The natural dye present in turmeric is known as

Turmeric (Curcuma longa) is a natural indicator used to distinguish between acidic and basic substances [c1][c2]. The primary natural dye and active pigment responsible for its characteristic yellow-orange color is curcumin [t1][t8]. Curcumin belongs to a group of compounds called curcuminoids, which also include demethoxycurcumin and bisdemethoxycurcumin [t2][t10]. Chemically, curcumin acts as a pH-sensitive colorant; it remains yellow in acidic or neutral environments but undergoes a structural change to a reddish-brown color in alkaline (basic) conditions, such as when it reacts with soap [c1][c2][t1]. In contrast, phenolphthalein and methyl orange are synthetic indicators used in laboratory titrations [c2][t1]. Curcumin is widely recognized for its pharmacological properties and its use as a bio-derived pigment in both culinary and analytical chemistry [t4][t5][t8].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Exploring Substances: Acidic, Basic, and Neutral > Table 2.4: Testing the nature of samples with turmeric paper > p. 15
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > p. 17
3. [3] https://www.sciencedirect.com/science/article/abs/pii/S0926669024017941
4. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC12731211/
5. [5] https://www.ncbi.nlm.nih.gov/books/NBK92752/
6. [6] https://pmc.ncbi.nlm.nih.gov/articles/PMC9881416/