<div><p>This study describes the <i>in vitro</i> inhibition of protein denaturation of extract/fractions of <i>Withania somnifera</i> and isolated withanolides including 20β hydroxy-1-oxo(22<i>R</i>)-witha-2,5,24 trienolide (<b>1</b>), (20<i>R</i>,22<i>R</i>-14α,20α)-dihydroxy-1-oxowitha-2,5,16,24 tetraenolide (<b>2</b>). The results showed that the extract/fractions of the plant evoked profound inhibitory effect on thermal-induced protein denaturation. The chloroform fraction caused the most dominant attenuation of 68% at 500 μg/mL. The bioactivity-guided isolation from chloroform fraction led to the isolation of compounds <b>1</b> and <b>2</b> that showed profound protein inhibition with 78.05% and 80.43% effect at 500 μg/mL and thus strongly complimented the activity of extract/fractions. In conclusion, extract/fractions of <i>W. somnifera</i> possessed strong inhibition of protein denaturation that can be attributed to these isolated withanolides.</p></div
