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Production of modified starches by gamma irradiation1
Radiation Physics and Chemistry
PERGAMON
Radiation Physics and Chemistry 54 (1999) 425±430
Production of modi®ed starches by gamma irradiationp Il-Jun Kang a, *, Myung-Woo Byun b, Hong-Sun Yook b, Chun-Ho Bae c, Hyun-Soo Lee c, Joong-Ho Kwon d, Cha-Kwon Chung a a
Department of Food and Nutrition, Hallym University, Chunchon, Kangwon-Do, 200-702, Korea Department of Food Irradiation, Korea Atomic Energy Research Institute, Taejon 305-353, Korea c Samyang Genex R&D Center, Yusung-Gu, Taejon 305-348, Korea d Department of Food Science and Technology, Kyungpook National University, Taegu 702-701, Korea b
Received 17 May 1997; accepted 9 August 1998
Abstract As a new processing method for the production of modi®ed starch, gamma irradiation and four kinds of inorganic peroxides were applied to commercial corn starch. The addition of inorganic peroxides without gamma irradiation or gamma irradiation without the addition of inorganic peroxides eectively decreased initial viscosity, but did not suciently keep viscosity stable. The combination of adding ammonium persulfate (APS) and gamma irradiation showed the lowest initial viscosity and the best stability out of the tested four kinds of inorganic peroxides. Among the tested mixing methods of APS, soaking was found to be more eective than dry blending or spraying. Therefore, the production of modi®ed starch with low viscosity as well as with sucient viscosity stability became feasible by the control of gamma irradiation dose levels and the amount of added APS to starch. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Modi®ed starch; Gamma irradiation; Corn starch; Inorganic peroxides; Viscosity stability
1. Introduction Corn starch is widely used in various food products as a ®lling, thickening or stabilizing agent in order to improve structure, texture, consistency and appeal. Although native starches have many uses in food products, modi®ed starches have almost unlimited food and nonfood applications (Mercier and Feillet, 1975; Rogols, 1986). As a useful method for the production of modi®ed starch, gamma irradiation, produces free radicals on starch molecules that can alter their size and structure (Ra et al., 1980; Ciesla et al., 1991; Grant and D'Appolonia, 1991; Sabularse et al., 1991). Several studies on the eects of ionizing radiation on wheat starch (Lai et al., 1959; Milner, 1961) and barley
This paper was presented at the 10th International Meeting on Radiation Processing, 11±16 May 1997, Anaheim, California, U.S.A. * Corresponding author. p
endosperm (Faust and Massey, 1966) have been conducted. Gamma irradiation is capable of hydrolyzing chemical bonds, thereby cleaving large molecules of starch into smaller fragments of dextrin that may be either electrically charged or uncharged as free radicals. These changes may aect the physical and rheological properties of irradiated foods, resulting in increased solubility of starch (Deschreider, 1959) and decreased swelling power (Tollier and Guilbot, 1970) and decreased relative viscosity (Vakil et al., 1973) of starch paste. Although gamma irradiation can decrease the viscosity of the starch, high doses of gamma irradiation are required for application in paper manufacturing and textile sizing (Kang and Byun, 1996). The change of viscosity in gamma irradiated starches with increasing time after irradiation also becomes a problem (Roushdi et al., 1983). This study reports the development, utilizing low level of gamma irradiation, of modi®ed starch that has
0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 2 7 4 ± 6
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I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
low viscosity and excellent stability of viscosity, which can be applicable to starch industry. 2. Experimental 2.1. Materials Corn starch containing approximately 12% moisture content was provided by Samyang Genex Co., Korea. Ammonium persulfate (APS), sodium persulfate (SPS), potassium persulfate (PPS) and calcium hypochlorite (Ca-Hypo) was purchased from Yakuri Chemicals Co. (Japan).
Starch specimen of 45 g (dry basis) was weighed, water was added to 300 g. After stirring the suspension for 10 min in a 958C water bath to gelatinize and cooling to 508C by cold water, initial viscosity of starch paste was measured with a Brook®eld Viscometer (Brook®eld Viscometer LVF). The stability of viscosity was measured at 1 h intervals at 508C. The color of the starch specimen was measured by a Minolta colorimeter (CR-200b, Japan) and expressed in Hunter's L (lightness), a (redness) and b (yellowness) values. All the experiments were replicated three times. The results were subjected to an analysis of variance using the Statistical Analysis System.
