Evaluating the effect of different physical pretreatments and cooking methods on nutritional (starch digestibility) and physicochemical properties of white rice grains (Fajr cultivar)

The effects of physical pretreatments including steaming, dry heating and a combination thereof (performed at different times) were evaluated on the content of resistant starch (RS), slowly digestible starch (SDS), and rapidly digestible starch (RDS), morphology, crystalline structure, and some other physicochemical properties of uncooked Iranian rice grains (Fajr cultivar). The grains were then subjected to cooking by various methods (i.e., boiling, rinsing, and steam-cooking) to investigate the effect of cooking on the nutritional properties obtained after applying physical pretreatments. Generally, reaction constant (k), hydrolysis index (HI), and estimated glycemic index (eGI) decreased after pretreatments. Physical pretreatments increased R1047/1022. Pretreated and cooked grains had significantly higher RS content (5–20%) than non-treated cooked samples. Morphology and crystalline structure were affected by pretreatments. Cooking by rinsing method is suggested for patients with type 2 diabetes mellitus because of lowering the HI (30%) and eGI (18%). Steam-cooking method is recommended for preparing a dietary rice meal due to the higher RS and SDS content. Pretreatment by steaming and cooking by boiling are suitable for people suffering from chewing problems. In conclusion, applying physical pretreatments and choosing appropriate cooking method can increase RS content, decrease eGI, and hence improve nutritional characteristics of rice grains.