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Variations of Konjac glucomannan (KGM) from Amorphophallus konjac and its refined powder in China
Food Hydrocolloids 18 (2004) 167–170 www.elsevier.com/locate/foodhyd
Short Communication
Variations of Konjac glucomannan (KGM) from Amorphophallus konjac and its refined powder in China Weixuan Fanga,b,*, Pengwu Wua,c a
Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 73 Guanshui Road, Guiyang 550002, People’s Republic of China b The Mineral and Geological Exploration Centre of Nonferrous metals, No. 12B Fuxing Road, Fuxingmenwai, Beijing 100814, People’s Republic of China c The Institute of Geophysical and Geochemical Exploration, CNNC, 5 Shuiwenxiang, Xi’an 710068, People’s Republic of China Received 27 October 2002; revised 16 December 2002; accepted 21 February 2003
Abstract Konjac glucomannan (KGM) is a water-soluble dietary fiber extracted from tubers of Amorphophallus konjac native to China. It has a low caloric content and is a soluble dietary fiber, used in foods and medicine ingredients. This paper reports changes of KGM from Amorphophallus konjac native in the southern part of China to KGM obtained in transplanting trials in the northern part of China. Fresh raw rhizoid-tuber of Amorphophallus konjac contains KGM of 8.03– 12.43%. Its refined powder contains KGM ranging from 71.6 to 51.3%, whereas superclass purified powder extracted from tubers of Amorphophallus konjac contains more than 90% KGM, with a maximum value up to 96.9%. The KGM contents in tubers of transplanted Amorphophallus konjac in the northern temperate zone in middle Shaanxi Province in this study range from 27.65 to 47.59%, all of which are less than a mean value of these (54.39%) in the original tuber. It may be proposed that transplanting Amorphophallus konjac from its native land in the subtropical and tropical zone to the northern temperate zone in the northern part of China would be feasible. q 2003 Elsevier Ltd. All rights reserved. Keywords: Konjac glucomannan; Amorphophallus konjac; Fresh raw rhizoid-tuber; Refined powder; Superclass purified powder
1. Introduction Konjac glucomannan (KGM) is extracted from the tuber of Amorphophallus konjac native to China. Primary components of the tuber mainly contain KGM. KGM is a high molecular weight polysaccharide consisting primarily of mannose and glucose sugars and is a source of soluble dietary fiber. KGM received much attention recently (Case & Hamann, 1994; Nishinari, Williams, & Phillip, 1992; Nishinari & Yoshimura, 1999; Shinsaku, Shigetomo, Naruhiro, & Yoshinori, 2002; Wu et al., 1997). KGM is beneficial to the health of human beings and its ability to cure some diseases is well documented (Huang, Zhang, & Peng, 1990; Vorster, Lotter, & Odendaal, 1988; Vuksan, Jenkins, & Spadafora, 1999; Walsh, Yaghoubian, * Corresponding author. Address: Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 73 Guanshui Road, Guiyang 550002, People’s Republic of China. E-mail address: [email protected] (W. Fang). 0268-005X/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-005X(03)00044-4
& Behforooz, 1984; Wu & Peng, 1997; Key, 1973; Bian cardi & Palmiero, 1989; Mao & Gu, 1998; Wei & Ma, 1998; James & Follett, 2000). First of all, it can delay stomach emptying when taken as an edible Amorphophallus konjacbased food. It may lead to a more gradual absorption of dietary sugar, which can reduce the elevation of blood sugar levels that is typical after a meal. According to preliminary (Huang et al., 1990) and controlled trials (Vorster et al., 1988; Vuksan et al., 1999), it has been found that after-meal blood sugar levels are lower in patients with diabetes given glucomannan in their food, and overall diabetic control is improved with glucomannan-enriched diets. Secondly, KGM is high in dietary fibre which is essential for human health. Thirdly, like other soluble fibres, it can bind to bile acids in the gut and carry them out of the body in the faeces, which requires the body to convert more cholesterol into bile acids (Wu & Peng, 1997). Finally, it may help weight loss by filling the stomach and making a person feel full. Walsh et al. (1984) reported weight loss averaging 5.5
