不同米種之米蛋白組成及其功能性之研究

Abstract

本研究目的為比較台稉 9 號、高雄秈 7 號及台農秈糯 2 號此三品種精白米中，米蛋白組成比例及蛋白理化特性和蛋白利用功能性的不同。 三品種間之胺基酸組成並無品種差異，從中分離出四類蛋白組成的比例僅於糯性米 (台農秈糯 2 號) 及非糯性米 (台稉 9 號和高雄秈 7 號) 具顯著差異，而與稉型米或秈型米較無關，糯性米中鹽溶蛋白及鹼溶蛋白的含量皆較非糯性米多，水溶蛋白的含量則以非糯性米多於糯性米。 研究中發現以酵素進行高溫的處理會對蛋白胺基酸組成、蛋白雙硫鍵含量及表面疏水性有所影響，並改變四類蛋白的含量比例，當中的水溶蛋白 (albumin) 及鹽溶蛋白 (globulin) 含量明顯因蛋白熱變性而減少，鹼溶蛋白 (glutelin) 則相對增加。 此外，經酵素高溫處理獲取蛋白後，其蛋白功能性與理化特性亦僅於糯性和非糯性米之間具顯著差異，於秈型米及稉型米中則無明顯不同，糯性米的乳化性及發泡性皆較非糯性米佳，而非糯性米之雙硫鍵含量則較糯性米多。 因此，若欲將米蛋白應用於新產品的開發上，必須先克服米蛋白中大量的雙硫鍵鍵結，並瞭解米中四類蛋白分別對各項功能性之影響。

In this study, the differences of rice protein content, protein physicochemical property and functional property among three types of polished rices, namely Taigeng No. 9, Kaohsiung shien 7 and Tainung-shien-no 2 were studied. These three rice varieties did not have significant differences on their amino acid compositions. However, they had significant differences on their ratio of rice protein fractions between glutinous rice (Tainung-shien-no 2) and non-glutinous rice (Taigeng No. 9, Kaohsiung shien 7) after fractional extraction analysis. Glutinous rice had more globulin and glutelin contents than that of non-glutinous rice. The content of albumin in non-glutinous rice was higher than in glutinous rice. Rice proteins of three rice varieties were isolated by enzymatic methods with high temperature conditions. We found that high temperature extraction would impact the amino acid composition, content of disulfide bond and surface hydrophobicity of rice protein. The proportion of rice protein fractions, such like albumin (water-soluble protein) and globulin (salt-soluble protein) were obviously reduced due to thermal denaturation of proteins, and the proportion of glutelin (alkali-soluble protein) were comparatively increased. Besides, rice protein isolate were also had significantly difference on its functional and physicochemical properties between glutinous rice and non-glutinous rice, and did not have relationship either with japonica type or indica type. The emulsion activity and foaming capacity of glutinous rice were both better than non-glutinous rice. And the latter had more content of disulfide bonds than the former. To utilize rice protein on development of new processed products in the future, further research should be conducted to overcome the large amounts of disulfide bonds in rice protein and understand how protein fractions will impact the functionality of rice protein.