Biosci. Biotechnol. Biochem., 68 (10), 2186–2189, 2004 Note Effect of Moisture Content on the Expansion Volume of Popped Seeds by Hot Air and Superheated Steam Using a Fluidized Bed System

y Yotaro KONISHI,1; Hiroyuki IYOTA,2 Kaori YOSHIDA,1 Junko MORITANI,1 Tamotsu INOUE,2 Nobuya NISHIMURA,2 and Tomohiro NOMURA2

1Department of Food Science and Nutrition, Graduate School of Human Life Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan 2Department of Mechanical and Physical Engineering, Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan

Received May 28, 2004; Accepted July 17, 2004

The effect of the initial moisture content (X0)of nation by overheating. These demerits can also decrease amaranth seeds on expansion volume after popping was the nutritional value, as in a loss of available due examined in hot air and superheated steam (SHS), using to the amino-carbonyl reaction,5–7) or a loss of linolenic a fluidized bed system (FBS). The moisturized seeds acid.8) An improved procedure using hot air, called the were prepared under various vapor pressures due to fluidized bed system (FBS), has been developed recent- various saturated salt solutions. In hot air, the max- ly. The operating conditions in the popping procedure, imum expansion volume was shown by seeds having X0 such as temperature or the flow rate of hot air, can be of 0.16 at 260 C for 15 sec, reaching 8.7-fold of the pre- controlled, minimizing the above-mentioned problems. popped seeds. Heating by SHS decreased the volume As for heat media, a drying method using superheated slightly. Thus, popping of amaranth seeds is influenced steam (SHS) has recently been applied to food process- not only by the moisture content of the seeds, but also by ing and cooking. Iyota et al.9) observed that starch moisture in the heat media. gelatinization in slices occurs more rapidly in an SHS stream at 260 C than in hot air, because steam Key words: Amaranthus hypochondriacus L; popping; condenses on the surface of the slices and therefore heat expansion volume; fluidized bed system; transfers much faster. However, SHS has not so far been superheated steam applied in a popping test. In this study, we examined the effects of temperature Amaranth (Amaranthus spp) is one of the most and exposure time to hot air and SHS on the expansion promising food crops, with high and volume of popped amaranth seeds, using an FBS on a contents in the seeds.1,2) Like , the seeds of laboratory scale. We also examined the effect of the amaranth can be popped when heated.3,4) Popped moisture content of the seeds on popping. amaranth seeds are soft in texture and taste like a Amaranthus hypochondriacus K-343 seeds (a product nutty-flavored popcorn. Thus popping is a simple of the U.S.A.), a generous gift from Shinkyo Sangyo processing of amaranth seeds for food uses. A traditional Co., Ltd., (Tabuse, Yamaguchi Prefecture, Japan), were confection of popped amaranth seeds with molasses or used. They had been stored in a dessicator at 4 C. To syrup is known as alegrı´a in Mexico or laddoos in prepare amaranth seeds with different moisture contents, India.1) seeds were placed under various vapor pressures due to A criterion of the quality of a given batch of amaranth various saturated salt solutions at 15 C for 2 weeks. The seeds is its popping ability. As for processing the seeds initial moisture contents (X0) of these seeds were and their texture, the expansion volume and the yield determined on a dry basis (kg water/kg dry weight). after popping are important factors. They depend on A schematic diagram of the experimental apparatus is popping procedures, the variety of amaranth, and the shown in Fig. 1. It is comprised of a blower (for hot air), moisture content of the seeds.3) As for the popping an electronic boiler (for SHS), super heaters, a flow procedure, heating on a hotplate has traditionally been meter, a test section (5.66 cm in diameter, 11 cm long) done, although there are some problems with the equipped with a 24-mesh screen, and an exhaust blower. product: low recovery of popped seeds due to heat For the popping tests, sample seeds (1 g) were inserted efficiency and inhomogeneity, and browning or carbo- from a sample holder to the test section before heated

y To whom correspondence should be addressed. Fax: +81-6-6605-2813; E-mail: [email protected] Abbreviations: FBS, fluidized bed system; SHS, superheated steam; X0, the initial moisture content (kg/kg dry weight) Popping of Amaranth Seeds 2187

Fig. 1. Diagram of a Fluidized Bed System for Popping Amaranth Seeds. Hot air and superheated steam (SHS) were produced with a blower and a boiler, respectively. These fluids were further heated under a thermo- controller, and ran at a flow rate of 1.64 m/sec into a test section via a diffuser. Temperature was measured with a thermocouple probe attached to the test section.

