Journal of Cereal Science

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1 Journal of Cereal Science 51 () Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: Retrogradation of waxy and normal corn starch gels by temperature cycling Xing Zhou a, Byung-Kee Baik b, Ren Wang c, Seung-Taik Lim a, * a Graduate School of Life Sciences and Biotechnology, Korea University, Seoul , Republic of Korea b Washington State University, Department of Crop & Soil Sciences, Pullman, WA , USA c Department of Food Science & Technology and Carbohydrate Bioproduct Research Center, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul , Republic of Korea article info abstract Article history: Received 1 June 9 Received in revised form September 9 Accepted 22 September 9 Keywords: Temperature cycling Retrogradation Corn starch Gelatinized waxy and normal corn starches at various concentrations ( 5%) in water were stored under temperature cycles of 4 C and C (each for 1 day) up to 7 cycles or at a constant temperature of 4 C for 14 days to investigate the effects of temperature cycling on the retrogradation of both starches. Compared to starches stored only at 4 C, both starches stored under the 4/ C temperature cycles exhibited smaller melting enthalpy for retrogradation (DH r ), higher onset temperature (T o ), and lower melting temperature range (T r ) regardless of the starch concentration tested. Fewer crystallites might be formed under the temperature cycles compared to the isothermal storage, but the crystallites formed under temperature cycling appeared more homogeneous than those under the isothermal storage. The effect of starch content on the retrogradation was greater when the starch gels were stored under cycled temperatures. The reduction in DH r and the increase in conclusion temperature (T c ) by retrogradation under 4/ C temperature cycles became more apparent when the starch concentration was lower ( or %). Degree of retrogradation based on melting enthalpy was greater in normal corn starch than in waxy corn starch when starch content was low. Ó 9 Elsevier Ltd. All rights reserved. 1. Introduction The starch granule, commonly composed of both amylose and amylopectin, is semicrystalline. The crystalline regions in granules appear in clusters of branched amylopectin chains. Amylose, mainly linear starch chains, is largely amorphous and randomly distributed between amylopectin clusters (Bemiller, 7). When the starch granule is heated in the presence of water, the semicrystalline structure in granules transforms to an amorphous form; this process is termed gelatinization. Gelatinized starch, however, tends to re-associate in an ordered crystalline structure during storage, which is termed retrogradation (Yuan et al., 1993). As the retrogradation of starch affects the acceptability and shelf life of starchy food, its control in rate and degree has been substantially studied by food scientists. Starch retrogradation occurs in three phases: nucleation, i.e. formation of critical nuclei; propagation, i.e. growth of crystals from the nuclei formed; and maturation, i.e. crystal perfection or continuous slow growth. The Abbreviations: DR, the degree of retrogradation; DSC, differential scanning calorimeter; T c, conclusion temperature; T o, onset temperature; T p, peak temperature; T r, melting temperature range; DH, melting enthalpy; DH g, melting enthalpy for gelatinization; DH r, melting enthalpy for retrogradation. * Corresponding author. Tel.: þ ; fax: þ address: limst@korea.ac.kr (S.-T. Lim). overall crystallization rate mainly depends on the nucleation and propagation rate (Eerlingen et al., 1993). A temperature near the glass transition temperature favors nucleation, whereas a higher temperature up to the melting temperature favors propagation (Baik et al., 1997; Durrani and Donald, 1995; Silverio et al., ). When the storage temperature of gelatinized starch was cycled between the temperature for nucleation and the temperature for propagation, the rate of retrogradation could be accelerated (Bemiller, 7; Slade et al., 1987). This type of temperature cycling process that induces a stepwise nucleation and propagation promotes the growth of crystalline regions and perfection of crystallites (Silverio et al., ). The degree of starch retrogradation and the property of the starch crystallites formed are influenced not only by the storage time and temperature, but also by starch concentration (Jang and Pyun, 1997; Liu and Thompson, 1998; Longton and Legrys, 1981) and the botanical origin of the starch, i.e. starch crystallinity, molecular ratio of amylose to amylopectin and structures of amylose and amylopectin molecules (Elfstrand et al., 4; Fredriksson et al., 1998; Jane et al., 1999; Klucinec and Thompson, 1999; Lai et al., ; Russell, 1987a; Sasaki et al., ; Vandeputte et al., 3; Varavinit et al., 3). Several studies have investigated starch gelatinization or retrogradation behavior as a function of a wide range of moisture content. It was generally agreed that maximum retrogradation enthalpy occurred at the so-called /$ see front matter Ó 9 Elsevier Ltd. All rights reserved. doi:.16/j.jcs.9.9.5

