Common Storage Disorders in Horticultural Produce

Every year, billions of kilograms of fruits and vegetables are lost after harvest – not due to pests or diseases, but because of poor storage conditions. Temperature swings, incorrect humidity, and exposure to harmful gases can trigger a range of storage disorders that silently degrade produce quality from the inside out. These are not infections caused by fungi or bacteria; they are physiological disorders, meaning the produce itself breaks down due to environmental stress. Understanding these disorders is essential for farmers, cold-chain managers, and food scientists who want to reduce postharvest losses and keep produce market-ready.

What are storage disorders? 🔗

Storage disorders are quality defects that develop in harvested fruits and vegetables when they are kept under suboptimal environmental conditions. Unlike pathological diseases (caused by microorganisms), storage disorders arise from physiological stress – the produce’s own cells malfunction in response to temperature extremes, improper humidity, or harmful atmospheric gases.

According to the University of Maine Cooperative Extension, postharvest losses of horticultural crops due to improper storage and handling can range from 10 to 40 percent. Fresh fruits and vegetables are living tissues that continue to respire, ripen, and eventually undergo senescence (cell death) after harvest. The speed of this deterioration depends heavily on storage temperature and relative humidity. When either of these factors falls outside the optimal range, physiological disorders are triggered.

The key storage factors involved include:

Temperature – both excessively high and low temperatures disrupt cellular metabolism. Humidity – too much moisture promotes condensation and rot, while too little causes shrivelling. Atmospheric gases – exposure to ammonia, excessive CO₂, or very low O₂ concentrations can cause tissue damage. Light exposure – light triggers unwanted chemical changes in certain crops, most notably potatoes.

Chilling injury: the cold that harms 🔗

One of the most widespread storage disorders is chilling injury (CI). It occurs when tropical and subtropical produce is stored at temperatures above freezing but below the crop’s tolerance threshold. This is not the same as freezing damage – no ice crystals form. Instead, the cold gradually disrupts cell membrane function, leading to a cascade of visible and internal defects.

How chilling injury develops 🔗

At the cellular level, low temperatures cause the lipid membranes of plant cells to shift from a flexible, fluid state to a rigid, gel-like phase. This change impairs the membrane’s ability to regulate what enters and exits the cell. As a result, enzymes and substrates that are normally kept in separate cell compartments mix together, triggering browning reactions and tissue breakdown. Research published in Frontiers in Plant Science highlights that solanaceous vegetables like tomatoes, peppers, and eggplants are particularly sensitive to temperatures below 12°C.

Common symptoms of chilling injury 🔗

Symptoms vary by crop but commonly include surface pitting (small sunken spots), internal browning or discoloration, water-soaked or translucent patches on the skin, failure to ripen properly, development of off-flavours, and increased susceptibility to fungal and bacterial decay. Bananas stored below about 14°C can develop greyish-brown peel discoloration and fail to ripen. Citrus fruits may show peel pitting and brown staining. Tomatoes lose flavour and develop surface lesions when stored below 10-12°C.

A critical challenge with chilling injury is that symptoms often do not appear while the produce is still in cold storage. They become visible only after the produce is transferred to warmer temperatures for marketing or consumption, as noted by the FAO postharvest handling guidelines. This delay makes early detection difficult and can lead to significant economic losses at the retail stage.

Greening of potatoes 🔗

Potato greening is one of the most recognisable storage disorders and a significant food safety concern. When harvested potato tubers are exposed to natural or artificial light during storage, their skin turns green. This colour change is caused by chlorophyll formation – a harmless pigment on its own. However, the real problem lies in what accompanies it.

Solanine: the hidden toxin 🔗

Light exposure simultaneously triggers the production of solanine (α-solanine), a toxic glycoalkaloid that develops in and just beneath the potato skin. According to the University of Alaska Fairbanks Cooperative Extension, the green colour serves as a visual indicator that solanine may be present, though the two processes (chlorophyll and solanine synthesis) are technically separate.

