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DSC study of mixtures of wheat flour and potato, sweet potato, cassava, and yam starches
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Journal of Food Engineering 86 (2008) 68–73 www.elsevier.com/locate/jfoodeng
DSC study of mixtures of wheat flour and potato, sweet potato, cassava, and yam starches I.S.M. Zaidul a,*, N. Absar a, S.-J. Kim a, T. Suzuki a, A.A. Karim b, H. Yamauchi a, T. Noda a,* a
Memuro Upland Farming Research Station, National Agricultural Research Center for Hokkaido Region, Shinsei, Memuro, Kasai, Hokkaido 082-0071, Japan b School of Industrial Technology, Universiti Sains Malaysia, 11800 P. Penang, Malaysia Received 25 May 2007; received in revised form 13 August 2007; accepted 9 September 2007 Available online 15 September 2007
Abstract Differential scanning calorimetry (DSC) traces at a 30 wt% suspension were studied for mixture of wheat flour and following starches: potato (PS), sweet potato (SPS), yam (YS), and cassava (CS) at 10% to 50% starch. In the endothermal transition, the gelatinization peak temperature of the first peak (TP1) was attributed to the wheat flour and that of the second peak (TP2), to the starches. The TP1 of the control wheat flour was lower (62.6 °C) than the TP2 of the control PS (67.1 °C), SPS (77.6 °C), YS (67.2 °C), and CS (69.7 °C). In the endotherm of the mixtures, the TP1 was always closer to that of control wheat (about 62 °C). In contrast, the TP2 of the mixtures was always shifted towards higher values than those of the control starches. However, the TP2 was found to be lower as the starch in the mixtures was increased, and the values ranged from 68.6 to 69.4 °C, 80.1 to 82.2 °C, 69.3 to 70.7 °C, and 73.3 to 74.3 °C for the wheat–PS, wheat–SPS, wheat–YS, and wheat–CS mixtures, respectively, at 10% to 50% starch. The apparent shifting towards higher temperatures resulted in a more prominent biphasic gelatinization behavior due to the influence of the wheat gluten in the mixtures of wheat flour and starches. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Wheat flour; Tuber and root starches; Substitution; Gelatinization temperature
1. Introduction Roots and tuber crops can be divided into the following major groups: tubers, including potato (Solanum tuberosum) and yam (Dioscorea spp.); roots, including cassava (Manihot esculenta Crantz) and sweet potato (Ipomoea batatas); edible aroids, including taro (Colocasia esculenta) and cocoyam (Xanthosoma sagittifolium). These crops are important calorie sources, particularly when compared to other tropical food sources (Hahn, John, Isoba, & Ikotun, 1989); in addition, approximately one-third of the world-
*
Corresponding authors. Tel.: +81 155 62 9278; fax: +81 155 62 2926. E-mail addresses: [email protected], [email protected]ffrc.go.jp (I.S.M. Zaidul), noda@affrc.go.jp (T. Noda). 0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.09.011
wide population depends on them (Howeler, Ezumah, & Midmore, 1993). Hahn et al. (1989) reported that tuber and root crops research and development have been neglected even though these staple crops are clearly important in the tropics as part of the food industry and as animal feed. This neglect is partially attributed to the assumption that these tuber/root crops are inferior because of their lower price than cereals and low protein content. In addition, it is often believed that there is an inverse relationship between root crop consumption and the standard of living. However, in recent years in many countries, there has been an increasing political and scientific awareness of the importance of increasing root crop production (Hahn et al., 1989). Tropical root and stem tuber crops are commonly converted into flour (Kordylas, 1990) to preserve them. These
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flours are used as ingredients and/ or processing aids in the food industry. The major constituent of these tuber and root flours is starch. Starch is the major carbohydrate in roots, ranging from 73.7% to 84.9% of the root dry weight (Sriburi, Hill, & Mitchell, 1999). However, starch is one of most important natural macromolecules and is known to be heterogeneous. The possibility of using potato and sweet potato starches in noodles and other wheat-based foods has been investigated by Chen, Schols, and Voragen (2003) and Noda et al. (2006); furthermore, the use of these starches as dough conditioners in bread manufacturing, stabilizers in ice cream, and thickeners in soups and sauces has been studied by Silva (1990) and Marques et al. (2006). However, food producers pay particular attention to the major structural changes that occur as a result of heating during processing and lead to a change in the functional behavior of starch because any application of starch involves the gelatinization or melting of the granule structure. Thus, proper understanding of the starch phase transitions or gelatinization is extremely important in food processing (Roos, 1995). The phenomenon of gelatinization is very complex, and several models, which are summarized by Jenkis and Donald (1998), have been proposed to explain this behavior. A useful review of this topic is well documented in Parker and Ring (2001) and Tester et al. (2004). Starch gelatinization is a combined process consisting of the hydration of an amorphous region and subsequent melting of crystalline arrays (Randzio & Orlowska, 2005). The stabilities of the crystalline domains vary within and between granules (Blanshard, 1987). Donovan (1979) reported that, at high water contents, the amorphous regions of the granules imbibed water and swelled, resulting in stripping or separation of the starch chains from the crystallites. When all crystals were stripped at high moisture levels, no crystallites remained to be melted at high temperature (Donovan, 1979). Evans and Haisman (1982) proposed the ‘‘cooperative melting theory” to explain the biphasic endotherm that results from the crystallite stability within the granules. The granules containing the least stable crystallites start to change upon heating. Water absorption by the granules lowers the melting points of crystallites, which results in quick melting of the remaining crystallites. This process reduces the constraints of any remaining crystallites to lower their melting points. This cooperative melting process happens quickly when there is sufficient water and yields a narrow or single DSC endotherm. At lower water contents, however, there is insufficient water for cooperative melting to take place. This results in a second endotherm (or a ‘‘shoulder”, depending on the water content), which represents crystallites melting after the cooperative process, at a higher temperature (Evans & Haisman, 1982). Eliasson (1983) studied a starch–gluten system to observe the gelatinization of starch in the presence of gluten from spring wheat using DSC. Author concluded that
