Abstract: The aim of the present study was to develop an optimal preparation procedure of polysaccharides from purple sweet potato (PPSP) consisting of hot water extraction, alcohol precipitation, deprotein and decolorization. A series of single factor experiments were conducted to investigate effects of extraction temperature, extraction time, pH, solid/liquid ratio, extraction times and concentration of alcohol in aqueous solution (as a precipitant) on PPSP yield. On the basis of this, three main affecting factors, including solid/liquid ratio, extraction time and extraction temperature were optimized for maximizing PPSP yield using a three-level orthogonal array design. Results showed that the optimal preparation procedure of PPSP consisted of twice extraction for 2 h at 70 ℃, pH 7.0 with a solid/liquid ratio of 1:15, precipitation with 85% aqueous alcohol, deprotein with 3% trichloroacetic acid, and decolorization with diatomite.

Key words: purple sweet potato, water-soluble polysaccharides, extraction technology, optimization