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Amaranth pop

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Amaranth pop

  1. 1. This article was downloaded by:On: 9 January 2011Access details: Access Details: Free AccessPublisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Drying Technology Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597247 Optimal Conditions for Popping Amaranth Seeds T. Inouea; H. Iyotaa; T. Uemuraa; J. Yamagataa; Y. Konishib; Y. Tatemotoc a Department of Mechanical and Physical Engineering, Osaka City University, Osaka, Japan b Department of Food Science and Nutrition, Osaka City University, Osaka, Japan c Department of Materials Science and Chemical Engineering, Shizuoka University, Hamamatsu, JapanTo cite this Article Inoue, T. , Iyota, H. , Uemura, T. , Yamagata, J. , Konishi, Y. and Tatemoto, Y.(2009) OptimalConditions for Popping Amaranth Seeds, Drying Technology, 27: 7, 918 — 926To link to this Article: DOI: 10.1080/07373930902988254URL: http://dx.doi.org/10.1080/07373930902988254 PLEASE SCROLL DOWN FOR ARTICLEFull terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdfThis article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.
  2. 2. Drying Technology, 27: 918–926, 2009 Copyright # 2009 Taylor & Francis Group, LLC ISSN: 0737-3937 print=1532-2300 online DOI: 10.1080/07373930902988254 Optimal Conditions for Popping Amaranth Seeds T. Inoue,1 H. Iyota,1 T. Uemura,1 J. Yamagata,1 Y. Konishi,2 and Y. Tatemoto3 1 Department of Mechanical and Physical Engineering, Osaka City University, Osaka, Japan 2 Department of Food Science and Nutrition, Osaka City University, Osaka, Japan 3 Department of Materials Science and Chemical Engineering, Shizuoka University, Hamamatsu, Japan to an increase in the boiling point temperature of the Amaranth seeds can be popped under suitable heating conditions. moisture content of the materials. On the basis of experimental results obtained in our laboratory, we Tatemoto et al. indicated the temperature in the sample have developed a prototype of a continuous processing system for increased because of the increment of pressure when the commercial application. In addition, the effects of gas temperature, mass transfer in a sample was low for fluidized bed drying flow rate, and feed speed on the popping quality of seeds, such as their volume expansion ratio and yield, were examined. with superheated steam and hot air.[1] Johanasson et al. The experimental results showed that the undersized yield ratio examined the variations in the internal pressure of wood increased with the flow speed, whereas it decreased with an increase chips during hot air drying and superheated steam in the gas temperature. In addition, to achieve a high expansion drying.[2] Rattanadecho et al. investigated the effect of theDownloaded At: 04:58 9 January 2011 ratio and maximum output, the feed speed was increased with the initial moisture content of the material on its total internal gas temperature. Furthermore, measuring the differential pressure in the test section of the experimental apparatus enabled the estima- pressure during hot air drying.[3] In addition, Perre et al. mea- tion of the quantity of seeds therein during the popping experiment. sured the internal pressure during drying in superheated steam and moist air using light concrete and softwood as Keywords Amaranthus hypochondriacus; Drying; Feed speed; sample materials.[4] Further, Asaeda et al. investigated Gas temperature; Popping; Volume expansion; Yield the effect of the total pressure gradient in the dried region of materials during the falling drying rate period on the INTRODUCTION drying rate in the case of drying techniques such as hot Puff drying methods are beneficial in terms of short air drying and superheated steam drying.[5] Iyota et al. drying time and improved texture of the dried food mate- reported that isobaric approximations are effective in esti- rial. Hence, this drying method is used for drying food mating the vapor diffusion rate in the dried region of mate- materials such as rice, chestnut, potato, and carrot. This rials with microsized pores, and vapor flow approximations drying is generally carried out in a pressurized container. are effective in estimating the vapor flow rate in the dried The material is fed into this container and heated under region of materials with pores that are filled almost with high pressure. The pressure is then abruptly reduced to vapor only.