UNIT 2.2.4

Respiration & Post-Harvest Physiology

Managing the breath of harvested produce

🎯 After this unit, you will be able to:

Explain why harvested produce continues to respire
Classify fruits by their respiration patterns (climacteric vs. non-climacteric)
Describe how temperature, gases, and humidity affect storage life
Apply this knowledge to extend shelf life of horticultural products

🍎 Life After Harvest

After harvest, fruits, vegetables, and other plant parts remain alive. They continue to respire, using stored carbohydrates (sugars, starches) and organic acids as fuel. This post-harvest respiration is the single most important factor determining storage life and quality .

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + heat + ATP

Key insight: Post-harvest storage is essentially a race against time—we try to slow respiration as much as possible without causing injury, preserving sugars, acids, and quality for as long as possible .

⚡ Why Respiration Matters After Harvest

Respiration after harvest leads to:

Loss of substrates: Sugars and starches are consumed → loss of sweetness, flavor, and energy reserves
Water loss: Transpiration continues, leading to shriveling and weight loss
Heat production: Respiratory heat can warm produce, accelerating deterioration
Quality changes: Texture softens, colors change, nutrients decline
Senescence: Eventually, tissues age and die

📊 Did you know? A single pallet of apples can generate 300-500 watts of heat from respiration—enough to raise the temperature of a cold room significantly if not removed by refrigeration .

📊 Classification by Respiration Rate

Different horticultural products have very different respiration rates, which determines their storage potential:

Class	Respiration rate (mg CO₂/kg·hr at 5°C)	Examples	Typical storage life
Very low	< 10	Nuts, dried fruits	Months to years
Low	10-20	Apple, pear, citrus, potato, onion	Months
Moderate	20-40	Tomato, peach, plum, apricot	Weeks
High	40-60	Strawberry, raspberry, mushroom	Days to 1 week
Very high	> 60	Asparagus, broccoli, pea	1-3 days

📈 [Graph: Respiration rates of different commodities at various temperatures — to be inserted]

General rule: The higher the respiration rate, the shorter the storage life. This is why leafy greens (high respiration) spoil quickly, while apples (low respiration) can store for months .

🍌 Climacteric vs. Non-Climacteric Fruits

Fruits are classified by their respiratory pattern during ripening:

🍎

Climacteric fruits

Show a dramatic rise in respiration (and ethylene production) during ripening. Can be harvested mature and ripened off the plant.

Examples: Apple, banana, tomato, mango, pear, avocado, papaya

🍇

Non-climacteric fruits

Respiration gradually declines after harvest. Must ripen on the plant; will not improve after harvest.

Examples: Citrus, grape, strawberry, cherry, pineapple

📈 [Graph: Respiration patterns of climacteric vs non-climacteric fruits — to be inserted]

Why This Matters for Post-Harvest Management

Climacteric fruits: Can be harvested green, stored for months, then ripened with ethylene when needed. Examples: bananas for export, winter pears .
Non-climacteric fruits: Must reach full flavor on the plant. They don't improve after harvest, so harvest timing is critical .

🍌 Banana Ripening Rooms

Bananas are harvested green, shipped at 13-14°C, then ripened at destination in special rooms with:

Ethylene gas: 100-150 ppm for 24-48 hours triggers the climacteric rise
Temperature control: 15-18°C for slow, even ripening
Humidity: 90-95% to prevent water loss

This system allows bananas to be available year-round, ripened exactly to consumer preference .

🌡️ Factors Affecting Post-Harvest Respiration

1. Temperature

Temperature is the most important factor. Respiration roughly doubles for every 10°C increase (Q₁₀ ≈ 2-3). This is the basis for cold storage .

❄️

Optimal storage temperatures

Apple: 0-3°C
Banana: 13-14°C
Potato: 4-10°C
Tomato: 10-12°C
Leafy greens: 0-2°C

⚠️

Chilling injury

Temperatures below optimal for that commodity cause membrane damage, electrolyte leakage, and increased respiration (stress response).

Susceptible: Banana (<13°C), tomato (<10°C), cucumber (<7°C)

2. Atmospheric Composition

Controlled Atmosphere (CA) storage modifies O₂ and CO₂ levels:

Low O₂ (1-3%): Slows respiration by limiting the electron transport chain
Elevated CO₂ (1-5%): Inhibits some enzymes, including those in the Krebs cycle
Typical air is 21% O₂, 0.03% CO₂—so CA dramatically changes the atmosphere

🍎 Did you know? Some apple varieties can be stored for 10-12 months in controlled atmosphere—that's why you can buy apples year-round! Without CA, they'd last only 2-3 months .

3. Humidity

High humidity (90-95%) reduces water loss, but too high (>98%) promotes fungal growth. Most produce is stored at 85-95% RH .

