臺灣小米種原農藝性狀與穀粒理化性質之探討

Abstract

小米(Setaria italica)為世界上穀類作物中之次要作物，是小穀類作物(Millets)中產量位居第二大宗者，其耐旱與耐貧瘠等特性使之成為某些邊緣地區之主食如中國大陸北方、印度和部分非洲國家。小米之營養價值由於人類飲食習慣的改變而在近年來備受重視，然而針對小米之營養價值和理化特性研究仍然非常有限。有鑑於此，本研究收集臺灣小米共133個品系，種植於臺中農試所並調查其農藝性狀，穀粒理化特性，分析內容包含直鏈澱粉含量測定、快速黏度分析與澱粉水解效率。 農藝性狀中具有統計上之顯著差異者包含株高、抽穗期、穗長與穗寬。株高的範圍54.7~124.7公分、平均93.7公分；抽穗天數的範圍53.7~109.5天、平均為75.2天；穗長範圍為9.6~56.72公分、平均為23.4公分；穗寬的範圍1.12~3.17公分、平均2.02公分；千粒重的範圍為0.96~2.85公克、平均1.85公克。從SEM觀察穀粒橫切面之結果顯示小米澱粉顆粒屬於多邊形(Polygonal)且可能為複粒澱粉(Compound granule)，於Type-IV和Type-IX之小米中可觀察到澱粉中心之空洞構造。小米收集系之直鏈澱粉含量介於0.7-16.9%，其中以Type-IV基因型之品系佔多數，與直鏈澱粉之含量結果相符合。各RVA參數於本小米收集系間皆具有廣泛的變異，然而PKV與BDV之參數透過Wx對偶基因型之解釋量不高，說明除了直鏈澱粉含量外，仍有其他因子明顯地控制小米之澱粉糊化特性。透過RVA之參數與澱粉水解效率，發現Type-III和Type-IX之品系PKV較Type-I高，然而其AAC含量卻與較Type-I低。於水解效率之結果亦可觀察到Type-III和Type-IX之品系RS與Type-I相近。以上現象皆說明Type-III和Type-IX品系之支鏈澱粉可能與Type-I品系有結構上的差異。於相近之直鏈澱粉含量範圍中水稻之澱粉水解效率較小米品系低，此現象可能為澱粉粒內部之空洞、通道與表面孔洞所導致。本研究針對133個小米品系針對農藝性狀與穀粒理化特性進行初步的調查，為未來小米的研究奠定基礎，其中變異性甚大之農藝性狀為將來各個育種目標提供有價值之育種資源。而透過RVA分析之穀粒理化特性中可發現諸多小米品系間，具有潛力運用於各類食品加工或小米產品之開發。

Foxtail millet (Setaria italica) is an important minor cereal crop in China, India, and Africa due to its strong adaptability to harsh environments. In Taiwan, foxtail millet is considered as a symbolic crop of the indigenous peoples. Since the human dietary habit has been changed, the nutrition value of foxtail millet has recently received a lot of attention. Numerous foxtail millet products are therefore being developed. However, the nutrition quality of foxtail millet has not been well studied as compared to other major cereals. A total of 133 foxtail millet landraces originated from Taiwan were evaluated by five agronomic traits and grain qualities. The grain qualities were conducted three aspects, starch granule structures analyzed by scan electron microscope (SEM), grain physicochemical properties analyzed by amylose content and rapid viscosity analyzer (RVA), and in vitro starch digestibility. Four agronomic traits, plant height, heading date, panicle length, panicle width, were significantly different among these accessions. Including Plant height ranged from 54.7 to 124.7 cm with the average of 93.7 cm; heading date ranged from 53.7 to 109.5 days with the average of 75.2 days; panicle length ranged from 9.6 to 56.72 cm with the average of 23.4 cm; panicle width ranged from 1.12~3.17 cm with the average of 2.02 cm; and 1000-seed weight ranged from 0.96~2.85 g with the average of 1.85 g. By observing the grain surfaces distinguished by four Wx genotypes. The internal cavities were found throughout the grain surface in Type-IV and Type-IX accessions. Further analysis of apparent amylose content suggests that most accessions owing waxy property were corresponded to Type-IV. The pasting property detected by RVA exhibited obvious variations among foxtail millet starch. However, the variance of some parameters explained by Wx genotypes were low, indicating other factors were together affecting the pasting property. In addition, the RS content of rice is higher than foxtail millet with the same range of AAC, suggesting foxtail millet starch is easier to be digested compare to rice. The Type-IV accessions have higher RDS than other types. However, the starch fractions of Type-III and Type-IX are similar to Type-I, suggesting the structure of amylopectin could be different between these types.