Triticeae glutens

"Triticeae" glutens are seed storage proteins found in mature seeds of grass tribe "Triticeae". Seed glutens of non-"Triticeae" plants have varieties of similar properties, but none singly can perform on a par with those of the "Triticeae" taxa, particularly the "triticum" species (bread wheat, durum wheat, etc). By its strictest definition gluten means the factors in bread wheat (Triticeae "Triticum aestivum") that give rise to the sticky capacity that allows dough to rise and retain its shape during baking. The same proteins or very similar proteins are also found in other triticeae genera and species. What distinguishes bread wheat from these other grass seeds is the quantity of these proteins and the level of subcomponents, with bread wheat having the highest protein content and a complex mixture of proteins from derived from 3 grass species (Aegilops speltoides, Aegilops tauschii strangulata, and triticum monococcum). Because of the sequence similarity of these glutens, gluten sensitivity (most importantly Coeliac disease)has a reactivity primarily restricted to grass seeds of this tribe (known reactivity to Triticum, Secale, Triticosecale, Hordeum, Aegilops, and Agropyron), but this may extend to related grass seeds of Aveneae. Between 2 and 10% of gluten sensitive individuals are also sensitive to oats, but it is not clear how much of this is due to contamination of triticeae seeds in oats or allergic responses (versus intolerance). Therefore when broadly applied the designation of Gluten-free applies to foods bearing the seed storage proteins derived from Triticeae.

"Triticeae" seed proteins fall into four groups: [ It is the sticky, glue like properties of glutens from this taxa that are most useful in the food production industry. Grass storage proteins - [http://www.friedli.com/research/PhD/gluten/chap2.html the Glutens] ]
* albumins - soluble in hypotonic solutions and are coagulated by heat
* globulins - soluble on 'isotonic' solutions
* prolamins - soluble in aqueous alcohol
* glutelins - are soluble in dilute acids or bases, detergents, chaotropic or reducing agents.

Of these proteins the last two, prolamin (in wheat - gliadin) and glutelin (in wheat - glutenin) form the classically defined gluten components in wheat.

Triticeae glutens are primarily important to a developing definition 'gluten-free' in dietary treatments for gluten sensitivity which are intended to exclude pathogenic proteins from the diet of susceptible individuals (namely coeliac disease). The poisonous motifs appear to be spread widely in "Triticeae", but not other taxa, for most coeliacs. However all 4 proteins are involved in wheat allergies, and proteins from non-wheats may not be involved in certain gluten allergies, or in idiopathic senstivities.

Prolamins and Glutelins

Proteins of the "Triticeae" endosperm that are generally rich in arginine, proline, glutamine, and/or asparagine.
* Prolamins
** "Triticum" (True Wheats) - gliadins
** "Hordeum" (Food Barleys) - hordeins (B-hordein is homolous to LMW-glutenin)
** "Secale" (Food Ryes) - secalins
* glutelins
** "Triticum" - glutenin
** "Hordeum" - [http://jxb.oxfordjournals.org/cgi/content/abstract/29/3/677 barley glutelin]
** "Secale" - rye glutelin

Genetics of Prolamins and Glutelins

Because of the usefulness of wheat glutens genetic studies have largely focused on wheat genetics. Wheat has three genomes (AABBDD) and it can encode for many variations of the same protein, even in the gliadin subcategories many types of gliadin per cultivar, "X" = genome (A, B, or D genome chromosomes (1 to 7))). The A and B genomes are derived from wild emmers wheat which in turn is a natural digenomic species that contains a triticum monococcum and aegilops speltoides like genome. The D genome is derived from the extant species Aegilops tauschii strangulatum.

*Glutenins and Gliadins on Chromosome 1
**short arm (Chromosome 1)
*** ω-gliadin - (Gli-"X"1 - A is null @ 84%, B (>8 alleles), D (>4 alleles))
*** glutenin, LMW - (Glu-"X"3 - A (>5 alleles), B (>7 alleles), D (>2 alleles))
*** γ-gliadins, most - (Gli-"X"3), homologous proteins exists in Barley.
*** β-gliadins, few - variants of γ-gliadin that migrate with β-gliadins?
** long arm (Chromosome 1)
*** glutenin, HMW (Glu-"X"1 - A (>2 alleles), B (>8 alleles), D (>4 alleles))
*Gliadins on Chromosome 6 (A, B and D genomes)
** short arm (~30 coding loci over A, B,D undeterminant alleles)
*** α-gliadin - (Gli-"X"2)
*** β-gliadins, most - (Gli-"X"2) variants of α-gliadin with alter isoelectric points.
*** γ-gliadins, few - (Gli-"X"2) variants of α-gliadin that migrate with γ-gliadins?