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pounds in adults when one gram of glucomannan was taken with a cup of water one hour before each meal for 8 weeks based on a double-blind study. No more than three species of edible plant contain KGM up to now, and Amorphophallus konjac is one of them (He, 2001). Refined powder, purified from the tuber of Amorphophallus konjac, contains significant amounts of KGM ranging from 50 to 98% (Hu, Li, Long, & Yi, 1998; Qiu, Tang, Lu, & Wu, 2000; Wang, Wu, & Li, 1998; Wu et al., 1997; Zhang, Wu, & Zhang, 1998). However, Variations of KGM in Amorphophallus konjac and its refined products have not been systematically studied. With original tubers of Amorphophallus konjac derived from the southern subtropical zone in southern Shaanxi Province Fang, Wu and Zuo (1996) firstly reported trace element contents of Amorphophallus konjac from results of a transplanting experiment in the northern temperate zone in Xi’an City, Shaanxi Province. It has proved that Amorphophallus konjac can be transplanted in the northern temperate zone in China including middle-northern part of Shaanxi and Liaoning Province as well as the arid zone between Yulin in northern Shaanxi and the southern part of Mongolia (Fang et al., 1996; Liu, Lan, Liu, & Qian, 1998a; Liu, Zhang, & Zhang, 1998b; Zhang & Wang, 1998a,b; Zhang et al., 1998). This paper reports on the variational behaviour of KGM grown in various parts of China.
2. Materials and methods With original tubers of Amorphophallus konjac sampled from the southern subtropical zone in Ziyang, Pingli, Langao, and Ankang Counties of southern Shaanxi Province, Amorphophallus konjac had been transplanted northward in Ganjiazhai village of Xi’an city, Yehu area of Lantian County, Weiqu area of Chang’an County, the middle part of Shaanxi Province since 1991. Samples of transplanted Amorphophallus konjac were collected from these cultivating areas. However, original tubers of Amorphophallus konjac were sampled from the northern margin of the southern subtropical zone in Ziyang County of southern Shaanxi Province in order to investigate differences between the original tubers and the tubers of the northward transplanting trial. Firstly, muddy materials on selected raw rhizoid-tubers of Amorphophallus konjac were washed with water, and their skin and small roots were cut off. Secondly, rhizoid-tubers of Amorphophallus konjac were sliced, and their sprouts were removed. Thirdly, their slices were heated in a drying apparatus to remove all moisture from them, and then their dried slices were put in grinding machine and were crushed to less than 0.125 mm in size. KGM in samples was analysed by the Forestry Science Institute of Shaanxi Province. A method for determination of KGM in Konjac powder is reported by Wang et al. (1998). 0.15 g of powdered sample were taken and put in
a 150 ml beaker. In order to separate free sugar from it, the sample was purified by 85% ethanol under continuous agitation with a stirrer, and then it was filtered and heated to remove the ethanol. The sample was dissolved in purified water in a 150 ml beaker at 35 8C under continuous agitation with a stirrer for 12 h. The digested solution was centrifuged for 20 min at 4000 rpm. The purified KGM solution was heated and digested for 1.5 h with boiling water, and then cooled. 0.5 ml 6 M NaOH was added and the solution was analysed by spectrophotometric analysis using a 752-Mode spectrophotometer made in Shanghai.
3. Results and discussion 3.1. Konjac glucomannan contents in raw fresh Amorphophallus konjac According to the preliminary trial reported by Zhang et al. (1998), fresh raw rhizoid-tuber of Amorphophallus konjac transplanted in the northern temperate zone in the northern part of China contains KGM from 8.03 to 8.40%, with a mean value of 8.15%, which is slight by lower than in their original tuber (8.53% KGM) derived from northern margin of the southern subtropical zone in Langao County of southern Shaanxi Province in the southern part of China. It is half as much as those (12.43% KGM) in the fresh raw rhizoid-tuber from the southern part of Shaanxi Province documented by Guo, Qiu, and Li (1996). 3.2. Variations of Konjac glucomannan with time Concentrations of KGM in raw rhizoid-tuber of Amorphophallus konjac increase with growing time (Zhang et al., 1998, Fig. 1). However, a dried sliced-sample only contains 17.78% KGM after it was stored in the laboratory for many years. KGM content in rhizoid-tubers of Amorphophallus
Fig. 1. Amounts of KGM in raw rhizoid-tuber of Amorphophallus konjac in different months (Reference: Zhang et al., 1998).
