2.3. Porosity of Glutinous Rice Grains

The porosity of rice grains (p, %) was determined based on bulk density (ρ_b, g/mL) and true density (ρ_t, g/mL) according to Bhattacharya et al., [19] with some modifications. The bulk density was determined by using a 25 mL pre-calibrated graduated cylinder. An aliquot (10 g) of glutinous rice grains were loaded into the graduated cylinder, and the cylinder was gently tapped using a spatula for 20 s to adjust the clear top level of grains; ρ_b was calculated by the ratio of mass of rice grain and volume occupied.

The true density was measured by the kerosene displacement method. An aliquot (10 g) of glutinous rice grains were gradually added in the graduated cylinder which was filled with a predetermined volume of kerosene (10 mL). The cylinder was mildly shaken on a L-RT30C platform rotator (United Products and Instrument Inc., Dayton, NJ, USA) while adding the rice, to vent the air bubbles adequately. ρ_t was calculated by the ratio of mass of rice grain and volume of kerosene displaced. All samples were tested at least three times each.

The porosity (p, %) was calculated from ρ_b and ρ_t according to the Equation (1):