Food microbiology factors: In predictive microbiology, “nutrient content” and “biological structures” (e.g., rinds, shells, peels) are classified as which type of factors affecting microbial growth in foods?

Introduction / Context:
Microbial growth in foods depends on intrinsic factors (properties of the food itself) and extrinsic factors (storage environment). Correctly categorizing variables helps design preservation strategies using the “hurdle” concept.

Given Data / Assumptions:

• Nutrient content is an inherent property of a food matrix.
• Biological structures (skins, shells, membranes) are also inherent barriers.
• We must choose the correct classification.

Concept / Approach:
Intrinsic factors include pH, water activity (aw), oxidation-reduction potential (Eh), nutrient content, natural antimicrobials, and biological structures. Extrinsic factors include temperature, relative humidity, and gas atmosphere during storage. Processing factors are interventions (heating, packaging). Therefore, nutrient content and biological structures are intrinsic.

Step-by-Step Solution:
List intrinsic vs extrinsic vs processing factors. Place nutrient content and protective structures under intrinsic. Select “Intrinsic factors.”

Verification / Alternative check:
Food microbiology texts consistently group these variables as intrinsic hurdles that influence what organisms can grow.

Why Other Options Are Wrong:

• Implicit: Not a standard category in predictive microbiology.
• Processing: Refers to applied treatments (e.g., pasteurization), not inherent properties.
• Extrinsic: Environmental conditions surrounding the food, not the food itself.

Common Pitfalls:
Confusing packaging atmosphere (extrinsic) with pre-existing internal barriers (intrinsic).

Final Answer:
They are intrinsic factors for microbial growth.