Storage Characteristics of Low Temperature Grain Warehouse using Ambient Cold Air in Winter

Transcription

1 Original Article J. of Biosystems Eng. 37(3): ( ) Journal of Biosystems Engineering eissn : pissn : Storage Characteristics of Low Temperature Grain Warehouse using Ambient Cold Air in Winter Xiao Feng Ning 1, He Li 2, Tae Hwan Kang 3, Chung Su Han 1 * 1 Dept. of Biosystems Engineering, Chungbuk National University, Chenog-ju, Korea, 2 Dept. of Mechatronics Engineering, Henan Agricultural University, Zheng-zhou, HeNan, China, 3 Dept. of Bio-Industrial Mechanic Engineering, Kong-Ju National University, Kong-ju, Korea Received: June 4 th, 2012; Revised: June 21 th, 2012; Accepted: June 29 th, 2012 Purpose: This study was conducted to investigate the storage and quality characteristics of brown rice under the low temperature warehouse conditions using ambient cold air in the winter. Methods: This new technique maintains rough rice warehouse temperature below 15 without cooling operation until the end of May. Four hundred tons of rough rice were stored in the low temperature grain warehouse, and were aerated from the top to the bottom using ambient cold air in February. The quality of rough rice was evaluated from February through October. Results: The results were as followings. Moisture contents of rough rice in the low temperature storage had decreased less than the ordinary temperature storage. Cracked rate of brown rice in the ordinary temperature storage and low temperature storage increased by 4~10.8% and 1.6~7.2%, respectively. The germination rate of rough rice under the ordinary and the low temperature warehouse decreased by 15.0~25.0% and 1.7~8.0%, respectively. The acid value of brown rice under the ordinary and the low temperature warehouse increased by 3.67~6.72 KOH mg/100g and 3.08~4.08 KOH mg/100g, respectively. Conclusions: The result indicates that low temperature storage using ambient winter air showed better maintaining germination of rice, less change of physiological activities and cracked kernel, and better maintaining of rice quality, comparing the ordinary temperature storage. Keywords: Low temperature storage, Moisture content, Germination rate, Cracked rate, Acid value Introduction The temperature and moisture content of rough rice affect the rice quality during storage. In Korea, most cultivated rough rice has been stored in an ordinary temperature grain warehouses. Li et al. (2006) suggested that the rough rice in an ordinary temperature storage lost its moisture content and increased cracked rice from April due to increasing of ambient temperature. In addition, the rice quality decreased rapidly through summer. Furthermore, according to Tariff Rate Quota, 10 percent of imported rice must have been sold for cooked rice in *Corresponding author: Chung-Su Han Tel: ; Fax: hansu@chungbuk.ac.kr retail groceries since Thus, it is imminent to develop the production systems and long term storage technology for high quality of rice. Kawamura et al. (1997, 2000) reported that the quality of rice stored below 0 C had no significant difference with newly harvested rice, and a temperature below 0 C minimized physiological activities in rice. Hence, a temperature below 0 C minimized the deterioration of rice quality during the storage. Lee et al. (2007) reported that low temperature storage bin using ambient cold air ventilation in winter maintained rough rice quality longer than the ordinary temperature storage. Furthermore, the activity degree of embryo of brown rice in the 15 C storage was higher than 35 C storage, and the whole rice ratio of white rice in the 15 C storage was higher than Copyright c 2012 by The Korean Society for Agricultural Machinery This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 35 C storage. In addition, the cooked rice used 15 C stored rice showed the higher glossy value, lower hardness and peak viscosity than those used 35 C stored rice (Choi et al., 2008). Previous research implied that low temperature grain warehouses is necessary to preserve rice quality. However, to build warehouse needs expensive initial cost and storage cost. In addition, many studies on grain low temperature storage using cooler have been carried out. However, limited attention has been given to the study of grain low temperature storage using natural ambient cold air in the winter. This study showed the comparisons of storage and quality characteristics between low temperature storage using ambient cold air in the winter and ordinary temperature storage. Furthermore, this study showed the data of storage characteristics of rough rice by storage periods. Materials and Methods Materials ChuCheong rice, harvested in ChungCheongBukDo GyoeSanGun, and was provided by Rice Processing Complex in GyoeSan SoSu for this study. The initial moisture contents of rough rice in the low and the ordinary temperature storage were ranged 13.53~13.94% and 13.55~14.33% respectively (All moisture contents are expressed on a wet basis unless otherwise noted). Experimental methods For the experiment, the ordinary temperature grain warehouse in GyeoSan SoSu Rice Processing Complex (330 m2) was remodeled into a low temperature grain warehouse using ambient cool air in the winter. 50 mm insulation panels(c-75*45*25*3.2+styrofoam) were installed on the ceiling and two coolers (15PS, SamWon, Korea) were installed respectively near the south wall and the north wall. In addition, 50 mm urethane was spread on the insulation panels to prevent the surface condensation. In order to prevent the grain lost and waste, which were caused by the reducing of air moisture in warehouse, a humidifier (KeoSan, Korea) was installed in warehouse. It can use the condensation water generated by cooler to increase the moisture of air. Four hundred tons of Chu Chenog rough rice was stored in the low temperature grain warehouse for 9 months from February to October. Figure 1. Internal temperature measurement locations in the low and the ordinary temperature grain warehouses. The rough rice in the low temperature storage was aerated from February 17 to March 20. Aeration from top to bottom of the low temperature grain warehouse was automatically carried out when the ambient temperature dropped to -10~-5 C. In addition, in order to ensure the best use of ambient cold air, we set different ambient temperature limit in a different month. The rough rice was sampled and tested for rice quality before and during storage. Rough rice samples were taken from the upper part (4.5 m), the center (1.5 m, 3 m) and the bottom part (0 m) from the storage warehouse floor. Moisture content, whiteness, crack ratio, and germination rate were determined to assess rice quality. Figure 1 shows the internal temperature measurement locations in the low and the ordinary temperature grain warehouses. Measurement Items The temperature of rough rice and storage warehouse The temperature of rough rice and storage warehouse for the low and the ordinary temperature grain warehouses were measured by a multi-stage temperature recorder (DA-100, YOKOGAWA, Japan) with K-type thermocouples (Ø5). The recorder was connected with a computer to record measurement results continuously. Portable temperature & relative humidity meter (TR-72U, T&D, Japan) was used to measure the relative humidity. Moisture content of rough rice Moisture content was measured based on wet-based moisture content by the Japanese Society of Agricultural Machinery standard (JSAM), rough rice(10±0.5 g) was placed in a forced-air drying oven (WFO600 ND, EYELA, Japan) at 135 C for 24 hours. Then measured moisture content (M135, %) converted into 105 C of standard 185

