93-6 |
|
S. CHAROENREIN1, D. Thirathumthavorn1, and S. Udomrati. (1) Food Science and Technology, Kasetsart University, Paholyothin road, Jatujak, Bangkok, 10900, Thailand Retrogradation, a recrystallization process of starch chains in the gel, provides functionally beneficial or undesirable quality. Some studies have indicated that retrogradation is faster at 4 °C. It is well documented that glass transition temperature relates to mobility of individual components of the system. In the glassy matrix, mobility of the crystallizable molecules is decreased, thus, retarding the recrystallization process. We hypothesized that temperature at above or below glass transition temperature (Tg’) might have some different effect on the retrogradation of starch gels. Our objective was to investigate the retrogradation rate of waxy rice starch gel during storage at temperatures above or below the glass transition temperature and to gain further understanding of the influence of glassy state on retrogradation process. The glass transition (Tg’) of fully gelatinized KK6 waxy rice starch (94% amylopectin) gel with 50% water content was investigated using differential scanning calorimetry (DSC). Starch gels in stainless steel DSC pans were frozen to –30 °C in a cooling bath and were stored at 4, 0, -3, -5, and –8 °C for 5 days. DSC was also used to estimate amylopectin recrystallization (enthalpy of melting at 44 to 70 °C) Our results demonstrated that Tg’ value of the gelatinized waxy rice starch gel annealed at -7 °C for 15 min was around –2.5 to -3.0 °C. Rice starch gels retrograded significantly when stored at 4 °C. Decreases in enthalpy of melting was observed in samples stored for 5 days at –3, -5 and -8 °C respectively. This is due to the more rigid glass matrix and less molecular mobility to facilitate recrystallization of starch chains with lower temperatures below Tg’. These results suggest that retardation of retrogradation of waxy rice starch gel can be manipulated by temperature below Tg’; however, acceleration of retrogradation will require additional study.
Session 93, Carbohydrate: General
|