PPSC Lumbini · Agriculture Service · 7th Level
Postharvest Management of Horticultural Crops
Topics 5.3.2 · 5.3.3 · 5.3.4 — Prepared for Lok Sewa Exam Preparation
📋 Contents
5.3.2
Causes of Postharvest Loss and Their Management
Syllabus: 5.3.2 — Horticulture, Paper II Section C
Definition
Definition
Postharvest loss is the measurable quantitative and qualitative loss occurring in the food supply chain from the time of harvest to final consumption. It includes loss in weight, nutritional value, economic value, and edibility.
Lok Sewa Key Fact
Nepal loses approximately 20–40% of fruits and vegetables after harvest due to improper handling, storage, and lack of cold chain infrastructure. This contributes directly to food insecurity and farmer income loss.
Classification of Causes
🦠 Biological / Biotic
- Fungi (most important) — Rhizopus, Botrytis, Penicillium
- Bacteria — soft rots (Erwinia, Pseudomonas)
- Insects & rodents — direct feeding damage
- Nematodes in storage soil
- Mites — cause skin damage
🌡️ Physical / Abiotic
- Mechanical injury during harvest/transport
- Compression/impact bruising
- Improper temperature (chilling injury, heat damage)
- Low/high relative humidity (wilting/decay)
- Improper packaging — crushing
⚗️ Physiological / Chemical
- Continued respiration — energy loss, weight loss
- Transpiration — water loss, wilting
- Ethylene production — accelerated ripening
- Enzymatic browning (phenolase activity)
- Senescence — natural aging
🏗️ Infrastructural
- Lack of cold storage facilities
- Poor road connectivity in hills/mountains
- Inadequate packaging materials
- Absence of cold chain management
- Poor market infrastructure
Detailed Causes — Physiological
| Factor | Process | Effect on Produce | Management |
|---|---|---|---|
| Respiration | Oxidation of sugars → CO₂ + H₂O + heat | Weight loss, quality deterioration, heat build-up | Low temperature, CA/MA storage |
| Transpiration | Water evaporation through skin/stomata | Wilting, shrivelling, weight loss (2–3% = visible wilt) | High RH (85–95%), wax coating, packaging |
| Ethylene (C₂H₄) | Produced by climacteric fruits; promotes ripening | Over-ripening, yellowing, softening, abscission | Low O₂, high CO₂, KMnO₄ absorbers, 1-MCP |
| Enzymatic browning | Polyphenol oxidase (PPO) + oxygen | Brown discoloration at cut surfaces | SO₂, citric acid, blanching, vacuum packaging |
| Senescence | Natural programmed aging | Softening, loss of flavor, nutritive value decline | Cold storage, CA storage, growth regulators |
Pathological Causes — Key Diseases
| Disease | Pathogen | Crop affected | Symptom |
|---|---|---|---|
| Soft rot | Erwinia carotovora | Most vegetables | Watery, foul-smelling decay |
| Gray mold | Botrytis cinerea | Strawberry, grape | Gray fuzzy mycelial growth |
| Blue/Green mold | Penicillium spp. | Citrus, apple | Blue-green powdery growth |
| Rhizopus rot | Rhizopus stolonifer | Stone fruits, potato | Cottony growth, watery rot |
| Crown rot | Fusarium spp. | Banana | Blackening of crown |
| Black rot | Alternaria spp. | Citrus, apple | Dark sunken lesions |
Management of Postharvest Losses
A. Pre-harvest Measures
- Variety selection — Choose varieties with longer shelf life and disease resistance
- Good Agricultural Practices (GAP) — proper nutrition, pest management during production
- Harvest at proper maturity — neither too early nor too late
- Integrated crop management — minimize field infections
B. Harvest Measures
- Harvest in cool morning hours to reduce field heat
- Use sharp, clean tools to minimize mechanical injury
- Avoid harvesting in wet conditions (promotes fungal spread)
- Handle produce gently — single layer in harvest baskets
C. Post-harvest Measures
| Method | Principle | Application |
|---|---|---|
