The main purpose of this entry is to discuss sourdough and the interest in using it in breadmaking.

What is a sourdough?

Essentially, a sourdough is a wild culture of microorganisms, more or less cared for and maintained over time. Sourdough begins with a mixture of flour and water, incorporating microorganisms from the water, flour, environment, and surfaces where they are prepared. These sourdoughs may include some salt, and the flours may vary in extraction level or include other grains such as rye. It’s even common to add small percentages of other ingredients at the start of preparation, like fruit peels, which also contribute interesting microbial loads. After several refreshments, we obtain a dough primarily composed of flour and water, with a high concentration of bacteria and yeast. Among the bacteria, lactic acid bacteria are prominent, but there are also acetic and even butyric bacteria (which are highly detrimental to the final taste of bread). By adequately controlling storage conditions, especially temperatures, as well as factors like hydration, salt content, etc., we can promote the growth and action of desired bacteria while minimizing the undesirable ones. That’s why it’s not advisable to store sourdough at very high temperatures.

What changes occur in a sourdough?

The action of microorganisms acidifies the sourdough. Generally, lactic acid predominates, with acetic acid to a lesser extent, though some sourdough can be excessively acetic. However, other acids are also produced in smaller concentrations. Thus, the first noticeable effect of sourdough is acidification and a decrease in pH, which affects the taste and aroma of the resulting bread.

The second effect of sourdough is enzymatic hydrolysis of components, including starch and proteins, as well as other components of flours like phytates. This enzymatic activity results in the formation of smaller fractions of starch and proteins, which can directly or indirectly alter the taste and aroma of bread, through Maillard reactions occurring during baking. Microorganisms present in the dough also contribute to this modification.

What are the advantages of sourdough for bread quality?

When used appropriately, sourdough will modify the taste and aroma of bread. Bread made with sourdough tends to be more acidic, although the type of acid generated depends on the conditions of sourdough preparation. They also have more intense aromas. This effect can be beneficial if mild, but excessively acidic bread is rejected by a significant portion of consumers, especially upon first tasting. Such acidic bread pairs well with strongly flavoured products but might overshadow milder flavours. However, ultimately, it’s a matter of personal preference.

Acidity can aid in preserving bread by reducing microbial spoilage. However, this is only significant for long-life bread like sandwich loaves since most bread is discarded for reasons other than microbial growth. Nonetheless, enzymatic degradation of flour components also reduces crumb hardening phenomena, thus aiding in longer preservation, or at least slowing down the process. It’s worth noting that bread marketed as sourdough often comes in larger pieces, necessitating adjustments in baking and contributing to slower dehydration. Yet, in this case, better bread preservation is due to the size of the loaves, not solely the presence of sourdough.

In summary, bread made with sourdough alters the final bread’s flavours and aromas and enhances its preservation. However, these modifications in flavours and aromas depend on the conditions of sourdough and final bread preparation, and in extreme cases, it might be rejected by consumers, or at least by a portion of them.

How does sourdough affect the nutritional quality of bread?

Much has been written on this topic, and our group has conducted a literature review on it. Let’s try to condense the most important points. Essentially, it can be summarised as follows: sourdough bread undergoes certain changes that suggest potential nutritional or health benefits. However, currently, there are no studies demonstrating that individuals following the same diet but switching from non-sourdough to sourdough bread have a lower risk of certain diseases, let alone the ability to cure any. First, we’ll discuss the positive aspects, then analyse these studies. It’s essential to consider that each study is conducted under different conditions, and what constitutes sourdough bread in one study may not align with legislation of different countries.

The first positive aspect of bread made with sourdough is its lower glycaemic index and the fact that starch is digested more slowly. This is undoubtedly beneficial and is often associated with a greater feeling of satiety or at least a delay in the return of hunger. However, it’s necessary to understand the reasons behind this reduction. Most likely, it’s due to the acidity of the dough, as it has been demonstrated that the presence of acids, especially before starch gelatinisation, has this effect. Therefore, this can also be achieved by incorporating different acids into the dough.

A second widely discussed effect is the increased digestibility of proteins, primarily linked to enzymatic activity, particularly proteases. This could be interesting in a low-protein diet, where it’s essential to maximise protein intake, or if bread is consumed for its protein quality. However, bread in our diet is not the primary source of protein, and these proteins are not of the highest quality. Generally, people in Western society do not have issues with protein deficiencies and would seek other protein sources to improve their intake. It has also been claimed that sourdough bread may be better for those with coeliac disease, which is a significant fallacy and a dangerous assertion. Coeliacs are intolerant to gluten, specifically certain amino acid sequences found primarily in gluten gliadins. As far as I’m aware, there is no study demonstrating that a sourdough, as described, is capable of removing these amino acid sequences. Therefore all sourdough bread is harmful to coeliac patients or those allergic to gluten. Indeed, there are studies incorporating specific microorganisms or enzymes to treat doughs and minimise these amino acid sequences. However, these are studies with very specific incorporations, typically not analysing the quality of the resulting bread. It’s crucial to note that excessive gluten hydrolysis negatively impacts dough quality for retaining gas produced during fermentation, thus affecting the final bread quality. These studies are unrelated to naturally cultured sourdough starters used in bakeries. Once this is clarified, some bakers claim that sourdough bread may be better digested by individuals with sensitivity to certain proteins. Again, we encounter a lack of solid evidence on this matter. This is something that is not firmly proven, but it’s true that the word “may” leaves it very open-ended.

A third effect of using sourdough starters is the increased bioavailability of minerals present in bread. Most minerals in bread are bound in the form of phytates, making them inaccessible to consumers. These phytates are hydrolysed by phytases, releasing these mineral substances. Phytase activity is greater with more time available, hence the benefit of sourdough starters and slow fermentations. However, in white bread, the mineral content is quite low, especially when compared to wholemeal bread. This action is of great interest in wholemeal bread but of much lesser significance in white bread. For those following from South America and other countries where enriching flour with minerals and vitamins is mandatory, it’s essential to consider the availability of these minerals.

The latest research on sourdough suggests an improvement in certain bioactive components and intestinal microbiota. However, as mentioned, more extensive studies are needed to firmly assert certain advantages of sourdough bread. Especially lacking are clinical studies involving patients or individuals, rather than solely focusing on bread composition.

At this point, it’s crucial to note that we must be cautious with studies that combine many factors. For example, if we compare white bread with wholemeal sourdough bread and find that the latter is healthier, we cannot conclude that sourdough is healthier. Nor can we conclude that wholemeal bread is healthier, but only that the combination of both practices is healthier.

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