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Functional and Digestive Characteristics of Extruded Rice Flour

¹USDA, ARS, Dale Bumpers National Rice Research Center, P.O. Box 287, Stuttgart, AR 72160. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 870-672-9300 (Ext. 227), Fax: 870-673-7581, Email address: rbryant@spa.ars.usda.gov ³USDA, ARS, Southern Regional Research Center, 1100 Robert E. Lee Blvd., New Orleans, LA 70124. ⁴USDA, REE, ARS, Beltsville Area, Office of the Director, Bldg, 001, BARCWEST RM 010, 10300 Baltimore Blvd., Beltsville, MD 20705. ⁵USDA, ARS, Mid South Area Office, P.O. Box 225, Stoneville, MS 38776.

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 was 0.67–5.86 and 86.45–10.03%, respectively. The fat absorption index was similar to that of unextruded flours with an average value of 0.96 g/g ± 0.12. Bulk density decreased with an increase in moisture, except waxy rice, which had a quadratic relationship. The viscosity profiles for long grain and parboiled rice were similar. Both initially increased in viscosity (>130 RVU), then decreased to ≈40 RVU. The final viscosity was ≈60 RVU. Waxy rice viscosity remained low (<20 RVU), then doubled upon cooling. The main difference in the digestion profiles was due to temperature. The flours extruded at 100°C digested significantly slower than those extruded at 125 and 150°C. Significant differences were not detected for a given temperature and moisture (P > 0.05) except for long grain and parboiled rice extruded at 100°C and 15% added moisture (F = 4.48, P = 0.03) and 150°C and 20% added moisture (F = 3.72, P = 0.05). Moisture appeared to have little effect for a given temperature, except when parboiled rice was extruded at 150°C. The digestion rate for 11 and 25% added moisture was significantly less than that for 20% (P ≤ 0.05).