| Pre-cooling | Rapid removal of field heat | Hydrocooling, forced air, vacuum cooling for leafy vegetables |
| Grading & sorting | Remove damaged/diseased produce | Prevents spread of disease in storage |
| Curing | Wound healing of skin | Potato (18–20°C, 2 wks), Onion (30–45°C, drying) |
| Wax coating | Reduces transpiration | Citrus, apple, mango — food-grade wax |
| Fungicide treatment | Controls postharvest pathogens | Thiabendazole, Imazalil for citrus |
| Irradiation | Destroys microorganisms | Gamma rays (Cobalt-60); extends shelf life significantly |
| Heat treatment | Surface disinfestation | Hot water dip (50–55°C for 2–5 min) for mango, papaya |
| Cold storage | Slows respiration & microbial growth | Most fruits and vegetables — temp varies per commodity |
| CA/MA storage | Modified gas atmosphere | Apple (2–3% O₂, 2–5% CO₂); extends shelf life 4–8× over cold storage |
| 1-MCP treatment | Blocks ethylene receptors | Apple, kiwi — delays ripening significantly |
🇳🇵 Nepal Context — Loksewa Important
Zero Energy Cool Chamber (ZECC) is highly relevant for Nepal. Built with double brick walls, sand filling and water — reduces temperature by 10–15°C and maintains ~90% RH without electricity. Ideal for marginal farmers in remote areas. Used for tomato, leafy vegetables, brinjal, cauliflower.
5.3.3
Storage of Vegetables and Fruits: Potato, Onion and Apple
Principles, Importance and Different Storage Structures
General Principles of Storage
- Temperature management — lower temperature → lower respiration rate → longer shelf life
- Relative humidity control — 85–95% RH for most produce; low RH causes wilting, high RH promotes fungal decay
- Ventilation — removes CO₂, heat, ethylene and moisture produced by respiration
- Sanitation — clean, disinfected storage structure prevents cross-contamination
- Avoiding ethylene accumulation — ethylene from ripening produce accelerates senescence in stored produce
- Proper maturity at harvest — immature or over-mature produce stores poorly
Importance of Storage
- Stabilizes market prices by extending availability beyond harvest season
- Protects producers from distress selling at harvest glut
- Ensures food availability in off-season and remote areas
- Increases farmers’ income by allowing sale when prices are high
- Reduces postharvest losses and waste
- Supports agro-industry by ensuring raw material supply throughout the year
Comparison: Potato, Onion & Apple Storage Requirements
🥔 Potato
Temp (Table)
3–4°C (cold storage)
10–15°C (ordinary)
10–15°C (ordinary)
Seed Potato
Diffused light, 10–15°C
RH
85–90%
Curing required
Yes — 18–20°C, 2 weeks
Key problem
Sprouting & greening
Sprouting control
CIPC (Isopropyl N-phenyl carbamate) sprout inhibitor; diffused light
Shelf life
6–10 months (cold storage)
🧅 Onion
Temp
0–1°C (cold) or 25–30°C (ambient — commercial)
RH
65–70% (LOW — to prevent sprouting and rot)
Curing required
Yes — 30–45°C, 48 hrs or field curing 7–10 days
Key problem
Sprouting and neck rot (Botrytis allii)
Sprouting control
MH (Maleic Hydrazide) applied 2–3 wks before harvest; good ventilation
Special note
Onion stored at intermediate temp (5–18°C) SPROUTS FASTEST — avoid this range
Nepal storage
Bamboo/wooden platform, hanging bundles, ventilated sheds
🍎 Apple
Temp
0–2°C (cold/CA storage)
RH
90–95%
CA storage
2–3% O₂ + 2–5% CO₂; extends to 8–12 months
Harvest maturity
Before climacteric rise (pre-climacteric stage)
Key problem
Scald, bitter pit, core flush (physiological disorders)
Nepal storage
Cellar storage in Jumla, Mustang; CA in Kathmandu valley
1-MCP use
Applied to delay ripening and extend shelf life
⚠️ Exam Trap — Onion RH
Unlike most vegetables, onion requires LOW relative humidity (65–70%) for storage. High RH promotes neck rot and sprouting. Most other vegetables require 85–95% RH. This difference is frequently asked in MCQs.
