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 stages with an intermediate tempering time between drying steps. The variables of the drying process were air temperature, tempering time and initial moisture level for tempering treatment. The quality of parboiled rice was measured as head rice yield and browning index (BI). The values of head yield were confined in a narrow segment, 68-74%, it was observed that temperature has a negative influence on head yield while tempering time affects it positively. The BI was mainly affected by air temperature. Tolerable light yellow parboiled rice was obtained using air temperature of 70 degrees C or below. Based on response surface methodology (RSM) it was obtained a second order polynomial model which describes satisfactorily the effects of drying conditions on head parboiled rice yield and BI. (C) 2000 Elsevier Science Ltd. All rights reserved.