Step 1: What are cardiac glycosides?
Cardiac glycosides like those in digitalis (digoxin, digitoxin) are the active therapeutic compounds. They work by inhibiting the Na⁺/K⁺-ATPase pump in the heart, increasing cardiac contractility.
Step 2: What happens if drying is delayed or done at high temperature?
Fresh plant material contains endogenous enzymes (glycosidases). If not dried quickly, these enzymes hydrolyse (break down) the glycosidic bonds in the cardiac glycosides, destroying the active compounds.
Step 3: Why 60°C specifically?
At around 60°C, the drying is fast enough to inactivate the plant enzymes before they act. But the temperature is not so high that the thermolabile glycosides themselves decompose.
Step 4: Why are the other options wrong?
Glycosides do not need activation by drying; they are already biologically active. Cardiac glycosides contain no significant volatile oils to remove. Colour and appearance are not the primary concern.
Step 5: Conclude.
The primary reason for immediate drying at a controlled temperature is to prevent enzymatic hydrolysis that would destroy the active cardiac glycosides.
Answer: Option (2) — To prevent enzymatic hydrolysis that would destroy the active constituents