W. Fang, P. Wu / Food Hydrocolloids 18 (2004) 167–170
169
Table 1 Konjac glucomannan contents from introduction trial of Amorphophallus konjac Zone
Dried sample
Location
H2O%
KGM%
Southern part of Shaanxi
PV18 PV19 PV23 Mean
Hongcun of Ziyang County Ziyanggou of Ziyang County Haoping of Ziyang County
4.984 4.817 6.018 5.273
44.72 57.08 61.37 54.39
Middle part of Shaanxi
PV45 PV46 PV47 PV50 PV51 PV52 PV53 PV56 PV58 Mean
Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Yehu of Lantian County Weiqu of Chang’an County
5.104 5.506 7.027 5.7 6.633 4.672 6.564 7.151 4.19 5.84
47.06 41.79 42.15 47.59 44.74 43.38 27.65 35.7 47.14 37.47
konjac decreases on storage and when the rhizoid-tubers of Amorphophallus konjac germinate in the Spring season (Jia, 1984). 3.3. Konjac glucomannan contents from transplanting trial of Amorphophallus konjac As listed in Table 1 and shown in Fig. 2, the KGM contents in their original tubers derived from the northern margin of the southern subtropical zone in Ziyang County of southern Shaanxi Province range from 44.72 to 61.37%, with a mean value of 54.39%. On the other hand, H2O contents in their dried sample are from 4.817 to 6.018%, with a mean value of 5.273%. Generally speaking, the KGM contents in their transplanting tubers in the northern temperate zone in northern Shaanxi Province in this study range from 27.65 to 47.59%, all of which are less than the mean value (54.39%) in their original tubers. However, the mean content of KGM in the transplanted tubers accounts for almost 69% of those in their original tubers. It is indicated that KGM contents in the transplanted tubers may be lowered after it is cultivated in northern Shaanxi Province. This may be due to alteration of the ecological environment for Amorphophallus konjac, which leads to lower productivity in KGM. Water contents in their dried sample of both are almost the same.
powder can be productively extracted from their original tubers since the mean value (54.39%) is higher than the lowest content of KGM in the refined powder. In spite of this, KGM contents in the transplanted tubers (as listed in Table 1) indicate that the refined powder still can be extracted from the transplanted tubers of Amorphophallus konjac, although they contain KGM from 27.65 to 47.59%. It may imply that a development project concerning Amorphophallus konjac transplantation from its native land in the subtropical and tropical zone northward to the northern temperate zone in the northern part of China would be feasible. If KGM contents are higher in rhizoid-tubers of Amorphophallus konjac or in its refined powder, they have more economic value in food manufacture, industrial utility, and medicinal use. This is why refined powder of Amorphophallus konjac is more in demand. Even though
3.4. Konjac glucomannan contents in refined powder extracted from tubers of Amorphophallus konjac As presented in Fig. 2, superclass purified powder extracted from tubers of Amorphophallus konjac contains more than 90% KGM, with a maximum value up to 96.9%. Nevertheless, its refined powder contains KGM ranging from 71.6 to 51.3%. Variations of KGM in the original tubers as listed in Table 1 indicate that the refined
Fig. 2. Variations of KGM contents in different class of products extracted from rhizoid-tuber of Amorphophallus konjac and transplanting tuber. Reference: superclass from Hu et al. (1998), Qiu et al. (2000) and Wu et al. (1997). Refined powder from Hu et al. (1998) and Wang et al. (1998). Original and transplanting tuber from this study.
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KGM contents in their tubers are lower than those in its original species, superclass purified powder of Amorphophallus konjac can be extracted from rhizoid-tuber of Amorphophallus konjac by an air separator (He, 2001) or by chemical separation such as maleic anhydride (Qiu et al., 2000).
