Microbiology

Step 1: Understand the concept of rancidity.
Rancidity refers to the spoilage of fats and oils in foods, often resulting in bad odor and taste. It is primarily due to the breakdown of lipids.
Step 2: Identify the role of lipolytic microbes.
Lipolytic microbes produce lipase enzymes that hydrolyze triglycerides (fats) into glycerol and free fatty acids. The release and oxidation of fatty acids cause rancid odors and flavors.
Step 3: Eliminate incorrect options.
Proteolytic enzymes break down proteins, not fats.
Photosynthetic microbes do not cause spoilage.
Saccharolytic microbes break down sugars, leading to fermentation, not rancidity.
Thus, rancidity is primarily associated with the action of lipolytic microbes.

Step 1: Analyze the function of each culture medium.
Mannitol salt agar is selective and differential, not enriched. It selects for staphylococci and differentiates based on mannitol fermentation.
MacConkey (MAC) agar contains bile salts and crystal violet—not eosin Y or methylene blue. It inhibits gram-positive bacteria and differentiates lactose fermenters.
Blood agar is a differential medium that differentiates bacteria based on their hemolytic properties (alpha, beta, gamma hemolysis) due to production of hemolysins.
EMB agar (Eosin Methylene Blue agar) does contain eosin Y and methylene blue—not bile salts or crystal violet.
Step 2: Conclude the correct statement.
Only statement (3) correctly describes blood agar as a differential medium based on hemolysin production.