Lysozyme, a natural antimicrobial enzyme, occurs in which of the following sources in nature and foods?

Introduction:
Lysozyme is a muramidase that hydrolyzes the β-1,4 linkages between N-acetylmuramic acid and N-acetylglucosamine in bacterial peptidoglycan, weakening cell walls and exhibiting antimicrobial effects. This question explores its natural distribution across biological materials and organisms relevant to food protection and innate immunity.

Given Data / Assumptions:

• Lysozyme is found in animal secretions and certain biological matrices.
• It can be sourced for food preservation, especially from egg white.
• Related muramidase activities may be present in some microbes.

Concept / Approach:
Classic sources of lysozyme include egg white, tears, saliva, and milk. While bacteria are typically targets, some bacteria and bacteriophages also produce lysozyme-like enzymes (autolysins or phage lysozymes) to remodel or lyse cell walls. Therefore, across the listed options, lysozyme or lysozyme-like muramidase activity can be associated with each category, making the inclusive answer appropriate.

Step-by-Step Solution:
Step 1: Confirm presence in egg white where lysozyme is abundant and commercially extracted.Step 2: Recognize secretion-based presence in human and animal fluids such as tears and milk.Step 3: Note that lysozyme or muramidase-like enzymes are produced by certain bacteria and phages for cell-wall turnover or lysis.Step 4: Choose the comprehensive option including all three sources.

Verification / Alternative check:
Food biochemistry and immunology texts cite egg white and human secretions as rich sources; microbial muramidases are documented in bacterial cell-wall metabolism and bacteriophage infection cycles.

Why Other Options Are Wrong:

• egg white: True but not exhaustive.
• bacteria: Possible via autolysins/lysozymes but not the only source.
• tears & milk: True but incomplete alone.
• saliva only: Overly narrow; lysozyme is not restricted to saliva.

Common Pitfalls:
Assuming lysozyme exists only in animal secretions; overlooking microbial muramidases that perform similar biochemical functions.

Final Answer:
all of these