Enzymatic and Bacterial conversions during Sourdough Fermentation

Introduction

Sourdough Fermentation involves complex interactions between enzymes in the flour and the metabolism of microorganisms, which greatly affect bread quality. These interactions influence the breakdown of carbohydrates, proteins phenolic compounds and fats.

Key benefits of Sourdough Fermentation

1. Carbohydrate Breakdown

   1. During sourdough fermentation, lactic acid bacteria break down sugars in the flour. Cereal enzymes release maltose and glucose, which are crucial for microbial growth.

2. Protein Degradation

   1. Enzymes in the flour and bacteria break down proteins into smaller pieces, such as peptides and amino acids. This process affects the dough's texture and helps develop the bread's flavor.

3. Phenolic Compound Metabolism (Breakdown)

   1. Phenolic compounds, such as ferulic acid, are metabolized by lactic acid bacteria, improving antioxidants properties and flavor.

4. Lipid Metabolism

   1. Lipid oxidation during dough mixing generates flavor volatiles and influences dough rheology. Lactobacilli can improve or inhibit lipid oxidation.

      
      

Detailed Insights into Fermentation Process

1. Starch Breakdown: Wheat and rye contain significant starch, which is degraded by cereal enzymes to produce fermentable carbohydrates. Heterofermentative lactobacilli, such as Fructilactobacillus sanfranciscensis (formerly Lactobacillus sanfranciscensis, preferentially metabolize maltose.

2. Solubilization of Arabinoxylans: Arabinoxylans in wheat and rye flour contribute to dough hydration and foam stability. Their solubilization during sourdough fermentation is primarily due to cereal enzymes, enhancing bread quality.

3. Exopolysaccharide Formation: Exopolysaccharides produced by lactic acid bacteria improve bread volume, texture, and dietary fiber content. The fermentation substrate and carbohydrate availability influence polysaccharide yield.

4. Protein Degradation and Amino Acid Breakdown: Proteolysis in sourdough is dependent on cereal proteases and microbial peptidases. The accumulation of bioactive peptides and amino acid metabolites, such as γ-aminobutyrate, can provide health benefits.

5. Metabolism of Phenolic Compounds: Lactic acid bacteria metabolize phenolic compounds, releasing bioactive phenolic acids and flavonoids. This process improves antioxidant properties and flavor, with strain-specific variations in metabolic activity.

6. Enzymatic Conversion of Phytate: Phytate in wheat and rye flours is hydrolyzed by cereal phytases during sourdough fermentation, increasing mineral bioavailability.

7. Lipid Metabolism: Lipid oxidation during dough mixing generates flavor volatiles. Lactobacilli can either enhance lipid oxidation or exert antioxidative effects, influencing for instance the formation of hydroxy fatty acids with antifungal properties.

Conclusion

Sourdough enhances bread quality through enzymatic and microbial conversions occurring during fermentation.

Summary

The document "Enzymatic and Bacterial Conversions during Sourdough Fermentation" explores the interactions between cereal enzymes and microbial metabolism in sourdough fermentation. Key processes include carbohydrate metabolism, protein degradation, phenolic compound metabolism, and lipid metabolism. These processes enhance bread quality by improving texture, flavor, and nutritional value. Sourdough fermentation remains relevant in contemporary food production due to its unique sensory properties and health benefits.

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Glossary

1. Arabinoxylans

   1. Arabinoxylans are a type of dietary fiber found in cereals like wheat and rye. They consist of arabinose and xylose sugars and contribute to the texture and stability of dough. During sourdough fermentation, the solubilization of arabinoxylans by cereal enzymes enhances dough hydration and foam stability, improving bread quality.

2. Antioxidants

   1. Antioxidants are substances that prevent oxidation, a chemical reaction that can produce free radicals and damage cells. They are important for maintaining health and preventing spoilage in foods.

3. Exopolysaccharide Formation

   1. Exopolysaccharides are complex sugars produced by bacteria during fermentation. These polysaccharides improve the texture, volume, and dietary fiber content of bread. The production of exopolysaccharides by some lactic acid bacteria in sourdough is influenced by the availability of carbohydrates like sucrose and maltose, as well as the fermentation substrate.

4. Ferulic Acid

   1. Ferulic acid is a type of phenolic compound found in the cell walls of plants, particularly in grains like wheat and rye. It has antioxidant properties and can contribute to the flavor and health benefits of foods.

5. Hydroxy Fatty Acids

   1. Hydroxy fatty acids are a type of fat that has an extra chemical group called a hydroxyl group (-OH) attached. This special feature can help fight fungi and also affect the taste of foods.

6. Lipid Metabolism:

   1. a.    Lipid metabolism is the process of breaking down and creating fats in the body. During sourdough fermentation, the breakdown of fats creates flavor compounds and affects the dough. Lactobacilli (a type of bacteria) can either increase fat breakdown, creating flavorful compounds, or reduce it, producing hydroxy fatty acids that help fight fungi.

7. Maltose

   1. Maltose is a type of sugar made of two glucose molecules. It is created when starch breaks down and is commonly found in malt.

8. Peptidases

   1. Peptidases are enzymes that further break down peptides into amino acids. They play a crucial role in protein digestion and metabolism.

9. Phenolic Compounds

   1. Phenolic compounds are a group of chemical substances found in plants. They have antioxidant properties and can affect the flavor and nutritional value of foods. Examples include flavonoids and tannins.

10. Phytate

    1. Phytate is a form of phosphorus found in plant seeds. It can bind minerals and reduce their bioavailability, but it is broken down during fermentation, increasing mineral absorption.

11. Proteolysis

    1. Proteolysis refers to the process of breaking down proteins into smaller peptides or amino acids. This process is carried out by enzymes called proteases.

12. Sucrose

    1. Sucrose is a type of sugar commonly known as table sugar. It is a disaccharide composed of glucose and fructose. Sucrose is found naturally in many plants and is often used as a sweetener in food.