Food substrate properties: Which of the following are intrinsic (food-inherent) factors that govern microbial growth in foods?

Introduction / Context:
In food microbiology, microbial growth depends on both intrinsic (food-inherent) and extrinsic (environmental) factors. Recognizing intrinsic factors is essential for designing preservation strategies and predicting spoilage risk for different commodities.

Given Data / Assumptions:

• Intrinsic factors are those inherent to the food matrix itself.
• Candidate factors include pH, moisture (water activity), and redox potential (Eh).
• We must decide whether all listed features qualify as intrinsic.

Concept / Approach:
Key intrinsic factors include pH (acid–base status), water activity (available water for metabolism), redox potential (electron availability), nutrient content, natural antimicrobials, and biological structures (peels, rinds). All three listed factors—pH, moisture as aw, and Eh—are classic intrinsic determinants of which organisms can grow and at what rate within a given food.

Step-by-Step Solution:
Identify the nature of each factor: pH, aw, and Eh are properties of the food, not the storage environment. Relate each factor to microbial physiology: acid tolerance, osmotic stress, and respiratory metabolism. Since all are intrinsic, select the inclusive option.

Verification / Alternative check:
Textbook models such as the “hurdle” concept explicitly list pH, aw, and Eh among intrinsic hurdles that suppress or permit growth, often combined with extrinsic controls like temperature and modified atmospheres.

Why Other Options Are Wrong:

• Single-factor options are incomplete; “None of these” contradicts established theory.

Common Pitfalls:
Confusing extrinsic factors (e.g., storage temperature, relative humidity, gas atmosphere) with intrinsic ones; here, only food-inherent properties are considered.

Final Answer:
All of these are intrinsic factors.