# Bread Biopreservation through the Addition of Lactic Acid Bacteria in Sourdough
## 1 Introduction  
Bread is a perishable food, and bacteria, yeasts, and fungi can cause its deterioration. It has a high humidity percentage, a water activity (\(\mathrm{a_{w}}\)) between 0.94 and 0.97, and a pH close to 6. Therefore, storage temperatures between 25-30 \({}^{\circ}\)C cause a greater probability of contamination after baking since it is the optimum temperature range for fungal growth. This is the most critical phase due to storage, wrapping, or cutting conditions [1]. The main contaminating microorganisms are fungi, with the most common genera being _Aspergillus_, _Penicillium_, _Mucor_, _Monilia_, _Endomyces_, _Cladosporium_, _Fusarium_, and _Rhizopus_[2]. Different strategies can be used to destroy the spores to avoid food deterioration, including infrared radiation, ethanol, propionic acid, packaging techniques, or sourdough. The latter increases the shelf life due to reduced pH and lactic and acetic acid production by lactic acid bacteria (LAB) [3]. The growth of fungi, bacteria, or yeast produces tremendous economic losses at the industrial level and rejection by the consumer. Moreover, fungal contamination significantly impacts food's nutritional and organoleptic characteristics, so fungi may affect the harvesting, processing, or consumption stage. This is mainly due to the large production of spores that are transmitted via the air. In addition, they can develop in unfavorable environments such as low temperatures, acidic or basic pH, low \(\mathrm{a_{w}}\), and high concentrations of preservatives [4]. The genus _Aspergillus_ can grow in a temperature range from 6 \({}^{\circ}\)C to 48 \({}^{\circ}\)C, with the optimum temperature being 25 \({}^{\circ}\)C. They can also develop between a pH of 2 and 11.2 or in a\({}_{\mathrm{w}}\) close to 0.85. Therefore, the main foods affected by this genus of fungus are cereals, fruit, nuts, and seeds. In addition, within this group, _Aspergillus flavus_ or _Aspergillus parasitticus_ are the largest producers of aflat (AF), and in the case of _Aspergillus carbonarius_, it is the main producer of Ochratoxin A (OTA) [4]. The genus _Penicillium_ can grow in a temperature range between \(-2\)\({}^{\circ}\)C and \(37\)\({}^{\circ}\)C, with the optimum temperature being 25 \({}^{\circ}\)C, and in a pH range between 1.6 and 10. The optimum a\({}_{\mathrm{w}}\) for its growth is close to 0.8, and it can grow at low oxygen concentrations. On the other hand, the main toxins they can produce are OTA, produced by _Penicillium expansum or Penicillium citrium_; and cyclopiazonic acid, produced by _Penicillium camemberti_ or _Penicillium commune_[4]. Biopreservation uses the antimicrobial potential of the food microbiota itself or that of the metabolites produced by it to prolong the shelf life of food and maintain quality for as long as possible [5]. An example is the fermentation of sourdough, which produces microbial metabolites that contribute to the flavor, aroma, texture, digestibility, nutritional quality, and preservation of bread. Sourdough fermentation is a conservative effect exerted by LAB, mainly due to the production of antimicrobial metabolites such as organic acids and phenolic compounds [6]. LAB has three mechanisms that determine its antifungal action. The first of these is its ability to produce antimicrobial compounds. The action of lactic acid stands out, although it is also worth noting the effects of other compounds such as phenolic acids, hydrogen peroxide, short-chain organic acids, and bioactive peptides. The second is due to competition for nutrients by LAB, because they are highly integrated into the substrate in which they grow. The last mechanism consists of the pH reduction produced during fermentation, which creates challenging conditions for the development of the fungus [7]. In recent years, the use of LAB in food has increased. These are capable of producing antifungal compounds, especially _L. plantarum_, against fungi of the genus _Aspergillus_. Therefore, different strains of _L. plantarum_ are used as sourdough starter cultures [2].