Potato Review Group

Contents

Tuber characteristics which influence physical damage

Influence of handling and equipment on physical damage

Factors influencing discolouration during bruising

Minimising damage during harvesting and handling

Equipment for assessing bruising and damage

Handling during or after storage: bruising

Handling during or after storage: ‘finger nail’ cuts to skin.

Damage (excluding bruising)

Wound healing

Further information:

Bruising and damage notes

 

 

Tuber characteristics which influence physical damage

  1. Bruising results from physical damage to cells and development of the dark pigment melanin. More …
  2. Tubers with a high water content may be less susceptible to damage. (More information on effects of: low dry matter concentration and turgor pressure)
  3. Damage may increase with tuber size (a large tuber has a greater kinetic energy than a small tuber dropped from the same height).
  4. Bruising may be more severe at low temperatures; this may be related to membrane damage. More …
  5. Cultivars differ in resistance to bruising but this is not related to differences in dry matter concentration. For information on cultivars see: the AHDB Potato Variety Database (external website, opens in a new window).
  6. Ascorbic acid declines during storage, increasing susceptibility to discolouration after bruising.
  7. Pressure bruising in bulk stacks increases with depth in the stack, particularly when water loss is high. More …
  8. Water content may be influenced by
    • tuber size / maturity
    • availability of water
    • nutrition, particularly potassium
    • for more details see: Dry matter concentration

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Influence of handling and equipment on physical damage

  1. The depth and volume of bruised tissue increase with increasing impact energy.
  2. Impact with a flat surface results in less bruising than does impact with a curved surface (e.g. rollers).
  3. A single large impact may result in more bruising than a number of smaller impacts with the same total energy.
  4. There is a cumulative effect of a series of impacts of the same energy.
  5. In a series of impacts of different energies, the highest energy impact will have the dominant effect.
  6. The potential for bruising should be assessed before handling tubers (see: Minimising damage).

More …

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Factors influencing discolouration during bruising

  1. The colour development of a “blackspot” bruise results from oxidation of phenols, particularly tyrosine.
  2. A high content of free tyrosine may result in severe blackspot if impaction occurs.
  3. Cultivars differ in the proportion of free tyrosine.
  4. A high copper content in soil can result in high levels of tyrosine.
  5. Increased protein production may reduce the proportion of free tyrosine.
  6. Zinc influences protein production.
  7. Application of zinc may reduce phenol content and tuber blackening, even when there is no affect on tuber yield.
  8. Magnesium influences pigment development and is important for membrane formation.
  9. Magnesium deficiency which reduces yield also increases the propensity to bruise.
  10. During the season, chemicals involved in the bruising process may increase in the tuber and, together with an increased dry matter concentration, this may increase the propensity to bruising.

More …

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Minimising damage during harvesting and handling

  1. Before harvesting or handling, sample a number of tubers.
  2. Place in “damage barrel” (commercial or home-made) and shake or rotate to simulate handling.
  3. Assess for damage to the surface (use Potato Council procedure).
  4. Place in a “hot box” overnight.
  5. Assess for bruising (use Potato Council procedure).
  6. Use results to estimate sensitivity of crop to damage and bruising.
  7. Use “electronic potato” to check harvesting / handling equipment for potential to cause damage.
  8. Adjust sensitivity of “electronic potato” according to sensitivity of crop.
  9. During harvesting / handling sample potatoes and place in “hot box” to check damage.
  10. High levels of damage can occur when dropping tubers into trailers (use impact absorbing mats) or hoppers (keep a layer of tubers at the bottom).
  11. An electronic potato can be used to identify sources of damage and relative severity of damage in harvesting and grading operations.

More …

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Equipment for assessing bruising and damage

Potato damage barrel

  1. Used to produce a reproducible amount of handling of potato tubers.
  2. This is intended primarily to simulate “scuffing” damage to the potato skin during handling and as such can be used to assess skin set before harvest.
  3. A damage barrel can be made from a concrete mixer. For consistent results the barrel should be operated for a set time.

Hot box

  1. Used to accelerate bruise development, so that bruising can be assessed after 8 – 12 hours.
  2. The hot box maintains tubers at 34 – 35 ºC and high humidity for that period.
  3. Commercial hot boxes are available, e.g. this one.
  4. Hot boxes may also be home made.