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the gelatinization peak temperature of the starch was higher in the presence of gluten proteins. Author also reported that the peak temperature was higher as the ratio of gluten to starch increased. The changes in the starch gelatinization parameters were believed to be due to less available water in the presence of the gluten (Eliasson, 1983). There is a need to analyze the most important properties, i.e., the gelatinization characteristics of tuber and root starches, since these are frequently incorporated in the preparation of a diverse range of foods. Differential scanning calorimetry (DSC) is widely accepted as the most suitable instrument for the evaluation of starch gelatinization. A water-dependent relationship has been established from DSC measurements for the starch endotherms during gelatinization (Donovan, 1979). Although the gelatinization effect of potato starch on wheat flour (Zaidul, Yamauchi, Endo, Takigawa, & Noda, 2007a) and the quality of noodles produced from wheat flour–potato starch blends have been studied (Noda et al., 2006), fundamental insights on the gelatinization process in the blends are still lacking much. Therefore, the objective of this study was to investigate the effects of mixing various tuber and root starches with wheat flour on the thermal transition of gelatinization peak temperatures using DSC. Further, the study may also emphasize whether any factor(s) could associate with the biphasic gelatinization behavior of the mixture of wheat flour and tuber/ crop starches. 2. Materials and methods 2.1. Materials Commercial hard-wheat flour milled from the Japanese cultivar, Kitanokaori, was purchased from the Ebetsu Flour Milling Co., Ltd., Ebetsu, Hokkaido, Japan. Potato starch (PS) (Solanum tuberosum L.) and sweet potato starch (SPS) (Ipomoea batatas) were purchased from Toukouren, Urahoro, Hokkaido, Japan, and the Haraigawa Starch Factory, Kimotsuki Agricultural Cooperative Association, Kanoya, Kagoshima, Japan, respectively. Cassava starch isolated from cassava tubers (CS) (Manihot esculenta) grown in Thailand was obtained from the Nippon Starch Chemical Co., Ltd., Osaka, Japan. Yam starch (YS) was isolated from fresh yam tubers (Dioscorea opposite spp.) obtained from the Kawanishi Agricultural Cooperative Association, Obihiro, Hokkaido, Japan, as described in our previous study (Zaidul, Norulaini, Omar, Yamauchi, & Noda, 2007b). 2.2. Analytical methods The moisture content, median granule size, and phosphorus, amylose, protein, and fat contents of wheat flour and PS, SPS, YS and CS have been determined in our previous study (Zaidul et al., 2007b).
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2.3. Preparation of blended samples The PS, SPS, YS, and CS were blended individually with wheat flour at the ratios of 0/100 (starch:wheat flour), 10/ 90, 20/80, 30/70, 40/60, 50/50, and 100/0. Mixing was on a weight basis as described by Zaidul et al. (2007b). 2.4. Thermal properties using differential scanning calorimetry (DSC) DSC analysis was conducted using a DSC 6100 (Seiko Instruments, Tokyo) according to Noda et al. (2004). Approximately 10 mg of a sample (dry weight basis) was weighed in a silver pan and distilled water (about 70 wt%) was then added to make a suspension of 30% (dry weight basis, w/w). A sealed pan with distilled water was used as a reference. Scans were run at a heating rate of 2 °C/ min from 25 to 130 °C. The gelatinization peak temperature (TP) was recorded. 2.5. Statistical analysis The DSC traces were determined in triplicate. The averages and Duncan t-test were computed to measure variations in wheat flour and different starches as well as in the mixtures of wheat flour and starch. The least significant difference at the 5% probability level (P < 0.05) was calculated for each parameter. 3. Results and discussion The median granule size and the phosphorus, amylose, protein, fat, and moisture contents of the samples were reported in our previous studies (Zaidul et al., 2007b). The median granule size of wheat flour was found to be larger than that of all the starches used in the experiments. Wheat flour had the highest phosphorus content, followed by PS, SPS, YS, and CS. The amylose of wheat flour was also higher than that of all of the starches used in the experiments. However, among starches, CS had the highest amylose content, followed by YS, SPS, and PS. In general,
tuber starches with higher amylose had less phosphorus, since the phosphate groups are covalently bound to amylopectin molecules. Therefore, PS had the highest phosphorus, followed by SPS, YS, and CS (Zaidul et al., 2007b). The protein and fat contents of wheat flour were 13.2% and 1.4%, respectively, whereas a negligible amount of protein and fat was present in the tuber/crop starches (Zaidul et al., 2007b). The gelatinization peak temperature (TP1) of the control wheat flour was significantly (P < 0.05) lower than that (TP2) of control starches. On the other hand, the TP2 of the control SPS was higher than those of the control PS, YS, and CS (Table 1). Figs. 1 to 4 represent the DSC traces of the gelatinization peak temperatures (TP) of the control wheat flour and starches and their mixtures at 10% to 50% starch, where the first peak (TP1) and the second peak (TP2) are manifestly ascribed to the wheat flour and starches, respectively. Birefringence and staining measurements suggest that the temperature of the first peak (TP1) arises solely from the melting transition of wheat starch granules (Liu & Lelie´vre, 1992). In contrast, the temperature of the second peak (TP2) might therefore mainly be attributed to the gelatinization of PS, SPS, YS, and CS. The area of the TP1 of control wheat flour in the heat endotherm started to decrease with the increase of PS, SPS, YS, and CS as the weight fraction of the wheat flour in the blend decreased. Similarly, the area of the TP2 of the control PS, SPS, YS, and CS endotherm became smaller with the increase of wheat flour in the mixtures. In Fig. 1, the DSC traces represent a single sharp effect of TP, which was attributed at 62.6 °C (TP1) for control wheat flour and at 67.1 °C (TP2) for control PS (Table 1). In the wheat–PS mixtures at 10% to 50% PS, the TP1 (at about 62 °C) was evidently closer to that of the control wheat flour. In contrast, the TP2 was higher with PS in the wheat–PS mixtures than in the control PS (Fig. 1). The TP2 tended to be lower with an increase of the PS in the mixture and was found to be significant (P < 0.05) at 50%. The reason for this anomalous shifting of the TP2 may be the interaction of the wheat gluten in the mixtures. The significant drop of the TP2 at 50% PS was presumably
Table 1 DSC traces of the gelatinization peak (TP1: first peak; TP2: second peak) temperatures of control wheat flour and PS, SPS, YS, and CS and the mixture of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS at different % (w/w) of starch % Starch (w/w) in the mixture
PS T P1 A (°C)
T P2 A (°C)
T P1 A (°C)
SPS T P2 A (°C)
T P1 A (°C)
YS T P2 A (°C)
T P1 A (°C)
CS T P2 A (°C)
T P1 A (°C)
Wheat flour
10 20 30 40 50 Control sample
61.6d 61.6d 61.8c 62.0b 62.1b n.a.
