Unit 3 - Pre-shipment Treatments & Storage Methods | Postharvest Technology of Fruit Crops

HORMA - 303

Postharvest Technology For Fruit Crops

UNIT III: Pre-shipment Treatments & Storage Methods

📚 Contents

1. Treatments Prior to Shipment
2. Methods of Storage
3. Physical Injuries and Disorders

A. Treatments Prior to Shipment

Once harvested, fruits undergo specific treatments to improve appearance, reduce decay, and extend shelf life before they are shipped to markets.

1. Chlorination (Sanitation)

• Purpose: To kill surface pathogens (bacteria/fungi) and remove dirt/pesticide residues. It does not cure internal infections but prevents cross-contamination during washing.
• Mechanism: Chlorine acts as a strong oxidizing agent.
• Method:
  Fruits are dipped or washed in water containing Hypochlorite (Sodium or Calcium hypochlorite).
  Concentration: Typically 100–200 ppm (parts per million) active chlorine.
  pH Management: The water pH is maintained between 6.5 and 7.5 for maximum effectiveness (Hypochlorous acid form).
• Note: Water is often changed frequently to prevent accumulation of organic matter which deactivates chlorine.

2. Waxing (Surface Coating)

• Purpose: Fruits naturally have a wax layer, but it is often removed during washing. Artificial waxing replaces this layer.
• Benefits:
  Reduces Transpiration (water loss), preventing shriveling.
  Improves Appearance (provides a glossy/shiny finish).
  Modifies internal atmosphere (acts as a barrier to gas exchange), slightly reducing respiration.
• Types of Waxes:
  Solvent Waxes: Shellac, Wood rosins.
  Water Emulsion Waxes: Carnauba wax (from palm leaves), Beeswax, Paraffin wax.
• Application: Dipping, foaming, or spraying followed by warm air drying.
• Crops: Commonly used on Citrus (Oranges, Kinnow), Apples, Mangoes, and Cucumbers.

3. Chemical Treatments

Chemicals are used to control post-harvest diseases and delay ripening.

• Fungicides:
  Used to control rots like Anthracnose and Stem-end rot.
  Examples: Carbendazim (Bavistin) @ 0.1%, Thiabendazole, Imazalil (for citrus molds).
  Usually applied as a hot water dip (50–52°C) or spray.
• Growth Regulators:
  Gibberellic Acid (GA₃): Delays rind senescence (aging/yellowing) in citrus (Navel oranges) and maintains firmness in cherries.
  Calcium (CaCl₂): Post-harvest dip (2-4%) improves firmness and prevents disorders like Bitter Pit in apples.
• Ethylene Inhibitors:
  1-MCP (SmartFresh): Applied as a gas in closed chambers to block ethylene action.

4. Biocontrol Agents (Biological Control)

• Definition: Using beneficial microorganisms ("good germs") to fight pathogenic microorganisms ("bad germs") instead of synthetic chemicals.
• Mechanism:
  Competition: The good microbe eats the nutrients/space faster than the pathogen.
  Antibiosis: Producing natural antibiotics.
• Examples:
  Trichoderma harzianum (Fungus) against rot-causing fungi.
  Bacillus subtilis (Bacteria) against brown rot in stone fruits.
  Candida oleophila (Yeast) applied on citrus and apples.

5. Natural Plant Products (Botanicals)

Eco-friendly alternatives to synthetic chemicals, gaining popularity in organic export markets.

• Neem Extracts: Azadirachtin (from neem) has antifungal properties.
• Aloe Vera Gel: Used as an edible coating; forms a barrier against moisture loss and oxygen.
• Essential Oils:
  Oils from Thyme, Clove, Cinnamon, and Lemongrass.
  Have strong antimicrobial properties. Can be incorporated into edible coatings or packaging.

B. Methods of Storage

The goal of storage is to slow down biological activity (respiration) and prevent pathogen growth.

1. Ventilated Storage (Ambient/Common Storage)

• Definition: Storing produce under natural atmospheric conditions but with good ventilation to remove heat of respiration.
• Zero Energy Cool Chamber (ZECC):
  Developed by IARI (New Delhi).
  Structure: Double-walled brick structure filled with wet sand.
  Principle: Evaporative Cooling. As water evaporates from the sand, it takes heat from inside the chamber.
  Effect: Reduces temperature by 10–15°C below ambient and maintains high Humidity (~90%).
  Use: Excellent for short-term storage of Mango, Citrus, and leafy vegetables in rural areas.

