Effect of conventional and microwave heating on physical and chemical properties of Jasmine brown rice in various forms

Abstract

AbstractTo study the impact of heating on Jasmine brown rice using microwaves compared to that using conventional method. Morphological, physicochemical properties of uncooked and cooked brown rice samples in native (BR), germinated (GBR) and germinated‐parboiled (PGBR) forms were investigated. It was found that the uncooked rice products had similar macro‐composition (amylose, fat and protein). The microwaves heated the rice four times faster than the conventional way. The cooked grains had large, long, narrow, canal‐like holes on the surface and inner portions. The conventional heating filled the grains with smaller, round holes. Both heating methods created B‐ and V‐type crystals with relative crystallinity of 7–8% at 2θ = 0°–35°, an endothermic peak at 42–61°C with enthalpy (ΔH) of 3–4 J/g, and texture with low hardness and stickiness. However, microwave additionally caused higher pasting temperature and viscosity values, and lower digestibility with higher RS at the expense of RDS and SDS. In terms of the rice forms, PGBR was sensitive to changes in the endothermic peak and digestibility. BR was to changes in the crystallinity, hardness and stickiness. GBR was to pasting properties. Microwave and conventional heating are good methods to diversely modify the properties of rice in various forms. However, diversity was noticed only in some properties.Practical ApplicationsThe cooked rice properties are affected by a combination of heating mechanisms and rice pre‐treatments. In comparison to the conventional heating mechanism of electronic rice cooker (ERC), the dipole/polar rotation mechanism of microwave oven (MW) induced higher values of porousness, pasting parameters and resistant starch content. The high porousness of the cooked rice supported migration of gas and liquid through such matrices suggesting rapid rate of drying, diffusion, etc. Powder from such cooked rice with higher pasting viscosity and retrogradation suggested a use in products required high viscous gel formation and then retrograded during storage such as bakery products for sugar‐blood‐control‐needed consumers. The digestibility results suggested that PGBR cooked by MW contained highest resistant starch which is the most beneficial to the specific consumer group. Hardness and stickiness of all rice types were equally acceptable as indifferently affected by both heating methods.