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.

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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.

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• 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.

Potatoes are one of the most consumed vegetables around the world. It is the 3rd most important crop in the world, after rice and wheat. In the United States alone, the starchy vegetable is the most consumed at 62% in 2021, according to Statistica. One of the reasons for this is the love for foods such as mashed potatoes and French fries. Because of this, the demand for potatoes is steadily high. To keep up with the demand, there should an abundant supply of potatoes. To do this, farmers and processors must do their best to minimize post-harvest losses. Causes of post-harvest losses in fruits and vegetables vary. In potato production, sprouting is one of the reasons for this.

In this post, we’ll discuss how sprouting occurs as well as the measures to suppress it.

HOW SPROUTING OCCURS

The primary reason potatoes sprout is their innate survival instinct. Sprouting allows the potato to reproduce and give rise to a new plant. Under favorable conditions, such as warmth, moisture, and access to light, the potato initiates sprouting as a means of generating offspring.

The process of sprouting begins when a potato detects conducive environmental conditions. Moisture is a critical factor that activates enzymes within the potato, initiating metabolic processes. The presence of moisture causes the potato to absorb it, softening the tissue and awakening the dormant buds. Once the buds are activated, they start elongating and pushing through the skin of the potato, giving rise to sprouting.

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Temperature plays a crucial role in the sprouting of potatoes. Cold temperatures act as an inhibitor, preventing sprouting, while warmer temperatures, typically ranging from 50°F (10°C) to 70°F (21°C), stimulate the growth of sprouts. Maintaining an optimal temperature range is important to avoid excessive elongation of sprouts, as this can lead to weak and leggy growth.

In addition to temperature, light also impacts potato sprouting. Exposure to light triggers the accumulation of a hormone called gibberellin in the sprouts, promoting elongation. Storing potatoes in a dark environment keeps the sprouts short and pale. However, prolonged exposure to light can cause the sprouts to turn green, indicating the production of solanine, a toxic compound that renders the potato inedible.

Sprouting has several detrimental effects on potatoes. It leads to increased respiration and moisture loss, resulting in reduced crop quality and value. The sprouts’ growth causes elevated levels of toxic glycoalkaloids, accelerated breakdown of starch leading to undesirable reducing sugars, and a decline in vitamin content. Moreover, sprouting accelerates the physiological aging of the potato, negatively affecting its appearance. For more on this, read this article.

IDENTIFYING AND REMOVING SPROUTED POTATOES

Sprouted potatoes are easy to spot, as they display distinctive characteristics that set them apart from fresh ones. Identifying these potatoes early on can help prevent potential health risks associated with their consumption.

To identify sprouted potatoes, look for long, pale shoots protruding from the eyes of the potato. The skin of the sprouted potato may also appear wrinkled or shriveled. In some cases, the sprouts may have even developed leaves or small roots. If any of these signs are present, it is clear that the potato has sprouted and should be dealt with promptly.

Once you’ve identified sprouted potatoes, it’s crucial to take immediate action to remove them from your pantry or storage area. These potatoes are more prone to spoilage, and leaving them among other fresh potatoes can accelerate the deterioration process, leading to potential food waste.

To properly dispose of sprouted potatoes, consider using a compost pile if available. Composting allows the potatoes to break down naturally and return nutrients to the soil. Alternatively, discard the sprouted potatoes in a manner that prevents animals from accessing them. While they may no longer be suitable for consumption, they can still serve a purpose in contributing to environmental sustainability.

EATING AND COOKING SPROUTED POTATOES

Although sprouted potatoes are not the best option for direct consumption, there are various ways to salvage and utilize them effectively.

One approach is to cut and cook the sprouted potatoes. If only the eyes have sprouted, you can salvage the rest of the potato by carefully cutting away the sprouted areas and any solanine. After removing these parts, you can proceed to cook the potato as you would with fresh ones. Boiling, mashing, or using them in soups or stews are all great options for salvaging sprouted potatoes.

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If you happen to have a dehydrator, you can salvage sprouted potatoes by making them into potato flour.

Start by slicing the sprouted potatoes into thin rounds and dehydrate them until they are thoroughly dried.Then grind the potato slices into a fine powder using a food processor. A blender will also do. This homemade potato flour is an excellent gluten-free alternative in baking.

STORING POTATOES TO PREVENT SPROUTING

In large-scale potato processing, ionizing radiation at low doses (0.1-0.2 kGy) is an effective method for preventing sprouting. Irradiation does this by breaking down the DNA and other cellular components in the potato’s eyes. As a result, the hormones that trigger sprouting are deactivated or destroyed, significantly reducing or preventing the growth of sprouts.

At home, you can also prevent sprouting by following these simple storage tips:

1. Clean the potatoes before storing: Thoroughly clean the potatoes by using a brush or vegetable scrubber to remove any dirt or debris from their surface. This step is crucial because dirt can harbor bacteria and contribute to early spoilage. After cleaning, allow the potatoes to dry completely before placing them in storage.
2. Store potatoes in a cool, dry place: An ideal storage location for potatoes is a cool and dark place with a consistent temperature ranging from 45°F (7°C) to 55°F (13°C). Excessive exposure to light and warm temperatures can promote the formation of chlorophyll, which is not desirable.
3. Use breathable storage containers: Avoid using plastic bags or airtight containers for potato storage, as these can trap moisture, creating a favorable environment for sprouting. Instead, opt for breathable storage containers like burlap sacks or mesh bags. These containers allow proper air circulation, reducing the chances of excess moisture buildup and sprouting.
4. Divide and conquer: If you have a large quantity of potatoes, it’s advisable to store them in smaller batches. By doing this, you can contain any potential sprouting to a limited number of potatoes, preventing it from spreading to the entire batch. This division helps minimize wastage, ensuring you can use the unaffected potatoes before they spoil.
5. Maintain regular spoilage checks: Check the potatoes in storage frequently for any signs of sprouting or rotting. To stop the other potatoes from being spoiled, throw away any potatoes that have already sprouted.

