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An approach for early-stage eco-design of an enzyme-based process has been developed by coupling process modeling, Life Cycle Assessment (LCA) and flowsheet design, in order to evaluate the real advantages of the direct synthesis of low molar mass dextrans (5-25 kg mol(-1)) from a sucrose substrate. This approach identifies the most promising development pathways and crucial unit operations that require, as a matter of priority, further investigation and experimentation. Process modeling is based on a comprehensive and multi-fidelity building of Life Cycle Inventories (LCI) to establish all materials and energy inputs and outputs of the processes involved with a flexible and satisfactory level of accuracy. This essentially binds (i) a high-fidelity polymerization model, namely PolyEnz, for the description of the synthesis of dextrans from sucrose using the DSR-M enzyme following a non-processive mechanism, (ii) flexible-fidelity models for description of subsequent purification, separation and drying steps, (iii) upstream processes in the value chain and life cycle system using real-world data from ecoinvent datasets. Three process benchmarks were constructed and compared to determine the most appropriate purification processes and operation conditions at a larger scale. In addition, various process triggers, including the initial concentration and type of substrate, the type of process water, the use of size exclusion chromatography for separation, and the use of freeze drying for the last production stage were subjected to a sensitivity analysis with the criteria being the overall energy demand, the potential environmental damage evaluated by the ReCiPe endpoint and the global warming potential.