Understanding Respiration and Respiratory Climacteric in Fruits and Vegetables

Fruits and vegetables don’t stop living the moment they are picked. They keep breathing – consuming stored sugars, producing carbon dioxide, and releasing heat – just as they did while still attached to the plant. This ongoing process, called respiration, is one of the most important metabolic activities governing how quickly produce ages after harvest. Understanding respiration and a special phenomenon called the respiratory climacteric can help farmers, food scientists, and even home consumers make better decisions about harvesting, storing, and consuming fresh produce.

What is respiration in fruits and vegetables? 🔗

Respiration is a biochemical process in which complex organic molecules like carbohydrates, lipids, and organic acids are broken down to release the energy that living cells need to maintain their internal processes. In simple terms, produce takes in oxygen and uses it to convert stored sugars into carbon dioxide, water, and energy (released as heat). This energy, stored as ATP (adenosine triphosphate), fuels all the cellular activities that keep the tissue alive after harvest.

The overall equation for aerobic respiration can be summarised as:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (heat + ATP)

Every living cell of the fruit or vegetable carries out this reaction. However, unlike a growing plant on the field, harvested produce cannot replace its carbohydrate or water reserves. Once stored sugars and starches are exhausted through respiration, ageing and decay follow rapidly. This is precisely why respiration rate is so closely tied to shelf life.

Aerobic versus anaerobic respiration 🔗

Depending on the availability of oxygen in their surroundings, fruits and vegetables can respire in two fundamentally different ways.

Aerobic respiration 🔗

When sufficient oxygen is available – which is the normal scenario in open-air storage – produce undergoes aerobic respiration. This is the preferred and far more efficient pathway. Substrates such as glucose are completely oxidised, yielding maximum energy along with carbon dioxide and water as by-products. According to Felix Instruments, glucose is the preferred substrate, and other compounds like organic acids and lipids are typically converted to glucose before entering the respiratory pathway.

Not all the energy generated during aerobic respiration is captured as ATP. A significant portion – up to 60% in pre-harvest fruits and as much as 90% after harvest – is lost as heat of respiration. This heat can warm up produce in storage, which in turn accelerates further respiration and deterioration if cooling systems are inadequate.

Anaerobic respiration (fermentation) 🔗

When oxygen levels around the produce drop too low, cells switch to anaerobic respiration, also called fermentation. This pathway is much less efficient and produces ethanol and carbon dioxide instead of water. The accumulation of ethanol and other fermentation by-products leads to off-flavours, off-odours, tissue discolouration, and eventually cell death.

The FAO warns that when oxygen falls to around 2% or less, fermentation replaces normal respiration, and the resulting alcohol promotes premature ageing and unpleasant tastes. This is why proper ventilation during storage and transport is critical – produce needs enough oxygen to maintain aerobic respiration, but not so much that respiration rates stay unnecessarily high.

Why does respiration rate matter for shelf life? 🔗

The relationship between respiration rate and post-harvest life is straightforward: the faster produce respires, the sooner it deteriorates. Respiration consumes the very sugars, organic acids, and other reserves that give fruits and vegetables their flavour, nutritional value, and structural integrity.

Highly perishable produce like asparagus, broccoli, berries, and leafy greens have high respiration rates and therefore short shelf lives. In contrast, commodities such as apples, potatoes, cabbage, and pumpkins respire slowly and can be stored for weeks or even months under proper conditions.

Respiration also depletes flavour compounds directly. For instance, broccoli florets stored at 4°C for three weeks can lose half to two-thirds of their stored sugars through respiration – a change closely associated with yellowing and flavour loss.

Factors that influence respiration rate 🔗

Several environmental and biological factors affect how fast harvested produce respires.

Temperature 🔗

Temperature is the single most important external factor. As a general rule, for every 10°C rise in temperature within the physiological range (0-30°C), biological processes including respiration increase two- to three-fold. This is why refrigeration is so effective at extending shelf life – lowering the temperature dramatically slows down the metabolic engine of the produce. However, tropical and subtropical fruits like bananas, tomatoes, and mangoes can suffer chilling injury if stored below their tolerance threshold, so cooling must be species-specific.