References:

J. Singh, L. Kaur (2016). Advances in Potato Chemistry and Technology (2nd edition). Academic Press.

H. Ramaswamy (2014). Post-harvest Technologies of Fruits & Vegetables. DEStech Publications, Inc.

A. Chakraverty (2014). Postharvest Technology and Food Process Engineering. CRC Press.

The post Potato Is Sprouting? Here’s What You Can Do appeared first on The Food Untold.

Unlike walnuts and pecans, peanuts are grown beneath the soil. And for this reason, they are prone to infections, especially aflatoxins. Aflatoxins are produced by the soil-dwelling fungi (mold) Aspergillus flavus and A. parasiticus. In peanuts and other nuts and grains, it is the most important of the mycotoxins from a human health perspective.

Aflatoxins are quickly and widely absorbed from the gut and are metabolized to toxic epoxides in the liver. These epoxides bind to and harm vital cell components like DNA, RNA, and protein enzymes. The primary clinical outcome of aflatoxin consumption is liver damage in all animal species. According to epidemiological studies, aflatoxins and the hepatitis B virus are cocarcinogens, and the risk of liver cancer is higher in areas where both aflatoxins contamination and hepatitis B are prevalent.

Internationally, aflatoxins in peanuts are required to not exceed 15 μg/kg. This considerably very low MRL (maximum residue limit) ensures that peanuts with high concentrations of aflatoxins cannot be traded. In the United States, the Food and Drug Administration (FDA) has set the allowable limit of aflatoxin levels in peanut products at 20 ppb.

Fortunately, there are several ways to remove aflatoxins in peanuts.

In commercial operations, aflatoxins are regularly removed from food or food ingredients. Solvent extraction methods have been used in most cases. Some foods or food ingredients have been treated with appropriate chemicals to inactivate aflatoxins. Some chemicals, such as ammonia, hydrogen peroxide, and sodium hypochlorite, have been found to be effective at inactivating aflatoxins.

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Let’s discuss further.

WHAT IS AFLATOXIN?

Mycotoxins are toxic secondary metabolites produced by certain fungi. When consumed in large amount or regularly may cause certain cancer. Of all mycotoxins, aflatoxins have unquestionably been the most studies. Consumers have been aware of their existence since 1960, when over 100, 000 turkey poults in England perished after consuming imported peanut from Africa and South America.

Aflatoxin is classified into two types, B1 and G1. Each of them has several subtypes. Aflatoxin B1, produced by A. flavus and A. parasiticus, is thought to be the most potent. In fact, it has been classified as carcinogenic (Group 1) to humans by the International Agency for Research on Cancer (IARC). For more discussion on these types of aflatoxin, refer to this file.

Aflatoxin production has been shown to occur in many food products, which include nuts, dried fruits, and cereals. In general, toxin production is directly related to a mold strain’s growth rate. In microbiological media suitable for mold growth, Asp. flavus strains can produce optimum concentrations of aflatoxin at 91°F (33°C), pH 5.0, and Aw (water activity) of 0.99. Some toxin can be detected within 24 hours under optimal growth conditions.

In peanuts, aflatoxin formation occur primarily during the curing of peanuts after they have been removed from the soil. Hence, it is crucial to perform proper handling and storage to control the growth of aflatoxins. Moisture and temperature during storage should especially be given more attention. They are the two most important factors that affect aflatoxin formation. The presence of aflatoxins in peanuts is obvious if there is discoloration, visible mold growth, and the nuts are shriveled.

Aspergillus spp.-contaminated peanuts. Source

With that being said, here are 5 effective methods that you can do you remove aflatoxins from peanuts.

5 EFFECTIVE METHODS OF REMOVING AFLATOXINS IN PEANUTS

Aflatoxin contamination can occur in the field prior to harvest, during harvesting, or during storage and processing. While certain treatments have been found to reduce aflatoxin formation in peanuts, the most effective way is to avoid it in the first place. This is not always possible. But there are technologies and methods that can prevent contamination that would otherwise occur.

A variety of industrial food-processing methods can also be used to manage the aflatoxins in peanuts. Some of these can also be performed at home. As simple as sorting by color, screening, and lot separation (either with or without blanching) can reduce the toxin levels. In subsistence farming situations, the manual sorting of inferior nuts is also an option. Aflatoxins are thought to be heat stable, but roasting peanuts can reduce B1 aflatoxins by 50–80%.

Sorting and cleaning

Sorting and cleaning is the simple yet effective way for removing aflatoxins from peanuts. This entails removing any discolored, moldy, or damaged and shriveled peanuts from the batch because they are more likely to contain aflatoxin. To remove any dirt or debris, peanuts can be washed in clean water. Although this method is simple and easy to use at home, it may not remove all of the aflatoxin found in peanuts. Hence, this should be combined with another method.

In some practices, water is treated so that the process is more effective. For example, peanuts may be soaked in electrolyzed acidic water. Electrolyzed acidic water has a low pH of around 2.5, and is used as an effective disinfectant in food contact surfaces. One study has found that soaking grains in electrolyzed acidic water for 15 minutes can reduce 80% to 90% of B1 aflatoxin in peanuts.

Roasting

One of the most widely used techniques for removing aflatoxin from peanuts is roasting. High heat causes the aflatoxin molecules in peanuts to disintegrate, rendering them safe to consume. It’s crucial to remember that not all roasting techniques are equally efficient. As already mentioned, aflatoxins are heat stable. Studies say the optimum temperature for the production of aflatoxins is between 81°F (27°C) and 86°F (30°C). But they can withstand heat at normal cooking temperatures.

It has been demonstrated that dry roasting, which involves roasting peanuts without any additional oil, is more efficient at lowering aflatoxin levels than oil roasting. Additionally, to ensure that all aflatoxin molecules are destroyed, peanuts must be thoroughly and evenly roasted. Dry roasting is typically done on a very high heat.

