Oranges turning green is a phenomenon that can sometimes occur when the fruit is exposed to certain conditions during growth or after harvesting. The green color is caused by chlorophyll pigments in the orange peel. Chlorophyll is usually masked by orange carotenoid pigments, but under certain circumstances the chlorophyll becomes visible, causing green patches or a green tinge on the peel. This does not harm the orange flesh which remains orange, but makes the peel unattractive. Understanding what causes this can help growers and consumers prevent and manage the problem.
Why Do Oranges Turn Green?
There are a few key reasons why oranges can turn green:
Cool Temperatures
Cooler temperatures during growth can cause chlorophyll levels to increase in citrus peel. Oranges grown in cooler climates or that experience cooler weather may start turning green on the tree. Temperatures below 50°F (10°C) favor chlorophyll synthesis over carotenoid pigments.
Light Exposure
Exposure to direct sunlight or high-intensity light can also increase chlorophyll content and cause greening. Oranges grown in shadier areas will stay more orange. After picking, direct sunlight shining on oranges can bring out more green tones.
Age/Maturity
Younger, less mature oranges tend to be greener. As they ripen, carotenoids build up and mask the green chlorophyll shades. However, ambient conditions can cause chlorophyll to still become visible in mature oranges.
Storage Conditions
After harvest, storage conditions can impact greening. Cool temperatures, high humidity, or ethylene exposure during storage or transport can trigger development of green pigments. Improper storage allows chlorophyll synthesis to continue.
Oil Gland Damage
Physical damage to oranges like abrasions or punctures can rupture the oil glands containing carotenoids. This allows chlorophyll to show through the damaged spots, causing green blemishes.
Genetic Factors
Some citrus varieties are genetically more prone to greening. Navel and Valencia oranges, for example, develop green spots more readily than other varieties. Their genes promote higher chlorophyll production.
When Does Greening Happen?
On the Tree
Oranges can start turning green before harvest. Cool weather during the growing season allows chlorophyll to accumulate. Green spots or a greenish cast can appear on immature fruit while still on the tree, especially on shaded inner branches.
After Picking
Post-harvest handling can also cause greening. Direct sun exposure, cool storage temperatures, humidity, and ethylene can all trigger chlorophyll synthesis after the oranges have been harvested. Improper storage and transport often leads to greening.
During Ripening
As chloroplasts transform carotenoids into chlorophyll, some greening occurs naturally as oranges ripen after picking. But temperature regulation and ethylene control during storage and transport can minimize this.
What Factors Promote Greening?
There are a few key environmental factors that promote development of green pigments in oranges:
Cool Temperatures
Chlorophyll production increases when temperatures drop below 50°F (10°C). Low temperatures slow carotenoid synthesis but allow chlorophyll production to continue.
Sunlight Exposure
Direct, intense light energizes chlorophyll production. Shaded oranges stay more orange. Post-harvest sun exposure can swiftly bring out green tones.
Humidity
High relative humidity above 90% provides ample moisture to support chlorophyll synthesis. Humid storage environments promote greening.
Ethylene
The gaseous plant hormone ethylene enhances chlorophyll production. Ethylene released during storage can hasten development of green pigments.
Physical Damage
Breaks in the peel allow chlorophyll to show through where carotenoids have been removed. Bruising and punctures lead to green blemishes.
Problematic Orange Varieties
Some orange varieties are more susceptible to developing green spots and discoloration. The main varieties that tend to turn green are:
Navel Oranges
Navel oranges readily develop green patches, especially on the shaded topside of the fruit. Their genes promote chlorophyll synthesis.
Valencia Oranges
Valencias are also genetically prone to greening. They become blushed with green spots when exposed to cool temperatures.
Blood Oranges
Moro and Tarocco blood oranges can take on greenish tones in some growing conditions. Their red pigments allow green hues to show through.
Cara Cara Oranges
The pink flesh of Cara Caras contrasts with green skin spots that form readily on this variety. Green spots develop on Cara Caras as chlorophyll accumulates in the peel.
Satsumas
Cool weather promotes green patches on Satsuma mandarins. Their thin peels allow green to come through under the right conditions.
Is it Safe to Eat Oranges with Green Peels?
Yes, oranges that have turned partly green are still safe to eat. The green color is just a cosmetic issue on the peel. The inside flesh remains fully orange and edible. Any green spots are superficial and do not affect orange quality.
However, heavily greened oranges may taste more bitter. Chlorophyll contributes grassy, bitter notes compared to sweet orange carotenoids. But oranges with a few green spots or a light green tinge are usually not noticeably different in flavor.
The flesh inside greenish oranges is still nutritious and safe. Only very moldy, rotten oranges with green mold penetrating into the fruit should be discarded. Otherwise, green peel can be peeled off and the orange eaten as normal.
Preventing Oranges from Turning Green
Growers and producers can take steps to prevent or minimize greening of oranges:
Maintain Warmer Temperatures
Keeping oranges at optimum temperatures around 60-85°F (15-30°C) inhibits chlorophyll synthesis and allows carotenoids to develop normally.
Limit Light Exposure
Storing oranges in dark conditions prevents light-induced greening. Use opaque bags or boxes to block light during transport and storage.
Manage Humidity
Controlling storage humidity below 90% helps curb chlorophyll production. Proper ventilation restricts excess moisture.
Control Ethylene
Restricting ethylene exposure prevents it from stimulating chlorophyll synthesis. Using ethylene absorbers helps manage greening.
Handle Carefully to Avoid Damage
Gentle handling prevents rupturing oil glands so green chlorophyll stays hidden beneath orange carotenoids.
Pick Optimal Varieties
Choosing varieties less prone to greening like Hamlin or Pineapple oranges avoids inherent genetic greening issues.
Use Post-Harvest Treatments
Dip, spray, or drenching solutions containing gibberellic acid can help mitigate greening when applied after harvest.
Managing Green Oranges
For oranges that have already turned partly green, here are some management options:
Store at Cooler Temperatures
Once greened, storing oranges at 37-41°F (3-5°C) can help stabilize and arrest further greening.
Keep in Dark Storage
Moving greened oranges into dark, opaque storage stops additional light-induced chlorophyll synthesis.
Separate Damaged Fruit
Isolating any oranges with skin splits or punctures avoids cross contamination of green spots.
Use Within a Couple Weeks
Green oranges are still usable if kept refrigerated, but should be consumed within 1-2 weeks before quality declines.
Preparing and Processing
Peeling, juicing, and segmenting greenish oranges removes unattractive peel while retaining edible flesh.
Sort for External Markets
Green oranges can be sorted out for processed products where appearance doesn’t matter, while fresh oranges are sold whole.
Conclusion
Oranges turning green is a common quality issue caused by chlorophyll pigments becoming visible in the peel. Cool temperatures, light exposure, humidity, ethylene, damage, and variety make oranges prone to greening during growth or post-harvest. While unattractive, slightly green oranges are still safe to eat. Proper temperature and storage management, gentle handling, and optimal varieties can help prevent and control greening. With some care and oversight, the problem of green oranges can be minimized.