Acknowledgements Chinese National Nonferrous Metal Industry Corporation (Grants No. CNNC95-D-27), Chinese State Key Project on Fundamental Research Planning (Grants No. 2001CB409805), and Visiting Scholar Fund of LODG of Institute of Geochemistry, Chinese Academy of Sciences, jointly financed this study. The authors express their special thanks due to both referees for improving the manuscript.
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Liu, Y. J., Lan, D. M., Liu, Y. F., & Qian, Z. (1998a). Preliminary trial on northward-migration of Amorphophallus rivieri. Inner Mongolia Forestry Science and Technology, Suppl, 36–38. in Chinese. Liu, P. Y., Zhang, S. L., & Zhang, X. G. (1998b). Research and utilization of Amorphophallus konjac K. Koch in China. Acta Botanica Yunnanica, Suppl. X, 48–61. Mao, C. P., & Gu, Z. L. (1998). Advances in Amorphophallus konjac research. Chinese Wild Plant Resource, 17(4), 15 –19. in Chinese. Nishinari, K., Williams, P. A., & Phillip, G. O. (1992). Review of the physico-chemical characteristics and properties of Konjac glucomannan. Food Hydrocolloids, 6, 199–222. Nishinari, K., & Yoshimura, M. (1999). Dynamic viscoelastic study on the gelation of Konjac glucomannan with different molecular weights. Food Hydrocolloids, 13, 227–233. Qiu, S. Y., Tang, Q. L., Lu, H. M., & Wu, X. Y. (2000). Study on purified and denatured Konjac. Journal of Guizhou University of Technology (Natural Science Edition), 29(3), 75–78. in Chinese with English abstract. Shinsaku, K., Shigetomo, T., Naruhiro, H., & Yoshinori, T. (2002). Preparation and rheological characterization of carboxymethyl Konjac glucomannan. Food Hydrocolloids, 16(4), 289 –294. Vorster, H. H., Lotter, A. P., & Odendaal, I. (1988). Benefits from supplementation of the current recommended diabetic diet with gel fibre. International Clinical Nutrition Review, 8, 140 –146. Vuksan, V., Jenkins, D. J., & Spadafora, P. (1999). Konjac-mannan (glucomannan) improves glycemia and other associated risk factors for coronary heart disease in type 2 diabetes. A randomized controlled metabolic trial. Diabetes Care, 22, 913 –919. Walsh, D. E., Yaghoubian, V., & Behforooz, A. (1984). Effect of glucomannan on obese patients: A clinical study. International Journal of Obesity, 8, 289–293. Wang, Z. L., Wu, W. X., & Li, K. Y. (1998). Research on determination of Konjac glucomannan (KGM) in Konjac refined powder. Food Science, 19(3), 56 –58. in Chinese with English abstract. Wei, Q., & Ma, X. H. (1998). Researches on the application and utilization of Amorphophallus konjac. Journal of Northwest Forestry College, 13(3), 62 –67. Wu, W. X., Li, K. Y., Zhang, Z. L., Wang, Z. L., Ding, D. N., Jin, J. Q., & Li, Y. L. (1997). Study on the chemical constitution of Konjac mannan. Chemistry and Industry of Forest Products, 17(2), 69–72. in Chinese with English abstract. Wu, J., & Peng, S. S. (1997). Comparison of hypolipidemic effect of refined Konjac meal with several common dietary fibers and their mechanisms of action. Biomedical and Environmental Sciences, 10, 27–37. Zhang, D. H., & Wang, Q. P. (1998a). Investigation and research of rare Amorphophallus konjac resource in the area between China and Burma. Resource and Market, 14(6), 245–246. in Chinese with English abstract. Zhang, X. H., & Wang, J. F. (1998b). Preliminary trial on northwardmigration of edible plant, Amorphophallus rivieri. Shaanxi Forest Science and Technology, 3, 65–67. in Chinese. Zhang, Z. L., Wu, W. X., & Zhang, X. H. (1998). Introduction trial with Amorphophallus rivieri beyond its native northern range. Economic Forest Research, 16(4), 12–15. in Chinese with English abstract.
