Abstract: One-factor-at-a-time combined with orthogonal array design method was used to optimize process conditions for pectin extraction from mulberry stalk bark by ammonium oxalate-oxalic acid hydrolysis and subsequent ethanol precipitation. The effects of solid-to-liquid ratio, pH, temperature and time on pectin extraction rate were investigated. Pectin extraction rates from the bark of different stalk positions of mulberry cultivars Husang 32, Yu 711, Nongsang 8 and Nongsang 14 at different growth stages were compared. The optimal conditions for extracting pectin from mulberry stalk bark were solid-to-liquid ratio (g/mL) 1:14, pH 2.0, temperature 90 ℃, and extraction time 120 min, and the addition of activated carbon at 1 g/100 mL for decolorization at 60 ℃ for 30 min resulted in the best decolorization. Under these conditions, the pectin extraction rate was roughly 12%. Cultivars, harvest periods and stalk bark positions showed a difference in the extraction rate of pectin. Among the four cultivars investigated, Husang 32 revealed the highest pectin extraction rate. In summer a higher pectin extraction rate from mulberry stalk bark was observed than in spring and autumn. In spring and autumn, the bark of the middle position of mulberry stalk exhibited a higher pectin extraction rate than that of the top and bottom. In summer, the pectin extraction rate from the bark of one-year-old mulberry stalk was higher than that of newly grown mulberry stalk. In addition, an increase in pectin extraction rate was found from fresh mulberry stalk bark as compared with its dried counterpart.

Key words: mulberry stalk bark, pectin, extraction rate