Role of LAB — Revision Notes

⚡ 30-Second Revision

LAB (Lactic Acid Bacteria): — Gram-positive, non-spore-forming, ferment sugars to lactic acid.
Primary Product: — Lactic acid ($CH_3CH(OH)COOH$).
Process: — Lactic Acid Fermentation (anaerobic).
Key Examples: — Curd, yogurt, cheese (initial), dosa/idli batter, pickles, sauerkraut.
Benefits:

- Preservation: Lowers pH, inhibits spoilage/pathogens. - Texture: Coagulates milk proteins (casein). - Flavor: Contributes unique taste/aroma. - Nutrition: Synthesizes vitamins (e.g., B12), improves digestibility. - Probiotic: Enhances gut health, immunity.

Curdling: — Lactic acid $\rightarrow$ pH drop $\rightarrow$ Casein denaturation/coagulation.
Dosa/Idli: — LAB for sourness/preservation; Yeast for leavening ($CO_2$).

2-Minute Revision

Lactic Acid Bacteria (LAB) are a vital group of microorganisms in household food processing, primarily known for performing lactic acid fermentation. This anaerobic process converts sugars, like lactose in milk, into lactic acid.

The lactic acid produced significantly lowers the pH of the food, which has several crucial effects: it causes milk proteins (casein) to coagulate, forming the characteristic texture of curd and yogurt; it acts as a natural preservative by inhibiting the growth of spoilage and pathogenic microbes; and it contributes to the unique tangy flavors of fermented foods.

Beyond dairy, LAB are essential for products like dosa and idli batter (where they work with yeast), pickles, and sauerkraut. Their benefits extend to nutritional enhancement, including the synthesis of B vitamins and improved digestibility, and many LAB strains are recognized as probiotics, promoting gut health and immunity.

Understanding the core mechanism of lactic acid production and its multi-faceted impact on food is key for NEET.

5-Minute Revision

Lactic Acid Bacteria (LAB) are indispensable in household food processing, driving the transformation of raw ingredients into a diverse array of fermented products. At their core, LAB are Gram-positive, non-spore-forming bacteria that perform lactic acid fermentation, an anaerobic metabolic pathway where sugars are converted primarily into lactic acid.

For instance, in milk, LAB like *Lactobacillus* and *Streptococcus* species ferment lactose into lactic acid. This acidification is the cornerstone of their utility.

The drop in pH due to lactic acid production leads to the coagulation of milk proteins (casein), giving curd and yogurt their characteristic semi-solid texture. This acidic environment also serves as a potent natural preservative, inhibiting the growth of most spoilage microorganisms and foodborne pathogens, thereby extending the shelf life of fermented foods.

Furthermore, LAB contribute significantly to the complex flavor and aroma profiles of these products, producing compounds beyond just lactic acid.

Beyond preservation and flavor, LAB enhance the nutritional value of foods. They can synthesize B vitamins (e.g., B12), improve the bioavailability of minerals by degrading anti-nutritional factors, and break down complex nutrients, making them easier to digest (e.

g., lactose hydrolysis for lactose-intolerant individuals). Many LAB are also classified as probiotics, offering health benefits like improved gut microbiota balance, enhanced immunity, and alleviation of digestive issues.

Key examples of LAB-fermented foods include curd, yogurt, cheese (initial fermentation), dosa and idli batter (mixed fermentation with yeast), pickles, and sauerkraut. For NEET, remember the primary product (lactic acid), its effects (pH drop, protein coagulation, preservation), and the diverse applications and benefits.

Prelims Revision Notes

1
Definition: — Lactic Acid Bacteria (LAB) are a group of Gram-positive, non-spore-forming, facultative anaerobic or microaerophilic bacteria that produce lactic acid as the major end product of carbohydrate fermentation.
2
Metabolic Process: — Lactic Acid Fermentation. This is an anaerobic process where sugars (e.g., lactose, glucose) are converted to lactic acid. The overall reaction for homofermentative LAB is: $C_6H_{12}O_6 \rightarrow 2CH_3CH(OH)COOH$.
3
Primary Product: — Lactic Acid.
4
Key Genera: — *Lactobacillus*, *Streptococcus*, *Lactococcus*, *Pediococcus*, *Leuconostoc*.
5
Role in Milk Products (Curd, Yogurt, Cheese):

* LAB ferment lactose (milk sugar). * Produce lactic acid, lowering the pH of milk. * Low pH causes casein (milk protein) to denature and coagulate, forming curd/yogurt. * Example species: *Lactobacillus bulgaricus*, *Streptococcus thermophilus*.

1
Role in Other Foods:

* Dosa/Idli Batter: Mixed fermentation by LAB (e.g., *Leuconostoc mesenteroides*) and yeast. LAB contribute sourness and preservation; yeast produces $CO_2$ for leavening. * Pickles/Sauerkraut: LAB (e.g., *Lactobacillus plantarum*) ferment sugars in vegetables, producing lactic acid for preservation and flavor. * Sourdough Bread: Symbiotic culture of LAB and yeast.

1
Benefits of LAB Fermentation:

* Preservation: Lactic acid lowers pH, inhibiting spoilage and pathogenic microorganisms (e.g., *Salmonella*, *Staphylococcus aureus*). * Nutritional Enhancement: * Increases digestibility by breaking down complex molecules.

* Synthesizes vitamins (e.g., Vitamin B12, folate). * Reduces anti-nutritional factors (e.g., phytates). * Hydrolyzes lactose, beneficial for lactose-intolerant individuals. * Flavor and Aroma: Produces various compounds (e.

g., diacetyl, acetaldehyde) that contribute to unique taste profiles. * Probiotic Effects: Many LAB strains are probiotics, improving gut health, balancing microbiota, and enhancing immunity.

1
Distinguish from Alcoholic Fermentation: — LAB produce lactic acid; yeast produces ethanol and $CO_2$. LAB cause curdling; yeast causes leavening.

Vyyuha Quick Recall

Let All Bacteria Create Preservation, Nutrition, Flavor, Probiotics.

Lactic Acid Bacteria
Curdling (protein coagulation)
Preservation (low pH)
Nutrition (vitamins, digestibility)
Flavor (unique taste)
Probiotics (gut health)