*2.3. Sodium Chloride Content on Bakery Products and Their Degree of Consumption*

The main source of salt in food in most European countries is generally foodstuffs such as bakery products, followed by meat and meat products, cheese and dairy products [23–25]. Bakery products have a major contribution to the daily intake of sodium in the diet, along with other products obtained from cereals such as biscuits, cakes, breakfast cereals, pastries, noodles, cereal bars, etc. The origin of sodium in these products is caused by the addition of sodium chloride to obtain them but also other raw materials and ingredients used. For example, a source of sodium is also ingredients such as baking powder or leavening agents [26]. It was found that the daily consumption of 150 g of bread containing 20 g of salt/kg of flour contributes with 25% of the average amount of salt consumed, which is 10 g/day/person. Bread is thus the main food contributor to the sodium chloride intake in the diet. Per capita, bread consumption varied between EU countries. The highest bread consumption was reported in Turkey (104 kg per year) and Bulgaria (95 kg) while the lowest one was reported in Great Britain (32 kg). It seems that the average consumption of bread by European people are 59 kg per year. Bread consumption is generally stable but in some countries such as Netherlands, Belgium, UK, Poland has been reported a slightly decrease. In 2015, in Poland, the bread consumption was of 145 g of bread daily. Thus, consumption of 145 g of wheat baguettes provides 4.4 g of salt per day, covering 87% of the maximum daily salt requirement given by the WHO. However, other types of bread consumption provide 1.6–2.2 g of salt, covering 32–44% of the demand [2]. According to the studies made on several European countries it was concluded that in Ireland bread accounts for 25.9% of total salt intake, in Turkey 25.5%, in Belgium 24.8%, in France 24.2%, in Spain 19.1% and in the UK 19% [12]. Compared to other European countries, in Romania, bread represents 30% of the total salt intake, which indicates a higher value compared to other European countries [27]. According to consumer taste tests, it was reported that the optimal salt content for white wheat flour bread was between 1.29% and 1.43%. In contrast, a similar study in Argentina reported a value of 1.74%, which was much higher than expected and could be due to some geographical preferences. There are major differences in the salt content of different types of bread. In France, for example, bread contains an average of 1.7% NaCl. This amount is found in bread, country style, French baguette whereas in croissant, puff pastry and sweet bakery products the amount of salt is lower of an average of 1.3 and 1% respectively [1]. In the UK bread has only 1.0% salt [12] whether it is white or brown whereas in the fruit buns, plain cake and fruited cake the amount of salt is lower between 0.32–0.72%. In Ireland, the amount of salt in bread is 1.10% in white bread and 1.09% in brown bread and in Germany the amount of salt in all types of bread and rolls is between 1.0–2.9% [1]. In Italy, the salt content of bread varies from 0.7 to 2.3% for artisanal bread and from 1.1 to 2.2% for bread produced to the industrial level [28] and in Spain all types of bread have an amount of 1.63% salt [1]. Thus, the bread contribution to salt consumption highly differs depending on the type and location. In Romania, the salt content of bread varies depending on its type from 0.17% for non-salt bread and 1.79% for potato bread. An important factor in the salt variation of bread is its type. Thus, for example, baguette bread has a lower salt content and potato bread a higher salt content. The most consumed bread in Romania is the one obtained from refined wheat flour, with a low selling price. This type of bread has an average salt content of 1.25% [27].

#### **3. The Technological Effect of Sodium Chloride in Bread Making**

Bread is one of the oldest foods consumed in the world and is obtained by baking a dough, prepared from wheat or rye flour, possibly mixed with other legumes or potatoes flours [29]. In bakery products, the salt is introduced into the dough phase in the form of saturated or concentrated solutions, but also in an undissolved state. This has a major impact on the dough rheological properties but also on the finished product quality [24].