Storage Structures
1. Home / Ordinary Storage
- No artificial temp/humidity control
- Potato: cool dry room, covered with sand
- Onion: thin layer on floor or hanging bundles
- Garlic: hung in bunches in veranda (baranda)
- Pumpkin: roof top or hanging
2. Field Storage (Pit/Trench)
- Trenches dug in ground, produce placed inside
- Covered with hay, straw and soil
- Best for temperate regions with frost winters
- Carrot, beet, turnip, potato, cabbage
- Disadvantage: no environmental control
3. Cellar Storage
- Underground storage, north-facing terraces
- All sides covered with earth except entrance
- Double-door + windows for ventilation
- 15°C cooler than ambient temperature
- Used for: apple and citrus in Nepal (Jumla, Mustang)
4. Rustic Storage (Diffused Light Store)
- For seed potato tubers only
- Built at high altitude to utilize low ambient temp
- Wooden racks with diffused sunlight
- Diffused light → small, compact sprouts (delayed growth)
- Green pigment develops → NOT for consumption
- Reduces seed requirements (healthier seed tubers)
5. Cold Storage
- Mechanical refrigeration; temp maintained per crop
- Potato: 3–4°C; Apple: 0–2°C; Onion: 0–1°C
- RH: 85–95% (except onion: 65–70%)
- Reduces respiration, microbial activity, ethylene
- Most widely used commercial storage method
6. Zero Energy Cool Chamber (ZECC)
- Double brick wall structure; cavity filled with sand
- Walls kept wet with water (evaporative cooling)
- Reduces temp by 10–15°C below ambient
- Maintains ~90% relative humidity
- No electricity required; low cost; locally made
- Capacity: 100–500 kg; short-term storage
- Most effective in dry season
7. Controlled Atmosphere (CA) Storage
- Precisely controlled O₂ (2–3%), CO₂ (2–5%)
- Low O₂ → inhibits ACC oxidase/synthase → less ethylene
- High CO₂ → inhibits ACC synthase activity
- Must be combined with low temperature
- Apple: stored up to 8–12 months
- Expensive — high tech; used commercially
8. Modified Atmosphere (MA) / MAP
- Gas modified initially only (e.g. polyethylene bags)
- No active control after sealing
- Simpler and cheaper than CA
- Gas changes over time due to respiration of produce
- Unsealed with perforations or sealed bags
- Used for: short-term retail packaging
⚠️ CA vs MA — Exam Distinction
CA storage: gas composition is continuously monitored and adjusted throughout storage. MA storage: gas is modified once at packaging and then changes dynamically — no active control. CA is more expensive and precise; MA is simpler and used for retail packaging.
Additional Methods
- Hypobaric storage — reduced atmospheric pressure (80–40 mm Hg) with refrigeration; removes ethylene; extends shelf life significantly; very expensive
- Vacuum packing — removes O₂; reduces aerobic bacteria and fungi; mainly for dry foods (cereals, nuts, spices); some fresh produce short-term
Special Notes: Potato Storage in Nepal
🇳🇵 Nepal Context
Nepal has about 1,600+ cold stores nationally, mostly in Terai. Major potato growing areas: Mustang, Solukhumbu, Sindhupalchowk. Rustic stores are common in hills for seed potato. ZECC and cellar stores support small-holder farmers in mid-hills.
- Curing: 18–20°C, 85–90% RH, 2 weeks — heals wounds, suberizes skin, prevents rotting
- Sprout inhibition: CIPC (Chlorpropham/Isopropyl N-Phenyl Carbamate) dust or fog treatment in cold storage
- Greening prevention: exclude light during storage — solanine (toxic glycoalkaloid) forms in light
- Cold sweetening: storing below 4°C converts starch to sugar — not ideal for processing potato; re-warm at 10–15°C before use
5.3.4
Preservation of Fruits and Vegetables
Methods, Principles and Applications
Definition & Objective
Definition
Preservation is the process of treating and handling food to stop or greatly slow down spoilage while maintaining nutritional value, texture, taste and color, making it available for consumption over a longer period.
