Chemicals and reagents

Four early polished indica rice cultivars, including Zhengui (ZG), Shuanggui (SG), Guichao (GC), and Suimi (SM, belongs to GC variety) were selected and purchased from a local market in Nanning, China. Rice was ground by a high-speed grinder (WND-200, Zhejiang Lanxi Weinengda Electric Appliance Co., Ltd., Lanxi, China), passed through a 100-mesh sieve (CT410, FOSS Scino Co., Ltd., Suzhou, China), and then stored at 25°C in desiccator until further analysis. Amylose contents in rice standards were 0.40, 10.60, 16.20, and 26.50% w/w, respectively, which was provided by China National Rice Research Institute. D-Glucose, α-amylase, and glucosidase were purchased from Sigma-Aldrich Ireland Ltd. (Dublin, Ireland). GOPOD was obtained from Megazyme (Bray, Ireland). Potassium hydroxide (cat. no.1310-58-3), sodium sulfite (cat. no.7757-83-7), sodium hydroxide (cat. no.1310-73-2) were from Sinopharm Chemical Reagent Co., Ltd. ethanoic acid (cat. no. 64-19-7), ethyl alcohol (cat. no. 64-17-5), acetic acid sodium salt (cat. no. 127-09-3), iodine (cat. no.7553-56-2), potassium iodide (cat. no.7681-11-0), ethanoic acid (cat. no.64-19-7) were from Shanghai anpu Experimental Technology Co., Ltd. All chemical reagents were of analytical grade.