Functional and digestive characteristics of extruded rice flour

Waxy (short grain), long grain, and parboiled (long grain) rice flours were extruded using three different temperatures and five different water feed rates. The water absorption and water solubility index of the extrudates wa s 0.67-5.86 and 86.45-10.03%, respectively The fat absorption index was sim ilar to that of unextruded flours with an average value of 0.96 g/g +/- 0.1 2. Bulk density decreased with an increase in moisture, except waxy rice, w hich had a quadratic relationship. The viscosity profiles for long grain an d parboiled rice were similar. Both initially increased in viscosity (>130 RVU), then decreased to approximate to 40 RVU. The final viscosity was appr oximate to 60 RVU. Waxy rice viscosity remained low (<20 RVU), then doubled upon cooling. The main difference in the digestion profiles was due to tem perature. The flours extruded at 100<degrees>C digested significantly slowe r than those extruded at 125 and 150 degreesC. Significant differences were not detected for a given temperature and moisture (P > 0.05) except for lo ng grain and parboiled rice extruded at 100 degreesC and 15% added moisture (F = 4.48, P = 0.03) and 150 degreesC and 20% added moisture (F = 3.72, P = 0.05). Moisture appeared to have little effect for a given temperature, e xcept when parboiled rice was extruded at 150 degreesC. The digestion rate for 11 and 25% added moisture was significantly less than that for 20% (P l ess than or equal to 0.05).