[6] the atmospheric pressure. This causes flash evaporation of Seeds of amaranth, which is one of the most promising the moisture contained within the material, accompanied food crops with high protein and mineral content,[7,8] can by volume expansion. be popped by rapidly evaporating the moisture contained This drying can be carried out by employing suitable within the seeds, accompanied by starch gelatinization in operating conditions without using a pressurized container. the seeds, when it is heated and dried rapidly. The popped For example, low permeability materials can be dried by seeds are soft in texture and taste like nutty-flavored hot air drying, whose gas temperature is higher than a boil- popcorn; therefore, popping is a simple method to render ing point temperature under atmospheric pressure. This amaranth seeds edible. In order to process seeds and drying induces internal evaporation in these materials and, improve their texture, measuring their yield and expansion thus, the internal pressure is easily increased; this also leads volume after popping is important; a high expansion volume improves texture and edibility and, therefore, the quality of the food product is improved.[9] Hot plates have been traditionally used for popping Correspondence: H. Iyota, Department of Mechanical and seeds. However, the resulting products have certain draw- Physical Engineering, Osaka City University, 3-3-138, Sugimoto, backs: (1) they have a low expansion volume, (2) they are Sumiyoshi-ku, Osaka City 558-8585, Japan; E-mail: iyota@ mech.eng.osaka-cu.ac.jp prone to browning or carbonization due to overheating, 918
  3. 3. OPTIMAL CONDITIONS FOR POPPING AMARANTH SEEDS 919 and (3) the recovery of popped seeds due to inhomogeneity expansion ratio, were examined on the basis of the results is low. These demerits also lead to low nutritional value; of the previous study conducted in our laboratory. e.g., a decrease in the amino acid score due to the occur- Next, on the basis of experimental results obtained in rence of an amino-carbonyl reaction.[10] Therefore, a fluidi- our laboratory, we developed a prototype of a continuous zed bed system is favorable for popping amaranth seeds, processing system for commercial application. In addition, because the operating conditions of such a popping to determine the optimal operating conditions such as the method, such as the temperature or flow rate of hot air, feed speed, volume expansion ratio, and undersized yield can be controlled, thus resolving the above-mentioned ratio, a continuous-type experiment was carried out. In this problems.[11] experiment, the effects of gas temperature, flow rate, and Nelly and Jenny used a household corn popper to pop feed speed on the popping quality of the seeds, such as their amaranth seeds under certain operating conditions and expansion ratio and yield, were examined. assessed their quality in terms of their yield, expansion Furthermore, measuring the differential pressure in the volume, swelling power, water solubility, and protein test section was considered, as a method of monitoring content.[12] In addition, Marek et al. reported that drying the progress of seeds treatment therein. at high puffing temperature made seeds more rigid and less viscous.[13] POPPING AMARANTH SEEDS However, popping treatment of amaranth seeds has First, the effect of gas temperature on the popping qual- not been done under optimum operational conditions in ity of the seeds, such as their volume expansion ratio, was consideration for product quality, such as expansion ratio examined, and the mechanism of popping was studied. and yield. This is because only a few popping apparatus have been specially designed for popping amaranth seeds, Material and Experimental Method and control techniques to maintain the optimal operating Amaranthus hypochondriacus seeds having a size of conditions have not yet been established. approximately 1.0 mm were used (product of the UnitedDownloaded At: 04:58 9 January 2011 In the previous study, we examined the effects of heating States). A schematic of the experimental apparatus time, gas temperature, and initial moisture content of seeds (Shinkyo Sangyo Co., Ltd., Japan) is shown in Fig. 1. It on the volume expansion ratio during hot air and super- comprises the following: (1) an electric boiler, (2) a hot heated steam drying using a fluidized bed system specially air blower, (3) super heater 1, (4) a flow meter, (5) super designed in our laboratory. In addition, the mechanism heater 2, (6) a strainer section, (7) a removable cylindrical of popping was studied by conducting a numerical study test section (56.6 mm in diameter and 110 mm in length, using a simple calculation model of popping.[14] made of Pyrex glass) equipped with a 24-mesh screen, In the present study, the effects of gas temperature on and (8) an exhaust blower. We show the experimental the popping quality of seeds, such as their volume results using hot air for the drying medium here. FIG. 1. Experimental apparatus for popping amaranth seeds.
