The structure and properties of gluten
Gluten HMM subunits importance (update 20-01-2020)
Extract from the study: The structure and properties of gluten
“…..omissis. One group of gluten proteins, the HMM subunits of glutenin, is particularly important in conferring high levels of elasticity (i.e. dough strength). These proteins are present in HMM polymers that are stabilized by disulphide bonds and are considered to form the ‘elastic backbone’ of gluten. However, the glutamine-rich repetitive sequences that comprise the central parts of the HMM subunits also form extensive arrays of interchain hydrogen bonds that may contribute to the elastic properties via a ‘loop and train*’ mechanism. Genetic engineering can be used to manipulate the amount and composition of the HMM subunits, leading to either increased dough strength or to more drastic changes in gluten structure and properties.
….omissis. These properties are usually described as viscoelasticity, with the balance between the extensibility and elasticity determining the end use quality. For example, highly elastic (‘strong’) doughs are required for breadmaking but more extensible doughs are required for making cakes and biscuits. Omisdsis….The grain proteins determine the viscoelastic properties of dough, in particular, the storage proteins that form a network in the dough called gluten (Schofield 1994). Consequently, the gluten proteins have been widely stud ied over a period in excess of 250 year, in order to determine their structures and properties and to provide a basis for manipulating and improving end use quality.
*
…omissis. As a result of the formation of a protein matrix, individual cells of wheat flour contain networks of gluten proteins, which are brought together during dough mix ing. The precise changes that occur in the dough during mixing are still not completely understood, but an increase in dough stiffness occurs that is generally considered to result from ‘optimization’ of protein–protein interactions within the gluten network. In molecular terms, this ‘optimization’ may include some exchange of disulphide bonds as mixing in air, oxygen and nitrogen result in different effects on the sulphydryl and disulphide contents of dough (Tsen & Bushuk 1963; Mecham & Knapp 1966).
I pro e i contro del glutine debole (Oriana Porfiri)
“I frumenti “alternativi” idonei per la pastificazione sono il farro dicocco, il grano khorasan o Triticum turanicum e popolazioni locali di grano duro come le saragolle, i grani antichi siciliani e vecchie varietà come il Senatore Cappelli. Questi frumenti sono stati “scelti” dagli agricoltori nel corso dei secoli per la loro adattabilità ambientale e la resa produttiva. La selezione in funzione della qualità di trasformazione (qualità tecnologica) è storia recente, degli ultimi 40-50 anni, nei quali la selezione operata dai costitutori vegetali è andata in direzione di aumentare il contenuto proteico e la quantità di glutine, accrescere la tenacità del glutine, ridurre il contenuto di amido, elevare la resa molitoria. Pertanto, nell’ambito dei grani “alternativi” è frequente individuare varietà con una quantità di glutine estratto più bassa rispetto a quelle moderne e, soprattutto, di scarsa tenacità (struttura del glutine più debole), di facile scomposizione, quindi più digeribile.
La pasta fatta con queste varietà di frumento
La pasta fatta con queste varietà di frumento hanno il pregio di essere adatte a coloro che soffrono di gluten sensitivity (sensibilità al glutine non celiaca) o vogliono mangiare “leggero”, ma per essere di qualità e avere tenuta alla cottura ha bisogno di un processo di pastificazione particolare. Tutto deve essere più lento: l’impasto, l’estrusione e l’essicazione. Inoltre, è impossibile stabilire una ricetta di lavorazione standardizzabile e buona per tutti: ogni prodotto, ogni raccolto, ogni località di provenienza della materia prima richiedono un aggiustamento dei parametri. Questi grani hanno molta variabilità e il pastificio deve costantemente correggere il tiro a misura delle caratteristiche qualitativo/tecnologiche, della quantità di proteine e di glutine dei grani di quell’anno. Sulla qualità della pasta influisce anche un terzo parametro, la quantità di amido presente, in particolare la frazione “resistente”, che è quella non digeribile e che ha un comportamento simile alle fibre, quindi contribuisce ad abbassare l’indice glicemico della pasta.”
a cura di Oriana Porfiri
agronoma ed esperta di cereli
Fonte: Notizie Pasta. Grani siciliani, pasta integrale, glutine debole e micotossine: 4 dilemmi affrontati con gli esperti 23 Ago. 2019, 01:00 | a cura di Gambero Rosso
Surdough fermentation (IV part)
Rheology of the sourdough: Influence of LAB action
“Effects of LAB to dough structure
The structural effects of sourdough in wheat-based system may first be due to the direct influence of low pH on structure-forming dough components, such as gluten, starch, arabinoxylan etc. (Angioloni et. al., 2006). Dough is very sensitive to changes in ionic strength and pH and such changes could have direct impact on the constituents of dough (Clarke et al., 2002). The drop in pH value caused by the produced organic acids influences the viscoelastic behaviour of dough. A correct description of the changes in dough behaviour is necessary to maintain handling and machinability in industrialized production (Wehrle et. al., 1997). A number of earlier studies have examined influence of acids and different pH values on the dough properties. All of these confirmed that changes in the absolute pH value of sourdough significantly influence sourdough components.