The dough is a heterogeneous system which contains carbohydrates, proteins, lipids, mineral salts, water, and air in different proportions, with different degrees of homogenization, being from a rheological point of view a viscoelastic mass and from a technological point a view a homogeneous semi-finished product. It is obtained by mixing flour with water, salt, with or without baking yeast and other auxiliary materials [29]. The dough rheological properties present an important role in the bread making process, being closely correlated with the quality characteristics of the finished product [24,30].

The most important stages in the bread making process are dough making, its processing and dough baking to obtain the finished bakery product [31]. The NaCl effect in bread making process is shown in Figure 2.

**Figure 2.** The role of sodium chloride in bread making process.

As it may be seen, salt, due to its ionic nature has significant influences in the dough making such as dough development, water absorption capacity, mixing time, its intensity, etc. [32–35].

Many parameters such as temperature, mixing time and the ratio between the amount of water and flour are essential in order to obtain optimal dough rheological properties [36]. The addition of salt decreases the flour water absorption capacity and increases the dough development time and its stability. The increase in dough development time shows that salt delays the formation of gluten during mixing, therefore extending the mixing time [37]. Consequently, the more salt is added, the higher the dough development time and the lower the dough softening is. Studies have shown that the dough consistency is lower as the salt addition is higher if the amount of water added to the dough making remains constant. Many researchers concluded that the effect of salt in the dough system is primarily related to the change in the gluten proteins hydration which changes the ratio between free water and bound water, in the sense of increasing the amount of free water. The addition of 2% salt decreases the hydration capacity of gluten by 8% without changing the hydration capacity of starch [38]. This was attributed to the conformational changes from gluten proteins which occur in the presence of salt. The conformational changes may occur due to the salt ions interaction with the electrically charged groups from the protein molecules. As a result, the intermolecular and intramolecular electrostatic repulsion forces between protein molecules are reduced, these becoming more compact. It was suggested that salt, for a wheat dough pH value of 5.6–6, decreases the intermolecular repulsion to a higher extent than the intra-molecular one. The results of these conformational changes of the protein molecules may lead to a decrease of the proteins ability to bind water, as they become more compact and less penetrable to water molecules. Moreover, the fewer hydrophilic groups are more available to interact with water. Additionally, some hydrophobic groups may be greater exposed, leading to more hydrophobic intermolecular interactions between protein molecules which become more compact for water and more resistant to the action of enzymes.

The increase in the amount of free water can also be attributed to the increase in intermicellar osmotic pressure (external to the protein micelle) following the salt dissolution in the free water from the dough system. As a result, there is a difference between internal and external osmotic pressure and in order to balance the osmotic pressure some of the initial water bounded to the gluten proteins diffuses outside, making them more compact and more resistant [39].

Salt increases the dough extensibility and its strength. This increase depends on the type of cation it includes [38]. Reducing the salt content from the bread recipe mainly affects dough elasticity, without impacting viscosity. Sodium and chloride ions compete for water from the dough system affecting the hydration of the wheat flour proteins. They cannot hold water for a longer period of time, which causes an increase in the amount of free water, changing dough rheological properties [40]. During fermentation, the salt may have an inhibitory effect depending on the yeast strain and its concentration in the dough system. Thus, for concentrations below 1.5% in relation to wheat flour, the inhibitory effect is less, but it will increase with higher salt concentration, due to the rise of osmotic pressure from the dough system. Studies have shown that salt mostly inhibits the maltose fermentation and, in a lower extent, the glucose, fructose and sucrose fermentation.

Some studies reported that the surge of salt addition in dough system led to a significant reduction in the maximum height of the dough, which causes an increase in the total volume of the gas released. Through salt addition the gluten network becomes stronger. Therefore, the gas capacity to retain gases grows as the amount of salt used in the dough recipe increases [41].