Objectives of preservation:
- Prevent microbial spoilage and enzymatic deterioration
- Extend shelf life and ensure year-round availability
- Reduce postharvest losses and add economic value
- Maintain nutritional quality and sensory attributes
- Support agro-processing and export of horticultural produce
Principles of Preservation
| Principle | Mechanism | Examples |
|---|---|---|
| Prevention of microbial growth | Remove, destroy or inhibit microorganisms | Sterilization, pasteurization, UV irradiation |
| Removal of water (aw) | Low water activity inhibits microbial growth | Drying, dehydration, freeze drying |
| Temperature reduction | Slows enzymatic and microbial activity | Refrigeration, freezing |
| Use of chemicals/preservatives | Inhibit microbial growth or enzymatic reactions | Salt, sugar, vinegar, SO₂, benzoate |
| Exclusion of oxygen | Prevents aerobic spoilage and oxidation | CA storage, vacuum packaging, canning |
| Lowering pH | Acidic environment inhibits most pathogens | Pickling, fermentation, citric acid treatment |
| High temperature treatment | Destroys microorganisms and enzymes | Blanching, pasteurization, canning, UHT |
Methods of Preservation — Classification
A. Physical Methods
❄️ Cold Preservation
- Refrigeration (0–8°C): short-term; slows but doesn’t stop deterioration
- Freezing (–18°C or below): long-term; enzyme activity minimal; blanch before freezing to inactivate enzymes
- Freeze drying: best quality; sublimation of ice; expensive; retains nutrients, flavor, structure
🌡️ Heat Treatment
- Blanching: brief heat (95–100°C, 2–5 min); inactivates enzymes (peroxidase, catalase) before freezing/drying
- Pasteurization: 63–72°C; destroys pathogens; used for juices
- Sterilization/Canning: 115–121°C (autoclave); destroys all microorganisms including spores
- UHT: 135–140°C for 2–4 sec; long shelf life at room temp
🌬️ Drying / Dehydration
- Sun drying: cheapest, traditional; chips, amla, ginger; inconsistent quality
- Cabinet dryer: controlled temp (55–70°C); better quality
- Spray drying: for juices and purees → powder form
- Osmotic drying: sugar/salt solution removes water before drying
☢️ Irradiation
- Gamma rays (Cobalt-60 / Cesium-137)
- Low dose (0.1–1 kGy): sprout inhibition (potato, onion)
- Medium dose (1–10 kGy): pathogen reduction
- High dose (10–50 kGy): sterilization
- Does not make food radioactive
B. Chemical Methods
| Preservative | Chemical | Use | Max limit (FSSAI/Nepal) |
|---|---|---|---|
| Sulphur dioxide (SO₂) | Na₂SO₃, K₂S₂O₅ (potassium metabisulfite) | Dried fruits, squash, juice — prevents browning, mold | 350 ppm (squash); 2000 ppm (dried) |
| Sodium benzoate | C₆H₅COONa | Pickles, squash, ketchup — inhibits yeasts and molds | 750 ppm |
| Potassium sorbate | C₆H₇KO₂ | Fruit products, wine — effective against molds and yeasts | 1000 ppm |
| Citric acid | C₆H₈O₇ | pH reduction, chelates metals; prevents browning | GMP (generally safe) |
| Vinegar (Acetic acid) | CH₃COOH | Pickling — lowers pH; inhibits bacteria | 1–2% in products |
| Common salt (NaCl) | NaCl | Brining, pickling — osmotic effect; dehydrates microbes | GMP |
| Sugar | Sucrose | Jam, jelly, preserve — high sugar → low water activity | GMP |
C. Biological / Fermentation Methods
- Lactic acid fermentation — sauerkraut (cabbage), kimchi, gundruk (Nepal) — Lactobacillus produces lactic acid, lowers pH, inhibits pathogens
- Alcoholic fermentation — fruit wines (apple cider, fruit wine) — yeast converts sugars to ethanol
- Acetic acid fermentation (Vinegar production) — from fruit juices; acetobacter converts ethanol to acetic acid
- Gundruk — traditional Nepali fermented leafy vegetable; mustard/radish leaves; important food security product in hills
- Sinki — fermented radish taproot; Nepal; important traditional preservation
🇳🇵 Traditional Preservation in Nepal — Loksewa Important
Gundruk and Sinki are traditional fermented products of Nepal made from mustard/cauliflower leaves and radish taproot respectively. They are important for food and nutritional security in hills and mountains where fresh vegetables are unavailable in winter. Both are recognized as indigenous fermented foods with significant agro-processing potential.
