FOOD2000 Chap.6 Postharvest Management and Cold Chains
Postharvest Management and Cold Chains
Postharvest management slows deterioration by controlling temperature, relative humidity, atmosphere, physical injury and exposure time across the whole supply chain. Cooling usually reduces respiration and microbial growth, but excessively low temperatures can injure susceptible commodities.
This chapter treats the cold chain as a sequence of linked control points and shows why one temperature reading cannot represent every product location or stage. Monitoring plans focus on likely slow-cooling zones and relate product history to quality observations rather than trusting a room set point.
What this chapter covers
- 01
Field heat removal and cooling rate
- 02
Cold-chain continuity
- 03
Relative humidity and water loss
- 04
Chilling and freezing injury
- 05
Modified and controlled atmospheres
- 06
Packaging, handling and monitoring
Worked example · free
Diagnose mixed quality in a pallet
- +1Treat product position as evidence of uneven exposure rather than random failure.
- +1Propose restricted airflow and slower removal of field or respiratory heat in the pallet centre.
- +1Map temperature at several positions over time and inspect stacking and vent alignment.
- +1Recommend a packaging, loading or airflow change and verify it in a repeated trial.
Key terms
- Cold chain
- Linked temperature-controlled stages from harvest through storage, transport, retail and use.
- Chilling injury
- Physiological damage caused when a susceptible commodity is held below its safe temperature but above freezing.
- Relative humidity
- Ambient water-vapour status relative to saturation at the same temperature, influencing produce water loss.
- Modified atmosphere
- A package or storage atmosphere whose gas composition differs from air and can change during storage.
Postharvest Management and Cold Chains FAQ
Why is lower temperature not always better?
Cooling slows many metabolic and microbial processes, but some tropical and subtropical commodities develop chilling injury below a commodity-specific threshold. The best condition balances deterioration control against physiological damage, freezing risk, energy use and the product's intended storage duration.
Why does relative humidity matter?
Fresh produce can lose water to the surrounding air, causing mass loss, wilting and texture decline. Higher relative humidity often reduces that gradient, but condensation and surface wetness can create other problems. Temperature, airflow, packaging and commodity susceptibility must therefore be considered together.
How should a cold-chain failure be investigated?
Map product temperature over time at multiple positions, not just room air or a single logger. Relate excursions to loading, rapid cooling, airflow, door opening, transport and retail stages. Pair the exposure record with commodity-specific quality measures, then test the proposed corrective action under comparable conditions.
What can modified atmosphere packaging get wrong?
The product continues to respire while gases move through the film, so package atmosphere depends on temperature, product load, surface area and film permeability. Oxygen that falls too low can promote fermentative metabolism and off-odours, while excess moisture can condense.
Verify the gas and quality response under the intended distribution conditions instead of assuming that a sealed or specially labelled pack automatically preserves freshness.
Exam move
Sketch the supply chain as control points and annotate each with temperature, time, humidity, atmosphere and injury risks. For scenario questions, distinguish room set point from product history. Practise balancing a benefit against a limit: cooling versus chilling injury, humidity versus condensation, and restricted gas exchange versus anaerobic metabolism. End with a monitoring plan that tests the recommendation.
Redraw the chain from harvest through rapid cooling, storage, transport, transfer, retail and consumer handling. At each stage identify the slowest expected heat-transfer location, the likely logger position and one event that can interrupt control. A current room reading is not a history, so practise reconstructing exposure from a time-temperature trace and linking each excursion to an operational event.
Compare cooling methods by mechanism rather than by name. Note how room, forced-air, water, vacuum and ice-based cooling differ in heat-transfer speed, water contact, package requirements, energy use and commodity tolerance. Give each method one plausible product and one reason it could be unsuitable elsewhere. Build commodity cards with a target range and a lower biological limit.
Explain that cooling usually slows respiration and growth, while temperatures below a safe threshold can cause chilling injury even above freezing. Add exposure duration because a short excursion and a prolonged hold may not cause the same damage. For moisture control, trace water-vapour gradients from tissue to air and connect them with mass loss, wilting and texture.
Then add the counter-risk of condensation and surface wetness. For atmosphere questions, distinguish active control from a package atmosphere that develops through product respiration and film permeability. State the benefit of reduced respiration and the failure mode of oxygen depletion or excessive carbon dioxide. Audit a fictional pallet using several product probes, not one accessible carton.
Pair the temperature record with firmness, colour, mass loss and decay at matched positions. If the centre performs worse, test airflow, vent alignment, stacking and loading geometry before blaming variety. End with a verification trial that compares the proposed process change under equivalent harvest maturity and package conditions.