On the finished bakery products, the addition of sodium chloride has an important role on their technological and sensory properties as it may be seen from Figure 3. From a technological point of view, it was concluded that the bread with 0.3% and 0.6% sodium chloride addition in wheat flour does not present significant differences compared to the bread recipe with 1.2% sodium chloride regarding its loaf volume, moisture and losses during baking. However, the lack of sodium chloride causes significant changes in the structure of the bread crumb and the shelf life after five days of storage. Regarding the flavor, crust formation and shelf life of low-sodium bread, important changes have been reported [35,42,43].

**Figure 3.** The role of sodium chloride on bakery products quality.

The reduction of sodium chloride content in bread influences the textural properties (due to the change in the dough rheological properties), its color and flavor (due to the more intense fermentation activity leading to a reduction in the amount of free reducing sugars resulted from the Maillard reaction) [24].

In bakery products, salt, in addition to its role on the flavor of the finished products, also acts as a preservative. The shelf life of the bread is closely related to its moisture content because it has been found that the migration of water from the crumb to the crust is related to the amount of salt present in the bread [35]. The shelf-life process of bread is due to the starch retrogradation [44], a process which means the tendency of its macromolecular components, amylose and amylopectin, to aggregate, to associate, resulting into a more insoluble form. Degradation is accompanied by the reappearance of crystalline areas into the starch structure partially destroyed during baking, which causes a more rigid crumb. Proteins also contribute to this structure, losing their elasticity and hydration. The water content and its condition play an important role in this process. Thus, products with a moisture content below 16% do not stale. The optimum humidity for staling is between 16–37%. In staling bread, bound water reaches 70% of the total water. The free water from the gel passes into crystalline structures, being strongly bound. It disappears from the bonding layer between the gluten and the partially gelatinized starch granules, causing stronger gluten-starch bonds, which reduces the elasticity of the structure [45]. Salt prevents water migration from crumb to crust and keeps the product fresh for a longer period of time compared to bread without salt addition [46]. The main responsible for foodstuffs' deterioration with high humidity content are microorganisms. Bread is known as a product with high humidity, with aw values between 0.96–0.98 [47]. In general, the addition of salt increases the gelatinization temperature of starch and delays its gelatinization process [39]. Through its action on starch and gluten, but also on the activity of water from the dough system, salt has a major contribution on starch staling [48]. For example, reducing NaCl from 1.2% to 0.3% decreases the shelf life of the bakery products with almost two days [24].

On the bread color, the reduction of the sodium chloride content in bread recipe or its lack thereof leads to products with a light-colored crust [31]. The brown color of the crust resulting from the bread baking process is due to the Maillard reaction, as an interaction between reducing sugars and amino acids. Therefore, a certain amount of free reducing sugars and amino acids is necessary for this reaction to take place. The lack of salt addition leads to a more intense fermentation which induces a high consumption of carbohydrates during the initial stages of the bread making process. Therefore, during baking the dough which presents less reduced sugars to form more melanoidins, will yield a bread sample with a light color. Many factors such as pH, protein/amino acid ratio, water, sugar amount from the dough system, temperature and baking time have a major influence on crust formation. The intake of sodium chloride produces a plasticizing effect during the baking process of bakery products, this favoring the Maillard reaction and therefore producing a darker crust [49]. Salt has the ability to control the yeast fermentation from the dough system and therefore, reducing the amount of salt will increase the activity of yeast. Fermentable carbohydrates are needed to the yeast fermentation process [50] and therefore, yeast fermentation will reduce the availability of free sugars involved in the Maillard reaction [24].

Sodium chloride is also responsible for the flavor of bakery products, which also intensifies the sweet taste of the finished product. Sodium salts such as sodium chloride or monosodium glutamate influences the food flavor in a positive way, improving it. However, Girgis et al. [51] concluded that consumers did not observe a gradual reduction of 5% sodium per week over six weeks (corresponding to a final reduction of 25% salt). A 20% reduction of sodium in bread did not affect the taste perception of 60 participants in this study. Instead, Lynch et al. [35] showed that a 50% reduction in salt changed the bread flavor. Salt-free bread has been described by them as sour and having the taste of yeast [12]. Research has shown that sodium, and to a lesser extent lithium, are the only salted cations with good effects on sensory food properties while calcium and potassium ions have a bitter or metallic taste, which is undesirable for consumers [52].

