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Transacylation reaction of citrus pectin by PE from tendril shoots of chayote (TSC) was observed by gel permeation chromatography (GPC), gel compression force, change in viscosity, and change in turbidity. Molecular mass of pectin remarkably increased from 70 to 443 and 670 kDa when pectin–TSC PE (4 units/ml) mixture in 0.2 M NaCl/0.01 M phosphate buffer (pH 6.5) was incubated at room temperature for 30 min and 2 h, respectively. Apparent increase in compression force (g) of 1% calcium-free pectin gel containing 0.8–16 units/ml of PE after incubation at room temperature for 30 min was observed, revealing the polymerization of pectin as affected by PE transacylation. Increase in viscosity of 0.5% pectin–PE solution (3–30 units/ml) during incubation for up to 60 min, and turbidity change (400 nm) of pectin–PE solution versus PE activity, reaction time, temperature, or NaCl level also evidenced the polymerization of pectin. PE transacylation appeared to be contributory to the pectin gel preparation in food industry.

Degree of esterification of pectin from jelly fig (Ficus awkeotsang Makino) achene seeds and the pH value decreased rapidly during extraction, while apparent reduction of free calcium content in the pectin extract was observed at the gelling stage. Compared to those of the native pectin, total ester linkages and methyl ester linkages of pectin extract decreased, and the bound calcium content increased during pectin gelling. However, non-methyl ester linkages (the difference between the total ester linkage and the methyl ester linkage) increased by approximately 40% during pectin gelling, revealing esterification reaction between C6 carboxyl groups and hydroxyl groups in the presence of pectinesterase. Scanning electron microscopy showed that pectin fragments from jelly curds were large with flake-like structure, while those from hot (85°C) ethanol-treated achenes were small and porous.

Pectinesterase (PE) was isolated from jelly fig (Ficus awkeotsang Makino) achenes, then the optimal conditions for de-esterification and transacylation reactions were determined. Molecular weight of pectin (DE = 62.8 %) when reacted with PE at pH 6.5 and 45 °C in 0.2 M NaCl for 20 mio remarkably increased from the original 72 kDa to 410 kDa, as determined by Fractogel TSK 65(S) gel permeation chromatography. Prolonging the incubation time of pectin-PE mixtores to 2 and 4 h also increased the molecular weights of pectin. Therefore, transacylation reaction was considered to occur and to increase the molecular weight of pectins when de-esterification reaction was catalyzed by pectinesterase (PE). La pectinesterase(PE) des plantes participe a la conversion de la protopectine en pectine soluble et en pectate par catalysation de la desesterification de la pectine. Diminuer les taux d'esterification est crucial pour le procede de maturation des fruits. Jelly fig (Ficus awkeotsang Makino) est une vigne ligneuse qui pousse sur les flancs montagneux du centre de l'ile de Taiwan. Une des caracteristiques de la PE de ses akenes est un pI plus faible que celui des autres plantes superieures. Dans cette etude, la PE extraite des akenes reagit avec de la pectine pour optimiser sa capacite de desesterification. Les changements de poids moleculaire des pectines sont observes. Les conditions optimum pour la reaction de desesterification de la PE de ces akenes sont similaires a celles de la reaction de transacylation: les 2 reactions se produisent en presence de PE.

The changes in molecular masses of pectin in 0.5% pectin−pectinesterase (PE) mixtures (2 units/mL) incubated at various temperatures, pH values, and NaCl levels for 30 min were observed by a Toyopearl TSK HW-65 (F) gel permeation chromatography. The molecular mass of pectin was remarkably increased from 103 to 266 kDa when the incubation temperature of pectin−tomato PE was increased from 25 to 45 °C. A further increase in molecular mass was observed when a pectin−citrus PE mixture was incubated at 65 °C. The values of pH and NaCl levels were also crucial to the transacylation activity of PEs. Reaction at pH 7.5 with tomato PE and citrus PE remarkably expanded the molecular mass of pectin to 410 and 670 kDa, respectively. The NaCl level of 0.3−0.5 and 0.3 M was favorable for the transacylation reaction of tomato PE and citrus PE, respectively. Only high methoxylpectin was the suitable substrate for PE to conduct the transacylation reaction. Keywords: Transacylation reaction; tomato PE; citrus PE; gel perme...