69.4a 69.3ab 69.2ab 69.1ab 68.6b 67.1cB
61.9b 61.6cd 61.7c 61.5d 61.5d n.a.
82.2a 81.9b 81.6c 81.1d 80.1e 77.6f
62.0e 62.4bc 62.2de 62.3cd 62.5ab n.a.
70.7a 70.2ab 69.9bc 69.7b,c 69.3c 67.2dB
61.9b 61.6d 61.8bc 61.7cd 61.9b n.a.
74.3a 73.9b 73.8b 73.7b 73.3c 69.7d
n.a. n.a. n.a. n.a. n.a. 62.6a
n.a., not applicable. A Values followed by the same letters in the same column are not significantly different at P < 0.05 level; the maximum relative standard deviation of TP1 and TP2 is 0.8% and 1.5%, respectively. B The values of the control PS and YS are not significantly different at P < 0.05 level either.
I.S.M. Zaidul et al. / Journal of Food Engineering 86 (2008) 68–73 2000 1800
71
2600 2400
PS
YS
1600
Endothermic heat flow [μW]
Endothermic heat flow [μW]
2200 1400 50:50
1200
60:40
1000 800 600
70:30 80:20
400
0 20
1800 1600 1400 1000 800 600 200
Wheat
30
50:50
1200 60:40 70:30 80:20 90:10
400
90:10
200
2000
40
50
60
70
80
90
0 20
100 110 120
Wheat
30
40
50
Temperature (oC) Fig. 1. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and potato starch (PS) and wheat flour–PS mixtures at 10% to 50% PS. The numbers labeling the traces give the ratios of the weights of wheat to PS (left to right) in the blends.
60
70
80
90
100 110 120
Temperature (οC) Fig. 3. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and yam starch (YS) and wheat flour–YS mixtures at 10% to 50% YS. The numbers labeling the traces give the ratios of the weights of wheat to YS (left to right) in the blends.
1800
2000 1800 SPS
1400
Endothermic heat flow [μW]
Endothermic heat flow [μW]
1600
1200 1000
50:50 60:40
800
70:30
600
80:20
400 90:10
200
1600
CS
1400
50:50
1200 60:40
1000 800
70:30 80:20 90:10
600 400
Wheat
200
Wheat
0 20
30
40
50
60
70
80
90
100 110 120
Temperature (οC) Fig. 2. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and sweet potato starch (SPS), and wheat flour–SPS mixtures at 10% to 50% SPS. The numbers labeling the traces give the ratios of the weights of wheat to SPS (left to right) in the blends.
due to the significant dilution of the wheat gluten that occurred at this level (Table 1 and Fig. 1). However, the smaller peaks at higher temperature (at about 100 °C) were gelatinization peaks that occurred as a result of the endothermal transition resulting from dissolving the amylose– lipid complex at 10% to 50% PS in the mixtures. A similar observation was found in the mixtures of wheat flour and SPS, where the TP1 was also at about 62 °C, whereas the TP2 was significantly (P < 0.05) higher in wheat–SPS mix-
0 20
30
40
50
60
70
80
90
100 110 120
ο
Temperature ( C) Fig. 4. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and cassava starch (CS) and wheat flour–CS mixtures at 10% to 50% CS. The numbers labeling the traces give the ratios of the weights of wheat to CS (left to right) in the blends.
tures than in the control SPS. However, the TP2 tended to be significantly (P < 0.05) lower with an increase of SPS in the mixtures (Table 1 and Fig. 2). The trends of the gelatinization temperatures of wheat–YS and wheat– CS mixtures were also similar to those of wheat–PS and wheat–SPS mixtures, in which the TP1 was observed at about 62 °C and the TP2 increased in both wheat–YS (Fig. 3) and wheat–CS mixtures (Fig. 4). Similarly, the TP2 also tended to be lower with an increase of YS and
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CS in the mixtures (Table 1 and Figs. 3 and 4). The endothermal transitions of the amylose–lipid complex occurred within 100 to 105 °C at 10% to 50% SPS, YS, and CS in the mixtures. Liu and Lelie´vre (1992) investigated the DSC melting transitions and reported that, at a 30% control starch suspension, a single endothermic transition occurred and the wheat starch endotherm was observed at about 10 °C lower than for rice starch. Thus, in their study, two endothermic transitions occurred with two separate peaks of wheat and rice starches in the DSC traces in which the blends of wheat and rice starches were present at a 30% suspension. According to theory, if the water content of a suspension is sufficient (above 65%), each granule absorbs water without restriction as it melts, and a single endothermic peak will be observed (Liu & Lelie´vre, 1992). In our observation, the differences between wheat flour and starches were 4.6, 15.0, 4.6, and 7.1 °C for PS, SPS, YS, and CS, respectively. Thus, the endothermic event ascribed to the TP2 of the mixtures shifted higher than those of the control samples. It was assumed that the shifting in the DSC traces of the TP2 of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS was the sum of the DSC outputs for each of the starch components and the wheat gluten of the mixtures. Liu and Lelie´vre (1992) also reported that the gelatinization traces for the wheat starch and rich starch mixtures were simply the sum of the DSC outputs for each of the starch components in the mixture. Unlike the case of the addition of wheat starch, the addition of wheat flour in the PS, SPS, YS, and CS had a most significant effect on the TP2 in the mixture (Table 1 and Figs. 2 to 4) due to the presence of gluten protein in the wheat flour. However, this apparent shifting of slightly higher temperatures resulted in a more prominent biphasic gelatinization behavior of the mixture due to the influence of the wheat gluten. Abdellatif and Patricia (2003) and Eliasson (1983) reported that the gelatinization peak temperature of the starch increased in the presence of gluten protein. Our observations were strongly supported by the observations of these authors. Randzio, Flis-Kabulska, and Grolier (2002) examined the phase transitions in the starch–water system. They observed that an increase in the water content resulted in a linear reduction in the temperature (at 62 °C) at the beginning of the exothermic transition, which was supported by our observations, for which we used 30% starch (w/w) suspensions (70 wt% water). Furthermore, the reduction of TP1 of the mixtures was comparable to that of the control samples. Delcour, Vansteelandt, Hythier, and Abe´cassis (2000) concluded that the slight changes in the starch gelatinization behavior that were caused by lipid or protein removal or differences in the granule size distribution would have a negligible effect on pasta quality. However, it was later determined that each variation of a starch property that has an impact on the water uptake, gel consistency, and gluten breakdown capacity of starch may indeed influence pasta quality (Delcour et al., 2000).