3 moisture content (M105, %), using the revised equation as follows (Yamasita, 1975). Rough Rice: M105 = (100-M135) Where, M105 : Standard moisture contents of rough rice at 105 C M105 : Measure moisture contents of rough rice at 135 C Cracked rate of brown rice Cracked rate among the fifty brown rice was determined by a visual exam using a grain scope (RC-50, Kett, Japan). Brown rice with light and heavy fissures was addressed as cracked brown rice. Total 250 brown rice from each sample were used to measure the cracked rate. Cracked rate was calculated by counting the number of cracked brown rice. Germination rate 100 rough rice were washed by tap water, and then put it in schale with 25 ml distilled water, and placed in a constant temperature and humidity chamber (TH-150L, JEIO TECH, Korea) at the temperature of 25 C and the relative humidity of 60%. Germination rate was calculated by counting the number of germinated grains within fourteen days (Lee et al., 2005; Kim et al., 2007). Hardness of brown rice The hardness of brown rice was measured by a hardness tester (KHT-20N, FUJIWAR A, Japan), and measurements of 20 samples were individually performed. Acid value of brown rice Content of fatty acid in rice was calculated by KOH/mg which was used to neutralize the free fatty acid in 100 g of ground sample. Twenty-five gram of ground brown rice was accurately weighed and put in a centrifuge bottle, and then 50 ml of benzene was added. The solution was shaken at 250 rpm for 30 min to extract lipids and then centrifuged for 30 min at 8000 rpm using a center of separator (Sorvall centrifuge, Germany). 25 ml of extracts was mixed with 25 ml phenolphthalein KOH solution was adjusted to ph 8.2, and blank test was taken with samples simultaneously. Acid value(fatty acid)= {(T-B)*8/(100-W)}*100, where T is titration of material (ml), B is blank test (AOCS, 1993), W is moisture content at 105 C. Results and Discussion Rough rice and grain warehouse temperature Figure 2 showed the changes of grain warehouse and rough rice temperature in the ordinary temperature grain warehouse along the storage periods. The ambient temperature affected the change of rough rice and grain warehouse temperature. The grain warehouse temperature increased up to 15 C, which is the standard temperature of low temperature storage, on April 5~10. The rough rice temperature also increased up to 15 C between May 2 and 7 days. Furthermore, the temperature of grain warehouse and rough rice showed the highest point in mid-august. Figure 2. The changes of internal temperature and rough rice in the ordinary temperature grain warehouse according to storage periods. 186

