why do lemon juice keeps apple slices from turning brown? thanks.
I found this quote in an article about citric and ascorbic acid, both of which are present in lemon juice:
<< A third group of preservatives targets enzymes in the food itself that continue to metabolize after harvest. The enzyme phenolase, for example, goes to work as soon as an apple or potato is cut. It browns the exposed surface. Acids such as citric acid and ascorbic acid (vitamin C) inhibit phenolase by making the pH uncomfortably low for the enzyme.>>
You can find the quote in this link:
http://pubs.acs.org/cen/science/8045/8045sci2.html
It is from a publication of the American Chemical Society
Lemon juice helps to keep apple slices from turning brown due to its high acidity and the presence of an antioxidant called ascorbic acid (vitamin C). When an apple is cut or bruised, an enzyme called polyphenol oxidase reacts with oxygen in the air and causes the apple to turn brown.
Here's how lemon juice prevents this browning process:
1. Acidity: Lemon juice is highly acidic, which inhibits the activity of polyphenol oxidase. By lowering the pH of the apple's surface, lemon juice slows down the browning reaction.
2. Ascorbic acid: Lemon juice contains ascorbic acid, which is a powerful antioxidant. When applied to the cut apple, ascorbic acid reacts with oxygen and prevents the oxidation process that leads to browning.
To apply lemon juice to apple slices:
1. Squeeze fresh lemon juice: Cut a lemon in half and squeeze the juice into a bowl. Make sure it is freshly squeezed, as pre-bottled lemon juice may have lower acidity and less ascorbic acid.
2. Dip or brush the slices: Dip the apple slices directly into the lemon juice or use a brush to apply the juice evenly onto the cut surfaces. Ensure that all exposed areas of the apple slices are coated.
3. Allow time for absorption: Let the apple slices sit for a few minutes to allow the lemon juice to fully coat and protect the exposed flesh.
By following these steps, you can effectively use lemon juice to preserve the appearance and freshness of apple slices.