Question 1

How does yeast make bread rise during baking?

Accepted Answer

Saccharomyces cerevisiae ferments simple sugars through glycolysis and alcoholic fermentation, producing carbon dioxide gas. The trapped CO₂ leavens the dough, causing it to rise. Fermentation conditions such as temperature and moisture influence the final texture and aroma of the baked product.

Question 2

What role do lactic acid bacteria play in cheese production?

Accepted Answer

Lactic acid bacteria such as Lactococcus lactis are used as starter cultures in cheese fermentation at approximately 32°C. These bacteria ferment lactose and produce lactic acid, which lowers pH and helps coagulate milk proteins. The controlled fermentation conditions determine the final cheese characteristics, flavor, and texture.

Question 3

Why is temperature control critical in dairy fermentation?

Accepted Answer

Temperature determines which microorganisms thrive and which metabolic pathways dominate. Buttermilk fermentation at 20–30°C allows Leuconostoc to convert citrate into diacetyl, creating a buttery flavor. Yogurt fermentation at approximately 45°C favors thermophilic lactic acid bacteria that synergistically convert lactose into lactic acid, lowering pH and coagulating proteins.

Question 4

What is diacetyl and how is it produced in buttermilk?

Accepted Answer

Diacetyl is a compound that imparts a buttery aroma and flavor to buttermilk. Leuconostoc species produce diacetyl by converting citrate during fermentation at 20–30°C. This metabolic process is central to developing the distinctive sensory qualities that characterize buttermilk as a fermented dairy product.

Question 5

How do microbes preserve food and extend shelf life?

Accepted Answer

Fermentative microorganisms metabolize carbohydrates into organic acids and other metabolites that inhibit spoilage organisms and lower pH. These conditions create an acidic environment hostile to pathogenic and spoilage microbes, thereby preserving food and extending shelf life while improving digestibility and contributing distinctive sensory qualities.

Question 6

What happens during the cheddaring and aging steps of cheese production?

Accepted Answer

After milk is curdled with rennet and heated to 38°C to expel whey, the curds are cheddared, salted, and aged. These steps develop flavor and texture in the cheese. Secondary ripening with molds such as Penicillium roqueforti or P. camemberti further develops aroma and rind structure in certain cheese varieties.

Question 7

How do bacteriophages affect large-scale dairy fermentation?

Accepted Answer

Bacteriophage contamination disrupts large-scale dairy fermentation by lysing starter cultures, compromising production reliability. Modern phage-resistant strains, including those developed using CRISPR/Cas systems that provide sequence-specific immunity, help maintain stable and reliable fermentation outcomes in industrial dairy operations.

Microbes in Food Production

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