2.2. Preparation of starch specimen
3. Results and discussion
Inorganic peroxides such as ammonium persulfate, sodium persulfate, potassium persulfate and calcium hypochlorite were mixed with corn starch in three dierent methodsÐdry blending, soaking and spraying methods. In the dry blending method, inorganic peroxide was weighed out maintaining the ratio (49:1) of starch (dry basis) to inorganic peroxide constant, and put to mix with corn starch in a small V-type mixer for 20 min until the mixture reaches homogeneity. Soaking method employed the wet-process of adding water to corn starch to make 40% concentration in dry basis in suspension, then peroxide was added in constant ratios of 1 to 3%. After stirring for 30 min, the suspension was dehydrated and dried. The actual amount of peroxide added to the starch was calculated by comparing the moisture content of starch cake and that of the leftover water content. In the spraying method, the peroxides were dissolved in a 3 vols of distilled water and sprayed evenly on the corn starch to make the ®nal ratio of constant 2% of the starch.
3.1. Eect of dierent peroxides and gamma irradiation on viscosity and viscosity stability of starch
2.3. g-irradiation The starch specimens were packed in polyethylene bags and were exposed at ambient temperature (152 0.58C) to a 60-Co source of 100,000 Ci having a dose rate of 1 kGyh ÿ 1. The dose levels applied to the samples were 0±50 kGy. A ceric cerous dosimeter was used to measure the exact total absorbed dose of gamma irradiation. All the materials were kept at room temperature under constant atmosphere and humidity. 2.4. Physical properties Viscosity, viscosity stability and the color were measured for the analysis of physical properties.
The eect of the addition of four dierent inorganic peroxides (2%) to starch by the dry blending method on the initial viscosity and viscosity stability of the starch paste was investigated (Table 1). At the same time, the above obtained results were compared to that of gamma irradiated starch samples at 10, 30 and 50 kGy (Table 1). As shown in Table 1, the viscosity of gamma irradiated starch was considerably decreased for increasing radiation dose levels. However, viscosity was not stable with time. The viscosity of starch treated with gamma irradiation increased with time, which becomes a problem in paper manufacturing and textile sizing applications. A similar initial decrease of viscosity in irradiated wheat starch has been reported (Ananthaswamy et al., 1971). Degradation of starch has been considered to be responsible for the viscosity changes caused by g-irradiation (Nene et al., 1975). According to Deschreider (1960), these changes were responsible for shortening of polysaccharide chains, depending upon the irradiation dose levels. For starch treated with inorganic peroxide (2%, dry blending), initial viscosity was also dramatically decreased (Table 1). Ammonium persulfate (APS) treatment showed the lowest initial viscosity and the best stability among the tested four kinds of inorganic peroxides. The addition of calcium hypochlorite showed little eect on the viscosity stability. Overall, the addition of inorganic peroxides with no gamma irradiation eectively decreased initial viscosity, but did not suciently keep viscosity stability. As compared to gamma irradiation, the addition of inorganic peroxide revealed similar eect to that of between 30±50 kGy gamma irradiation. In the case of viscosity stability, starch treated with inorganic peroxide showed better result than that of gamma irradiation.
I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
427
Table 1 Eects of gamma irradiation and inorganic peroxides on the initial viscosity and viscosity stability of starch paste1 Time(h)2 Sample
0
1
2
3
4
5
6
0 kGy 10 kGy 30 kGy 50 kGy 2% APS 2% SPS 2% PPS 2% Ca-Hypo APS + 10 kGy SPS + 10 kGy PPS + 10 kGy Ca-Hypo + 10 kGy Oxidized Starch3
1358021364 9740282 1290215 2602 10 4432 5 4702 10 5842 11 7202 13 1512 8 2002 13 2932 11 3362 8 882 4
106 > 106 > 130002 56 1220218 525 210 581 25 741 211 1580221 206 210 273 211 352 28 497 211 912 2
106 > 106 > 28700275 2660227 546 27 587 27 826 213 2130225 230 26 305 28 400 213 604 29 932 4
106 > 106 > 305002 125 56002 38 55425 61025 884211 3000> 24928 329213 487211 752213 9624
106 > 106 > 356002133 6100275 56124 63829 915218 3000> 268211 35629 564218 916211 962 5
106 > 106 > 402502153 130002125 564 25 650 25 1008215 3000> 280 28 370 211 671 213 1320218 98 23
106 > 106 > 481002146 155002115 5902 11 6592 7 10562 15 3000> 3002 12 3952 10 9162 15 15902 13 1022 4
1
Starch paste(15%) was made from corn starch treated with gamma irradiation, inorganic peroxides(2%, dry blending) and inorganic peroxide plus gamma irradiation.2The viscosity stability of starch paste after gelatinization was measured at 1 h intervals at 508C.3Commercial oxidized starch 3009 made by Samyang Genex Co., Korea.4Each value is mean2 standard deviation of triplicate determinations and expressed as centipoise (cP).
and peroxide, the results revealed inadequate stability of viscosity compared to commercial oxidized starch.
