Taking an environmentally sensitive approach to pest management
Fresh cut apple slices are a flavorful and nutritious addition to any meal. However, the challenge to serving cut apples has been to keep the flesh from turning an unappealing brown color within minutes of exposing the flesh to air. This change in color is commonly called oxidative or enzymatic browning and is caused by a chemical reaction. The enzyme that causes browning after slicing the apple flesh is polyphenol oxidase.
One of the common methods used to slow browning includes dipping the cut flesh in an acidic solution. At a low pH (less than 2) polyphenol oxidase is deactivated. Ascorbic acid, also known as vitamin C, is often sold as a powdered product (Fruit-Fresh®) in the canning section of grocery stores and can be dissolved in water to retard browning. Cut apples can also be dipped into a solution of lemon or lime juice. Alternatively, fruit slices can be soaked in salted water for 10 seconds or ginger ale for 10 minutes to slow browning. Blanching cut apples in boiling water for two minutes and then rinsing them in cold water will also denature the enzyme. Although these methods slow the browning process, they also impart off-flavors to the apples. Pre-sliced apple slices sold as a bagged product in grocery stores or fast-food restaurants are typically treated with the preservative, calcium ascorbate to maintain the appearance of the fruit and prolong the shelf-life.
To avoid off-flavored cut fruit, apples that are less prone to browning can be selected. Cortland and Granny Smith apples are considered naturally low-browning cultivars, with Golden Delicious intermediate, and Red Delicious is high-browning. EdenTM is a very low browning apple cultivar developed by Dr. Shahrokh Khanizadeh at Agriculture and Agri-Food Canada in 2004. Unfortunately, this cultivar has not been propagated by nurserymen in the United States. More recently, four non-browning cultivars, Arctic Granny, Arctic Golden, Arctic Gala and Arctic Fuji have been developed by Okanagan Specialty Fruits, a company in Summerland, British Columbia. These are cisgenic cultivars in which an existing gene is used to silence the polyphenol oxidase enzyme, resulting in non-browning flesh when the fruit is cut or bruised. Using this cisgenic approach, genes from other species are not introduced and original cultivars will be maintained without the introduction of new ones by this company. Okanagan Specialty Fruits expects that products from these cisgenic apples will be available in grocery stores soon.
With this variety of methods to slow or prevent browning of cut apples, individuals can choose one that suits their purpose and continue to enjoy the benefits of eating fresh fruits.
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REVISED: August 1, 2012