There are several key factors that cause spoilage,"over-ripeness" or the general degradation of quality in fresh fruits and vegetables. Certainly the maturity of the fruit is a prime contributor, but also temperature, length of time the product has been picked, damage to the fruit caused by handling, and one factor that many consumers may not be aware of... is Ethylene gas.
Ethylene is a naturally occuring gas that can be a benefit as well as a detriment in fruit, vegetable and floral handling. As an example, if a shipper needs all of a particular shipment of fruit (bananas, apple, tomatoes, peaches, mangoes, etc) to ripen at the same time, the decision may be made to expose the fruit to higher concentrations of Ethylene. This "triggers" the fruit to ripen faster, it does not ripen the fruit, does not burn it, does not induce any flavors..it merely tricks the fruit into ripening faster. If however, Ethylene from a shipment of apples or other producing fruit comes into contact with flowers, the flowers will typically wilt and then decay within a few days.
Although there are commercial manufacturers or producers of Ethylene, our concern is with the form that is produced naturally by fruit. Ethylene is a physiological part of the ripening process and the production increases as the fruit gets older and riper. Additionally, when a piece of fruit is damaged by bruising or by cuts or nicks, one of the reactions to that damage is for the fruit to produce more Ethylene. Ancient Egyptians learned that by "gashing" figs, the ripening process was sped up.
Ethylene shortens the shelf life of many fruits by hastening fruit ripening and floral senescence. Tomatoes, bananas and apples will ripen faster in the presence of ethylene. Bananas placed next to other fruits will produce enough ethylene to cause accelerated fruit ripening. Ethylene will shorten the shelf life of cut flowers and potted plants by accelerating floral senescence and floral abscission. Flowers and plants which are subjected to stress during shipping, handling, or storage produce ethylene causing a significant reduction in floral display.
The chart below was developed by UC Davis and that shows typical reactions to Ethylene.
|Effects of Ethylene|
|Asparagus||VL||M||Toughening of stems, yellowing of tips|
|Bananas||M||H||Accelerated ripening, Decay|
|Broccoli||VL||H||Yellowing of florets, increased decay|
|Carrots||VL||L||Formation of bitter compounds resulting in off flavors|
|Cauliflower||L||K||Discoloration of the curd, abscission of outer leaf bases|
|Lettuce||VL||H||Russet spotting on leaves|
|Onions||VL||L||Increased sprouting during storage|
|Peas||L||H||Yellowing of calyx tissue|
|Radicchio||L||H||Pink discoloration of mid-ribs|
|Sweet Potatoes||L||M||Development of "Off Flavors"|
|Tomatillos||L||M||Color change from green to yellow, softening|
|Tomatoes||M||H||Loss of firmness, ripening from green to red|
|Watermelon||L||H||Loss of firmness, becomes "spongy"|
So the challenge for a consumer who wants to prolong the shelf life of a recent fresh Produce purchase, is to control or greatly reduce the exposure of their purchase to Ethylene.
The most basic form of Ethylene control for a consumer is to separate Ethylene producing fruit from non-producing fruit and vegetables, and to then refrigerate the produce at the optimum storage temperature listed in our Storage guide.
There are several products on the market that tout their ability to "Extend the freshness of Produce", from plastic bags and containers to "wraps" and "special boxes". Unfortunately, most of these products really do not perform well and the savings you get from any longer shelf life will never off-set the high cost of the product.
At the present time, the only product that does a good job of removing Ethylene from the environment is potassium permanganate. Any "shelf-life extenders" that do not contain this compound are really only another variation of the "separate and refrigerate" method mentioned above.
The one consumer product that we have found that actually scrubs the air and reduces the Ethylene in enclosed storage bins, is called the Healthy Harvest Freshness Extender.