Salt and salt reduction in bakery products

1.8. Salt and salt reduction

Salt's main function is to bring out the flavour of the baked product. Salt tends to bring out the good flavours and mask the off-flavours. Usage levels used to be around 2 %. Legislation may vary from country to country because the intake of too much salt is considered as a health risk. In the European Union there is a directive to reduce salt levels in bread to 1,5 % (on flour weight). In Scandinavia one has to pay extra taxes if the salt level in the bread is higher then 1,2 %. Bread made with less then 1,2 % salt will taste insipid and bread made with more then 2,2 % will taste too salty.

Salt helps control yeast activity and strengthens the protein matrix which forms the crumb structure of the bakery food. It is, therefore, of utmost importance that the salt is completely dissolved in doughs.

In addition to impacting flavour, salt also inhibits fermentation due to the osmotic pressure effect. Yeast cells will partially dehydrate due to the osmotic pressure. This can be illustrated easily by putting some salt on fresh yeast. After a while the yeast will liquefy due to the fact that the salt will attract the water from the yeast cell. As the cell membrane is semi permeable, water will migrate from the cell and the mixture will seem to liquefy. In reality the yeast cell undergoes a change which can be compared with the change that happens to a grape when it becomes a raisin, it just dries out.

The fact that salt influences the fermentation can be used to control the fermentation : salt can be added for instance to sponges to slow down the fermentation rate. Slowing down fermentation rate means that less sugars are metabolised into acids. The result is that the pH of the dough will be higher and the crust colour will be darker. To remember that high pH gives a darker colour, one can think about a chocolate cake. Chocolate is alkaline and to get a darker, deeper colour of a chocolate cake, one must increase the pH.

Salt influences enzyme activity. This is especially important with doughs containing rye flour, since rye flour is relatively high in enzyme activity and in the rate that it ferments.

Salt toughens the gluten, it has a conditioning effect on the dough. Weaker flours could actually be strengthened by adding salt. It can be used to improve the handling properties of the dough by reducing the stickiness. Even though it strengthens the gluten, it delays its formation during mixing. Salt lengthens the mixing time so it is common to delay the addition of the salt to the mixer. Faster flour hydration is also seen with delayed salt. The reason why salt toughens the gluten must be sought in the fact that gluten is made of negatively charged proteins.   Negatively charged molecules will repel and not attract each other. It is believed that the positive sodium-ions Na+ of the salt play a role in bringing the protein molecules closer to each other.

Lastly, bread with no salt will also has a crust which is lighter in colour (given the same baking time and oven temperature). This can be explained as follows. Salt will slow down fermentation, so when there is no salt, the yeast activity will increase i.e. the yeast will metabolise more sugar in a given period of time. As a result there will be less sugars left in the dough and the pH of the dough will be lower (more acids will be formed). Sugars play (together with proteins, moisture and heat) an important role in the Maillard reaction. But the Maillard reaction is also influenced by the pH : a higher pH will speed up the Maillard reaction. So in this case where the pH is lower and where there are less sugars left, the colour of the crust is lighter.

In the above picture the influence of salt on the bread is visualised. Bread with no salt has a coarse crumb the reason being that the gluten network was not a well formed as in the bread with 2 % salt. The sample with 5 % salt on the other hand has a dense and compact crumb. The reason for this is that the yeast was inhibited to produce CO2, so the volume of the bread stayed low. It can be also clearly seen that the colour of the crust is pale.

Recently there has been quite some pressure on the bakery sector to reduce the salt content in bread, cakes, muffins etc. Potassium chloride as an acceptable substitute for sodium chloride as it as basically the same rheological effects on the dough. If however the salt is replaced by the same amount of potassium chloride the bread will have a bitter after taste. This after taste greatly disappears after 2 or 3 days. It also can be masked by the use of eggs and butter. So the problem does not occur in products such as muffins or cakes.

Potassium chloride also has a lower inhibiting effect on the yeast. So proofing times will be shorter. The same thing is true for the mixing times. When using a 2 % NaCl level on the flour, and the salt is replaced by a 50:50 mixture of sodium chloride and potassium chloride, the mixing time will be about 15 % shorter. So if you have a mixing time of 20 minutes it will become 17 minutes about.

Finally it needs to be noted that potassium chloride dissolves not as easy in water compared to sodium chloride. Hence it is important to choose "fine" potassium chloride and not a coarse grade. The undissolved grains will cause dark brown spots on the crust of the product. These are quite visible on products like muffins and cakes. In some countries such as the Netherlands, potassium has a negative image and producers don't like to list an ingredient that has potassium in its name.

Salt reduction

The consumption of high levels of sodium (salt contains 38,1 % sodium) has been linked to hypertension in a portion of the general population. The blood pressure in “salt sensitive” individuals can be affected (increased or decreased) by the consumption of salt. Not everybody seems to have the same sensitivity for salt. Therefore, much effort has been spent on the complete or partial replacement of common salt (sodium chloride).

First of all two things must be made clear.

