Monday, June 4, 2012

Ripening of Bananas with Ethylene-Safe or Harmful

The big question

Many people have asked me whether ripening of bananas with chemicals is harmful to health. I understand their concern. This is because numerous artificial compounds are used in foods nowadays. Again, banana is a favourite fruit to many, so they may want to be sure if it is safe for eating. I will address this question in depth in this article.

The process of banana ripening

During the growth and development period of bananas, there are many chemical and physical changes that occur. These have an impact on the fruit quality after harvesting. Normally, ripening is the final stage in fruit maturation. During ripening, the fruit changes colour, flavour, texture and aroma to optimal eating sensorial and textural properties. The agent that triggers these changes during maturation of bananas is a chemical called Ethylene. Ethylene is a gas naturally produced by plants e.g to trigger leaves to turn yellow and fall off during certain seasons like winter.

What is Ethylene

Ethylene is a ripening hormone – a chemical substance produced by fruits with the specific biological action of accelerating the normal process of fruit maturation and senescence (dying or going into dormancy).
Ethylene can promote ripening in tomatoes, bananas, citrus, pineapples, dates, pears, apples, melons, mangoes, avocados and papayas.

Factors that trigger production of ethylene in fruits

-Natural process such as maturation and weather
-Injury-Injured fruits ripen or go bad quickly than injury free ones.
-Attack by insects and birds- fruits eaten by birds ripen faster.

How was the effect of ethylene discovered

Traditionally, lemon growers stored harvested green lemons in sheds which were kept warm by kerosene heaters. Lemons were stored until they turned yellow and ripened for market. However, when modern heating systems were introduced in sheds, the lemons  never turned yellow on time. Research found out that the main factor that influenced ripening in kerosene warmed sheds was the small amounts of ethylene given off by kerosene heaters.

Traditional application of Ethylene in ripening of bananas

When I was a kid, I used to see my grandfather store bananas covered with dry banana leaves. Some times, he used to keep them in a room where fire was lit regularly. These bananas ripened faster than the uncovered ones.

Some communities used to dig a hole, place dry bananas leaves there and burn them. This was followed by placing fresh leaves on top of burnt leaves and then bananas on top. After placing bananas, they again covered with more leaves. The bananas stored this way ripen faster than those which were not covered. What these practices were doing is increase production and accumulation of high levels of ethylene to hasten the ripening of bananas.

There is also a common practice of placing avocados or bananas in a airtight paper bag to hasten ripening. The ethylene produced by these fruits accumulates in the bag, accelerates ripening, the ripening fruits produce more ethylene and the ethylene production process repeats itself.

Sometimes, unripe bananas or avocados are placed together with a ripening passion fruit to hasten the ripening process

Modern Day application of Ethylene to ripen bananas

Once people realized what hastened the ripening of bananas, it was conceived that it is possible to delay or hasten the ripening process. This led to either application or absorption of ethylene from fruits during storage and transportation.

Fruits are normally transported over long distances to reach their intended market. In order for the bananas to survive the transit time from source to the market it must be picked at 3/4 maturity when they appear green. After arrival in the destination country a very small controlled release of ethylene is used to trigger the natural ripening process.

Nowadays, most commercial warehouses, ships and trucks all fitted either with ethylene absorption technology or ethylene generation machines to help control ripening process of many fruits.

Why do supermarket bananas turn bright yellow by the time you get home

I have this experience a lot. I buy bananas in the supermarket which are slightly yellow (sometimes green). When I get home, I am shocked to see them turn bright yellow within few hours. This is an effect of ethylene. Probably, they were applied with ethylene immediately prior to shelving.

High levels of Ethylene in Kitchen appliances

A refrigerator is one of the kitchen appliance that might have high levels of ethylene. When fruits are stored in the refrigerator and it is kept closed to retain the desired temperature, it also enables an increased concentration of ethylene to accumulate. Therefore, when fresh fruits are brought in, they ripen quickly and go bad instead of storing for long.

Advantages of using controlled Ethylene to ripen bananas

Ethylene helps to regulate the ripening process. Therefore without ethylene the ripening process in uncontrolled. This has many disadvantages:
-Presence of uneven ripened bananas.
-Requirements for regular sorting to separate ripe and unripe.
-Ripe bananas would go bad within a very short period if exposed to uncontrolled ethylene.

Disadvantages of Ethylene ripened bananas

Normally, bananas ripened by application of external ethylene lack that characteristic flavour and aroma of naturally ripened fruit. But they are in no way inferior in terms of nutrients.

Fruits and vegetables that are sensitive to Ethylene

Ethylene is good but can accelerate aging and eventual spoilage of many fruits and vegetables. Therefore it is advisable not to store ethylene-sensitive fruits and vegetables together with ethylene releasing fruits. Some of ethylene-sensitive vegetables are: broccoli, cabbage, cauliflower, lettuce etc.

Does use of Ethylene allow ‘cheating’ of consumers

As a personal view, I do not think this is possible. Although ethylene can be used to ripen immature fruits due to greed of profits, this in no way amount to cheating.

Is use of Ethylene an ‘artificial’ process

No! Ripening of bananas with ethylene is not an artificial process. Ethylene is just used to slow, hasten or regulate a natural process. Ethylene in itself is a naturally produced gas. Even without additional of external ethylene, fruits will produce it any way.

Is ethylene a harmful compound or toxic to human health?

No!. So far, ethylene is a natural gas which can be manufactured artificially and has not been found to have harmful effects on human health.[link]



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