The genetic studies indicate that in wheat, each protein type can be encoded by several loci and several different alleles for each loci can be found in different genomes, allowing a great number of uniquely encoded isoforms.

Biochemistry of "Triticeae" prolamins and glutelins

Chemical behavior

*Gliadins, as an example of the prolamins, in "Triticeae". gliadins are separated on the basis of electrophoretic mobility and isolelectric focusing.
** α-/β-gliadins - soluble in low percentage alcohols.
** γ-gliadins - ancenstral form of cysteine rich gliadin with only intrachain disulfide
** ω-gliadins - soluble in higher percentages of alcohol and acidic acetonitrile.

*Cultivar glutelins in "Triticeae"
** Glutenin is 35-40% of wheat (Triticum aestivum) protein.
** Glutenin in wheat forms long covelantly interlinked polymers of two repeating subunits.
*** High molecular weight (HMW) - proline-less (Glu-1 locus)
*** Low molecular weight (LMW) - α-gliadin-like polypeptide (Glu-3 locus)
** Barley ("Hordeum") has two glutelins, soluble at high pH, precipitates at low pH.
*** α-glutelin (major component, HMW) - cuts at 1 to 3% rel. saturation ammonium sulfate
*** β-glutelin (minor component) - cuts at 18% rel. saturation ammonium sulfate
** Rye ("Secalin") has one glutelin
*** HMW - (equivalent of Barley α-glutelin)
*** LMW - subspecies "sylvestre" has (Glu-R3) glutenin-like (Ssy1, Ssy2 and Ssy3 loci)cite journal | author = Shang H, Wei Y, Long H, Yan Z, Zheng Y | title = Identification of LMW glutenin-like genes from Secale sylvestre host. | journal = Genetika | volume = 41 | issue = 12 | pages = 1656–64 | year = 2005 | pmid = 16396452]

As substrates for enzymes

Modification of Glutamine
Prolamins and to a lessor degree glutelins are excellent substrates for deamidation particularly by mammalian tissue transglutaminases (tTG). Deamidation is a process in which the R-C0-NH2 portion of glutamines (or asparagine) is hydrolyzed to R-CO-OH forming glutamic acid or aspartic acid. In glaidin the -QQP-, -QVP-, -QLP-, -QYP- tripeptides in the context of favorable adjacent peptides are readily deamidated.cite journal | author = Mazzeo M, De Giulio B, Senger S, Rossi M, Malorni A, Siciliano R | title = Identification of transglutaminase-mediated deamidation sites in a recombinant alpha-gliadin by advanced mass-spectrometric methodologies. | journal = Protein Sci | volume = 12 | issue = 11 | pages = 2434–42 | year = 2003 | pmid = 14573857 | doi = 10.1110/ps.03185903] Most proteins have few or no such transglutaminase sites; however alpha gliadin has 13 such sites. Human tissue transglutaminase not only deamidates gliadin, but it also crosslinks itself to gliadin, which has immunological consequences. Gliadin also has a small peptide that appears to alter the distribution of transglutaminase in the gut but is not crosslinked, the mechanism of its 'innate' behavior is not clear. tTG also crosslinks gliadin to other proteins via these sites, generating anti-food responses, anti-self protein responses, and self-crossreactive responses to food proteins that result in secondary autoimmunities. The role of tTG in the extracellular matrix is to crosslink lysine side chains of proteins such as collagen to proteins, however glutens appear to infiltrate into the small intestine, interfering with this process and resulting in a false immune recognition of the matrix and surrounding cells as "foreign", leading, ultimately, tothe destruction of the intestinal mucousa. Seeds of certain plants may elicit the innate and cellular responses as a defensive response to overconsumption of seeds.

