All fruits and vegetables produce some ethylene gas, but to varying degrees. Ethylene gas production is a natural response during ripening of produce and is commonly used in the industry to ripen fruit, particularly bananas and tomatoes.
Vegetables, with the exception of tomatoes are classed as non-climacteric which means that as they ripen, there is a very little natural production of ethylene. Major ethylene producers are climacteric and are primarily fruit: apples, apricots, bananas, plums, peaches, pears, tomatoes and cantaloupes/ muskmelons.
In the presence of ethylene, besides stimulating ripening, unfavorable chemical changes do occur in some crops. Ethylene sensitive vegetables are green beans, broccoli, Brussels sprouts, cabbage, cauliflower, swiss chard, cucumbers, lettuce, peas, green peppers, zucchini, watermelon and carrots. Among these sensitive crops, green color is most prevalent and visually, it is color that is most affected by ethylene gas followed by flavor.
The general unfavorable effects of ethylene are:
1. Changes in color – breakdown of chlorophyll and synthesis of carotenoids and anthocyanins.. Tissues turn yellow to orange and red which is associated with various oxidative processes.
2. Changes in texture due to cell wall degradation by enzymic action – tissues become soft and watery which leads to decay.
3. Changes in flavor – the conversion of starch to sugar increases the sweetness, reduction in acidity and the development of volatile aromatic compounds.
When produce is wounded by dropping, scratching etc., ethylene production can be induced even in non-ethylene producing crops. This can lead to many secondary effects upon the metabolism of the wounded tissue including:
1. Initiate the activity of several enzymes such as polyphenol oxidase and growth hormones such as gibberellin. These metabolic changes contribute to tissue suberization (callus formation) leading to the formation of wound periderm consisting of several layers of thick cells.
2. Discoloration (browning) of damaged tissue involves the oxidation of phenolic compounds by phenoloxidases into melanins and other off-color pigments. Currently, carrots and parsnips are mostly affected, a result of surface tissue abrasion occurring during harvest and post-harvest handling.
3. Development of unusual flavors and odors. The best known and documented is isocourmarin in carrots which creates a bitter flavor that cannot be removed once established.
Ethylene sensitive crops should never be stored in the presence of ethylene producing crops. Good ventilation of the storage atmosphere is required along with the installation of potassium permanganate pads in the air flow system to capture and absorb free ethylene produced in the storage environment.
Ensure that you take Ethylense sensitivity and production into strong consideration when storing, transporting, and packaging your produce. Friesen Plastics Inc. can provide ethylene absorbent sachets and packaging to ensure you maximize the shelf life of your product.
Post Credit: Many thanks to Paul Ragan, Fruit and Vegetable production advisor, for the hard work he put into writing and researching this information.
