Chilling injury is a significant issue that can severely affect the quality, shelf life, and marketability of temperature-sensitive vegetables. This physiological disorder occurs when vegetables are stored below their optimal temperatures, leading to various undesirable effects, such as tissue softening, loss of flavor, the development of off-flavors, and increased susceptibility to decay.

For farmers, retailers, and consumers, understanding the causes and preventive measures for chilling injury helps maintain the quality and longevity of vegetables.

Let’s discuss this further.

What Is Chilling Injury?

Chilling injury is a type of cold damage that affects vegetables when they are exposed to temperatures below their tolerance levels but above freezing. According to the Food and Agriculture Organization (FAO) chilling injury occur at temperatures below 55°F to 60°F (13°C to 16°C).

Unlike freezing, which causes obvious ice crystal formation and severe cell damage, chilling injury can be more insidious, gradually affecting the vegetable’s quality. Symptoms include softening of tissues, surface pitting, internal discoloration, loss of flavor, and increased susceptibility to decay due to weakened cell structures.

You might also like: Potato Is Sprouting? Here’s What You Can Do

For instance, tomatoes stored at temperatures below 50°F (10°C) might develop an undesirable texture, and cucumbers can become water-soaked and mushy. These changes not only reduce the aesthetic appeal of the produce, but also diminish its nutritional value and taste.

Factors Contributing to Chilling Injury

Preventing chilling injury begins with understanding the factors that make vegetables susceptible to this condition. Key factors include vegetable variety, harvest maturity, storage temperature, and storage duration.

1. Vegetable Variety

Not all vegetables are equally sensitive to chilling injury. Some varieties are highly susceptible, while others can tolerate lower temperatures without significant damage. For example:

• Highly Susceptible Vegetables: Cucumbers, peppers, and tomatoes are particularly prone to chilling injury. When stored below 50°F (10°C), they may experience softening, discoloration, and loss of flavor. The texture becomes compromised, and the taste can turn bland or develop off-flavors, making them less appealing to consumers.

• More Tolerant Vegetables: Vegetables like carrots, cabbages, and potatoes are more resilient to cold temperatures. These crops can be stored at temperatures as low as 32°F (0°C) without suffering major damage. Their natural structure allows them to withstand colder environments, which is why they are often stored in refrigerated conditions without adverse effects.

Understanding the specific sensitivity of each vegetable variety is crucial for determining the appropriate storage conditions to prevent chilling injury.

2. Harvest Maturity

The stage at which vegetables are harvested plays a significant role in their susceptibility to chilling injury. Vegetables harvested either too early or too late are at greater risk:

• Early Harvest: Vegetables harvested before reaching full maturity may not have fully developed their natural defenses against cold temperatures. For instance, immature tomatoes, picked before their green color begins to change, are more likely to suffer from chilling injury, showing symptoms like pitting and a mealy texture.

• Late Harvest: On the other hand, vegetables harvested beyond their peak maturity are also vulnerable. Overripe produce, such as bananas or avocados, tends to become overly soft and develop off-flavors when stored at low temperatures. These vegetables may already be in the early stages of decay, making them more susceptible to cold damage.

Harvesting at the correct stage of maturity is critical to reducing the risk of chilling injury during storage.

3. Storage Temperature

The temperature at which vegetables are stored is the most critical factor in preventing chilling injury. Most vegetables have specific temperature ranges that they can tolerate without suffering damage. Exposing them to temperatures below these ranges can cause cellular damage, leading to:

• Tissue Softening: This compromises the texture of vegetables, making them less firm and appealing. Softened tissues are more prone to mechanical damage during handling and transport.

• Loss of Flavor: Chilling injury often results in a bland taste or the development of off-flavors, such as bitterness or mustiness. This can significantly reduce the vegetable’s appeal to consumers.

• Increased Susceptibility to Decay: Cold-damaged tissues are more vulnerable to microbial invasion, accelerating spoilage. This can lead to significant post-harvest losses, which are estimated to be as high as 25% in some cases.

Maintaining the correct storage temperature is essential to preserving the quality of vegetables and minimizing the risk of chilling injury.

4. Storage Duration

The length of time vegetables are stored at low temperatures also influences the risk of chilling injury. The longer the exposure to suboptimal temperatures, the greater the likelihood of damage:

• Short-Term Storage: Even brief exposure to temperatures slightly below the optimal range can cause chilling injury if the storage duration is extended. For example, cucumbers stored at 45°F (7°C) for more than two weeks may begin to show signs of chilling injury, such as softening and discoloration.

You might also like: Are Fresh Foods Superior To Canned And Frozen?

