Abstract: The structure and physico-chemical properties of red pigment prepared from cultured cells of a high-yield microbial strain conserved in our laboratory by extraction into 95% ethanol and sequential purification on macroporous resin column and   silica gel column were investigated. The stability of the pigment to sunlight, temperature, pH value, hydrogen peroxide (H2O2) as an oxidant, sodium benzoate as a preservative, acidity agents, sucrose, vitamin C and metal ions was evaluated. Results showed that the red pigment was identified as prodigiosin by the methods of UV/vis, ESI-MS and 1H-NMR, with a maximum absorption peak at a wavelength of around 533 nm under acidic conditions. It was very easy to dissolve in organic solvents and had excellent stability at pH ≤ 5. In addition, the pigment exhibited strong tolerance to radiation and high sucrose concentration, but poor resistance to light and high temperature. Moreover, no significant effect of sodium benzoate, VC and H2O2 on the pigment was found at low concentrations. Acidity agents and the metal ions Na+, Al3+, Mn2+, K+, Mg2+ and Ca2+ exhibited hyperchromic effects on the pigments, while Fe3+ had severe undesirable effect, and Zn2+ had little effect.

Key words: bacteria, red pigment, structure, physicochemical properties