| 摘要: | 本研究探討不同品種甘藷澱粉之物理化學性質及重要澱粉生合成關鍵酶的基因表達差異。甘藷為國產糧食作物中地位僅次於稻米，富含澱粉，可被廣泛利用及開發成各種工業及食用商品，藉由總澱粉、總碳水化合物、直鏈澱粉、透光度、連續糊化黏度、熱性質分析、質地分析、膨潤力、溶解度及凝膠延展性的測定，鑑定6種不同品種甘藷澱粉成分與理化性質及各個不同參數之間的關係，可得知不同甘藷品種澱粉的性質差異，並挑選物理化學化性質差異較大之甘藷品種，了解與其澱粉生合成途徑有關之關鍵酶的基因表達。
結果發現不同甘藷品種間澱粉成分與理化性質差異最大為台南18號及台農31號，其中以台南18號有最多之澱粉含量、直鏈澱粉、透光度，而台農31號則相反，澱粉質地與連續糊化黏度、熱性質分析有關，甘藷澱粉中直鏈澱粉越多越容易形成較多結晶，使糊化冷卻後結構較為緊密，有最大的回升黏度，代表在冷卻後台南18號結構較為硬、流動性低，膠質感和咀嚼性也會較高，且直鏈澱粉越多容易形成粉質質地，較適合做成內餡，可做為後續甘藷推薦於加工之參考，並運用在各類食品加工添加物。
不同甘藷澱粉原料理化性質皆有所差異，進一步了解不同的澱粉生合成的關鍵酶對於直、枝鏈澱粉的影響。藉由Real-time PCR測定澱粉生合成途徑之ADP葡萄糖焦磷酸化酶(APGase)、顆粒結合型澱粉合成酶(GBSS)、澱粉合成酶(SS)、澱粉分支酶(SBE、SBEII)、澱粉脫支酶(DBE)及異澱粉酶(ISA)等關鍵酵素RNA之相對表現量，發現台南18號的APGase、GBSS及SS之相對RNA表現量均顯著高於台農31號，這也與上述理化分析的結果一致，但SBE、DBE不管是在台南18還是台農31號之表達量都非常的低，而SBEII及ISA則是台農31號顯著高於台南18號。在APGase、GBSS、SS、SBE、DBE等酵素活性測定中活性最低為ADPase，活性最高為SSS。總之，本研究之結果可作為國內外食品業界相關研究之參考，有利於提升甘藷澱粉加工利用多元性，增加甘藷之附加價值與國際競爭力，並提高農民的收益。
Sweet potato (Ipomoea batatas (L.) Lam.) is the world's fifth largest economical crop, and also one of the important domestic crop except rice. They are rich in starch, and can be widely used and developed into a variety of merchandises. In Taiwan, most sweet potatoes were used for animal feeds in 1970s, but some of them for human consumption and food processing purposes. In recent years, people have changed their eating habits and diet, food processing and preserving from sweet potato consequently draw attentions in publics. In particularly, physical and chemical properties of starch from sweet potato processing quality are favored by consumers. Therefore, the purposes of this study were to : (1) analyze the relationships between the desired physicochemical properties of different varieties of sweet potato starch, (2) applications of the potential varieties with desired physicochemical properties to food process industry, and (3) link between starch content and starched-related enzymes.
Tainung (TN) 10, 17, 31, Tainan 18, Japanese Kyushu 14, and TN 57 (as control)wre used in this study. Physical and chemical properties of sweet potatoes were determined, including starch flour yield (extraction rate), starch content, total sugar, amylose, amylopectin, and gel consistency, swelling power and solubility, transparency, hardness, adhesion, elasticity, cohesion, gumminess and chewiness, and continuous liquid starch paste viscosity. Results show that TN 31 contained higher total sugar and starch than others. Tainan 18 had higher amylose and starch contents, but its amylopectin content and transparency were the lowest compared to others. Moreover, TN 10 showed the lowest dry matter content and the highest transparency. Generally, more amylose easily formed and became crystallizing tight, so that after cooling gelatinized structure more closely. Hence, cooling structure from Tainan 18 was supposed to be more rigid, low liquidity, and chewing gum. Amylose was more easily formed silty texture, and Tainan 18 might be made more suitable for stuffing.
To understand the relationship between starch content and starched-related enzymes, 7 key enzymes from different starch biosynthesis with significant amylose and amylopectin were selected, including ADP-glucose pyrophosphorylase (AGP), granule-bound starch synthase (GBSS), starch synthase (SS), starch branching enzyme (SBE), starch branching enzyme (SDBII), starch debranching enzyme (DBE), and Isoamylase (ISA). RNA contents of these 7 enzymes from both TN31 and Tainan 18 were detected by real-time PCR. Sweet p otato actin7 gene was also used as internal control for real-time PCR. The relative RNA levels of AGP, GBSS, and SS in TN31 and Tainan 18 were found more significant higher than other enzymes. These results agree with our previous results that both TN31 and Tainan 18 had higher amylose and starch contents. |
