Post-harvest Physical Injury

Causal Agent: Physical or Mechanical Injury

Crops Affected: various fruits and vegetables

Symptoms:

• Post-harvest physical injury can occur on most fruit and vegetables during any of the many handling processes or during storage.
• Injuries may include:

• Impact splits – These may be seen on fruits, roots, and tubers from an impact that occurs if they are dropped from a significant height (this varies with the product)
• Internal bruising – These are not visible externally, but are caused by impact
• Superficial – These include surface grazes, skinning, or scratches to the skins and outer layer of cells
• Crushing/compression – These may be observed on leafy vegetables and other soft produce
• These may also occur in firmer produce in some situations, such as in bulk piling (to excess depths)
• Shatter cracking – This is the result of direct, high-force physical injury, often due to rough handling
• High turgor (full of water) carrots tend to be more prone to damage
• Cuts – These are penetrating slices or cuts which damage deeper tissues
• Breakage – Portions of the produce may be broken off completely (e.g. roots, leaves, etc.)
• Wilting – The loss of water in leaves, roots, etc., may manifest as shriveling, rubberiness, colour loss, etc.

Causes:

The various injuries may manifest immediately on the surface of the product; however, some injuries are more internal in nature, and may take some time to develop and be visible.

Blackspot Bruising

• Individual cells are ruptured below the skin without breaking the skin
• Bruises typically develop within a couple of days and are only visible when potatoes are peeled

Shatter Bruising

• This is typically due to rough or improper handling
• Thin cracks or splits occur in the flesh of the tuber, particularly in larger tubers
• Thumbnail cracks, which occur when cold tubers are handled in storage, are a form of shatter bruising

Crushing/Compression

• Depending on the crop and the severity of the injury, this can range from pressure bruises through to cracking
• This occurs as a result of excessive weights or bulk pile depths
• Softer produce is more susceptible to crushing

Splits/Cuts

• These can occur from a variety of causes, including different equipment or handling issues
• Improper belt speeds, insufficient padding or belt/roller loading, sharp edges or corners, damaged pallets, or handling equipment with pointy, sharp, or rough protrusions can all cause cuts or splits

Harvest Conditions and Post-harvest Injury:

There are a number of factors that affect the susceptibility of harvested crop products to post-harvest injury. Crop maturity, harvest temperatures, and moisture conditions have a significant influence on harvested produce quality. Ideally, all produce should be fully (or appropriately) mature when harvested. For potatoes, tops should have naturally died down or have been killed prior to harvest. Top killing encourages skin set.

Harvest Conditions

• Potatoes should ideally be harvested at temperatures between 7°C and 15°C and with good, average soil moisture
  • When potatoes are harvested at warmer temperatures (greater than 18-20°C) and under drought stress, expect more blackspot bruising and potentially more storage diseases, such as leak and pink rot
  • When potatoes are harvested at temperatures less than 7°C and with higher soil moisture and tuber water content, you can expect to see a greater incidence of shatter bruising
    • This is also true with other root vegetables.
  • Repeated exposure of tubers to temperatures less than 5°C can lead to sugar to starch conversion and darker fry colour
  • Frozen tubers will occur when temperatures go below 0°C
    • It is almost impossible to store a crop of potatoes with more than 5 percent frozen tubers
  • Other vegetables will also be affected by freezing
    • In some cases, allowing them to thaw prior to harvest will be acceptable

Management:

• Avoid harvesting carrots (and other root vegetables) at cooler soil temperatures (e.g. avoid early mornings) or when they are fully turgid
• Store bulk vegetables according to established pile guidelines (depth, aeration, temperature)
• Store produce in appropriate sizes/volumes to prevent compression or bruising injury
• Rough handling of produce during harvest, grading, and in the post-harvest and storage stages can result in increased incidence of storage diseases, reduce product quality and subsequent crop value
  • Ensure all equipment is properly calibrated prior to use
  • Avoid drops of greater than 12 inches (30cm) and avoid over-piling
  • Ensure that handling equipment is properly operated, to minimize damage
• Proper post-harvest curing for wound healing is also an important step