Preservatives and Bread Preservation

Preservatives and Bread Preservation

In this entry, we will discuss additives that help prolong the shelf life of bread. However, before delving into these, it is essential to understand why bread deteriorates.

Bread Ageing Processes

Bread undergoes three distinct ageing phenomena. Firstly, there is a change in the bread’s texture. Secondly, microbial growth may occur. Lastly, the aroma of the bread may change, either due to the loss of typical components or the rancidity of fats. The latter effect is generally overlooked, as it usually occurs after the first two, which tend to limit the bread’s shelf life. If rancidity is an issue, attention should be paid to the fats used, and antioxidant substances can be employed, but these topics will not be covered in this entry.

Texture Changes

When it comes to texture changes, we must distinguish between two types of bread: those with simple formulations and crispy crusts, and softer breads with added oils or fats, soft crusts, and longer shelf lives. For the former, once baking is completed, the bread typically has a dry, crispy crust and a moist, soft crumb. Moisture tends to migrate from the crumb to the crust, drying out the crumb and making the crust tougher and less crispy. If the bread is wrapped in a plastic bag, this effect becomes evident within a few hours. Placing the bread on a surface that allows for some transpiration can help balance the moisture transfer, but the bread will still dry out and lose quality over time. This process is slower for larger, more rounded pieces, as moisture has to travel a greater distance to the exterior, so larger pieces maintain their quality longer.

To minimise moisture migration from the crumb to the crust and from the crust to the exterior, hydrocolloids can be used, as discussed in a previous entry. The inclusion of certain fibres can have a similar effect. However, high doses of hydrocolloids can also prevent moisture from escaping the dough during baking, resulting in less crispy bread. These pieces can freeze better as they do not tend to flake, but they lose their crispness.

For soft breads, such as sandwich loaves, where the crust is soft, plastic packaging is used to minimise moisture loss and prevent the bread from drying out. These breads also experience increased crumb hardness over time, primarily due to starch retrogradation. While amylose retrogradation is typically blamed for this, it is also influenced by amylopectin retrogradation and the fine structure of both. Starch retrogradation is enhanced at low temperatures, which is why these breads tend to harden more when refrigerated.

To reduce starch retrogradation, emulsifiers are often used, as mentioned previously. The most effective anti-staling emulsifiers are monoglycerides, with higher purity providing greater effect (separating out diglycerides). Other emulsifiers like SSL (sodium stearoyl lactylate) or lecithin also exhibit anti-staling effects, but to a lesser degree. Lipases can provide a similar anti-staling effect by hydrolysing lipids in the dough to naturally generate mono- and diglycerides. Intermediate stability amylases can also be used to hydrolyse gelatinising starch during baking, reducing subsequent staling due to retrogradation. These enzymes act at higher temperatures than the usual fungal amylases used in baking, allowing them to act on the gelatinising starch but becoming inactivated by the end of baking.

It is also worth noting that breads with higher specific volumes tend to stale less during storage, due to changes in internal moisture transmission, among other factors. Similarly, slow fermentations, which enhance enzyme activity in the dough, tend to minimise bread staling. Sourdoughs, either through this enzymatic activity or by generating substances that help retain water, like dextrans produced by certain microorganisms, can also help reduce or delay staling.

Microbial Growth

Initially, bread is sterilised during baking, so any microbial contamination occurs post-baking. Therefore, the first measure to reduce microbial growth in bread is to maintain strict hygiene post-baking. Proper cooling, packaging in aseptic environments, and thorough cleaning of contact surfaces can significantly minimise microbial growth. The lower the initial microbial load, the less microbial development there will be.

When it is necessary to minimise microbial growth, the baking industry often uses propionic acid or propionates. Using antimicrobial substances in bread dough is challenging because yeast must act during fermentation. Therefore, common preservatives like sorbates cannot be used. The advantage of propionates is their greater efficacy against other microorganisms than against yeast. Although they initially inhibit yeast activity, yeast can act properly after eliminating the competition. To counteract the negative impact of propionates on yeast, especially in the early stages, the yeast dose is usually increased, or more tolerant yeast strains are used.

Although propionates are widely used in baking, they are not the most effective preservatives. In products like cakes, sorbates are more common due to their higher efficacy against microorganisms. Sorbates have been used in baking, sprayed on finished loaves, preventing adverse effects on fermentation but only acting on the surface, not the interior. In sliced and packaged bread, mould development in the crumb is common, which surface-applied sorbates cannot prevent. Recently, encapsulation techniques have advanced significantly, enabling the inclusion of encapsulated sorbates or sorbic acid. This method allows the sorbate to remain coated, usually by fats, during the initial baking stages (mixing and fermentation) without affecting yeast activity. The coating melts during baking, releasing the sorbate to prevent subsequent microbial growth.

A low pH also reduces microbial growth, and thus mould appearance. Sourdough bread, due to its lower pH, slows microbial growth, as do other highly acidic breads. Some microorganisms produce antimicrobial compounds and can be added during fermentation (usually before yeast addition) to generate these compounds and extend bread shelf life. Certain acids, like acetic acid, are more effective antimicrobials than others at the same pH.

Another option to reduce microbial growth without chemical additives is using plant extracts or essential oils with high antimicrobial properties. Spices like cinnamon, clove, rosemary, and thyme can be useful, but their influence on the final product’s organoleptic quality must be considered. These extracts’ economic aspects and their potential effects on yeast fermentation must also be considered. Although many studies are being conducted in this area, not all can be commercially applied.

Cold storage can also slow microbial growth, but as previously mentioned, it accelerates crumb hardening due to starch retrogradation. Soft-crust breads can be frozen, but the costs of frozen storage and transport and limited freezer space in retail outlets make this impractical in most cases. However, gluten-free breads are sometimes sold frozen. If unsure whether bread will be consumed before its best-before date, freezing can be a good option.

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