Wheat Flour: The Structure Builder of Baked Goods

Why is wheat flour so important in baked goods? and Why is it so hard to replace it in gluten – free and keto products?

Bakery products are one of the most important sources of energy for human beings. It is estimated that 20% of the daily calories are consumed in the form of these products. However, their consumption can have health effects on consumers such as obesity, when consumed in excess, and the well-known celiac disease; associated with the structural proteins of gluten (glutenin and gliadin). The possible adverse health effects associated with the consumption of high-calorie flours, and gluten proteins, have led to the resurgence of ancestral cereals and the development of alternative flours from legumes and nuts to replace wheat flour. 

Wheat Flour

Wheat flour is an essential ingredient for the production of bakery products such as bread, cakes, cookies, muffins, among others. It performs a series of functions in these products, but mainly functions as a structural component of these confections, especially in breads. The structure of breads is mainly due to the proteins glutenin and gliadin, which upon contact with water form an elastic gluten network that allows for the retention of gasses produced by fermentation or chemical agents such as baking soda and baking powder. The type of flour, protein content, type of wheat, and the presence or absence of conditioning agents give wheat flour its particular characteristics. In addition to gluten proteins, other compounds responsible for the structure of bakery products present in wheat flour are starch and pentose gums, whose contribution increases or decreases according to the type of product to be manufactured.^2,3,4 

Function of Wheat Flour 

Wheat flour as mentioned before performs a series of functions in the production of bakery products, and its particular composition has been the main driver of the development of bakery throughout history.

Among the most important functions of wheat flour are:

Provide structure

Wheat flour is the main responsible for the structure of a variety of bakery products, particularly bread. This is due to its content of gluten, starch, and pentose gums. The structure provided by the gluten network allows the dough to expand by the gasses (carbon dioxide), giving bread its characteristic texture.^6,7

Gluten, along with starch, is the main responsible for the structure of yeast-leavened products. On the other hand, in products with low water content, gluten is the major contributor to structure since starch gelatinization does not occur. The greatest influence of gluten is observed in the structure development during the stages before baking. Meanwhile, starch is responsible for the structure of the products during the final stages after baking. ^6,7,8

Absorb liquids

The ability of wheat flour to absorb liquids is mainly due to its protein and carbohydrate content in the form of starch and gums. This property helps stabilize the products and bind the ingredients into a homogeneous dough. ^3,6,7,8

The degree of water absorption is a very important property in bread production. High water absorption is essential to maintain the freshness of bread and influences the amount of flour required to form the same amount of dough. High water absorption values in a flour represent lower costs for producers since less flour is required to achieve similar results. ^7,8,9

The most important factor in water absorption in flours is protein content, which ranges from 11-13%. It has been estimated that half of the absorbed water is due to starch, one-third to protein content, and approximately one-quarter to the gums present in wheat flours. ^3,6,7,8

Flavor and Color

White wheat flour has a mild flavor with a slight nutty sensation. Other types of flour, such as whole wheat flour, have a stronger and more complex flavor that is desired by some consumers. ^3,6,7,8

In addition to flavor, wheat flour has a unique contribution to color. It contributes to the color due to its content of potentially reducing proteins and sugars, which participate in the Maillard browning reaction. On the other hand, whole wheat flours contribute to the color of bakery products due to their characteristic color associated with the bran content. ^3,6,7,8

Flours with higher protein content contribute more to the darkening of bakery products. Therefore, bread flour will produce a darker crust than pastry or cake flour. ^3,6,7,8

Nutritional Value

Wheat flours contribute complex carbohydrates, vitamins, minerals, dietary fiber, and proteins. Whole wheat flour has a higher content of fiber, vitamins, and minerals that processed wheat flour. ^3,6,7,8

SENSORY ATTRIBUTES OF BREAD

Sensory attributes are the properties or characteristics that allow a product to be described according to human sensory perceptions. These attributes can be descriptive or acceptance-based depending on the type of sensory panelists employed. Descriptive attributes are generally established by a trained panel of sensory judges.¹⁰

The sensory attributes of bread can be classified into four main groups: (1) appearance, (2) odor, (3) texture, and (4) flavor.¹¹

Appearance attributes refer to the visual properties of food products perceived by the sense of sight, such as the color of the crust, color of the crumb, texture, loaf volume, among others.^13,14

The color of the crust is associated with the presence of proteins and reducing sugars that may participate in Maillard browning reactions.^13,14,15

The color of the crumb is mainly associated with the type of flour used, with whole wheat flour providing a distinctive brown color while all-purpose or bleached wheat flour produces a white crumb.^13,14,15

Texture is associated with the type of flour, water content, kneading method, and proofing time. The type of flour contributes to the protein content that ensures the production of the gluten network. Kneading is responsible for introducing air bubbles that will be expanded during fermentation and baking processes. Proofing time will influence the size of the bubbles and the expansion of the gluten network that will occur due to this time.^13,14,15

During sensory evaluations of bread, lists of descriptive terms for these foods are developed. The lists are broad and varied.

Table 1 summarizes the most representative terms for the sensory description of bread.