So let us examine some practical examples. Let's start with a cake. Consider the composition of a cake as represented in the following table. In the 3rd column we noted the mg of Na+ per 100 g of the raw material. By multiplying the data of column 2 and 3, we obtain the quantity of Na+ in the cake.

raw material
%
mg Na+/g
mg Na+ in recipe
granulated sugar
25,60
0,00
0,00
cake flour
19,40
2,00
0,39
whole egg
19,20
1,40
0,27
vegetable oil
18,10
0,00
0,00
water
11,90
3,50
0,41
salt
0,35
381,00
133,35
wheat starch
2,60
15,00
0,39
sodium bicarbonate
0,30
274,00
82,20
SAPP
0,50
207,50
103,60
whey powder
1,40
10,90
15,26
emulsifiers
0,65
42,00
27,30
total
100,00
-
363,17

So 100 g of this recipe contains 363,17 mg of sodium. So apart from the salt also the sodium bicarbonate and the sodium acid pyrophosphate (i.e. the baking powder) has a substantial contribution to the sodium level of the recipe. It is easier to replace the ingredients of the baking powder than it is to replace the salt. The sodium bicarbonate can be replaced by potassium bicarbonate or ammonium bicarbonate. However one has to take into account that potassium has a bit of an image problem (although some professors have confirmed that the impact it has on blood pressure is much lower than the impact sodium has) and that the ammonium salt has a bit of an odour problem, especially during the baking process.

With regards to the acid source in the recipe one can use for instance glucono-delta-lactone or sourdough. On top of that sourdough has the advantage that it will contribute to the overall aroma of the cake. Carefully prepared and produced sourdough can even reinforce the vanilla or citrus flavour in cake. At the same time - as here we are not concerned about the development of the gluten network - we can even reduce the salt level.

Using these considerations in the above recipe, we get the following:

raw material
%
mg Na+/g
mg Na+ in recipe
granulated sugar
25,60
0,00
0,00
cake flour
19,40
2,00
0,39
whole egg
19,20
1,40
0,27
vegetable oil
18,10
0,00
0,00
water
11,90
3,50
0,41
salt
0,30
381,00
114,30
wheat starch
2,60
15,00
0,39
potassium bicarbonate
0,30
0,00
0,00
sourdough
0,50
19,40
9,7
whey powder
1,40
10,90
15,26
emulsifiers
0,65
42,00
27,30
total
100,00
-
168,02

This recipe contains about 55 % less sodium. Of course each and every baker has to consider his own recipe because as you know there are as many recipes as there are bakers. But a more than 50 % reduction of the sodium content is a nice result.

In the same way lets have a look at the recipe of a bread. Now for bread the substitution is a little more complicated because it is the salt itself that is the main contributor to the sodium level in the dough. It is however important to keep the overall taste of the product in mind, the overall seasoning and saltiness and not to focus too much on the taste of salt. Here is well sourdough is the perfect and 100 % natural replacement of salt. In addition sourdough will have a positive effect on the rheological behaviour of the dough as well as on the staling of the bread. For more information about this, please consult the chapter on sourdough.

raw material
%
mg Na+/g
mg Na+ in recipe
bread flour
58,80
2,00
1,18
water
38,20
3,50
1,34
yeast
1,50
0,00
0,00
salt
1,10
381,00
4,19
soy lecithin
0,40
0,00
0,00
total
100,00
-
6,71

So 100 g of bread dough contains 6,71 mg of sodium and after baking the amount will rise to about 7,7 mg per 100 g of bread. By using sourdough one can reduce the salt by about 50 % without having a negative effect on the rheological behaviour of the dough.

To conclude this chapter, some words about the microbiological shelf life. Salt will slow down the growth of moulds and by reducing the salt in the dough, one favours the development of mould. However first of all it should be remembered that mould growth depends on a number of factors such as aw-value, initial contamination etc. For more information about this aspect, see the chapter on the microbiological shelf life of bread.

However also here certain sourdoughs can be a solution. Wheat flour can be fermented not only with lactic acid bacteria but also with other types of bacteria which will produce a number of acids during the fermentation. The following table gives an idea of the type of acids that will be produced by the bacteria.

raw material
% lactic acid
% acetic acid
% propionic acid
fermented wheat flour
5,0 - 7,0 %
< 2 %
13,0 - 15,0 %

Actually it is a bit more complicated than that. Apart from the above mentioned acids also other acids such as butyric and malic acids are formed and there is a synergetic effect between all these organic acids. After fermentation the amount of propionic acid will be around 30 - 32 %. However during the subsequent drying operation, together with the fact that propionic acid is relatively rather volatile, the final product will contain 13,0 - 15,0 % propionic acid. And as we all know propionic acid is an excellent anti-microbial agent. One has to keep in mind that the effectiveness depends on the pH of the dough. A pH around 5,0 is ideal. At a pH higher than 5,2 the effectiveness declines. A dosage level of 1,5 - 2 % of the fermented wheat flour is normally sufficient to protect the bread on condition that also all other precautions have been taken to avoid contamination.

Another aspect of the usage of fermented wheat flour is the declaration. The product can be declared as fermented wheat flour or as sourdough. However if the bread is analysed, propionate will be found and one can wonder why the propionate is not mentioned in the ingredient list. Well I don't think it should be declared because it is also not declared in for instance cheese where the propionate is also produced in a natural way.

Also a word of caution. It is impossible to distinguish the propionate that was produced in the all natural way by fermentation and the one obtained from a chemical reaction. Some (Italian) companies offer so called 100 % natural fermented wheat flour but cannot be trusted. Insist on seeing the fermentation plant and if they refuse because of the so called "confidentiallity" of the process, just don't believe them and go and look elsewhere. These companies buy some products from China (which cannot always be trusted) and add chemical propionate. If necessary I can advise you about companies that can be trusted.



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NoŽl Haegens

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