Have you ever wondered why your fresh fruits instantly turn murky soon after being sliced? Or why your guacamole turns tinges of brown just minutes after preparing it?
This happens due to a natural process called enzymatic browning. It is what makes your food look unpalatable but worry not — this article unveils the secrets to keep foods fresh and delicious! In this article, we will also dive into the science behind browning, and why, in some cases, it isn’t a bad thing.
What is Enzymatic Browning and Why Does it Happen?
Enzymatic browning is an oxidation reaction (the addition of oxygen) that takes place in foods, mostly fruits and vegetables which are rich in phenols and Polyphenol Oxidase (PPO) (an enzyme found in the cells of these fruits and vegetables). Phenols are natural compounds which give foods their colour and flavour. Simply put, these phenols are the building blocks that prevent plants against damage and contribute to their taste and appearance. When sliced, the enzyme and the phenols which are usually tapped in the food’s tissue come in contact with oxygen which leads to the formation of quinones which intern polymerise (small molecules joining to form larger molecules) to form melanin, the brown pigment we see. This reaction is shown below:
The good news is that eating foods even though they are brown is not harmful. It only alters the taste and texture which may make it unappetizing.
Fun Fact: Browning is Not Always Bad
Browning is also responsible for developing the dark colour and rich flavour of tea and cocoas beans. During the processing of these products, enzymatic browning is controlled. When the quinones polymerise into melanins, this ‘controlled’ browning enhances taste and aroma.
How Can You Prevent Browning At Home?
- Spray lemon juice or any juice rich in vitamin C (orange juice) on the surface of the cut fruits. The acidity from this juice disrupts the pH and slows down enzymatic activity, allowing food to remain fresh for longer.
- Store the cut fruits in water to limit exposure to oxygen. Without oxygen, the PPO enzyme cannot turn phenols into quinones.
- Keep cut fruits and vegetables in the fridge to slow down the enzymatic reaction. Enzymes function best in specific temperatures and pH. At lower temperatures, the PPO enzymes become denatured (loses shape) which prevents it from functioning properly.
While preventing the browning of fruits and vegetables seems like a simple task we do subconsciously, understanding the scientific reason behind it helps us to better control it. Using lemon juice or storing the cut slices in water are household methods that are easy and effective for domestic use. However, the food industries rely on more advanced, complicated techniques such as vacuum sealing, the use of chemical preservatives and blanching. These techniques require calculation of the perfect concentration of these preservatives, finding out the exact temperature and quality control of all these methods. These tiny steps are crucial to ensure that the taste of the fruit or vegetable is maintained while increasing its shelf life.
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