Abstract: Starch granule-associated proteins (SGAPs) from indica rice were isolated by sodium dodecyl sulfate (SDS) buffer from alkali washed rice flour and then identified by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Results indicated that the SGAPs from the top, middle and bottom starch layers mainly consisted of granule-bound starch synthase I (GBSS I), which slightly varied with respect to other components. Among these layers, the content of SGAPs in the middle layer was the highest, with GBSS I accounting for up to 99.8% and gluten accounting for only 0.11% of the total. Using the response surface methodology, the optimized conditions for SGAPs extraction from the middle layer starch were obtained as follows: SDS 10.90%, boiling time 4.10 min and MgSO4 0.90 mmol/L. Under these conditions, the yield of SGAPs was (1 028.61 ± 0.05) μg/g.

Key words: rice, starch granule-associated proteins, HPLC-MS/MS, granule-bound starch synthase I, response surface methodology