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The Meaning of Flour Strength “W” Value

by luciano

(Insight 3 of Genetic Potential and Process Conditions in Determining Gluten Strength, Digestibility, and Immunogenicity)

The W value does not directly reflect the number or strength of the intrinsic bonds of wheat proteins, but rather represents a functional measure of the resistance of the protein network formed during dough mixing.
This network is the result of the interaction between genetic polymerization potential and the ability of proteins to reorganize and establish new intermolecular bonds under processing conditions.

Does the W value measure the “strength of wheat proteins”?
No.

The W value (Chopin alveograph) measures the energy required to deform and rupture a dough bubble, therefore describing the mechanical resistance of the protein network formed after hydration and mixing. It does not directly measure either the structure of individual proteins or the strength of their internal bonds.

Does the W value represent the strength of bonds present in gliadins and glutenins in the grain?
No.

In the grain, gliadins mainly contain intramolecular disulfide bonds, while glutenins are partially polymerized through intermolecular disulfide bonds. However, these bonds mainly stabilize individual molecules or small aggregates and do not correspond to the network responsible for dough strength.

Functional gluten is built mainly during mixing.

So what does the W value really reflect?
The W value reflects the overall resistance of the protein network formed during mixing, namely:

1 – how much network has been built
2 – how continuous the network is
3 – how capable it is of opposing deformation
In other words, W is a functional measure of the network, not a chemical measure of bonds.

How does wheat genetics influence W?
Genetic makeup influences:

1 – type and quantity of glutenin subunits
2 – number and position of cysteine residues
3 – glutenin/gliadin ratio
These factors determine polymerization potential, i.e., the theoretical ability of proteins to participate in forming intermolecular bonds during mixing. Thus, genotype establishes how large and complex the network can become, not how large it already is in the grain.

Does W depend only on genetic potential?
No.

W depends both on genetic potential and on the ability of proteins to reorganize and create new bonds during mixing.

This ability is influenced by:

1 – mobility of protein chains
2 – accessibility of reactive groups
3 – rate of thiol–disulfide exchange
4 – hydration, mechanical energy, temperature, and redox conditions
Two wheats with similar genetic potential may therefore develop networks of different strength.

Can a wheat with lower genetic potential develop a higher W?
Yes, within limits.

A wheat with fewer theoretical cross-linking sites but more mobile and reactive proteins may exploit its potential better and form a more efficient network than a wheat with higher theoretical potential but poor utilization of that potential.

Is there a maximum limit to this compensation?
Yes.

A wheat poor in polymerizable glutenins will never reach the W values typical of strong wheats, even under ideal processing conditions. Genetic potential therefore imposes an upper ceiling, while the process determines how close one comes to that ceiling.

Can W be said to measure the “number of bonds”?
No.

W does not measure the number of bonds, but the collective mechanical effect of the network that those bonds help stabilize.

✅ Conclusion
The W value does not reflect either the strength of internal bonds in gliadins and glutenins or the number of bonds present in the grain. It represents a functional measure of the resistance of the protein network that forms during mixing.

This network results from the interaction between:

1 – genetic polymerization potential (what can be built)
2 – capacity for reorganization and new bond formation under processing conditions (what is actually built)
In summary:

✔ What matters most is the network that forms in gluten
✔ But this network is limited by what exists at the origin

In-Depth
What Determines the Genetic Starting Potential of Wheat
The genetic starting potential of a wheat, understood as the intrinsic capacity of its proteins to form an extended and structurally effective gluten network, is mainly determined by the composition and molecular organization of storage proteins. Four factors play a central role.

1 – Type of HMW-GS and LMW-GS Subunits
High-molecular-weight glutenin subunits (HMW-GS) form the main backbone of glutenin polymers. Different allelic variants encode subunits with different length, conformation, and number of cysteine residues.

Some subunits promote longer and more branched chains, while others lead to shorter polymers. Consequently, the type of HMW-GS present directly influences the ability to build a continuous elastic framework.

Low-molecular-weight glutenin subunits (LMW-GS) play a complementary role, acting as connectors and branching points between main chains. The HMW-GS/LMW-GS combination therefore defines the basic polymer architecture.

Impact on potential: determines the load-bearing structure of the network.

2 – Number and Position of Cysteines
Cysteine residues are the chemical sites through which disulfide bonds form.

Not only how many cysteines are present matters, but also where they are located in the protein sequence. Cysteines in exposed regions favor intermolecular bonding, while cysteines in sterically shielded regions tend to form intramolecular bonds.