Horticultural Products and Their Preservation Methods
| Product | Raw material | Preservation principle | Key additive/process |
|---|---|---|---|
| Jam | Fruit pulp + sugar | High sugar (65–68 TSS), low aw, pectin gel | Sugar 65–68%, pectin, citric acid; boil to gel point |
| Jelly | Fruit juice + sugar | High sugar, pectin gel (clear) | Pectin, sugar 65%, citric acid; strained juice only |
| Marmalade | Citrus fruit slices + juice | High sugar + natural peel pectin | Citrus peel pieces suspended in gel; bitter taste |
| Pickle | Vegetables/fruits | Low pH (acetic acid) or salt (osmotic) | Vinegar/salt + spices; Oil pickle (Nepal) |
| Squash | Fruit juice | Sugar 40–45%, SO₂ or benzoate | 25% juice + 40% sugar + 1.5% citric acid + 350 ppm SO₂ |
| Cordial | Fruit juice (clear) | High sugar, preserved clarified juice | Strained, clarified juice, sugar, preservative |
| Nectar | Fruit pulp diluted | Pasteurization + sugar | 25–30% fruit content, total soluble solids adjusted |
| Ketchup/Sauce | Tomato/fruit | Heat + acidity + salt + sugar | pH < 4.2, cooked, salt, vinegar, sodium benzoate |
| Chutney | Fruit/vegetable + spices | Cooking + acid + salt | Mixed ingredients boiled with vinegar and spices |
| Candy/Glazed fruit | Whole/sliced fruit | Osmotic impregnation with sugar | Progressive immersion in sugar solutions; amla, ginger candy |
| Murabba | Whole fruit in syrup | High sugar preserves whole fruit structure | Amla, apple, carrot in heavy sugar syrup (≥65 TSS) |
| Dried/Dehydrated | Fruit slices/vegetables | Low water activity (aw < 0.6) | Blanch + SO₂ + dry (sun or mechanical) |
📌 Pectin — Key for Jam/Jelly Making
Pectin is a polysaccharide in cell walls of fruits. It forms a gel in the presence of sugar (≥65%) + acid (pH 3.0–3.5) + heat. High-pectin fruits: guava, apple, citrus peel, plum. Low-pectin fruits (mango, strawberry, pineapple) need added pectin. The gel point test: drop in cold water — forms a firm ball when ready.
Blanching — Critical Pre-treatment
What is Blanching?
Brief exposure to boiling water (95–100°C) or steam for 2–5 minutes, followed by immediate cooling in ice water (quenching). It is a mandatory pre-treatment before freezing or drying vegetables.
Objectives of Blanching:
- Inactivates enzymes (peroxidase, catalase, lipoxygenase) that cause off-flavor, browning, texture changes during storage
- Reduces microbial load on surface
- Removes trapped gases from tissue (improves packaging)
- Softens tissue for efficient packing
- Fixes/brightens green color (chlorophyll stabilization)
- Removes raw flavor and aroma
⚠️ Under-blanching vs Over-blanching
Under-blanching: activates enzymes rather than inactivating — WORSE than no blanching. Over-blanching: loss of water-soluble vitamins (C, B vitamins), texture damage. Peroxidase is used as indicator enzyme — if peroxidase is inactivated, all other enzymes are also inactivated.
⚡ Quick Revision — Exam Ready Facts
Postharvest Loss %
- Nepal: 20–40% F&V loss
- Globally: ~30% food wasted
- Developing countries: mostly postharvest losses
- Developed countries: mostly consumer waste
Storage Conditions (Key)
- Potato: 3–4°C, 85–90% RH
- Onion: 0–1°C, 65–70% RH (LOW!)
- Apple: 0–2°C, 90–95% RH
- Leafy vegetables: 0–2°C, 98–100% RH
- Banana: 13–14°C (chilling sensitive!)