2 58 X. Zhou et al. / Journal of Cereal Science 51 () intermediate water level when the starch concentration was 6%, but the precise relationship between starch concentration and retrogradation enthalpy varied according to storage temperature (Jang and Pyun, 1997) and starches of different origin (Liu and Thompson, 1998). Silverio et al. () have investigated the effect of temperature cycling on the retrogradation of amylopectins isolated from different starches. Park et al. (9) found that % waxy corn starch gel retrograded at the cycled temperatures had a larger amount of resistant starch but remained softer than those stored at 4 C. However, the influences of amylose content and starch concentration together with temperature cycling on starch retrogradation have not been reported. Differential scanning calorimetry (DSC) has been widely used to study the thermal behavior of starch gelatinization and retrogradation. The DSC melting endotherm of starch provides the enthalpy as well as temperatures for melting the crystalline structure in starch, which reflects the degree and perfection of the crystallinity (Durrani and Donald, 1995). The melting enthalpy (DH) is often positively related to the amount of crystals (double or single helical structure) of the starch (Liu et al., 6). The onset temperature (T o ) represents the melting temperature of the least stable crystallites. The peak temperature (T p ) suggests the melting temperature for the majority of starch crystallites. The conclusion temperature (T c ) indicates the melting temperature of the most perfect crystallites. The melting temperature range (T r ), i.e. T c T o, indicates the degree of heterogeneity of the crystallites (Biliaderis, 1992). The higher the melting temperature (T o, T p, T c ) and the narrower the melting temperature range (T r ), the more stable and uniform the crystallites are (Durrani and Donald, 1995). In this study, temperature cycles of 4 C for 1 day and C for 1 day, together with various starch concentrations ( 5%) were used to investigate the effects of temperature cycling and starch concentration on the retrogradation of waxy and normal corn starches. Crystallinity in the retrogradated starches was evaluated in the terms of melting enthalpy and temperatures using DSC. 2. Experimental 2.1. Materials and normal corn starches were gifts from Samyang Genex Company (Seoul, Korea). The moisture content of waxy corn starch was 13.2% and that of normal corn starch was 12.6%, determined by heating at 5 C for 5 h. Both starches contained crude protein less than.35%, and ash less than.15% (manufacturer data) Gelatinization and retrogradation The starch (dry solid) was weighed into an aluminum DSC pan and distilled water was added until the starch was fully wet. The excess moisture was allowed to evaporate in a balance until the total weight of starch and water reached mg to achieve the desired starch concentration of,, or 5%. The pan was hermetically sealed, and equilibrated for 24 h at 4 C. After equilibration the DSC pans were heated in a convection oven for 15 min at 5 C to gelatinize the starch (Silverio et al., ). After cooling to room temperature ( min), the DSC pans of gelatinized starch were stored for 14 days under two different conditions: at constant 4 C (stored in the cold chamber), or under the temperature cycles of 4 C for 1 day and C for 1 day (4/ C). For temperature cycling, after storage in the cold chamber at 4 C for 1 day, the DSC pans were immediately taken out and stored in a convection oven kept at C for 1 day, and then this step was repeated DSC analysis A differential scanning calorimeter (DSC6, Seiko Instruments Inc., Chiba, Japan) was used to determine the thermal characteristics of starch gelatinization and retrogradation. To determine gelatinization characteristics, the equilibrated DSC pans were directly heated by DSC from to 1 C at a rate of 5 C/min. For retrogradation properties, the DSC pans of retrograded starches were heated under the same conditions every 2 days or after each temperature cycle. Indium and mercury were used for temperature calibration, sapphire was used for heat capacity calibration, and an empty pan was used as a reference. All measurements were performed in triplicate. The respective enthalpy (J/g) was expressed on a dry starch weight basis. The degree of retrogradation (DR) was calculated as the ratio of enthalpy of retrogradation to enthalpy of gelatinization Statistical analysis All numerical results are averages of at least three independent replicates. Data were analyzed by one-way analysis of variance Endothermic Heat Flow % (16.4J/g) % (17.6J/g) % (18.5J/g) 5% (19.6J/g) % (14.4J/g) % (14.5J/g) % (14.7J/g) M2 5% (15.J/g) M1.1m W G M1.1m W G Fig. 1. DSC gelatinization thermograms of waxy and normal corn starches at various concentrations in water. Data in brackets are values of melting enthalpy for gelatinization (DH g ). Each value is the mean of triplicate measurements.

