Question

Incubation parameters to get thermophilic count are______

• A. 42°C for 24 hours
• B. 42°C for 48 hours
• C. 55°C for 24 hours
• D. 55°C for 48 hours

Hint:

Standard incubation parameters for milk quality testing:
- Psychrotrophic Count = 7°C for 10 days.
- Thermoduric Count = Lab pasteurization followed by 30°C for 48 hours.
- Thermophilic Count = 55°C for 48 hours.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Microorganisms are categorized into psychrotrophs, mesophiles, and thermophiles based on their optimum growth temperatures.
Thermophilic bacteria are organisms that grow at high temperatures, typically ranging from 45°C to 65°C, with an optimum growth temperature around 55°C.
In the dairy industry, thermophiles are important because they can survive pasteurization temperatures and multiply within processing equipment, such as pasteurizers.

Step 2: Detailed Explanation:
To assess the sanitary conditions of dairy processing plants, microbiological standards define specific protocols for determining the thermophilic count in milk.
The standard procedure involves plating the milk sample on Standard Plate Count Agar (PCA) to isolate and enumerate these organisms.
The selection of incubation parameters is critical to inhibit mesophilic growth while promoting the growth of thermophiles:
-Temperature:
An incubation temperature of \(55 \pm 1^\circ\text{C}\) is used. This high temperature effectively prevents the growth of mesophilic bacteria, ensuring that only true thermophilic species form colonies.
-Time:
An incubation period of 48 hours is required.
While some thermophiles grow rapidly, many species require a full 48 hours to develop visible, countable colonies on agar plates.
An incubation period of 24 hours is insufficient for accurate quantification, as many slow-growing colonies would be missed.
Therefore, the standard parameters for determining the thermophilic count are 55°C for 48 hours.

Step 3: Final Answer:
The standard incubation parameters used to determine the thermophilic count are 55°C for 48 hours.