Impact on potential: defines how many connection points are theoretically available to build the network.

3 – Glutenin/Gliadin Ratio
Glutenins mainly provide elasticity and strength, whereas gliadins mainly contribute viscosity and extensibility. A ratio shifted toward glutenins favors stronger networks; a relative excess of gliadins tends to dilute network continuity.

Impact on potential: determines how much “scaffolding” versus “fluid phase” is available.

4 – Polymer Size Distribution
Even in flour, glutenin polymers exist in a size distribution. Some wheats show a higher proportion of very large polymers (often called glutenin macropolymer, GMP). An initial distribution oriented toward larger polymers favors formation of a continuous network during mixing.

Impact on potential: indicates the level of pre-organization toward extended structures.

Summary
Genetic starting potential does not correspond to the number of bonds already present in the grain, but to the intrinsic capacity of proteins to participate in building an extended network during mixing.

It is mainly determined by:

✔ Type of HMW-GS and LMW-GS subunits
✔ Number and position of cysteines
✔ Glutenin/gliadin ratio
✔ Polymer size distribution

These factors define what is chemically and structurally possible. Processing conditions determine how much of this potential will actually be expressed in the final gluten network.

4

4

Why intermolecular bonds “make” gluten strong

by luciano

(In-depth note 1 of Genetic potential and processing conditions in determining gluten strength, digestibility, and immunogenicity)

Gluten is a protein network that emerges when gliadins and glutenins are hydrated and subjected to mechanical energy (mixing/kneading) or thermal energy (heating). Its “strength” (tenacity/elasticity and ability to withstand stress) depends on two families of interactions:

1 – Covalent disulfide bonds (S–S).
These are the most “structural” cross-links. In glutenins (especially HMW-GS and LMW-GS), intermolecular disulfide bonds build polymers (often referred to as GMP / glutenin macropolymer) that provide the elastic backbone of the network.
2 – Non-covalent interactions (hydrophobic, hydrogen bonds, ionic interactions).
They are weaker but extremely numerous and “modulate” the network: they contribute to cohesion, viscosity, reorganization, and the response to hydration/temperature/solvents. Many studies show that changes in secondary structure and non-covalent interactions accompany (and sometimes amplify) the effects of disulfide bonds.
A key point:

the network is not static. During processing, thiol–disulfide exchange reactions (–SH/–S–S–) occur that remodel network connectivity: more opportunities to form/reorganize S–S bonds → generally a “stronger” and/or more resilient network.

Practical implications for dough

From an operational standpoint, gluten strength does not depend only on the genetic potential of the flour, but also on how the system is “set up” to express and organize its intermolecular bonds.

Adequate hydration:
Water acts as a plasticizer and allows proteins to move, interact, and realign. Hydration levels that are too low limit network formation; higher hydration promotes molecular mobility and bond reorganization, making gluten more extensible.

Mixing energy:
Mechanical action facilitates contact between protein chains and accelerates thiol–disulfide exchange reactions. Insufficient mixing leads to an incomplete network; excessive energy, on the other hand, can cause bond breakage and excessive reorganization, with a loss of structure.

Resting time:
Rest phases (autolyse, bulk fermentation) allow non-covalent interactions and disulfide bonds to redistribute toward more stable configurations, improving the balance between elasticity and extensibility.

Chemical conditions:
pH, salts, and the presence of oxidizing or reducing agents directly influence the equilibrium between –SH groups and –S–S– bridges, thereby modulating cross-link density within the network.

Genetic Potential and Processing Conditions in Determining Gluten Strength, Digestibility, and Immunogenicity