3 X. Zhou et al. / Journal of Cereal Science 51 () A Endothermic Heat Flow % % % % % %.1mW 5%.1mW 5% B Endothermic Heat Flow % % % % % % 5% 5%.1mW.1mW Fig. 2. (A) DSC thermograms of waxy and normal corn starches retrograded at 4 C for 2 and 14 days at various starch concentrations; (B) DSC thermograms of waxy and normal corn starches retrograded for 1 and 7 temperature cycles of 4 C for 1 day and C for 1 day at various starch concentrations. (ANOVA) using ORIGIN 8. (OriginLab Inc., USA). The statistical significance were determined by Tukey s test (p <.5). 3. Results and discussion 3.1. DSC thermograms for gelatinization For both waxy and normal corn starches, notable changes in the DSC thermograms of starch gelatinization occurred when starch concentration increased (Fig. 1). Multiple endothermic peaks were observed when the starch concentration was above %. While the endothermic peak (G) around 7 C remained relatively unchanged, the peak (M 1 ) between 8 and C and the peak (M 2 ), which appeared at above C in normal corn starch, became more evident and moved to higher temperatures when the starch concentration increased. The G and M 1 endotherms were associated with starch gelatinization, which occurred by the disruption of amylopectin double-helices, whereas the M 2 endotherm appeared at above C in normal corn starch was due to the melting of the amylose lipid complex (Donovan, 1979; Evans and Haisman, 1982; Garcia et al., 1997; Jang and Pyun, 1996; Liu et al., 7; Russell, 1987b). Amylopectins in waxy and normal corn starches have similar structure profiles (Jane et al., 1999), however the melting enthalpy for gelatinization (DH g, calculated by the G or G þ M 1 endotherm size, depending on the starch concentration) of normal corn starch was smaller than waxy corn starch at all starch concentrations tested (Fig. 1), which was probably due to less amylopectin content in normal corn starch than in waxy corn starch. There has been much controversy in trying to explain the presence of the two endotherms (G and M 1 ) for starch gelatinization. Some authors (Donovan, 1979; Evans and Haisman, 1982; Russell, 1987b) attribute the existence of the two transitions taking place at different starch contents to heterogeneity in water distribution. Biliaderis et al. (1986) suggests a partial melting, followed

4 6 X. Zhou et al. / Journal of Cereal Science 51 () Melting Fig. 3. Onset temperature (T o ) (open symbol) and the conclusion temperature (T c ) (solid symbol) of waxy (upper) and normal (lower) corn starches at various concentrations: % (square), % (round), % (up triangle) and 5% (diamond). Starches were retrograded at 4 C for 14 days (left) or under the temperature cycles of 4 C for 1 day and C for 1 day up to 7 cycles (right). by reorganization (crystallite perfection) and final melting of perfected crystallites in a DSC scan. Since starch crystallite perfection is a slow process, it is less likely to occur in a short time, such as during the DSC scan. Garcia et al. (1997) used SEM and TEM to observe the structural changes of cassava starch granules during gelatinization and illustrated that a competition of granules for water during heating would take place when the starch concentration was high. In other words, the presence of the two endotherms (G and M 1 ) indicates heterogeneity in water distribution during starch gelatinization. Starch may solubilise in different manners when its moisture content is changed. After gelatinization, the heterogeneous distribution of water as well as some water limitation among the starch molecules might influence the rate and degree of starch retrogradation too DSC thermogram for retrogradation and normal corn starches retrograded at a constant temperature of 4 C exhibited broad endotherms at all concentrations tested (Fig. 2A). The shapes of these retrogradation endotherms varied as a function of starch concentration. After storage for 2 days, the main peak was observed at about 55 C for % waxy corn starch, moving to a higher temperature as starch concentration increased. A lower-temperature shoulder was apparent for waxy corn starch of % and 5% concentration. After further storage to 