To remove aflatoxins from peanuts properly, ensure to reach a temperature of 320°F (160°C) or higher. This study has shown that at a temperature of 320°F or higher, aflatoxins can be completely degraded. Another study showed that adding sodium chloride and citric acid can substantially improve the effectiveness of the process. If you wish to replicate the process, the authors recommend using up to 5% of citric acid. More than that may adversely affect the taste of peanuts.

Chemical treatment

Commercially, chemical treatment to remove aflatoxins in peanuts is widely practiced. What is involved in this method are common disinfectants or sanitizers in the food industry. One of them is hydrogen peroxide, a strong oxidizer. The peanuts are soaked in a hydrogen peroxide and water solution for a set amount of time before being thoroughly rinsed. One study said that treating peanuts with 0.075% of hydrogen peroxide for 1 minutes can reduce aflatoxin levels by up to 90%. Another good thing is that hydrogen peroxide residue can be removed by drying. Furthermore, it is environmentally friendly since it breakdowns into oxygen and water once exposed to light.

Although this method has been shown to significantly reduce aflatoxin levels in peanuts, it may also have a subtle effect on the taste and quality of the peanuts.

Other chemicals used to remove aflatoxins in peanuts include ammonia, sodium hypochlorite, and benzoyl peroxide.

Irradiation

Irradiation is one of the most effective methods in making foods shelf life stable, in general. But its high cost required makes it less utilized. Irradiation can remove aflatoxins by exposing the peanuts to ionizing radiation to break down the aflatoxin molecules. Most applications of irradiation require a maximum overall average dose of 10 kGy (kilogray).

For the purpose of microbial reduction, the doses range between 1 to 10 kGy. However, the outcome is positively correlated with an increase in the radiation dose. In one study, a 10 kGy dose reduced the toxin levels in peanuts to 58.6. Another study used lower doses of 4, 6, and 8 kGy, which reduced the aflatoxin levels to 7.6%, 17.3%, and 23.25% respectively. Nonetheless, irradiation is a viable option in reducing the aflatoxins in peanuts to below the maximum allowed levels.

While effective, the irradiation process may become less appealing to consumers who are reluctant to consume irradiated foods due to possible exposure radiation. It is crucial to remember that the radiation used to irradiate food is extremely low and has been approved as safe by regulatory bodies such as the Food and Drug Administration (FDA) and World Health Organization (WHO).

Furthermore, the taste, texture, or nutritional value of the peanuts are unaffected by irradiation. Peanuts are rich in proteins and fats. And these macronutrients are barely unaffected by radiation at usual doses.

Biological control

Biological control is a technique for removing aflatoxins from peanuts that involves using naturally occurring predators or competitors of the fungus that causes the toxin. Many factors influence a fungus’s ability to compete for a host. These include the soil type, pH level, water content, mineral available, nitrogen and carbon availability. The soil microbiome, primarily fungi and bacteria, influences fungi’s ability to produce secondary metabolites.

Using a strain of the A. flavus that does not produce aflatoxins is one example of bio-control. Aflatoxin levels in peanuts are decreased when this strain is introduced to the soil where peanuts are grown because it outcompetes the strain that produces the toxin. This 2020 study evaluated 18 non-aflatoxigenic strains of A. flavus. 6 of them reduced the aflatoxin levels produced by the native aflatoxigenic strains by 50%. Although promising, this strategy faces challenges that prevent it from being a clear solution to reducing aflatoxins in peanuts. For example, its biology is not well understood due to the diversity of A. flavus.

An alternative to this is using other species that can effectively affect the fungi from producing aflatoxins.

In this 2018 Korean study, the authors used Aspergillus oryzae M2040, a strain isolated from fermented soybean. 1% inoculation level of the A. Oryzae strain showed that it can effectively displace A. flavus and inhibit aflatoxin production.

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Another example is the bacterium Bacillus subtilis, whose many strains are safe for human consumption. It also produces enzymes that break down aflatoxins. This Japanese study used strains of B. subtilis that proved to be inhibitory on the growth of both A. flavus and A. parasiticus.

References:

Y. Motarjemi, G. Moy, E. Todd (2014). Encyclopedia of Food Safety. Academic Press.

Y. Motarjemi, H. Lelieveld (2014). Food Safety Management: A Practical Guide for the Food Industry. Academic Press

G. Cooper (2018). Food Microbiology. Library Press.

J. Jay, M. Loessner, D. Golden. (2005). Modern Food Microbiology (7th edition). Springer.

B. Ray (2005). Fundamental Food Microbiology (3rd edition). CRC Press.

I. Shaw (2013). Food Safety: The Science of Keeping Food Safe. John Wiley & Sons, Ltd.

The post How To Remove Aflatoxins From Peanuts? appeared first on The Food Untold.

Are you headed to buy some pineapples at the market? The best time to buy pineapples is anywhere between March through July. Between these times, you can find pineapples at their peak quality — sweetest and juiciest. But luckily, pineapples are readily available all year round. If you suddenly crave for some pineapple, and do not have an idea how to pick one, there are several signs to look for. Here they are.

THE DISTINCT SWEET PINEAPPLE SMELL

Some fruits when ripe do not give off a smell without cutting them open. But pineapples are different. They are an aromatic tropical fruit. This means they are able to give off that distinct sweet pineapple aroma without the need to slice them. The aroma is stronger when you put your nose closer to the base of the fruit or stem end. If you do not smell the sweet odor, the pineapple is most probably not ripe yet The reason why ripe pineapples can give off a smell because of volatile aromatic compounds.

The volatile aromatic compounds that provide the distinctive sweet aroma of pineapple vary, different on several factors. These include the pineapple variety, storage condition, area it was grown, and more particularly the stage of ripening. Extensive researches have found that pineapple contain at least 280 volatile compounds. These compounds include acids, lactones, hydrocarbons, esters, sulfur-containing compounds and carbonyl compounds.