  4. 4. 920 INOUE ET AL. Sample seeds (1 g) were fed into the test section for carrying out the popping experiment. After heating, the cylindrical test section with the popped seeds was removed from the strainer section at an arbitrary time. The volume expansion ratio of the seeds, g (volume of popped seeds= volume of raw seeds), was evaluated from the apparent volume of the popped seeds measured using a 20-mL graduated cylinder. The popped seeds were observed using a high-speed camera, and their condition was monitored. We conducted experiments at least twice in some experi- mental conditions to confirm the reproducibility. Changes in Moisture Content and Volume Expansion Ratio Figure 2 shows the high-speed camera images obtained during the popping of the amaranth seeds. The shape of the seeds changed during the experiment, as shown in Figs. 2a–c. The breaking of the seed coat during the experi- ment is shown in Fig. 2b. Figures 3a and 3b show the effects of heating time on the moisture content and volume expansion ratio of the seeds, respectively. The initial moisture content of theDownloaded At: 04:58 9 January 2011 amaranth seeds was 0.13 kg=kg. The flow rate of gas in the test section was 1.6 m=s—slightly higher than the incipient fluidization velocity of raw amaranth seeds. The moisture content of the seeds dropped rapidly at a temperature above 200 C during the experiment, as shown in Fig. 3a; g increased because of the inherent popping, as shown in Fig. 3b. At 170 C, the moisture con- tent decreased slowly without an increase in g, indicating that the amaranth seeds dried without popping. As shown in Fig. 3b, popping occurred at 200 C for 5 s; only 10% of the seeds popped (determined by counting the number of popped seeds). Above 230 C, the seeds started popping rapidly (5 s), and all the seeds had popped within 15 s. FIG. 3. Effect of heating time on moisture content and volume expan- sion ratio (initial moisture content: 0.13 kg=kg). In addition, g at gas temperature above 260 C was higher than that at 230 C after heating for 15 s. This is because the internal pressure of seed increased drastically in a short time and the popping occurred more extremely Effect of Gas Temperature on Volume Expansion Ratio as the gas temperature increased. In the following experi- Figure 4 shows the effects of gas temperature on the ments, heating was carried out for 15 s. volume expansion ratio and quality of the popped seeds. The gas temperature was 170–320 C. The heating time was constant at 15 s. Figure 4a shows a seed that was incompletely popped after heating; its g was approximately 1.2 at 200 C. g at gas temperatures of 230 C–290 C (Figs. 4b–d) was higher than that at 200 C, and it reached 8.4 at 260 C, as shown in Fig. 3b; this implies that the seeds were successfully popped. A decrease in g and higher degree of browning occurred at gas temperature above 290 C. The degree of browning FIG. 2. High-speed camera images showing popping of amaranth seeds. above 320 C was higher than that at 290 C, as shown in
  5. 5. OPTIMAL CONDITIONS FOR POPPING AMARANTH SEEDS 921 FIG. 4. Images of amaranth seeds after treatment at various gas temperatures (initial moisture content: 0.13 kg=kg). Figs. 4d and 4e. These results suggest that the operating Continuous Processing System for Popping temperature of 290 C is inappropriate for carrying out Amaranth Seeds the popping experiment. The specifications of the continuous processing system Here, the effects of gas temperature on the popping are as follows: the popping process is continuous-type,Downloaded At: 04:58 9 January 2011 quality of amaranth seeds are summarized. The amaranth seeds are heated in a fluidized bed, exhaust gas is circulated seeds popped when their internal pressure exceeded the ten- to achieve high energy efficiency, maximum electric power sile strength of their coat as a result of water evaporation is less than 1500 W (100 V) for domestic use, and the size of occurring during heating. Further, their seed coat has a the system is as small as possible. very low permeability for steam generated during heating. This implies that the seeds should be heated quickly so that Experimental Method the internal pressure increases before the moisture in the A schematic of a prototype of the above-mentioned con- seeds evaporates completely. tinuous processing system is shown in Fig. 5. It comprises In particular, at low gas temperature, the seeds did not the following: (1) blower 3, (2) a heater, (3) a strainer sec- pop or they popped partially, because their internal pres- tion, (4) a cylindrical test section (55 mm in diameter and sure did not increase up to a sufficient level. On the other 220 mm in length, made of Pyrex glass) equipped with a hand, at very high gas temperature, the seeds popped 24-mesh screen, (5) a cyclone, (6) blower 4, (7) a feeder, incompletely because the tensile strength of their coat and (8) a paddle. reduced due to thermal denaturation. The