There has been a surge of interest in the establishment of citrus waste biorefineries. One strategy in such biorefineries would be to extract pectin and saccharify it enzymatically to produce D-galacturonic acid, which has potential as a platform chemical for the production of compounds of commercial interest, such as meso-galactaric acid and L-galactonic acid. A mathematical model of the hydrolysis of pectic substrates by the pool of enzymes present in pectinase preparations would be a useful tool for guiding the design and optimization of the saccharification process. Current deterministic models of this process are highly simplified and, as a result, are not useful tools. In the current manuscript, we develop stochastic models, based on the Monte Carlo method, to describe the action of two important enzymes found within pectinase preparations, namely endopolygalacturonases and exopolygalacturonases. Our work represents a first step towards the development of a complete model that integrates the action of the various enzymes present in pectinase preparations. (C) 2017 Elsevier B.V. All rights reserved.