Understanding starch granule architecture and its relationship to starch functionality

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Despite significant advances in knowledge about starch biosynthesis and structure, questions related to the initiation of crystal formation in the amyloplast and the specific architecture of the starch granule from different botanical sources, still persist. The goal of our research is to understand the architecture of starch granules and relate the knowledge gained to the behaviour of starch in multi-component food matrices. We propose to investigate starch granule architecture using iodine as a marker on native, granular dry starch, a novel technique we developed recently. Using iodine as a tool, we demonstrated mobility in native granular starches of linear polymers with degree of polymerization (dp) of up to 35 at moisture contents as low as 8% and up to dp 105 at a moisture content of 20 %. We further showed that starches from different botanical sources had significantly different iodine binding properties at moisture contents below 20%. These observations suggest that in native granules, there are stearically unrestricted segments of linear polymers that are free to move and form a single helical complex with iodine, exhibiting characteristic color at low moisture contents. By combining the iodine complexing technique with other controlled enzymatic and chemical modifications to the starch, we propose to further deduce the granular architecture of starches from different botanical sources. The proposed research will improve our understanding on one of the most prevalent polymers in nature. Moreover, this research has relevance in the application and uses of starches in foods. Research from our laboratory has shown that under limited moisture conditions, depending on the processing conditions, there is kinetic limitation that governs starch granule swelling, gelatinization and polymer rearrangement. Understanding granule architecture will aid in better understanding how polymers within granules disperse, phase-separate and form subsequent complexes upon cooling and storage. Preliminary data from our laboratory have shown that modulating the processing conditions can influence the subsequent network formed in the product and we can alter the rate of breakdown of starch into glucose during digestion, i.e., alter the glycemic response.