On the basis of the above results, the eect of the combination of gamma irradiation and inorganic peroxide on the starch viscosity was examined. Gamma irradiation (10 kGy) after dry mixing of peroxides at 2% showed to decrease initial viscosity by more than 50% when compared with that of inorganic peroxide addition alone (Table 1). The change was most noticeable with calcium hypochlorite. Gamma irradiation after APS treatment showed the lowest initial viscosity and the best stability among the four kinds of inorganic peroxides tested. Although viscosity stability was improved by the combination of gamma irradiation
3.2. Eect of dierent mixing methods In order to improve viscosity stability, APS (2%) was mixed with corn starch in three dierent methodsÐdry blending, soaking and spraying methods. Where the initial viscosity of starch in soaking was the lowest, the viscosity stability of starch in dry blending was better than the other methods employed (Table 2).
Table 2 Eects of dierent mixing methods with 2% ammonium persulfate (APS) on the initial viscosity and viscosity stability of starch paste1 Time (h)2 Mixing method
g-irradiation
0
1
2
3
4
5
6
Dry blending Soaking Spraying Dry blending Soaking Spraying
0 kGy 0 kGy 0 kGy 10 kGy 10 kGy 10 kGy
443283 28024 35025 15127 7225 10729
5252 9 3002 7 4162 8 2062 5 822 6 1582 11
5462 6 3322 5 6722 11 2302 5 902 4 3162 10
5502 5 3792 10 9362 10 2492 8 932 3 5712 8
5612 4 4172 8 15602 15 2682 10 972 4 8602 11
5642 5 4352 7 2330218 2802 8 1022 3 1030218
590 26 460 210 3000223 300 212 104 26 1350225
1 Starch paste(15%) was made from non-irradiated and 10 kGy-irradiated corn starch after mixing 2% ammonium persulfate(APS) in three dierent mixing methods.2The viscosity stability of starch paste after gelatinization was measured at 1 h intervals at 508C.3Each value is mean standard deviation of triplicate determinations and expressed as centipoise (cP).
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Gamma irradiation (10 kGy) after mixing 2% APS in three dierent methods showed to decrease initial viscosity and to increase viscosity stability (Table 2). In particular, gamma irradiation after mixing APS by soaking was eectively improved viscosity stability; viscosity after 6 h at 508C was similar to that of commercial oxidized starch. Its considered that eective oxidative reaction, which results in decreasing viscosity, can occur when the capacity of reaction between the starch and APS is sucient. When mixed in the form of powder(dry blending), an eective oxidation reaction is not expected to occur because of the lack of reaction capacity between the starch and APS. Spraying methods likewise showed less eective because APS was simply applied to starch surface. On the other hand, in wet mixing (soaking method), APS is completely dissolved to a water soluble ionic state which can penetrate into the starch molecule. When starch is irradiated after soaking, the eect is expected to be excellent because of the ample reaction capacity between the starch and peroxydisulfate ion.
3.3. Eect of dierent amounts of APS and gamma irradiation dose levels After APS was added to starch at the ratio of 1±3% by soaking, the eect of gamma irradiation (10 kGy) on the viscosity stability was investigated. Initial viscosity was shown to decrease as the amounts of APS added to starch increased (Fig. 1). Compared to 1% and 1.5% APS, the addition of more than 2% APS dramatically improved viscosity stability of starch. When the gamma irradiation dose level was increased with the constant amount of APS at 2%, overall initial viscosity tended to decrease, whereas viscosity stability stayed almost the same (Fig. 2). These results suggest that the production of modi®ed starch with various levels of viscosity as well as with excellent stability became feasible by the control of gamma irradiation dose levels and the amount of added APS. The cleavage of starch polymer by gamma irradiation is accompanied by the production of free radicals that reduce viscosity of starch by chain reaction. Also, the
Fig. 1. Eects of ammonium persulfate on the viscosity stability of starch paste. Starch paste (15%) was made from 10 kGy irradiated corn starch after mixing 1±3% ammonium persulfate by soaking method.
I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
429
Fig. 2. Eects of gamma irradiation dose levels on the viscosity stability of 2% APS added starch paste. Starch paste (15%) was made from 10±30 kGy irradiated corn starch after mixing 2% ammonium persulfate by soaking method.
