Ultrasonic modulated rice bran protein concentrate: Induced effects on morphological, functional, rheological, and thermal characteristics

Abstract

The effect of low frequency (20 kHz) ultrasonication at varying amplitude (20%, 30%, 40% for 30 min) on the morphological, functional, rheological, and thermal characteristics of rice bran protein concentrate (RBPC) from three different rice varieties: Pusa Basmati- 1509, 1121 and Sugandha were undertaken for the study. Scanning Electron Microscopy images showed that sonication treatment changed the microstructure of RBPC as some pores appeared on the smooth particles surface and more disordered structures compared to the untreated sample. Sonication treatment decreased mean particle size, D[4,3] from 89.77 μm (untreated) to 64.34 μm (20% amplitude), and increased surface hydrophobicity significantly (p < 0.05), from 1.34 ± 0.0080 (untreated) to 1.65 ± 0.0081 (20% amplitude) of 1121 RBPC variety. The FTIR analysis showed that sonication treatment altered RPBC secondary structure as β sheets, and random coils increased while reducing α-helix and β-turns. Sonication treatment at a lower amplitude of 20% made RBPCs brighter in color as lightness, redness, and yellowness values increased. The results showed that sonication treatment has improved the foaming capacity (FC), foaming stability (FS), and oil binding capacity (OBC) of all RBPC varieties. The FC increased significantly from 34.10 ± 0.27 (untreated) to 50.13 ± 0.98 (30% amplitude), FS (60 min) from 21.19 ± 0.63 (untreated) to 44.20 ± 0.26 (30% amplitude), and OBC from 1.42 ± 0.05 (untreated) to 1.61 ± 0.01 (30% amplitude) of 1509 RBPC variety, respectively (p < 0.05). Furthermore, water binding capacity and emulsion activity were reduced for all RBPC varieties after sonication, while solubility and digestibility improved for the 1121 variety, whereas reduced for the 1509 and Sugandha RBPC varieties. Frequency sweep analysis showed that sonication treatment reduced both the storage modulus and loss modulus of RBPC dispersions. Moreover, protein gel linkages transformed from non-covalent to covalently cross-link with increasing % amplitude for the 1121 RBPC variety. Ultrasonication at a lower 20% amplitude, first decreased the denaturation temperature (Tp) of 1121 RBPC variety from 72.5 °C to 63 °C, then increased it to 77.3 °C at higher 40% amplitude. In conclusion, under the conditions investigated in this study, sonication treatment has the potential to modify the foaming and oil-binding properties of RBPCs.