Characterization of Protein Fractions of Rice Bran to Devise Effective Methods of Protein Solubilization

Abstract

Cereal Chem. 74(5):662-668Proteins from the defatted brans of representative rice cultivars were fractionated into albumins, globulins, prolamins, and acid-soluble glutelins, accounting for 34, 15, 6, and 11% of the total bran proteins, respectively. The remaining insoluble residue protein, after treatment with 0.1M sodium hydroxide, resulted in the solubilization of 95% of the residue protein, representing 32% of the total bran protein. The relative molecular mass (M r ) values determined by size-exclusion HPLC were 10-100 kDa, 10-150 kDa, 33-150 kDa, and 25-100 kDa for the fully dissociated polypeptides of albumins, globulins, prolamins, and acid-soluble glutelins, respectively. Despite a breakdown of disulfide bonds of the residue protein during sodium hydroxide solubilization, the M r of the majority of the fully dissociated polypeptides of this fraction ranged from 45 to 150 kDa. Insolubility of residue protein was due mainly to its strong aggregation and extensive disulfide bond cross-linking. Efficient methods may be developed for solubilizing up to 98% of rice bran protein by the use of dissociating and disulfide breaking agents currently in use in the food industry.Effective, efficient methods have not been developed for isolating and solubilizing rice proteins. Approaches taken to solubilize rice protein have been limited to alkali extraction and the addition of mercaptoethanol as a disulfide breaking agent, or the use of 6-8M urea or 0.5% SDS as extracting buffers in alkaline pH (Wen and Luthe 1985, Snow andBrooks 1989). However, using up to 8M urea was not effective in dissociating a significant portion of rice glutelin polypeptides (Snow and Brooks 1989). Furthermore, protein undergoes major changes in conformation during alkaline extraction. Therefore, a resourceful means for the characterization of rice proteins is needed to understand the molecular basis of solubility. Developing methodology for the solubilization and isolation of proteins in broken kernels, rice bran, and other rice coproducts will lead to value-added, innovative and new products from these underutilized commodities.Cereal proteins are often classified on the basis of solubilities in water, salt, alcohol solutions, and acids. The soluble fractions are albumins, globulins, prolamins, and glutelins, respectively. Solubility fractionation, known as Osborne classification, is crude because of the impurity of solubility classes. For instance, wheat prolamins or gliadins consist of a single polypeptide chain of different sizes stabilized by intrachain disulfide bonds (Jones et al 1959, Woychik et al 1964. The relative molecular mass (M r ) ranged from 25 to 100 kDa. The M r of rice albumin ranged from 10 to 200 kDa, and the M r of rice globulins ranged from 16 to 130 kDa (Iwasaki et al 1982). Another attribute of solubility fractionation of cereal proteins is the substantial amount of protein left unextracted (the protein fraction that is not soluble in these solvents). In hard red spring wheat, this residue protein fraction could repr...

Preparation and Characterisation of Protein Hydrolysates from Indian Defatted Rice Bran Meal

“…Protein has been extracted from rice bran for various food and pharmaceutical applications [2][3][4][5][6] . Rice bran protein has been used as hypoallergenic milk replacers in infant formulas 4) .…”

Physico-chemical and structural properties of four rice bran protein fractions based on the multiple solvent extraction method

“…RBPF was prepared according to modified Hamada's method (Hamada et al 1997). Briefly, 2 g DRB was consecutively extracted with 100 ml of the multiple solvents: 2% NaCl was firstly used to fractionate by shaking (Environ Shaker; Lab-Line Instruments, Melrose Park, USA) at 150 rpm (25°C and 1 h).…”

“…In addition, it is assumed that these treatments might change the physicochemical and structural properties. Even though the method of Hamada (1997) indicated a higher yield, its procedure was more complicated than other methods. However, this method presents a fundamental for rice bran protein relatively than other methods, while the uncover of the natural rice bran protein and the interaction of structural and functional properties have rarely been reported.…”

“…Hamada reported a multiple solvent method to extract the rice bran proteins on the basis of Osborne's method (Hamada 1997;Osborne 1907). Hamada's method employed a sequential procedure using water, NaCl solution, 60% ethanol, and 0.1 N NaOH, which gave higher-quality protein and yield higher than 90% (Adebiyi et al 2009).…”

Emprego de metodologia enzimática na obtenção de extratos protéicos de farinha de trigo

“…[2][3][4][5] A gliadina e glutenina combinadas possuem a propriedade de formar, juntamente com a água e a aplicação de energia mecânica, uma rede tridimensional viscoelástica, insolúvel em água, denominada glúten. 6 Em virtude da grande importância em tecnologia dos cereais, as proteínas do glúten têm sido bastante estudadas.…”