inorganic peroxide used as additives are easily decomposed by gamma irradiation to produce free radicals (House, 1962). Therefore, it is considered that the combination of gamma irradiation and inorganic peroxide has synergistic eect on the formation of free radicals within the starch molecules, which can play a decisive role for decreasing initial viscosity and increasing viscosity stability of starch. As a consequence, the reduction of viscosity and the increase of viscosity stability in starch, which can accompany more radical productions, became possible by the increment of the addition of APS and by irradiation dose levels. 3.4. Changes of color Color changes of starch specimens before and after gamma irradiation, were analyzed using colorimeter (Table 3). No noticeable changes in ``a'' value was observed among the starch samples. The ``b'' value which stands for yellowness increased with gamma ir-
Table 3 Eects of gamma irradiation and ammonium persulfate on the color pro®les of starch specimen Hunter's color value1 Sample
L
a
b
10 kGy 30 kGy 50 kGy 2% APS 3.5% APS 2% APS + 10 kGy 3.5%APS + 10 kGy 3.5%APS + 20 kGy Oxidized Starch2
93.62 0.43 93.12 0.3 92.52 0.8 93.32 0.3 93.52 0.6 92.62 0.5 93.32 0.4 91.52 0.7 95.02 0.4
ÿ2.42 0.2 ÿ2.52 0.1 ÿ2.62 0.1 ÿ2.82 0.2 ÿ2.72 0.2 ÿ3.12 0.3 ÿ2.92 0.2 ÿ2.62 0.1 ÿ2.32 0.1
2.7 20.3 5.0 20.4 7.5 20.3 2.0 20.3 2.6 20.2 3.9 20.3 4.4 20.2 5.6 20.3 1.9 20.1
1 L, degree of lightness (white + 100 t 0 black); a, degree of redness (red + 100 t 0 ÿ80 green); b, degree of yellowness (yellow + 70 t 0 ÿ80 blue).2Commercial oxidized starch 3009 made by Samyang Genex Co., Korea.3Each value is mean2 standard deviation of triplicate determinations.
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I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
radiation or with the addition of APS, which seems mainly due to the caramelization reaction of monosaccharides cleaved from starch polysaccharides by gamma irradiation. Also, the addition of APS to starch showed to enhance caramelization reaction via the increased production of monosaccharides from starch polymers. More caramelization reaction seemed to occur with the addition of APS plus gamma irradiation than with the treatment of gamma irradiation alone or APS alone. In addition, the ``L'' value (lightness) was in¯uenced due to the changes of yellowness. References Ananthaswamy, H.N., Vakil, U.K., Sreenivasan, A., 1971. Some physicochemical changes in gamma-irradiated wheat. Proceedings of Symposium on Basic Mechanisms in Radiation Biology and Medicine, Feb 11, 13. New Delhi, p. 347. Ciesla, K., Zoltowski, T., Mogilevsky, L.Y., 1991. Detection of starch transformation under gamma irradiation by small-angle X-ray scattering. Starch/Staerke 43, 11. Deschreider, A.R., 1959. Systematic study of ¯our treated with gamma rays, 1 Action on polysaccharides. Fermentatio 1, 31. Deschreider, A.R., 1960. Changes in starch and its degradation products on irradiating wheat ¯our with gamma rays. Starch/Staerke 12, 197. Faust, M., Massey, L.M., Jr, 1966. The eect of ionizing radiation on starch breakdown in barley endosperm. Rad. Research 29, 33. Grant, L.A., D'Appolonia, B.L., 1991. Eect of low-level gamma radiation on water-soluble non-starchy polysaccharides isolated from hard red spring wheat ¯our and bran. Cereal Chem. 68, 651.
House, D.A., 1962. Kinetics and mechanism of oxidations by peroxydisulfate. Chem. Rev. 62, 185. Kang, I.J., Byun, M.W., 1996. Development of modi®ed starch by gamma irradiation. Korean J. Food Sci. Technol. 28, 514. Lai, S.P., Finney, K.F., Milner, M., 1959. Treatment of wheat with ionizing radiations, 4 Oxidative, physical and biochemical changes. Cereal Chem. 36, 401. Mercier, C., Feillet, P., 1975. Modi®cation of carbohydrate components by extrusion cooking of cereal products. Cereal Chem. 52, 283. Milner, M., 1961. Technological eects of gamma irradiation of wheat. In: Proceedings of the Fifth International Congress of Biochemistry, 8, Moscow 1961. Pergamon Press Ltd, p. 108. Nene, S.P., Vakil, U.K., Sreenivasan, A., 1975. Eect of gamma radiation on physico-chemical characteristics of red gram (Cajanus cajan) starch. J. Food Sci. 40, 943. Ra, J., Michel, J.P., Saint-Lebe, L., 1980. Theoretical study of the radiopolymerization of starch. Starch/Staerke 32, 227. Rogols, S., 1986. Starch modi®cations: A view into the future. Cereal Foods World 31, 869. Roushdi, M., Harras, A., El-Meligi, A., Bassim, M., ElShelkh, K., 1983. Eect of high doses of gamma rays on corn grains. Starch/Staerke 35, 15. Sabularse, V.C., Liuzzo, J.A., Rao, R.M., Grodner, R.M., 1991. Cooking quality of brown rice as in¯uenced by gamma-irradiation, variety and storage. J. Food Sci. 56, 96. Tollier, M.T., Guilbot, A., 1970. Development of certain physicochemical properties of the starch granule as a function of irradiation conditions. Starch/Staerke 22, 296. Vakil, U.K., Aravindakshan, M., Srinivas, H., Chauhan, P.S., Sreenivasan, A., 1973. Nutritional and wholesomeness studies with irradiated foods: India's program, IAEA, SM166/12. Vienna, p. 673.
