From Christopher B. Watkins
Summary:
1-Methylcyclopropene (1-MCP) is currently the most effective inhibitor of ethylene action and has been increasingly used to improve the storage potential and quality of fruits and vegetables. 1-MCP is registered for use in a variety of crops, including apples, apricots, avocados, bananas, broccoli, kiwis, pears, mangoes, melons, peaches, nectarine, persimmons, plums, and tomatoes. Registered crops usually vary from country to country.
This article reviews the effects of 1-MCP on the quality of these crops and its effects on physiological and pathological diseases. Most of the existing literature on 1-MCP focuses on laboratory trials and has little information on its impact on product quality at the commercial level. Apples require little post-ripening after harvest and are the world's first commercially available 1-MCP crop and the most experienced crop. However, for other fruits, such as bananas, mangoes, kiwifruit, etc., the successful commercialization of 1-MCP needs to consider the interaction between 1-MCP concentration, processing temperature and processing time, so as to achieve the effect of delaying but not inhibiting normal ripening. Preharvest factors (variety, maturity) and postharvest treatment will affect the use of 1-MCP. For leafy vegetables and nonfruit vegetables, the effect of 1-MCP may only be noticeable under harsh conditions such as high temperatures and exposure to exogenous ethylene. Finally, the commercial application of 1-MCP-based technologies depends on the input-output ratio of the application.
The registration of 1-MCP, which is used to inhibit ethylene action, ushered in an exciting era for postharvest scientists. 1-MCP is not only used to study the role of ethylene in the post-maturation aging process, but also as a basis for new technologies in the horticultural industry. However, while ethylene control is important in the storage and transportation of fruit, vegetable and ornamental flower products, the commercial application of 1-MCP is not an easy task. Research to date has shown that, just like any conventional technique, such as cryogenic and modified atmosphere storage, the effect of 1-MCP on product quality is uncertain. We need to understand how to use 1-MCP and how to integrate with existing processing systems to make 1-MCP effective.
Review
There is now much literature on the effects of 1-MCP on the postharvest preservation of fruits, vegetables and ornamental horticultural products, and by 2007, more than 50 fruit and vegetable test results had been obtained, including complete and fresh-cut fruits, vegetables, and ornamental horticultural products. However, despite much literature, there is relatively little information on the commercial use of 1-MCP. BUT THERE IS ONE EXCEPTION, AT LEAST FOR APPLE, WHERE 1-MCP-BASED FRESHNESS PRESERVATION TECHNOLOGY IS USED WORLDWIDE. Two factors limit the commercial use of 1-MCP.
First of all, 1-MCP is still a relatively new product, registered for use in only a limited number of countries. It was registered in Chile and Argentina in 2002 and registered in New Zealand, South Africa and the United States in 2003 for commercial use on Apple, while other commercial tests are underway. The results will be announced soon.
1-MCP has been applied to 16 horticultural products, but much of the commercial research in this area has been patented. For example, under confidentiality agreements, 1-MCP-based technologies are being studied around the world to increase the long-distance shipping capacity and market share of various fruits. The commercialization of 1-MCP represents a model for future technological development. Public research institutions are studying some basic problems, and the specific topic of the commercial application of 1-MCP is done by some specialized commercial research institutions. Table 1 lists the registered crops for Part 1-MCP.
Commercial applications based on 1-MCP, at least in the United States, at least in the Apple Store, are being studied by AgroFresh. However, sometimes some experiments end with the subjects' lack of commercial value in order to see the differences between treatments, which may also provide misleading inferences about the commercialization of 1-MCP in certain crops.
