Wheat prolamines

A response surface model of the effects of HA protein concentration (gliadin, the wheat prolamin), HA polyphenol concentration (tannic acid, TA), alcohol, and pH on the amount of haze formed was constructed using a buffer model system (Siebert et al., 1996a). Figure 2.12 shows the effects of protein and polyphenol on haze predicted by the model at fixed levels of pH and alcohol. The model indicates that as protein increases at fixed polyphenol levels, the haze rises to a point and then starts to decline. Similarly, when polyphenol increases at a fixed protein level, the haze increases to a maximum and then declines. 

Skerritt, J.H., Hill, A.S., Andrews, J.L. 2000. Antigenicity of wheat prolamins Detailed epitope analysis using a panel of monoclonal antibodies. J Cereal Sci 32 259-279. 

All wheat prolamins are characterized by the presence of repeated sequences. These are rich in proline and glutamine and appear to be based on similar motifs in the S-rich and S-poor groups. However, whereas these repeats are present only in the N-terminal parts of the S-rich prolamins, they account for almost the whole protein in the S-poor group. The repetitive sequences present in the HMW subunits are located in the center of the proteins, and are based on several motifs which are not related to those present in the S-rich and S-poor prolamins (Figure 13.8) [21, 22]. 

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. 

Identification of oat (Avena) cultivars by HPLC was first reported by Lookhart and coworkers (153-155) in combined electrophoresis/HPLC experiments. The HPLC technique used was a modification of the procedure described by Bietz (137) for wheat. Generally, the prolamin fraction, i.e., the alcohol-soluble fraction, of oat species generates complex polyacrylamide gel-electrophoresis (PAGE) and RP-HPLC patterns, with increasing complexity as ploidy of the selections increased. Readily (visible) identification of the cultivars was possible only when PAGE and RP-HPLC results were combined. An HPLC procedure for the characterization of the major oat protein fractions was developed by Lapvetelainen et al. (156). Salt-soluble, alcohol-soluble, and alkali-soluble protein fractions were extracted with 0.1 M NaCl, 52% ethanol, and 1% SDS in 0.05 M borate (pH 10), respectively. For the five cultivars examined, RP-HPLC separations of salt- and alkali-soluble proteins were very similar, whereas the prolamin fraction enabled culti-var differentiation, except for very closely related cultivars. 

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. 

GL Lookhart, LD Albers. Correlations between reversed-phase high-performance liquid chromatography and acid- and sodium dodecyl sulfate-polyacrylamide gel electrophoretic data on prolamines from wheat sister lines differing widely in baking quality. Cereal Chem 65 222-227, 1988. 

WDEIA is a serious affection where symptoms are not only connected to wheat protein consumption, but they also appear after the introduction of wheat proteins into the digestive track, and following physical effort. Research on IgE of patients suffering from WDEIA showed that wheat gliadins are responsible for the disease, as well as corresponding taxonomic prolamines of closely related cereals (Varjonen et al., 1997). 

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. 

Shewry, PR., MUes, M.J., Tatham, A.S. (1994). The prolamin storage proteins of wheat and related cereals. Progress in Biophysics and Molecular Biology, 61, 37-59. 

Prolamins are insoluble in water but soluble in 70-80% aqueous alcohol. Upon hydrolysis they yield much proline and amide nitrogen. They are deficient in lysine. Example - Gliadin of wheat and Zein of com. 

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