ZECC Key Numbers
- Temp reduction: 10–15°C below ambient
- RH maintained: ~90%
- No electricity required
- Double brick wall + sand + water
- Most effective in dry season
CA Storage (Apple)
- O₂: 2–3%
- CO₂: 2–5%
- Temp: 0–2°C
- Shelf life: 8–12 months
- vs normal cold: 3–4 months
Jam Standard
- TSS: minimum 65°Brix
- Fruit content: minimum 45%
- Pectin + sugar + acid = gel
- pH: 3.0–3.5
- Gel point: ball in cold water
Nepal Traditional Products
- Gundruk — fermented leafy vegetables
- Sinki — fermented radish taproot
- Khalpi — fermented cucumber
- Masyaura — fermented veg + black gram
- Lapsi products — hog plum candy/pickle
Ethylene Management
- Produced by: climacteric fruits
- Absorber: KMnO₄ (potassium permanganate)
- Inhibitor: 1-MCP (SmartFresh)
- Reduced by: CA storage (low O₂)
- Ripening agent: Ethephon (2-CEPA)
Sprouting Control
- Potato: CIPC (Chlorpropham)
- Onion: MH (Maleic Hydrazide) — pre-harvest spray
- Both: low temperature storage
- Both: gamma irradiation (0.1–0.3 kGy)
- Potato: diffused light (rustic store)
📝 Practice MCQs — Loksewa Pattern
1. Which of the following is NOT a cause of postharvest loss?
A. Mechanical injury
B. Ethylene production
C. Transpiration gain (water uptake)
D. Fungal infection
✓ Answer: C — Transpiration causes water LOSS not gain; all others cause losses
2. Onion is stored at a relative humidity of:
A. 85–90%
B. 65–70%
C. 95–98%
D. 75–80%
✓ Answer: B — Onion requires LOW RH (65–70%) unlike most vegetables that need high RH
3. Zero energy cool chamber reduces temperature by how much below ambient?
A. 5–8°C
B. 10–15°C
C. 20–25°C
D. 3–5°C
✓ Answer: B — ZECC reduces temperature by 10–15°C and maintains 90% RH
4. Rustic storage is specifically designed for storing:
A. Apple
B. Onion
C. Seed potato
D. Citrus fruits
✓ Answer: C — Rustic storage uses diffused light for seed potato tubers at high altitude
5. In CA storage of apple, the recommended O₂ and CO₂ levels are:
A. 5% O₂, 10% CO₂
B. 2–3% O₂, 2–5% CO₂
C. 10% O₂, 2% CO₂
D. 1% O₂, 15% CO₂
✓ Answer: B — CA storage for apple: 2–3% O₂ and 2–5% CO₂ at 0–2°C
6. The sprouting inhibitor used for onion before harvest is:
A. CIPC
B. Ethephon
C. Maleic Hydrazide (MH)
D. 1-MCP
✓ Answer: C — MH (Maleic Hydrazide) is applied 2–3 weeks before harvest for onion. CIPC is used for potato in storage.
7. Gundruk is a traditional Nepali product made by:
A. Drying radish taproots
B. Lactic acid fermentation of leafy vegetables
C. Sugar preservation of amla
D. Vinegar pickling of mustard
✓ Answer: B — Gundruk is fermented (lactic acid) leafy vegetables (mustard, cauliflower leaves)
8. Minimum TSS (Total Soluble Solids) required for jam as per food standards:
A. 45°Brix
B. 55°Brix
C. 65°Brix
D. 75°Brix
✓ Answer: C — Jam requires minimum 65°Brix TSS with at least 45% fruit content
9. The enzyme used as indicator for adequacy of blanching is:
A. Amylase
B. Lipase
C. Peroxidase
D. Catalase
✓ Answer: C — Peroxidase is the most heat-resistant enzyme; if it’s inactivated, all others are too
10. Cellar storage in Nepal is mainly used for:
A. Potato and onion
B. Mango and banana
C. Apple and citrus
D. Leafy vegetables
✓ Answer: C — Cellar storage is dug in north-facing terraces, 15°C cooler than ambient; used for apple and citrus in Nepal