Table 1. Registration of 1-MCP in 2006
| country | crop |
| Argentina | Apples, pears, plums, tomatoes |
| Australia | Apples, avocados, melons, tomatoes, pears |
| Austria | apple |
| Belgium | apple |
| Brazil | Apples, avocados, bananas, guavas, mangoes, melons, papayas, tomatoes |
| Canada | Apples, pears, plums, tomatoes |
| Chile | Apples, avocados, bananas, cherimoya, guavas, mangoes, pears, plums, tomatoes |
| China | Apples, kiwis, persimmons |
| Costa Rica, Guatemala, Honduras | Avocado, banana, mango, melon, papaya, pineapple, plantain, tomato |
| Israel | Apples, avocados, persimmons |
| France | Apples, plums |
| Germany | apple |
| Korea | Apples, avocados, persimmons |
| Mexico | Apples, avocados, cucumbers, dates, kiwis, mangoes, melons, nectarine, papaya, peaches, pears, pepper, persimmons, plums, pumpkins, tomatoes |
| New Zealand | Apples, avocados, kiwis, melons, persimmons, tomatoes |
| Nicaragua | Avocado, banana, mango, melon, papaya, pineapple, plantain, tomato |
| South Africa | Apples, avocados, kiwis, plums, tomatoes |
| Switzerland | apple |
| Netherlands | apple |
| United Kingdom | apple |
| United States | Apples, apricots, avocados, bananas, broccoli, kiwis, mangoes, melons, nectarine, papaya, peaches, pears, persimmons, plums, tomatoes |
1-MCP effect on crops
Most studies have been conducted on apples, avocados, bananas, plums, peaches and nectarines, pears, and tomatoes. However, among these fruits, 1-MCP is the most effective for apples due to their unique ripening properties. Depending on the texture change after harvest, fruits can be divided into two ripening types. The first type of fruit, represented by apples and Asian pears, has a crunchy texture when ripe, and in general, the market (consumers) expect this type of fruit to maintain a similar texture as when harvested. The second group of fruits, represented by bananas, peaches, pears and tomatoes, form solute pulp when ripe, accompanied by changes in color and flavor, such as soluble solids content, acidity and aroma. For the second type of fruit, how to use 1-MCP is a problem, because this type of fruit needs to delay ripening rather than inhibit ripening, so the 1-MCP concentration and processing time need to be precisely adjusted.
Apple:
Fresh-keeping technology based on 1-MCP is the most widely used in apple storage. The reason why it can be widely used is that 1-MCP can maintain the hardness of apples throughout the sales process. CA storage maintains the hardness of apples during storage, but decreases during subsequent transportation and sale. In contrast, the fruits of some varieties treated with 1-MCP showed little change over shelf life.
The preservation technology based on 1-MCP was quickly applied to the apple industry, making it a very good model crop for evaluating the advantages and disadvantages of this technology, and this technology has also begun to be applied to other varieties of fruit. There are many varieties of apples, each with different ripening rates, harvesting standards, postharvest treatment procedures, and storage periods under ordinary storage and modified atmosphere storage, all of which affect the effectiveness of 1-MCP. For example, some varieties are less effective than those that are more effective, either exhibiting little effect or losing their effect quickly during storage. This is related to the internal ethylene production rate of the fruit at harvest and the ability of this variety to produce new ethylene action sites.
At harvest, the internal ethylene production rates of apples of "Empire (Enpai)", "Cortland", "Mackintosh (Xu)", "Ida Red" and "King" were 9.8, 0.9, 67.0, 1.8 and 78.6 μL· respectively. L-1。 In addition, the effect of the same variety will also be different, usually the early harvest of the fruit is better than the late harvest, the planting area, the amount of ethylene produced at the time of fruit harvest and the ethylene formation capacity during storage will also affect the use of 1-MCP.
On the other hand, the length of time between the harvest time and the processing time will also affect the treatment effect of 1-MCP, and the sooner the treatment effect is after harvesting, the better the treatment effect, preferably within a week.
"Anna" apples treated with 1-MCP are lower in flavor, ripeness and overall aroma, but on the palate they are firmer, crispier, juicier and have no flesh.
Apples are susceptible to a range of physiological diseases. Interestingly, 1-MCP inhibits or delays some diseases, such as aging and peel browning, on the one hand, but at the same time increases sensitivity to other diseases, such as greater sensitivity to external CO2. The effects of 1-MCP on physiological diseases of apples and other fruits can be classified according to the role of ethylene in causing or preventing these disorders (Table 2). The effect of 1-MCP on certain diseases is unknown. For example, the same variety "Imperial (Enpai)", which is also treated with 1-MCP, has a higher chance of browning the flesh at 3°C than at -0.5°C (see Table 3).
