Post-Harvest Reviewer

Lesson 4: Identification of Postharvest Problems and Malpractices

Postharvest Losses

  • major problems in agriculture are wastage of food and agricultural commodities

  • one third of food produced globally is lost every year

    • 15% for grains (rice and corn)

    • 28% fruits

    • 40% vegetables

  • Inefficiencies results: food insecurity, price increase, food shortage

Factors Contributing to Postharvest losses

  1. Internal factors - moment of harvesting, handling, pre-cooling, transportation, storage, processing, marketing, biological, microbial, chemical

    a. Harvesting - absence of maturity indices, poor weather, improper/rough handling

    b. Pre-cooling - high cost and limited availability of facilities

    c. Transportation - poor infrastructure/roads, inadequate systems, lack of refrigerated transport

    d. Storage - control of cleanliness, temperature, and humidity

    e. Grading - packing and packaging

    f. Biological - respiration rate, ethylene production, compositional production, changes (affecting color, texture, flavor, and nutrition), mechanical injuries, water stress, sprouting, rooting, physiological disorders, and pathological breakdown. As well as, temperature, humidity, air velocity, and atmospheric composition (oxygen, carbon dioxide, ethylene)

    g. Microbial - fungi and bacteria, molds: produce mycotoxins

    h. Chemical - Maillard reaction (browning and discoloration), harmful chemicals such as: pesticides, and lubricating oil

  2. External factors - environmental factors & socio-economic patterns and trends

    a. Temperature - higher temperature results in shorter storage life

    b. Relative humidity - affects the exchange of water vapor between stored food, fresh- high humidity; dried- low humidity to avoid mold growth

    c. Altitude - affects temperature, with a drop of about 6.5°C per kilometer increase in elevation above sea level.

    d. Time - longer storage time increase deterioration and damage

    e. Socio-economic - increase demand for food, importation that can introduce new insect species

Lesson 5: Comparative Postharvest Performance of Fruits and Vegetables

Postharvest Triangle of Interactions

  • nature of commodity such as morphological, anatomical, physiological, and physical, influence responses to physical, chemical and biological environment

Key Processes During Postharvest Handling

  • Commodity = Respiration, Transpiration, Ethylene Metabolism

    • Respiration - breakdown of food reserves to CO2, water and energy in the presence of O2

      aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 2830 kJ (38 ATP)

      1. Internal factors: type of issue, product size, stages of development, in fruits it will depend as if it is climacteric or non-climacteric

      (climacteric- can ripe using ethylene biosynthesis, can be harvested even if not fully ripe)

      (non-climacteric - don’t have peak of ethylene production, need to be harvested when fully ripe)

      1. External factors: mechanical damage, sanitary condition, temperature, physical barriers (waxes, plastic films, etc.)

    • Transpiration - loss of water as vapor from product’s are exposed to air, loss results to shriveling, wrinkling, browning

      1. Internal factor- species/ variety, type of tissue, external appendages and openings in the surface

      2. External factor - humidity, temperature, air movement, altitude, physical barriers

Ethylene Metabolism

  • climacteric fruits are sensitive to ethylene, produce larger quantity of ethylene (auto catalysis)

  • non-climacteric fruits produce very small quantities of ethylene

What is Ethylene?

  • Senescence/ Ripening hormone

  • Only plant hormone in gas form

  • produced by all plant cells

Ethylene Metabolism

  • high concentration results to degreening and increase metabolism

  • leafy vegetables are sensitive to ethylene (withering and yellowing)

Ripening process

  • physiological process occur at cellular level

  • after anabolic process, catalytic reactions starts degradation of starch, chlorophyll, organelles and cellular collapse/death

  1. Loss of chlorophyll (not in veggies)

  2. Production of carotenoids and anthocyanins

  3. Starches converted into sugars

  4. Changes in organic acids, proteins, and fats

  5. Reduction in tannins and fungistatic compounds

Lesson 6: Ethylene Response of Harvested Commodities

Ripening and Senescence

  • encompass various elements such as ripening-related genes, transcription factors, enzymes, inhibitors, signaling molecules, and metabolic routes, occurring in both climacteric and non-climacteric fruits

Ripening

  • closely linked with seed maturation

  • orchestrates the gradual softening and/or lignification of pericarp layer

  • accumulation of sugars, acids, pigments, and the release of volatiles

  • texture (softening due to cell wall degradation and changes in cuticle properties)

  • flavor (increase in sugar content and decrease in organic acids)

  • aroma (generation of volatile compounds imparting distinctive scents)

Senescence

  • final phase of a developmental program

  • characterized by a degenerative process that unfolds in a coordinated timeframe

  • viewed as an evolutionary tactic intricately linked with reproduction and survival

Role of Ethylene in Ripening

  • ethylene governs alterations in firmness and color, which entail the reduction of chlorophyll

  • heightened levels of carotenoids or anthocyanins

  • increased sugars

  • the synthesis of volatile organic compounds (VOCs).

Role of Ethylene in Senescence

  • These enzymes are:

    • pectine methyl esterases

    • polygalacturonase

    • cellulase

    • galactosidases

    • pectate lyase (PL)

    • xyloglucan transglucosylase/hydrolases

    • expansins

  • Ethylene regulates these genes and enzymes during ripening and senescence.

Ethylene Alternative

  • Calcium carbide (CaC2), ripening agent (kalburo)

    • reacts with water, releasing acetylene (ethylene analogue that mimics action of ethylene)

Procedures:

  • carbide application (15 grams per 100 pieces of fruit)