Barley prolamins

Only proteins that contain proline bind polyphenols. Asano et al. (1982) demonstrated that the haze-forming activity of a protein is roughly proportional to the mole percentage of proline it contains (see Fig. 2.3). DNA has codes for exactly 20 amino acids. If each of these were equally present in a protein, there would be 5 mol% of each one. In fact, most proteins have much less proline than this. There are a few exceptions. Casein has about 8 mol% proline and the grain prolamins (proline-rich, alcohol-soluble proteins) are even higher. Hordein, the barley prolamin, contains about 20 mol% proline. As a result, it readily forms haze with polyphenols and is the main beer haze-active (HA) protein. Hordein contains even more glutamine (Q) than proline (P), and often these amino acids are adjacent in the protein (see Fig. 2.4). In fact, the sequence P-Q-Q-P occurs... 

Hordein Generic name of the barley prolamins. This protein fraction is extracted with alcohol and is mainly located in the endosperm. 

Wheat, rye, and barley have a common ancestral origin in the grass family. Oats are more distantly related to the analogous proteins in wheat, rye, and barley and the oat prolamins (avenin) have substantially lower proline content. Avenin accounts for 5-15% of the total protein in oats, whereas in wheat, barley, and rye, prolamins constitute 40-50% of the total protein (Kilmartin et al., 2006). Some investigators believe that there are similarities between the protein structure of oats and some wheat-like sequences, which may indicate that large amounts of oats could potentially be toxic to patients with celiac disease. However, the putative toxic amino acid sequences are less frequent in avenin than in other prolamins, which explains the less toxic nature of oats (Arentz-Hansen et al., 2004 Ellis and Ciclitira, 2001, 2008 Shan et al., 2005 Vader et al., 2002, 2003). 

Most of the applications of HPLC for protein analysis deal with the storage proteins in cereals (wheat, corn, rice, oat, barley) and beans (pea, soybeans). HPLC has proved useful for cultivar identihcation, protein separation, and characterization to detect adulterations (illegal addition of common wheat flour to durum wheat flour) [107]. Recently Losso et al. [146] have reported a rapid method for rice prolamin separation by perfusion chromatography on a RP POROS RH/2 column (UV detection at 230nm), sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), and molecular size determination by MALDl-MS. DuPont et al. [147] used a combination of RP-HPLC and SDS-PAGE to determine the composition of wheat flour proteins previously fractionated by sequential extraction. 

FG Chirdo, CA Fossati, MC Anon. Fractionation of wheat, barley, and rye prolamines by cation exchange FPLC. J Agric Food Chem 42 2460 -2465, 1994. 

Cereal prolamins, named glutenins and gliadins in wheat, secalins in rye, and horde-ins in barley, are major storage proteins of the cereal grain endosperm. These sulfur-rich proteins comprise an N-terminal domain of proline- and glutamin-rich repeats and a C-terminal domain responsible for intrachain disulfide bonds (Breiteneder and Radauer 2004). So far, y-3 hordein (Hor v 21) from barley, Sec c 20 from rye, as well as Tri a 19 and Tri a 26 from wheat are included in the IUIS allergen list. 

In genetically susceptible individuals, ingestion of cereal prolamins from wheat, barley, rye, and possibly oats initiates an inflammatory disorder during which the small intestinal mucosa is damaged. This process is accompanied by malabsorption, activation of the intestinal immune system, and... 

Gliadins are prolamins, a group of plant storage proteins with a high proline content, found in the seeds of cereal grains wheat (gliadin), barley (hordein), rye (secalin), corn (zein) and, as a minor protein, avenin in oats. 

The sulfur-rich prolamins are quantitatively the most abundant group in wheat, barley and rye, accounting for approximately 80-90% of total prolamin fractions. They include polymeric and monomeric components and consist of at two families in each species, the B- and y-hordeins of barley two types of y-secalin of rye and a, 3 and y-gliadins and LMW glutenin subunits of wheat. The sulfur-poor prolamins include C-hordeins of barley, (O-secalin of rye and co-gliadin of wheat. 

The study of gliadin related C-hordeins served as a model for understanding the structure of the other S-poor prolamins [26]. The co-gliadins are homologous to rye (O-secalins and barley C-hordeins. 

Wheat, barley, and rye are classified in the same subfamily (Festucoideae) and tribe (Triticeae) of the grass family (Gramineae), and this close relationship is reflected in the structures of their prolamin storage proteins. Only in wheat, however, do these proteins form a cohesive mass (gluten). Barley and rye are diploids, each with seven pairs of chromosomes, while wheat species are diploid, tetraploid, or hexaploid (Figure 3.14). 

Prolamines a group of simple (unconjugated) proteins, soluble in 90% ethanol. They occur in cereals, and contain up to 15 % proline and 30-45 % glutamic add, but they have only low contents of essential amino acids. The chief representatives are gliadin (wheat and rye), zein (maize contains no tryptophan or lysine) and hordein (barley contains no lysine). Oats and rice do not contain P. 

Marchylo and Kruger [26,52] developed and optimized conditions to separate barley and malt prolamins (hordeins) by RP-HPLC, and used these methods for cultivar identification based on qualitative and quantitative differences. Elution profiles were largely independent of growth location, year, and protein content. Identification of barley cultivars by hordein lE-HPLC was also reported [164], Barley HPLC varietal identification was reviewed by Marchylo [165],... 

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