4. Ethylene

Ethylene accelerates respiration and ripening in climacteric fruits. Even tiny amounts (0.1 ppm) can trigger responses. Management strategies include:

Removing ethylene from storage rooms (using KMnO₄ scrubbers, catalytic converters)
1-MCP treatment to block ethylene receptors
Separating ethylene producers (apples) from ethylene-sensitive produce (leafy greens)

5. Physical damage

Bruising, cutting, and wounds increase respiration dramatically as tissues mount stress responses and repair damage. This is why careful handling is essential .

📏 Respiratory Quotient (RQ) in Storage

The respiratory quotient (RQ = CO₂ produced / O₂ consumed) indicates which substrates are being used:

Substrate	RQ value	Example
Carbohydrates	1.0	Most fruits and vegetables
Organic acids	> 1.0 (up to 1.5)	Citrus, apples during senescence
Fats/lipids	< 1.0 (0.7-0.8)	Nuts, seeds, avocado

Monitoring RQ in storage can detect problems:

RQ rising above 1.0 suggests shift from sugars to acids—may indicate stress or senescence
RQ < 1.0 suggests fermentation (anaerobic conditions)—bad! Causes off-flavors

🍐 Dynamic Controlled Atmosphere

Modern CA storage sometimes uses dynamic controlled atmosphere where O₂ levels are reduced until RQ just starts to rise (indicating the lower limit of tolerance). This maximizes storage life while avoiding anaerobic damage .

🔧 Post-Harvest Technologies

❄️

Refrigerated storage

Slows all metabolic processes. Most common and essential technology.

🌬️

Controlled atmosphere (CA)

Reduces O₂, increases CO₂. Used for apples, pears, kiwifruit.

📦

Modified atmosphere packaging (MAP)

Plastic films create modified atmosphere through respiration. Used for fresh-cut produce, berries.

🧪

1-MCP (SmartFresh™)

Blocks ethylene receptors, delaying ripening. Used for apples, pears, tomatoes.

💧

Edible coatings

Waxes, chitosan create barrier to gas exchange. Used for citrus, apples, cucumbers.

🌡️

Heat treatments

Brief hot water or air kills pathogens, can induce stress resistance.

📊 [Diagram: Effects of CA storage on respiration rate over time — to be inserted]

🇪🇹 Post-Harvest Challenges in Ethiopia

Common Losses

Post-harvest losses in Ethiopia are estimated at 20-40% for many horticultural crops due to:

Limited cold chain infrastructure
Rough handling during transport
Lack of proper storage facilities
Mixed storage (ethylene producers with sensitive produce)

Opportunities

Zero-energy coolers: Evaporative cooling using charcoal and water can reduce temperatures 10-15°C in dry areas
Improved storage: Simple improvements like ventilated crates, shade, and careful handling
Value addition: Drying, processing of surplus

🥭 Mango Export from Ethiopia

Ethiopian mango exporters face long shipping times to Middle Eastern and European markets. Success requires:

Harvesting at correct maturity (firm, mature-green for climacteric varieties)
Rapid cooling to 13°C within hours of harvest
Temperature control throughout transport
Ethylene management during shipping

Understanding the climacteric nature of mangoes allows exporters to deliver fruit that ripens properly at destination .

📌 Summary: Optimal Storage Conditions

Commodity	Temperature (°C)	RH (%)	CA conditions	Storage life
Apple	0-3	90-95	1-3% O₂, 1-5% CO₂	3-12 months
Banana (green)	13-14	90-95	2-5% O₂, 2-5% CO₂	2-4 weeks
Tomato (mature green)	12-15	85-90	3-5% O₂, 3-5% CO₂	2-4 weeks
Potato	4-10	90-95	Not common	4-9 months
Leafy greens	0-2	95-100	1-3% O₂, 5-10% CO₂	1-3 weeks

Reflection question: A smallholder farmer in Ethiopia grows tomatoes for the local market. During harvest season, she loses about 30% of her crop to spoilage within a week of harvest. Based on what you've learned, what low-cost improvements could she make to handling, storage, or marketing to reduce these losses?

📌 Key terms introduced

Post-harvest respiration Climacteric fruit Non-climacteric fruit Controlled atmosphere (CA) Modified atmosphere packaging (MAP) 1-MCP (SmartFresh™) Chilling injury Respiratory quotient (RQ) Cold chain Zero-energy cooler

✅ Check your understanding

Why do fruits and vegetables continue to respire after harvest, and why does this matter for storage?
Explain the difference between climacteric and non-climacteric fruits. Give two examples of each.
How does low temperature extend storage life? What's the risk of too-low temperature?
What is controlled atmosphere storage, and how does it affect respiration?
A shipment of bananas arrived at a market ripened unevenly. What might have gone wrong during transport?

Discuss your answers in the course forum.

Plant Biochemistry for Horticulture · HORT 202 · Dilla University · Last updated March 2026