影響米穀粉及速食米飯澱粉消化特性因子之探討

Abstract

米飯及米食產品等澱粉質食物是國人重要的碳水化合物來源，近年來研究顯示澱粉質食物的澱粉消化特性如消化速率緩急和常見的生活型態疾病如糖尿病具有相關性。澱粉消化特性可透過體外澱粉消化測定模式依消化速率區分為快速消化澱粉(rapidly digestible starch, RDS)、緩慢消化澱粉(slowly digestible starch, SDS)及抗性澱粉(resistant starch, RS)，作為澱粉質食品的品質指標之一。若飲食中的碳水化合物的快速消化澱粉(RDS)含量較低，可減緩餐後血糖及胰島素的上升，並可延長飽足感。本研究擬依據體外澱粉消化測定模式，篩選具潛力的國產稻米品種，了解加工條件對米食產品及米飯的澱粉消化澱粉的影響，開發或改善具延緩消化澱粉特性的米食產品之製備方式及條件。首先收集國產主要米種分析其理化及澱粉分子特性，再選擇具代表性米種分別進行米穀粉產品及米飯的加工條件測試，探討延緩澱粉消化特性的最適加工條件。結果顯示，在米穀粉加工方面，當加水量低於7倍，米種的視直鏈澱粉含量和RDS含量呈負相關性，且延長冷藏時間有助於降低非糯性米種的RDS含量。在米飯部分，以較低的溫度、最短的時間及較少的水量烹煮米飯，可以保留較多完整的澱粉顆粒來延緩米飯的澱粉消化特性，再透過冷藏與低溫乾燥的共伴效應使澱粉分子結構重整形成不完美結晶結構以降低復水後速食米飯的澱粉消化特性。本研究探討國產大宗米種的基本理化及分子特性後，運用於米穀粉食品及速食米飯產品之製程條件選擇，將有助於國內米食產業未來生產具健康訴求之米食產品，做為國人日常飲食之選擇，期能對國人健康提升有所助益，並提高國產米食的消費量。

Rice being the staple food in Taiwan and Asia is the main source of carbohydrate in many countries. The nutritionally important fractions of food starches can be classified as rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) based on the rate of digestion according to Englyst’s assay. RDS content of starchy food is positively correlated to glycemic response. Oppositely, starchy food containing higher content of SDS leads to less glycemic response and makes it more nutritional for reducing the risk of raising glycemic response. In this study, we aimed to evaluate optimum process conditions for rice flour based foods and instant rice for reducing starch digestibility from domestic rice varieties. The results showed that the amount of water added for cooking and extending refrigeration duration impacted majorly on the starch digestibility of both low-amylose and high amylose for rice flours. By properly selecting a lower temperature, comparing to the traditional electronic cooker, with minimum time as well as adding limited water significantly reduced RDS of cooked rice. Evidence of SEM photogram showed that lower temperature cooking made the starch gelatinized without disruption all starch granule, leading to the lower starch digestibility. One day refrigeration was enough for the conformation of starch structure. The synergy of refrigeration and lower temperature drying significantly reduced the starch digestibility. In addition, molecular structure of rice starch significantly not only affected the starch digestibility of rice flour based products, but also the rehydrated instant rice. It appears possible to reduce rice starch digestibility by establishing optimum processing conditions for different rice varieties.