4. Conclusions The gelatinization peak temperature (TP) of DSC traces of control wheat flour and potato (PS), sweet potato (SPS), yam (YS), and cassava (CS) starches and the mixture of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS were represented to the first gelatinization peak (TP1) and second gelatinization peak (TP2) and ascribed to wheat flour and starches, respectively. The TP2 of control starches (67.1–77.6 °C) was found to be higher than that of control wheat flour (62.6 °C). In the mixture, the TP1 was always closer to that of control wheat (about 62 °C), whereas the TP2 always shifted towards higher values than those of the PS, SPS, YS, and CS. However, the TP2 tended to decrease with higher PS, SPS, YS, and CS in the mixtures, and the maximum shifted values were 69.4, 82.2, 70.7, and 74.3 °C for the wheat–PS, wheat– SPS, wheat–YS, and wheat–CS mixtures, respectively, at 10% PS, SPS, YS, and CS. This anomalous shifting of the higher temperatures (TP2) resulted in a more prominent biphasic gelatinization behavior of the mixtures due to the influence of the wheat gluten. The endothermal transitions of the amylose–lipid complex occurred within 100 to 105 °C at 10% to 50% PS, SPS, YS, and CS in the mixtures. The data of this work may supply knowledge on the partial substitution of tuber and root starches in the wheat flour used in the food industry. The method is easily adapted to determine the influence of the wheat gluten in wheat flour and other tuber or root starch mixtures. Further studies are needed to examine the textural properties of wheat flour and tuber/root starch mixtures using a rheoner. Acknowledgements This work was financially supported by the Japan Society for the Promotion of Science (JSPS) and partially by a Grant-in-Aid for the Research and Development Project for a New Bio-industry Initiative from the Bio-oriented Technology Research Institution (BRAIN), Japan. This work also was partially financed by Cooperation of Innovative Technology and Advanced Research in Evolution Area (CITY AREA), Japan. References Abdellatif, A. M., & Patricia, R. D. (2003). The effect of mixing and wheat protein/gluten on the gelatinization of wheat starch. Food Chemistry, 81, 533–545. Blanshard, J. M. V. (1987). Starch granule structure and function: A physicochemical approach. In T. Galliard (Ed.), Starch: Properties and potential (pp. 16). Chichester: John Wiley and Sons. Chen, Z., Schols, H. A., & Voragen, A. G. J. (2003). Starch granule size strongly determines starch noodle processing and noodle quality. Journal of Food Science, 68, 1584–1589. Delcour, J. A., Vansteelandt, J., Hythier, M.-C., & Abe´cassis, J. (2000). Fractionation and reconstitution experiments provide insight into the role of starch gelatinization and pasting properties in pasta quality. Journal of Agricultural and Food Chemistry, 48, 3774–3778.
I.S.M. Zaidul et al. / Journal of Food Engineering 86 (2008) 68–73 Donovan, J. W. (1979). Phase transitions of the starch–water system. Biopolymers, 18, 263–275. Eliasson, A. C. (1983). Differential scanning calorimetry studies on wheat starch–gluten mixture. Journal of Cereal Science, 30, 199–205. Evans, I. D., & Haisman, D. R. (1982). The effect of solutes on the gelatinization temperature range of potato starch. Starch-Starke, 34, 224–231. Hahn, S. K., John, C. G., Isoba & Ikotun, T. (1989). Resistance breeding in root and tuber crops at the international institute of tropical agriculture (IITA), Ibadan, Nigeria. Crop Production, 8, 147–168. Howeler, R. H., Ezumah, H. C., & Midmore, D. J. (1993). Tillage systems for root and tuber crops in the tropics. Soil & Tillage Research, 27, 211–240. Jenkis, P. J., & Donald, A. M. (1998). Gelatinization of starch: a combined SAXS/WAXS/DSC and SANS study. Carbohydrate Research, 308, 133–147. Kordylas, J. M. (1990). Processing and preservation of tropical and subtropical foods. London: Macmillan Education Ltd, pp. 74–108. Liu, H., & Lelie´vre, J. (1992). A differential scanning calorimetry study of melting transitions in aqueous suspensions containing blends of wheat and rice starch. Carbohydrate Polymers, 17, 145–149. Marques, P. T., Pe´re´go, C., LeMeins, J. F., Borsali, R., & Soldi, V. (2006). Study of gelatinization process and viscoelastic properties of cassava starch: Effect of sodium hydroxide and ethanol glycol diacrylate as cross-linking agent. Carbohydrate Polymers, 66, 396–407. Noda, T., Tsuda, S., Mori, M., Takigawa, S., Endo, C. M., Kim, S. J., et al. (2006). Effect of potato starch properties on instant noodle quality in wheat flour and potato starch blends. Starch-Starke, 58, 18–24.