14 days, the major peak after the first 2 days storage was still evident, but the region of the former lower-temperature shoulder was much enhanced, becoming the main peak for % and 5% waxy corn starch. For % and % waxy corn starch, only one peak was apparent, shifting to lower temperatures as the storage time increased. These observations are in agreement with the results of Liu and Thompson (1998). The retrogradation thermogram for normal corn starch stored under 4 C was similar to that for waxy corn starch. However, a main peak and a low temperature shoulder were only apparent in 5% normal corn starch, and the peak temperature was lower than that of waxy corn starch. A broad distribution of the endotherm may indicate the heterogeneity of retrograded starch crystallites. The development of a lower-temperature shoulder or the shift of peak temperature to lower temperature indicates that the increase of the endotherm of retrograded starch during storage at 4 C largely results from the growth of less perfect crystallites. When the starch gels were stored under the 4/ C temperature cycles, the thermograms of the retrograded starches exhibited narrower peaks than those for the starch isothermally retrograded at 4 C, regardless of concentration (Fig. 2B). It indicates that the crystallites formed under temperature cycles were more homogeneous than those formed under a constant 4 C. The endothermic peak for melting of the retrograded starch became larger with the increase in concentration. Contrary to the starch stored at a constant 4 C, the peak melting temperature of retrograded starch at the cycled temperatures increased during storage. Therefore it

5 X. Zhou et al. / Journal of Cereal Science 51 () Melting Temperature Range ( C) Fig. 4. Melting temperature range (T r ) of retrograded waxy (upper) and normal (lower) corn starches at various concentrations: % (-), % (C), % (:) and 5% (A). Starches were retrograded at 4 C for 14 days (left) or under the temperature cycles of 4 C for 1 day and C for 1 day up to 7 cycles (right). Starch of % concentration retrograded at 4 C (B) was included for comparison. appears that more stable crystallites were formed under 4/ C temperature cycled storage Melting temperatures for retrogradation The melting temperature of retrograded waxy and normal corn starches exhibited similar trends under the two retrogradation conditions studied (Fig. 3). When stored at a constant 4 C, starch of low concentration showed lower conclusion temperatures (T c ) than those of high concentration. After storage at 4 C for 14 days, the T c values were 59.6 C and 7.6 C for % and 5% waxy corn starch, respectively, and those for % and 5% normal corn starch were 59.5 C and 69.6 C, respectively. The T c values of both starches at various concentrations are significantly (p <.5) different. Compared to T c, the onset temperatures for melting (T o ) exhibited smaller changes with concentration. Only T o values of % and 5% starches are shown in Fig. 3. The T o values were 33.4 C and 31.1 C for % and 5% waxy corn starch, respectively, and 34.3 C and 31.5 C for % and 5% normal corn starch, respectively, after storage at 4 C for 14 days. Consequently, the melting temperature ranges (T r ) were 26.2 C and 39.5 C for % and 5% waxy corn starch, and 25.2 C and 38.1 C for % and 5% normal corn starch, respectively, after storage at 4 C for 14 days (Fig. 4). Starch at lower concentration exhibited smaller T r and lower T c, indicating that the crystallites formed at lower starch concentration were more homogeneous, but less stable to thermal treatment. The T c values of both waxy and normal corn starches were little affected (no difference at p <.5) by storage time, whereas the T o increased: from 28.3 to 33.2 C(p <.5) in % waxy corn starch and from 26.1 to 32.6 C(p <.5) in % normal corn starch during 14 days storage at 4 C. When both waxy and normal corn starches were stored under the 4/ C temperature cycling, T o values were higher by C compared with T o values at constant 4 C, regardless of the starch concentration studied. Silverio et al. () reported that T o was only controlled by propagation temperature, regardless of the