The pH profile may affect the time frame during which the acid influences the constituent ingredients of the dough. The changing pH values during sourdough fermentation period may also afford passage through a range of pH values close to the optimum for various enzymes present in the dough system. It is so-called secondary (indirect) effect of sourdough acidification (Clarke et al., 2004). The activity of proteolytic and amylolytic enzyme present may be influenced to a greater degree by the pH profile of the biological acidification fermentation period in contrast to the rather instantaneous nature of the chemically acidified regime. Optimum activity of these enzymes, which play significant role in changes of dough constituents, achieve optimum activity at pH 4-5 for the proteolytic and pH 3.6 – 6.2 for the amylolytic enzymes (Belitz & Grosh, 1992). Other enzymes that might affect the structural components of the dough the activity of which is pH dependent include peroxidases, catalases, lipoxigenases and polyphenol oxydases (Belitz & Grosh, 1992; Clarke et. al., 2002). Results obtained by the the fundamental rheological tests, baking tests, and farinograms show that activity of some enzymes in the biologically acidified dough led to structural changes in the dough (Corsetti et. al., 2000; Clarke et. al., 2002; Clarke et. al., 2004). Corsetti et. al. (2000) also reported that even limited photolytic degradation of wheat proteins affects the physical properties of gluten, which in turn can have a major effect on bread firmness and staling.
Surdough fermentation (III part)
Carbohydrate metabolism
“The ratio between lactic and acetic acid is an important factor that might affect the aroma profile and structure of final product. Acetic acid, produced by heterofermentative LAB, is responsible for a shorter and harder gluten, while lactic acid can gradually account for a more elastic gluten structure (Lorenz, 1983; Corsetti & Settani, 2007).
Influence of Acidification on Dough Rheological Properties Daliborka Koceva Komlenić, Vedran Slačanac and Marko Jukić Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, Croatia 2012- www.intchopen. )”
Metabolism of proteins
“According to the results of studies performed by Gerez et. al. (2006) 13 nine lactobacilli and four pediococci were able to use gluten as a nitrogen source. Gerez et. al. (2006) also reported an increase in essential amino acids (treonine, valine, lysine and phenylalanine) in a gluten based medium fermented by LAB strains.
Subsantial hydrolysis of gliadinin and glutenin proteins occurs during sourdough fermentation. Proteolityc activity in sourdough originates not only from LAB enzymes, than derives also from the cereal materials present in sourdough (Thiele, 2002; Thiele, 2004). Except activity of own enzymes, LAB contribute to overall proteolysis during sourdough fermentation by creating optimum (acidic) conditions for activity of cereal proteinases (Vermeulen et al. 2006). The partial hydrolysis of glutenins during sourdough fermentation results in depolymerisation and solubilisation of the gluten macro peptide (GMP). After 24 hours of fermentation with defined lactobacill strains, all gluten proteins were SDS-soluble (Thiele et. al., 2003). Glutathione (GSH) is the most relevant reducing agent in wheat doughs (Grosh & Wieser, 1999). Heterofermentative lactobacilli express glutathione reductase during growth in dough and reduce extracellular oxidized glutathione (GSSG) (Jänsch et. al., 2007). The continuous transformation of GSSG to GSH by LAB metabolism maintains high SH levels in wheat doughs, and increase the amount of SH-groups in gluten proteins (Vermeulen et. al., 2006)
The level of individual amino acids in wheat dough depends on the pH level of dough, fermentation time and the consumption of amino acids by the fermentative microflora (Thiele et. al., 2002). In wheat sourdoughs, Lb. brevis linderi, Lb safransciensis, Lb. brevis and Lb. plantarum have been reported to increase the levels of aliphatic, dicarboxylic and hydroxyl amino acids (Gobbetti et. al., 1994a, Gobbetti et. al., 1994b). The yeasts, S. cerevisiae and S. exiguous decrease the total level of amino acids. Influence of Acidification on Dough Rheological Properties Daliborka Koceva Komlenić, Vedran Slačanac and Marko Jukić Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, Croatia 2012- www.intchopen.)”