Atmospheric composition 🔗

Reducing the oxygen concentration around produce can slow down respiration. This principle underlies controlled atmosphere (CA) storage and modified atmosphere packaging (MAP), both widely used in commercial supply chains. The oxygen level must drop below about 5% to meaningfully reduce respiration, but it should not go so low as to trigger anaerobic fermentation. Simultaneously, a moderate increase in carbon dioxide concentration helps inhibit both respiration and ethylene action.

Physical damage 🔗

Wounding, bruising, or cutting of produce increases respiration rates sharply. For example, sliced apple tissue can respire two to three times faster than an intact apple under the same conditions. Mechanical injury also stimulates ethylene production, which further accelerates ripening and senescence.

Type of tissue and maturity stage 🔗

Younger, actively growing tissues respire faster than mature ones. Similarly, the stage of maturity at harvest affects subsequent respiration patterns – especially in the case of climacteric fruits, discussed below.

The respiratory climacteric: a turning point in ripening 🔗

One of the most significant phenomena in fruit physiology is the respiratory climacteric – a dramatic, temporary surge in respiration rate that certain fruits exhibit at the onset of ripening. This spike signals the transition from maturation to ripening and is closely linked with a parallel burst in ethylene production.

According to the FAO’s post-harvest training manual, the start of ripening in climacteric fruits is accompanied by a rapid rise in respiration rate known as the respiratory climacteric. After this peak, respiration gradually slows as the fruit develops its characteristic flavour, aroma, colour, and texture.

Climacteric fruits 🔗

Climacteric fruits are those that can be harvested at the mature-but-unripe stage and will continue to ripen off the plant. Common examples include bananas, tomatoes, apples, mangoes, avocados, papayas, peaches, and melons.

The defining feature of climacteric ripening is the autocatalytic production of ethylene. As explained by the University of Maryland Extension, once ethylene production starts in a climacteric fruit, it triggers the production of even more ethylene – a positive feedback loop that rapidly accelerates ripening. This autocatalytic ethylene system (referred to as “system 2” in scientific literature) is unique to climacteric fruits and is what makes the respiratory spike so pronounced.

During the climacteric rise, several important changes happen simultaneously: starches convert to sugars, acids decrease, cell walls soften, green chlorophyll breaks down to reveal underlying pigments, and volatile aroma compounds are synthesised. These coordinated changes transform an unpalatable, hard, green fruit into something sweet, colourful, and fragrant.

Non-climacteric fruits 🔗

Non-climacteric fruits follow a very different pattern. They do not exhibit a respiratory burst or a surge in ethylene production during ripening. Instead, their respiration rate declines steadily after harvest. Examples include citrus fruits (oranges, lemons, grapefruits), grapes, strawberries, cherries, pineapples, and cucumbers.

Because non-climacteric fruits lack the autocatalytic ethylene mechanism, they must be harvested when they are already fully ripe. Their sugar and acid content does not improve after picking. This is why you can buy green bananas and expect them to ripen at home, but a sour orange will never become sweeter once removed from the tree.

It is worth noting that while non-climacteric fruits produce small amounts of ethylene and do respond to external ethylene exposure to some extent, research published in the Journal of Experimental Botany suggests these responses are far less dramatic compared to climacteric species.

The role of ethylene in the climacteric process 🔗

Ethylene (C₂H₄) is a gaseous plant hormone that plays a central role in fruit ripening, particularly in climacteric species. Two distinct ethylene production systems operate during fruit development:

System 1 operates during the immature and pre-climacteric stages. It produces low, basal levels of ethylene and is self-inhibiting – meaning the presence of ethylene actually suppresses further ethylene production. This system is present in both climacteric and non-climacteric fruits.

