Stability and Antibacterial Activity of Purple Cabbage Pigment

The pigment in the leaves of purple cabbage was extracted from, and its stability and antibacterial activity were measured by spectrophotometry. The pigment extracted looked carmine, the original color of purple cabbage, and was stable when exposed to acidic aqueous solution at pH 2. As pH increased, its color gradually changed from carmine to blue, then to green, with the occurrence of a red-shift of maximum absorption wavelength. The preservation rates of the pigment after illumination under natural light for 2 and 6 days were more than 91% and more than 79%, respectively, and the value after 2 hours of heating at temperatures below 70 ℃ was still more than 90%, suggesting that the pigment has good tolerance to light and heating. In the presences of some metal ions including sodium, potassium, calcium, magnesium or oxygen, the pigment was stable, whereas the attendance of iron would deteriorate it. The pigment had significant concentration-dependent inhibitory effect against Staphyloccus aureus and Bacillus subtilis at a concentration of 10 mg/100 mL, but no anti-E. coli effect was observed.