Solanine acts as a natural defence mechanism for the potato plant, protecting it against insects and herbivores. In humans, consuming potatoes with high solanine levels can cause gastrointestinal symptoms such as nausea, vomiting, and diarrhoea. In rare, severe cases – particularly when potatoes are heavily greened and consumed in large quantities – neurological symptoms have been documented. The North Dakota State University Extension notes that solanine is present in all parts of the potato plant, with the highest concentrations in sprouts and green-skinned tubers.

Factors that accelerate greening 🔗

Several factors influence the rate and severity of potato greening. Light intensity and duration are the primary triggers – even 24 to 48 hours of direct light exposure can initiate greening. White-skinned potato varieties tend to green more readily than red or russet types. Immature and freshly harvested tubers with thin, unsettled skin are more vulnerable. Higher storage temperatures (around 20°C versus 5°C) also accelerate the process. Modern transparent packaging, while preferred by consumers who want to inspect produce before buying, unfortunately increases light exposure during retail display.

Prevention strategies 🔗

Preventing potato greening is straightforward: store tubers in complete darkness at cool temperatures (7-10°C for table potatoes) with good air circulation. During cultivation, proper hilling (mounding soil around plants) protects developing tubers from sunlight. In retail settings, using opaque packaging materials and limiting display duration under bright lights can significantly reduce greening. Peeling the affected skin and cooking can reduce solanine content by 30-40%, but heavily greened potatoes should be discarded.

Internal breakdown in sweet potatoes 🔗

Sweet potatoes are a tropical crop, and their roots are highly sensitive to cold storage. Internal breakdown is a chilling-related disorder that develops when sweet potato roots are held at temperatures below approximately 12-13°C. This makes sweet potatoes one of the more delicate crops in cold-chain management.

Symptoms and progression 🔗

The UC Davis Postharvest Technology Center describes the key symptoms of chilling injury in sweet potatoes as internal pulp browning, fungal decay, root shrivelling, and the development of hard cores that persist even after cooking. Externally, the roots may show sunken, pitted areas on the surface. Internally, the flesh can range from brown to black discoloration – a stark contrast to the normal orange or white colour.

According to research from the Alabama Cooperative Extension System, short periods at temperatures as low as 10°C may not cause immediate damage, but after several days at or below this threshold, the injury becomes evident. What makes this disorder particularly problematic is that symptoms may not be immediately visible. Internal breakdown can progress silently in cold storage and become apparent only when the roots are cut open or cooked.

The role of curing 🔗

Proper curing is the most effective preventive measure for internal breakdown. Curing involves holding freshly harvested sweet potatoes at 25-32°C with high relative humidity (above 90%) for several days to a week. This process promotes wound healing, toughens the periderm (skin), and prepares the roots for long-term storage. After curing, sweet potatoes should be stored at 12.5-15°C with 85-90% relative humidity. Under these conditions, a storage life of 6 to 10 months is achievable.

Temperatures above 16°C, on the other hand, increase respiration and sprouting rates, which also reduces storage quality. This narrow optimal window (12.5-15°C) is what makes sweet potato storage particularly challenging compared to many other root crops.

Ammonia injury in onions 🔗

Ammonia injury is a less commonly discussed but practically important storage disorder, particularly in large-scale cold storage facilities that use ammonia-based refrigeration systems. When there is a leak in the cooling system, ammonia gas can come into direct contact with stored produce.

How ammonia damages onions 🔗

Onions are especially vulnerable to ammonia exposure during storage. The UC Davis Postharvest Technology Center describes ammonia injury in dry onions as the development of brown-black blotches on the bulb surface, caused by gas leakage during cold storage. Ammonia reacts with the moisture on the onion’s outer scales and tissue, causing a chemical burn that destroys cells and leads to dark, necrotic patches.

This type of injury is entirely preventable through proper maintenance of refrigeration equipment. However, when it does occur, the damage can be extensive – affecting large quantities of stored onions simultaneously if the leak goes undetected. Ammonia-injured onions become unmarketable due to their discoloured appearance and are also more susceptible to secondary infections by fungi and bacteria.

Broader ammonia risks in cold storage 🔗

Ammonia injury is not limited to onions. Any produce stored in facilities using ammonia refrigerants is at risk if a leak occurs. Beyond produce damage, ammonia leaks also pose a serious health hazard to workers. A case report published in PMC documented a worker at a potato storage plant who suffered severe respiratory and neurological injury after exposure to ammonia from a broken coolant pipeline. This underscores the importance of regular equipment inspections, ammonia leak detection systems, and emergency response protocols in cold storage facilities.

