Preparation of functional pectic gel by homogenizing Citrus furit peel in chelating agent solution

用螯合剂（植酸盐或柠檬酸盐）溶液从新鲜柑橘果皮中提取丙酮不溶物（AIS）。当将提取物在冰箱（5 ℃）中储存过夜时，提取物凝结成凝胶状态。凝胶显示出最高的硬度与0.03 M植酸盐溶液在pH 8和0.1 M柠檬酸盐溶液在pH 6。在0.03 M植酸盐溶液（pH 9）和0.1 M柠檬酸盐溶液（pH 8）中获得溶解在提取物中的果胶物质的最高量。随着植酸溶液pH值的升高，提取物中植酸的含量增加。柑桔皮中果胶酯酶（PE）在pH 6 -9范围内有较强的活性。用商品果胶研究了提取物的凝胶化机理。由柠檬果胶、酶和氯化钙（CaCl_2）组成的反应混合物在冰箱中孵育24小时期间凝固。使用粘度计测量反应初始阶段的混合物的相对粘度。含4mg%CaCl_2的混合物在pH 8时粘度最大。而在不含CaCl_2或失活酶的混合物中，粘度在孵育过程中不发生变化。添加植酸盐或柠檬酸盐的混合物降低其粘度。根据这些结果，认为提取物的胶凝机理如下。(1)柑橘果皮中与果胶结合的多价阳离子如Ca^++和Mg^++被植酸盐或柠檬酸盐的螯合作用捕获。(2)果胶溶解在碱性植酸盐或柠檬酸盐溶液中，用PE酶解，得到果胶酸（或低甲氧基果胶）和甲醇。(3)果胶酸的游离羧基与果皮细胞质中的Ca^++离子结合形成果胶酸钙溶胶。(4)果胶酸盐溶胶在储存于再蒸发器中期间重排成凝胶，并且凝胶化完成。

Acetone insoluble solid (AIS) prepared from fresh peel of Citrus fruit was extracted with chelating agent (phytate or citrate) solutions. The extract coagulated into a gel state when it was stored overnight in a refrigerator (5ﾟC). The gel showed the highest firmness with 0.03 M phytate solution at pH8 and 0.1 M citrate solution at pH6. The highest amount of pectic substance dissolved in the extract was obtained in 0.03 M phytate solution (pH9) and 0.1 M citrate (pH8) solutions. The amount in the extract increased as pH of phytate solution rose. Strong activity of pection esterase (PE) in Citrus peel was observed in pH6-9. Gelling mechanism of the extract was studied using commercial pectin. Reaction mixture consisting of lemon pectin, the enzyme and calcium chloride (CaCl_2) coagulated during incubation for 24 hr in a refrigerator. Relative viscosity of the mixture in the initial stage of reaction was measured using a viscometer. The mixture containing 4mg% CaCl_2 gave maximum viscosity at pH8. However, in the mixtures containing no CaCl_2 or inactivated enzyme, viscosity did not change during incubation. Adding phytate or citrate to the mixture decreased its viscosity. From these results, a gelling mechanism of the extract is considered as follows.(1) Polyvalent cation such as Ca^<++> and Mg^<++> bound with pectin in Citrus fruit peel is caught by chelating action of phytate or citrate.(2) Pectin dissolved in alkaline phytate or citrate solution is enzymatically hydrolyzed into pectinic acid (or low methoxyl pectin) and methylalcohol by PE.(3) Free carboxyl group of pectinic acids combines with Ca^<++> ion derived from cytoplasm of peel, and Ca-pectate sol forms.(4) The pectate sol is rearranged to gel during storing in a refregirator and gelation is complete.