Table 2. 1-MCP effect on physiological diseases
| Disease classification | |
| Prevents aging by inhibiting ethylene production | Intrafruit routs caused by apple aging Browning and fruit collapse caused by pear aging (aging, water heart disease) Apricot internal browning after harvesting |
| Reduces cold damage by suppressing ethylene | Tiger skin disease and browning of fruit hearts in apples and pears The internal flesh of the avocado browns The flesh of pineapple is browned Sweet persimmon tissue gelation The cold damage of melons |
| Increased cold damage due to inhibition of ethylene | The fruit of peaches and nectarines routs Red spot disease inside plums Cold damage of citrus and bananas |
| Prevents ethylene-induced diseases by inhibiting ethylene production | Browning of lettuce leaves Carrot isocoumarin accumulation Ethylene induces water-stained spoilage of watermelon fruit |
| Increase CA-related diseases by inhibiting ethylene production | Apple is more sensitive to external CO2 |
Table 3. "Imperial" apples harvested from three orchards in the Hudson Valley and western New York were untreated or made with 1 μL· L–1 1-methylcyclopropene treated for 24 h, pulp browning (%)
| Storage temperature(°C) | Browning of pulp (%) | |||
| Hudson Valley | Western New York | |||
| -1-MCP | +1-MCP | -1-MCP | +1-MCP | |
| 0.5 | 6b | 2b | 12c | 14c |
| 3.0 | 0c | 54a | 21b | 41a |
Note: Stored for 10 months at a gas composition of 2% CO2 and 2% O2 at a temperature of 0.5°C or 3°C, respectively, and evaluated after storage at 20°C for another 7 days, different letters indicate significant differences between the means in each region (P<0.05).
1-MCP-based technology is likely to continue to be used in the apple industry, but there are many new problems as the scope of application expands (different varieties, different climates).
apricot
1-MCP treatment can inhibit the softening of apricots, even when the fruit is ripe at the time of treatment. Depending on the variety and maturity at the time of treatment, the effect of 1-MCP on inhibition of softening varies, but the effect is obvious. 1-MCP can reduce maturation caused by collision damage. 1-MCP treatment inhibits the production of volatile substances after treatment, but sensory evaluation is not easy to detect.
1-MCP-treated fruits may be of worse quality in refrigeration than untreated fruits, with more browning on the inside of the fruit, but the incidence of this condition is reduced if the fruit is removed from the freezer and processed.
avocado
The effect of 1-MCP on avocados is related to "concentration" and "processing time". And the processed fruit is harder and slower in softening and color change. The requirement for successful use of 1-MCP is to delay but not inhibit the postripening of avocados.
1-MCP technology is expected to be an effective means of reducing physiological diseases, such as internal rather than external cold damage (CI). In addition, excessive delay in maturation increases rot. Therefore, extending the shelf life is not necessarily beneficial. The resistance of the fruit itself to disease and the control of field pathogens before harvest may be more important for storage.
banana
1-MCP can extend the storage period of bananas, and the effect is related to "concentration" and "processing time".
Successful use of 1-MCP on bananas requires delayed post-ripening, followed by uniform post-ripening, but achieving this can be difficult. The ripeness of the fingers in the banana bunches is not consistent, the color development is uneven, and the 1-MCP treatment will cause the ripening process to be partially interrupted. The harvesting, post-harvest processing and transportation of bananas are exclusively managed by limited companies, in which case there is essentially no publicly available information on the commercial application of 1-MCP.
broccoli
The only vegetable registered for use of 1-MCP is broccoli, and the effect of 1-MCP delaying the yellowing and rotting of broccoli is related to "concentration" and "processing time". However, as with many studies of leafy vegetables, non-respiratory leap fruits, and ornamental plants, the effects of 1-MCP cannot be detected unless broccoli is treated with exogenous ethylene. The commercial application of 1-MCP in broccoli and other similar crops may only be effective when the external environment is harsh, such as high temperatures and the presence of exogenous ethylene.
