Effect of parboiling conditions on physicochemical properties and digestibility of rice

預煮處理是利用水熱處理稻穀的加工方法，製程包括浸泡、蒸煮、乾燥。HMT (Heat moisture treatment) 對澱粉物化性質產生物理修飾。本研究探討不同處理條件下，蒸穀米理化性質及消化性。選用台南11號稻穀，併用HMT與預煮處理，加壓蒸煮10 (S10)、20 (S20) 分鐘，S10處理前 (B10) 後 (A10)，併入HMT (13%水分與121oC，30分鐘)。顯示蒸穀米顏色呈深紅黃色，與白米相較亮度下降，a值與b值上升，且A10組顏色最深；完整米率 (HRY) 以A10最高 (71.45 %)，加入HMT能有效改善完整米率；於SEM圖中，可觀察蒸穀米中心有孔洞，導致蒸穀米之完整米率的下降；光學顯微鏡圖可觀察到預煮處理前加入HMT可維持蛋白質之結構；蒸穀米粒體外澱粉消化實驗中，預煮處理可使RS量上升3至5倍 (N: 1.95%; S10: 7.95%; S20: 11.01%; B10: 10.48%; A10: 10.42%)，尤以CA10之預估升糖指數 (eGI) 下降最多 (102.39下降至92.43)，其中CA10之SDS含量有顯著提升 (37.08%上升至45.83%)，蒸穀米具有較低之米粒體外澱粉消化性；由X-ray繞射圖譜及示差熱掃描分析中可觀察到直鏈澱粉-脂質複合物 (ALC) 特徵結晶波峰及解離吸熱峰。米粒煮熟後由A-type轉變為V-type，加入HMT及提高預煮時間皆會使V-type特徵結晶波峰強度增加；預煮處理與結合HMT會導致ALC之熱焓值解離吸熱峰上升，ALC具熱可逆性，從兩次DSC掃描可觀察到預煮處理後之ALC升成量皆較多；質地分析中，CS10與CS20質地與白米組CN相近，CB10為堅硬不軟黏，CA10為堅硬偏黏之質地；感官綜合喜好性品評以CS20組與白米組CN相近，CB10組最差。由以上結果得知，預煮處理與熱處理會使米粒呈較深的顏色、可以改善完整米率、並提高RS、SDS與ALC含量，降低米飯之消化性，可作為開發低消化性米飯之用。Parboiling is a hydrothermal treatment including soaking, steaming and drying. Heat-moisture treatment (HMT) can alter the physicochemical properties of starch via physical modification. This study was to understand effects of parboiling and HMT on physicochemical properties and digestibility of different parboiled rices. A japonica, rough rice (Tainan 11), was used in this study. Various parboiling conditions including pressure steaming 10 minutes (S10)、20 minutes (S20)、combined with HMT (13% moisture, 121oC, 30minutes) before S10 (B10) and after S10 (A10). Lightness of parboiled rice was decreased, a severe parboiling resulted in dark red and yellow appearance. The combined of parboiling and HMT was helpful for increasing Head rice yield (HRY). Parboiling process with quick drying lead to form fissure or a hole except for A10. More protein structure were preserved protein in sample B10. From DSC thermogram can observe that amylose-lipid complex (ALC) dissociation peaks was observed around 110℃, which was increased by severe parboiling. The XRD patterns was shifted from A-type to V-type after parboiling process. In vitro starch digestibility test and resistant starch (RS) contents were increased with increasing severity of parboiling process, CA10 exhibited least estimated glycemic index (eGI) of 92.43, with a RS of 10.42 % and SDS of 45.83% . With lower digestibility and higher RS content, parboiled rice would be beneficial to control postprandial blood glucose and get more RS. And thus used as a healthy staple food