Question

Peptonising bacteria leads to ropiness in milk through production of ________ from nitrogenous substances.

• A. Lignin
• B. Pectins
• C. Peptones
• D. Mucins

Hint:

Ropiness pathways in milk:
- From Carbohydrates $\rightarrow$ Gums/Polysaccharides (e.g., Alcaligenes viscolactis).
- From Proteins (Nitrogenous) $\rightarrow$ Mucins (via proteolytic/peptonizing bacteria like Bacillus spp.).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Ropiness is a major physical defect in milk characterized by an increase in viscosity, where the milk becomes slimy and can be drawn into long, elastic threads.
This defect is caused by the metabolic activities of specific bacterial contaminants.
Detailed Explanation:
Ropiness in milk generally occurs through two distinct pathways:
1. Polysaccharide-mediated ropiness: Caused by organisms like Alcaligenes viscolactis, which synthesize extracellular capsular gums and mucopolysaccharides from milk carbohydrates.
2. Proteolytic (or Peptonizing) ropiness: Caused by peptonizing bacteria, which are primarily proteolytic species of Bacillus, Micrococcus, or Pseudomonas.
These bacteria produce extracellular proteolytic enzymes that hydrolyze casein (the primary nitrogenous substance in milk).
Instead of carrying out complete proteolysis, they break down casein into intermediate nitrogenous complexes, specifically highly viscous glycoproteins known as mucins (or mucin-like substances).
These sticky, gelatinous mucins accumulate in the milk, altering its rheological properties and causing a slimy, ropey consistency.
Let us review the other options:
- Lignin and Pectins are plant-derived structural carbohydrates and are not produced in milk.
- Peptones are simple, soluble, low-molecular-weight protein cleavage products that do not form the highly viscous networks required to produce the characteristic ropey texture.

Step 2: Final Answer:
Peptonizing bacteria lead to ropiness by producing mucins from nitrogenous substances.