Effect of low pressures homogenization on the physico-chemical and functional properties of rice flour

Abstract

Research was conducted to explore the use of low pressure homogenization for extending functionality of rice flours. The impact of low pressure homogenization (0, 30, 50 MPa and 0, 1, 2, 3 passes) on the particle size distribution of long (LRF) and medium (MRF) rice grain flour was evaluated. The pressure level and the number of passes resulted in a lower particle size in both rice flours. Higher pressures and 3 passes led to an increase in the particle size due to aggregation of smaller particles. The effect of low pressure homogenization (0, 30 or 50 MPa - 3 passes) on the physicochemical (composition, bulk density, thiol groups, hydration, emulsifying properties, hydrophobicity, crystallinity) thermal and pasting properties was analyzed. Homogenization increased swelling, oil absorption capacity and surface hydrophobicity of LRF and MRF samples even at 30 MPa. The bulk density and the emulsion stability of samples decreased by pressure. However, the emulsifying activity and thiol groups did not change in LRF, while increased in MRF particularly at 30 MPa. SEM micrographs revealed the microstructure changes, but no significant differences were observed in starch crystallinity. FTIR spectra suggested the modification of the flour constituents, particularly in MRF, reaching higher intensities. The disintegration and modification of the large molecules, increasing availability of binding sites, and partial gelatinization of starch granules, led to flours with different pasting performances. Correlation analysis confirmed that the particle size reduction played a determinant role in the structural and physicochemical changes of both rice flour varieties used.