Table 2.

Current techniques to reduce the glycemic index of rice.

Applied Technology	Findings on Starch Digestion Behaviors	Possible Mechanisms	Ref.
Parboiling with different steaming conditions	Different pressure and time of steaming led to reduction in the GI of rice. Steaming at 1.5 kg/cm2 for 20 min was found to be more appropriate for lowering GI (~47) of Pusa Basamti 1121 rice.	The change in nutritional profiles and multi-scale structure of rice grain led to vary the GI of parboiled rice under different steaming conditions.	[95]
Parboiling, polishing 10%, parboiling plus polishing	The kinetic digestion rate constant (k) of 10% polished rice, brown rice, parboiled rice, and parboiled-polished rice were 3.68, 3.25, 3.9, 2.49 (×10−2 min−1), respectively.	The presence of the aleurone layer and pericarp on the surface of parboiled rice might act as barriers to enzymes and limit the starch hydrolysis.	[96]
Parboiling with different soaking conditions	Parboiled rice had lower GI than non-parboiled rice. A significant reduction in GI was found in glutinous rice. Soaking with 0.2% acetic acid led to more decreased digestion rate of treated rice than soaking with medium with/without NaCl.	The two main changes that occurred during parboiling are gelatinization and recrystallization, which could result in increased quantities of resistant starch and reduced GI. Starch–protein interaction might have limitation in the starch’s ability to be digested. Saline medium might have raised postprandial plasma glucose by promoting amylase activity and accelerating the digestion of starch.	[80]
Parboiling and heat-moisture treatment	Pressure cooking and heat-moisture treatment after parboiling rice could reduce about 10% GI compared to un-treated sample.	The increase in RS and SDS after treatment led to a reduction in the rate of digestion.	[97]
Ultrasound (15/30 min, 40–100% amplitude, 665 W) and chilling (4 °C, 24 h) on KMDL105 rice and CN1 rice	Sonicated modification increased approximately 11.96% eGI of KMDL105 rice compared with native sample, while ultrasound-chilled treatment on rice showed a reduced pattern. The treated CN1 rice had lower eGI (~8%) than its native when modified by either ultrasound or ultrasound-chilled method.	Ultrasound modification affects the starch crystalline structure. However, the combination between ultrasound and chilling led to rearrangement of starch molecules that help lower eGI.	[20]
Open steaming and pressure parboiling with different rice varieties	In terms of GI, non-parboiled rice varied from 76.88 to 83.37. Rice that was parboiled had a lower GI than rice that was not parboiled (between 75.54 and 79.90 for pressure parboiling and between 77.02 and 80.37 for open steaming parboiling).	The increase in RS during parboiling process led to a decrease in the GI of rice. Amylose content and hardness of rice also inversely affect digestion rate. Complexation between amylose and lipid also might occur and change digestion behaviors.	[98]
Brown rice, parboiled brown rice, germinated parboiled brown rice, and polished rice	The analysis GI of rice using the method of International Standard Organization was carried out in the following order: polished rice (83.10 ± 5.10) > brown rice (66.21 ± 7.78) > germinated parboiled brown rice (60.58 ± 6.48) > parboiled brown rice (50.10 ± 5.37).	In the high quantity of dietary fiber in brown rice, parboiled brown rice, and germinated parboiled brown rice, the rate of digestion may be slowed down. In addition, the starch structure, amount of amylose, dietary fiber, and bioactive substances may all play a role.	[29]
Gamma irradiation (5 kGy and 10 kGy) using Cobalt-60 gamma irradiator	An increase in amylose content was found when rice grain was treated with 10 kGy irradiation (+42.8%). The GI of unirradiated, 5 kGy, and 10 kGy rice were 75.02, 68.35 (−8.89%), and 66.51 (−11.34%), respectively, found using an in vivo starch digestibility study on animals.	Gamma radiation modifies the structure in both amorphous and crystal regions, leading to the splitting or deformation of glycosidic bonds.	[34]
Parboiling with different rice genotypes	An approximate 10% reduction in GI was found when applying the parboiled treatments.	Higher gelatinization levels in parboiled rice may raise the RS and lower the GI. Gelatinized starch generates type-III RS after parboiling, which slows starch digestion.	[16]
Parboiling with various conditions	A 20.9% GI reduction in parboiled rice compared with untreated rice was found when the paddy was soaked at 75 °C for 4 h.	Parboiling technique could make the smooth morphology, formation of V-type crystals, and a tight internal structure, which might reduce the digestion rate.	[15]