Effect of sucrose on glass transition, gelatinization, and retrogradation of wheat starch

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 (DeltaH(ice)) of wheat starch-sucrose mixtures (with total moistures of 40-60%) were decreased to a range of -7 to -20 degreesC 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 (DeltaH(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 degreesC for a 1:1 starch-sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40 degreesC). At 40% total moisture, samples with sucrose stored at 4, 32, and 40 degreesC for four weeks had higher retrogradation enthalpy (DeltaH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in DeltaH values at storage temperature of 4 degreesC, whereas recrystallization of samples with sucrose stored at 32 and 40 degreesC decreased. The peak temperature (T-p), peak width (deltaT), and enthalpy (DeltaH) 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, Tp increased at the higher storage temperature, while deltaT 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 deltaT and T-p.