EFFECTS OF POSTHARVEST OPERATIONS ON THE GELATINIZATION AND RETROGRADATION PROPERTIES OF LONG-GRAIN RICE

Abstract

The effects of rough rice pre-drying, drying, and storage treatments on the gelatinization and retrogradationproperties of long-grain rice (cv. Cypress) were studied via differential scanning calorimetry (DSC). The experimentalvariables included two pre-drying conditions (immediate and delayed drying), two drying conditions (high and low airtemperatures), and four storage treatments (no storage, and storage at 4, 21, and 38C for 20 wk). Gelatinization of therice flour in water occurred at temperatures from 73 to 86C, with an enthalpy of 8.3 to 9.7 J/g. Storage temperature hada significant effect on the gelatinization characteristics. Rice stored at 38C exhibited higher (p < 0.0005) gelatinizationenthalpy and peak temperature than did rice stored at 4 and 21C. Pre-drying treatments had no significant effect on thegelatinization enthalpy and peak temperature, but did on the onset temperature (p < 0.05). The pre-drying and/or dryingtreatments had significant (p < 0.05) effects on the retrogradation onset and conclusion temperatures of gelatinized rice.Storage of rough rice significantly (p < 0.0001) increased retrogradation enthalpy, but did not affect the peak temperatureof the retrogradation endotherm.