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2024+post+harvest+biology+and+technology

Postharvest Biology and Technology

Agriculture relies on postharvest technology for:

  • Improved Quality: Enhances taste, maintains nutritional value, and ensures the freshness of products.

  • New Products and Niche Markets: Develops innovative food items to cater to specific consumer demands, such as organic or specialty foods that can command higher prices.

  • Light Processing of Foods: Involves minimal processing methods that retain the natural qualities of food while making it convenient for consumers.

  • Food Safety: Implements various practices to minimize contamination and spoilage, ensuring that food products are safe for consumption.

  • Reduced Losses: Aims to minimize food waste through optimal handling, storage, and transportation practices.

Characteristics of Horticultural Crops

Horticultural crops are:

  • Alive and Respiring: These crops continue metabolic processes after harvest, influencing their shelf life and quality.

  • High in Water Content: Typically contain a high percentage of water, impacting their susceptibility to dehydration and spoilage.

  • Genetically and Physiologically Diverse: Includes a wide range of species and varieties with varying growth requirements and postharvest behaviors.

Factors Contributing to Postharvest Losses

Key factors include:

  • Temperature: Improper temperature management can accelerate decay and spoilage of produce.

  • Water Relations: Maintaining adequate moisture is critical; transpiration can lead to significant losses if not managed.

  • Handling Damage: Rough handling can cause bruising and physical injuries, leading to quicker deterioration.

  • Diseases: Pathogens like Penicillium Mold and others can thrive if proper sanitation is not maintained.

  • Ethylene Production: Naturally produced by some fruits, it can trigger ripening and senescence, leading to quicker food spoilage.

  • Continued Growth: Improper storage conditions may allow crops to continue their life processes, degrading quality.

  • Nutritional Deficiencies: Suboptimal nutrient levels can affect produce resilience and storage life.

Damage Causes

  • Heat Damage: Exposure to high temperatures can quickly degrade quality.

  • Chilling Injury: Certain crops are sensitive to cold; improper refrigeration can cause damage.

  • High CO2 Injury: Excess levels of CO2 can harm produce and inhibit proper respiration.

  • Low O2 Injury: Insufficient oxygen levels can lead to anaerobic respiration, causing off-flavors and spoilage.

  • Physical Injury: Bruising from falls or rough handling can compromise the quality of crops.

  • Diseases: Examples include Anthracnose, which can spread rapidly under improper conditions.

Respiration in Postharvest Products

Perishable products are alive, growing, and aging, producing energy through respiration (oxidizing sugars). A primary goal of postharvest storage is reducing respiration rates to slow down metabolism and prolong shelf life.

Importance of Temperature

Deterioration rates correlate highly with respiration rates; higher temperatures can increase respiration exponentially. For every 10°C rise in temperature, respiration rates can increase by 2 to 3 times. This rate of increase leads to quicker water loss and higher susceptibility to diseases, emphasizing the importance of maintaining cool temperatures throughout storage and transport.

Classification of Horticultural Commodities by Respiration Rates

  • Very Low: Dried fruits, nuts (minimal respiration, long shelf life)

  • Low: Apples, garlic, mature potatoes (moderate respiration, moderate storage needs)

  • Moderate: Apricots, cabbages, fresh figs (higher sensitivity to conditions)

  • High: Artichokes, cut flowers (need careful management to avoid quick spoilage)

  • Extremely High: Asparagus, broccoli, mushrooms, peas (require rapid cooling and careful handling)

Temperature Control

Specific temperature ranges correspond to respiration rates for various crops. For example, broccoli exhibits high respiration at temperatures above 0°C, making cool storage essential in maintaining quality and reducing the risk of disease.

Cooling Methods

Postharvest cooling begins in the field to minimize heating. Common methods include:

  • Forced Air Cooling: Rapidly cools produce by blowing cold air directly over the items.

  • Hydro Cooling: Uses cold water or ice to quickly lower produce temperature.

  • Evaporative Cooling: Relies on the evaporation of water to cool the air around the produce.

  • Icing: Applying ice directly onto the crops to maintain low temperatures during transport.

Reducing Respiration Through Storage Techniques

Controlled Atmosphere (CA) Storage: Involves reducing oxygen levels and increasing carbon dioxide levels around stored produce, effectively slowing down respiration and decay rates. This method is highly effective for fruits and vegetables.

Water Management in Postharvest

Products primarily consist of water; loss affects quality and transport efficiency. Water loss increases with higher temperatures and decreases relative humidity.

Vapor Pressure Deficit (VPD)

VPD drives water loss; it quantifies the difference in water vapor content between produce and surrounding air, influencing transpiration rates. A high VPD can lead to rapid drying of crops.

Preventing Water Loss

Strategies include:

  • Reducing Temperature: Helps lower respiration and moisture loss.

  • Increasing External Vapor Pressure: Using specialized packaging can help retain moisture.

  • Managing Condensation: Proper airflow and temperature control can prevent excess moisture that fosters disease.

Modified Atmosphere Packaging (MAP)

MAP alters the atmosphere around the produce to increase CO2 levels and decrease O2 levels while preventing condensation, extending shelf life and maintaining quality during transport.

Diseases as Causes of Loss

Fungal diseases, such as Grey Mold, represent a substantial cause of loss in postharvest handling. Key practices in managing these diseases include maintaining proper temperature, sanitation protocols, and regularly inspecting stored items.

Understanding Ethylene Effects

Ethylene accelerates ripening; its careful control is crucial. Techniques for managing ethylene include storing sensitive items at lower temperatures and applying inhibitors that block ethylene synthesis.

Continued Growth Issues

Sprouting and continued growth can negatively impact produce quality, effectively rendering items unsuitable for sale. Proper temperature management and the use of growth inhibitors can mitigate these issues.

Physiological Disorders

Abnormal growing conditions, such as those resulting from temperature extremes and nutritional imbalances, can lead to physiological disorders that degrade produce quality.

Preventing Damage During Handling

Implementing careful harvesting practices is critical: use lined bins to reduce bruising and ensure gentle handling to prevent physical damage to the crops.

Testing Knowledge

Controlled atmosphere storage lowers oxygen and raises carbon dioxide levels, effectively slowing down respiration. Higher respiration rates correspond with a significantly shorter storage life of fruits and vegetables, emphasizing the importance of proper storage techniques to prolong shelf life.