Microbes in Household Products | Biology Class 12 - NEET PDF Download

Introduction to Microbes

• Microbes are microscopic organisms found everywhere—in soil, water, air, inside living organisms, and extreme environments (e.g., thermal vents at 100°C, deep soil, snowy layers, acidic conditions).
• Microbes, despite their microscopic size, are the most abundant and diverse forms of life on Earth. They play a crucial role in various ecosystems and can thrive in extreme environments where other organisms cannot survive.

 There are several types of microbes, including: 

• Protozoa: These are single-celled organisms that can be found in various habitats, including soil and water. 
• Bacteria: These are single-celled organisms that can be found in almost every environment on Earth, including extreme conditions. Some bacteria are beneficial, while others can cause diseases. 

Bacteria: (a) Rod-shaped, magnified 1500X; (b) Spherical shaped, magnified 1500X; (c) A rodshaped bacterium showing flagella, magnified 50,000X

• Fungi: These organisms play a crucial role in decomposition and nutrient cycling. Some fungi can be harmful, but many are beneficial to humans. 
• Viruses: These are microscopic agents that can infect living organisms. Some viruses can cause diseases, while others can be beneficial. 
• Viroids: These are small infectious agents that consist of RNA and can cause diseases in plants. 
• Prions: These are infectious agents composed of protein that can cause diseases in animals and humans. 

Microorganisms, such as bacteria and certain fungi, can be grown on nutrient-rich media, leading to the development of visible colonies. These cultures, which are visible to the naked eye, are useful for studying microorganisms. 

 (a) Colonies of bacteria growing in a petri dish; (b) Fungal colony growing in a petri dish 

 Some  microbes can cause diseases in humans, animals, and plants. However, it is important to understand that not all microbes are harmful. In fact, many microbes are beneficial to humans in various ways. This chapter will explore some of the most important ways in which microbes contribute to human welfare.

Microbes in Household Products

Microorganisms are central to the manufacture and functioning of many household products. They are exploited directly in food and beverage fermentations and indirectly by providing enzymes and biochemicals used in detergents, cleaners and preservation. The following sections describe common household applications, the microbes involved, the biochemical basis and practical notes for preparation and safe use.

(i) Microbes in Curd Production

Curd is produced by the bacterial fermentation of milk. The important group responsible is the lactic acid bacteria (LAB), for example Lactobacillus species. These bacteria ferment milk sugars (primarily lactose) to lactic acid which coagulates milk proteins (casein), giving curd its texture and flavour.

• When a small amount of curd (starter) is added to fresh milk, the starter contains millions of LAB which multiply when kept at suitable temperatures and convert milk into curd.
• The acidification partially digests milk proteins and changes the physicochemical properties of milk, improving digestibility and shelf life.
• Fermentation can enhance the nutritional value by increasing certain B‐vitamins in some cases and by producing live beneficial bacteria (probiotics) that help control pathogenic microbes in the gut.

Practical notes: maintain hygienic conditions when preparing curd, use an active starter, and keep the milk at an appropriate temperature (commonly 30-45°C for household curd) until set. Excessive heating or contamination can alter the outcome.

(ii) Microbes in Fermented Foods

Fermentation is a metabolic process used widely in household food preparation. Microbes convert carbohydrates into acids, gases or alcohol, often improving flavour, texture, nutritional value and storage life.

• Dough for dosa and idli: The batter for dosa and idli is fermented by mixed microflora including lactic acid bacteria and yeasts present in the environment and on grains. Microbial activity produces carbon dioxide (CO2) and organic acids that make the batter light and give characteristic flavour. The metabolic pathway is primarily lactic acid fermentation with contributions from heterofermentative microbes producing CO2.
• Bread dough: Baker's yeast, Saccharomyces cerevisiae, ferments sugars to produce CO2 and ethanol (alcoholic fermentation). The CO2 causes the dough to rise; the alcohol evaporates during baking and contributes to flavour.
• Traditional fermented drinks and foods: Fermented beverages such as toddy (fermented palm sap) are produced by natural microbial fermentations. Fermentation is also used in processing fish, soybeans (e.g., certain regional fermented soybean products), bamboo shoots and many other traditional foods.