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Noda, T., Tsuda, S., Mori, M., Takigawa, S., Endo, C. M., Saito, K., et al. (2004). The effect of harvested dates on the starch properties of various potato cultivars. Food Chemistry, 86, 119–125. Parker, R., & Ring, S. G. (2001). Aspects of the physical chemistry of starch. Journal of Cereal Science, 34, 1–17. Randzio, S. L., Flis-Kabulska, I., & Grolier, J.-P. E. (2002). Reexamination of phase transitions in the starch–water system. Macromolecules, 35, 8852–8859. Randzio, S. L., & Orlowska, M. (2005). Simultaneous and in situ analysis of thermal and volumetric properties of starch gelatinization over wide pressure and temperature ranges. Biomacromolecules, 6, 3045–3050. Roos, Y. H. (1995). Food components and polymers. In S. L. Taylor (Ed.), Phase transitions in foods (pp. 109). San Diego CA: Academic Press. Silva, J. L. (1990). Sweet potatoes. In K. H. Remy (Ed.), Processing and products (pp. 15). Mississippi: Mississippi State University. Sriburi, P., Hill, S. E., & Mitchell, J. R. (1999). Effects of L-ascorbic acid on the conversion of cassava starch. Food Hydrocolloids, 13, 177–183. Tester, R. F., Karkalas, J., & Qi, X. (2004). Starch – composition, fine structure and architecture. Journal of Cereal Science, 39, 151–165. Zaidul, I. S. M., Yamauchi, H., Endo, C.-M., Takigawa, S., & Noda, T. (2007a). Thermal analysis of mixtures of wheat flour and potato starches. Food Hydrocolloids, in press. Zaidul, I. S. M., Norulaini, N. A. N., Omar, A. K. M., Yamauchi, H., & Noda, T. (2007b). RVA analysis of mixtures of wheat flour and potato, sweet potato, yam, and cassava starches. Carbohydrate Polymers, 69, 784–791.
Journal of Food Engineering 86 (2008) 68–73 www.elsevier.com/locate/jfoodeng
DSC study of mixtures of wheat flour and potato, sweet potato, cassava, and yam starches I.S.M. Zaidul a,*, N. Absar a, S.-J. Kim a, T. Suzuki a, A.A. Karim b, H. Yamauchi a, T. Noda a,* a
Memuro Upland Farming Research Station, National Agricultural Research Center for Hokkaido Region, Shinsei, Memuro, Kasai, Hokkaido 082-0071, Japan b School of Industrial Technology, Universiti Sains Malaysia, 11800 P. Penang, Malaysia Received 25 May 2007; received in revised form 13 August 2007; accepted 9 September 2007 Available online 15 September 2007
Abstract Differential scanning calorimetry (DSC) traces at a 30 wt% suspension were studied for mixture of wheat flour and following starches: potato (PS), sweet potato (SPS), yam (YS), and cassava (CS) at 10% to 50% starch. In the endothermal transition, the gelatinization peak temperature of the first peak (TP1) was attributed to the wheat flour and that of the second peak (TP2), to the starches. The TP1 of the control wheat flour was lower (62.6 °C) than the TP2 of the control PS (67.1 °C), SPS (77.6 °C), YS (67.2 °C), and CS (69.7 °C). In the endotherm of the mixtures, the TP1 was always closer to that of control wheat (about 62 °C). In contrast, the TP2 of the mixtures was always shifted towards higher values than those of the control starches. However, the TP2 was found to be lower as the starch in the mixtures was increased, and the values ranged from 68.6 to 69.4 °C, 80.1 to 82.2 °C, 69.3 to 70.7 °C, and 73.3 to 74.3 °C for the wheat–PS, wheat–SPS, wheat–YS, and wheat–CS mixtures, respectively, at 10% to 50% starch. The apparent shifting towards higher temperatures resulted in a more prominent biphasic gelatinization behavior due to the influence of the wheat gluten in the mixtures of wheat flour and starches. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Wheat flour; Tuber and root starches; Substitution; Gelatinization temperature
1. Introduction Roots and tuber crops can be divided into the following major groups: tubers, including potato (Solanum tuberosum) and yam (Dioscorea spp.); roots, including cassava (Manihot esculenta Crantz) and sweet potato (Ipomoea batatas); edible aroids, including taro (Colocasia esculenta) and cocoyam (Xanthosoma sagittifolium). These crops are important calorie sources, particularly when compared to other tropical food sources (Hahn, John, Isoba, & Ikotun, 1989); in addition, approximately one-third of the world-
*
Corresponding authors. Tel.: +81 155 62 9278; fax: +81 155 62 2926. E-mail addresses: [email protected], [email protected]ffrc.go.jp (I.S.M. Zaidul), noda@affrc.go.jp (T. Noda). 0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.09.011
wide population depends on them (Howeler, Ezumah, & Midmore, 1993). Hahn et al. (1989) reported that tuber and root crops research and development have been neglected even though these staple crops are clearly important in the tropics as part of the food industry and as animal feed. This neglect is partially attributed to the assumption that these tuber/root crops are inferior because of their lower price than cereals and low protein content. In addition, it is often believed that there is an inverse relationship between root crop consumption and the standard of living. However, in recent years in many countries, there has been an increasing political and scientific awareness of the importance of increasing root crop production (Hahn et al., 1989). Tropical root and stem tuber crops are commonly converted into flour (Kordylas, 1990) to preserve them. These
