Effect of Extrusion Cooking on the Enhancement of Soluble Dietary Fiber and Structure Properties of Dietary Fiber in Defatted Rice Bran

Abstract

The defatted rice bran was modified by extrusion cooking, and the effects of extrusion cooking on enhancement of soluble dietary fiber (SDF) and structural properties of dietary fiber in rice bran were studied. Taking SDF content as an index, the optimum extrusion conditions of rice bran were determined by single factor experiment as follows: water content of 35%, extrusion temperature of 160 ℃, and screw speed of 250 r/min. After extrusion cooking treatment, the SDF content of rice bran increased from 4.34% to 14.34%. The microstructure of SDF from extruded rice bran was expanded loosely, the water holding capacity and expansion capacity of SDF significantly increased, while the oil holding capacity of SDF significantly decreased. The infrared spectrum of SDF did not produce a new absorption peak, the peak position moved to the long wavenumber direction, and the absorption intensity decreased. The position of crystal diffraction peak of SDF did not change significantly, and the relative crystallinity decreased. The microstructure of insoluble dietary fiber (IDF) from extruded rice bran was broken, the expansibility of IDF significantly increased, the oil-holding capacity of IDF significantly decreased, and the water-holding capacity had no obvious changes. The results of infrared spectra and crystallization properties both showed that cellulose and hemicellulose still existed in IDF from rice bran after extrusion cooking, but the structure of IDF was destroyed and the relative crystallinity of IDF decreased. The results showed that extrusion cooking treatment could change the structure properties of rice bran dietary fiber, providing a theoretical basis for the development and application of dietary fiber products.

Keywords

• extrusion cooking
• defatted rice bran
• soluble dietary fiber
• insoluble dietary fiber
• structure properties