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K. TANANUWONG and D. S. Reid. Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616-8598 Processing of starch based foods usually involves the transformation of a semicrystalline polymer structure of granular starch into an amorphous state via gelatinization. Since the physical state of an amorphous matrix greatly affects quality and storage stability of foods, the glass transitions of the gelatinized starches have been widely investigated. However, there is still a need for more information on the glass transition behavior of starch gels prepared under a range of different conditions. The objective of this work was to investigate effects of initial water content, heating temperature and starch microstructure on the glass transition of frozen starch gels. Gels from waxy corn, native corn, potato and pea starches, with 1.1 – 3.0 g water / g dry starch, were prepared by heating up to the peak temperature of G endotherm (partial gelatinization) or the ending temperature of M1 endotherm (full gelatinization). Differential Scanning Calorimetry was used to determine the glass transition temperatures of frozen starch gels (Tg*) and additional unfrozen water arising from gelatinization (AUW) of starch-water systems. The samples were also annealed at a temperature near Tg* in order to amplify the glass transition phenomena. The results showed that Tg* of the partially gelatinized gels was independent of the initial water content, while Tg* of the fully gelatinized gels increased as the initial water content increased. These observations might reflect different levels of structural disruption associated with different heating conditions, resulting in different gel structures and different concentrations of the sub-Tg unfrozen matrix. The microstructure of the original starch did not greatly effect Tg* of the gels. Annealing increased Tg* possibly due to an enhanced freeze-concentration process as evidenced by a decrease in AUW. These results emphasized the importance of the unfrozen matrix composition to the characteristics of frozen starch gels. Changing the gelatinization conditions influences the concentration of this matrix, and hence the glass transition temperature of the starch gels.
Session 93, Carbohydrate: General
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