Short Communication
Variations of Konjac glucomannan (KGM) from Amorphophallus konjac and its refined powder in China Weixuan Fanga,b,*, Pengwu Wua,c a
Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 73 Guanshui Road, Guiyang 550002, People’s Republic of China b The Mineral and Geological Exploration Centre of Nonferrous metals, No. 12B Fuxing Road, Fuxingmenwai, Beijing 100814, People’s Republic of China c The Institute of Geophysical and Geochemical Exploration, CNNC, 5 Shuiwenxiang, Xi’an 710068, People’s Republic of China Received 27 October 2002; revised 16 December 2002; accepted 21 February 2003
Abstract Konjac glucomannan (KGM) is a water-soluble dietary fiber extracted from tubers of Amorphophallus konjac native to China. It has a low caloric content and is a soluble dietary fiber, used in foods and medicine ingredients. This paper reports changes of KGM from Amorphophallus konjac native in the southern part of China to KGM obtained in transplanting trials in the northern part of China. Fresh raw rhizoid-tuber of Amorphophallus konjac contains KGM of 8.03– 12.43%. Its refined powder contains KGM ranging from 71.6 to 51.3%, whereas superclass purified powder extracted from tubers of Amorphophallus konjac contains more than 90% KGM, with a maximum value up to 96.9%. The KGM contents in tubers of transplanted Amorphophallus konjac in the northern temperate zone in middle Shaanxi Province in this study range from 27.65 to 47.59%, all of which are less than a mean value of these (54.39%) in the original tuber. It may be proposed that transplanting Amorphophallus konjac from its native land in the subtropical and tropical zone to the northern temperate zone in the northern part of China would be feasible. q 2003 Elsevier Ltd. All rights reserved. Keywords: Konjac glucomannan; Amorphophallus konjac; Fresh raw rhizoid-tuber; Refined powder; Superclass purified powder
1. Introduction Konjac glucomannan (KGM) is extracted from the tuber of Amorphophallus konjac native to China. Primary components of the tuber mainly contain KGM. KGM is a high molecular weight polysaccharide consisting primarily of mannose and glucose sugars and is a source of soluble dietary fiber. KGM received much attention recently (Case & Hamann, 1994; Nishinari, Williams, & Phillip, 1992; Nishinari & Yoshimura, 1999; Shinsaku, Shigetomo, Naruhiro, & Yoshinori, 2002; Wu et al., 1997). KGM is beneficial to the health of human beings and its ability to cure some diseases is well documented (Huang, Zhang, & Peng, 1990; Vorster, Lotter, & Odendaal, 1988; Vuksan, Jenkins, & Spadafora, 1999; Walsh, Yaghoubian, * Corresponding author. Address: Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 73 Guanshui Road, Guiyang 550002, People’s Republic of China. E-mail address: [email protected] (W. Fang). 0268-005X/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-005X(03)00044-4
& Behforooz, 1984; Wu & Peng, 1997; Key, 1973; Bian cardi & Palmiero, 1989; Mao & Gu, 1998; Wei & Ma, 1998; James & Follett, 2000). First of all, it can delay stomach emptying when taken as an edible Amorphophallus konjacbased food. It may lead to a more gradual absorption of dietary sugar, which can reduce the elevation of blood sugar levels that is typical after a meal. According to preliminary (Huang et al., 1990) and controlled trials (Vorster et al., 1988; Vuksan et al., 1999), it has been found that after-meal blood sugar levels are lower in patients with diabetes given glucomannan in their food, and overall diabetic control is improved with glucomannan-enriched diets. Secondly, KGM is high in dietary fibre which is essential for human health. Thirdly, like other soluble fibres, it can bind to bile acids in the gut and carry them out of the body in the faeces, which requires the body to convert more cholesterol into bile acids (Wu & Peng, 1997). Finally, it may help weight loss by filling the stomach and making a person feel full. Walsh et al. (1984) reported weight loss averaging 5.5
168
W. Fang, P. Wu / Food Hydrocolloids 18 (2004) 167–170
pounds in adults when one gram of glucomannan was taken with a cup of water one hour before each meal for 8 weeks based on a double-blind study. No more than three species of edible plant contain KGM up to now, and Amorphophallus konjac is one of them (He, 2001). Refined powder, purified from the tuber of Amorphophallus konjac, contains significant amounts of KGM ranging from 50 to 98% (Hu, Li, Long, & Yi, 1998; Qiu, Tang, Lu, & Wu, 2000; Wang, Wu, & Li, 1998; Wu et al., 1997; Zhang, Wu, & Zhang, 1998). However, Variations of KGM in Amorphophallus konjac and its refined products have not been systematically studied. With original tubers of Amorphophallus konjac derived from the southern subtropical zone in southern Shaanxi Province Fang, Wu and Zuo (1996) firstly reported trace element contents of Amorphophallus konjac from results of a transplanting experiment in the northern temperate zone in Xi’an City, Shaanxi Province. It has proved that Amorphophallus konjac can be transplanted in the northern temperate zone in China including middle-northern part of Shaanxi and Liaoning Province as well as the arid zone between Yulin in northern Shaanxi and the southern part of Mongolia (Fang et al., 1996; Liu, Lan, Liu, & Qian, 1998a; Liu, Zhang, & Zhang, 1998b; Zhang & Wang, 1998a,b; Zhang et al., 1998). This paper reports on the variational behaviour of KGM grown in various parts of China.