by luciano

Introduction
Gluten is the protein complex that forms when wheat storage proteins—mainly gliadins and glutenins—are hydrated and subjected to mechanical work. During this process, they organize into a continuous three-dimensional network responsible for the viscoelastic properties of dough.
Gluten strength is not an intrinsic and immutable property of individual wheat proteins, but rather an emergent characteristic of the supramolecular organization that develops when storage proteins are hydrated and exposed to mechanical energy during mixing (Shewry & Tatham, 1997; Wieser, 2023). Gluten quality therefore results from the interaction between the initial molecular composition and process-induced structural transformations.
In the grain, gliadins consist mainly of monomeric proteins stabilized by intramolecular disulfide bonds, whereas glutenins are also present as polymers stabilized by intermolecular disulfide bonds, which constitute the structural basis of gluten elasticity (Shewry & Tatham, 1997; Wieser, 2023). Disulfide bridges therefore represent the main covalent cross-links responsible for the formation of a continuous protein network.
It is essential to distinguish between the strength of an individual bond and the ability to form an extended network of bonds. From a chemical perspective, the bond energy of a disulfide bridge is essentially constant; differences among varieties do not arise from “stronger” bonds, but from variations in the number, position, and accessibility of cysteine residues, as well as from the composition of high- and low-molecular-weight glutenin subunits (Wieser, 2023). These features define the genetic cross-linking potential, namely the intrinsic predisposition of proteins to participate in the formation of intermolecular bonds.
The existence and structural importance of disulfide bonds in gluten have been confirmed through direct identification of S–S connections by mass spectrometry, which enabled mapping of specific intra- and intermolecular bonds in gluten proteins (Lutz et al., 2012). This evidence supports the concept that the gluten network is stabilized by a dense web of covalent connections.
During mixing, genetic potential is converted into real structure through dynamic processes of disulfide bond breakage and reformation, mainly via thiol–disulfide exchange reactions (Lagrain et al., 2010). Consequently, the gluten network does not simply correspond to the polymers already present in the grain, but rather represents a reorganized structure that develops as a function of hydration, mechanical energy, temperature, and redox conditions.
Protein composition also influences the architecture of the polymers that form. It has been shown that certain gliadins containing an odd number of cysteine residues can be incorporated into polymeric fractions and act as elements that limit or modulate chain extension (Vensel et al., 2014). This highlights that network quality depends not only on the amount of polymeric proteins, but also on their molecular nature.
In parallel, classic studies have shown that glutenin polymers undergo depolymerization and repolymerization during dough processing, and that the content of glutenin macropolymer (GMP) is closely correlated with dough and gluten strength (Weegels et al., 1996). This dynamic behavior underscores the decisive role of processing conditions in modulating the expression of genetic potential.

Structural Implications for Digestibility
Gluten strength and protein network structure influence not only dough rheology, but also the accessibility of proteins and starch to digestive enzymes. Recent studies show that glutens characterized by a more compact and extensive network are associated with a lower rate of starch digestion and different kinetics of protein degradation, suggesting that the gluten matrix functions as a physical barrier to enzymatic action (Zou et al., 2022).
At the molecular level, gluten proteins are rich in proline and glutamine, a composition that confers intrinsic resistance to major gastrointestinal proteases. As a result, gluten digestion frequently leads to the formation of relatively long and poorly degradable peptides (Di Stasio et al., 2025).
Among these, fragments derived from α-gliadins—such as the well-known 33-mer peptide—exhibit high resistance to proteolysis and contain epitopes recognized by the immune system in individuals with celiac disease (Hernández-Figueroa et al., 2025). The likelihood of formation and persistence of such peptides is influenced by both wheat genotype and gluten structural organization.

Role of Processing in Modulating Peptides
Processing conditions, particularly fermentation, can significantly modify gluten structure and the peptide profile generated during digestion. Sourdough fermentation, through the combined activity of endogenous flour enzymes and microbial proteases, can partially hydrolyze gluten proteins and alter the distribution of released immunogenic peptides (Ogilvie et al., 2021).
Peptidomic analyses of breads subjected to in vitro digestion reveal considerable peptide diversity, correlated with wheat genotype, agronomic conditions, and processing technologies (Lavoignat et al., 2024). This confirms that the final peptide profile is not determined solely by protein sequence, but also by network architecture and its processing history.
The use of standardized semi-dynamic digestion protocols (such as INFOGEST) allows realistic simulation of oral, gastric, and intestinal phases, enabling quantification of resistant and potentially toxic peptide formation (Freitas et al., 2022). Advanced liquid chromatography–mass spectrometry techniques allow absolute quantification of these fragments and comparative evaluation of varieties and processes.
In parallel, the use of supplemental enzymes or selected microorganisms has been explored as a strategy to enhance degradation of particularly resistant gluten peptides, demonstrating that targeted interventions can significantly reduce the concentration of problematic fragments (Dunaevsky et al., 2021).

Integrated Perspective
Taken together, these findings lead to an integrated view:
The initial molecular composition defines the upper limit of possible gluten connectivity.
Mixing and fermentation determine how much of this potential is actually expressed.
The resulting network structure influences not only technological strength, but also digestibility and the profile of released peptides.

In summary:
✔ What matters most is the network that forms in gluten
✔ But this network is constrained by what exists at the origin
✔ And the resulting network also determines the digestive fate of proteins

Gluten HMM subunits importance (update 20-01-2020)

by luciano

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).