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  • Jan Lievens

Correct Engineered Applied Postharvest Technologies

Updated: Jan 11

Correct Engineered Applied Postharvest Technologies could save your company big money by giving you access to a quality platform what your customer is looking for…

Let us look a bit closer what is really involved…

Fresh horticultural commodities are unique packages of water! In fact, freshness is water, and freshness sells!

Water loss is one of the main causes of deterioration that reduces the marketability of fresh fruits and vegetables.

Profitability in fresh fruit, vegetable, and flower sales depends on the ability to deliver as much of this water as possible to consumers.

Effects of water loss: Many fruits, vegetables, and flowers become shrivelled after losing only a small percentage of their original weight due to water loss. Severe desiccation results in considerable losses, e.g., wilted leafy vegetables may require excessive trimming to make them marketable, and grapes may shatter loose from clusters if their stems are severely dried. Seriously shrivelled fruits, vegetables, and flowers are unmarketable and must be discarded. Water loss represents saleable weight loss and reduced profits.

Factors that affect water loss: Relative humidity, the temperature of the product and its surrounding atmosphere, and air velocity all affect the amount of water lost from fresh fruits, vegetables, and flowers. Water loss from warm products to warm air is particularly serious under windy conditions or during transport in an open vehicle.

HUMIDITY

The quality of fresh produce in storage depends to a great extent on the humidity.

Humidity is more difficult to control than temperature and often does not receive adequate consideration when storages are designed.

If the air is too dry, there may be enough water loss to affect the texture and cause visible shrivelling or wilting. It can even make the product unsaleable.

It is known that there are certain varieties of Stone fruit that have deterioration from as little as 0.8% weight loss…

Fruits such as apples and pears are most resistant to moisture loss, but during several months of storage they may lose 2-3% or more in weight because of water loss.

A moisture loss of 4-5% results in spongy texture and visible shrivelling of apples and pears.

Table Grapes get dry stems, brown berries and other problems…

Blueberries start shrivelling fast which results in big losses fast,

Excessive humidity, on the other hand, is conducive to growth of mould and decay organisms, particularly when water droplets form on the surface of pome and drupe fruits.

There is increasing evidence that extremely high humidity, particularly in the early part of cold storage, can contribute to physiological disorders in certain cultivars of apple.

With most commodities, however, the problem is one of maintaining enough moisture in the storage. (A few vegetables such as onions, garlic, squash, and pumpkin require low relative humidity.)

Vegetables are, in general, very susceptible to moisture loss in storage, with leafy vegetables losing moisture most readily; in an unfavourable environment they can suffer damaging water loss in a few hours.

A moisture loss of 4% or more may necessitate trimming of the outside wilted leaves. Softening or wilting of root crops or cabbage heads is to be apparent when the total moisture loss exceeds 5-6%, whereas moisture loss more than 8% renders the product unsaleable.

Unlike pome and drupe fruit (i.e., stone fruit), which is susceptible to increased decay and physiological disorders at high relative humidity, most vegetables requiring storage at high relative humidity are resistant to increased decay or physiological disorders.

For most vegetables that are susceptible to rapid water loss, the incidence of decay is usually not accelerated by the presence of condensation on the surface of the product if storage temperatures are maintained near those recommended for the product.

For a given relative humidity, moisture loss is greater with high produce temperature.

Thus, to minimize moisture loss it is essential to cool the produce promptly after harvesting with proper RH control and management.

In a refrigerated storage, the best way to maintain high humidity is to use an evaporator coil that is large enough to provide rapid cooling of the air without requiring operation at a low temperature combined but you will need added professional RH applications.

An undersized cooling coil must be operated with a low surface temperature to cope with demands, especially during loading of the storage, that cause moisture to condense and freeze on the coil and effectively remove water from the storage environment.

This lowers the humidity and results in abnormal moisture loss from produce. Also, the accumulation of frost reduces the air flow over the coil and lowers its cooling efficiency still further. There is proof how humidity of the storage atmosphere is related to the temperature of air leaving the coil.

The use of jacketed storages is one way of providing for a large cooling surface to minimize product moisture loss.

However, the main constraints in the application of jacketed storages to fresh produce are lack of precooling capacity, growth of microorganisms, changes in product flavour and texture in response to high humidity, and additional construction costs.

Where adequate humidity can be obtained in no other way, water should be added to the storage by humidifiers that introduce water in a gas form.

It is extremely important not to spray water directly on the produce because any water on the surface of the produce encourages microbial growth. Alternatively, produce stored in bulk bins (about 385 kg) or field boxes (about 20 kg) may be enclosed with a perforated polyethylene to maintain an atmospheric humidity of 94-98%.

Caution: A polyethylene barrier around produce that has not been precooled slows field heat removal and increases deterioration of the product.

Whenever mentioned in this article, humidity is expressed in terms of relative humidity (RH). RH is the actual amount (or percentage) of moisture in the atmosphere at a given time as related to the maximum amount (100%) that could be retained at the same temperature.

The movement of moisture between an object and the atmosphere depends on the relative, not the absolute, humidity.

The RH of the atmosphere changes with the temperature.

As the temperature is reduced, the RH increases to 100%, at which level the atmosphere is said to be saturated.

The temperature at which this occurs is called the dew point.

And that is why you need controlled humidity management.

And remember maintaining high relative humidity is sometimes difficult because refrigeration removes moisture, think of your own fridge in the kitchen.

Next time I will go in detail into the question what is water and what are the simpler scientific explanations…To create and manage your own content, open the Blog Manager by hovering over your blog feed and clicking Manage. Here you can create, edit and delete posts and manage categories. You can also update your post settings and SEO, duplicate or draft posts, turn off commenting, or delete a post altogether by clicking Edit on each blog post.


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