Functional properties of extruded rice flours vary with processing temperature.

Rice grain has a few unique attributes. It's easy to digest, has a bland taste, a white color, various hypoallergenic properties, and it lacks gluten. It has become a popular ingredient for use in developing novel cereal foods, especially for persons suffering from gluten sensitivity, such as celiac sprue and other chronic diseases.

Extrusion has become a popular, economical and convenient process for making new cereal-based foods. But there is a need to characterize the physicochemical and functional properties for extruded rice flours. USDA-ARS scientists investigated the functional properties of long-grain, high-amylose (LG) and short-grain, low-amylose (SG) extruded rice flours at temperatures ranging from 70 C to 120 C. The researchers also incorporated these flours into a fried snack so that they could evaluate the flours' functional properties and see how they affect the product's characteristics.

The extrudate with which the researchers worked was either dried at room temperature or frozen overnight and then dried. The scientists evaluated the dried material for its functional properties, such as rapid viscosity, water absorption index (WAI), water solubility index (WSI) and fat absorption index (FAI). The results showed that in the high-amylose grain, the WAI and WSI increased with extrusion temperature. With the low-amylase grain, the WAI decreased, but the WSI increased as the temperature increased. Both the setback and final viscosities decreased with an increase in extrusion temperature, but the cold paste viscosity increased.

So it appears that flour extruded at higher extrusion temperatures is suitable for making soups, beverages and batter-type products. Lower-temperature extruded or unextruded flours are suitable for making bread or rice-fry-like products. The researchers confirmed this by substituting 25% rice flour into a wheat-based fry snack. The fat absorption changed from 35% to 50%, showing that a substantial decrease in fat absorption can be achieved by incorporating rice flour into fried foods and batters.

Further information. Ranjit Kadan, Food Processing and Sensory Quality Research Unit, USDA- ARS Southern Regional Research Center, 1100 Robert E. Lee Blvd., P.O. Box 19687, New Orleans, LA 70179; phone: [phone]; fax: [phone]; email: [e-mail].