Proteolysis
While prolamins and glutelins are excellent deamidase and transaminase substrates the highly repetitive motifs, particularly polyproline/glutamine tracts, are often poor substrates for gastroentestinal endoproteases, such as those produced in the GI tract. One clear example is a 33-mer of α-2 gliadin. Another digestion resistant region is a 25-merwhich contains the innate peptide.cite journal |author=Mamone G, Ferranti P, Rossi M, "et al" |title=Identification of a peptide from alpha-gliadin resistant to digestive enzymes: Implications for celiac disease |journal= |volume= |issue= |pages= |year=2007 |pmid=17544966 |doi=10.1016/j.jchromb.2007.05.009] . The alpha gliadins, which bear these sites, specifically are poisonous to young rats when fed at concentrations higher than 1%cite journal |author=Stĕpánková R, Tlaskalová-Hogenová H, Fric P, Trebichavský I |title=Enteropathy induced in young rats by feeding with gliadin--similarity with coeliac disease |journal=Folia Biol. (Praha) |volume=35 |issue=1 |pages=19–26 |year=1989 |pmid=2653886 |doi=] and the addition of Mannosidase inhibitors increases the sensitivity specifically to alpha gliadins.cite journal |author=Köttgen E, Beiswenger M, James LF, Bauer C |title=In vivo induction of gliadin-mediated enterocyte damage in rats by the mannosidase inhibitor, swainsonine: a possible animal model for celiac disease |journal=Gastroenterology |volume=95 |issue=1 |pages=100–6 |year=1988 |pmid=3131176 |doi=] These properties of certain alpha-gliadins appear to have evolved to prevent long-term or dedicated consumption of certain wheat grasses by certain species. This is one of the ironic properties of wheat, since a major advantage of wheat is the amount of protein in the wheat, however, some of this is wasted to the gut flora (or host immune system) since it cannot be broken down. One suggested remedy to this problem are new enzymes that help specifically break prolamins in the stomach. This may prevent the onset of wheat related disease in susceptible individuals, but no such screening is currently effective and once the clinical state is reached most individuals are so sensitive to wheat gliadins that, effectively, complete digestion in the stomach would be required.

Immunochemistry of "Triticeae" glutens

The immunochemistry of "Triticeae" is important in several autoimmune diseases (see section on Human Disease), and gluten sensitivity and gluten allergy in general. It can be subdivided into innate responses (direct stimulation of immune system), Class II mediated presentation (HLA DQ), Class I meditiated stimulation of killer cells, and Antibody recognition. The DQ restricted class II mediated presentation of gliadin to T-helper lymphocytes appears to be the primary process involved in Coeliac Disease.

"Triticeae" glutens and industry

Glutens are an essential part of the modern food industry. The industry of wheat goes back to before the Neolithic period when people process grain berries (or corns) singley by hand. During the early phase of cultivation wheats were selected for their harvestability and growability under various climate conditions resulting in the first cultivars. This industry spread into many areas of western eurasia during neolithization, carrying the more primitive cultivars. These grains were capable of being used for soups (speltiods) or tediously ground into simple flours and baked goods. During the second phase an Emmer wheat was produced that was an alloquadraploid species and this contained more gluten making baking more efficient this also spread during the neolithization but in places such cultivars were a minority. One variant of emmer wheat is called durum wheat and is the source of semolina flour, used in making pastas and other food pastes. Comparable varieties are found through out Eurasia. Finally, emmers wheat was combined with a goat grass (Aegilops tauschii) to form allohexaploid bread wheat, which has a soft fine texture after rising and cooking. The industrial properties of this wheat are based in its glutens, glutens of high elasticity, high heat tolerance of other glutens or that change when subjected to heat to produce stronger polymers.

Comparing wheat gluten with corn ("Zea") glutens

Corn is prepared for breading by boiling in water with alkali, resulting in a de-skinned material called nixtamalized masa. Masa can be used for industrial purposes (tortillas, tamales, chips), but it must be used quickly because its glutens change rapidly and binding decreases rapidly. Masa does not store well and chemicals are added to enhance preservation at the expense of quality. At its peak attempting to use masa as dough generally results in a crumbly flat bread, correctable by regrinding masa to a fine flour and adding gums (such as Xanthan Gum). In contrast the glutens in wheat have more adhesive properties that change when prepared in different ways. The glutenins, for examplestretch, but can also fix their shape at high temperatures, causing bread to maintainits characteristic rise.