• Long-Term Storage: The effects of chilling injury are cumulative. Studies have shown that vegetables stored at 35°F (1°C) for more than three weeks are at a significantly higher risk of developing chilling injury compared to those stored for just one week. As the duration increases, symptoms like increased susceptibility to decay and off-flavor development become more pronounced.

Effective Measures to Prevent Chilling Injury

Preventing chilling injury involves a combination of pre-harvest, harvest, and post-harvest practices. Here are some key strategies:

1. Pre-Cooling

Pre-cooling is a crucial step in reducing the risk of chilling injury. This process involves rapidly lowering the internal temperature of vegetables after harvest to slow down their metabolic processes. Effective pre-cooling methods include:

• Forced-Air Cooling: Air is circulated over the produce to quickly remove heat.

• Hydrocooling: Vegetables are cooled by immersion in cold water.

• Vacuum Cooling: Air pressure is reduced to allow the rapid evaporation of water, which cools the produce.

Pre-cooling to a temperature of 32-35°F (0-2°C) within 24 hours of harvest is recommended for many vegetables to reduce the risk of chilling injury.

2. Appropriate Packaging

Selecting the right packaging materials is essential for maintaining the quality and freshness of vegetables. Key considerations include:

• Breathability: Use materials like perforated plastic bags or mesh bags that allow air circulation, preventing moisture buildup and condensation.

• Moisture Absorption: Incorporate materials like silica gel packets to control humidity within the package.

• Protective Padding: Use tissue paper or bubble wrap to prevent bruising and damage during transport and storage.

• Avoid Overpacking: Ensure sufficient space between vegetables to allow proper air circulation and prevent pressure-related damage.

Following these guidelines can significantly reduce the risk of chilling injury.

3. Controlling Humidity

Maintaining optimal humidity levels is another critical factor. Humidity refers to the amount of moisture present in the air within the storage environment. It plays a critical role in preserving the quality and extending the shelf life of perishable produce.

Vegetables stored at temperatures below their optimal range can suffer from chilling injury, which can be exacerbated by improper humidity levels. Adequate humidity helps mitigate some effects of chilling injury by maintaining vegetable texture and preventing moisture loss, but it must be carefully controlled to avoid contributing to decay or mold growth.

Leafy greens, such as lettuce and spinach, require higher humidity levels (90% – 95%) to prevent wilting and dehydration, as their delicate tissues are highly susceptible to moisture loss. Root vegetables, like carrots and beets, also generally require high humidity to avoid drying out and maintain their crispness.

In contrast, bulb vegetables such as onions and garlic prefer lower humidity levels to prevent rot and sprouting, as excess moisture can lead to decay. Fruiting vegetables, including bell peppers and cucumbers, have moderate humidity needs to balance moisture retention while avoiding issues like mold or excessive moisture that can contribute to spoilage.

4. Maintaining Optimal Storage Temperature

Research the specific temperature requirements for each type of vegetable. For example, root vegetables like carrots and potatoes often require colder conditions (32°F to 40°F) compared to leafy greens or tomatoes. Temperature-controlled storage facilities or climate-controlled containers are ideal for maintaining these conditions. Regular monitoring of storage temperatures is also essential to ensure they remain within the recommended range.

6. Applying Modified Atmosphere Packaging (MAP)

Modified Atmosphere Packaging (MAP) is a preservation technique that involves altering the composition of gases within the packaging. This change in the composition of gas slows down the respiration rate and delays the ripening process of the produce. As a result, the physiological and biochemical changes that can cause chilling injury are minimized.

In the usual setting, the typical atmospheric gases—oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂)—are adjusted to optimal levels for the specific product being packaged. For example, reducing the oxygen content can slow down oxidation and microbial growth, while increasing carbon dioxide levels can inhibit the activity of spoilage microorganisms. Nitrogen, an inert gas, is often used to displace oxygen and act as a filler gas.

Conclusion

Prevent chilling injury to vegetables can be managed through proper understanding and application of storage techniques. By considering the specific needs of different vegetable varieties, optimizing storage conditions, and using appropriate technologies like pre-cooling, MAP, and humidity control, farmers and retailers can significantly reduce the risk of chilling injury.

These measures not only help preserve the quality and freshness of vegetables but also reduce post-harvest losses, ensuring that consumers receive the best possible produce.

The post Understanding and Preventing Chilling Injury in Vegetables appeared first on The Food Untold.

Are fresh foods superior to canned and frozen? Well, for most of the time, fresh foods are the best in terms of quality (flavor, texture, and nutrients). This is almost true if you were the one who raised and harvested them, and the food in question is in season. But if the food is out of season, we would be dealing with produce that require transport and extended storage period. In most cases, additional process like canning or freezing has to be carried out. This is to ensure the produce reaches the customer without compromising quality.

You might also like: What Does Blanching Fruits And Vegetables Achieve?

