Properties And Development Of Heterogeneous Starch Granules From High-amylose Rice And Maize

Starch consists of two main components:amylose and amylopectin. Amylose content has a pronounced effect on the properties and applications of starch. High-amylose starch has high content of resistant starch, can lower the glycemic response to a meal and reduce the risk of developing type Ⅱ diabetes mellitus, obesity, and cardiovascular disease. Therefore, high-amylose starch has potential health benefits for human beings. High-amylose cereal endosperm is rich in heterogeneous starch granules with markedly different morphologies and sizes. However, their properties and development is not clear until now. In this study, the properties and development of heterogeneous starch granules from high-amylose rice and maize were investigated using a range of microscopy, histochemistry and spectroscopy techniques. This study not only could provide important information for the development and properties of heterogeneous starch granules from high-amylose cereal crops, but also was useful for the cultivations, exploitations and applications of high-amylose cereal crops. The main results were shown as followings:1. A range of methods were established to in situ analyze the properties and development of starch and separate the different-sized starch granules. The morphologies, compositions, gelatinization processes, gelatinization patterns, gelatinization temperatures and volume swelling of starch granules from different plant sources were in situ observed and analyzed using the established methods. The spatial distribution of starch granules was investigated in the mature cereal kernel. The large-, medium- and small-sized granules were also separated from maize starch. The results indicated that the established methods of in situ analysis were very suitable for studying the properties and development of heterogeneous starch granules, and the purification methods could separate heterogeneous granules from high-amylose maize starch.2. The morphologies, structures and gelatinization properties of heterogeneous starch granules from high-amylose rice were in situ observed and analyzed using a range of microscopy and histochemistry techniques. These results showed that high-amylose rice starch contained the individual, aggregate, elongated, and interior hollow granules with different morphologies. The distribution of amylose and the molecular alignment of amylopectin were significantly different among these heterogeneous starch granules. The individual starch granule had the lowest amylose content and the weakest resistance to gelatinization. The interior hollow starch granule had the highest amylose content and the strongest resistance to gelatinization. The elongated starch granules had higher resistance to gelatinization than the aggregate starch granules.3. The spatial distribution in mature kernel and the formation in developing endosperm of heterogeneous starch granules from high-amylose rice were in situ mapped using resin semithin section technique. The results revealed that the individual starch granules existed mainly in the middle region of the endosperm, and formed before 5 days after fertilization (DAF). The elongated starch granules existed mainly in the peripheral starchy endosperm cells adjacent to the subaleurone layer, formed at 5 DAF, and then rapidly accumulated until 16 DAF. The aggregate starch granules existed mainly in the starchy endosperm cells between the subaleurone layer and the middle of the endosperm, formed at 5 DAF, and then rapidly accumulated until 10 DAF. The interior hollow starch granules existed mainly in the subaleurone layer cells, formed at 7 DAF, and then rapidly accumulated until 16 DAF.4. The morphologies, structures and gelatinization properties of heterogeneous starch granules from high-amylose maize were in situ observed and analyzed using a range of microscopy and histochemistry techniques. These results showed that high-amylose maize starch contained the individual, aggregate and elongated granules. The individual, aggregate and elongated starch granules were round, irregular and rod/filamentous in shape, respectively. The polarization colors of iodine stained starch granules showed that the molecular alignment of amylopectin were significantly different among these heterogeneous starch granules. The amylose was mainly distributed in the hilum region and the circumference of heterogeneous starch granules. The amylose content was higher in the aggregate and elongated starch granules than in the individual starch granules. The individual and elongated starch granules had the weakest and strongest resistance to gelatinization, respectively.5. The large-, medium-, and small-sized granules were separated from maize starches using the glycerol centrifugation method. Their structural and functional properties were investigated and compared. The results showed that the granule size had no significant effect on the structural and functional properties of normal maize starch. However, the different-sized granules of high-amylose maize starch showed significantly different structural and functional properties. The amylose content, amylopectin long branch-chain and average chain length, short-range order degree, gelatinization temperature, and resistant starch content of high-amylose maize starch significantly increased with decrease of granule size. The relative crystallinity, amylopectin short branch-chain and branching degree, swelling power, water solubility, gelatinization enthalpy, and hydrolysis and digestion degrees of high-amylose maize starch significantly decreased with decrease of granule size. The hierarchical cluster, which was constructed on the basis of structural and functional properties from native and different-sized granules of normal and high-amylose maize starches, indicated that the large-sized granules of high-amylose maize starch was very similar to the normal maize starch and significantly different from the medium-and small-sized granules of high-amylose maize starch.