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One study found that the esters Ethyl hexanoate and methyl hexanoate are the most concentrated in pineapples. These two have a fruity smell, and they have found use as a flavoring agent in food. In fact, Ethyl hexanoate is used to impart apple-like flavor in beers. Methyl hoxanoate is also produced industrially to produce pineapple odor in perfumes.

THE BRIGHT YELLOW PINEAPPLE SKIN

Most young fruits are green, and turn yellow as they mature. Pineapples are no different. Most pineapples in the supermarket are bright yellow with a hint of green. This color indicates that the pineapple is at its peak ripeness. Pineapples start to turn bright yellow from the base. The further the color change has progressed towards the crown, the more ripe the pineapple.

Avoid pineapple that is dark yellow or orange with some brown spots. This indicates that this is already overripe. Brown leaves are also an indication. While overripe pineapples are edible, they are not enjoyable to eat. Overripe pineapples contain high amount of fructose, which some individuals have a hard time digesting.

Some green parts of the skin is fine. But stay away from pineapple that is totally green as this is often underripe.

An unripe pineapple is not sweet or juicy. And there is no way artificial way to ripen it since pineapple is an example of non-climacteric fruit. Non-climacteric fruits are harvested only when ripe because their ripening process stops once harvested or removed from the mother plant.

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There are some pineapples that are still green, but are actually ripe already. This is why it is important to look for other indications.

You would also want to visually check the appearance of the leaves as they indicate freshness.

HEAVIER THAN IT LOOKS

After checking the color of the fruit, the next thing that we instantly do is feel it with our bare hand. Does it feel heavier than it looks? They say a fruit that is heavy for its size is already ripe. It is true for most fruits, even for pineapples. A pineapple that looks heavier is sweet, juicy, and more enjoyable. The next time you visit a fruit stand or supermarket for a pineapple, try to pick two, and feel the weight with your hand. Choose the one that is heavier.

It is worthy noting that assessing the ripeness of pineapple using this method alone is not a sure thing. Remember that pineapples come in varieties, shapes, and sizes.

FIRM BUT SQUEEZABLE

This is perhaps that most reliable way of telling the ripeness of a pineapple—the squeeze test. The reason why most consumers do this when they pick a pineapple.

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An unripe pineapple when touched is hard, and you cannot squeeze it at all. Once a pineapple is ripe, it is firm but slightly soft that you can squeeze it.

Just watch for pineapples that are too soft. They may either be overripe or starting to rot. When you press them with a bit of pressure, your finger leaves a little indent. Over ripe pineapples also smell like vinegar or alcohol. This happens because the sugars have started to undergo fermentation.

EASY TO REMOVE LEAVES

The spiky green leaves of a pineapple called fronds are also a good indication to check for ripeness. One pineapple usually has 30 leaves. These green leaves will be deeply attached in an unripe pineapple and challenging to pull without exerting a lot of force.

But this is not the case for a ripe pineapple. The fronds of a ripe pineapple should easily come off when pulled.

The post Post-harvest: How To Pick A Pineapple? appeared first on The Food Untold.

Modified atmosphere packaging (MAP) is a special form of packaging wherein the internal package atmosphere is modified so that the gaseous composition differs from that of air, which is replaced with nitrogen and/or carbon dioxide. In most cases, the gas composition is 78.08 % nitrogen, 20.96 % oxygen, and 0.03 % carbon dioxide. But this still depends on the type of food product, the permeability of the packaging material, microbiological activity, and respiration of the food. High-fat products is best packed with carbon dioxide, whereas baked goods should be packed with nitrogen. High oxygen MAP (up 70% oxygen) is ideal for red meats as it helps retain the red color.

This packaging technology can be traced back in the 1800s when French chemist Jacques Étienne Bérard observed a delayed ripening process in fruits in an oxygen-depleted atmosphere. The Académie des Sciences awarded him a prize for being a pioneer in ripening of fruit study.

Today, MAP is a part of our daily life as it is employed for various foods—from fresh fruits to processed meats. So what does modified atmosphere packaging does, anyway? Well, MAP can effectively lengthen the shelf life by as much as 200%. It can also retain the quality and freshness of various food stuff, reducing the need for artificial preservatives or stabilizer.

Most minimally processed foods use MAP in combination with aseptic technology and refrigerated temperature. When used together with aseptic packaging, MAP becomes a more effective technology.

HOW MODIFIED ATMOSPHERE PACKAGING IS DONE

There are two methods of modifying the atmosphere within the package of a product: passive process and active process.

In the passive process (produce respiration), the generation of the modified atmosphere depends on the respiration of the produce. Respiration refers to the utilization of sugars in order to produce energy in plants. This is a continuous process even after harvest of fruits and vegetables. The product of respiration is carbon dioxide consumption and carbon dioxide liberation. The result of this is the gradual decrease in oxygen to the desired level as the level of carbon dioxide increases. The reduced respiration rate and conserved energy lead to extended shelf life. Since the passive process relies on produce respiration, it is a slow process that its benefits of MAP are not quickly realized. Fresh respiring fruits and vegetables are the most common application of this method.

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In the active process (gas flushing), on the other hand, a gas mixture of known concentration of oxygen, carbon dioxide, and nitrogen is flushed to the package headspace. This immediately suppresses ethylene and respiration. Before the gas flushing, a machine vacuums all of the air and toxic gases out of the packaging. And then through the same perforation, the gas mixture is flushed to the package.

THE ROLES OF OXYGEN, NITROGEN, AND CARBON DIOXIDE

The key to MAP’s effect is limiting the supply of oxygen while increasing the levels of carbon dioxide and/or nitrogen.

Oxygen

Oxygen has several ways of spoiling food. It is a highly a powerful oxidizing agent. When it reacts with certain compounds, it leads to deteriorative reactions. An example of this is browning reaction that occurs after cutting an apple. This change in color is a result of oxidation due to exposure of the flesh to air. Another degradative process that leads to losses in food quality is lipid oxidation. The presence of oxygen in fat-containing foods triggers a reaction that produces adverse effects, such as off-flavor, off-odor, and color change.