4 Ning et al. Storage Characteristics of Low Temperature Grain Warehouse using Ambient Cold Air in Winter Figure 3. The changes of internal temperature and rough rice in the low temperature grain warehouse according to storage periods. Figure 4. The change of moisture content in the ordinary and low temperature grain warehouse according storage periods. Figure 3 represented rough rice and grain warehouse temperature in the low temperature warehouse using ambient cool air in winter along the storage periods. The figure 3 showed that the grain warehouse temperature increased up to 15 C on May 3~8. That is, the low temperature grain warehouse maintained its internal temperature below 15 C longer by 30 days than the ordinary temperature storage. Rough rice temperature of 15 C was also consistently maintained without being affected by ambient temperature change in the low temperature grain warehouse. These results implied that ambient cold air system could be used for rice low temperature storage with low cost and high efficiency. Moisture content of rough rice Figure 4(a) showed the changes of moisture content of rough rice in the ordinary temperature grain warehouse. It showed that the initial moisture content of rough rice taken from the top, middle and bottom parts were ranged from to 13.94%. During storage, the moisture contents have decreased with range of 0.46~1.18% by May, however, from June through the end of October, moisture contents increased by approximately 0.11 to 0.81%. These results could be summarized that the rough rice absorbed the moisture from high humidity environment during the rainy season. Furthermore, the moisture content of rough rice decreased to the range of 13.06~ 13.44% by the end of October, and thus it decreased by 0.23~0.87% from the initial content. Moisture content change of rough rice in the low temperature warehouse using ambient cool air in winter was shown in figure 4(b). The changes were not significant by the end of May, however, since the end of June, it continued to increase until the end of August because of absorbing moisture by operating humidifier. After 9 months storage, the moisture content decreased up to 13.76~13.95%. This result showed that the moisture content loss of the low temperature warehouse rice was 187

5 less than that of the ordinary temperature warehouse. Cracked rate of brown rice Figure 5 showed the changes of cracked rate of brown rice in the ordinary and low temperature warehouses. Cracked rate of samples from the top, middle and bottom parts in the ordinary temperature warehouse increased with range of 4.0~10.8% after 9 months. This was resulted from internal stress of brown rice due to rise and fall of moisture content with the relative humidity changes. The cracked rate of brown rice samples from the low temperature warehouse increased relatively less by approximately 1.6~7.2% than the ordinary temperature storage. Germination rate of rough rice Figure 6(a) represented the changes of rough rice germination rates in the ordinary temperature warehouse. The initial germination rates were down from 94.0~ 99.3% to 78.0~84.3% after 9 months of storage, and decreased range of the germination rate was from 11.6 to 19.6%. The changes of germination rates of rough rice in the low temperature warehouse were shown in Figure 6(b). The germination rate changed from 96.6~100% at the beginning of storage to 94.3~98.0% after 9 months of storage. Its decreased range was relatively less than the germination rate from the ordinary temperature stored rice. Similar results were observed by Lee et al. (2007) for low temperature storage of rough rice. Hardness of brown rice Figure 7 showed the changes of hardness of brown rice in the ordinary and low temperature warehouses. Hardness of samples from the top, middle and bottom parts in the ordinary temperature warehouse increased with range of 0.14~0.71 kgf after 9 months storage. However, the hardness of samples from the low temperature (a) Ordinary temperature (b) Low temperature Figure 5. The changes of cracked rate of brown rice in the ordinary and low temperature warehouses according to storage periods. (a) Ordinary temperature (b) Low temperature Figure 6. The changes of rough rice germination rates in the ordinary and low temperature grain warehouse according to storage periods. 188

6 (a) Ordinary temperature (b) Low temperature Figure 7. The changes of brown rice hardness in the ordinary and low temperature grain warehouse according to storage periods. (a) Ordinary temperature (b) Low temperature Figure 8. The changes of brown rice acid value in the ordinary and low temperature grain warehouse according to storage period. warehouse decreased with the range of 0.03~0.68 kgf after 9 months storage. These results implied that the hardness of ordinary temperature warehouse rice was higher than the low temperature warehouse, resulting that the moisture content loss of the low temperature warehouse rice was less than the ordinary temperature warehouse. Acid value of brown rice Figure 8 showed the changes of acid value of brown rice in the ordinary and low temperature warehouses. It showed that the acid value of rice samples from the top, middle and bottom parts in the ordinary temperature warehouse were ranged 9.69~11.92 KOH mg/100g after 8 months storage. The acid value increased with range of 1.90~4.18 KOH mg/100g. However, the acid value of samples from the low temperature warehouse were 8.34~9.83 KOH mg/100g, which were lower than that in the ordinary temperature. This result implied that the low temperature storage method could prevent deterioration of rice. The increase in the acid value with increasing storage time was also observed by Noh (2009) and Han et al. (2010) for grain storage. These results are probably due to the changes of ambient temperature and humidity led to grain fat-splitting and acid value increase. Summary and Conclusions The purpose of this study was to investigate the differences of storage characteristics and rice quality between low temperature storage using ambient cold air in the winter and ordinary temperature storage. The rice qualities were analyzed based on factors such as moisture content, cracked rate, germination rate, hardness and acid value. The result indicates that low temperature 189