effects of gas temperature, flow rate, and feed speed It is very important to optimize the operating conditions on the popping quality of the seeds, such as their volume such as the gas temperature, flow rate, and initial moisture expansion ratio and yield, were examined. For this experi- content during popping. Among these factors, gas tem- ment, we have arranged a configuration of continuous perature affects not only the heat flux in the seeds but also processing system in Fig. 5 to measure the flow rate using the tensile strength of the seed coat. Hence, the gas tem- a flow meter; we have used experimental apparatus in our perature should be optimized for enhancing the popping laboratory subsidiary as shown in Fig. 1. The valve (11 quality of amaranth seeds. in Fig. 1) and blower 3 (1 in Fig. 5) were connected and blower 4 (6 in Fig. 5) was removed. The experimental conditions are shown in Table 1. The DEVELOPMENT OF CONTINUOUS PROCESSING flow rate U (m=s) was estimated by using a flow meter (4 in SYSTEM Fig. 1) and by measuring the differential pressure in the On the basis of the results presented above, a prototype heater section (2 in Fig. 5). The gas temperature Tgas ( C) of a continuous processing system was developed for com- was measured using a thermocouple attached to the end mercial application. In addition, to determine the optimal of the strainer section. operating conditions such as the feed speed, volume expan- For the batch popping experiment, 3 g of sample was sion ratio, and undersized yield ratio, a continuous-type inserted from the top side of the test section, all at once. experiment was carried out. For the continuous popping experiment, the seeds were
  6. 6. 922 INOUE ET AL. TABLE 1 Experimental conditions for batch-type and continuous-type processing Operation Batch-type Continuous-Type Drying medium Hot Air Hot Air Gas temperature 180, 220, 260, 300 220, 260, 300, 340 Tgas ( C) Flow rate U (m=s) 3.5 2.8, 3.5, 4.1, 4.7 Sample quantity 3 100 m (g) Feed speed F (g=s) 0.18,0.33, 0.47, 0.58 the popped seeds was higher than that of the raw seeds. This implies that the flow rate of the gas and the length of the test section (220 mm) are important factors to be considered for successful separation of raw and popped seeds. The apparent volume of raw seeds and product—seeds collected after the popping process by cyclone and the remaining seeds in the test section—was measured with aDownloaded At: 04:58 9 January 2011 200-mL graduated cylinder and expressed as the expansion ratio g (the volume of seeds collected after the popping process=the volume of raw seeds). Next, the product was classified into two groups by size using a sieve (aperture size: 1.18 mm). The undesirable yield ratio was calculated from the undersized yield ratio / (mass of seeds having size less than 1.18 mm=mass of total yield). In this experiment, the initial moisture content of the seeds was 0.15 kg water=kg dry weight. Estimating Quantity of Seeds by Measuring Differential Pressure First, measuring the differential pressure in the test section was considered, as a method of monitoring the progress of seeds treatment therein. Figure 6 shows the relationship between the differential pressure and the quantity of seeds in the test section (gas FIG. 5. Prototype of continuous processing system for popping temperature: 20 C). The differential pressure in a fluidized amaranth seeds. bed is given by Eq. (1) when all the seeds are floating.[15] Under this condition, the gravitational force is equal to the frictional force. The values estimated using Eq. (1) inserted at different feed speeds F (g=s) using the feeder. are indicated by a dotted line in this figure. The total sample quantity for each experimental condition was 100 g. mg DPt ¼ ð1Þ In addition, the differential pressure DP (Pa) was At measured using a pressure gauge (9 in Fig. 5), and the temperature in the test section (20 mm above the entrance where m, g, and At are the quantity of seeds in the fluidized of the test section; 10 in Fig. 5) was measured to monitor bed, gravitational acceleration, and cross-sectional area of the condition of the seeds during the experiment. the fluidized bed, respectively. The popped and the raw seeds were separated in the test It can be observed in Fig. 6 that at m ¼ 1 g, DPt was section, and the popped seeds were carried by air flow from almost constant regardless of the flow rate (1.5–4.0 m=s). the test section to the cyclone, because the air resistance of In addition, DPt increased with the quantity of seeds