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Oxygen is one of the few requirements for microorganisms to survive. But this can be stopped by reducing the levels of oxygen inside the packaging and replacing it with carbon dioxide and/or nitrogen. The ability of aerobic spoilage bacteria to proliferate is slowed by the extremely low oxygen (usually 2%–3%) and moderately high carbon dioxide (5%–20%) levels present in a package, extending the shelf life of the product.

But there are some MAP applications wherein the oxygen levels are higher. An example of this is during packaging of unprocessed meats to maintain the red color of oxymyoglobin. Or to permit respiration of produce. By packing fresh red meat in a MAP of 80% oxygen and 20% carbon dioxide, the shelf life of the meat can be increased from three to seven days at 32°F (0°C) to 35.6°F (2°C). However, this could lead to issues with oxidative rancidity in fatty fish or the formation of off-colors in cured meats.

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Carbon dioxide and nitrogen

Carbon dioxide suppresses microbial activity in two ways. First, it lowers the pH of the product by forming mild carbonic acid when it dissolves in water in the food. And second, it has a negative impact on the enzymatic and biochemical processes that take place in the cells of both food and microorganisms.

To prevent rotting in fresh fruits and vegetables, a carbon dioxide concentration of 10% to 15% is needed. Some crops (such strawberries and spinach) can survive this level, but the majority cannot, making MAP inappropriate.

For processed (non-respiring) foods, the atmosphere should be oxygen at the lowest possible and carbon dioxide as high as possible without causing the package to collapse or changing the flavor or appearance of the product. Ground coffee is one of those that benefit from MAP. By packaging ground coffee in a MAP of carbon dioxide/nitrogen mixture, oxidation is prevented and the volatile aroma compounds are preserved.

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Nitrogen gas is common is processes that involve hermetic sealing of the package. This gas is tasteless, odorless, colorless, nonflammable, and nontoxic. And unlike oxygen, nitrogen is nonreactive with foods. So it offers protection from spoilage, oxidation, weight loss, dehydration, and freezer burn. In contrast to vacuum packaging, MAP uses high barrier film that prevents the modified atmosphere from escaping. With nitrogen, the package becomes pressurized, allowing it to stay loose-fitting. This avoids the skintight vacuum packaging, and prevents the packaging from collapsing. Nitrogen is the reason why snacks such as potato chips remain crispy.

However, there should be control over the degree of atmospheric modification. This is because there is a risk of physiological disturbances in the living tissues.

DISADVANTAGES OF MODIFIED ATMOSPHERE PACKAGING 

MAP is widely used today because of its effectiveness in extending the shelf life of products while reducing the need for chemical preservatives. However, it has its downsides as well.

MAP works by reducing the levels of oxygen within the packaging materials. Although this slows down the growth of harmful microorganisms, it does not work well against anaerobic bacteria. These kinds of bacteria, particularly Clostridium botulinum, are capable of thriving without oxygen. Other microorganisms of concern in MAP-packed foods include Aeromonas hydrophila, E. coli,  Campylobacter jejuni, Salmonella, and Listeria. To retard their growth, foods in MAP must have short storage times and be held at low temperatures. Controlling the water activity (at least 0.92 or lower) and using salt can also help.

The original gas composition in MAP gradually decreases over time, reducing its capability to protect the product against harmful elements. These depend on several actors such as product respiration, the load of aerobic and anaerobic bacteria, bacterial respiration, gas permeation via packaging materials/seals, temperature, light. Hence, choosing the right packaging material is important, in addition to proper storage and handling. Gas permeability and moisture vapour permeability are important parameters. Packaging materials for MAP are classified based on their barrier properties against oxygen.

If the packaging material is of poor quality, the nitrogen or carbon dioxide will be replaced with the surrounding oxygen through diffusion. If the packaging provides a strong barrier, the gases will stay inside the container for a longer amount of time, protecting the product.

References:

 E. M. Yahia (2009), Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press

V. Vaclavik, E. Christian (2014). Essentials of Food Science (4th edition). Springer.

J. Jay, M. Loessner, D. Golden (1994). Modern Food Microbiology (7th edition). Springer.

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

P. Fellows (2000). Food Processing Technology: Principles and Practice (2nd edition). CRC Press.

H. Ramaswamy (2015). Post-harvest Technologies of Fruits and Vegetables. DEStech Publications, Inc.

The post What Does Modified Atmosphere Packaging (MAP) Do? 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.

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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.

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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.

Blanching is one of the few food processing operations that are nearly exclusive for vegetables and some fruits. However, Blanching is rarely utilized for soft fruits because of the possible losses in flavor, texture, color, and water-soluble components. Basically, blanching is a process that involves plunging food into a boiling water for a short period of time (around 1 to 3 minutes). Commercially, this is done by using a bath of hot water or passing the food through an atmosphere of saturated steam. The quick heat treatment is followed by immediate cooling under cold running water or in iced water. Rapid cooling avoids excessive heat that may damage the product. Blanching treatments on experimental basis has to be established. This depends on the nature of the vegetable or fruit, its size, shape, and the level of enzymes.

But what exactly does blanching fruits and vegetables achieve?

BLANCHING DEACTIVATES ENZYMES

Well, blanching is merely a pre-treatment process whose main purpose is deactivate enzymes in fruits and vegetables. These naturally occurring enzymes are responsible for the negative changes such as discoloration or browning, off-flavor, texture change, and nutrient degradation. This is usually carried out right after the preparation of raw materials and before the main process, usually freezing. Although freezing preserves fruits and vegetables, it does not completely stop the enzyme activity. By blanching prior to freezing, the produce in its frozen state prevents the loss of flavor, color, as well as texture for several months. When canning using large cans, the time needed to reach sterilization temperatures may be sufficient to allow enzyme activity to happen. Furthermore, blanching helps dispel air from intercellular spaces, which assist in the formation of a headspace vacuum during canning. This just tells how important blanching is prior to canning operation.

