Effects of drying conditions on head rice yield and browning index of parboiled rice

Long-grain paddy of intermediate amylose content was parboiled by steaming to obtain samples of gelatinized rice. The drying was performed in two stag es with an intermediate tempering time between drying steps. The variables of the drying process were air temperature, tempering time and initial mois ture level for tempering treatment. The quality of parboiled rice was measu red as head rice yield and browning index (BI). The values of head yield we re confined in a narrow segment, 68-74%, it was observed that temperature h as a negative influence on head yield while tempering time affects it posit ively. The BI was mainly affected by air temperature. Tolerable light yello w parboiled rice was obtained using air temperature of 70 degrees C or belo w. Based on response surface methodology (RSM) it was obtained a second order polynomial model which describes satisfactorily the effects of drying condi tions on head parboiled rice yield and BI. (C) 2000 Elsevier Science Ltd. A ll rights reserved.