  7. 7. OPTIMAL CONDITIONS FOR POPPING AMARANTH SEEDS 923 value of DPt was almost equal to that at m ¼ 3 g, as shown in Fig. 6 (Tgas ¼ 20 C). This implies that the relationship between the quantity of seeds and differential pressure is independent of the gas temperature. At 220 C, DPt decreased after 10 s as the popped seeds were carried away from the test section. This time is referred to as the popping time tp (s) in this study. At high gas temperatures (260 and 300 C), the popping time reduced (6 and 4 s, respectively). Results of Continuous-Type Popping Experiment Variations in Differential Pressure Figure 8 show the variations in DPt in the test section FIG. 6. Relationship between quantity of seeds and differential pressure during the continuous-type experiment. in test section (gas temperature: 20 C). At 260 C and 0.18 g=s, when the gas temperature was the minimum in this figure, DPt increased rapidly for 10 s (3–5 g). The errors between the measured and the estimated and then continued to increase slowly until the end of the values of DPt were below 15% at U ¼ 3.5 m=s and m ¼ 1, 3, experiment (t ¼ 500 s), as shown in Fig. 8. At 300 C, and 5 g. These errors occurred because the seeds were 0.18 g=s, DPt remained constant (4–5 Pa) after 10 s. Under dispersed in the test section during the experiment and these conditions, more than 1–1.2 g of seeds was present some seeds were not floating at a certain moment. in the test section during the popping experiment, which was estimated from DPt calculated using Eq. (1).Downloaded At: 04:58 9 January 2011 Results of Batch-Type Popping Experiment At 300 C and 0.58 g=s, when the feed speed was the maxi- Next, batch-type experiments were carried out to study mum, DPt increased rapidly after 60 s as the quantity of seeds the basic characteristics of amaranth seeds popped using in the test section increased, and the seeds ceased to pop. this system. Under this condition, continuous operation could not be car- Figure 7 shows the effects of gas temperature on DPt ried out, because the feed speed was higher than the popping in the test section during a batch-type experiment. The capacity of the system. On the other hand, at 340 C and heating time required for the popping was decided by 0.58 g=s, continuous operation could be carried out. measuring DPt in the test section. For the batch-type Next, the limit of continuous operation and the pro- experiment, 3 g of sample seeds was fed into the test section duct quality, such as g and /, were estimated. Table 2 from the top, without using the feeder. the experimental results obtained under each operating It can be observed in Fig. 7 that at 180 C and 3.5 m=s, condition employed in this study. when the gas temperature was the minimum, DPt increased At 220 C, 0.18 g=s, and 3.5 m=s, when the gas for 3 s as the seeds were fed, and then it remained constant, temperature was the minimum, continuous operation indicating that popping never occurred. In addition, this could not be carried out successfully, because the seeds FIG. 7. Effect of gas temperature on differential pressure in test section FIG. 8. Differential pressure in test section during continuous-type (sample seeds quantity: 3 g, flow rate: 3.5 m=s). experiment (flow rate: 3.5 m=s).
  8. 8. 924 INOUE ET AL. TABLE 2 Mass and volume measurements of popped amaranth seeds Total seeds Under-sized yield Gas temp. Feed speed Flow rate U Volume V Mass m Expantion ratio g ratio (1.18 mm) Tgas ( C) F (g=s) (m=s) (ml) (g) (m3=m3) g (mass%) Ã 220 0.18 3.5 Ã 260 0.18 2.8 3.5 807 83.1 6.9 4 4.1 769 83.5 6.6 9 4.7 704 83.7 6.0 17 Ã 0.33 3.5 300 0.18 2.8 734 83.0 6.3 3 3.5 677 83.4 5.8 2 4.1 670 82.9 5.7 6 0.33 3.5 754 83.3 6.4 3 0.47 785 82.8 6.7 4 Ã 0.58 Ã 340 0.18 3.5Downloaded At: 04:58 9 January 2011 0.33 648 82.2 5.5 2 0.47 692 83.0 5.9 2 0.58 742 83.2 6.3 3 Raw seeds 117 100.0 1.0 100 Ã Outside the range of operating conditions. accumulated in the test section with time. At 260 C, as / increased rapidly. This is because not only the popped 0.18 g=s, and 3.5 m=s, continuous operation was carried seeds but also the raw seeds were carried away by air flow out successfully. However, at 260 C, 0.33 g=s, and due to increased air resistance at high flow rates. / at 3.5 m=s, the seeds accumulated in the test section with 300 C and 3.5 m=s was less than that at 260 C time and continuous operation could not be carried out. and 3.5 m=s because the popping time tp was shorter. At 300 C, continuous operation was carried out both at U ¼ 2.8–4.1 m=s and F ¼ 0.18 g=s and at U ¼ 3.5 m=s and F ¼ 0.33–0.47 g=s. At 340 C and 0.58 g=s, the maximum output was achieved. On the other hand, at 0.18 g=s, continuous opera- tion could not be carried out successfully, because the seeds were carbonized easily due to overheating. The optimal operating conditions for achieving opti- mum product quality, such as high volume expansion and undersized yield ratio, were then established using the values shown in Table 2. Effect of Flow Rate on Undersized Yield Ratio Figure 9 shows the effects of flow rate and gas temperature on g and /. At 260 C, 3.5 m=s, and 0.18 g=s, the maximum volume expansion ratio was realized in this continuous-type pop- FIG. 9. Effect of flow rate and gas temperature on volume expansion ping experiment (g ¼ 6.9). At U ¼ 4.1–4.7 m=s, g decreased ratio and undersized yield ratio (feed speed: 0.18 g=s).