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Additionally, blanching, combined with peeling/cleaning food, helps save on energy consumption, space, and equipment cost. It also helps remove pesticide and reduce microbial load.

Just a reminder though. Like pasteurization, blanching is a mild heat treatment. Sure, the heat involved destroys bacteria. But the temperature and time are not sufficient to destroy many pathogens.This is another reason why blanched produce requires further preservation treatment such as freezing, canning, and drying.

A CLOSER LOOK AT PLANT ENZYMES

Basically, enzymes are proteins whose role is to speed up chemical reactions to support life. Our body also contains enzymes. They help build muscles, digest food and destroy toxins. Enzymes are essential to life. In fact, without enzyme, our body would not function.

Enzymes also hold the same importance in fruits and vegetables. They remain active after harvest. The bad thing is that their activity results in undesirable changes in fruits and vegetables. One of the most commonly discussed in food science is enzymatic browning in fruits such as apples. Apples contain phenols and polyphenoloxidase (PPO), a type of enzyme. When an apple is cut or sliced, these two become exposed to oxygen, starting an oxidation reaction. The PPO enzyme converts the phenols into the brown pigment melanin. The application of heat to denature the PPO enzyme is one way to prevent this from taking place.

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Aside from PPO, the enzymes lipoxygenase, polygalacturonase, and chlorophyllase are also responsible for the quality losses in fruits and vegetables. The enzymes catalase and peroxidase do not usually cause deterioration during storage of produce. Since they are heat-resistant enzymes, they can be marker enzymes to determine if the blanching operation has been carried out properly.

HOW DO WE BLANCH?

Blanching involves dipping the vegetable or fruit in boiling or near-boiling water for 1 to 3 minutes. The actual time will vary depending on several factors such as the type of vegetable or fruit, the size of the food, blanching temperature and the method of heating. These factors must be considered carefully. Underblanching may cause more damage to the food than without blanching does. The heat is enough to damage and disrupt tissues and release enzymes, instead of activating them. This mixes the enzymes and the substrates, causing accelerated damage. On top of that, underblanching may only destroy some of the enzymes, causing increased activity of others and accelerated deterioration.

Small foods like green peas require blanching 1 to 1.5 minutes at 212 °F (100 °C). Vegetables broken into small flowerets like cauliflower and broccoli require blanching for 2 to 3 minutes. Corn on the cob requires blanching for 7 to 11 minutes, depending on the size. Asparagus requires blanching for to 4 minutes, depending on the thickness.

Few vegetables such as green peppers and onions do not require blanching to prevent increased enzyme activity during storage. Majority of fruits also do not require blanching. This is especially true for soft fruits.

In certain green vegetables, adding sodium metabisulsphiote (Na₂S ₂O₅) or sodium carbonate (Na₂CO₃) is beneficial. Doing so decreases the pH level slightly, preventing color change. Color loss occurs in vegetables due to the degradation of chlorophyll to phaeophytin during processing and storage. However, studies have found out that alkaline conditions helps minimize changes in color. In fact, this study revealed that chlorophyll retention is more effective at higher pH conditions.

References

P. Fellows (2000). Food Processing Technology (2nd Edition). CRC Press

V. Vaclavik and E. Christian (2014). Essentials of Food Science (4th edition). Springer

H. Ramaswamy (2015). Post-harvest Technologies of Fruits & Vegetables. DEStech Publications, Inc.

The post What Does Blanching Fruits And Vegetables Achieve? 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.

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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.

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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.

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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.

Whenever we talk about the post-harvest physiology of plant tissues, one of the most discussed are the plant hormones. The so-called classic plant hormones are abscisic acid, auxins, cytokinins, ethylene, and gibberellins. They are plant growth regulators (PGR). Like the name suggests, they aid in the growth and development of cells. Specifically, they help increase return bloom, modify maturity of the fruit, increase branching, and discard excess fruit. Among these 5 growth hormones, studies have been more focused on ethylene, largely because of its direct effect on ripening and senescence, and less is known about the involvement of the other hormones. Furthermore, ethylene’s mode of measurement is relatively easy.

In this article, we’ll discuss ethylene in more detail.

WHAT IS ETHYLENE?

Ethylene (C₂H₄) is a naturally occurring plant growth hormone in plants. It is a two-carbon hydrocarbon with a double bond (an alkene). It is colorless and nearly odorless (sweet smell of ether). All tissues of the higher plant essentially produce ethylene—from seeds to the fruit.

As a plant growth hormone, it controls many processes in the plant.

And it has a profound effect in these processes, particularly in fruit ripening and senescence, even at trace amounts. Among the 5 PGR, ethylene is unusual. At room temperature, it is a volatile gas. Therefore, it can diffuse quickly between plant tissues or from one commodity to another. This is the reason why bananas, a moderate ethylene producer, help other fruits to ripen faster.

While ethylene has several benefits to plant growth and development, its presence may also be detrimental if not controlled. In fact, a significant portion of post-harvest losses come from hastened senescence and deterioration. One of the common method farmers do to prevent this is harvest the produce unripe, and then artificially ripen it by spraying ethylene. This allows farmers to transport their produce at the optimum freshness and quality.

While delaying the ripening process in fruits minimizes losses, it is good to know which fruits are sensitive to ethylene, and which are not. Fruits picked unripe but have little to no sensitivity to ethylene may never go ripe.

The Food and Drug Administration has approved the use of ethylene as a commercial ripening agent. And no residue standards have been placed, indicating it to be safe.

ETHYLENE SYNTHESIS

In higher plants, ethylene is produced within plant tissue in a simple two-step biochemical pathway. The synthesis of ethylene involves the amino acid methionine, which is first converted to S-adenosyl-l-methionine (SAM). In the first dedicated step of ethylene biosynthesis, SAM is converted to aminocyclopropane-1-carboxylic acid (ACC). The enzyme involve in this process is ACC synthase, which is normally the rate limiting step. That means an increase in ethylene production is accompanied by an increase in levels of ACC in the plant tissue. The so-called Yang cycle allows the recycling of 5′-methylthioadenosine (MTA), a by-product of this step, to methionine. This leads to the production of ethylene using a small pool of free methionine.