kiwi
Kiwi fruit is extremely sensitive to exogenous ethylene, which can promote the ripening of kiwifruit. The effect of 1-MCP on post-ripening of kiwifruit is uncertain. The use of 1-MCP treatment after harvest of kiwis can delay softening, but the effect of 1-MCP will disappear even if the concentration is as high as 10~100μL·L-1 during refrigeration. 1-MCP is largely ineffective for fruit that is refrigerated and post-processed, and the advantage of 1-MCP technology may lie in providing flexibility in grading, packaging, and shipping operations, but overall, the benefits of 1-MCP appear to be limited for kiwifruit.
mango
Depending on the decrease in fruit hardness and color change (from green to yellow), 1-MCP treatment can prolong the number of days of ripening, while delaying the increase of soluble solids concentration and the increase of volatile flavor substances. Of course, this effect is related to the concentration of 1-MCP and the processing time. However, studies in Brazil have found that low doses of 1-MCP (30~120ppb) can delay maturation and accelerate post-maturation when the concentration reaches 500ppb. On the contrary, some studies have shown that a higher concentration of 1-MCP (25~100μL·L-1) is required to achieve the effect, which may be caused by the diffusion of the peel between varieties. Although 1-MCP treatment combined with sealed polyethylene bags can provide a viable technology at room temperature, such a high concentration of 1-MCP is not cost-effective to use. The rot rate (stem rot) of fruits treated with 1-MCP also doubled
Melons
1-MCP reduces the softening rate of melons. Maturity at the time of processing is important; 1-MCP has a greater inhibitory effect on softening of green fruits than yellow fruits, but may cause the hardness to remain unacceptable. High concentration 1-MCP treatment results in separation between the peel and epidermal tissue at post-ripening, especially in less mature fruits. The study by Ergun et al. inhibited the softening of yellow melons, but the study of Gal et al. did not, possibly because of the higher concentration of 1-MCP used in the previous study. With 300 nL· L–1 1-MCP treats fruits in the green-yellow stage, delaying yellowing and softening. 1-MCP can prolong the storage life of melons. The internal quality of treated fruits is better than that of untreated fruits, and the sensitivity to cold damage and rot is lower.
Peach and nectarine
The effect of 1-MCP on peaches and nectarines is also related to "concentration" and "processing time", the effective concentration range is larger from 0.4 to 5 μL·L-1, and the softening of peaches can be delayed, but the effect is usually small and short-lived. The softening of fruit by 1-MCP can be controlled more consistently by reusing 1-MCP, but it is not commercially practical. Interestingly, although 1-MCP has a limited role at room temperature, 1-MCP increases the development of cold-hazard-related diseases at low temperatures. THESE RESULTS SUGGEST THAT NORMAL ETHYLENE-MEDIATED MATURATION IS NECESSARY TO PREVENT SUCH DAMAGE AND SUGGEST THAT THE USE OF 1-MCP FOR EXTENDED CRYOGENIC STORAGE PERIODS MAY BE LIMITED.
pear
The effect of 1-MCP on pears is related to "concentration" and "processing time", however, the concentration of 1-MCP that delays but does not inhibit fruit ripening is variable and is affected by variety, changes in fruit ripeness at harvest, storage conditions and storage period. THESE FACTORS MAKE IT DIFFICULT TO FORMULATE THE CORRECT 1-MCP CONCENTRATION FOR COMMERCIAL APPLICATIONS OF 1-MPC, AND FRUIT UNRIPENING IS A COMMON OBSERVATION IN 1-MCP STUDIES. In addition, the inhomogeneity of the 1-MCP reaction and the separation of the maturation process (peel color and softening) can create problems at the retail stage. ONE WAY TO OVERCOME THE UNDESIRED SENSITIVITY OF PEARS TO 1-MCP IS PRETREATMENT, WHICH INCLUDES THE SELECTION OF 1-MCP CONCENTRATION, STORAGE TIME AND GAS COMPOSITION, AND TEMPERATURE.
An important benefit of 1-MCP is that it reduces the sensitivity of the fruit to vibration and impact damage, as well as to browning of the peel, suggesting that the use of 1-MCP in postharvest processing operations confers benefits. The successful commercial application of 1-MCP depends on the variety and postharvest treatment.