type of the starch. Storage at C during the propagation step might melt some unstable crystallites formed at 4 C, which accounted for the T o increase under 4/ C temperature cycles (Baik et al., 1997; Durrani and Donald, 1995; Elfstrand et al., 4; Park et al., 9; Silverio et al., ). The remaining crystallites could be melted at higher temperatures. T c values of both waxy and normal starches at % and % concentration increased by about 4 C and 2 C after 14 days, respectively, whereas those at % and 5% concentration were relatively unchanged compared with the T c values at constant 4 C. The greater T o but relatively similar T c under temperature cycled storage compared to those stored at 4 C resulted in much smaller T r values. The crystallites formed under the 4/ C temperature cycled storage were more uniform and heat stable than those formed at a constant 4 C. The stability of the crystallites of both waxy and normal corn starches was more improved at lower concentration, as indicated by a large increase in T c. However, the crystallites of both

6 62 X. Zhou et al. / Journal of Cereal Science 51 () Melting Enthalpy for retrogradation (J/g) Fig. 5. The melting enthalpy for retrogradation (DH r ) of waxy (upper) and normal (lower) corn starches at various concentrations: % (-), % (C), % (:) and 5% (A). Starches were retrograded at 4 C for 14 days (left) or under the temperature cycles of 4 C for 1 day and C for 1 day up to 7 cycles (right). Starch of % concentration retrograded at 4 C (B) was included for comparison. starches became more homogeneous at high concentration during storage, as indicated by the large decrease in T r Melting enthalpy for retrogradation (DH r ) The DH r of waxy corn starch stored at a constant 4 C was strongly influenced by starch concentration, and maximum retrogradation occurred at 5% starch concentration, whereas that of normal corn starch was less affected by the studied starch concentrations (Fig. 5, no significant difference at p <.5). When stored under 4/ C temperature cycles, the DH r values of waxy and normal corn starches were relatively smaller compared to those of starches stored at constant 4 C (Fig. 5). Again, the propagation temperature might have melted some unstable crystallites formed at 4 C, accounting for the decrease in DH r under 4/ C temperature cycles (Baik et al., 1997; Durrani and Donald, 1995; Elfstrand et al., 4; Silverio et al., ). This could also be regarded as the annealing affect in which more stable crystallites were developed under the propagation temperature, as indicated by the higher T o, at the expense of the less stable crystallites (Durrani and Donald, 1995; Shi and Seib, 1995; Silverio et al., ). The reduction in DH r became more pronounced when the starch concentration was low (Fig. 5). After 14 days storage, the DH r of % waxy corn starch was.1 J/g when stored at the constant 4 C, but 3.5 J/g when stored under 4/ C temperature cycles. The DH r of 5% waxy corn starch was 16.3 J/g with a constant 4 C storage and 14.5 J/g with cycled temperature storage (p <.5). The DH r values of % and 5% normal corn starches dropped from 9. J/g to 6.4 J/g (p <.5) and from 9.4 J/g to 9. J/g (no significant difference at p <.5), respectively, by storing starch under the cycled temperature rather than constant 4 C. As discussed previously, the crystallites formed at a lower starch concentration under 4 Cwere more homogeneous but less stable. The stable crystallites formed at lower concentration of starch after storage at 4 C could be due to the melting of more unstable crystallites during the subsequent storage at C. This melting resulted in a significant decrease in DH r, whereas the crystallites were further perfected under a propagation temperature of C, as indicated by the higher T o and T c. The crystallites formed in low concentrations revealed a greater degree of annealing under 4/ C temperature cycles. These results were consistent with those reported by Ward et al. (1994), who found that 25% amylopectin showed smaller DH r but higher T o than % amylopectin when both were nucleated at 1 C and then propagated at 23 C Degree of retrogradation (DR) Degree of retrogradation (DR) is often expressed as the ratio of DH r to DH g (Baik et al., 1997; Jane et al., 1999; Vandeputte et al., 3; Varavinit et al., 3; Ward et al., 1994). When starch gelatinized at a concentration greater than % was retrograded at constant 4 C, DR of normal corn starch was lower than that of waxy