  9. 9. OPTIMAL CONDITIONS FOR POPPING AMARANTH SEEDS 925 Figure 11 shows the relationship between the temperature of the fluidized bed and the quantity of seeds in the test section under the same conditions as those shown in Fig. 10. The quantity of seeds was estimated from the differen- tial pressure in the fluidized bed calculated using Eq. (1). In addition, because the seeds were dispersed in the test section during the experiment, the temperature of the flui- dized bed, Tt ( C), was assumed to vary between the temperature at the entrance of the test section (¼ Tgas) and the temperature within the test section measured using the thermocouple 20 mm above the entrance of the test section (10 in Fig. 5). FIG. 10. Effect of feed speed and gas temperature on volume expansion At 260 C and 0.18 g=s, the temperature of the fluidized ratio and undersized yield ratio (flow rate: 3.5 m=s). bed was the minimum, approximately 230 C, as shown in Fig. 11. Under these conditions, there was approximately 2.2 g of seeds present in the test section (at 500 s). At In addition, the value of undersized yield ratio (/ ¼ 2) was 300 C and 0.18 g=s, the temperature of the fluidized bed less or equal to that reported before.[9,12] was the minimum (285 C), and it remained constant during In the following experiments, the flow rate was held the experiment. At F ¼ 0.33–0.47 g=s, the temperature of constant at 3.5 m=s, and the undersized yield ratio was the fluidized bed decreased as the quantity of seeds in the the minimum. test section increased. In addition, at 340 C and 0.58 g=s, the temperature ofDownloaded At: 04:58 9 January 2011 Effect of Feed Speed on Volume Expansion Ratio the fluidized bed remained constant at 260 C, which was Figure 10 shows the effects of feed speed and gas less than that at 300 C and 0.18 g=s. This difference in temperature on g and /. the temperature of the fluidized bed may have strongly The maximum volume expansion ratio was realized affected the volume expansion ratio, as shown in Fig. 10; (g ¼ 6.9) at 260 C, 3.5 m=s, and 0.18 g=s, as shown in g at 340 C and 0.58 g=s was higher than that at 300 C Fig. 9. In addition, g at 300 C and 3.5 m=s was less than and 0.18 g=s. that at 260 C and 3.5 m=s, because the seeds were carboni- From these results, it was found that not only the gas zed easily due to overheating. Furthermore, at Tgas ¼ 300– temperature but also the feed speed affected the tempera- 340 C, g increased with the feed speed (0.47–0.58 g=s). ture of the fluidized bed. In addition, we could prevent Here, the reason why g was high at high feed speed and overheating of the seeds to increase the feed speed. In high gas temperature (300–340 C) is clarified. short, to achieve maximum output and a high volume expansion ratio, the feed speed should be increased with the gas temperature. These results indicated that we should consider the effect of feed speed on the product quality especially when using a small-sized test section for heating (low heating capacity of the heating medium). In addition, measuring and regulating the differential pressure in the test section are important to maintain the optimal operating conditions of the continuous processing system. This will constitute a topic of study for the future. CONCLUSIONS In this study, on the basis of experimental results obtained in our laboratory, we developed a prototype of a continuous processing system for commercial applica- tion. In addition, the effects of gas temperature, flow rate, and feed speed on the popping quality of seeds, such as their volume expansion ratio and yield, were examined. The results of a continuous-type popping experiment FIG. 11. Relationship between temperature of fluidized bed and quan- suggested that the undersized yield ratio increased with tity of seeds in test section (flow rate: 3.5 m=s). the flow rate, and it decreased at high gas temperature.
