the peak value of specific energy of paddy. It did not correspond to the gelatinization temperature of the starch, but the fall in energy values were reported (Fig. ) between C, the peak being at 90 C, which corresponds to the end of gelatinization as indicated by Fig.1. Hence an increase in the specific heat level towards the gelatinization phase and after that a decrease in the value of the same was also observed in the case of paddy as it was for brown rice. The reason could be due to the interference of husk. The outer husk covering might have delayed the energy drop and hence the rise in specific heat values at that time, after which it decreased a little again to rise. The trend after the gelatinization range was not specific for the paddy sample. Hence no suitable explanation could be given at this period. Specific heat of brown rice was found to be higher than rough rice, it may be due to presence of husk as the outer covering of the rough rice, that acts as a barrier in the heat flow, which is well know for its low thermal conductivity. Fig.. DSC curve showing base line and standard sapphire line and Cp line of the Brown rice

6 Fig.. DSC curve showing base line and standard sapphire line and Cp line of the Rough rice To obtain the functional relationships between the temperature and specific heat, the specific heat curve of the rice sample was divided into two segments, one up to the end point of gelatinization temperature and the other after that. The first segment was fitted with third degree, fourth-degree polynomial and sigmoidal functions (Fig.). Correlation coefficient squared (r ) and mean relative deviation modulus (P) were used as the criteria for the accuracy of the fit. This is presented in Table 1. It was analyzed that, sigmoidal fit was best suited for the initial phase. The second segment fitted into a linear relationship with R >0.98 (Fig.6) for the brown rice. Specific Heat, kj/kg-k Brownrice Paddy Temperature, C Fig. Specific heat curves for Brown Rice and Paddy 6

7 7 Specific Heat, kj/kg-k Observed Sigmoidal fit Poly Poly Temperature, C Fig. Best fitted curves for Specific heat of Brown Rice below gelatinization temperature 6 Specific Heat, kj/kg-k 1 y = -0.0x , R = Temperature, C Fig. 6 Best fitted curves for Specific heat of Brown Rice above gelatinization temperature Specific Heat, kj/kg- C observed linear Polynomial nd polynomial rd sigmoidal Temperature, C Fig. 7 Best fitted curves for Specific heat of Rough Rice below gelatinization temperature For paddy the best fitted curve found to be sigmoidal and nd degree polynomial equation with high correlation coefficient and low P value i.e. <10 (Table 1). An uncertain trend was observed in the value of specific heat value, post gelatinization phase of rough rice. It can be due to the presence of husk. May be after gelatinization phase the water content present in the specimen 7

8 tend to evaporate and again condenses due to the presence of husk, thereby influencing the specific heat value. Hence an average value of the specific heat value, till a temperature range of 10 C can be taken as.01 kj/kg- C, for rough rice. Table 1 Equation fitted to the specific heat curves Segment Equation Models R P First segment sigmoidal.99+( )/(1+exp((t before gelatinization Linear 1.)/1.66) 0.0T for brown rice Polynomial rd degree -E-06T T T First segment Polynomial th degree sigmoidal -E-07T + E-0T T T (0.-1.8)/(1+exp((T before gelatinization Linear 1.7)/6.98) 0.09T for rough rice Polynomial 0.000T T nd degree Polynomial rd degree -7E-07T T T ndsegment Linear xT brown rice Conclusion The gelatinization temperature range of the milled Basmati rice, which has more than 0 % amylose content, has the value ranging between C. there might be a correlation between starch gelatinization and specific heat of the cereal grains. It can be concluded that due to rapid absorption of energy due to hydrogen bonding, during starch gelatinization, in the presence of moisture, there is an increase in the specific heat value in the material. Which again decreases after the end point of gelatinization consistently for both paddy and brown rice. The paddy has lesser specific heat values as compared to brown rice due to the presence of husk, during gelatinization. Various models fitted into the specific heat and temperature equations showed that (Table 1), sigmoidal fit has the best fit for both brown rice and paddy with high R >0.98 and P value less than 10, which is an acceptable range. Sigmoidal equation can be suitably used to predict the specific heat of both brown rice and paddy before gelatinization temperature range. 8

9 References Chakrabarti, S.M. and Johnson, W.H Specific heat of flue-cured tobacco by differential calorimetry. Transactions of ASAE, 1(): Dutta, S.K., Nema, V.K. and Bhardwaj, R.K Thermal properties of gram. Journal of Agricultural Engineering Research, 9: Juliano, B.O (editor). Rice: Chemistry and Technology, Chapter, nd edition, American Association of Cereal Chemists Karunakar, B. Mishra, S. K. and Bandyopadhyay, S Specific heat and thermal conductivity of shrimp meat. Journal of Food engineering, 7: -1 Koch, P Specific heat of oven dry spruce, pine wood and bark. Wood Science,1(): 0-1. McMillin, C.W Specific heat of oven dry loblolly pine wood. Wood Science, (): Mohsenin, N.N Thermal Properties of Foods and Agricultural Materials, Gorden and Breach science Publishers, New York Muir, W.E. and Viravanichai, S Specific heat of wheat. Journal of Agricultural Engineering Research, 17: 8-. Özdemir, M. and Derves, O The thin-layer drying characteristics of hazelnuts during roasting. Journal of Food Engineering,, -. Tang, J., Sokhansanj, S., Yannacopoulos, S., and Kasap, S.O Specific heat capacity of lentil seeds by differential scanning calorimetry. Transactions of ASAE, (): 17-. Wang, N. and Brennan, J.G The influence of moisture content and temperature on the specific heat of potato measured by differential scanning calorimetry. Journal of Food engineering, 19:

The specific heat of wheat

The specific heat of wheat Cao, Y.*, Li, G.#, Zhang, Z., Chen, L., Li, Y., Zhang, T. Academy of State Administration of Grain, Beijing, P. R. China, Email: lgt@chinagrain.org * Corresponding author # Presenting