This effect of sodium chloride on sensory perceptions are due to the fact that free Na<sup>+</sup> ions in solution are the mainly responsible for the perception of salty taste on the tongue while the contribution of Cl− ion in terms of taste is not yet fully clarified. Due to the interaction between sodium chloride and wheat proteins during dough formation, sodium ions interconnect with dough components due to their ionic interactions with negatively charged amino acids [1]. Pflaum et al. [53] reported that Na<sup>+</sup> and Cl<sup>−</sup> ions are not irreversibly bounded in bread, sodium ions being released by chewing. The speed with which sodium is released in the first seconds when chewing takes place is quite important for the perception of salty taste by the consumers. The rate of release of the salty taste during chewing depends on the structure of the bread crumb and the amount of NaCl in the product. Bread with low amounts of NaCl has been described as having a more acidic or yeasty taste. Moreover, significant changes in crumb structure have been reported when different amounts of NaCl were added [12].

It has been shown that the use of sodium as compound in different ingredients significantly reduces the perception of the bitter taste [54]. It seems that the positive effects of sodium chloride on the aroma are due to its effect on the water activity. Reducing the amount of free water by adding salt changes the ratio between free water and the bounded water, which influences the volatility of flavor compounds [55]. Moreover, an essential contribution in the formation of flavor compounds is due to the Maillard reaction [56]. As mentioned above, melanoidins are also responsible for the golden-brown color of the bread crust during baking and therefore unsalted or low-salt bread will have a light crust, a weaker aroma, and a bland taste [24]. Obtaining bread with a low salt content (up to 0.3%) is technically easy to be done via a few changes in the bread making process, with a finished product maintaining the same qualities, except for taste. An interesting technique in this respect, although not one that can be applied to all production systems, involves the

inhomogeneous distribution of salt in the bread, which allows a 28% reduction of the salt content, while maintaining the intensity of the salty taste [12].

The textural properties of bread are very important in terms of their acceptance and choice by consumers. They can be evaluated both sensorially and instrumentally. Salt, as mentioned before, has a major impact on the gluten network development during the dough mixing process. The addition of sodium chloride leads to a strengthening effect on the gluten network, stabilizes the fermentation rate of the yeast, increases the dough mixing time, and improves the aroma and porosity of the bread crumb [57].

During the dough making and baking, the appearance of gas bubbles leads to the dough expansion and finally, the loaf volume and texture of the finished product. Gas bubbles have a limited expansion correlated with their stability and possible gases released from the dough system. Therefore, it is very important that the walls of the gas bubbles to be stable during baking but also during other technological stages. Moreover, the dough must present a good gas retention capacity for porosity, elasticity and a specific loaf volume in order to be accepted by consumers [1].

As the salt content of the dough decreases, the activity of the yeast increases leading to a finished product with a higher loaf volume. At low salt amounts levels of 0.7–0.8% the yeast cells multiplication increases, but above this concentration the yeast multiplication process is slowed down due to the plasmolysis process from the yeast cells. Moreover, the addition of salt in the dough reduces the activity of enzymes, both proteolytic and amylolytic, due to the action of salt on the protein part of enzymes [45]. However, less salt can induce a weakening effect on the protein network and to a lower gas retention capacity which will lead to bread with irregular porosity and low loaf volume [31].

From a textural point of view, a comparative study between a bread without salt and a bread with a salt content of 4% reported that there was a high difference between bread samples of about 40% in the firmness value of the bread crumb after a 24 h storage period. This shows that the firmness of the bread crumb decreases with the reduction of the amount of salt from bread and is closely related to the increase of the loaf volume of the finished product [58]. The increase in firmness with the presence of salt in bread can be explained by the conformational changes of the gluten proteins in the salt presence [45].
