Microbes in Household Food Processing — Revision Notes

⚡ 30-Second Revision

Curd: — LAB (*Lactobacillus*, *Streptococcus*) convert lactose $\rightarrow$ lactic acid. Coagulates milk proteins, tangy taste.
Bread: — Baker's yeast (*Saccharomyces cerevisiae*) ferments sugars $\rightarrow$ $CO_2$ + ethanol. $CO_2$ causes leavening.
Idli/Dosa: — Mixed culture (bacteria, yeast) ferments rice/dal batter $\rightarrow$ lactic acid + $CO_2$. Leavening and sourness.
Cheese: — LAB + Rennet for curdling. Ripening by specific bacteria (*Propionibacterium shermanii* for Swiss cheese $CO_2$ holes) or fungi (*Penicillium* for Roquefort/Camembert).
Toddy: — Fermentation of palm sap by natural yeasts $\rightarrow$ ethanol.
Benefits: — Enhanced flavor/aroma, increased shelf life, improved digestibility, increased nutritional value (e.g., Vit B12 in curd).
Probiotics: — Live beneficial microbes in adequate amounts conferring health benefits (e.g., in fresh curd/yogurt).

2-Minute Revision

Microbes are indispensable in household food processing, primarily through fermentation. This involves beneficial bacteria and fungi transforming raw ingredients. For curd, Lactic Acid Bacteria (LAB) like *Lactobacillus* convert milk lactose into lactic acid, which coagulates milk proteins (casein) and imparts a tangy flavor, while also increasing Vitamin B12.

In bread making, baker's yeast (*Saccharomyces cerevisiae*) ferments sugars in dough, producing carbon dioxide ($CO_2$) that causes the dough to rise (leavening) and ethanol that evaporates during baking.

Idli and dosa batters are fermented by a mixed culture of bacteria and yeasts, leading to $CO_2$ production for puffiness and lactic acid for sourness. Cheese production is more complex: LAB and rennet curdle milk, followed by ripening where specific microbes (e.

g., *Propionibacterium shermanii* for $CO_2$ holes in Swiss cheese, *Penicillium* fungi for Roquefort/Camembert) develop unique flavors and textures. These processes not only enhance sensory qualities but also improve digestibility, nutrient bioavailability, and act as natural preservatives.

Remember the specific microbes, their products, and the resulting changes for NEET.

5-Minute Revision

Microbes are crucial for a variety of household food products through controlled fermentation. This biological process, carried out by bacteria and fungi, converts complex organic compounds into simpler ones, yielding desirable changes in food characteristics.

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Curd/Yogurt: — The transformation of milk into curd is initiated by Lactic Acid Bacteria (LAB), including species like *Lactobacillus acidophilus*, *Lactobacillus bulgaricus*, and *Streptococcus thermophilus*. These bacteria ferment the lactose (milk sugar) into lactic acid. The accumulation of lactic acid lowers the pH, causing the casein proteins in milk to coagulate and form the thick, semi-solid curd. This process also enhances the nutritional value by increasing Vitamin B12 content and improving protein digestibility. The 'starter' is a small amount of previous curd.

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Bread: — **Baker's yeast, *Saccharomyces cerevisiae*, is the key microbe for bread making. When mixed with flour and water, the yeast ferments the sugars present in the dough. This alcoholic fermentation** produces carbon dioxide ($CO_2$) gas and ethanol. The $CO_2$ gets trapped within the gluten network, causing the dough to rise (leavening), which gives bread its light and porous texture. The ethanol evaporates during baking.

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Idli and Dosa: — These South Indian delicacies rely on the fermentation of a batter made from rice and black gram. A **mixed culture of bacteria (e.g., *Leuconostoc mesenteroides*, *Streptococcus faecalis*) and yeasts** are involved. They produce lactic acid, which imparts a sour taste and preserves the batter, and $CO_2$ gas, which causes the batter to rise and become fluffy.

