Effects of Steam Explosion on Structural and Properties of Soluble Dietary Fiber in Rice Bran from Different Varieties

Rice bran from 3 rice varieties, namely Daohuaxiang, Changlixiang and Ganwanxian No.40 were used as raw materials to investigate the effect of steam explosion on structural and properties of soluble dietary fiber in rice bran of different varieties. The structure alteration of SDF in rice bran treated by steam explosion was observed by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The impact of steam explosion on SDF functional properties of rice bran was studied by a series of evaluation indicators, such as water holding, oil holding, cholesterol adsorption, glucose adsorption, α-amylase inhibition and antioxidant capacity. The results showed that steam explosion could increase some absorption peaks intensity in the infrared spectrum of SDF, decrease crystallinity and form loose and porous structure of rice bran SDF from 3 rice varieties. The SDF contents in Daohuaxiang, Changlixiang and Ganwanxian No.40 rice bran by steam explosion were increased by 87.22%, 94.72% and 70.31%, respectively. Notably, the functional properties of steam-exploded rice bran from 3 rice varieties, such as water retention, oil retention, cholesterol adsorption capacity under human gastric fluid environment, glucose adsorption capacity, ABTS⁺ and OH free radical scavenging rate and total antioxidant capacity were significantly increased compared with control group (P<0.05). The α-amylase inhibition activity of SDF in steam-exploded Changlixiang rice bran and Ganwanxian No.40 rice bran increased by 7.60% and 21.72%, respectively. The SDF in steam-exploded Daohuaxiang No.40 rice bran showed stronger water retention, cholesterol adsorption ability (pH2) and higher clearance rate of DPPH·, which reached 1.06 g/g, 43.93 μmol/g and 14.25%, respectively. In contrast, the SDF from Changlixiang rice bran by steam explosion exhibited higher oil retention, α-amylase activity inhibition ability and total antioxidant capacity, which reached 4.02 g/g, 86.53% and 3.82 μmol/g, respectively. The SDF in Ganwanxian No.40 rice brans showed stronger ability to adsorb glucose, and the radical scavenging ability for ABTS⁺· and ·OH was 625.16 mg/g, 98.26% and 27.85%, respectively. In summary, the SDF content in bran of 3 rice varieties by steam explosion was increased and their functional properties were improved compared with the control group, the SDF treated by steam explosion from 3 rice varieties showed different functional properties.