Physicochemical, Rheological and Moisture Adsorption Characteristics of Two Basmati Rice (<em>Oryza sativa</em> L.) Varieties Differing in Amylose Content

Abstract

Purpose: The purpose of this study was to determine the physicochemical, viscosity and moisture sorption properties of high-amylose (At-306) and low-amylose (At-405) basmati varieties. Research Method: The viscometer method was used to measure the apparent viscosity of the flour samples at 65 and 75°C. Moisture adsorption isotherms were determined by the gravimetric method at 28, 35 and 45°C. Findings: The bulk-density, grain-hardness, gelatinization temperature, protein and amylose contents of the At-306 and At-405 varieties were in the range of 794-780 kg m-3, 55.5-49.7 N, 70.34-66.14°C and 8.80-8.00% and 26.70-15.37%, respectively. At-405 samples showed significantly higher viscosity (8-13.5 Pa s) at 65°C and lower viscosity (1.4-5.3 Pa s) at 75°C but the opposite trend was observed for the At- 306. The flow behavior index, varied with temperature between 0.55-0.54 and 0.75-45, respectively, for At-306 and At-405. At-306 showed a higher equilibrium moisture content (EMC) value compared to At- 405 when aw>0.70. The GAB isothermal model best described the experimental EMC data (R2adj>0.98 and MRD<3.8). At-306 has a higher specific surface area (≈115.5 m2 g-1 d.b) and higher monolayer moisture content (≈3.3 g/100 g) than At-405. The effective pore size of At-306 and At-405 varied between 1.04-12.82 and 0.73-9.18 nm, respectively. The isosteric-heat of adsorption was significantly higher for At-405 than At-306. Research Limitations: Further studies with medium amylose basmati are needed to confirm the applicability of these findings. Originality/ Value: This result provides some information of the physicochemical, rheological and storability characteristics of low and high basmati flours for the food industry application.