Question Bank • QB_DFE_EXP_051 MSQ • 2 Marks

Section 7: Dairy and Food Engineering

Preservation of Food

Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods

Question Statement:

Which of the following factors increase the thermal resistance ($D$-value) of bacterial spores in food processing?

Options:

  • (A) Presence of high concentrations of fats and oils in the food matrix
  • (B) Neutral $pH$ ($pH \approx 7.0$) compared to acidic $pH$ ($pH < 4.5$)
  • (C) High concentration of dissolved sucrose or solutes (low water activity)
  • (D) Addition of strong organic acids reducing $pH$ below 4.0

Answer Key:

A, B, C

Step-by-Step Solution & Explanation

Factors increasing microbial thermal resistance: • Lipids/fats provide a protective hydrophobic coating reducing local water availability (A). • Neutral $pH$ offers maximal heat resistance; acidic $pH$ (
lt;4.5$) synergistically destroys spores (B is TRUE, D is FALSE). • Sugars and low $a_w$ protect against thermal protein denaturation (C).
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