However, the common belief is that fresh, especially fresh-from-the-farm fruits and vegetables are always superior to canned and frozen. For this reason, most people opt for fresh produce. Well, the truth is that the difference is not significant. And there are some instances that frozen foods contain more vitamins and minerals than their fresh counterparts. The same thing can be said for canned foods.

Here’s how.

FLASH FREEZING OF PRODUCE AT ITS PEAK QUALITY

Fruits and vegetables are perishable food items. To prevent them from deteriorating quickly, they are usually flash frozen at the same location where harvested. Clarence Birdseye, an American inventor, developed the concept of flash freezing in 1942 when he was looking for a way to eat fresh vegetables during the winter. Flash freezing is a process whereby the food is subjected to extremely low temperature in just a few hours. In the case of vegetables, they are first washed and blanched prior to freezing. Blanching involves placing the vegetables in boiling water for several minutes to kill the harmful microorganisms.The process also helps preserve the color, texture, and flavor by deactivating enzymes. Enzyme activity speeds up the degradation of fruits and vegetables.

Blanching is generally not performed for fruits prior to flash freezing as the blanching temperature may adversely affect their quality. However, adding vitamin C or sugar to fruits prior to flash freezing helps slow down enzyme activity.

Because flash freezing reaches ultra low temperatures in a short period, only small ice crystals form. This reduces the damage to the cell membrane of the produce. And since the produce is frozen at its peak quality, the nutrients and minerals are retained and maintained. In some cases, produce that has been frozen can contain more vitamins and minerals as compared to fresh produce that has been transported for a long period, or displayed at the market or sitting in your kitchen prior to consumption.

In fact, this work studied vitamin retention between frozen and fresh fruits and vegetables. The study found no consistent differences between frozen and fresh. However, frozen blueberries, corn, and green beans contained more vitamin C than their fresh counterparts. Furthermore, frozen broccoli contained more riboflavin (B vitamin) than fresh.

CANNING INCREASES BIOAVAILABILITY OF SOME NUTRIENTS

Canning involves placing foods in jars and then heating them at a temperature that prevents the growth of harmful microorganisms. However, the temperature can also lead to losses in nutrients as the vitamins leech into the liquid. The same thing happens when we boil vegetables or fruits at home. Exposure to oxygen and light also affects nutrients negatively. But more is lost during processing that involves heat. This is especially true for fruits and vegetables rich in water-soluble vitamins and minerals. Vitamins C and B vitamins are particularly sensitive.

You might also like: How Nutrient Loss Occurs In Fruits and Vegetables

But how much exactly is lost during canning though?

Well, the amount of nutrient loss is not that significantly different from that of produce not consumed immediately. Remember that a vegetable or fruit starts dying once removed from the mother plant. And in some instances, some canned foods contain more nutrients than fresh.

How?

The heating and cooking increase the bioavailability of some nutrients.

One good example of this is canned tomatoes, the most consumed vegetables in the United States. When canned, tomatoes can significantly increase its lycopene content. This work studied the effect of heat treatment on carotenoid (lycopene is a carotenoid) content of cherry tomatoes. Canned tomatoes increased its lycopene content two-folds. The canned tomatoes contained 11.60 mg/100 g of lycopene, whereas the raw tomatoes only contained 5.12 mg/100 g of lycopene. Lycopene is an antioxidant that helps reduce the risk of developing prostate cancer.

Cooking also have a similar positive effect in the heart-protecting carotenoid content in carrots, spinach, and cabbage.

The post Are Fresh Foods Superior To Canned And Frozen? appeared first on The Food Untold.

Fruits and vegetables are rich in nutrients. They contain vitamins, minerals, and plant chemicals that our bodies need to stay healthy. And a lot of these nutrients are not found in animal food. A good example of an essential nutrient is vitamin C. This vitamin is not sourced from animal food in significant amounts. And our bodies cannot synthesize vitamin C either. So a meat-based diet will not be sufficient. In order to consume an adequate amount of vitamin C, one must get it from fruits or vegetables, or otherwise from supplements.

But when it comes to the actual amount of nutrients, produce are at their peak just right after harvest. Detached from the mother plant, their nutrients gradually break down. According to Food and Agriculture Organization of the United (FAO), post-harvest losses of vitamin C in green vegetables can be high after a few days of storage. In fact, a 2007 study revealed that vegetables generally lose 15-77% of vitamin C a week after harvest. The rate of loss varies depending on the produce. One study found that mature spinach could lose up to 80% of vitamin C after 3 days. Nutrient loss accelerates if they are mishandled or exposed to elements such as heat and light during storage. But a lot of factors come into play, really.

Here’s how exactly fruits and vegetables lose nutrients over time.

Keep reading.

