Glutelin, cereal

Glutelins. Also insoluble in water and in 7% aqueous ethanol. Soluble in acids and alkalis. Also found in cereals. 

Cereal proteins when classified by the Osborne sequential extraction method yield four different classes albumins, which are water soluble, globulins, which are soluble in salt solutions, prolamins, which are soluble in alcohol-water mixtures, and glutelins, which are soluble in dilute acid or alkali. Chen and Bushuk added a fifth fraction by dividing the glutelin into two fractions, one soluble in dilute (0.05 m) acetic acid and the other insoluble in this reagent.5... 

Glutelins. Soluble in very dilute acid or base and insoluble in neutral solvents. These proteins occur in cereals, such as glutenin in wheat and oryzenin in rice. 

Prolamins, a group of storage proteins occurring in cereals. They are soluble in 50-90% ethanol and can be so separated from the alcohol-insoluble glutelins. Prolamins are globular proteins (M, ... 

Cereal kernels contain about 70% carbohydrates and 8 to 17% proteins. About 80% of wheat proteins are gluten. Gluten from the cereals named previously is composed of prolamins (high in prohne and glutamine) and glutelins, which are storage proteins... 

Some cereal proteins are quite soluble in aqueous solution (albumins, globulins) but the functional proteins—prolamins and glutelins—are difficult to solubilize. This is important because, for example, we do not want wheat gluten proteins to be soluble in a dough system. However, in order to characterize proteins, it is usually necessary to have them in solution. Because the property of solubility is such an important one with respect to cereal proteins, we will dedicate this chapter to the topic. In keeping with the objectives of the book, we will attempt to approach the subject from the most general and fundamental basis. 

Previous chapters have emphasized the important role of the MWD in determining many functional properties of cereal proteins. Measurement of MWD has met two main problems. The first one is the difficulty of solubilization, particularly of the glutelins. The second is that many of the standard methods for measurement lose their sensitivity above a certain MW. Colligative properties such as osmotic pressure and freezing point depression are related to the number of molecules and therefore give a measure of the number-average MW (MJ. 

Many cereal endosperm storage proteins—especially glutelins— are, in their native forms, disulfide-bonded oligomers or polymers. Even if soluble, such proteins may resolve poorly upon RP-HPLC and elute as broad peaks [22], in part due to their many possible polymeric forms. Reduction is necessary to release disulfide-bonded subunits from cereal glutelins or oligomeric prolamins for analysis [19,32,42,76]. Thus, protein resolution, extractability, and stability are often improved by extraction under reducing conditions. To prevent reoxidation and further enhance resolution, resulting cysteine residues may be stabilized by alkylation, usually with 4-vinylpyridine [19,21,29,70,76]. 

RP-HPLC of storage proteins can also predict quality in other cereals. In barley, RP-HPLC of hordeins [112,224] and high-MW glutelins [225] can reveal malting quality. In maize, Paulis et al. [226] showed by RP-HPLC that there are more y-zeins in quality protein maize than in normal maize this relates to lysine content and nutritional quality. RP-HPLC can relate protein composition to kernel hardness, density, and vitreosity of both normal maize and quality protein maize genotypes [227-229]. Differences between alcohol-soluble proteins of hard and soft endosperm of normal and quality protein maize show that the zein distribution influences kernel texture and hardness [230-232]. 

The glutelin fraction of cereal protein is more heterogeneous than the other storage proteins and consists of several different proteins. Wheat gliadin, for example, is separable into four major fractions a, j3, y and a> but, in all, the gliadin may have as many as 46 components revealed by gel electrophoresis... 

Glutelins.— Vegetable proteins found chiefly in cereal grain. They are insoluble in water and aqueous alcohol in all concentrations, but may be dissolved by dilute acids or alkalies. They are not coagulated by heat. Glutenin, from wheat, and oryzenin, from barley, are the most definite members of the class. 

Proteins are the second largest group of compounds in endosperm (12-15%). Cereal proteins are classified based on their solubility characteristics water soluble albumins (5-10%), dilute salt-solution soluble globuhns (5-10%), aqueous alcohol soluble prolamins (40-50%) and dilute acid or alkah soluble glutelins (30-40%) (Godon, 1994). Cereal proteins, similar to other plant proteins, are low in some of the essential amino acids, for example lysine. Glutamic acid is the major amino acid in wheat. 

Glutelin High-molecular-weight protein fraction that is soluble in dilute acids and bases and insoluble in neutral solvents. They are the main proteins associated with the protein matrix of cereal grains. Glutelins and prolamins together form the gluten. 

---