7 X. Zhou et al. / Journal of Cereal Science 51 () % 9 % Degree of Retrogradation (DR) % % % 9 % Degree of Retrogradation (DR) % % 5 5 Fig. 6. The degree of retrogradation (DR) for waxy (blank) and normal (filled) corn starches at various concentrations. Starches were retrograded at 4 C for 14 days (upper) or under the temperature cycles of 4 C for 1 day and C for 1 day up to 7 cycles (lower). corn starch, whereas DR of normal corn starch at % concentration was higher than that of waxy corn starch (Fig. 6). These results were roughly in agreement with those reported by Liu and Thompson (1998). They claimed that the lower retrogradation enthalpy of 5% normal corn starch was due to a smaller proportion of amylopectin in normal corn starch than in waxy corn starch, since retrogradation of starch occurring below C is primarily due to the amylopectin (Fredriksson et al., 1998). This theory does not explain why normal corn starch at % concentration retrograded to a larger extent than its waxy corn starch counterpart. It is more likely that at lower concentrations, amylose partially contributes to the amylopectin crystalline formation in normal corn starch. Similar to the case of the isothermal storage, normal corn starches of high concentration (i.e. >%) exhibited lower DR than that of waxy corn starches when stored under 4/ C temperature cycles (Fig. 6), and showed high DR when starch content was % or %. Furthermore, the retrogradation endotherm was too small to be calculated for % waxy corn starch after the first 4/ C

8 64 X. Zhou et al. / Journal of Cereal Science 51 () temperature cycle, whereas a relatively large retrogradation endotherm was observed for % normal corn starch stored under the same condition (Fig. 2B). Similar results were reported by Shi and Seib (1995). They observed no retrogradation endotherm in waxy corn starch or waxy rice starch at 25% concentration after storage at 4 C for 1 day followed by storage at 23 C for 4 weeks. On the other hand, normal wheat and corn starches at 25% concentration showed significant retrogradation under the same storage conditions. These differences in starch retrogradation between waxy and normal starches occurred because the rate of nucleation at 4 C was slow for waxy starch at 25% concentration compared to those starches containing amylose. The amylose molecules in the normal corn starch at low concentration probably promoted the retrogradation of amylopectin molecules of gelatinized normal starch during storage. To date, the exact influence of amylose on starch retrogradation remains unclear (Vandeputte et al., 3). Russell (1987a) studied the retrogradation properties of high amylose corn, waxy corn, potato and wheat starches at 43% concentration and reported that a degree of cooperation appears to exist between amylose and amylopectin. Gudmundsson and Eliasson (199) showed that synergistic interactions between amylose and amylopectin occurred during retrogradation when the starch had very high amylose content (75 9%), and the total starch concentration was about 5%. They deduced that at low amylopectin content the amylose component functions as nuclei and/or co-crystallizes with the amylopectin to some degree. Fredriksson et al. (1998) also found that high amylose barley starch retrograded to a higher extent than waxy and normal barley starches when the starch concentration was about 5%. At a starch concentration of 5%, amylose may promote crystallization of amylopectin, especially when amylose is present in a greater amount than amylopectin. In our study, normal corn starch retrograded to a larger extent than waxy corn starch especially at the early storage period, either at constant 4 C or under 4/ C temperature cycles when the starch content was low (% or %), and % waxy corn starch gave no DH after 1 cycle. The amylose in normal corn starch may have synergistic interactions