| | Why do horticulture crops break down so quickly?
Deterioration can be rapid as the harvested product continues to lose water and is physiologically active. Mature crops are also more susceptible to pathogens, due to aging tissues and potential wounds.
What can be done to reduce post-harvest breakdown?
1. Harvest produce at the correct stage of development (avoid over-ripe or immature)
Recognizing the differences between various harvested crops will help to determine the appropriate way to handle the particular crop.
Immature or overripe produce will store differently than mature produce. The more mature a harvest product is, the harder it is to store and the quicker it needs to be marketed. Overripe produce often breaks down rapidly and will accelerate ripening of adjacent produce.
Immature produce may need to be handled differently to ensure marketable quality. Some crops will ripen after harvest, provided that they are physiologically mature, while others will stay at the stage and condition they are harvested at.
2. Minimize wounding or damage
Minimizing harvest damage can improve storability of most crops. Wounds are an open door for the entry of post-harvest pathogens and can increase moisture loss dramatically. Curing can improve storability of onions and potatoes, as this can allow some level of wound healing and will tighten up skins. These same crops will benefit from a top-kill procedure or lifting, as this improves skin set and preparation for harvest.
Careful and minimal handling of most crops will reduce the level of damage and improve the quality. Some crops should be packaged in the field to reduce handling.
3. Consider the temperature of the harvested product
Harvested produce continues to be physiologically active after removal from the plant. For most produce, removing field heat will slow aging and decrease metabolic activity and respiration. Harvesting the crop in cool conditions will reduce the amount of heat that needs to be removed and will reduce cold storage costs.
Heat removal can be accomplished in a number of ways, including packing in ice slurries or using forced air, vacuum cooling or room cooling. The choice of cooling method will depend on the type of produce, as some crops are sensitive to free or surface moisture, some crops are stored in bulk or separately and some crops will not tolerate excessive cooling.
4. Carry out grading procedures
Post-harvest grading can include trimming, washing, grading for size/uniformity, etc. and will improve salability. Removing material such as damaged leaves, cull product, excessively damaged or diseased produce will improve the overall post-harvest quality. Damaged material can accelerate ripening of adjacent produce and increase the likelihood of disease development and spread.
Washing of produce is acceptable for some crops, as this improves salability and removes dirt, pathogens, spray residues, etc. Wash water must be disinfected regularly, as contamination can take place. Note, some crops are sensitive to disinfection products (e.g. bleach).
What impact can cold conditions or frost have on post-harvest handling?
Cool growing conditions can slow down the growth, development and maturation of many horticulture crops, resulting in a higher amount of immature produce and an increased risk of frost damage and crop loss. Immature produce will have to be handled differently.
Some crops may have delayed or altered ripening when growing conditions are below average or when they have been exposed to frost. Some protection may be required to minimize injury and ensure a crop can be harvested, however, abandoning a crop is sometimes the best option.
When crops have been exposed to cool or frozen conditions or frost, it is advisable to handle them differently. For example, the temperature at which potatoes are harvested affects their susceptibility to bruising. Tubers that are warmer than 18-20°C will be more susceptible to black spot bruising, while tubers that are harvested at pulp temperatures less than 7°C will be more susceptible to shatter bruising. Potatoes that have been frozen will not store well and may endanger the whole stored crop.
Some crops may have elevated levels of different minerals following frost, such as nitrates, which may impact their quality.
Useful resource: The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks
Prepared by Robert Spencer, Ag-Info Centre, Alberta Agriculture & Forestry |
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