Why does homemade tomato pickle darken in storage?

Question

Learn why your homemade tomato pickle can darken over time. Discover how oxidation and light exposure can affect its vibrant red color.

Answer 1

Homemade tomato pickle darkens in storage primarily due to the Maillard reaction, a chemical reaction between amino acids and reducing sugars, and oxidation of phenolic compounds present in tomatoes. These processes are accelerated by heat, light, and the presence of oxygen.

Detailed Explanation:

The darkening of homemade tomato pickle is a common occurrence and is attributed to several factors:

1. Maillard Reaction: This is a non-enzymatic browning reaction that occurs between amino acids and reducing sugars (like glucose and fructose) present in tomatoes. The reaction is accelerated by heat and time, leading to the formation of melanoidins, which are brown-colored compounds. The higher the temperature during cooking and the longer the storage period, the more pronounced the darkening will be.
2. Oxidation: Tomatoes contain phenolic compounds that can undergo oxidation when exposed to air. This oxidation process is catalyzed by enzymes and can also occur spontaneously. The resulting oxidized compounds are often darker in color. Inadequate sealing of the pickle container allows oxygen to enter, promoting this oxidation.
3. Caramelization: If sugar is added to the pickle recipe, caramelization can contribute to the darkening. Caramelization occurs when sugars are heated to high temperatures, resulting in the formation of brown pigments.
4. Metal Ions: Trace amounts of metal ions, such as iron or copper, can catalyze oxidation reactions and contribute to color changes. Using reactive cookware (like uncoated cast iron) can introduce these metal ions into the pickle.

Pro Tip:

To minimize darkening, store your tomato pickle in a cool, dark place in airtight containers. Adding a small amount of ascorbic acid (vitamin C) can act as an antioxidant and help prevent oxidation.