Simultaneous recovery and purification of rice protein and phosphorus compounds from full-fat and defatted rice bran with organic solvent-free process

We studied a process that enables simultaneous recovery of protein and phosphorus compounds from rice bran. Phosphorus substances in full-fat and defatted rice bran such as phytic acid and inorganic ions were solubilized under acidic conditions in the first step. After that, inorganic and/or organic phosphate salts were recovered in insoluble form under weak alkaline conditions. Furthermore, protein fractions obtained after phosphorus compounds had been removed were solubilized under alkaline conditions. After solubilization, protein fractions with high content were recovered by isoelectric precipitation (IP) followed by electrolyzed water treatment (EWT). The highest protein content (52.3 w/w%) was attained when machine defatted rice bran was treated through the process. Energy-dispersive X-ray spectroscopy (EDX) and inductively coupled plasma atomic emission spectrometry (ICP-AES) analyses demonstrated efficient desalting from the protein fractions by EWT and higher phosphorus contents (15.1–16.4 w/w% P) in the phosphorus fractions compared with commercial phosphate rock. In addition, no heavy metal ions in either protein or phosphorus fractions were detected. These results suggest that the newly developed process is suitable for practical recovery of highly concentrated protein and phosphorus compounds from rice bran without enzymes or chemicals such as organic solvents, buffering agents, and surfactants.