Other notable storage disorders 🔗

Superficial scald in apples 🔗

Superficial scald is a significant cold storage disorder in apples and pears. It appears as irregular brown or black patches on the fruit skin after several months of cold storage. The disorder is linked to the oxidation of a natural compound called α-farnesene, which accumulates in the waxy skin layer during storage and breaks down into conjugated triene hydroperoxides that cause cell death. Controlled atmosphere storage with reduced oxygen levels can help mitigate scald.

Blackheart in potatoes 🔗

Blackheart develops when potato tubers are stored in poorly ventilated environments with insufficient oxygen. The internal tissue turns black due to the death of cells at the tuber’s centre. This happens because the outer cells consume all available oxygen, leaving the interior oxygen-starved. High storage temperatures that increase respiration rates can worsen the problem.

Russet spotting in lettuce 🔗

Exposure to ethylene gas during storage causes small, rust-coloured spots on lettuce leaves. Ethylene can accumulate in mixed storage environments where ethylene-producing fruits like apples or bananas are kept alongside ethylene-sensitive vegetables. Proper ventilation and separation of ethylene producers from sensitive crops prevents this disorder.

General prevention measures for storage disorders 🔗

While each disorder has specific triggers, several overarching principles apply to minimising storage disorders across horticultural produce.

Maintain optimal temperature – this is the single most important factor. Cool-season crops (lettuce, carrots, broccoli) generally store well at 0-2°C, while warm-season and tropical crops (tomatoes, sweet potatoes, bananas) require higher temperatures (10-15°C). Always match the storage temperature to the crop’s specific requirements.

Control relative humidity – most produce stores best at 85-95% relative humidity. Use humidifiers, wet floor systems, or evaporative cooling to maintain appropriate levels. Monitor humidity with hygrometers rather than relying on visual assessment of the produce.

Ensure proper ventilation – adequate air circulation removes excess CO₂, prevents oxygen depletion, and disperses ethylene gas. Poor ventilation is a direct contributor to blackheart, off-flavour development, and accelerated senescence.

Eliminate light exposure – for crops like potatoes and onions, storage in complete darkness is essential to prevent greening and sprouting respectively.

Inspect and maintain refrigeration systems – regular checks of ammonia-based cooling equipment prevent gas leaks that can damage both produce and human health.

Cure roots and tubers properly – sweet potatoes, yams, and similar crops benefit enormously from a proper curing period before long-term storage.

Why understanding storage disorders matters 🔗

Globally, around 1.3 billion tonnes of food are lost or wasted every year, and a significant share of this occurs during postharvest storage and handling. For horticultural produce, losses from storage disorders are not just an economic problem – they affect food security, nutritional availability, and the livelihoods of millions of farmers, especially in developing countries where cold-chain infrastructure is limited.

By understanding the specific causes and symptoms of storage disorders – from chilling injury and potato greening to ammonia damage and internal breakdown – stakeholders across the supply chain can make informed decisions about storage conditions, equipment maintenance, and crop handling. The goal is not perfection, but consistent management of the key variables: temperature, humidity, ventilation, and atmospheric composition.

What do you think? How can smallholder farmers in tropical regions, who often lack access to cold storage facilities, protect their produce from storage disorders? And could emerging low-cost technologies like evaporative cooling chambers offer a viable solution for reducing postharvest losses at the farm level?

References

1. https://extension.umaine.edu/publications/4135e/
2. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1488666/full
3. https://www.fao.org/4/ae075e/ae075e14.htm
4. https://www.uaf.edu/ces/publications/database/food/greening-of-potatoes.php
5. https://www.ndsu.edu/agriculture/extension/publications/garden-table-my-potatoes-turned-green-now-what
6. https://postharvest.ucdavis.edu/produce-facts-sheets/sweet-potato
7. https://www.aces.edu/blog/topics/lawn-garden/harvesting-and-curing-sweet-potatoes/
8. https://postharvest.ucdavis.edu/produce-facts-sheets/onions-dry
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC9577859/