PERGAMON
Radiation Physics and Chemistry 54 (1999) 425±430
Production of modi®ed starches by gamma irradiationp Il-Jun Kang a, *, Myung-Woo Byun b, Hong-Sun Yook b, Chun-Ho Bae c, Hyun-Soo Lee c, Joong-Ho Kwon d, Cha-Kwon Chung a a
Department of Food and Nutrition, Hallym University, Chunchon, Kangwon-Do, 200-702, Korea Department of Food Irradiation, Korea Atomic Energy Research Institute, Taejon 305-353, Korea c Samyang Genex R&D Center, Yusung-Gu, Taejon 305-348, Korea d Department of Food Science and Technology, Kyungpook National University, Taegu 702-701, Korea b
Received 17 May 1997; accepted 9 August 1998
Abstract As a new processing method for the production of modi®ed starch, gamma irradiation and four kinds of inorganic peroxides were applied to commercial corn starch. The addition of inorganic peroxides without gamma irradiation or gamma irradiation without the addition of inorganic peroxides eectively decreased initial viscosity, but did not suciently keep viscosity stable. The combination of adding ammonium persulfate (APS) and gamma irradiation showed the lowest initial viscosity and the best stability out of the tested four kinds of inorganic peroxides. Among the tested mixing methods of APS, soaking was found to be more eective than dry blending or spraying. Therefore, the production of modi®ed starch with low viscosity as well as with sucient viscosity stability became feasible by the control of gamma irradiation dose levels and the amount of added APS to starch. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Modi®ed starch; Gamma irradiation; Corn starch; Inorganic peroxides; Viscosity stability
1. Introduction Corn starch is widely used in various food products as a ®lling, thickening or stabilizing agent in order to improve structure, texture, consistency and appeal. Although native starches have many uses in food products, modi®ed starches have almost unlimited food and nonfood applications (Mercier and Feillet, 1975; Rogols, 1986). As a useful method for the production of modi®ed starch, gamma irradiation, produces free radicals on starch molecules that can alter their size and structure (Ra et al., 1980; Ciesla et al., 1991; Grant and D'Appolonia, 1991; Sabularse et al., 1991). Several studies on the eects of ionizing radiation on wheat starch (Lai et al., 1959; Milner, 1961) and barley
This paper was presented at the 10th International Meeting on Radiation Processing, 11±16 May 1997, Anaheim, California, U.S.A. * Corresponding author. p
endosperm (Faust and Massey, 1966) have been conducted. Gamma irradiation is capable of hydrolyzing chemical bonds, thereby cleaving large molecules of starch into smaller fragments of dextrin that may be either electrically charged or uncharged as free radicals. These changes may aect the physical and rheological properties of irradiated foods, resulting in increased solubility of starch (Deschreider, 1959) and decreased swelling power (Tollier and Guilbot, 1970) and decreased relative viscosity (Vakil et al., 1973) of starch paste. Although gamma irradiation can decrease the viscosity of the starch, high doses of gamma irradiation are required for application in paper manufacturing and textile sizing (Kang and Byun, 1996). The change of viscosity in gamma irradiated starches with increasing time after irradiation also becomes a problem (Roushdi et al., 1983). This study reports the development, utilizing low level of gamma irradiation, of modi®ed starch that has
0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 2 7 4 ± 6
426
I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
low viscosity and excellent stability of viscosity, which can be applicable to starch industry. 2. Experimental 2.1. Materials Corn starch containing approximately 12% moisture content was provided by Samyang Genex Co., Korea. Ammonium persulfate (APS), sodium persulfate (SPS), potassium persulfate (PPS) and calcium hypochlorite (Ca-Hypo) was purchased from Yakuri Chemicals Co. (Japan).
Starch specimen of 45 g (dry basis) was weighed, water was added to 300 g. After stirring the suspension for 10 min in a 958C water bath to gelatinize and cooling to 508C by cold water, initial viscosity of starch paste was measured with a Brook®eld Viscometer (Brook®eld Viscometer LVF). The stability of viscosity was measured at 1 h intervals at 508C. The color of the starch specimen was measured by a Minolta colorimeter (CR-200b, Japan) and expressed in Hunter's L (lightness), a (redness) and b (yellowness) values. All the experiments were replicated three times. The results were subjected to an analysis of variance using the Statistical Analysis System.
2.2. Preparation of starch specimen
3. Results and discussion
Inorganic peroxides such as ammonium persulfate, sodium persulfate, potassium persulfate and calcium hypochlorite were mixed with corn starch in three dierent methodsÐdry blending, soaking and spraying methods. In the dry blending method, inorganic peroxide was weighed out maintaining the ratio (49:1) of starch (dry basis) to inorganic peroxide constant, and put to mix with corn starch in a small V-type mixer for 20 min until the mixture reaches homogeneity. Soaking method employed the wet-process of adding water to corn starch to make 40% concentration in dry basis in suspension, then peroxide was added in constant ratios of 1 to 3%. After stirring for 30 min, the suspension was dehydrated and dried. The actual amount of peroxide added to the starch was calculated by comparing the moisture content of starch cake and that of the leftover water content. In the spraying method, the peroxides were dissolved in a 3 vols of distilled water and sprayed evenly on the corn starch to make the ®nal ratio of constant 2% of the starch.