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The ACC oxidase (the ethylene-forming enzyme) then converts ACC to ethylene. It is worth noting that the last step of ethylene synthesis requires oxygen. This is why ethylene production is inhibited at low oxygen levels. A study by Hansen (1942) and Burg and Thimann (1959) revealed that ethylene production stopped in apples and pears stored under nitrogen, but production restored upon reexposure to oxygen.

Various studies have also proposed other precursors of ethylene. But it is well established that methionine is the main precursor in higher plants.

CLIMACTERIC AND NON-CLIMACTERIC FRUITS

Based on the rate of respiration, fruits can be classified into two groups: climacteric and non-climacteric. Before we classify fruits, let’s define first what respiration is.

According to The Food and Agriculture Organization of the United (FAO), respiration is basically a reaction of all plant materials. This is the most important physiological activity in plants, and has a direct bearing on the quality of produce. This process involves utilization of sugars produced during photosynthesis and oxygen to produce energy (carbon dioxide, water, and heat) for growth. And it is a continuous process—in the field and after harvest. However, a large number of fruits exhibit a sudden rise in respiratory activity after harvest. This is referred to as the climacteric rise in respiration, a behavior first noted by the upsurge of carbon dioxide gas at the end of the maturation phase of apples. Then after the climacteric, respiration slows down as the fruit ripen.

But what does ethylene have to do with respiration in fruits? It is simple. Climacteric fruits produce ethylene as they ripen. This is why climacteric fruits are capable of ripening during the post-harvest period. Non-climacteric fruits, on the other hand, exhibit a steady fall in respiratory activity. Because of this, non-climacteric fruits should only be harvested once they have ripened sufficiently since little to no ethylene is produced once removed from the parent plant. This behavior was first observed in lemons, and then in oranges.

The below table lists some of the climacteric and non-climacteric fruits and vegetables

ETHYLENE PRODUCTION RATES

Two ethylene systems operate in fruits and vegetables during development and ripening: system I and system II.

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System I ethylene operates in both climacteric and non-climacteric plant tissues as basal ethylene production. It is responsible for ethylene production at immature stages of the fruit. System I ethylene is also responsible for the ethylene production as a result of wounding and other (a)biotic stresses.

At the onset of ripening, system II ethylene takes over. At this point, the production of ethylene switches from autoinhibitory to autostimulatory. In climacteric fruits, the transition is characterized by the sudden increase in autocatalytic ethylene production, accompanied by a spike in the rate of respiration. During ripening, ethylene production is associated with the upregulation of the enzymes ACC synthase and ACC oxidase, both of which increase in activity.

We have listed some climacteric fruits (and vegetables). But they are not created equal. Which ones produce ethylene more? The distinction between climacteric and climacteric fruits was first based on the pattern of respiration. Today, they are identified by the differences in ethylene production.

The below table shows the classification of fruits and vegetables according to ethylene production rates.

METHODS OF CONTROLLING ETHYLENE

Ethylene is generally beneficial. It helps the firmness of the fruit to soften, increase its sugar content, release aroma compounds, and develop flavor. But if uncontrolled, may result in post-harvest losses (hastened senescence, and deterioration). This is especially true for produce meant for long-term storage or transport to distant places. In some fruits and vegetables, ethylene may induce certain undesirable effects. These include yellowing in brocolli, sprouting in potato, and color loss in leafy vegetables.

To delay or inhibit the action of ethylene in fruits and vegetables, several methods can be used.

Low temperature

In general, low temperatures slow down metabolism, and this include ethylene production in plant tissues. This is the reason why it is ideal to store the produce at chilling temperature. But when storing, it is good to know the compatibility of the produce in relation to tolerance to ethylene. Produce that does not tolerate ethylene must be stored away from another that generates ethylene at a fast rate.

Another reason to separate produce during storage is that some tropical fruits are chilling-sensitive. For most temperate produce, the optimum storage temperature is 30–32 °F (-1.0-0.0 °C) for the non-chilling-sensitive varieties, and 38–40 °F (3.3-4.4°C) for the chilling-sensitive varieties. For more on susceptibility of fruits and vegetables to chilling injury, visit this guide by FAO.

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Oxygen removal

Oxygen is essential in ethylene production. Hence, an environment where the atmosphere is controlled helps delay ripening. This study investigated the effect of ethylene, oxygen, and carbon dioxide on the ripening process of bananas. Results revealed that high CO₂ concentrations and low O₂ concentrations retarded ethylene synthesis as well as ripening in the uninitiated fruit.

A similar study investigated the effect of low O₂ and high CO₂ on ethylene and ACC in ripening apples. Results revealed low ethylene production at the climacteric stage in the presence of either high CO₂ and low O₂. However, low O₂ only inhibited the conversion of ACC to ethylene. Whereas high CO2 inhibited the formation of ACC, as well as the conversion of it to ethylene.

Modified atmosphere packaging is one good example of inhibiting ethylene production by oxygen removal. In this method, the packaging material is enriched with CO2 and deprived of O2.

Use of ethylene biosynthesis inhibitors

Ethylene biosynthesis inhibitors, like the name suggests, help delay ripening in fruits and vegetables by interrupting the ethylene biosynthesis. In studying the action of ethylene in plant tissues, three inhibitors are commonly utilized:

• 2-aminoethoxyvinyl glycine (AVG)

• Silver ions (Ag)

• 1-methylcyclopropene (1-MCP)

AVG is an inhibitor of ACC synthase while both Ag and 1-MCP are inhibitors of ethylene receptors. Studies have revealed AVG to be an effective ACC synthase (the key enzyme in ethylene biosynthesis) inhibitor. It can be applied as a pre- and post-harvest treatment to delay ripening. One study applied pre-harvest spray of AVG prior to the commercial harvest of several varieties of apples, including Senshu, Red Fuji, Redchief Delicious, and Lodi. The pre-harvest treatment resulted in higher firmness and reduced respiration for 30 days.

