🍲 Low Temperature Preservation

This lesson explains core food science and nutrition concepts with practical relevance to food quality, safety, and human health.

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Low Temperature Preservation

Principles

Low temperature preservation slows down the rate of microbial growth, enzymatic reactions, and chemical deterioration in foods. While it does not destroy microorganisms (unlike thermal processing), it significantly retards their metabolism and multiplication. The lower the temperature, the slower the rate of deterioration.

The Q10 value represents the factor by which the rate of a reaction increases for every 10 degree C rise in temperature. For most spoilage reactions, Q10 ranges from 2 to 3, meaning that lowering the temperature by 10 degree C approximately halves the spoilage rate.

Refrigeration (Chilling)

Chilling involves storing food at temperatures between 0 and 7 degree C. At these temperatures, the growth of most pathogenic bacteria is significantly reduced, though psychrotrophic organisms (e.g., Listeria monocytogenes, Pseudomonas) can still grow slowly.

Applications include short-term storage of fresh fruits and vegetables, dairy products, meat, fish, and prepared foods. The shelf life of refrigerated foods ranges from a few days to several weeks depending on the product.

Modified Atmosphere Packaging (MAP) — combining refrigeration with altered gas composition (reduced O2, elevated CO2) significantly extends shelf life of fresh produce, meat, and bakery products.

Freezing

Freezing involves reducing the temperature of food to -18 degree C or below, converting most of the water into ice crystals and making it unavailable for microbial growth and chemical reactions.

Rate of Freezing

• Slow freezing — produces large ice crystals that damage cell structure, leading to drip loss and textural changes upon thawing
• Quick freezing — produces small, uniform ice crystals that cause minimal cell damage; preferred for quality retention

IQF (Individually Quick Frozen)

IQF is a method where individual pieces of food (peas, corn kernels, shrimp, berries) are frozen separately in a blast freezer or fluidized bed freezer at -30 to -40 degree C. Each piece freezes individually, preventing clumping and allowing consumers to use desired quantities without thawing the entire pack.

Cold Chain Management

The cold chain refers to the unbroken series of refrigerated production, storage, and distribution activities that maintain the desired low temperature range from producer to consumer. A break in the cold chain leads to temperature abuse, accelerated microbial growth, and food safety hazards.

Key components include pre-cooling at farm level, refrigerated transport, cold storage warehouses, and retail display refrigeration. In India, the National Centre for Cold Chain Development (NCCD) works to strengthen cold chain infrastructure, particularly for perishable agricultural commodities. Approximately 25–30% of India's fruit and vegetable production is lost post-harvest, largely due to inadequate cold chain facilities.

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Low temperature preservation — refrigeration, freezing, IQF, and cold chain management.
Section context	Revise this lesson with the rest of Principles of Food Science and Nutrition for stronger conceptual continuity.