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Effect of Sucrose on Glass Transition, Gelatinization, and Retrogradation of Wheat Starch

¹Department of Health Food Science, Chungkang College of Cultural Industries, San 37, Haewol-Li, Majang-Myun, Ichon 467-840, Korea. ²Department of Biotechnology, Yonsei University, Shinchon-Dong, 134, Seodaemun-Gu, Seoul 120-749, Korea. ³Corresponding author. Fax: 82-2-312-6821. Phone: 82-2-361-2883. E-mail: yrpyun@yonsei.ac.kr

Differential scanning calorimetry (DSC) was used to study the effect of sucrose on wheat starch glass transition, gelatinization, and retrogradation. As the ratio of sucrose to starch increased from 0.25:1 to 1:1, the glass transition temperature (T_g, T_g′) and ice melting enthalpy (ΔH_ice) of wheat starch-sucrose mixtures (with total moistures of 40–60%) were decreased to a range of −7 to −20°C and increased to a range of 29.4 to 413.4 J/g of starch, respectively, in comparison with wheat starch with no sucrose. The T_g′ of the wheat starch-sucrose mixtures was sensitive to the amount of added sucrose, and detection was possible only under conditions of excess total moisture of >40%. The peak temperature (T_m) and enthalpy value (ΔH_G) for gelatinization of starch-sucrose systems within the total moisture range of 40–60% were increased with increasing sucrose and were greater at lower total moisture levels. The T_g′ of the starch-sucrose system increased during storage. In particular, the significant shift in T_g′ ranged between 15 and 18°C for a 1:1 starch-sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40°C). At 40% total moisture, samples with sucrose stored at 4, 32, and 40°C for four weeks had higher retrogradation enthalpy (ΔH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in ΔH values at storage temperature of 4°C, whereas recrystallization of samples with sucrose stored at 32 and 40°C decreased. The peak temperature (T_p), peak width (δT), and enthalpy (ΔH) for the retrogradation endotherm of wheat starch-sucrose systems (1:0.25, 1:0.5, and 1:1) at the same total moisture and storage temperature showed notable differences with the ratio of added sucrose. In addition, T_p increased at the higher storage temperature, while δT increased at the lower storage temperature. This suggests that the recrystallization of the wheat starch-sucrose system at various storage temperatures can be interpreted in terms of δT and T_p.