Silver ions help retard ripening by competing for the binding sites of the receptors of ethylene. However, they are more potent if applied as silver thiosulfate (STS). It is more mobile and less toxic than silver nitrate.

1-MCP works by also by binding to the ethylene receptors. Aside from delaying ripening in fruits, 1-MCP also works to maintain the freshness of flowers and ornamental plants. A gaseous compound, 1-MCP is often used in enclosed areas such as greenhouses and storage facilities.

Other references

deMan, J. Finley, W. Jeffrey Hurst, Chang Yong Lee (2018). Principles of Food Chemistry (4th edition). Springer.

S. Damodaran, K. Parkin (2017). Fennema’s Food Chemistry (5th edition). CRC Press.

H. Ramaswamy (2015). Post-harvest Technologies of Fruits & Vegetables. DEStech Publications, Inc.

N. A. Michael Eskin and F. Shahidi (2013). Biochemistry of Foods (3rd edition). Elvesier Inc.

P. Golob, G. Farrell, and J. Orchard (2002). Crop Post-Harvest: Science and Technology (Vol. 1 Principles and Practice). Blackwell Science Ltd.

The post Ethylene And Ripening In Fruits And Vegetables appeared first on The Food Untold.

Are you looking for an effective way of storing mushrooms and extend their shelf life? Mushrooms are just one of the many food items that are better in the refrigerator. A chiller temperature between 34 °F (1 °C) to 45 °F (7°C) ensures that what inside stays fresh. However, unlike most refrigerated food items, mushrooms are very different. While others do fine inside an airtight container, mushrooms need a very different approach.

But sadly, some people treat mushrooms the same way as those other refrigerated foods. Some would wrap mushrooms in plastic before storing them the refrigerator. This is definitely a bad way of storing them. Instead of prolonging the shelf life of the mushrooms, it just speeds up the deterioration process. What’s wrong here?

What’s worst with mushrooms is that even if extra care is given during storage, they still have a relatively short shelf life. Mushrooms last 7 days to 2 weeks, depending on the kind. Nonetheless, storing mushrooms properly will ensure a prolonged shelf life. So what’s the best way of storing mushrooms?

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MUSHROOMS AND RELATIVE HUMIDITY

There are actually many kinds of mushrooms. Each of these kind has a varying composition, as well as the amount of nutrients. But generally, mushrooms contain around 85–95% moisture content, 3% protein, 4% carbohydrate, 1% minerals and vitamins, and 0.3–0.4% fat. What would make a difference here is the very high moisture content. Because of this, mushrooms require an environment that has a high relative humidity.

What is relative humidity?

Relative humidity refers to the amount of moisture content present in the atmosphere. This is expressed as a percentage, which indicates the amount of moisture that can be retained by the atmosphere given the same temperature.

The recommended relative humidity for storing mushrooms is between 80-90%. If it is lower than 80%, and the mushrooms are exposed to a constant low humidity, they will eventually lose moisture. This usually results in undesirable changes in the physical and chemical properties. These changes include brown spot formation, slimy, and sometimes pitted—common indication that it is time to discard them.

This is why air tight or enclosed containers are not ideal for mushrooms. They not only provide low moisture, but they also prevent proper air flow. But do not provide excessive air flow either or the mushrooms will quickly dry out.

Here is how to properly store mushrooms.

STORING MUSHROOMS

When you source mushrooms from a store, ensure you are purchasing them fresh. Once home, you want to bring the temperature of the mushrooms down immediately. Mushrooms continue to produce and release heat even after picking. This, too, hastens spoilage. To store them in the refrigerator, place them in a paper bag unwashed, and then fold the top, and place the bag on a shelf, ideally, in the main compartment.

Question— why not in an enclosed or airtight container?

Simple. A paper bag is a porous material— it contains minute holes. These holes allow the paper bag to absorb the excess moisture from the mushrooms to prevent them from going soggy, moldy, and slimy. Or simply, they keep the mushrooms safe and fresh.

Commercially, the humidity of the environment and the respiration rate of mushrooms are what the growers control to prevent spoilage and losses.

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MUSHROOMS AND MODIFIED ATMOSPHERE PACKAGING

The variables that define the shelf life of mushrooms are carefully controlled to prevent losses. These variables are the CO2, oxygen, and humidity. One way to do this is by employing modified atmosphere packaging (MAP). MAP is just one of the many techniques employed in the food industry to extend the shelf life of various food products. This technique is ideal for storing mushrooms as it provides a cheap yet effective way of minimizing or inhibiting biochemical processes.

The level of oxygen is one factor that dictates the rate of respiration of mushrooms, specifically. The higher the concentration of oxygen that there is, the higher the respiration rate of the mushrooms. And therefore the faster they spoil. By altering the gas composition that surrounds the mushrooms inside the package, the processes that contribute to deterioration are delayed. Using MAP, the oxygen levels can be decreased while increasing the levels of carbon dioxide in the pack. Doing so prevents spoilage and results in prolonged shelf life of mushrooms. MAP is usually combined with low temperature storage (both lower rates of processes in food).

When selecting packaging film for mushrooms, the film’s characteristics are carefully assessed if applicable. Mushrooms are one of the few high-respiring produce. For this reason, typically films such as OPP (oriented polypropylene) and LDPE (low-density polyethylene) do not work well since they are not gas-permeable enough.

Certain packaging films ideal for produce like mushrooms are modified atmosphere/modified humidity packaging (MA/MH) films. These films not only control the gas composition, but as well as the humidity. Films with modified humidity favorable to mushrooms avoid moisture loss, wilting, and other undesirable changes. This allows mushroom growers to transport their product to distant areas.

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