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The effect of temperature and SO2 concentration on fraction yields (starch, gluten and fibre yields) and protein content of starch during wet milling were investigated using response surface method. Soaking time was adequate to accomplish saturation of the grain. A 32 factorial design including triplicate of central point was performed. The starch and fibre yields decreased with temperature. The effect of SO2 on fraction yields was significant; for gluten, the effect was dependent on the level of temperature. The predicted optimum conditions required to maximise starch and gluten yields together with the minimisation of protein content in starch fraction included steeping at 53.9 °C (1.6 h) with 0.041 w/v% of SO2 concentration. The predicted starch and gluten yields were 45.0% ± 1.35% and 17.5% ± 0.80%, respectively. The predicted protein content for starch fraction was 0.60% ± 0.015%. These predicted values were satisfactorily checked by an experiment at optimal soaking conditions.