Important Triticeae Composites

When the flour is combined with water and yeast the dough can be risen and subsequently fixed by heat resulting in a hard outer shell with a soft palatable interior. This makes bread amicable for both transport and preserves the bread for several days (in dry conditions). Barley can be sprouted for a short period and roasted, the resulting malt can be ground for food or combined with bread yeast (currently a brewers variety) to produce beer and distilled spirits such as whiskey, vodka and sour-dough malts. Adding mild acid to rye flour activates it for bread making (Sourdough breads used in northern Europe).Adding egg to "T. durum" semolina flour can be used to make pastas, or without egg a pasta variant used to make Chinese dumplings. Wheat or semolina flour can be added other ingredients such as fish, meat or milk to create food pastes. Wheat can be further processed to a very fine flour and sifted, alternatively the glutens either can be extracted and readded to other products. While many seed glutens and food gums when combined with food starch, come close to creating the refined products of wheat flour and durum flour, no combination can come close to the qualities of these flours at a comparable price.

Malting

Some triticeae cultivars, like barley, have relatively low protein values. This makes them more acceptable for brewing without wasting soil nutrients. Seed storage proteins in grass seeds (i.e., gluten in wheat) are designed to help the plant grow during its early life, and among the seed proteins are enzymes that convert starch to sugar.s. Later the prolamins are broken down to provide the young seeds with a source of nitrogen and energy giving the "Triticeae" seedling a great boost during early life.

Once the starch is converted to sugar it can be readily fermented by "Saccharomyces cerevisiae". However, first the sprouting process should be stopped. In order to do this, the partially sprouted grains are placed in a roasting oven and roasted until the sprouts are sterilized and dried. This process of sprouting and drying is called malting. Then the roasted sprouts are ground, rehydrated and fermented. This produces a crude beer. Evidence for beer industry has been found in ancient Egypt, and some archaeologistsWho|date=February 2008 believe that neolithization of Northern Europe may have been preferential for barley as a result of its preferential capacity for fermentation.

Gluten Deamidation

The deamidation potential for wheats is discussed above. Glutens are generated by the wheat starch industry. Glutens however are more difficult to handle once starch and other proteins are removed, for example alcohol soluble glutens cannot be mixed with dairy since the alcohol denatures and precipitates dairy proteins. Therefore, gluten is often modified for commercial use by deamidation by treatment with acid at high temperatures, or enzymatic treatment with deamidase or transglutaminases. The increase charge increases the hydrophilicity of gliadins causing them to stretch out in solution. Deamidation of 20% of glutamine side chains to glutaminate suffices to generate a soluble product. This renders gluten soluble enough without alcohol to mix with other products like milk.

Gluten sensitivity reveals unexpected infiltration of Triticeae into Foods

Wheat and barley glutens have crept into a number of foods that are unexpectedbased on the names, such as soy sauces, vinegar, chips. Oats are contaminatedwith wheat, and in most brands greatly contaminated.

Examples of hidden wheat in foods Added wheat, barley or rye:
* Soy Sauce- may actually have more wheat than soy
* Modified food starch - made from wheat (from Triticum aestivum linneaus), may not be pure
* Drug manufacturing - modified food starch, in off the shelf products in coating materials. As a source of vitamins.
* Vinegar - may be made from barley.
* Beer, wine coolers - although beer is made from barley.
* Tea - barley tea and other herbals may have barley added.

Wheat gluten added:
* School pastes
* Binding agent in food pastes and pastas
** ketchup
** fish sausages
** buckwheat 'soba' noodles
* adhesion agent for
** flavored chips (corn, potato, etc)
** ice-cream
** unflavored foods made on same processing equipment as above

Inadvertent contamination:
* Oats - contaminanted by introgression from similar appearing wheat
** In fields - wild seeded Triticeae
** In storage equipment - such as Silos
** In transportation equipment - trucks, tractors, etc.
* Corn, millet, other cereals processed in facilities with wheat
** milling equipment
** handler error

"Triticeae" and human disease

Gluten-sensitive enteropathy/coeliac disease can be mediated by gluten from all known edible cultivars of Triticeae. Certain allergies appear only to be caused by wheat proteins and a subset of Aegilopodies subspecies, many other immunological reactions remain undetermined.Fact|date=February 2008

References