Pectin Glycerol Ester

Pectin is extracted from citrus peel, apple pomace, sugar beet, and other plant materials. Structurally it comprises polygalacturonic acid and its methyl ester, and a number of neutral sugars [15]. It is widely used in food applications (e.g., jams and jellies, confectionery, beverages, desserts) and in some pharmaceutical applications. It is susceptible to enzyme reactions, and the following three pectolytic enzymes are well known: polygalacturonase (cleaving the galacturonan backbone), pectin meth-ylesterase (hydrolyzing the methyl ester), and pectin lyase (which catalyzes the scission of the backbone [16].

It is of interest to use a nonpectin enzyme to carry out biotransformation of pectin. One reaction is to convert the pectin to its glycerol ester through transester-ification (Scheme 1). Since glycerol is very hydrophilic, this modification should make the pectin more water soluble at low pH values.

To find a suitable enzyme to catalyze the transesterification reaction (methyl ester to glycerol ester) under mild conditions, we screened a number of lipases and esterases. We found two lipases (Candida cylindracea lipase and porcine pancreatic lipase) to exhibit catalytic activity for this reaction. The reaction conditions entailed elevated temperatures, with the use of glycerol as the solvent and an acyl acceptor. The enzyme catalyzed the esterification of the carboxyl group of the pectin to the C1 (primary) alcohol of the glycerol to form the monoester. No substantial glycerol

Pectin

Pectin glycerate

Scheme 1 Synthesis of pectin/glycerol ester.

Pectin

Pectin glycerate

Scheme 1 Synthesis of pectin/glycerol ester.

diester (i.e., cross-linked structure) was found. Pectin methylesterase (PME) was also studied and found not to have catalytic activity under the same reaction conditions.

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