Effect of parboiling conditions on physicochemical properties and digestibility of rice

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.