Microbial fermentation is central to food biotechnology, enhancing flavor, texture, preservation, and stability. Fermentative microorganisms metabolize carbohydrates into organic acids, alcohols, and other metabolites that inhibit spoilage organisms and improve digestibility while contributing distinctive sensory qualities.
In baking, amylases naturally present in flour hydrolyze starch into monosaccharides such as glucose, which Saccharomyces cerevisiae ferments anaerobically. Through glycolysis followed by alcoholic fermentation, yeast generates carbon dioxide and ethanol; the trapped CO₂ leavens the dough, while fermentation conditions such as temperature and moisture influence final texture and aroma.
In dairy fermentation, lactic-acid bacteria (LAB) such as Lactococcus lactis and Leuconostoc spp. are selected for acid tolerance and desirable metabolic traits. Controlled conditions determine product characteristics. For example, buttermilk is produced at 20–30 °C, where Leuconostoc converts citrate into diacetyl, yielding a buttery aroma. Many cheese varieties begin with inoculation at ~32 °C, followed by rennet coagulation and heating to ~38 °C to promote whey expulsion. Later steps—including cheddaring, salting, and aging—shape texture and flavor. Secondary ripening with molds such as Penicillium roqueforti or P. camemberti further develops aroma and rind structure.
Traditional yogurt fermentation occurs at ~45 °C, favoring thermophilic LAB such as Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Their synergistic metabolism converts lactose into lactic acid, lowering pH and coagulating milk proteins.
A persistent challenge in dairy fermentation is bacteriophage contamination, which can disrupt large-scale production by lysing starter cultures. Modern phage-resistant strains, including those developed using CRISPR/Cas systems that provide sequence-specific immunity, help maintain stable and reliable fermentation outcomes.
In food production, microbes enhance flavor, boost nutrition, and extend shelf life.
In the baking industry, yeast, such as Saccharomyces cerevisiae, ferments simple sugars and releases carbon dioxide, causing the dough to rise.
In the dairy industry, lactic acid bacteria ferment milk into different products, depending on the temperature and the strain.
Buttermilk is produced at 20-30 °C, where Leuconostoc species convert citrate into diacetyl, adding a buttery flavor.
Cheese fermentation occurs around 32 °C and uses starter cultures of Lactococcus lactis.
For example, to make cheddar cheese, milk is curdled with an enzyme complex called rennet, then heated to 38 °C to expel the whey. The curds are cheddared, salted, and aged to develop flavor and texture.
Yogurt fermentation, at about 45°C, uses Lactobacillus and Streptococcus species to convert lactose into lactic acid, which thickens the milk and inhibits other microbes.
Then, the temperature is lowered to stabilize the acidity and consistency of the product.
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