fluids were blown at a flow rate of 1.64 m/sec. The apparent bulk volume of the popped seeds was measured with a 20 ml-graduated cylinder and was expressed as the expansion ratio (the volume of popped seeds/the volume of raw seeds). As shown in Fig. 2A, the sample seeds (X0 of 0.15) were fully popped at 230 C or higher temperatures for 10–30 sec in hot air. No popping occurred at 170 Cor 200 C. Therefore, in the subsequent experiments, the popping test was done for 15 sec. Figure 2B shows the expansion ratio of the popped seeds at various temper- atures in hot air and SHS. In hot air, maximum expansion reached 8.7-fold at 260 C. It was found that at temperatures above 290 C the expansion ratio decreased, with browning of products. SHS decreased the expansion ratio by 12–20% compared to hot air heating (Fig. 2B). In SEM analysis (see the inserted photo in Fig. 2A), most of the popped amaranth seeds showed the two soap-bubble configuration3) or the butterfly form.10) The embryonic tissue, which surrounds the starchy perisperm Fig. 2. Effect of Heating Time (A) and Temperature (B) on the in amaranth seeds, mostly remained even after popping. Expansion Ratio of Popped Amaranth Seeds in Hot Air and SHS. 3) Similar observations have been reported by Tovar et al. In this experiment, amaranth seeds with an X0 of 0.15 were used. Figure 3 shows the effect of the initial moisture The expansion ratio was calculated as the volume after popping/the content of amaranth seeds on the expansion ratio after volume before popping. The inserted photo is an amaranth seed popping in hot air and SHS. In hot air, the maximum popped at 260 C in hot air. The sample was coated with Pt–Au and analyzed with a Hitachi S-3500N scanning electron microscope. Em, expansion ratio was shown by KI-treated seeds having embryo; Ps, starchy perisperm. The scale bar is 1 mm. an X0 of 0.16, similar to that of raw seeds having an X0 of 0.15 (Fig. 2). Other investigators have reported that the highest expansion volumes were shown by amaranth heating again decreased the volume slightly (Fig. 3). seeds having moisture contents of 12–14 g/100 g in wet The mechanism of popping of amaranth seeds has 10,11) 3,4) weight, which corresponds to X0 of 0.14–0.16. SHS been proposed previously. It is similar to the popping 2188 Y. KONISHI et al.

seeds moisturized beyond X0 of 0.16, while the distribution of water is unknown, the water might act as a plasticizer of the pericarp or seed coat, as suggested in popcorn,14) decreasing the inner pressure to be held. Indeed, we have observed that the higher X0 the seeds had, the softer the seeds became by measuring the yield load with a rheometer (Iyota et al., manuscript in preparation). As for heat media, SHS does not appear to be suitable for popping (Figs. 2 and 3). One of the reasons is perhaps steam condensation on the surface of the seeds, due to which the seed pericarp or coat as a barrier to popping is softer or weaker than in hot air, decreasing the inner pressure to be held, although more information is needed to explain this phenomenon. Fig. 3. Effect of Initial Moisture Content on the Expansion Ratio of Popped Amaranth Seeds. In conclusion, we found optimum conditions for To vary the X0 of the amaranth seeds, the seeds and a small vessel popping amaranth seeds using an FBS. Application of containing water or a saturated solution of various salts were put into the system might be useful for developing amaranth for desiccators and held at 15 C for 2 weeks. The eight salts selected food uses. The nutritive values of the popped amaranth were: LiBr, X0 of 0.07; MgCl2, 0.11; K2CO3, 0.12; KI, 0.16; NaCl, seeds using our system are under investigation. 0.18; KCl, 0.22; K2SO4, 0.32; and water, 0.38. As a control, raw amaranth seeds were kept under the same conditions, which gave X0 of 0.13. Vacuum-dried seeds were also prepared (X0 of 0.03). Thus References ten kinds of samples were prepared for the popping test. The data is shown as means SD of three experiments. 1) National Academy Council, Amaranth: Modern Pros- pects for an Ancient Crop. National Academy Press, of popcorn.12–14) When amaranth seeds are heated, the Washington, D.C. (1984). heat causes vaporization of the water contained in the 2) Williams, J. T., and Brenner, D., amaranth starch matrix. The steam produced fills the pores of the (Amaranthus species). In ‘‘ and ’’, starch granules, increasing the temperature and pressure. ed. Williams, J. T., Chapman and Hall, London, pp. 129– This phenomenon gelatinizes the starch granules and 186 (1995). 3) Tovar, L. R., Valdivia, M. A., and Brito, E., Popping ruptures the pericarp and seed coat, which acts like a amaranth grain, state of the art. In ‘‘Amaranth: Biology, pressure vessel. As a result, the perisperm is transformed Chemistry, and Technology’’, ed. Paredes-Lo´pez, O., into a bubbly matrix, yielding a spongy structure. In CRC Press, Boca Raton, pp. 143–154 (1994). amaranth seeds, densely packed occurring in 4) Berghofer, E., and Schoenlechner, R., Grain amaranth. the embryo have also been considered to act as a barrier In ‘‘Pseudocereals and Less Common Cereals’’, eds. because the embryo surrounds the starchy perisperm, in Belton, P. S., and Taylor, J. R. N., Springer-Verlag, contrast to popcorn. The proteins denatured by steam Berlin, pp. 219–260 (2002). make it possible for high pressure to develop within the 5) Pant, K. C., Effect of heat processing (popping) on seed.3,4) protein nutritional quality of grain amaranth. Nutr. Rep. In this study, we observed that popping amaranth Int., 32, 1089–1098 (1985). seeds in hot air required temperatures above 230 C for 6) Bressani, R., Kalinowski, L. S., Ortiz, M. A., and Elias, L. R., Nutritional evaluation of roasted, flaked and 15 sec, in agreement with previous reports.3,7) The popped A. caudatus. Arch. Latinoam. Nutr., 37, 525–531 decrease in popping volume at temperatures lower and (1987). higher than 260 C (Fig. 2B) might be due to insufficient 7) Tovar, L. R., Brito, E., Takahashi, T., Miyazawa, T., inner pressure within the seeds and to collapse of the Soriano, J., and Fujimoto, K., Dry heat popping of pericarp as a barrier at high temperatures, respectively. amaranth seed might damage some of its essential amino We also observed that a maximum expansion volume acids. Plant Food Hum. Nutr., 39, 299–309 (1989). of the popped seeds was in response not only to the 8) Singhal, R. S., and Kulkarni, P. R., Effect of puffing on moisture content of the seeds but also to moisture oil characteristics of amaranth (rajgeera) seeds. JAOCS, present in the heat media. 67, 952–954 (1990). 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