The moisture content in fresh vegetables can be as high as 65% to 96%, but once harvested, they gradually lose water during storage and transportation. This dehydration leads to wilting, reduced weight, and significant economic losses. Even a small loss of 5% of their water content can cause wilting or shriveling, while some vegetables may not show visible wilting but still experience changes in taste, texture, color, and overall quality.
Mild dehydration can disrupt the metabolic balance of vegetables and increase the activity of hydrolytic enzymes. For example, when sweet potatoes are dried, starch breaks down into sugar, making them sweeter. Severe dehydration causes the concentration of cell fluids to rise, leading to an accumulation of ions like ammonia and hydrogen, which can damage cells and even destroy the structure of protoplasm. Excessive dehydration also increases abscisic acid levels, promoting ethylene production, which speeds up aging and leaf drop. Additionally, wilting reduces turgor pressure and alters mechanical properties, weakening the vegetable's ability to resist disease and store for longer periods. The more dehydrated the tissue, the more likely it is to become infected by microbes and lose its resistance quickly.
Therefore, controlling water loss is crucial during post-harvest handling, storage, and transport. However, there are exceptions. For instance, onions and garlic benefit from controlled drying before storage, which helps them enter dormancy. Chinese cabbage should be slightly dried before storage to reduce its freezing point and improve cold tolerance.
To prevent water loss after harvest, several effective measures can be taken:
First, packaging, waxing, or coating. One of the simplest ways to reduce water loss is to cover vegetables with plastic film or other waterproof materials, place them in bags, boxes, or cartons. Polyethylene film is an excellent choice. However, it’s important to note that packaging can slow cooling and must be chosen carefully to avoid absorbing moisture. Using compound wax or rosin on packaging can help prevent this. Although more expensive, these methods are valuable in commercial settings. Waxy coatings on the surface of produce, combined with proper packaging, can significantly reduce moisture loss.
Second, increasing air humidity. Maintaining high relative humidity in storage areas is another effective method. While high humidity can promote bacterial growth, it can be managed with the use of fungicides. Automated humidifiers can spray mist or steam into storage spaces, or water can be sprinkled on the floor, wet straw curtains can be hung, or condensation tubes can be kept slightly above the storage temperature. Keeping the humidity around 95% in the warehouse helps prevent moisture loss.
Third, proper ventilation. Whether using natural or mechanical ventilation, adequate airflow is essential to remove heat and prevent temperature fluctuations. However, wind speed should be kept low—between 0.3 to 3 m/s—as it has minimal impact on moisture retention.
Fourth, using a sandwich-type cold storage. This system consists of two walls with cold air circulating between them. The outer wall is insulated and moisture-resistant, while the inner wall is not. The evaporator is placed between the walls, allowing heat exchange without directly contacting the stored product. This prevents frost formation and maintains high humidity inside, reducing water loss.
Fifth, using a breeze library. Cold air is distributed through holes on the top of the storage area or is humidified before being introduced, effectively preventing moisture loss.
Proper preservation of fruits and vegetables plays a vital role in maintaining quality. Each product requires tailored treatment to ensure it stays fresh and retains its optimal condition throughout the supply chain.
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