with amylopectin for recrystallization at low starch concentration. It is well known that starch retrogradation occurs as two kinetically distinct processes: rapid gelation of amylose via formation of a double helical chain segment followed by helix helix aggregation; and slow recrystallization of the short amylopectin chains (Baik et al., 1997; Miles et al., 1985; Ring et al., 1987). When waxy corn starch of a low concentration (i.e., less than %) is gelatinized, the amylopectin clusters are relatively far apart, making it difficult for them to re-associate. Amylose molecules in normal corn starch of low concentration could freely leach out during gelatinization, and gelate quickly (Ratnayake and Jackson, 7). Some double helical chains of gelated amylose molecules might act as nuclei, which facilitate recrystallization of amylopectin molecules. It is also possible that the gelation of amylose could make less water available for amylopectin molecules, thus causing the amylopectin clusters to combine. As a result, DR of normal corn starch stored at the constant 4 C could be higher than that of waxy corn starch counterpart in this study. When starch was subjected to 4/ C temperature cycling treatment, storage at 4 C for 1 day was too short for waxy corn starch of % concentration to form extensive nucleation, and the crystallites formed were relatively weak. On subsequent storage at C, those unstable crystallites could be melted. On the other hand, amylose in % normal corn starch might function as nuclei and also co-crystallize with amylopectin at 4 C. The formed crystallites might readily proceed a subsequent propagation during the storage at C. At a higher concentration, because of the heterogeneity in the water distribution during starch gelatinization, some of the clusters were close to each other after gelatinization and easily recrystallized, due to the reduced mobility of amylopectin molecules. This might reduce the amount of leached out amylose, subsequently lowering its synergistic effect on retrogradation of amylopectin molecules. It was also observed that after three temperature cycles, DR of waxy corn starch at % concentration exceeded that of normal corn starch. Retrogradation of amylopectin occurred faster in normal than in waxy corn starch at the early stage of storage due to the partial contribution of amylose to the amylopectin retrogradation in normal corn starch. Retrogradation of amylopectin leveled off in normal corn starch after three temperature cycles, whereas it continued in waxy corn starch resulting in greater DR, because of higher proportion of amylopectin in waxy than normal corn starch. 4. Conclusion Retrogradation characteristics of corn starch gels can be modified by using temperature cycling. The degree of recrystallization was less under 4/ C temperature cycling compared to isothermal 4 C storage, based on DH of the DSC endotherm. The crystallites formed, however, appeared more homogeneous with higher thermal stability by temperature cycling. Under temperature cycling, annealing of starch was greater when the starch content was low (% vs. 5%), implying the significance of chain mobility. Level of retrogradation was greater in normal corn starch than in waxy corn starch at a low concentration ( or %), indicating that the amylose might have synergistic interactions with amylopectin for recrystallization. Overall data show that the temperature cycling induces different retrogradation behavior compared to typical isothermal storage, and is applicable to control retrogradation properties of starchy foods. References Baik, M.Y., Kim, K.J., Cheon, K.C., Ha, Y.C., Kim, W.S., Recrystallization kinetics and glass transition of rice starch gel system. Journal of Agricultural and Food Chemistry 45, Bemiller, J.N., 7. Carbohydrate Chemistry for Food Scientists, second ed. AACC International. Biliaderis, C.G., Structures and phase-transitions of starch in food systems. Food Technology 46, Biliaderis, C.G., Page, C.M., Maurice, T.J., Juliano, B.O., Thermal characterization of rice starches: a polymeric approach to phase-transitions of granular starch. 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