Food Science: Why Blanched Vegetables (Sometimes) Turn Brown (2024)

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Food Science: Why Blanched Vegetables (Sometimes) Turn Brown? ›

Enzymic browning is an oxidation reaction that takes place in some foods, mostly fruit and vegetables, causing the food to turn brown. Oxidation reactions occur in food and non-food items.

Once the fruit or vegetable is cut, some of the cells are opened up to the air. The enzyme polyphenol oxidase then has access to oxygen in the air and a reaction occurs, which results in the fruit or vegetable turning brown.

Many green ingredients contain enzymes that can turn them brown, either by degrading the structure of chlorophyll or by catalysing the oxidation of phenolic compounds.

The enzyme polyphenol oxidase (also known as tyrosinase) located in the cells gets exposed to and reacts with oxygen in the air when fresh fruits and vegetables are peeled or cut open. The browning of fruits and vegetables is caused by a chemical reaction known as oxidation.

When fresh fruits and vegetables are peeled or cut open, the enzyme called polyphenol oxidase (also called tyrosinase) contained in the cells is exposed to and reacts with the oxygen in the air. The reaction that occurs, which is called oxidation, is what turns the fruits and vegetables brown.

Physical methods to regulate enzymatic browning include thermal treatment, prevention of oxygen exposure, use of low temperature, and irradiation. Heat treatment, such as blanching, can easily inhibit the enzymatic activity because enzymes, which are composed of proteins, are denatured [7,8].

Apart from potatoes and apples, other fruits and vegetables turn brown when cut, too, that should be treated in an almost similar manner. These also include eggplants, bananas, mushrooms, lettuce, pear, cauliflower, and especially avocados. Don't sit and watch these produce turn brown!

A brown discoloration of the internal hollow stem tissue may be associated with a boron deficiency. Some recently developed varieties are resistant to hollow stem.

Bottled lemon juice can be made into a holding solution to prevent enzymatic browning by mixing ½ cup lemon juice with 2 quarts of water. Note: Citric acid and lemon juice are not as effective in preventing browning as ascorbic acid solutions.

The beans turn brown because of something called the Maillard reaction. This is a fancy scientific term that basically means: heat causes the sugars and amino acids in the beans to react and create new flavors and aromas.

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It is an oxidation reaction that takes place due to exposure in oxygen (present in air). Visit the link https://bit.ly/2X4099j to know oxygen is required for oxidation. Peeled or sliced potatoes, brinjals, bananas, apples get brown or black upon exposure to air.

This unappetizing phenomenon is actually due to a chain of biochemical reactions known as “enzymatic browning.” When an apple is injured (or cut into pieces), the plant tissue is exposed to oxygen.

The main factors that determine the rate of enzymatic browning of fruit and vegetables include the concentrations of active PPO and phenolic compounds present, the temperature, the pH, and the oxygen availability of the tissue. Antibrowning agents may be used to delay the enzymatic browning in fruit and vegetables.

When fruit tissue is damaged because of heat, cold, age or mechanical stress, its cells break open and the phenolic compounds and the enzyme are released and mix with oxygen in the air. As a result the damaged tissue turns brown almost immediately.

Basically, it is a chemical reaction between amino acids and simple sugars in food which then leads to the formation of brown colour. During the process, simultaneous chemical reactions occur when amino acids and simple sugars in the food are transformed by the heat applied.

But just a browning of a fruit and vegetable isn't necessarily a sign that it has gotten bad, but it's a sign that we should eat it right away or prepare it right away and eat it as soon as possible.

Squeeze some lemon juice onto the cut surfaces of the fruits or vegetables before storing them. The acid in the lemon juice helps slow down the browning process.

Think of an apple, even though it may start to brown right away, it takes a long time for the entire apple slice to change color. Even then, you cut off the brown and the inside remains unaffected. Fruits and veggies are also so rich in nutrients that the body will still profit if a loss occurs. So drink up!