2. Materials and methods With original tubers of Amorphophallus konjac sampled from the southern subtropical zone in Ziyang, Pingli, Langao, and Ankang Counties of southern Shaanxi Province, Amorphophallus konjac had been transplanted northward in Ganjiazhai village of Xi’an city, Yehu area of Lantian County, Weiqu area of Chang’an County, the middle part of Shaanxi Province since 1991. Samples of transplanted Amorphophallus konjac were collected from these cultivating areas. However, original tubers of Amorphophallus konjac were sampled from the northern margin of the southern subtropical zone in Ziyang County of southern Shaanxi Province in order to investigate differences between the original tubers and the tubers of the northward transplanting trial. Firstly, muddy materials on selected raw rhizoid-tubers of Amorphophallus konjac were washed with water, and their skin and small roots were cut off. Secondly, rhizoid-tubers of Amorphophallus konjac were sliced, and their sprouts were removed. Thirdly, their slices were heated in a drying apparatus to remove all moisture from them, and then their dried slices were put in grinding machine and were crushed to less than 0.125 mm in size. KGM in samples was analysed by the Forestry Science Institute of Shaanxi Province. A method for determination of KGM in Konjac powder is reported by Wang et al. (1998). 0.15 g of powdered sample were taken and put in
a 150 ml beaker. In order to separate free sugar from it, the sample was purified by 85% ethanol under continuous agitation with a stirrer, and then it was filtered and heated to remove the ethanol. The sample was dissolved in purified water in a 150 ml beaker at 35 8C under continuous agitation with a stirrer for 12 h. The digested solution was centrifuged for 20 min at 4000 rpm. The purified KGM solution was heated and digested for 1.5 h with boiling water, and then cooled. 0.5 ml 6 M NaOH was added and the solution was analysed by spectrophotometric analysis using a 752-Mode spectrophotometer made in Shanghai.
3. Results and discussion 3.1. Konjac glucomannan contents in raw fresh Amorphophallus konjac According to the preliminary trial reported by Zhang et al. (1998), fresh raw rhizoid-tuber of Amorphophallus konjac transplanted in the northern temperate zone in the northern part of China contains KGM from 8.03 to 8.40%, with a mean value of 8.15%, which is slight by lower than in their original tuber (8.53% KGM) derived from northern margin of the southern subtropical zone in Langao County of southern Shaanxi Province in the southern part of China. It is half as much as those (12.43% KGM) in the fresh raw rhizoid-tuber from the southern part of Shaanxi Province documented by Guo, Qiu, and Li (1996). 3.2. Variations of Konjac glucomannan with time Concentrations of KGM in raw rhizoid-tuber of Amorphophallus konjac increase with growing time (Zhang et al., 1998, Fig. 1). However, a dried sliced-sample only contains 17.78% KGM after it was stored in the laboratory for many years. KGM content in rhizoid-tubers of Amorphophallus
Fig. 1. Amounts of KGM in raw rhizoid-tuber of Amorphophallus konjac in different months (Reference: Zhang et al., 1998).