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flours are used as ingredients and/ or processing aids in the food industry. The major constituent of these tuber and root flours is starch. Starch is the major carbohydrate in roots, ranging from 73.7% to 84.9% of the root dry weight (Sriburi, Hill, & Mitchell, 1999). However, starch is one of most important natural macromolecules and is known to be heterogeneous. The possibility of using potato and sweet potato starches in noodles and other wheat-based foods has been investigated by Chen, Schols, and Voragen (2003) and Noda et al. (2006); furthermore, the use of these starches as dough conditioners in bread manufacturing, stabilizers in ice cream, and thickeners in soups and sauces has been studied by Silva (1990) and Marques et al. (2006). However, food producers pay particular attention to the major structural changes that occur as a result of heating during processing and lead to a change in the functional behavior of starch because any application of starch involves the gelatinization or melting of the granule structure. Thus, proper understanding of the starch phase transitions or gelatinization is extremely important in food processing (Roos, 1995). The phenomenon of gelatinization is very complex, and several models, which are summarized by Jenkis and Donald (1998), have been proposed to explain this behavior. A useful review of this topic is well documented in Parker and Ring (2001) and Tester et al. (2004). Starch gelatinization is a combined process consisting of the hydration of an amorphous region and subsequent melting of crystalline arrays (Randzio & Orlowska, 2005). The stabilities of the crystalline domains vary within and between granules (Blanshard, 1987). Donovan (1979) reported that, at high water contents, the amorphous regions of the granules imbibed water and swelled, resulting in stripping or separation of the starch chains from the crystallites. When all crystals were stripped at high moisture levels, no crystallites remained to be melted at high temperature (Donovan, 1979). Evans and Haisman (1982) proposed the ‘‘cooperative melting theory” to explain the biphasic endotherm that results from the crystallite stability within the granules. The granules containing the least stable crystallites start to change upon heating. Water absorption by the granules lowers the melting points of crystallites, which results in quick melting of the remaining crystallites. This process reduces the constraints of any remaining crystallites to lower their melting points. This cooperative melting process happens quickly when there is sufficient water and yields a narrow or single DSC endotherm. At lower water contents, however, there is insufficient water for cooperative melting to take place. This results in a second endotherm (or a ‘‘shoulder”, depending on the water content), which represents crystallites melting after the cooperative process, at a higher temperature (Evans & Haisman, 1982). Eliasson (1983) studied a starch–gluten system to observe the gelatinization of starch in the presence of gluten from spring wheat using DSC. Author concluded that
69
the gelatinization peak temperature of the starch was higher in the presence of gluten proteins. Author also reported that the peak temperature was higher as the ratio of gluten to starch increased. The changes in the starch gelatinization parameters were believed to be due to less available water in the presence of the gluten (Eliasson, 1983). There is a need to analyze the most important properties, i.e., the gelatinization characteristics of tuber and root starches, since these are frequently incorporated in the preparation of a diverse range of foods. Differential scanning calorimetry (DSC) is widely accepted as the most suitable instrument for the evaluation of starch gelatinization. A water-dependent relationship has been established from DSC measurements for the starch endotherms during gelatinization (Donovan, 1979). Although the gelatinization effect of potato starch on wheat flour (Zaidul, Yamauchi, Endo, Takigawa, & Noda, 2007a) and the quality of noodles produced from wheat flour–potato starch blends have been studied (Noda et al., 2006), fundamental insights on the gelatinization process in the blends are still lacking much. Therefore, the objective of this study was to investigate the effects of mixing various tuber and root starches with wheat flour on the thermal transition of gelatinization peak temperatures using DSC. Further, the study may also emphasize whether any factor(s) could associate with the biphasic gelatinization behavior of the mixture of wheat flour and tuber/ crop starches. 2. Materials and methods 2.1. Materials Commercial hard-wheat flour milled from the Japanese cultivar, Kitanokaori, was purchased from the Ebetsu Flour Milling Co., Ltd., Ebetsu, Hokkaido, Japan. Potato starch (PS) (Solanum tuberosum L.) and sweet potato starch (SPS) (Ipomoea batatas) were purchased from Toukouren, Urahoro, Hokkaido, Japan, and the Haraigawa Starch Factory, Kimotsuki Agricultural Cooperative Association, Kanoya, Kagoshima, Japan, respectively. Cassava starch isolated from cassava tubers (CS) (Manihot esculenta) grown in Thailand was obtained from the Nippon Starch Chemical Co., Ltd., Osaka, Japan. Yam starch (YS) was isolated from fresh yam tubers (Dioscorea opposite spp.) obtained from the Kawanishi Agricultural Cooperative Association, Obihiro, Hokkaido, Japan, as described in our previous study (Zaidul, Norulaini, Omar, Yamauchi, & Noda, 2007b). 2.2. Analytical methods The moisture content, median granule size, and phosphorus, amylose, protein, and fat contents of wheat flour and PS, SPS, YS and CS have been determined in our previous study (Zaidul et al., 2007b).