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Cheese: — Cheese production is a multi-step process. First, milk is curdled using LAB starter cultures (for acid production) and an enzyme called rennet (for protein coagulation). The solid curd is then separated from whey. The subsequent ripening process involves specific bacteria and fungi that break down fats and proteins, developing characteristic flavors, aromas, and textures. For example, the large holes in Swiss cheese are due to $CO_2$ produced by *Propionibacterium shermanii*, while the blue veins in Roquefort cheese are from the fungus *Penicillium roqueforti*.

Benefits of Fermentation:

Enhanced Flavor and Aroma: — Production of various volatile compounds.
Increased Shelf Life: — Acids and alcohols inhibit spoilage microbes.
Improved Digestibility: — Breakdown of complex molecules.
Increased Nutritional Value: — Synthesis of vitamins (e.g., B12), increased bioavailability of minerals.

Probiotics: Many fermented foods, like fresh curd and yogurt, contain probiotics – live microorganisms that, when consumed in adequate amounts, confer a health benefit to the host. It's important to note that not all fermented foods are probiotic (e.g., baked bread).

Prelims Revision Notes

Microbes in Household Food Processing - NEET Revision Notes

I. General Principles of Fermentation:

Definition: — Anaerobic metabolic process where microorganisms convert carbohydrates into acids, gases, or alcohol.
Purpose: — Food preservation, flavor/texture enhancement, nutritional improvement.
Key Products: — Lactic acid, Carbon dioxide ($CO_2$), Ethanol.

II. Specific Food Products and Microbes:

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Curd/Yogurt:

* Microbes: Lactic Acid Bacteria (LAB) - *Lactobacillus* species (*L. acidophilus*, *L. bulgaricus*), *Streptococcus thermophilus*. * Process: LAB convert lactose (milk sugar) $\rightarrow$ lactic acid. * Effect: Lactic acid lowers pH, coagulates milk proteins (casein), gives tangy taste. Increases Vitamin B12. * Starter: Small amount of previous curd.

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Bread:

* Microbe: Baker's yeast - *Saccharomyces cerevisiae* (a fungus). * Process: Alcoholic fermentation of sugars in dough $\rightarrow$ $CO_2$ + ethanol. * Effect: $CO_2$ causes leavening (dough rising), creating porous texture. Ethanol evaporates during baking.

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Idli/Dosa:

* Microbes: Mixed culture of bacteria (*Leuconostoc mesenteroides*, *Streptococcus faecalis*) and yeasts. * Process: Fermentation of rice and black gram batter. * Effect: Production of lactic acid (sourness) and $CO_2$ (leavening/puffiness).

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Cheese:

* Initial Curdling: LAB (acid production) + Rennet (enzyme, primarily chymosin, coagulates casein). * Ripening: Specific microbes break down fats/proteins, develop flavor/texture. * Swiss Cheese: Large holes ('eyes') due to $CO_2$ produced by *Propionibacterium shermanii* (also gives nutty flavor).

* Roquefort Cheese: Blue veins, specific flavor from fungus *Penicillium roqueforti*. * Camembert Cheese: White rind, specific flavor from fungus *Penicillium camemberti*.

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Toddy:

* Microbes: Naturally occurring yeasts. * Process: Fermentation of palm sap $\rightarrow$ ethanol (alcoholic beverage).

III. Benefits of Microbial Fermentation:

Enhances flavor and aroma.
Increases shelf life (natural preservation).
Improves digestibility of food components.
Increases nutritional value (e.g., Vitamin B12 synthesis).

IV. Probiotics:

Definition: — Live microorganisms that, when consumed in adequate amounts, confer a health benefit to the host.
Examples: — Found in fresh curd, yogurt, kefir.
Distinction: — Not all fermented foods are probiotic (e.g., baked bread, where microbes are killed).

Vyyuha Quick Recall

To remember key microbes and their products:

Curd Loves Lactic Acid Bacteria (LAB) Bread Yeasts Create CO2 (Saccharomyces cerevisiae) Swiss Propionibacterium Shermanii Has Holes