7 storage method showed better rice quality than the ordinary temperature storage method. Conclusions obtained from this research can be summarized as follows: (1) The temperature of low temperature grain warehouse increased up to 15 C, which is low temperature storage standard, on May 3, and then it maintained longer by 30 days than the ordinary temperature grain warehouse. (2) The moisture content of rough rice decreased roughly by 0.23~0.87% in the ordinary temperature grain warehouse, and the low temperature grain warehouse had relatively less change on the moisture contents. (3) Cracked rate of brown rice in the ordinary temperature storage increased approximately 4.0~10.8%. In the low temperature storage, cracked rate showed the range of 1.6~7.2%, which was less by 2.4~3.6% than ordinary stored rice. (4) Germination rates in the ordinary and the low temperature warehouse decreased by 11.6~19.6% and 0.3~3.3% respectively. These results showed the low temperature storage had been keeping germination rate better than the ordinary temperature storage. (5) Hardness of brown rice in the ordinary temperature storage increased with range of 0.14~0.71 kgf after 9 months storage, whereas, in the low temperature warehouse hardness of brown rice decreased with range of 0.03~0.68 kgf after 9 months storage. (6) The acid values of samples from the low temperature warehouse showed the range of 8.34~9.83 KOH mg/100g, which were lower than that in the ordinary temperature. Conflict of Interest No potential conflict of interest relevant to this article was reported Acknowledgement We appreciate the Korea Chungbuk National University for financial support and encouraging us to attempt this study in References AOCS Official methods and recommended practices of the American oil chemists society, Cd 3d-63. 4th edition Choi, Y. H., S. L. Kim, E. G. Jeong, J. Song, J. T. Kim, J. H. Kim and C. G. Lee Effects of Low-Temperature Storage of Brown Rice on Rice and Cooked Rice Quality. Korean Journal of Crop Science 53(2): (In Korean) Han, C. S., X. F. Ning, J. W. Park and H. Li Development of Low Temperature Storage Technique for High-Quality Maintenance of Rough Rice Using Cold Air in Winter and Space Cooling System in the Southland(III). Research Report. (In Korean) Kawamura, S., M. Natsuga, S. Kouno and K. Itoh Super-low Temperature Storage for Preserving Rice Quality. In Proc. Joint International Conference on Agricultural Engineering & Technology, Dhaka, Bangladesh, Volume III, Kawamura, S., K. Takekura, T. Ogawa and K. Itoh Long-Term Storage of Rough Rice at Temperatures below Ice Point. ASAE Paper No St. Joseph, Mich.: ASAE. Kim, K. Y., G. M. Lee, K. I. Noh, K. Y. Ha, J. Y. Son, B. K. Kim, J. K. Ko and C. K. Kim Varietal Difference of Germination, Fat acidity, and Lipoxygenase Activity of Rice Grain Stored at High Temperature. Korean J. Crop Sci 52(1): (In Korean) Lee, J. S., C. S. Han, T. M. Ham and K. S. Yon Low temperature storage of rough rice using cold-air in winter(i). Journal of Biosystems Engineering 30(3): (In Korean) Lee, J. S., H. K. Hong., H. Li., J. S. Park., T. M. Ham and C. S. Han Low temperature storage of rough rice using cold-air in winter(ii)-low Temperature Storage Characteristics of Rough Rice Using a Cooling System in the Top of a Bin-. Journal of Biosystems Engineering 32(1): (In Korean) Li, H., C. S. Han., S. C. Cho., H. J. Kim., J. M. Choi., Y. C. Kim., D. H. Ahn and J. S. Lee Study on the Conversion of Ordinary Temperature Storage Warehouse into Low Temperature Storage Systems(I)-Storage Characteristics of Rough Rice by Ordinary Temperature Storage Warehouse-. Proceedings of the KSAM 2006 Winter conference 11(1): (In Korean) 190

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