ULTRASSOUND IMPROVES THE RICE BRAN PROTEIN EXTRACTION

Defatted rice bran (DRB) is a byproduct of rice industry with approximately 19% of protein. Ultrasonic assisted extraction allows greater selectivity, reduces extraction time and provides more homogeneous mixtures. The effect of ultrasound on DRB proteins extraction was evaluated by a Fractional Factorial Design 2^(4-1) (FFD). The studied variables were: pH (8-10); ultrasound exposure (5-15 min) (Ultrasonic Probe VC 505, Sonics); amplitude power (40-80%); and DRB/water ratio (100-180 g/L); temperature (25 ºC) and frequency (20 KHz) were fixed. The protein extracted (g protein/100 g DRB) was determined by Kjeldhal (conversion factor = 5.95). The pH (x1) had a positive effect (p < 0.05) on the response; an increase from the lower level (8) to the higher level (10) improves the protein extracted in 1.49%. The DRB/water ratio (x4) had negative effect (p < 0.05); the reduction from the higher level (180 g/L) to lower level (100 g/L) improves the protein extraction. The ultrasound exposure and amplitude power had no effect (p > 0.05) in the response. A high pH value (pH 10) improves the protein extraction, due protein solubility pH-dependence; the pH modifies protein net charge resulting in electrostatic repulsion and rupture of hydrogen bonds. The effect of DRB/water ratio may be explained by mass transfer and the interaction protein-water. A higher water proportion improves the driving force and the mass transfer from the solid to the medium. The highest protein extraction (6.34% ± 0.04) was obtained in the following condition: x1 = 10; x2 = 100 g/L; x3 = 15 min; and x4 = 40%. The FFD allowed to select the variables with effects in the DRB protein extraction (pH and DRB/water ratio), which can be further explored by statistical process optimization techniques, aiming to increase the yield of the DRB protein extraction process.