Microbes in Household Products

Microorganisms are not only disease-causing agents; many are also highly useful in daily life. In household food preparation, selected bacteria, yeasts, and fungi help convert raw materials into products with better taste, texture, aroma, digestibility, and storage quality.

Major Groups of Useful Microbes

1. Lactic Acid Bacteria (LAB):
   Lactic acid bacteria convert sugars in milk into lactic acid, which causes souring and coagulation. They are central to curd formation and also play a role in flavour development in several dairy products.
2. Yeast:
   Yeast, especially Saccharomyces cerevisiae, ferments sugars and releases carbon dioxide. This gas makes bread dough rise, becoming soft and porous.
3. Fungi:
   Certain fungi, such as Penicillium roqueforti and Penicillium camemberti, are used during cheese ripening to develop special flavour, texture, and appearance

• Milk is converted into curd by lactic acid bacteria (LAB), mainly Lactobacillus and other LAB species.
• LAB grow in milk and produces acids.
• These acids coagulate and partly digest the milk proteins.
• The product formed is curd.
• The nutritional value is improved: curd contains increased amounts of Vitamin B₁₂.
• LAB present in curd checks the growth of disease-causing microbes in the stomach.

• Cream is first soured with lactic acid bacteria before being churned.
• Flavour and aroma are developed by specific bacteria added to the cream: Streptococcus cremoris and Leuconostoc dextranicum
• The churning process separates butter from the liquid portion.
• The liquid by-product obtained is buttermilk.

• Yogurt is prepared from milk using a controlled bacterial culture.
• The microorganisms used are: Lactobacillus bulgaricus and Streptococcus thermophilus
• Fermentation is commonly carried out at approximately 40°C.
• The characteristic flavour of yogurt is linked to compounds such as acetaldehyde.

• Cheese is made by separating casein, the main milk protein.
• The process involves curdling, using the enzyme rennin along with lactic acid bacteria.
• After curdling, the product is subjected to ripening.
• Ripening involves controlled microbial action that develops the characteristic flavour, texture, and appearance.
• Microbes used in general cheese production: Streptococcus lactis, Streptococcus species, Lactobacillus species and Leuconostoc species

Swiss Cheese:

• During the ripening of Swiss cheese, Propionibacterium shermanii is involved.
• This bacterium produces carbon dioxide (CO₂).
• The CO₂ forms the characteristic large holes in Swiss cheese.

Roquefort Cheese:

• Roquefort cheese is ripened using Penicillium roqueforti.
• This fungus is responsible for the characteristic flavour of Roquefort cheese.

Camembert Cheese:

• Camembert cheese is prepared using Penicillium camemberti.
• This fungus gives the cheese its characteristic soft texture and taste.

• The batter for idli and dosa undergoes microbial fermentation before cooking.
• The microorganism primarily involved is Leuconostoc mesenteroides.
• Fermentation makes the batter lighter, softer, and suitable for cooking.

• Bread dough is fermented using baker's yeast, Saccharomyces cerevisiae.
• Yeast ferments the sugars in the dough and releases carbon dioxide (CO₂).
• The CO₂ gas is trapped in the dough, causing it to rise and become porous.
• Baking sets the expanded dough into bread.

• Toddy is a traditional fermented beverage prepared from palm sap or coconut sap.
• Other commonly fermented foods include fermented fish, fermented soybeans, and bamboo shoots.
• These products develop characteristic smell, taste, and texture through microbial metabolism.