3.1. Eect of dierent peroxides and gamma irradiation on viscosity and viscosity stability of starch
2.3. g-irradiation The starch specimens were packed in polyethylene bags and were exposed at ambient temperature (152 0.58C) to a 60-Co source of 100,000 Ci having a dose rate of 1 kGyh ÿ 1. The dose levels applied to the samples were 0±50 kGy. A ceric cerous dosimeter was used to measure the exact total absorbed dose of gamma irradiation. All the materials were kept at room temperature under constant atmosphere and humidity. 2.4. Physical properties Viscosity, viscosity stability and the color were measured for the analysis of physical properties.
The eect of the addition of four dierent inorganic peroxides (2%) to starch by the dry blending method on the initial viscosity and viscosity stability of the starch paste was investigated (Table 1). At the same time, the above obtained results were compared to that of gamma irradiated starch samples at 10, 30 and 50 kGy (Table 1). As shown in Table 1, the viscosity of gamma irradiated starch was considerably decreased for increasing radiation dose levels. However, viscosity was not stable with time. The viscosity of starch treated with gamma irradiation increased with time, which becomes a problem in paper manufacturing and textile sizing applications. A similar initial decrease of viscosity in irradiated wheat starch has been reported (Ananthaswamy et al., 1971). Degradation of starch has been considered to be responsible for the viscosity changes caused by g-irradiation (Nene et al., 1975). According to Deschreider (1960), these changes were responsible for shortening of polysaccharide chains, depending upon the irradiation dose levels. For starch treated with inorganic peroxide (2%, dry blending), initial viscosity was also dramatically decreased (Table 1). Ammonium persulfate (APS) treatment showed the lowest initial viscosity and the best stability among the tested four kinds of inorganic peroxides. The addition of calcium hypochlorite showed little eect on the viscosity stability. Overall, the addition of inorganic peroxides with no gamma irradiation eectively decreased initial viscosity, but did not suciently keep viscosity stability. As compared to gamma irradiation, the addition of inorganic peroxide revealed similar eect to that of between 30±50 kGy gamma irradiation. In the case of viscosity stability, starch treated with inorganic peroxide showed better result than that of gamma irradiation.
I. Kang et al. / Radiation Physics and Chemistry 54 (1999) 425±430
427
Table 1 Eects of gamma irradiation and inorganic peroxides on the initial viscosity and viscosity stability of starch paste1 Time(h)2 Sample
0
1
2
3
4
5
6
0 kGy 10 kGy 30 kGy 50 kGy 2% APS 2% SPS 2% PPS 2% Ca-Hypo APS + 10 kGy SPS + 10 kGy PPS + 10 kGy Ca-Hypo + 10 kGy Oxidized Starch3
1358021364 9740282 1290215 2602 10 4432 5 4702 10 5842 11 7202 13 1512 8 2002 13 2932 11 3362 8 882 4
106 > 106 > 130002 56 1220218 525 210 581 25 741 211 1580221 206 210 273 211 352 28 497 211 912 2
106 > 106 > 28700275 2660227 546 27 587 27 826 213 2130225 230 26 305 28 400 213 604 29 932 4
106 > 106 > 305002 125 56002 38 55425 61025 884211 3000> 24928 329213 487211 752213 9624
106 > 106 > 356002133 6100275 56124 63829 915218 3000> 268211 35629 564218 916211 962 5
106 > 106 > 402502153 130002125 564 25 650 25 1008215 3000> 280 28 370 211 671 213 1320218 98 23
106 > 106 > 481002146 155002115 5902 11 6592 7 10562 15 3000> 3002 12 3952 10 9162 15 15902 13 1022 4
1
Starch paste(15%) was made from corn starch treated with gamma irradiation, inorganic peroxides(2%, dry blending) and inorganic peroxide plus gamma irradiation.2The viscosity stability of starch paste after gelatinization was measured at 1 h intervals at 508C.3Commercial oxidized starch 3009 made by Samyang Genex Co., Korea.4Each value is mean2 standard deviation of triplicate determinations and expressed as centipoise (cP).
and peroxide, the results revealed inadequate stability of viscosity compared to commercial oxidized starch.