  10. 10. 926 INOUE ET AL. In addition, the results suggested that the feed speed 3. Rattanadecho, P.; Pakdee, W.; Stakulcharoen, J. Analysis of multi- should be increased with the gas temperature to achieve phase flow and heat transfer: Pressure buildup in an unsaturated porous slab exposed to hot gas. Drying Technology 2008, 26, 39–53. maximum output and a high volume expansion ratio. 4. Perre, P.; Moser, M.; Martin, M. Advances in transport phenomena Furthermore, the quantity of seeds was estimated by mea- during convective drying with superheated steam and moist air. Inter- suring the differential pressure in the test section during the national Journal of Heat and Mass Transfer 1993, 36 (11), 2725–2746. continuous-type popping experiment. 5. Asaeda, M.; Yamashita, Y. Effect of total pressure generated during various drying methods on drying rate. Preprint of 44th Annual Meeting of the Society of Chemical Engineers, Japan, 1979; 223–224 NOMENCLATURE (in Japanese). F Feed speed (g=s) 6. Iyota, H.; Imakama, H. Vapor Diffusion and Flow within Dried Zone mt Quantity of seeds in test section (g) during Falling Drying Rate Period of Non-Hygroscopic Porous Slab; DP Differential pressure (Pa) Society of Chemical Engineers: Japan, 2007 (in Japanese). DPt Differential pressure in fluidized bed (Pa) 7. National Academy Council. Amaranth: Modern Prospects for an Ancient Crop; National Academies Press: Washington, DC, 1984. Tgas Gas temperature ( C) 8. Williams, J.T.; Brenner, D. Grain amaranth. In Cereals and Tt Temperature of fluidized bed ( C) Pseudocereals; Williams, J.T., Ed.; Chapman and Hall: London, t Heating time (s) 1995; 129–186. U Flow rate (m=s) 9. Tovar, L.T.; Valdivia, M.A.; Brito, E. Popping amaranth grain, state X Dry basis moisture content (kg=kg) of the art. In Amaranth O. Paredes-Lopez, Ed.; Biology, Chemistry, and Technology; 1994; 143–154. Greek Letters 10. Pant, K.C. Effect of heat processing (popping) on protein nutritional quality of grain amaranth. Nutrition Reports International 1985, 32, g Expansion ratio (m3=m3) 1089–1099. / Undersized yield ratio (mass %) 11. Sikolya, L.; Lengyel, A.; Kalmar, I.; Gulyas, L. New machines for amaranth drying and popping. In Proceedings of the 15th Interna- Subscripts tional Drying Symposium, Budapest, Hungary, 2006; 1650–1654.Downloaded At: 04:58 9 January 2011 12. Nelly, L.; Jenny, R. Popping of amaranth grain (Amaranthus 0 Initial caudatus) and its effect on the functional, nutritional and sensory properties. Journal of the Science of Food and Agriculture 2002, 82, 797–805. REFERENCES 13. Marek, M.; Arkadius, R.; Henryk, K.; Piotr, Z.; Katarzyna, M. 1. Tatemoto, Y.; Manatari, Y.; Sakurai, K.; Noda, K.; Komutsu, N. Rheological behavior of hot-air-puffed amaranth seeds. International Drying characteristics of porous material in a fluidized bed of fluidiz- Journal of Food Properties 2006, 9, 195–203. ing particles with superheated steam. Journal of Chemical Engineering 14. Iyota, H.; Konishi, Y.; Inoue, T.; Yoshida, K.; Nishimura, N.; of Japan 2003, 36 (6), 655–662. Nomura, T. Popping of amaranth seeds in hot air and superheated 2. Johansson, A.; Fyhr, C.; Rusmuson, A. High temperature convective steam. Drying Technology 2005, 23, 1273–1287. drying of wood chips with air and superheated steam. International 15. Kunii, D.; Levensipiel, O. Fluidization Engineering; John Wiley Journal of Heat and Mass Transfer 1997, 40 (12), 2843–2858. Sons: 1967.

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