High pressure induced water absorption and gelatinization kinetics of paddy

Abstract

Abstract The effect of high pressure on water absorption, diffusion and gelatinization Characteristics of paddy (Basmati cv.) were studied in the pressure range 350–550 MPa. Two different soaking conditions were considered, in first condition, grains were pre-soaked at 40 °C for 6 h prior to treatment, and in second condition grains were treated directly without pre-soaking. These two conditions were exposed to pressure at 350, 450 and 550 MPa; temperature of 30, 40 and 50 °C for 300, 600, 900 and 1200 s, respectively. The pressure was found to act synergistically with temperature influencing the water absorption in grains and facilitating moisture absorption up to 50% (db) in pre-soaked grains. However, the rate of water absorption was even higher in case of un-soaked grains with diffusivity values of 9.30 × 10−10 m2/s. Therefore, treatment of unsoaked grain at 450 MPa at 30 °C for 600 s was found sufficient to reach 40% moisture content (db). On the other hand, maximum gelatinization up to 25% was achieved in pre-soaked grains treated at highest pressure and temperature studied (550 MPa for 50 °C). The rate of gelatinization followed first-order kinetic model at any given pressure and temperature and the rate constant (k) was observed to be vary minimally with pressures and temperatures. The Arrhenius model and Eyring's model was used for the prediction of the activation energy (Ea) and activation volume (ΔV) for the reaction, which was indicative of restricted gelatinization of paddy starch. Industrial relevance In order to use high pressure as an alternative technique to thermal parboiling, a full understanding of pressure-induced water absorption, diffusion and gelatinization kinetics are necessary. Adoption of high pressure processing for water absorption by paddy can be very much promising in order to reduce the processing time.