Fermented Dough for Dosa and Idli

Toddy Production

Key fermentation types in household products

• Lactic acid fermentation: Common in curd, idli/dosa batter and some pickles; produces lactic acid which acts as preservative and flavouring agent.
• Alcoholic fermentation: Performed by yeasts in bread, beer and wine; produces ethanol and CO2.
• Acetic acid fermentation: Conversion of ethanol to acetic acid by acetic acid bacteria (used for vinegar production).
• Propionic acid fermentation: Carried out by Propionibacterium species in certain cheeses; CO2 production forms characteristic holes (eyes) in Swiss‐type cheese.

(iii) Microbes in Cheese Production

Cheese production uses a variety of microbes (bacteria, yeasts and fungi) to create diverse textures and flavours. Microbial cultures are selected to produce specific biochemical changes during curd formation and ripening.

• Different cheese varieties arise from different combinations of starter cultures, ripening conditions and secondary microbes that grow during maturation.
• The large holes in Swiss cheese are due to CO₂ produced in large amounts by bacteria such as Propionibacterium sharmanii, which also contribute to the characteristic flavour.
• Roquefort and other blue cheeses are ripened by moulds (fungi) that grow within the cheese and produce enzymes and flavour compounds responsible for the distinctive aroma and taste.

Swiss Cheese

Practical notes: cheese production requires control of temperature, salt, moisture and microbial starters. Some cheeses use defined starter cultures (known species and strains) while others rely on environmental microbes for secondary fermentation.

(iv) Microbes in Baking and Household Beverages

• Saccharomyces cerevisiae is the principal yeast used in household and bakery fermentations to leaven bread and other baked goods.
• Home brewing of alcoholic beverages is based on yeast fermentations; hygiene and controlled fermentation conditions are necessary to avoid spoilage and formation of undesirable compounds.
• Vinegar is produced by acetic acid bacteria converting ethanol into acetic acid; this is a common household product for culinary and cleaning uses.

(v) Microbial Products Used in Household Cleaning and Detergents

Microorganisms are not only used directly in food; they are also sources of industrially important enzymes and biochemicals that appear in household products.

• Enzymes in detergents: Microbial enzymes such as proteases, lipases, amylases and cellulases are produced by bacteria (e.g., Bacillus spp.) and fungi and added to laundry detergents to break down protein, fat, starch and cellulose stains at lower temperatures.
• Citric acid: Produced industrially by the fungus Aspergillus niger; citric acid is used in household cleaning products and as a food acidulant.
• Biodegradable surfactants and bio‐based cleaners: Microbial processes are used to produce eco‐friendly ingredients in cleaning products, reducing reliance on harsh chemicals.

Practical notes: enzymes enable efficient cleaning at lower temperatures and reduce energy use. Detergent formulations are designed so the enzymes remain active under expected wash conditions (pH, temperature, water hardness).

(vi) Probiotics, Starter Cultures and Safety

Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host. Common probiotic genera used in household food products include Lactobacillus and Bifidobacterium. Probiotic properties depend on strain, dose and viability.

• Starter cultures are defined strains used to ferment milk, dough or other substrates; they provide reproducible results in taste, texture and safety compared with natural (wild) fermentations.
• Hygiene, correct temperatures and clean utensils are essential for safe home fermentations to prevent the growth of pathogenic bacteria.
• Some microbes used in food production may be opportunistic pathogens in immunocompromised persons; therefore, safe handling and appropriate use are important.

(vii) Summary and Practical Recommendations

Microbes are indispensable in many household products and processes. Lactic acid bacteria and yeasts are the most commonly encountered groups in domestic food fermentations such as curd, idli/dosa batter and bread. Microbial enzymes and biochemicals enhance the performance of cleaning agents and reduce environmental impact. Safe practices - using clean equipment, proper starters, controlled temperatures and good storage - ensure desirable outcomes and prevent spoilage or disease.

Remember these practical tips:

• Use a reliable starter (or a previously prepared curd) for consistent curd and yoghurt results.
• Maintain appropriate fermentation temperatures and times for the product being prepared.
• Keep containers and utensils clean to avoid contamination by undesirable microbes.
• Store fermented products under refrigeration when required to slow microbial growth and prolong shelf life.