Unit 3: Loss of Product Quality During Storage

Learning Objectives
  • Define "quality" of fruits and vegetables based on consumer parameters.
  • Describe processes during ripening that define quality and loss of quality.
  • Identify various causes for loss of quality during storage.
  • Explain potential sources of disease causing quality loss during storage and marketing.
  • Describe methods to reduce losses due to disease during storage and marketing.
Introduction
  • Quality loss occurs from harvest to consumption.
  • Quality does not typically improve, except for some fruits that ripen post-harvest.
  • Ensure only the best products are harvested (i.e., "garbage in, garbage out").
Definition of Quality
  • Quality varies by consumer preference, but generally consists of:
    • Taste or Flavor: Sweetness, acidity, and balance.
    • Appearance: Color and presence of physical defects.
    • Texture: Consistency, e.g., crunchy or soft.
    • Aroma: Distinct scents that may indicate ripeness.
    • Size: Uniformity and appropriateness for variety.
  • For more on grading factors, refer to the CFIA website.
Maturity Indices
  • Maturity indices help determine the quality and readiness of fruits and vegetables.
  • Example: A ripe apple is sweet and crunchy, while still immature apples have different texture and flavor profiles.
Fruit Ripening
  • Ripening involves numerous physiological changes:
    • Changes in pH: Indicates a reduction in acidity.
    • Increase in Soluble Solids: Higher sugar content enhances flavor.
    • Loss of Firmness: Enzymatic activity softens the fruit.
    • Chlorophyll Degradation: Change from green to red (e.g., in tomatoes due to increased lycopene).
    • Respiration Increase: Higher CO2 levels accompany ethylene production; necessary for metabolic activity.
  • Overripe fruits lose flavor and texture, becoming susceptible to diseases.
Causes of Quality Loss During Storage

  1. Color Loss:

    • Typically, leafy vegetables lose their green color due to chlorophyll breakdown, often exacerbated in darkness.
    • Example: Broccoli may develop off-odors alongside color loss.

  2. Dehydration:

    • Water loss is driven by differences in water vapor pressure; moisture loss occurs rapidly in low humidity.
    • Fresh produce should be stored at 85-100% relative humidity to minimize dehydration.
    • Dehydrated fruits lose weight and visual appeal, affecting economic returns.

  3. Weight Loss:

    • Economic losses arise when produce is discarded due to physical blemishes or dehydration.
    • Proper handling and storage diminish discards that don’t meet grade standards.

  4. Sprouting:

    • Vegetables like potatoes will sprout if stored at higher temperatures; low temperatures can inhibit sprouting.
    • Use of sprout inhibitors (chemical or natural) is common in large-scale production.

  5. Physiological Disorders:

    • Disorders often arise from environmental stress or nutritional deficiencies during growth.
    • Management includes identifying susceptible varieties and reducing storage time.

  6. Freezing and Chilling Injuries:

    • Freezing injury occurs when produce thawing breaks down cell structure, promoting disease proliferation.
    • Chilling injury primarily affects tropical/subtropical produce at temperatures below about 10°C.
    • Both injuries can severely affect storage quality.
Postharvest Diseases
  • Postharvest Disease Losses: Significant economic impact due to rotting and decay after harvest.
  • Pre-harvest Infections: Pathogens can infect crops while growing; susceptibility increases as fruits mature.
  • Latent Infections: Microorganisms may remain dormant until favorable conditions arise post-harvest.
Managing Postharvest Diseases
  • Pre-harvest Treatments: Careful crop management and fungicide application can prevent infection.
  • Postharvest Sanitation: Chlorine is often added to washing processes to reduce microbial populations.
  • Temperature Control: Low temperatures slow pathogen growth; however, must be managed to prevent chilling injuries.
  • Humidity Control: Reducing humidity can inhibit pathogen growth, but high humidity is preferred to prevent dehydration.
  • Chemical Treatments: Fumigants or coatings can be utilized to manage disease during storage.
  • Controlled Atmospheres: Alters gas compositions to suppress disease processes.
  • Biotechnological Advances: Genetic modifications, such as delayed ripening in tomatoes, are being researched to enhance product quality and shelf life.
Study Questions
  1. What are the five parameters determining fresh fruits and vegetables' eating quality?
  2. What changes occur in ripening tomatoes that enhance their quality?
  3. Why are fruits often harvested before full ripeness?
  4. What causes green vegetables to yellow during storage?
  5. How does the temperature of produce affect dehydration rates?
  6. Why is dehydration loss problematic for fresh produce?
  7. Discuss methods to prevent sprouting in potatoes and onions.
  8. How can frozen produce lead to issues when stored together?
  9. Why can't produce be entirely free from pathogens?
  10. What makes harvested produce more prone to diseases?
  11. How can pathogens be managed during washing pre-storage?
  12. Why maintain chlorine levels in recycled cooling water?
  13. Why is sulfur dioxide used post-harvest for grapes?