In the study of bread staling, progress is limited due to its complex system. Two primary wheat constituents, gluten and starch, and the major bread ingredients water and sucrose were used for molecular interaction studies in model systems. Starch retrogradation in breads and their microstructures were examined to observe the effects of ingredients in practical system. Sorption isotherms and $\sp2$H, $\sp{13}$C, and $\sp{17}$O NMR were used to examine molecular interactions and study water mobility in model systems. DSC was used for thermal transition studies. Light and polarized light microscopies were used for microstructure and starch crystal observations. Sucrose and gluten, and sucrose and starch "interacted" in the model systems. The "interacted" sucrose-gluten or sucrose-starch mixtures showed water absorption behaviors intermediate between that of pure sucrose and gluten or starch. The water mobility of sucrose-gluten mixtures was decreased with the increase of sucrose concentration, while for that of sucrose-starch mixtures it was increased with the increase of sucrose concentration. Water plasticized gluten more effectively than starch perhaps because gluten is complete amorphous while starch contains about 40% amorphous regions. Sucrose also plasticized gluten or starch. However, in sucrose-water-gluten or starch mixture, sucrose showed less plasticization effect (antiplasticizer). Sucrose had a strong antiplasticization effect in the gluten mixtures but not in the starch mixtures. Starch gelatinization endothermic energy increased with the increase of moisture content indicating that gelatinization is dependent on availability of water. With constant moisture content, both salt and sucrose increased gelatinization peak temperatures and endothermic energies. However, salt had greater retarding effect on gelatinization than did sucrose. Bread was sealed in cans and kept at room temperature for 4 days. Bread made from hard wheat flour had more intact microstructure and low starch crystalline melting endothermic energy than bread made from soft wheat or all-purpose flour. Among 3 types of surfactants added to bread doughs, sodium stearoyl lactylate produced bread with the most highly homogeneous distribution of medium sized air cells and intact cell walls. Sucrose ester (HLB 16)-added bread had the lowest starch crystalline melting endothermic energy, and thus would decrease retrogradation more than the other surfactants.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7819 |
| Date | 01 January 1990 |
| Creators | Lo, Leah Lih-Ju |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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