You might also like: Ethylene And Ripening In Fruits And Vegetables

HARVESTING AND RESPIRATION

The first thing that affects the freshness of fruits and vegetables is the manner they are harvested. Harvesting by machine increases the risk of damaging the produce. Many root vegetables are hardy, and they are usually harvested this way. Carrots, parsnips, and potatoes are usually harvested by machine.

Delicate vegetables such as tomatoes and salad leaves are easily damaged, which speeds up the nutrient loss. Harvesting by hand helps minimize the damage and increase the shelf life of produce. Since delicate vegetables are vulnerable to bruises and cuts, it is ideal to harvest them before fully ripe. Damage causes cells to break open, exposing the nutrients.

Ideally, fruits and vegetables must be harvested once they have reached their peak ripeness or desirability. At this stage, they are full of flavor and nutrients. They do not die after harvest though. This is very evident in onions, potatoes, and other root vegetables which sprout. They continue to respire, and take in oxygen for days, weeks or even longer. Some produce can stay notably fresh for longer periods. For example, potatoes can stay fresh in a cool, dark place for 3 months.

The main factor that dictates the rate of nutrient loss is the finite nutrients in store. After harvest, produce cannot replace organic materials such as carbohydrates and proteins. Fruits and vegetables use them up during respiration. During this process, the produce lose moisture and heat. This in return leaves us fewer nutrients once we consume it. The loss is much quicker in fruits and vegetables with higher respiration rates. Furthermore, the longer the produce respires, the more nutrients are lost. Sweet corn, mushrooms, asparagus, and peas have extremely high respiration rates. Aging follows once the nutrient reserves have been exhausted.

HEAT, OXYGEN, AND LIGHT

During processing, cooking, and storage, it is inevitable to expose the produce to many elements. Heat, oxygen, and light particularly accelerate the loss of nutrients. Many vitamins are sensitive to these elements. This is why cooking fruits and vegetables lose nutrients during cooking. More is lost when they are cooked in water. This is especially the case for water-soluble vitamins and minerals. Many vegetables could lose half of their vitamin C after boiling. Studies have shown that vitamin C and B vitamins are most sensitive. Fat-soluble vitamins D, E and K , fiber and minerals are less fragile and largely not affected by cooking.

You might also like: Are There Fruits That Continue To Ripen After Harvest?

Not known to many, exposure to oxygen does affect the nutrients in fruits and vegetables. When cutting fruit or vegetable, the inside gets exposed to air. The apparent effect here is discoloration in fruits like apples and bananas. However, the presence of oxygen also affects many vitamins. Vitamins are antioxidants—they react to oxygen. And the longer a fruit or vegetable is exposed, the less vitamins it will have. Vitamin C is most the sensitive to oxidation.

Light also affects the nutrients in fruits and vegetables. B vitamins are especially sensitive to heat and light. However, the adverse effect is not always the case. A study by the U.S. Department of Agriculture (USDA) found out that spinach leaves exposed to continuous light were more nutrient-dense than those exposed to continuous dark. The light increased the amount of carotenoids and vitamins C, E, K and B9 (folate).

WAYS OF PREVENTING NUTRIENT LOSS IN FRUITS AND VEGETABLES

One of the most common ways of preserving nutrients of fruits and vegetables is storing in a low temperature environment. Most delicate vegetables should be chilled. The low temperature slows down physical and chemical reactions in the cells, thus protecting the nutrients. Storing broccoli at 32ºF (0ºC) for 7 days retains most of its vitamin C. If stored at 68ºF (20ºC), broccoli can only retain up to 44% of vitamin C. Transport vehicles have refrigerated facilities to provide a temperature-controlled environment. This keeps the produce as fresh as possible. In atmospherically-controlled facilities, fruits like pears and apples can remain fresh for up to 1 year.

However, the flavor of some hard vegetables such as potatoes, squash, onions can be affected by the chill air in the fridge. They will do fine in a cool, dark, ventilated area such as a cabinet or a kitchen pantry.

You might also like: Are Fresh Foods Superior To Canned And Frozen?

Many people believe that fresh is better than frozen. It is true if the produce is for immediate consumption. Food grown and those purchased locally is superior in nutrition. However, if the produce takes time to reach the destination, it is better frozen than fresh. Vegetables that are frozen right after harvest tend to preserve more nutrients than their fresh counterparts. This is very helpful for produce that take several days before it reaches the store.

To fight nutrient loss against oxidation, one common way is storing fruits and vegetables in air-tight containers. This prevents the produce from being exposed to oxygen. When cutting fruits, cut them in large pieces. The less surface area that there is, the more nutrient that is retained.

The post How Nutrient Loss Occurs In Fruits and Vegetables appeared first on The Food Untold.