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Influence of Bran Particle Size in Einkorn Flours: Effects on the Gluten Matrix and Dough Properties

by luciano

Highlights:

1️⃣ Einkorn (Triticum monococcum) possesses a predominantly visco-colloidal dough matrix, due to the greater prevalence of gliadins compared to polymeric glutenins, which results in doughs that are less elastic and more viscous than those of modern wheat.

2️⃣ Bran particle size represents a crucial technological parameter in wholegrain flours, influencing water absorption, dough cohesion and fermentation stability.

3️⃣ In einkorn, an intermediate bran particle size may have a structuring effect on the dough, acting as a colloidal filler within the matrix and contributing to the stabilization of gas bubbles during fermentation.

4️⃣ Genetic variability among einkorn genotypes significantly influences technological quality, with relevant differences in dough behavior, bread volume and final aromatic profile.

5️⃣ Some einkorn lines show relatively lower gluten immunogenicity compared to hexaploid wheats, although they are not suitable for the diet of celiac patients. However, they may be useful for certain individuals (see end of chapter 11).

1. Introduction

Einkorn wheat (Triticum monococcum) represents one of the oldest wheat species cultivated by humans and possesses technological characteristics that differ significantly from those of modern wheats. In particular, the rheological properties of einkorn flours differ substantially from those of modern bread wheat, especially with regard to the structure and behavior of the gluten matrix.

The protein composition of einkorn is characterized by a relative predominance of gliadins (including γ-gliadins) and by a lower quantity and quality of polymeric glutenins. Gliadins mainly contribute to the viscous properties of the dough, while polymeric glutenins are responsible for elastic properties and for the formation of a stable three-dimensional gluten network.

This specific protein composition results in a rheological system in einkorn that behaves predominantly as a pasty-viscous system rather than an elastic one (Figure 1). Consequently, doughs obtained from einkorn flours are generally less elastic, more viscous and have a limited capacity to retain gas during fermentation.

Scientific references

Wieser, H. (2007). Chemistry of gluten proteins. Food Microbiology. DOI: 10.1016/j.fm.2006.07.004

Abdel-Aal, E.-S. M. et al. (1998). Genetic and environmental effects on gluten proteins of einkorn wheat. Journal of Cereal Science. DOI: 10.1006/jcrs.1997.0143

2. Role of Bran in Dough: General Concepts

Bran represents a fundamental component of wholegrain flours and can significantly influence the rheological properties of dough and the quality of the final product. The effect of bran on dough is generally attributed to two main mechanisms: interaction with water and mechanical interference with the dough structure.

2.1 Water absorption effect

Bran particles possess a remarkable capacity to absorb water due to their high content of dietary fiber, particularly arabinoxylans and cellulose. As the specific surface area of bran particles increases, their capacity to bind water also increases.

✅ This phenomenon results in a reduction of water available for other dough components, particularly starch and gluten proteins. Consequently, the distribution of water in the dough can significantly modify the formation and stability of the protein matrix.

2.2 Mechanical effect of bran particles

In addition to the water-related effect, bran can exert a mechanical effect on the dough structure. Bran particles of large size may act as discontinuous elements within the dough matrix, interfering with the continuity of the gluten network.

In modern wheats, characterized by a relatively strong and elastic gluten network, coarse bran particles can physically interrupt the protein network, resulting in a reduced ability of the dough to retain gas and, consequently, a decrease in final bread volume.

References

Noort, M. W. J. et al. (2010). The effect of particle size of wheat bran on bread quality. Journal of Cereal Science. DOI: 10.1016/j.jcs.2010.03.003

Hemdane, S. et al. (2016). Wheat bran in bread making: A critical review. Food Chemistry. DOI: 10.1016/j.foodchem.2015.09.092

3. Effect of Bran Particle Size on Dough Properties

The size of bran particles represents a particularly important technological parameter, as it influences both water absorption capacity and mechanical interaction with the dough structure.

3.1 Fine bran

Fine bran presents a high specific surface area. This results in a greater capacity to absorb water compared to larger particles.

In the presence of fine bran, the following are generally observed:

1️⃣ lower water availability for proteins and starch
2️⃣ higher water absorption by bran
3️⃣ more homogeneous distribution of particles in the dough.

From a technological point of view, these effects may lead to the formation of more viscous and compact doughs, with a more limited but generally more uniform development of dough structure.

3.2 Coarse bran

Bran with larger particle size presents a lower specific surface area and therefore tends to absorb less water during the initial phases of mixing.

However, larger particles may exert a stronger mechanical effect on the dough structure. In modern wheats this phenomenon may cause discontinuities in the gluten network, resulting in reduced dough stability and lower final bread volume.

4. Technological Specificity of Einkorn

In the case of einkorn, the effect of bran must be interpreted in light of the specific characteristics of its protein matrix.

As previously described, the gluten network of einkorn is generally weaker than that of modern wheats and does not form an equally developed continuous elastic structure. Dough behavior is dominated more by viscosity and colloidal cohesion phenomena rather than by a well-organized elastic gluten network.

✅ In this technological context, bran does not necessarily act as an element that breaks a strong gluten network, as occurs in modern bread wheat. However, it may still interfere with dough cohesion or contribute to the stabilization of the overall structure of the system.

References

Hidalgo, A. & Brandolini, A. (2014). Nutritional properties of einkorn wheat. Journal of the Science of Food and Agriculture. DOI: 10.1002/jsfa.6382

Brandolini, A. et al. (2008). Technological quality of einkorn wheat. Journal of Cereal Science. DOI: 10.1016/j.jcs.2008.01.001

5. Recent Evidence on the Technological Properties of Einkorn

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