油脂對米飯理化特性及澱粉消化性之影響

Abstract

本研究目的旨在探討油脂（三酸甘油酯），包括：棕櫚油、大豆油及亞麻仁油其不飽和程度，對米飯理化特性及澱粉消化性之影響。實驗選用台稉9號精白米，添加油脂烹煮之米飯穀粉，經示差熱掃描分析 (DSC) 可於90℃至115℃間，觀察到直鏈澱粉－脂質複合物 (ALC) 之解離吸熱峰，解離溫度以棕櫚油最高 (95.3℃)，對照組白米飯則最低 (90.4℃)，在X射線繞射 (XRD)下，米粒經烹煮後晶體圖譜由A-type 轉變為V-type，添加油脂後其特徵波峰強度間並無明顯差異；米飯體外澱粉消化性，隨油脂飽和程度增加，棕櫚油具有最低的預估升糖指數 (eGI) (85.6) 和含量最高的抗性澱粉 (RS) (11.2%)，其次依序為大豆油 (87.1 和 8.5%)、亞麻仁油 (90.3 和 3.8%) 及白米飯 (92.4 和 0.8%)，結果顯示棕櫚油可形成較穩定之複合物，對酵素水解抗性較佳。三酸甘油酯主要針對澱粉的短期回凝進行延緩，僅於4℃貯藏第一天回凝熱焓值 (ΔH) 有下降，但對於澱粉之長期回凝（3至5天）則無影響。回凝米飯之消化性隨米飯貯藏時間延長而降低，以亞麻仁油增加RS之量最多。於XRD之圖譜，可觀察到米飯澱粉於回凝過程中，由V-type 轉變成 B-type，經復熱後再次轉變為V-type，結構間具熱可逆之特性。米飯經回凝復熱後，ALC之解離溫度提高；復熱之米飯澱粉消化性與新鮮米飯比較，RS含量間並無顯著差異，顯示由於ALC熱可逆性，仍可保留複合物維持其酵素之抗性。經由實驗結果得知，不飽和程度越低之油脂，其形成ALC之結構也越安定，可顯著降低米飯澱粉之消化性，將有助餐後血糖之控制，並且獲得較多的RS，作為飲食之參考。

This study was to understand effects of oils with different unsaturation, including palm oil (PO), soybean oil (SO), and flax oil (FO), on physicochemical properties and starch digestibility of cooked rice. Polished rice grains of variety japonica, Taikeng 9, were used for the study. After cooking with the oils (10%, d. b.), there existed in DSC thermograms for cooked rice flours, amyplose-lipid complex (ALC) dissociation peaks from 90℃ to 115℃. Adding PO exhibited the highest dissociation temperature (95.3℃). The XRD patterns changed from A-type to V-type after cooking. In vitro starch digestibility and resistant starch (RS) contents were affected by oils. With increasing saturation of oils, PO yielded the least estimated glycemic index (eGI) of 85.6 and the greatest RS content of 11.2% among all samples. respectively. The results indicated PO could form stable ALC structure, which was resistant to enzymic hydrolysis. Triglycerides mainly retard the short-term 1 day storage starch retrogradation., but did not affect the long-term starch retrogradation (3-5 days storage). Digestibility of reotrograded rice decreased with the storage time, FO had increased the most RS content. In XRD patterns, it could be find structure between V-type and B-type is thermoreversible in the process of storage and reheating. After reheating of retrograded rice, the dissociation temperature of ALC increased. Because of thermal reversibility of ALC, RS contents of reheated rices compared with fresh rices did not have significant different. This study showed that the extend of unsaturation affected the stability of ALC. The less unsaturation, the more stable of ALC. With lower starch digestibility and higher RS content, rice cooking with oils would be a good way to control postprandial blood glucose and get more RS.