Effect of High Pressure Treatment and Degree of Milling on Gelatinization and Structural Properties of Brown Rice

Abstract

Brown rice (BR), medium-milled rice (MR), and fully milled white rice (WR), with different degrees of milling (DOM), 0, 6.6, and 10.4 %, respectively, were high pressure (HP) treated at 200 to 500 MPa for 5 to 15 min. Water absorption, swelling, and gelatinization properties, and microstructural changes were investigated. HP treatment (≥200 MPa) or partial milling (DOM 6.6 %) resulted in water absorption comparable with that of white rice. Swelling behavior was affected by milling and processing temperature. Both HP treatment and milling promoted gelatinization properties. In addition, partial milling reduced the pressure resistance of rice grain, while differences in water absorption, swelling behavior, and gelatinization properties due to milling were reduced by HP treatment. Further, the degree of gelatinization (DG) increased with HP treatment with 400 MPa and 10 min defined as the threshold values for pressure and holding time, respectively. DG values, observed with 400 MPa-10 min treatments, were 41.2, 50.2, and 39.9 %, respectively for BR, MR, and WR. Results demonstrated that HP treatment, combined with milling, is technically feasible and produces rice and rice flour with enhanced DG and swelling behavior. These basic data can be used to improve the processing efficiency and quality of brown rice-based product.