Continuous production of pectic oligosaccharides from onion skins with an enzyme membrane reactor

The aim of this research was to valorize onion skins, an under-utilized agricultural by-product, into pectic oligosaccharides (POS), compounds with potential health benefits. To achieve high hydrolysis performance with the multi-activity enzyme Viscozyme L, an innovative approach was investigated based on a cross-flow continuous membrane enzyme bioreactor (EMR). The influence of the various process conditions (residence time, enzyme concentration, substrate concentration) was investigated on productivity and yield. The composition of the POS mixtures in terms of mono- and oligosaccharides was assessed at the molecular level. At optimized conditions, a stable POS production with 22.0 g/L/h volumetric productivity and 4.5 g/g POS/monosaccharides was achieved. Compared to previous results obtained in batch for the enzyme Viscozyme L, EMR provided a 3–5× higher volumetric productivity for the smallest POS. Moreover, it gave competitive results even when compared to batch production with a pure endo-galacturonase enzyme, demonstrating its feasibility for efficient POS production.