Table 1: Appearance attributes of bread

Attribute	Definition	Reference
Crust Color	Degree of browning of the crumb,from white to dark brown	16
Crumb Color	Degree of browning of the crumb,from white to dark brown	16
Crumb Cells	Number of cell per cm2	17
Homogeneity of the Crumb	Homogeneity of the crumb	19,20
Crumb Thickness	Thickness of the transversal cut of the crumb	18

Odor Attributes

The odor of bread is mainly determined by the aromatic substances produced during the different stages of its manufacture, which are perceived through the nasal and retronasal pathways. Odor and aroma are two concepts commonly used without differentiation, however, they define two different pathways of perception for these volatile substances. Odor is perceived through the nasal pathway, while aroma is due to the volatile compounds that are perceived through the retronasal pathway during food ingestion.

The odor and aroma attributes are widely influenced by the bread formulation, fermentation method and time, and baking conditions. Approximately 540 volatile compounds have been described in the composition of aromatics generated during bread manufacturing, of which only a small fraction are responsible for the characteristic odor and aroma of bread. These include: 2-acetyl-1-pyrroline, (E)-2-nonenal, 3-methylbutanal, diacetyl, methional, and (Z)-2-nonenal for the bread crust; and for the bread crumb, the following compounds are present: (E)-2-nonenal, (E,Z)-2,6-nonadienal, (E,E)-2,4-decadienal, 2,3-butanedione, methional, 1-octen-3-ol, and (E,E)-2,4-nonadienal.^21,22,23

Table 2 summarizes the most representative terms for the sensory description of bread for odor attributes.

Table 2: Odour and Aroma of Bread

Attribute	Definition	Reference
Wheat aroma	Typical of wheat flours mixed with water in 1:2 proportion	24,25,26,27
Malt	Sweet aroma typical of condensed milk	15,25
Ferment	Typical aroma of fermented dough	19
Toasted	Associated with Maillard reaction byproducts	15

Texture Attributes

Texture attributes of bread represent a vital aspect in its organoleptic acceptability. These are associated with the sensations of the crust and crumb perceived by the tactile sensors in the mouth (tongue, palate, etc.) during consumption. There are a wide variety of terms used to describe the textural properties, among which are the hardness or softness of the bread. These are the most simple sensory characteristics to describe by consumers, and are inherently related to the gluten content of the bread, as well as the method of preparation, kneading, resting, and baking conditions. The most relevant factor in the decrease of the shelf life of this product due to its organoleptic acceptability is called “staling”, which refers to the decrease during time of certain properties that generate the sensory acceptability of bread. This phenomenon mainly occurs due to the retrogradation of the bread, which loses its characteristic softness through a loss of moisture and, consequently, softness. ^30,31,32,33

Techniques for the instrumental measurement of these organoleptic properties have been developed, which simulate the actions performed during the chewing process, such as the Texture Profile Analysis (TPA) technique.^29,34

Table 3 summarizes the most representative attributes for the sensory description of bread textural attributes.

Table 3: Textural attributes of bread

Atributo	Definición	Referencia
Firmness	Resistance of the crumb when compressed	35
Elasticity	Ability to return to its original state after compression	19
Moistness of the Crumb	Quantity of saliva required for consumption	29,36
Adhesivity	Adhesivity to the paladar	19
Cohesivity	Resistance of the material when deformed up until it rupture	35
Crust Crunchiness	Crunch sensation of the crust	20,26

Flavor Attributes

The flavor of bread is the combination of a series of sensations perceived during the chewing process, composed of taste elements, aroma, and trigeminal sensations related to the trigeminal nerve.³⁷

Different factors affect the flavor of bread due to the aromatic compounds and lactic and acetic acids produced during the fermentation process, in addition to the initial composition of the wheat flour.^36,38

The proportion of lactic/acetic acid is responsible for the perceived sour taste in bread, and it is influenced by temperature, dough consistency, and the quantity and duration of the manufacturing steps, including the most influential, fermentation.^36,38

During fermentation, a series of volatile and non-volatile compounds responsible for the perceived flavor and aroma in bread are produced, and the concentration and generation of these compounds are largely due to the bacterial flora present in the dough.³⁹

Some of the factors to consider during bread production include:

• Degree of wheat flour extraction: the concentration of lactic acid increases when using wheat flours with a high degree of extraction between 65-100%.⁴⁰
• Maillard browning reactions: during this reaction, a series of aromatic compounds are generated that contribute to the flavor of the crust.⁴¹

Table 4 shows some of the most important flavor attributes in bread production.

Table 4: Flavor Attributes of Bread

Attribute	Definition	Reference
Wheat Aroma	Typical of wheat flours mixed with water in 1:2 proportion	24,25,26,27
Malt	Sweet aroma characteristic of condensed milk	15,25
Ferment	Aroma of fermented products	19
Toasted	Toasted flavor, characterized by Maillard byproducts	15
Wheat	Characteristic flavor of wheat germ	25
Toasted Flavor	Degree of toast of the crust	36
Sweetness	Sweet flavor characteristic of sucrose	42
Yeast	Flavor of fermented products	43
Acidity	Degree of acidity sensation	38
Nuts	Typical of roasted almonds	24,44

SUMMARY

In conclusion, wheat flour is the main structure builder in most baked products due to their gluten content. Gluten replacement in keto and gluten – free products is a special kind of challenge for bakers around the world. Several alternatives to wheat flour have been developed to susbstitute this ingredient in baked goods with different degrees of succes, the combination of several alternatives flour in combination with other ingredients such as emulsifiers and hydrocolloids may be required to accomplish all of the functional properties of wheat flour.

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