Question

What should be the temperature for pasteurization of fruit juices?

• A. 30-$40^\circ\text{C}$ for 20-30 minutes
• B. 50-$60^\circ\text{C}$ for 20-30 minutes
• C. 70-$80^\circ\text{C}$ for 20-30 minutes
• D. 85-$90^\circ\text{C}$ for 20-30 minutes

Hint:

Fruit Processing Thermal Standards:
- Fruit Juice Pasteurization (Batch): $85\text{--}90^\circ\text{C}$ for $20\text{--}30\text{ minutes}$.
- Flash Pasteurization (HTST): $88\text{--}92^\circ\text{C}$ for $15\text{--}30\text{ seconds}$.
- Sterilization of Non-Acid Vegetables: $115\text{--}121^\circ\text{C}$ under pressure.

Answer 1

The Correct Option is D

Concept:
Pasteurization is a mild thermal processing method applied to acidic fruit juices, beverages, and liquid food products to destroy pathogenic microorganisms and inactivate spoilage enzymes (such as pectin methylesterase and polyphenol oxidase).
Unlike total sterilization ($>100^\circ\text{C}$), pasteurization operates below the boiling point to preserve heat-sensitive vitamins, volatile aromas, and natural fresh flavors.
The time-temperature combination must be carefully controlled to ensure microbiological safety without degrading product quality.

Step 1: Thermal Resistance in Acidic Media:
Fruit juices naturally have a low pH ($\text{pH} < 4.5$), which inhibits the germination and growth of deadly spore-forming bacteria like Clostridium botulinum.
Therefore, the primary thermal targets in fruit juice processing are vegetative yeasts, molds, and lactic acid bacteria, along with native plant enzymes.

Step 2: Evaluating the Time-Temperature Standards:
- Commercial batch (holding) pasteurization of bottled fruit juices and squashes typically requires heating the product to $85^\circ\text{C}\text{ to }90^\circ\text{C}$ and holding it for $20\text{ to }30\text{ minutes}$ (or high-temperature short-time HTST at $90\text{--}95^\circ\text{C}$ for $15\text{--}30\text{ seconds}$).
- Lower temperatures such as $30\text{--}40^\circ\text{C}$ or $50\text{--}60^\circ\text{C}$ fail to inactivate pectolytic enzymes and do not eliminate heat-tolerant yeasts.
- While $70\text{--}80^\circ\text{C}$ is often used for milk pasteurization ($72^\circ\text{C}$ for $15\text{ s}$), complete enzyme inactivation in acidic fruit juices standardly requires $85\text{--}90^\circ\text{C}$.

Step 3: Final Answer:
Thus, the recommended temperature and duration for the pasteurization of fruit juices is $85\text{--}90^\circ\text{C}$ for $20\text{--}30\text{ minutes}$, which is option (D).