Effect of Different Drying Process on the Protein-Thiol Content and the Physicochemical Properties of Water-Extracted Rice Bran Powder

The effect of drying process of the water extracted rice bran powder on the protein-thiol and physicochemical properties was investigated. The rice bran extracted was prepared with water as solvent at high temperature and pressure using the autoclave equipment (121 °C, 15 psi, and 20 min) before undergone drying method using either spray dryer (BṺCHI Mini Spray Dryer B-290, LABOGENE, Denmark) or freeze dryer (CoolSafe 4-15L Freeze Dryers, LABOGENE, Denmark). The water-extracted rice bran powder (WRBP) yield, protein-free thiol compound, physical and functional properties were analyzed. The protein-thiol concentration was quantified using the 5,5 dithiobis (2-nitrobenzoic acid (DTNB) method while protein concentration was directly measured at 280 nm by UV-Vis Spectrophotometer. This was followed by physical properties (water solubility) and functional properties (foaming capacity and stability, water and oil absorption capacity) analysis. The powder yield of freeze-dried WRBP (7.69 ±0.29%) was significantly (p<0.05) higher than spray-dried WRBP (4.43 ±0.24%). The protein concentration of spray-dried WRBP (4.02 ±0.36 mg/mL) was higher than freeze-dried WRBP (3.91 ±0.75 mg/mL). Meanwhile, freeze-dried WRBP (1.22 ±0.36 nmol thiol/mg protein) had a higher thiol concentration than spray dried WRBP (1.18 ± 0.30 nmol thiol/mg protein). However, both results were not significantly different (p>0.05) between the drying method. Spray-dried WRBP had significantly (p<0.05) higher solubility in water compared to that of freeze-dried WRBP with values 1.22 ± 0.21% and 0.63 ± 0.34%, respectively. Freeze-dried WRBP had higher water and oil absorption capacity. There was no significant difference (p>0.05) in foaming capacity and stability for both drying treatments. In conclusion, the drying method for WRBP production could significantly affect the WRBP physicochemical properties.