It’s the curse of apple slices—brown apples. We’ve all been there; you leave a few apple slices out too long, or take too long to eat your way around an apple, and you’re confronted with an unpleasant sight. Your once crispy, juicy white apple has turned a dismal shade of brown. Not very appetizing. The good news is that a brown apple is perfectly safe to eat. The bad news is that it’s ugly. The cause is enzymatic browning, a molecular reaction that occurs when certain enzymes and a class of chemicals known as phenolic compounds, or phenols, naturally found in some plants combine and react in the presence of oxygen. One of the products of their chemical reaction is a brown pigments called melanin. And it’s not only apples that are susceptible to this phenomenon. Pears, bananas, avocados, eggplants and potatoes can also undergo enzymatic browning, because they, like apples, contain phenols.
Fun fact: Bruises in fruit are caused by the enzymatic browning too!
Slicing (or biting into) an apple allows the phenols and enzymes that are normally kept separate by the plant’s cell structure to commingle. As soon as this phenol-enzyme mixture is exposed to oxygen the browning process begins. The longer it sits, the more brown pigments are formed, until all the available phenols have been used up and the fruit is as brown as it’s going to get.
Enzymes are simply proteins, but they have very special functions in nature. Enzymes allow chemical reactions to take place that otherwise would never occur (at least not in any significant amount) because they require too much energy (most chemicals are pretty lazy; they usually prefer the path of least resistance). Enzymes are the sort of lever or pulley of the biological world–they make jobs (reactions) that should be impossible much easier to accomplish, and they never get tired! They will repeat the action over and over until they run out of supplies! Sometimes the results of these reactions are undesirable, like enzymatic browning in cut fruits, but enzymes are key in many foods that are important to our American culture too! For example, the enzyme rennet is needed to change liquid milk into the curds that make cheese; the enzyme lactase breaks down lactose for us in our bodies (unless you’re lactose intolerant); and the food industry uses measurements of certain enzyme levels in food to determine the freshness of seafood, the safety of pasteurized milk, and other helpful info. Not to mention this very same enzymatic browning reaction contributes to the desirable color of tea, coffee, and raisins.
Because enzymes are proteins, they, like all proteins, denature in the presence of heat or acidity. When a protein denatures, it loses its unique shape and therefore its function. Enzymes interact with other molecules by acting much like a puzzle piece, so shape means everything; once they’ve lost it, poof! They’re toast. Once denatured, an enzyme cannot revert to its original shape, so the effect is permanent.
You may know that adding lemon juice to sliced apples is a common way to prevent browning. However, lemon juice tends to make things taste lemony.
Fresh Sliced™ works for apples, bananas, pears, peaches, grapes, potatoes, eggplant, and avocados.