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CC BY-NC V4.0, Open Access
Dissertation
UNDERSTANDING PHYSICAL AND CHEMICAL CHANGES IN STARCH AND FIBER DURING DIRECT EXPANDED EXTRUSION PROCESSING
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000003162
Handle:
https://hdl.handle.net/2376/124255
Abstract
High-fiber snacks and breakfast cereals are among the products of interest to promote high-fiber consumption. These products are commonly produced by extrusion processing using the phenomenon of direct expansion. Maintaining the desirable texture/expansion of high-fiber extruded products is challenging. Fundamental explanations for the interactions of starch and fiber and the causes for the reduction in expansion need further understanding for the effective incorporation of fiber into extruded products. This research aimed to determine the physical and molecular changes in starch and fiber during extrusion and how these changes influence the expansion of the extrudates.Insoluble fiber (cellulose) and corn starch were mainly used in this research. The expansion of extrudates reduced significantly with increasing cellulose content. Starch-cellulose extrudates had small and more uniform cell sizes but possessed thinner and some ruptured cell walls. It was concluded that the cellulose could interfere with starch chain reassociation through intermolecular hydrogen bonding during the expansion process. The subsequent study further explained that the reduced expansion of extrudates was mainly due to the physical incompatibility of starch and cellulose. Cellulose was confirmed not to undergo phase changes and molecular changes, while the starch did undergo changes. There could be two main reasons for the reduced expansion. Firstly, the phase separation of cellulose (particles) and starch melt (continuous viscoelastic phase) interfered with the reassociation of starch molecules during the expansion. The second was the uneven distribution of cellulose within the starch matrix because cellulose particles tend to aggregate during extrusion processing.
The high methoxyl pectin (HMP) of citrus peel potentially maintained the expansion of starch-cellulose extrudate and enhanced its total dietary fiber content compared to low methoxyl pectin (LMP). HMP helped improve the extensibility of the melt rheology and the compatibility of starch and cellulose, favoring the expansion of extrudates. Thus, using HMP coupled with insoluble fiber is recommended to produce high-fiber extruded products.
Further studies should focus on preventing fiber aggregation and improving the compatibility of starch and insoluble fiber to increase insoluble fiber content without compromising the expansion, for instance, exploring the uses of hydrocolloids and ingredient mixing strategies.
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Details
- Title
- UNDERSTANDING PHYSICAL AND CHEMICAL CHANGES IN STARCH AND FIBER DURING DIRECT EXPANDED EXTRUSION PROCESSING
- Creators
- Pichmony Ek
- Contributors
- Girish M. Ganjyal (Advisor)Barbara A. Rasco (Committee Member)Carolyn F. Ross (Committee Member)Steven R. Saunders (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Food Science, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 172
- Identifiers
- 99900652004701842
- Language
- English
- Resource Type
- Dissertation