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

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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.