On the basis of the above results, the eect of the combination of gamma irradiation and inorganic peroxide on the starch viscosity was examined. Gamma irradiation (10 kGy) after dry mixing of peroxides at 2% showed to decrease initial viscosity by more than 50% when compared with that of inorganic peroxide addition alone (Table 1). The change was most noticeable with calcium hypochlorite. Gamma irradiation after APS treatment showed the lowest initial viscosity and the best stability among the four kinds of inorganic peroxides tested. Although viscosity stability was improved by the combination of gamma irradiation
3.2. Eect of dierent mixing methods In order to improve viscosity stability, APS (2%) was mixed with corn starch in three dierent methodsÐdry blending, soaking and spraying methods. Where the initial viscosity of starch in soaking was the lowest, the viscosity stability of starch in dry blending was better than the other methods employed (Table 2).
Table 2 Eects of dierent mixing methods with 2% ammonium persulfate (APS) on the initial viscosity and viscosity stability of starch paste1 Time (h)2 Mixing method
g-irradiation
0
1
2
3
4
5
6
Dry blending Soaking Spraying Dry blending Soaking Spraying
0 kGy 0 kGy 0 kGy 10 kGy 10 kGy 10 kGy
443283 28024 35025 15127 7225 10729
5252 9 3002 7 4162 8 2062 5 822 6 1582 11
5462 6 3322 5 6722 11 2302 5 902 4 3162 10
5502 5 3792 10 9362 10 2492 8 932 3 5712 8
5612 4 4172 8 15602 15 2682 10 972 4 8602 11
5642 5 4352 7 2330218 2802 8 1022 3 1030218
590 26 460 210 3000223 300 212 104 26 1350225
1 Starch paste(15%) was made from non-irradiated and 10 kGy-irradiated corn starch after mixing 2% ammonium persulfate(APS) in three dierent mixing methods.2The viscosity stability of starch paste after gelatinization was measured at 1 h intervals at 508C.3Each value is mean standard deviation of triplicate determinations and expressed as centipoise (cP).
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Gamma irradiation (10 kGy) after mixing 2% APS in three dierent methods showed to decrease initial viscosity and to increase viscosity stability (Table 2). In particular, gamma irradiation after mixing APS by soaking was eectively improved viscosity stability; viscosity after 6 h at 508C was similar to that of commercial oxidized starch. Its considered that eective oxidative reaction, which results in decreasing viscosity, can occur when the capacity of reaction between the starch and APS is sucient. When mixed in the form of powder(dry blending), an eective oxidation reaction is not expected to occur because of the lack of reaction capacity between the starch and APS. Spraying methods likewise showed less eective because APS was simply applied to starch surface. On the other hand, in wet mixing (soaking method), APS is completely dissolved to a water soluble ionic state which can penetrate into the starch molecule. When starch is irradiated after soaking, the eect is expected to be excellent because of the ample reaction capacity between the starch and peroxydisulfate ion.
3.3. Eect of dierent amounts of APS and gamma irradiation dose levels After APS was added to starch at the ratio of 1±3% by soaking, the eect of gamma irradiation (10 kGy) on the viscosity stability was investigated. Initial viscosity was shown to decrease as the amounts of APS added to starch increased (Fig. 1). Compared to 1% and 1.5% APS, the addition of more than 2% APS dramatically improved viscosity stability of starch. When the gamma irradiation dose level was increased with the constant amount of APS at 2%, overall initial viscosity tended to decrease, whereas viscosity stability stayed almost the same (Fig. 2). These results suggest that the production of modi®ed starch with various levels of viscosity as well as with excellent stability became feasible by the control of gamma irradiation dose levels and the amount of added APS. The cleavage of starch polymer by gamma irradiation is accompanied by the production of free radicals that reduce viscosity of starch by chain reaction. Also, the
Fig. 1. Eects of ammonium persulfate on the viscosity stability of starch paste. Starch paste (15%) was made from 10 kGy irradiated corn starch after mixing 1±3% ammonium persulfate by soaking method.
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Fig. 2. Eects of gamma irradiation dose levels on the viscosity stability of 2% APS added starch paste. Starch paste (15%) was made from 10±30 kGy irradiated corn starch after mixing 2% ammonium persulfate by soaking method.
