Study on physicochemical propertyof pigment from stem and leaf of purple sweet potatoes

Extraction method of ethanol solution was employed to extract the pigment from the stem and leaf of purple sweet potatoes.The stability of pigment under different physicochemical conditions were investigated.The results suggested that the value of pH had significant effects on the color of pigment.In the acid solutions,the color of pigment was found to keep high stability under low temperature condition.Due to the obvious decomposition caused by illumination,the pigment should be laid in the dark place.No significant effect of metal ions including Ca2+,Mg2+,Zn2+,Cu2+,and Na+ on the stability of pigment was found.The absorbency of solution decreased with the increase of Fe3+ and Sn4+ concentrations,which resulted in the light color of solution.Therefore,during the processing,sweet potatoes should be avoided to contact the ions of Sn4+ and Fe3+ to preserve the stability of its pigment.The effect of cane sugar,potassium sorbate and VC had non-significant effect on the stability of pigment.