Sweet persimmons
With or without deastringency, 1-MCP can delay persimmon softening. However, the concentration of 1-MCP required to obtain the effect varies widely, from 0.1 μL·L-1 to 3 μL·L-1, and this difference may be related to the variety. The delay between harvest and treatment reduces the effectiveness of 1-MCP and treatment within 12 hours of harvest is recommended. The facility for deastringency treatment is just enough for 1-MCP treatment at almost no additional cost. 1-MCP treatment also reduced calyx shedding and fruit softening associated with cold damage, suggesting that 1-MCP treated fruits can be stored at lower temperatures to improve fruit storage potential.
plum
1-MCP can delay the softening of the plum fruit and the change of skin color. For plum varieties that normally produce ethylene, the effect of 1-MCP is related to "concentration" and "processing time", but not to inhibition of respiratory leap type fruits. The effect of 1-MCP is also affected by fruit ripeness and can be effective at ripening stages with better quality characteristics. Although the experimental results show that the 1-MCP-based technique is effective for plums, the most important issue is to determine the 1-MCP "concentration" and "processing time" required for different varieties. Experiments have found that 1-MCP works better on packaged plum fruit than in bulk.
tomato
1-MCP can delay the ripening of tomato fruit, but the effect is related to the variety, "1-MCP concentration and treatment time" and ripening period. Tomatoes processed in the green ripening stage do not ripen as evenly as fruits processed in the more ripe stage. 1-MCP treatment can bring consumers a better quality product, even when the tomatoes are post-ripened. Inconsistent ripening within the fruit (chamber cavity and fruit outer wall) resulting from 1-MCP treatment may affect the acceptability of fresh-cut tomatoes
Effect of 1-methylcyclopropene on physiological and pathological disorders
1-MCP, in addition to its impact on the ripening and aging of fruits and vegetables, can greatly affect the sensitivity of these products to physiological and pathological diseases. In commercial applications based on 1-MCP technology, these effects must be considered.
Physiological diseases can be divided into several categories according to the different effects of ethylene on diseases, not surprisingly, diseases related to aging or ethylene are inhibited by 1-MCP, but the effect of 1-MCP on cold damage is of great concern. One is that cold damage is related to ethylene formation, so 1-MCP can suppress cold damage; However, another type of cold damage is related to normal ripening, so while treating fruits with 1-MCP inhibits ripening, cold damage also increases. However, increased ethylene production induced by 1-MCP treatment can inhibit cold damage in citrus. The other group appears to be related to the 1-MCP effect and interactions between stored gas components.
Pathological diseases can be classified as those that increase, decrease, or are not affected by the use of 1-MCP (Table 4). Interestingly, ethylene may be an important part of resistance in fruits and vegetables because it regulates defense genes that may be affected by 1-MCP.
Table 4. Examples of pathological diseases in which 1-methylcyclopropene is administered in fruits and vegetables, the incidence increases, decreases, or is not affected
| Effects on diseases | crop | pathogenic bacteria |
| increase | apple | Anthrax bacteria, Penicillium |
| avocado | Anthrax, a genus of siated bacteria | |
| citrus | Chlorella pathogen, Penicillium dactylis fingers, and Pedicillus nigra | |
| mango | Anthrax bacteria, Hyacinthoma | |
| papaya | Anthrax bacteria, black rot pathogens, black spot pathogens, cocoa coccidiosporus | |
| decrease | apple | Botrytis filiformis, Penicillium extensives, Anthracnose apicalis |
| melon | Fusarium | |
| peach | Penicillium extensions | |
| plum | Stone fruit brown rot | |
| No impact | citrus | Green mold |
| kiwi | Botrytosis |
With the commercialization of 1-MCP, the impact of 1-MCP on disease resistance in fruits and vegetables may be more important. Commercial applications are more diverse in sources than in laboratory conditions, and disease infestation may be higher. For example, the increase in the incidence of avocados is associated with a longer storage period, so preharvest disease control is even more important for fruits and vegetables to be treated with 1-MCP.