inorganic peroxide used as additives are easily decomposed by gamma irradiation to produce free radicals (House, 1962). Therefore, it is considered that the combination of gamma irradiation and inorganic peroxide has synergistic eect on the formation of free radicals within the starch molecules, which can play a decisive role for decreasing initial viscosity and increasing viscosity stability of starch. As a consequence, the reduction of viscosity and the increase of viscosity stability in starch, which can accompany more radical productions, became possible by the increment of the addition of APS and by irradiation dose levels. 3.4. Changes of color Color changes of starch specimens before and after gamma irradiation, were analyzed using colorimeter (Table 3). No noticeable changes in ``a'' value was observed among the starch samples. The ``b'' value which stands for yellowness increased with gamma ir-
Table 3 Eects of gamma irradiation and ammonium persulfate on the color pro®les of starch specimen Hunter's color value1 Sample
L
a
b
10 kGy 30 kGy 50 kGy 2% APS 3.5% APS 2% APS + 10 kGy 3.5%APS + 10 kGy 3.5%APS + 20 kGy Oxidized Starch2
93.62 0.43 93.12 0.3 92.52 0.8 93.32 0.3 93.52 0.6 92.62 0.5 93.32 0.4 91.52 0.7 95.02 0.4
ÿ2.42 0.2 ÿ2.52 0.1 ÿ2.62 0.1 ÿ2.82 0.2 ÿ2.72 0.2 ÿ3.12 0.3 ÿ2.92 0.2 ÿ2.62 0.1 ÿ2.32 0.1
2.7 20.3 5.0 20.4 7.5 20.3 2.0 20.3 2.6 20.2 3.9 20.3 4.4 20.2 5.6 20.3 1.9 20.1
1 L, degree of lightness (white + 100 t 0 black); a, degree of redness (red + 100 t 0 ÿ80 green); b, degree of yellowness (yellow + 70 t 0 ÿ80 blue).2Commercial oxidized starch 3009 made by Samyang Genex Co., Korea.3Each value is mean2 standard deviation of triplicate determinations.
430
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radiation or with the addition of APS, which seems mainly due to the caramelization reaction of monosaccharides cleaved from starch polysaccharides by gamma irradiation. Also, the addition of APS to starch showed to enhance caramelization reaction via the increased production of monosaccharides from starch polymers. More caramelization reaction seemed to occur with the addition of APS plus gamma irradiation than with the treatment of gamma irradiation alone or APS alone. In addition, the ``L'' value (lightness) was in¯uenced due to the changes of yellowness. References Ananthaswamy, H.N., Vakil, U.K., Sreenivasan, A., 1971. Some physicochemical changes in gamma-irradiated wheat. Proceedings of Symposium on Basic Mechanisms in Radiation Biology and Medicine, Feb 11, 13. New Delhi, p. 347. Ciesla, K., Zoltowski, T., Mogilevsky, L.Y., 1991. Detection of starch transformation under gamma irradiation by small-angle X-ray scattering. Starch/Staerke 43, 11. Deschreider, A.R., 1959. Systematic study of ¯our treated with gamma rays, 1 Action on polysaccharides. Fermentatio 1, 31. Deschreider, A.R., 1960. Changes in starch and its degradation products on irradiating wheat ¯our with gamma rays. Starch/Staerke 12, 197. Faust, M., Massey, L.M., Jr, 1966. The eect of ionizing radiation on starch breakdown in barley endosperm. Rad. Research 29, 33. Grant, L.A., D'Appolonia, B.L., 1991. Eect of low-level gamma radiation on water-soluble non-starchy polysaccharides isolated from hard red spring wheat ¯our and bran. Cereal Chem. 68, 651.
House, D.A., 1962. Kinetics and mechanism of oxidations by peroxydisulfate. Chem. Rev. 62, 185. Kang, I.J., Byun, M.W., 1996. Development of modi®ed starch by gamma irradiation. Korean J. Food Sci. Technol. 28, 514. Lai, S.P., Finney, K.F., Milner, M., 1959. Treatment of wheat with ionizing radiations, 4 Oxidative, physical and biochemical changes. Cereal Chem. 36, 401. Mercier, C., Feillet, P., 1975. Modi®cation of carbohydrate components by extrusion cooking of cereal products. Cereal Chem. 52, 283. Milner, M., 1961. Technological eects of gamma irradiation of wheat. In: Proceedings of the Fifth International Congress of Biochemistry, 8, Moscow 1961. Pergamon Press Ltd, p. 108. Nene, S.P., Vakil, U.K., Sreenivasan, A., 1975. Eect of gamma radiation on physico-chemical characteristics of red gram (Cajanus cajan) starch. J. Food Sci. 40, 943. Ra, J., Michel, J.P., Saint-Lebe, L., 1980. Theoretical study of the radiopolymerization of starch. Starch/Staerke 32, 227. Rogols, S., 1986. Starch modi®cations: A view into the future. Cereal Foods World 31, 869. Roushdi, M., Harras, A., El-Meligi, A., Bassim, M., ElShelkh, K., 1983. Eect of high doses of gamma rays on corn grains. Starch/Staerke 35, 15. Sabularse, V.C., Liuzzo, J.A., Rao, R.M., Grodner, R.M., 1991. Cooking quality of brown rice as in¯uenced by gamma-irradiation, variety and storage. J. Food Sci. 56, 96. Tollier, M.T., Guilbot, A., 1970. Development of certain physicochemical properties of the starch granule as a function of irradiation conditions. Starch/Staerke 22, 296. Vakil, U.K., Aravindakshan, M., Srinivas, H., Chauhan, P.S., Sreenivasan, A., 1973. Nutritional and wholesomeness studies with irradiated foods: India's program, IAEA, SM166/12. Vienna, p. 673.