Electronic potato

  1. Used to identify areas of impact during potato handling operations and to provide an indication of the relative strength of different impacts.
  2. These are available commercially.

More …

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Handling during or after storage: bruising

  1. This is particularly important with regard to seed crops, where handling may include application of seed treatments and where wound healing after handling will be important.
  2. Tubers are more susceptible to bruising at low temperatures.
  3. Tubers which have been stored at low temperatures should be warmed before handling.
  4. If water loss has occurred during storage, tubers are likely to be more susceptible to bruising.
  5. Cell membranes deteriorate during long term storage and tubers become more susceptible to damage.
  6. Wound healing occurs more slowly at low temperatures.
  7. Wound healing may be slower and less effective after long term storage.
  8. Healing of bruises may be slower than healing of cuts and healing of deep bruises may be slower than healing of shallow bruises.

More …

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Handling during or after storage: ‘finger nail’ cuts to skin

  1. Some cultivars appear predisposed to ‘finger nail’ damage (10-18 mm curved cracks to a depth of 5 mm).
  2. The method of warming tubers from cold storage prior to handling has been shown to effect the type and degree of damage.
  3. Finger nail cracks may be increased by heating in dry air (< 35 % RH) compared with handling straight from cold store.
  4. Finger nail cracks may greatly reduced by heating in damp air (70 – 80 % RH).
  5. Handing after storage can also result in bruised, split or crushed tubers particularly if tubers are not warmed (less effect of humidity than on fingernail cracks).

More …

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Damage (excluding bruising)

  1. Tubers with a very high water content may be more susceptible to shatter damage.
  2. Tubers will be more susceptible to “scuffing” damage before skins have set. More …
  3. Cultivars differ in rate of skin set and in resistance to damage.
  4. High levels of damage can occur when dropping tubers into trailers (use impact absorbing mats) or hoppers (keep a layer of tubers at the bottom).
  5. An electronic potato can be used to identify sources of damage and relative severity of damage in harvesting and grading operations. (See: Equipment)
  6. Soil conditions influence damage at harvesting:
    • stones and clods increase damage
    • some soil on tubers can provide a “cushioning” effect and thus reduce damage (particularly soils with a high content of organic matter)
    • damage may be high in very dry soil (which has little adhesion to tubers) or very wet soil (from which it is difficult to separate tubers)

More …

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Wound healing

  1. Physical damage will influence water loss and potential for infection by pathogens (Fusarium dry rot, gangrene, tuber blight and Pectobacterium soft rots).
  2. The deeper the wound the slower the rate of wound healing. The rate of water loss is also increased by depth of wound, with significantly higher levels of water loss from deeper wounds.
  3. The more immature the skin is the greater the rate of water loss from a given wound and the longer the wound takes to heal. The wound periderm (skin) will also be inferior to that of a more mature tuber. Immaturity therefore predisposes the tuber to damage and increases the negative effects of any damage sustained.
  4. Optimum conditions for wound healing (curing) are a temperature of 25 C and > 90 % relative humidity (but not a saturated atmosphere). At lower temperature of humidity wound healing occurs more slowly and the risk of disease infection increases.

More …

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Further information

Bruising and damage notes

Tuber quality 2020 (Includes an introduction to / review of bruising and damage)

Tuber quality review 2012 (Includes effect of temperature on bruising)

Recent research on bruising 2008 (Influence of water availability; sensitivity to bruising)

Bruising 2005 (Bruising is difficult to predict but risk assessment can be helped by pre-harvest sampling)

Tuber quality 2004 (Includes scuffing damage)

Skin and tuber quality 2003 (Includes: variability in bruising incidence; an experimental technique for measuring bruising – not produced commercially)

Bruising and damage 2001 (Physical and biochemical influences on bruising; wound healing; handling after storage)

Skin set and appearance 2000 (Includes fingernail cracks)

Bruising 1999 (Measuring bruising: electronic potato, hot box and damage barrel)

Bruising and damage 1998 (Causes of physical damage; physiology of bruising, including micro-nutrition)

Bruising 1994 (Biochemical pathway for bruising)

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