稻米品種結構與米食加工之關系

Abstract

本實驗選用十四種省產稻米為材料，其中包括五種秈米（台中在來一號，台中秈十七號，高雄秈七號，台中秈十號，台秈一號），五種梗米（台農六十七號，台農七十號，台南九號，台中一八九號，高雄一四二號）及四種糯米（台中秈糯一號，紅腳糯，台中糯七十號，新竹糯四號），分析其支鏈澱粉之微細結構及理化性質，進而探討其相關性。 實驗結果顯示，秈米支鏈澱粉的分子量小，分支數少，平均鏈長較長，大約為18-22 個葡萄糖基，而梗米及糯米的平均鏈長，則分別為15 -18 及17-20 個葡萄糖基。所有的稻米支鏈澱粉，最短分支鏈皆由6 個葡萄糖基組成。十四種稻米支鏈澱粉的鏈長分佈圖皆呈兩個波峰型態。一般而言，秈米具有較多的長鏈，其中，三種高直鏈澱粉含量的的秈米即台中在來一號，台中秈十七號及高雄秈七號，其支鏈澱粉更含有少量鏈長大於一百個葡萄糖基的超長鏈部分。 秈米支鏈澱粉因為具有較多的長鏈，故其藍價以及最大吸收波長皆高，且因分子呈長桿構形（elongated rod conformation ）以致有較高的固有黏度。 Fourteen varieties of rice from Taiwan, including five indica, five japonica and four waxy cultivars, were used in this study for the examination of fine structure and physicochemical properties of the amylopectin. The results indicated that the amylopectin of indica rice, when compared with that of jopinica and waxy vatieties, had lower molecular weight, average degree of polymerization (DP), and average chain number. The shortest average DP was 6 glucose units for all 14 rice varieties. The average chain lengths (CL) of amylopectin were 18-22, 15-18 and 17-20 for indica, japonica and waxy rice, respectively. Amylopectin of the indica varieties, but not the other varieties, with high amylose content was comp osed of a small amount of extra long chain (DP>100). The CL distribution profiles of amylopectins for these 14 varieties could be divided into two fractions, corresponding to CL of 10-15 and 40-44. Amylopectin of the indica rice ha.d a relatively high blue value and A max, implying that a high proportion existed as long branches . The amylopectin of three indica varieties with lower DP exhibited higher intrinsic viscosity, which might be attribut ed to the more elongated rod conf ormation of the small amount of extra long chain amylopectin. It is proposed that these extra long chains within amylopectin would result in the unique eating quality of the cooked indica rice.