Deesterification of pectin using commercial pectin methylesterase-containing plant extracts

A vast variety of bacterial, fungal, and plant-derived pectin methylesterases (PMEs) have been characterized in literature for their ability to deesterify pectins. However, when compared to fungal PMEs, the availability, characterisation and application of commercial enzyme preparations comprising plant PMEs is still lacking. Here, we characterized the PME activity in commercially available crude plant extracts originating from papaya (papain), pineapple (bromelain), and kiwi (actinidin). The highest PME activity towards pectin was determined in papain preparations, which did not comprise pectin-backbone degrading side activities. The pH and temperature optimum of the salt-dependent papain PMEs ranged from 7.0 to 8.0 and 50–70 °C, respectively. Using enzymatic fingerprinting, it was shown that papain PMEs exhibited a processive mode of action towards lemon pectin. Papain PMEs had a broad substrate specificity, as 61, 83, and 58% of the methylesters were released from lemon, apple and sugar beet pectin, respectively. The release of acetic acid from sugar beet pectin indicated the presence of acetyl esterases in the papain preparations. Both the determined processive mode of action and broad substrate specificity allows to consider papain preparations as an alternative to commercial fungal-derived PME preparations to modify the methylester distribution pattern of pectin for food applications.