THE EFFECTS OF SOME SPECIAL TREATMENTS IN THE DEGREENING OF FLORIDA ORANGES AS MEASURED BY RESPIRATION RATE

Abstract

For many years it has been customary to treat certain varieties of citrus fruits, especially early oranges, with ethylene gas for the purpose of removing the green from the rinds. This process is referred to by the trade as coloring but should more properly be termed degreening. That the term coloring is ill-chosen may be seen from the fact that though the maximum amount of yellow rind pigments (carotenoids) is not reached by the time that oranges are mature green, present degreening methods serve only to remove the green pigments (chlorophylls) and do not increase the yellow pigments already present (20). (A special process of adding natural vegetable dyes to the peel is commonly used today and fruits so treated must be stamped color added.) The procedure now followed for degreening (28) is to stack field crates of oranges in rooms which are equipped with means for heating, introducing ethylene, maintaining proper humidity, and circulating fresh air. The fruit is kept at approximately 85? F (29.4? C), 80 to 100% relative humidity and is treated with ethylene in low concentrations. Under these conditions a fruit which is quite green may require as much as 60 hours to degreen whereas a fruit in which chlorophyll has begun to decompose while on the tree requires proportionately less time. This method is essentially the same as it was 20 years ago, with improvements being found only in construction of rooms and mechanical equipment. The need for degreening arises solely from a consumer preference for colored oranges, for in Florida (29) and in other regions having semitropical and subtropical climates some of the early orange varieties mature before losing their green color. Citrus fruits of any variety growing as an inside crop on densely foliated trees often retain much of their greenness long after maturity. It is common knowledge (12) that maturity refers to a stage of development and ripening refers to the process by which a mature fruit becomes edible or desirable as food. Apples, bananas, and pears, which contain a starch reserve, may become mature before harvest but may not ripen until the action of enzymes and life processes have hydrolyzed the starches to sugars, produced a certain amount of softening, and effected other changes such as rendering bitter principles insoluble.