Introduction:
Turmeric is a commonly used spice in cooking and has a distinct yellow color. However, there are certain substances that can change the color of turmeric from yellow to reddish brown. In this response, we will discuss the substances that can cause this color change and explain the scientific reasons behind it.

Substances that can turn turmeric from yellow to reddish brown:

1. Acids: Strong acids such as hydrochloric acid (HCl) or sulfuric acid (H2SO4) can turn turmeric from yellow to reddish brown. This is due to the reaction between the acid and the pigments present in turmeric.

2. Alkalis: Strong alkalis such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) can also change the color of turmeric. Similar to acids, alkalis react with the pigments in turmeric, resulting in a reddish brown color.

3. Heat: Applying heat to turmeric can cause it to change color. When turmeric is heated, the pigments undergo chemical reactions, leading to a change in color. This change is often observed as a transition from yellow to reddish brown.

4. Other chemicals: Certain chemicals, such as metallic salts or oxidizing agents, can also alter the color of turmeric. These substances can react with the pigments in turmeric, causing a shift in color.

Explanation:

The yellow color of turmeric is mainly due to the presence of a group of compounds called curcuminoids. Curcumin, one of the curcuminoids, is responsible for the vibrant yellow color. However, these curcuminoids can undergo chemical reactions when exposed to certain substances or conditions, resulting in a change in color.

When turmeric comes into contact with acids or alkalis, the curcuminoids react with the chemicals present in these substances. This reaction leads to a structural change in the curcuminoids, causing a shift in their absorption of light. As a result, the color of turmeric changes from yellow to reddish brown.

Similarly, when turmeric is heated, the curcuminoids undergo thermal decomposition. This decomposition alters the chemical structure of the curcuminoids, leading to a change in color.

Certain chemicals, such as metallic salts or oxidizing agents, can also cause a color change in turmeric. These substances can react with the curcuminoids, resulting in a shift in the absorption of light and a subsequent change in color.

Conclusion:
Turmeric, known for its yellow color, can be transformed into a reddish brown hue when exposed to certain substances or conditions. Acids, alkalis, heat, and certain chemicals can all cause this color change by reacting with the curcuminoids present in turmeric. Understanding the science behind these color changes allows us to appreciate the versatility of turmeric and its reactions with different substances.