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2.3. Preparation of blended samples The PS, SPS, YS, and CS were blended individually with wheat flour at the ratios of 0/100 (starch:wheat flour), 10/ 90, 20/80, 30/70, 40/60, 50/50, and 100/0. Mixing was on a weight basis as described by Zaidul et al. (2007b). 2.4. Thermal properties using differential scanning calorimetry (DSC) DSC analysis was conducted using a DSC 6100 (Seiko Instruments, Tokyo) according to Noda et al. (2004). Approximately 10 mg of a sample (dry weight basis) was weighed in a silver pan and distilled water (about 70 wt%) was then added to make a suspension of 30% (dry weight basis, w/w). A sealed pan with distilled water was used as a reference. Scans were run at a heating rate of 2 °C/ min from 25 to 130 °C. The gelatinization peak temperature (TP) was recorded. 2.5. Statistical analysis The DSC traces were determined in triplicate. The averages and Duncan t-test were computed to measure variations in wheat flour and different starches as well as in the mixtures of wheat flour and starch. The least significant difference at the 5% probability level (P < 0.05) was calculated for each parameter. 3. Results and discussion The median granule size and the phosphorus, amylose, protein, fat, and moisture contents of the samples were reported in our previous studies (Zaidul et al., 2007b). The median granule size of wheat flour was found to be larger than that of all the starches used in the experiments. Wheat flour had the highest phosphorus content, followed by PS, SPS, YS, and CS. The amylose of wheat flour was also higher than that of all of the starches used in the experiments. However, among starches, CS had the highest amylose content, followed by YS, SPS, and PS. In general,
tuber starches with higher amylose had less phosphorus, since the phosphate groups are covalently bound to amylopectin molecules. Therefore, PS had the highest phosphorus, followed by SPS, YS, and CS (Zaidul et al., 2007b). The protein and fat contents of wheat flour were 13.2% and 1.4%, respectively, whereas a negligible amount of protein and fat was present in the tuber/crop starches (Zaidul et al., 2007b). The gelatinization peak temperature (TP1) of the control wheat flour was significantly (P < 0.05) lower than that (TP2) of control starches. On the other hand, the TP2 of the control SPS was higher than those of the control PS, YS, and CS (Table 1). Figs. 1 to 4 represent the DSC traces of the gelatinization peak temperatures (TP) of the control wheat flour and starches and their mixtures at 10% to 50% starch, where the first peak (TP1) and the second peak (TP2) are manifestly ascribed to the wheat flour and starches, respectively. Birefringence and staining measurements suggest that the temperature of the first peak (TP1) arises solely from the melting transition of wheat starch granules (Liu & Lelie´vre, 1992). In contrast, the temperature of the second peak (TP2) might therefore mainly be attributed to the gelatinization of PS, SPS, YS, and CS. The area of the TP1 of control wheat flour in the heat endotherm started to decrease with the increase of PS, SPS, YS, and CS as the weight fraction of the wheat flour in the blend decreased. Similarly, the area of the TP2 of the control PS, SPS, YS, and CS endotherm became smaller with the increase of wheat flour in the mixtures. In Fig. 1, the DSC traces represent a single sharp effect of TP, which was attributed at 62.6 °C (TP1) for control wheat flour and at 67.1 °C (TP2) for control PS (Table 1). In the wheat–PS mixtures at 10% to 50% PS, the TP1 (at about 62 °C) was evidently closer to that of the control wheat flour. In contrast, the TP2 was higher with PS in the wheat–PS mixtures than in the control PS (Fig. 1). The TP2 tended to be lower with an increase of the PS in the mixture and was found to be significant (P < 0.05) at 50%. The reason for this anomalous shifting of the TP2 may be the interaction of the wheat gluten in the mixtures. The significant drop of the TP2 at 50% PS was presumably
Table 1 DSC traces of the gelatinization peak (TP1: first peak; TP2: second peak) temperatures of control wheat flour and PS, SPS, YS, and CS and the mixture of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS at different % (w/w) of starch % Starch (w/w) in the mixture
PS T P1 A (°C)
T P2 A (°C)
T P1 A (°C)
SPS T P2 A (°C)
T P1 A (°C)
YS T P2 A (°C)
T P1 A (°C)
CS T P2 A (°C)
T P1 A (°C)
Wheat flour
10 20 30 40 50 Control sample
61.6d 61.6d 61.8c 62.0b 62.1b n.a.
69.4a 69.3ab 69.2ab 69.1ab 68.6b 67.1cB
61.9b 61.6cd 61.7c 61.5d 61.5d n.a.
82.2a 81.9b 81.6c 81.1d 80.1e 77.6f
62.0e 62.4bc 62.2de 62.3cd 62.5ab n.a.
70.7a 70.2ab 69.9bc 69.7b,c 69.3c 67.2dB
61.9b 61.6d 61.8bc 61.7cd 61.9b n.a.
74.3a 73.9b 73.8b 73.7b 73.3c 69.7d
n.a. n.a. n.a. n.a. n.a. 62.6a
n.a., not applicable. A Values followed by the same letters in the same column are not significantly different at P < 0.05 level; the maximum relative standard deviation of TP1 and TP2 is 0.8% and 1.5%, respectively. B The values of the control PS and YS are not significantly different at P < 0.05 level either.
I.S.M. Zaidul et al. / Journal of Food Engineering 86 (2008) 68–73 2000 1800
71
2600 2400
PS
YS
1600
Endothermic heat flow [μW]
Endothermic heat flow [μW]
2200 1400 50:50
1200
60:40
1000 800 600
70:30 80:20
400
0 20
1800 1600 1400 1000 800 600 200
Wheat
30
50:50
1200 60:40 70:30 80:20 90:10
400
90:10
200
2000
40
50
60
70
80
90
0 20
100 110 120
Wheat
30
40
50
Temperature (oC) Fig. 1. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and potato starch (PS) and wheat flour–PS mixtures at 10% to 50% PS. The numbers labeling the traces give the ratios of the weights of wheat to PS (left to right) in the blends.
60
70
80
90
100 110 120
Temperature (οC) Fig. 3. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and yam starch (YS) and wheat flour–YS mixtures at 10% to 50% YS. The numbers labeling the traces give the ratios of the weights of wheat to YS (left to right) in the blends.
1800
2000 1800 SPS
1400
Endothermic heat flow [μW]
Endothermic heat flow [μW]
1600
1200 1000
50:50 60:40
800
70:30
600
80:20
400 90:10
200
1600
CS
1400
50:50
1200 60:40
1000 800
70:30 80:20 90:10
600 400
Wheat
200
Wheat
0 20
30
40
50
60
70
80
90
100 110 120
Temperature (οC) Fig. 2. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and sweet potato starch (SPS), and wheat flour–SPS mixtures at 10% to 50% SPS. The numbers labeling the traces give the ratios of the weights of wheat to SPS (left to right) in the blends.
due to the significant dilution of the wheat gluten that occurred at this level (Table 1 and Fig. 1). However, the smaller peaks at higher temperature (at about 100 °C) were gelatinization peaks that occurred as a result of the endothermal transition resulting from dissolving the amylose– lipid complex at 10% to 50% PS in the mixtures. A similar observation was found in the mixtures of wheat flour and SPS, where the TP1 was also at about 62 °C, whereas the TP2 was significantly (P < 0.05) higher in wheat–SPS mix-
0 20
30
40
50
60
70
80
90
100 110 120
ο
Temperature ( C) Fig. 4. Differential scanning calorimetry (DSC) traces showing the gelatinization peak temperature (TP) of control wheat flour and cassava starch (CS) and wheat flour–CS mixtures at 10% to 50% CS. The numbers labeling the traces give the ratios of the weights of wheat to CS (left to right) in the blends.
