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

以新鲜柑橘果皮为原料，用植酸盐或柠檬酸盐络合剂提取丙酮不溶固体(AIS)。提取物在冰箱(5ﾟC)中储存一夜后凝结成凝胶状态。0.03M的植酸盐溶液和0.1M的柠檬酸溶液分别在pH值为8时和pH为6时凝胶的硬度最高。在0.03M植酸盐溶液(PH9)和0.1M柠檬酸溶液(PH8)中，提取液中果胶物质的溶出量最高。萃取物中的量随植酸溶液pH的升高而增加。在pH值为6-9的条件下，柑橘果皮中果胶酯酶(PE)活性较强。以市售果胶为原料，研究了提取液的成胶机理。由柠檬果胶、酶和氯化钙(CaCl2)组成的反应混合物在冰箱中孵化24小时。用粘度计测量了反应初期混合物的相对粘度。含4 mg%CaCl2的混合物在pH值为8时粘度最大。然而，在不含CaCl2或灭活酶的混合物中，在孵育过程中粘度没有变化。在混合物中加入植酸盐或柠檬酸盐可降低其粘度。结果表明：(1)果胶与柑橘果皮中的多价阳离子如Ca^&lt；++&gt；和Mg^&lt；++&gt；通过植酸或柠檬酸的络合作用被捕获。(2)溶解于碱性植酸盐或柠檬酸溶液中的果胶被PE酶解成果胶酸(或低甲氧基果胶)和甲醇。果胶溶胶在再生器中储存过程中重新排列成凝胶，胶凝完成。

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.