2. Refrigerated Storage (Cold Storage)

• Principle: Low temperature reduces enzyme activity, respiration rate, and microbial growth. (Q₁₀ effect: For every 10°C drop, reaction rate halves).
• Key Requirements:
  Temperature Control: Must be precise (e.g., Apple 0–1°C; Mango 13°C).
  Relative Humidity (RH): usually 85–95% to prevent water loss.
  Air Circulation: To ensure uniform cooling and prevent hot spots.

3. Modified Atmosphere Storage (MAS)

• Definition: The atmosphere around the fruit is modified naturally by the fruit's own respiration within a sealed package.
• Mechanism:
  Fruit uses O₂ and releases CO₂.
  High CO₂ and Low O₂ slow down respiration/ripening.
• Implementation: Using Polymeric Films (LDPE, PVC bags) with specific permeability (tiny pores).
  Passive Modification: We seal the bag, and the fruit changes the gas mix itself.
• Disadvantage: If temperature fluctuates, respiration spikes, oxygen depletes completely → Anaerobic respiration (fermentation/off-flavor).
• Application: widely used in "MAP" (Modified Atmosphere Packaging) for retail packs of strawberry, pomegranate arils.

4. Controlled Atmosphere (CA) Storage

• Definition: A precise system where gas composition (O₂, CO₂, N₂), Temperature, and Humidity are actively monitored and maintained at specific set points.
• Difference from MAS: In MAS, gas levels fluctuate; in CA, they are fixed by machines.
• Typical Conditions:
  Oxygen (O₂): Reduced from 21% (air) to 1–3%.
  Carbon Dioxide (CO₂): Increased from 0.03% (air) to 1–5%.
• Benefits:
  Extends storage life by 2–3 times compared to normal refrigeration.
  Allows year-round availability of seasonal fruits (e.g., Apples stored for 9–10 months).
• Risks: If O₂ drops too low (<1 alcohol="" fermentation="" li="" occurs="" taste="">

Feature	Refrigerated Storage	CA Storage
Control	Only Temp & Humidity	Temp, Humidity & Gas
Cost	High	Very High (requires gas tight rooms)
Life	Medium (3-4 months for apple)	Long (8-10 months for apple)

C. Physical Injuries and Disorders

Disorders are physiological breakdowns (non-infectious), meaning they are not caused by germs but by environment or metabolism.

1. Physical Injuries

• Mechanical Damage:
  Impact: Dropping fruit (bruising).
  Compression: Overstacking boxes (crushing).
  Vibration: Shaking during transport (abrasion).
• Consequence: ruptures cells, releases enzymes (browning), and creates entry points for fungi.

2. Temperature-Related Disorders

• Chilling Injury (CI):
  Occurs in Tropical/Subtropical fruits held above freezing but below their critical threshold (usually 10–13°C).
  Symptoms: Pitting (sunken spots), surface discoloration, failure to ripen, loss of flavor.
  Examples: Blackening of Banana skin below 12°C; Wooliness (dry texture) in Peaches.
• Freezing Injury:
  Occurs when temperature drops below the freezing point of the tissue (usually < -1°C or -2°C).
  Mechanism: Ice crystals form inside cells, puncturing the cell wall. When thawed, the tissue collapses and becomes mushy/watery.
• Heat Injury (Sunscald):
  Caused by direct exposure to intense sun or hot water treatment.
  Symptoms: Bleached or necrotic (dead) patches on the skin.

3. Chemical/Physiological Disorders

• Bitter Pit (Apple):
  Cause: Calcium (Ca) Deficiency.
  Symptoms: Small, brown, sunken spots on the fruit surface and flesh, bitter taste.
• Scald (Superficial Scald):
  Cause: Accumulation of volatile compounds (farnesene) in the skin during cold storage.
  Symptoms: Brown, skin-deep discoloration (looks like a burn). Common in Apples/Pears.
• Black Heart (Potato/Pineapple):
  Cause: Oxygen starvation (O₂ deficiency) in the center of the produce due to poor ventilation or high CO₂.
  Symptoms: The core turns black.

📚 References

Wills, R., McGlasson, W.B., Graham, D., & Joyce, D. (1998). Post Harvest: An Introduction to the Physiology and Handling of Fruits, Vegetables and Ornamentals. CABI.

Sudheer, K.P. & Indira, V. (2007). Post Harvest Technology of Horticultural Crops. New India Publ. Agency.

Kader, A.A. (2002). Postharvest Technology of Horticultural Crops. University of California.

Bhutani, R.C. (2003). Fruit and Vegetable Preservation. Biotech Books.

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