W. Fang, P. Wu / Food Hydrocolloids 18 (2004) 167–170
169
Table 1 Konjac glucomannan contents from introduction trial of Amorphophallus konjac Zone
Dried sample
Location
H2O%
KGM%
Southern part of Shaanxi
PV18 PV19 PV23 Mean
Hongcun of Ziyang County Ziyanggou of Ziyang County Haoping of Ziyang County
4.984 4.817 6.018 5.273
44.72 57.08 61.37 54.39
Middle part of Shaanxi
PV45 PV46 PV47 PV50 PV51 PV52 PV53 PV56 PV58 Mean
Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Ganjiazhia of Xi’an Yehu of Lantian County Weiqu of Chang’an County
5.104 5.506 7.027 5.7 6.633 4.672 6.564 7.151 4.19 5.84
47.06 41.79 42.15 47.59 44.74 43.38 27.65 35.7 47.14 37.47
konjac decreases on storage and when the rhizoid-tubers of Amorphophallus konjac germinate in the Spring season (Jia, 1984). 3.3. Konjac glucomannan contents from transplanting trial of Amorphophallus konjac As listed in Table 1 and shown in Fig. 2, the KGM contents in their original tubers derived from the northern margin of the southern subtropical zone in Ziyang County of southern Shaanxi Province range from 44.72 to 61.37%, with a mean value of 54.39%. On the other hand, H2O contents in their dried sample are from 4.817 to 6.018%, with a mean value of 5.273%. Generally speaking, the KGM contents in their transplanting tubers in the northern temperate zone in northern Shaanxi Province in this study range from 27.65 to 47.59%, all of which are less than the mean value (54.39%) in their original tubers. However, the mean content of KGM in the transplanted tubers accounts for almost 69% of those in their original tubers. It is indicated that KGM contents in the transplanted tubers may be lowered after it is cultivated in northern Shaanxi Province. This may be due to alteration of the ecological environment for Amorphophallus konjac, which leads to lower productivity in KGM. Water contents in their dried sample of both are almost the same.
powder can be productively extracted from their original tubers since the mean value (54.39%) is higher than the lowest content of KGM in the refined powder. In spite of this, KGM contents in the transplanted tubers (as listed in Table 1) indicate that the refined powder still can be extracted from the transplanted tubers of Amorphophallus konjac, although they contain KGM from 27.65 to 47.59%. It may imply that a development project concerning Amorphophallus konjac transplantation from its native land in the subtropical and tropical zone northward to the northern temperate zone in the northern part of China would be feasible. If KGM contents are higher in rhizoid-tubers of Amorphophallus konjac or in its refined powder, they have more economic value in food manufacture, industrial utility, and medicinal use. This is why refined powder of Amorphophallus konjac is more in demand. Even though
3.4. Konjac glucomannan contents in refined powder extracted from tubers of Amorphophallus konjac As presented in Fig. 2, superclass purified powder extracted from tubers of Amorphophallus konjac contains more than 90% KGM, with a maximum value up to 96.9%. Nevertheless, its refined powder contains KGM ranging from 71.6 to 51.3%. Variations of KGM in the original tubers as listed in Table 1 indicate that the refined
Fig. 2. Variations of KGM contents in different class of products extracted from rhizoid-tuber of Amorphophallus konjac and transplanting tuber. Reference: superclass from Hu et al. (1998), Qiu et al. (2000) and Wu et al. (1997). Refined powder from Hu et al. (1998) and Wang et al. (1998). Original and transplanting tuber from this study.
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KGM contents in their tubers are lower than those in its original species, superclass purified powder of Amorphophallus konjac can be extracted from rhizoid-tuber of Amorphophallus konjac by an air separator (He, 2001) or by chemical separation such as maleic anhydride (Qiu et al., 2000).
Acknowledgements Chinese National Nonferrous Metal Industry Corporation (Grants No. CNNC95-D-27), Chinese State Key Project on Fundamental Research Planning (Grants No. 2001CB409805), and Visiting Scholar Fund of LODG of Institute of Geochemistry, Chinese Academy of Sciences, jointly financed this study. The authors express their special thanks due to both referees for improving the manuscript.
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