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Large portions of rice bran protein cannot be solubilized by mild solvents, but endoprotease use increases protein recovery. Bran was treated with 2 commercial proteases to achieve 8% to 9% peptide bond hydrolysis. The exo-plus endprotease was preferred to just using endopeptidases as it allowed the production of protein hydrolysates with enhanced functional properties. Solubility and emulsification activity and stability of hydrolysates produced with the protease blends were greater than that produced with endoprotease alone. These high value hydrolysates, produced from rice bran, an underutilized rice milling coproduct, are suitable for many processed foods, particularly those requiring potent solubility and emulsification at mildly acidic conditions.

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...

Heat‐denatured soy protein was hydrolyzed by Alcalase to 2.0% or 4.0% degree of hydrolysis (DH), heated again at 100°C and deamidated with B. circulans peptidoglutaminase. The extent of deamidation was 6.0% and 8.2% for 2.0 DH hydrolysates and 12.8% and 16.0% for 4.0 DH hydrolysates heated for 15 and 30 min, respectively. Deamidation increased protein solubility and substantially enhanced emulsifying activity under mildly acidic (pH 4–6) as well as alkaline conditions. Deamidation improved emulsion stability and foaming power of heat‐denatured hydrolysed soy proteins. Enzymatically deamidated soy protein hydrolysates had improved functional properties compared to nondeamidated hydrolysates and the native soy protein.

Enzymatic methods were developed for the deamidation of food proteins. Modification of proteins by peptidoglutaminase was dependent on their size and conformation. After such treatments as heat or alkali solubilization, which might have partially broken hydrogen and disulfide bonds, peptidoglutaminase deamidation of proteins increased by proteolysis as a function of percent peptide bond hydrolysis (DH), up to 54-fold at 20% DH. With prior heat treatment at 100 °C for 15 min, followed by proteolysis and alkali solubilization of soy protein, casein, and gluten, over 48, 37, and 39% protein deamidation can be achieved, respectively.