tures than in the control SPS. However, the TP2 tended to be significantly (P < 0.05) lower with an increase of SPS in the mixtures (Table 1 and Fig. 2). The trends of the gelatinization temperatures of wheat–YS and wheat– CS mixtures were also similar to those of wheat–PS and wheat–SPS mixtures, in which the TP1 was observed at about 62 °C and the TP2 increased in both wheat–YS (Fig. 3) and wheat–CS mixtures (Fig. 4). Similarly, the TP2 also tended to be lower with an increase of YS and
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CS in the mixtures (Table 1 and Figs. 3 and 4). The endothermal transitions of the amylose–lipid complex occurred within 100 to 105 °C at 10% to 50% SPS, YS, and CS in the mixtures. Liu and Lelie´vre (1992) investigated the DSC melting transitions and reported that, at a 30% control starch suspension, a single endothermic transition occurred and the wheat starch endotherm was observed at about 10 °C lower than for rice starch. Thus, in their study, two endothermic transitions occurred with two separate peaks of wheat and rice starches in the DSC traces in which the blends of wheat and rice starches were present at a 30% suspension. According to theory, if the water content of a suspension is sufficient (above 65%), each granule absorbs water without restriction as it melts, and a single endothermic peak will be observed (Liu & Lelie´vre, 1992). In our observation, the differences between wheat flour and starches were 4.6, 15.0, 4.6, and 7.1 °C for PS, SPS, YS, and CS, respectively. Thus, the endothermic event ascribed to the TP2 of the mixtures shifted higher than those of the control samples. It was assumed that the shifting in the DSC traces of the TP2 of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS was the sum of the DSC outputs for each of the starch components and the wheat gluten of the mixtures. Liu and Lelie´vre (1992) also reported that the gelatinization traces for the wheat starch and rich starch mixtures were simply the sum of the DSC outputs for each of the starch components in the mixture. Unlike the case of the addition of wheat starch, the addition of wheat flour in the PS, SPS, YS, and CS had a most significant effect on the TP2 in the mixture (Table 1 and Figs. 2 to 4) due to the presence of gluten protein in the wheat flour. However, this apparent shifting of slightly higher temperatures resulted in a more prominent biphasic gelatinization behavior of the mixture due to the influence of the wheat gluten. Abdellatif and Patricia (2003) and Eliasson (1983) reported that the gelatinization peak temperature of the starch increased in the presence of gluten protein. Our observations were strongly supported by the observations of these authors. Randzio, Flis-Kabulska, and Grolier (2002) examined the phase transitions in the starch–water system. They observed that an increase in the water content resulted in a linear reduction in the temperature (at 62 °C) at the beginning of the exothermic transition, which was supported by our observations, for which we used 30% starch (w/w) suspensions (70 wt% water). Furthermore, the reduction of TP1 of the mixtures was comparable to that of the control samples. Delcour, Vansteelandt, Hythier, and Abe´cassis (2000) concluded that the slight changes in the starch gelatinization behavior that were caused by lipid or protein removal or differences in the granule size distribution would have a negligible effect on pasta quality. However, it was later determined that each variation of a starch property that has an impact on the water uptake, gel consistency, and gluten breakdown capacity of starch may indeed influence pasta quality (Delcour et al., 2000).
4. Conclusions The gelatinization peak temperature (TP) of DSC traces of control wheat flour and potato (PS), sweet potato (SPS), yam (YS), and cassava (CS) starches and the mixture of wheat–PS, wheat–SPS, wheat–YS, and wheat–CS were represented to the first gelatinization peak (TP1) and second gelatinization peak (TP2) and ascribed to wheat flour and starches, respectively. The TP2 of control starches (67.1–77.6 °C) was found to be higher than that of control wheat flour (62.6 °C). In the mixture, the TP1 was always closer to that of control wheat (about 62 °C), whereas the TP2 always shifted towards higher values than those of the PS, SPS, YS, and CS. However, the TP2 tended to decrease with higher PS, SPS, YS, and CS in the mixtures, and the maximum shifted values were 69.4, 82.2, 70.7, and 74.3 °C for the wheat–PS, wheat– SPS, wheat–YS, and wheat–CS mixtures, respectively, at 10% PS, SPS, YS, and CS. This anomalous shifting of the higher temperatures (TP2) resulted in a more prominent biphasic gelatinization behavior of the mixtures due to the influence of the wheat gluten. The endothermal transitions of the amylose–lipid complex occurred within 100 to 105 °C at 10% to 50% PS, SPS, YS, and CS in the mixtures. The data of this work may supply knowledge on the partial substitution of tuber and root starches in the wheat flour used in the food industry. The method is easily adapted to determine the influence of the wheat gluten in wheat flour and other tuber or root starch mixtures. Further studies are needed to examine the textural properties of wheat flour and tuber/root starch mixtures using a rheoner. Acknowledgements This work was financially supported by the Japan Society for the Promotion of Science (JSPS) and partially by a Grant-in-Aid for the Research and Development Project for a New Bio-industry Initiative from the Bio-oriented Technology Research Institution (BRAIN), Japan. This work also was partially financed by Cooperation of Innovative Technology and Advanced Research in Evolution Area (CITY AREA), Japan. References Abdellatif, A. M., & Patricia, R. D. (2003). The effect of mixing and wheat protein/gluten on the gelatinization of wheat starch. Food Chemistry, 81, 533–545. Blanshard, J. M. V. (1987). Starch granule structure and function: A physicochemical approach. In T. Galliard (Ed.), Starch: Properties and potential (pp. 16). Chichester: John Wiley and Sons. Chen, Z., Schols, H. A., & Voragen, A. G. J. (2003). Starch granule size strongly determines starch noodle processing and noodle quality. Journal of Food Science, 68, 1584–1589. Delcour, J. A., Vansteelandt, J., Hythier, M.-C., & Abe´cassis, J. (2000). Fractionation and reconstitution experiments provide insight into the role of starch gelatinization and pasting properties in pasta quality. Journal of Agricultural and Food Chemistry, 48, 3774–3778.
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