System 2 kicks in at the onset of ripening in climacteric fruits only. It is autocatalytic – ethylene stimulates the production of even more ethylene, creating the characteristic burst. According to a review in Horticulturae, this positive feedback mechanism maintains the ethylene peak until the fruit reaches an overripe state.

Ethylene’s effects on ripening are wide-ranging: it triggers chlorophyll degradation (colour change), activates enzymes that soften cell walls, promotes the conversion of starches to sugars, and stimulates the synthesis of flavour and aroma volatiles. In commercial settings, these properties are exploited through artificial ripening rooms where fruits like bananas and mangoes are exposed to controlled ethylene concentrations to ensure uniform ripening.

Practical applications: managing respiration and the climacteric 🔗

Understanding respiration patterns has direct implications for how produce is harvested, transported, and stored.

Harvest timing 🔗

Climacteric fruits can be picked at the mature-green stage and ripened later using ethylene treatment. This flexibility is enormously valuable for long-distance trade – bananas shipped from tropical countries, for example, are harvested green and ripened at destination markets. Non-climacteric fruits, on the other hand, must be harvested at or near peak ripeness, making their logistics more challenging.

Temperature management 🔗

Rapid cooling after harvest (pre-cooling) is one of the most effective ways to slow respiration. Each 10°C drop in temperature can approximately double or triple the storage life of most produce. However, species-specific temperature thresholds must be respected to avoid chilling injury in sensitive crops.

Controlled and modified atmosphere storage 🔗

By reducing oxygen levels to 1-5% and increasing carbon dioxide to 1-5%, controlled atmosphere storage slows respiration, delays ethylene production, and inhibits the growth of decay-causing organisms. This technology is widely used for long-term storage of apples, pears, and kiwifruit. Modified atmosphere packaging applies the same principle at a smaller scale for retail products like pre-packaged salad mixes.

Ethylene management 🔗

For climacteric produce, controlling ethylene exposure is key. Ethylene scrubbers and absorbents (such as potassium permanganate sachets) can be placed in storage rooms to delay premature ripening. Conversely, ethylene generators are used in ripening rooms when uniform and timely ripening is desired. The chemical 1-methylcyclopropene (1-MCP), sold commercially under brand names like SmartFresh, blocks ethylene receptors on fruit cells, effectively preventing the fruit from responding to ethylene and thereby extending storage life.

Separating produce wisely 🔗

Because climacteric fruits release ethylene that can accelerate ageing in nearby produce, it is important to store ethylene-producing items (like apples and bananas) separately from ethylene-sensitive items (like lettuce, broccoli, and cucumbers). This simple practice can significantly reduce waste, both in commercial cold chains and in your home refrigerator.

Emerging nuances in the climacteric classification 🔗

While the classification of fruits into climacteric and non-climacteric categories is useful, recent research shows that the boundary between the two groups is not always sharp. Some fruits, such as certain melon cultivars, Asian pears, and some plum varieties, can display both climacteric and non-climacteric behaviour depending on the genotype. Strawberries and grapes, traditionally classified as non-climacteric, have been found to harbour active ethylene receptors and respond to exogenous ethylene to varying degrees. These findings suggest that ethylene plays a more universal role in fruit ripening than previously thought, and that the binary classification may be an oversimplification of a more complex biological spectrum.

What do you think? Now that you know how respiration drives the post-harvest life of produce, could you use this knowledge to rethink how you store fruits and vegetables at home? And for those working in the food supply chain – how might more precise control of temperature, atmosphere, and ethylene change the economics of fresh produce distribution?

References

1. https://felixinstruments.com/blog/fruit-respiration-impact-on-fruit-quality/
2. https://www.fao.org/4/t0073e/t0073e02.htm
3. https://www.postharvest.net.au/postharvest-fundamentals/vegetable-physiology/respiration/
4. https://felixinstruments.com/blog/oxygen-in-post-harvest-monitoring-control/
5. https://extension.umd.edu/resource/ethylene-and-regulation-fruit-ripening
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3550874/
7. https://www.mdpi.com/2311-7524/10/8/840
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC4006172/